Materials Chemistry & Physics (v.131, #1-2)
Dielectric characteristics of (Mg1/2Co1/2)Al2O4 ceramics at microwave frequencies
by Cheng-Hsing Hsu; Hsin-Han Tung; Chen-Kang Hsu (pp. 1-3).
► New microwave dielectric properties of (Mg1/2Co1/2)Al2O4 ceramics were investigated. ► Compared to previous reports such as (Mg1/2Zn1/2)Al2O4, a significant improvement in the dielectric properties has been accomplished. ► Excellent microwave dielectric properties ( ɛr∼8.75, Q×f value∼107,300, and τfvalue∼−54ppm/°C) can be obtained for (Mg1/2Co1/2)Al2O4 sintered at 1600°C.The microwave dielectric properties and the microstructures of (Mg1/2Co1/2)Al2O4 ceramics prepared by conventional solid-state route have been studied. The dielectric constant values ( ɛr) saturated at 8.3–8.7. The Q× f values of 4500–107,300GHz can be obtained when the sintering temperatures are in the range of 1480–1600°C. The temperature coefficient of resonant frequency τf was not sensitive to the sintering temperature. The ɛr value of 8.75, Q× f value of 107,300GHz, and τf value of −54ppm°C−1 were obtained for (Mg1/2Co1/2)Al2O4 ceramics sintered at 1600°C for 4h. For applications of high selective microwave ceramic resonator, filter and antenna, (Mg1/2Co1/2)Al2O4 is proposed as suitable material candidate.
Keywords: Ceramics; Dielectric properties; Sintering; (Mg; 1/2; Co; 1/2; )Al; 2; O; 4
A modified electroless route to monodisperse and uniform nickel nanoparticle
by Zhipeng Cheng; Jiming Xu; Hui Zhong; Juan Song (pp. 4-7).
► Monodisperse and uniform nickel nanoparticles were synthesized and characterized. ► Trace concentration of EDTA is necessary for uniformity of the nickel nanoparticles. ► The formation process is discussed based on the experimental results. ► Uniform nickel nanoparticles are superparamagnetic.Monodisperse and uniform nickel nanoparticles with an average diameter of ∼30nm were synthesized through a modified electroless route in which nickel hydroxide (Ni(OH)2) colloid, H2O/ethylene glycol (EG) mixing solution, and sodium hypophosphite were used as Ni source, solvent, and reducing agent, respectively. Different from the conventional electroless process, only a trace concentration of complexing agent, ethylenediaminetetraacetic acid (EDTA), was used in this route. At the optimum H2O/EG volume ratio, monodisperse nickel nanoparticles of high crystallinity were obtained. The presence of trace concentrations of EDTA is necessary for uniformity of the synthesized nickel nanoparticles. The formation process is discussed based on the experimental results.
Keywords: Nanostructures; Chemical synthesis; Electron microscopy; Magnetic properties
Electrochemically dispersed nickel oxide nanoparticles on multi-walled carbon nanotubes
by Bohua Wen; Shichao Zhang; Hua Fang; Wenbo Liu; Zhijia Du (pp. 8-11).
► Nickel oxide nanoparticles were electrochemically dispersed on the exterior of MWNT. ► These nanoparticles enhance the specific capacitance of electrodes more than ten-fold. ► Nickel oxide particles dispersed reach specific capacitance ∼1250Fg−1. ► The composite electrodes exhibit excellent rate capability and cyclability.It is the first report that the uniformly dispersed nickel oxide nanoparticles were synthesized on the substrates of multi-walled carbon nanotubes (MWNT) via electrochemical technique. The morphology and chemical state of the NiO x/MWNT composite were characterized using scanning electron microscopy and X-ray photoelectron spectroscopy. The electrochemical test results revealed that the surface-decorated composite with oxide particle sizes of 15–30nm can deliver specific capacitance about 190Fg−1, ten-fold greater than that of pure MWNT. Meanwhile, the electrode displayed excellent cycling stability with nearly 100% coulombic efficiency over 1000 cycles and good rate capability with acceptable specific capacitance fading, indicating that this novel nanostructured composite electrode was a promising candidate for electrochemical capacitors.
Keywords: Composite materials; Electrochemical techniques; Microporous materials; Nanostructures
Synthesis, processing, and characterization of negative thermal expansion zirconium tungstate nanoparticles with different morphologies
by Prashanth Badrinarayanan; Md. Imteyaz Ahmad; Mufit Akinc; Michael R. Kessler (pp. 12-17).
► The negative coefficient of thermal expansion (CTE) of ZrW2O8 nanoparticles was characterized and compared with bulk ZrW2O8. ► The α phase CTE for nanoparticles from both sol–gel and hydrothermal methods were higher than that of bulk ZrW2O8. ► The differences in the α phase CTE between the nanoscale and bulk ZrW2O8 were due to differences in the extent of moisture desorption on heating.Zirconium tungstate (ZrW2O8) is a unique ceramic oxide, which exhibits a large negative coefficient of thermal expansion (CTE). While the negative CTE of bulk ZrW2O8 has been extensively characterized, the negative thermal expansion behavior of ZrW2O8 nanoparticles has never been studied. In this work, ZrW2O8 nanoparticles are synthesized with different morphologies using sol–gel and hydrothermal methods. The structural features of the nanoparticles are compared through Raman spectroscopy. The negative CTE values of ZrW2O8 nanoparticles are determined from 25°C to 600°C using isothermal X-ray diffraction measurements and are compared with the values obtained for bulk ZrW2O8. In the α-phase, the CTE was measured to be −12.0×10−6 and −13.2×10−6K−1 and in the β-phase, the CTE was found to be −4.3×10−6 and −5.1×10−6K−1 for powders synthesized by sol–gel and hydrothermal routes, respectively. The α-phase CTE for nanoparticles from both methods were higher than that of bulk ZrW2O8 (−8.9×10−6). The role of moisture desorption on heating in contributing to the differences observed in the α-phase CTE between the nanoparticles and bulk ZrW2O8 is discussed.
Keywords: A. Ceramics; A. Nanostructures; D. Desorption; D. Thermal expansion
Magneto-caloric effect in the pseudo-binary intermetallic YPrFe17 compound
by Pablo Álvarez; Pedro Gorria; José L. Sánchez Llamazares; María J. Pérez; Victorino Franco; Marian Reiffers; Jozef Kováč; Inés Puente-Orench; Jesús A. Blanco (pp. 18-22).
Display Omitted► YPrFe17 exhibits a broad Δ S M( T) associated with the ferro-to-paramagnetic phase transition ( T C≈290K). ► We obtain |Δ S M| ≈2.3Jkg−1K−1 and RCP≈100Jkg−1for a magnetic field change of 1.5T. ► A single master curve for Δ S M is found when compared with other isostructural R2Fe17 binary alloys.We have synthesized the intermetallic YPrFe17 compound by arc-melting. X-ray and neutron powder diffraction show that the crystal structure is rhombohedral withR3¯m space group (Th2Zn17-type). The investigated compound exhibits a broad isothermal magnetic entropy change Δ S M( T) associated with the ferro-to-paramagnetic phase transition ( T C≈290K). The |Δ S M| (≈2.3Jkg−1K−1) and the relative cooling power (≈100Jkg−1) have been calculated for applied magnetic field changes up to 1.5T. A single master curve for Δ S M under different values of the magnetic field change can be obtained by a rescaling of the temperature axis. The results are compared and discussed in terms of the magneto-caloric effect in the isostructural R2Fe17 (R=Y, Pr and Nd) binary intermetallic alloys.
Keywords: Intermetallic compounds; Magnetic materials; Crystal structure; Thermomagnetic effects
Designing polystyrene honeycomb-like microstructure with high water adhesion
by Tianxian He; Li Zhang; Wenli Deng (pp. 23-26).
Being inspired by the attachment systems of climbing plant Parthenocissus tricuspidata, similar polystyrene (PS) honeycomb-like microstructure was fabricated via a novel hierarchical anodic aluminum oxide (HAAO) template. This template was prepared by a new raw material: silica gel chromatography plate (aluminum foil). Characterized results revealed that the prepared polystyrene layer is hydrophilic and has a high adhesion with water. These findings are very guidable for designing advanced composite adhesive materials in future.
Keywords: A. Microporous materials; B. Coatings; C. Electromechanical techniques; D. Adhesion
Trimethylamine gas sensor based on Cr3+ doped ZnO nanorods/nanoparticles prepared via solvothermal method
by Xiangfeng Chu; Sumei Zhou; Yongping Dong; Wenqi Sun; Xiutao Ge (pp. 27-31).
Cr3+-doped ZnO nano-rods with different doping concentrations are prepared via solvothermal method. The doped ZnO nano-rods are characterized by X-ray diffraction and scan electron microscopy, respectively. It was found that no Cr2O3 peaks appeared in the XRD patterns of Cr3+ doped ZnO when the mole ratio of Cr3+/Zn2+ was in the range of 1–10mol%. The effect of Cr3+ doping on the resistances of the Cr3+-doped ZnO nano-rod sensors was investigated and the results revealed that all Cr3+ did not enter the lattice of ZnO. The amount of Cr3+ had a great influence on the response (Ra/Rg). The sensor based on 3mol% Cr3+ doped ZnO nano-rods (120°C, 10h) exhibited high response and good selectivity to trimethylamine, especially, the responses to 0.001ppm and 0.01ppm trimethylamine reached 1.2 and 6.8, respectively. The response time and the recovery time for 0.001ppm trimethylamine were 120s and 80s, respectively.
Keywords: ZnO; Nanorod; Gas sensor; Trimethylamine
Enhanced piezoelectric properties of Fe2O3–2TiO2 codoped Li0.05(Na0.5K0.5)0.95(Nb0.975Sb0.025)O3 lead-free ceramics with uniform microstructure
by Yongjie Zhao; Yuzhen Zhao; Rongxia Huang; Rongzheng Liu; Heping Zhou (pp. 32-36).
In this study, Fe2O3 and TiO2 codoped Li0.05(Na0.5K0.5)0.95(Nb0.975Sb0.025)O3[(1− x) Li0.05(Na0.5K0.5)0.95(Nb0.975Sb0.025)O3– x(Fe2O3–2TiO2) ( x=0–0.008)] ceramics were prepared by conventional solid state reaction method, and the microstructure and electrical properties of these samples were investigated. The X-ray diffraction and Raman scattering results show the phase structure of the ceramics undergoes with the increase of Fe2O3–2TiO2 content. The grain size distribution of non-doped Li0.05(Na0.5K0.5)0.95(Nb0.975Sb0.025)O3 ceramics was relatively wide. The microstructure was composed of grains ranging 0.2–3.0μm in size. However, with increasing Fe2O3–2TiO2 content, the grain size distribution became relatively narrow. Meanwhile, the piezoelectric coefficient ( d 33) and electromechanical coupling coefficient ( k p) showed peak values of 252 pC/N, and 0.424, respectively, which were achieved in the sample with x=0.002 sintered at 1020°C.
Keywords: Lead-free piezoelectrics; Enhanced property; Uniform microstructure; Fe; 2; O; 3; –2TiO; 2; codoped
Synthesis of carbon-doped MgB2 superconducting nanowires
by Shao-Min Zhou; Yao-Ming Hao; Shi-Yun Lou; Yong-Qiang Wang (pp. 37-40).
A systematic study was conducted on the fabrication, structural characterization, and magnetic properties of MgB2 wire-like nanostructures with C doping between 0% and 20%. Based on chemical vapor deposition technique, non/C-doped MgB2 nanowires (NWs) with an average diameter of 60nm and length up to several micrometers were produced by homemade MgB2 nanotubes, the mixture gases (Ar+CH4+H2), and Ni catalyst. Electron and X-ray diffraction confirm that the as-synthesized non/C-doped MgB2 NWs are single crystalline with primitive hexagonal lattice structure. DC magnetization measurements indicate a high superconducting transition temperature (39K) for nondoping MgB2 NWs and that on increasing the carbon content the transition broadens and shifts toward lower temperatures. The technique is an attractive synthetic method since its flexibility allows for optimization of the doping synthesis. In particular, a comprehensive investigation of influence of NW doping on superconductivity is reported for the first time.
Keywords: Nanostructure; Binary boride; Superconducting; Carbon
Rapid electrochemical preparation of PVA-protected Pt nanoparticles and their behavior towards methanol oxidation
by Luiz H.S. Gasparotto; Germano Tremiliosi-Filho (pp. 41-43).
► Rapid and simple Pt nanoparticle production. ► PVA drastically affects the size and distribution of Pt nanoparticles. ► Small-sized Pt nanoparticles exhibited high electrocatalytic activity for methanol oxidation.PVA-protected Pt nanoparticles were electrochemically synthesized using hexachloroplatinic acid as a metal precursor and tested for methanol oxidation. Field emission gun microscopy (FEG) revealed that the absence of PVA allowed the Pt electrodeposit to grow to the micrometer regime, while its presence refined the grain size. The deposition time also played a role in the particle size. Pt nanoparticles with sizes ranging from 70nm to 300nm were obtained using long-time potential pulse, while the reduction of the time pulse narrowed the particle-size distribution producing nanoparticles of 20–40nm in diameter, which exhibited high electrocatalytic activity for methanol oxidation.
Keywords: Platinum nanoparticles; Size and population effects; Rapid electrochemical preparation; Methanol oxidation
High pressure structural transformation of selected metal organic frameworks – A theoretical investigation
by Mousumi Mani Biswas; Tahir Cagin (pp. 44-51).
► Metal Organic Frameworks (MOF) undergo structural transformations at high pressure. ► Pressure induced structural transformations of 6 isoreticular MOFs are presented. ► Molecular simulations show around 50% reduction of their original volume. ► Transformation reversibility depends on linker chemistry and presence of hydrogen.Metal organic frameworks are susceptible to flexible structural transformations under the influence of external stimuli. Although guest dependent flexible transformations has been observed for several MOFs; but studies on pressure induced transformation is limited. In applications such as gas storage and separation, MOFs may encounter high pressures leading to change in structural behavior, porosity, etc. Hence it is important to study the effect of high pressure on MOF structure. Here we present high pressure induced structural transformations of 6 isoreticular MOFs: IRMOF-1, IRMOF-3, IRMOF-6, IRMOF-8, IRMOF-10 and IRMOF-14. Using molecular simulations we show that at high pressure these MOFs deformed to ∼50% of their original volume. This deformation is due to reorganization of the linkers and ZnO4 tetrahedra. There is large torsion along the dihedral angle O–C–C–C. Structural transformations for MOFs with substituted benzene organic linkers are reversible. For others reversibility depends on the presence of hydrogen in the crystal.
Keywords: Microporous materials; High pressure; Molecular dynamics; Mechanical properties; Phase transitions
Ferromagnetic Ni decorated ordered mesoporous carbons as magnetically separable adsorbents for methyl orange
by Ningning Liu; Longwei Yin; Luyuan Zhang; Changbin Wang; Ning Lun; Yongxin Qi; Chengxiang Wang (pp. 52-59).
► Magnetically separable Ni-decorated ordered mesoporous carbon (OMC) was successfully synthesized. ► The adsorption capacities for MO dyes on ordered mesoporous carbons, Ni-OMC and activated carbon powder were comparatively investigated. ► The effects of surface area, pore structure, and Ni deposition on the absorption capacities for MO were investigated. ► The ferromagnetic Ni decorated OMC can be easily dispersed in aqueous solution and removed by an external magnetic field.Magnetic ordered mesoporous carbons (OMCs) with Ni nanoparticle (average size: 10nm) homogeneously modified on surfaces of OMCs were successfully fabricated via a facile casting route. The microstructure, pore size distribution, pore structure, and surface area of the synthesized OMCs and Ni decorated OMCs (Ni-OMCs) were characterized by X-ray diffraction, field emission scanning electron microscopy, high-resolution transmission electron microscopy and N2 sorption. The characterization by magnetic hysteresis loops suggests a ferromagnetic behavior for the Ni-OMCs samples with a magnetization saturation of 2.34emug−1 at 300K, high enough for magnetic separation. The ferromagnetic Ni-OMCs were used as magnetically separable high-performance adsorbents for methyl orange (MO). The adsorption capacities for MO on the Ni-OMCs as magnetically separable adsorbents were investigated comparatively with pristine OMCs and activated carbon powder (ACP). The results show that the adsorption capacities for MO on the OMCs and Ni-OMCs adsorbents could be well described according to Langmuir isotherm with MO molecule preferentially adsorbed in the structured mesopores, suggesting the adsorption type of monolayer coverage of MO dye onto the mesoporous samples. The effects of surface area, pore structure, and the Ni deposition on the adsorption capacities for MO were systematically investigated. The effects of several important parameters such as contact time, temperature, adsorbent dosage and adsorbate concentration on the adsorption capabilities were studied in detail. The ferromagnetic Ni decorated OMCs as adsorbents for MO, were easily dispersed, separated and removed in an external applied magnet field, and can be more convenient for large scale applications than filtration or centrifugation separation route.
Keywords: Mesoporous carbon; Metallic nickel; Methyl orange; Magnetic; Adsorption
Effect of B and C doping on structure and magnetostriction of high-Pr content alloys
by Gu Zhengfei; Deng Ting; Li Junqin; Cheng Gang; Geng Shengdong; Gao Xinqiang; Ao Daichao; Du Yusong (pp. 60-63).
► High-Pr content alloys containing B and C are prepared with MgCu2-type structure. ► B and C atoms occupied interstitial or substitutional sites in the alloys. ► Lattice parameter increases at first with increasing B content and then decreases. ► Magnetostriction of the high-Pr content alloys is improved by B and C doping. ► High-Pr content alloys containing B and C are promising magnetostrictive materials.The structure and magnetostriction of the high-Pr content (Tb0.2Pr0.8) (Fe0.4Co0.6)1.88− xC0.05B x (0≤ x≤0.08) alloys homogenized at 700°C for 7 days have been investigated by X-ray diffraction and magnetic measurement. It was found that the matrix of the (Tb0.2Pr0.8) (Fe0.4Co0.6)1.88− xC0.05B x alloys belongs to (Tb, Pr) (Fe, Co, C, B)2 phase with MgCu2-type structure. The Curie temperatures are derived from M–T curves, which showed a slight increase when 0≤ x≤0.06, then decreases with further increasing x. The composition dependence of magnetostriction λa(= λ∥− λ⊥) for (Tb0.2Pr0.8) (Fe0.4Co0.6)1.88− xC0.05B x alloys reaches a maximum value at x=0.01 at room temperature. The double split (440) lines of the Laves phase overlap gradually with increasing x and finally approach to form a broadened peak for x=0.03. The spontaneous magnetostriction λ111 decreases with increasing boron contents.
Keywords: Magnetostriction; Cubic Laves phase; (Tb; 0.2; Pr; 0.8; ) (Fe; 0.4; Co; 0.6; ); 1.88−; x; C; 0.05; B; x; alloys; Curie temperature and spontaneous magnetization
The effects of synthesis parameters on the formation of PbI2 particles under DTAB-assisted hydrothermal process
by Gangqiang Zhu; Mirabbos Hojamberdiev; Peng Liu; Jianhong Peng; Jianping Zhou; Xiaobin Bian; Xijin Huang (pp. 64-71).
► Submicron- and micron-sized PbI2 particles were hydrothermally synthesized. ► Structural transformation form belt-like to rod- and microtube-like was observed. ► Phase-pure PbI2 particles could be hydrothermally obtained at pH <7. ► Increasing amount of DTAB resulted in structural transformation of PbI2 particles. ► The optical band gap energy of PbI2 was slightly affected by morphology.Submicron- and micron-sized lead iodide (PbI2) particles with well-controlled morphologies were successfully fabricated via a low-temperature hydrothermal process assisted by dodecyltrimethylammonium bromide (DTAB) as cationic surfactant. The as-synthesized powders were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–vis spectroscopy. The effects of synthesis parameters (temperature, time, pH, and surfactant amount) were systematically investigated. The obtained results showed that the submicron structure was belt-like at 100–120°C, transformed to rod-like by increasing temperature to 140°C and it became a microtube-like at 160–200°C. By changing the pH of the synthesizing solution, it was found that a pure PbI2 phase could be obtained below 7. With the addition of increasing amount of surfactant, microparticles were converted to microrods→submicron belts→microtubes. The time-dependent experimental results revealed that the dissolution–recrystallization and dissolution–recrystallization–self-oriented-attachment were considered to be the possible mechanisms for the formation of the belt- and tube-like PbI2 submicron- and micron-sized particles, respectively. The optical properties of the PbI2 particles synthesized at 100–200°C for 8h under hydrothermal conditions were also studied.
Keywords: A. Semiconductors; B. Chemical synthesis; C. Electron microscopy; D. Optical properties
Polyaniline/polysulfone composite film electrode for simultaneous determination of hydroquinone and catechol
by Xiaojuan Feng; Yanlong Shi; Zhongai Hu (pp. 72-76).
► We prepared a composite film which has bi-layers with asymmetric microstructure and relatively rich porosity which provides larger surface area for electrochemical reaction. ► The outer polysulfone layer is propitious for the organic molecules to enrich on the composite film, which brings great enhancement in electron transfer kinetics. ► The composite film electrode can be used to detect qualitatively or quantitatively hydroquinone and catechol in the single solute or mixed systems.Polyaniline (PAN)/polysulfone (PSF) composite film electrodes were successfully prepared by electropolymerization using cyclic votammetry technique. The composite film electrodes show a great enhancement in electron transfer kinetics, and the separation between oxidation and reduction peaks (Δ Ep) decreases from 200 to 35mV for hydroquinone (H2Q) and from 275 to 42mV for catechol (CC) at bare Pt and composite film electrodes respectively. In their mixed systems, the redox peak of H2Q and two pairs of redox peaks of CC on this composite film electrode could be obviously distinguished which indicates the composite film electrodes have excellent electrocatalytic activity and reversibility towards the oxidation of two diphenols (hydroquinone and catechol). The linear relationships between the peak current and concentration are observed for single solute and mixed systems within the certain concentration range, implying that the composite film electrodes have potential application in the qualitative or quantitative analysis of diphenol.
Keywords: PAN/PSF composite film electrode; Electrocatalytic activity; Diphenol
Effect of fluorine addition on boron doped ZnO transparent electrode by room temperature spray method and thermal treatment
by Gil Ho Kim; Deok Hyun Hwang; Seong Ihl Woo (pp. 77-83).
► In this paper we investigate the crystalline, optical and electrical performance of ZnO thin film containing boron and fluorine. ► The boron and fluorine substitution in the ZnO lattice has positive effects in terms of increasing the free electron density and crystallinity of thin film, and these effects consequently improve the optical and electrical properties. ► The obtained B, F–ZnO thin film has great potential as a material for transparent conducting electrode.A room temperature spraying method which reduces the liquid chemical to an aerosol of submicron size droplets was used to deposit B, F–ZnO (precursor: B=0.02, 0≤F≤0.1) thin films. X-ray diffraction studies demonstrate that B, F–ZnO (precursor: B=0.02, 0≤F≤0.1) thin films have a wurtzite crystal structure. All XRD peaks have shifted higher angle and the crystal orientation was changed at certain amount of fluorine (>6at%) in precursor solution. Analysis of X-ray diffraction patterns and X-ray photoelectron spectra revealed that fluorine which was combined with zinc atom (F–Zn) was successfully doped into the ZnO crystal lattice. Analogously to these studies, the scanning electron micrographs show that the grain size tends to decrease. The optimal result of the B, F–ZnO (precursor: B=0.02, 0≤F≤0.1) films was obtained at B=0.02, F=0.06, with a low resistivity level of about 0.17×10−3Ωcm and a high transmittance of 90% in the visible light spectrum (300–800nm). We propose that the substitution of boron and fluorine in the ZnO lattice has positive effects in terms of increasing the free electron concentration and density of thin film. These results can be improved the optical and electrical properties.
Keywords: Transparent conductive oxide; Zinc oxide; Chemical deposition; Thin film
Isothermal crystallization in polypropylene/ethylene–octene copolymer blends
by Petr Svoboda; Krunal Trivedi; Dagmar Svobodova; Pavel Mokrejs; Vladimir Vasek; Keisuke Mori; Toshiaki Ougizawa; Takashi Inoue (pp. 84-93).
Display Omitted► Crystallization kinetics was tremendously decreased when the EOC content was very high (such as 70–80%). ► EOC in small amount acts as a nucleation agent for PP and increases the bulk crystallization rate. ► The analysis according to Avrami's equation revealed that the n exponent and the k rate constant initially increase and then decrease with increasing EOC content. ► The analysis according to Hoffman–Lauritzen theory revealed transitions in crystallization regimes at 130 and 136°C and the increase in activation energy U*. ► Comparison of crystallization of the blend to pure PP revealed an existence of competition of crystallization with phase separation.Crystallization kinetics of polypropylene (PP)/ethylene–octene copolymer (EOC) blends was measured by differential scanning calorimetry (DSC) and by optical microscopy at various temperatures (123–140°C). By DSC it was found that small amounts of EOC (10–30%) increase the bulk crystallization kinetics; in some cases even 80% increase was observed. Larger amounts of EOC (50–80%) have caused a decrease in crystallization kinetics. Optical microscopy has revealed that crystallization kinetics of a single spherulite is decreased by the presence of EOC, and at the same time there are more spherulites in the blend. EOC acts as a nucleation agent increasing the bulk crystallization rate and at the same time it acts as an obstacle to the growing front of a spherulite when the PP lamellae have to go around the EOC obstacle. This was confirmed by detailed analyses according to Avrami and Hoffman–Lauritzen. Structure was also observed by transmission electron microscopy (TEM). At low PP content (20%) PP forms very small isolated particles with size smaller than 1 micrometer. At 40% of PP a structure resembling a co-continuous one was found. When the PP is a majority phase (20–40% of EOC) rather large EOC particles were found. TEM also revealed presence of PP lamellae in EOC regions that together with T g shift of PP and also EOC suggested partial miscibility. While at low temperatures the crystallization is very fast, at higher temperatures there is a competition of phase separation and crystallization.
Keywords: Crystallization; Electron microscopy (TEM); Optical microscopy; Nucleation
Photoactivation and perturbation of photoluminescent properties of aqueous ZnS nanoparticles: Probing the surfactant-semiconductor interfaces
by S.K. Mehta; Sanjay Kumar (pp. 94-101).
The variation in PL emission intensity of growing ZnS NPs during first hour of their growth depends upon the nature of surfactants used for their stabilization.Display Omitted► Photoluminescence (PL) intensity of growing ZnS NPs increases linearly with time. ► Significant PL enhancement in anionic surfactant stabilized ZnS NPs on irradiation. ► PL decay with delay time after removing from UV-irradiation in all the surfactants. ► Better PL stability of ZnS NPs stabilized in anionic surfactants than cationic ones.The in situ photochemistry of aqueous colloidal ZnS has been studied in relation to variety of the surfactants as surface passivating agents. The photoluminescence (PL) intensity of ZnS nanoparticles (NPs) has been drastically enhanced as compared to their bare counterparts due to surface passivation by surfactants depending upon their molecular structure. Cationic surfactants of alkyltrimethylammonium bromide series with different chain lengths (C16, C14 and C12) have been tested. The PL emission of ZnS NPs decreases with decrease in chain length because of ineffective stabilization and passivation of surface because the larger sized NPs were produced in the surfactant with smaller chain length. On the other hand, three anionic surfactants with C12 chain length with different head groups have been capable of comparatively effective passivation to produce stable NPs with better luminescence. The changing nature of surface states during growth and long time ripening of ZnS NPs has also been monitored by comparing time evolution PL emission in different surfactants. The influence of UV-light irradiation in enhancing the PL emission has been found to be surfactant structure dependent with maximum enhancement observed with the surfactants having π-electrons in their head group functionalities. The anionic surfactants also display better tendency to retain the enhanced PL of ZnS NPs for longer time durations.
Keywords: ZnS NPs; Nucleation; Photoluminescence spectroscopy; Surfactants; Interfaces; Surface passivation
Formation mechanism of fibrous cobalt oxalate precipitated from alkaline Co2+–NH3–C2O42−–H2O system
by Zhiyong Liu; Zhihong Liu; Qihou Li; Tianzu Yang; Duomo Zhang (pp. 102-107).
The cobalt oxalate particles with fibrous morphology has the lengths of 20–160μm, widths of 0.4–6.5μm, and aspect ratios of 24–50.Display Omitted► The cobalt oxalate particles with fibrous morphology were obtained by precipitating CoCl2 and mixed (NH4)2C2O4, NH3·H2O solutions in a double jets process. ► The samples with fibrous morphology synthesized were characterized. ► The sample is a new species that has not been recorded in JCPDS files. ► The formation mechanism of cobalt oxalate was studied.The cobalt oxalate particles with fibrous morphology were obtained by precipitating CoCl2 and mixed (NH4)2C2O4, NH3·H2O solutions in a double jets process. The samples were characterized by SEM, XRD, FTIR, TG/DTA and GCMS. Thermodynamic calculations and experiments revealed that the formation of Co(NH3) n2+ ( n=1,2,…,6) results in species variation of cobalt oxalate precipitated in alkaline Co2+–NH3–C2O42−–H2O system. It was found that there are two kinds of cobalt oxalates precipitated in Co2+–NH3–C2O42−–H2O system with the change of synthetic conditions. One is β-CoC2O4·2H2O with a square columnar morphology. The other is Co(NH3)1.5C2O4·2H2O with a fibrous morphology, a species of cobalt oxalate without being recorded in newest JCPDS files. The formation mechanism of fibrous cobalt oxalate powders is that Co(NH3)1.5C2O4·2H2O precipitates in alkaline Co2+–NH3–C2O42−–H2O system.
Keywords: A. Composite materials; B. Chemical synthesis; B. Precipitation; D. Nucleation
Preparation and properties of poly(vinyl alcohol)- g-octadecanol copolymers based solid–solid phase change materials
by Haifeng Shi; Jianhua Li; Yanmei Jin; Yiping Yin; Xingxiang Zhang (pp. 108-112).
► In this paper, our objective is just focused on the preparation and characterization of such SSPCMs aiming at providing one suitable material for improving the thermal stability and preventing the liquid leakage from the matrix. Here, the SSPCMs can be fabricated by grafting to method between poly(vinyl alcohol) and octadecanol, which the grafting ratio can be controlled by adjusting the feeding components. ► The thermal properties, crystalline structure and morphology were detailed studies by WAXD, FT-IR, TGA and DSC, proving that the PVA- g-octadecanol process the better thermal storage ability and thermal stability. Compared with pure octadecanol, the heat fusion of PVA- g-octadecanol decreased due to the mobility confinement and the lower rearrangements of C18 alkyl side chains. ► This result is for the first time reported, and is a meaningful result for the investigation of the solid–solid phase change materials, and the preparation process provides one template-directed approach to obtain the high-performance materials with the better heat storage and thermal stability.The heat storage and phase transition behavior of a series of poly(vinyl alcohol)- g-octadecanol copolymers (PVA- g-C18OH) with apparent grafting ratios ranging from 283 to 503%, synthesized through “ grafting to” method, has been investigated by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), wide-angle X-ray diffraction (WAXD) and polarized optical microscopy (POM). PVA- g-C18OH copolymers exhibit the better thermal stability against C18OH, and the thermal energy storage ability (Δ Hm) is of dependence on the apparent grafting ratios. Compared with C18OH, the lower thermal storage efficiency possible is attributed to the less CH2 groups entered into the crystalline domains and the frustrated mobility of the grafted C18 alkyl side chains between PVA backbones. The results show that PVA- g-C18OH copolymers have the better thermal stability and storage ability, which can be wildly applied in the aspect of thermal energy storage.
Keywords: Poly(vinyl alcohol); Solid–solid phase change materials; Octadecanol; Grafting to
Effect of oxygen partial pressure on Ag crystallite formation at screen-printed Pb-free Ag contacts of Si solar cells
by Joo-Youl Huh; Kyoung-Kook Hong; Sung-Bin Cho; Sung-Kyun Park; Byung-Chul Lee; Kuninori Okamoto (pp. 113-119).
► The mechanism for the formation of Ag crystallites is proposed for Ag pastes containing Bi2O3-based glass frit. ► The rate of Ag crystallite formation is greatly enhanced by increasingPO2 in the firing ambient. ► The sensitivity of Ag crystallite formation toPO2 is apparent even in a spike firing. ► The Ag crystallite formation occurs without an aid of liquid Bi formation.In order to understand the mechanism underlying the formation of Ag thick-film contacts to the emitter Si of crystalline Si solar cells, the reactions between Pb-free Ag pastes containing Bi2O3-based glass frit and an n-type (100) Si wafer during firing at 800°C were examined by varying the ambient oxygen partial pressure(PO2). When the Bi2O3-based glass frit alone was reacted with the Si wafer, the redox reaction leading to the formation of liquid Bi was insensitive toPO2 in the firing ambient. When a mixture of glass frit with Ag powder was reacted with the Si wafer, however, the firing reaction was significantly influenced byPO2 in the ambient gas. With increasingPO2, the reaction leading to the formation of liquid Bi was gradually suppressed, whereas the reaction producing Ag crystallites became increasingly active, resulting in more Ag crystallites at the contact interface. The present study results strongly support the hypothesis that the Ag crystallites are formed by the reaction between the dissolved Ag+ and O2− ions in the molten glass and Si wafer without the aid of liquid Bi formation.
Keywords: Semiconductors; Glasses; Crystal growth; Precipitation
Adsorption and intercalation processes of ionic surfactants on montmorillonite associated with their ionic charge
by Keng-Jen Lin; U-Ser Jeng; King-Fu Lin (pp. 120-126).
► The adsorption of SDS by MMT results from the Donnan equilibrium for ions. ► The adsorption of CTAB by MMT results from the Coulomb attraction. ► The swelling modulus of MMT in water is 17.59Pa, first time being measured in the literature.The adsorption of sodium dodecylsulfate (SDS) and cetyltrimethylammonium bromide (CTAB) by montmorillonite (MMT), respectively, in aqueous solution and their resulting intercalating structures after removal of water were investigated. The former adsorption results from the Donnan equilibrium for ions leading to hydrophilic nature of SDS/MMT hybrid, whereas the latter results from the Coulomb attraction or so-called cation exchange leading to hydrophobic nature of CTAB/MMT. X-ray scattering and transmission electron microscopy investigations on the dried SDS/MMT hybrids reveal that the adsorbed SDS neither substantially increases the interlayer distance nor changes the rough spherical texture of pristine MMT, whereas the adsorbed cetyltrimethyl ammonium cations significantly increase the interlayer distance of MMT resulting a well-integrated CTAB/MMT lamellar structure.
Keywords: Montmorillonite; Ionic surfactant; Nanostructure; Intercalation
Silicon nitride gradient film as the underlayer of ultra-thin tetrahedral amorphous carbon overcoat for magnetic recording slider
by Gui-Gen Wang; Xu-Ping Kuang; Hua-Yu Zhang; Can Zhu; Jie-Cai Han; Hong-Bo Zuo; Hong-Tao Ma (pp. 127-131).
► The ultra-thin carbon films with different silicon nitride (Si-N) film underlayers were prepared. ► It highlighted the influences of Si-N underlayers. ► The carbon films with Si-N underlayers obtained by nitriding especially at the substrate bias of −150V, can exhibit better corrosion protection propertiesThere are higher technical requirements for protection overcoat of magnetic recording slider used in high-density storage fields for the future. In this study, silicon nitride (Si-N) composition-gradient films were firstly prepared by nitriding of silicon thin films pre-sputtered on silicon wafers and magnetic recording sliders, using microwave electron cyclotron resonance plasma source. The ultra-thin tetrahedral amorphous carbon films were then deposited on the Si-N films by filtered cathodic vacuum arc method. Compared with amorphous carbon overcoats with conventional silicon underlayers, the overcoats with Si-N underlayers obtained by plasma nitriding especially at the substrate bias of −150V, can provide better corrosion protection for high-density magnetic recording sliders.
Keywords: Thin films; Interfaces; X-ray photo-emission spectroscopy (XPS); Corrosion
Synthesis of hydroxyapatite particles in catanionic mixed surfactants template
by Nesa Esmaeilian Tari; Mohammad M. Kashani Motlagh; Beheshteh Sohrabi (pp. 132-135).
Display Omitted►The mixture of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with different ratio were used as the template for synthesizing HAP particles. ► The overall morphology of the obtained powders at anionic-rich region (SDS:CTAB, 99:1) solution is rod like with high regularity. ► In the presence of cationic rich region (SDS:CTAB, 1:99) the resulted particles was sheet like. ► The resulted HAP nano particles in the presence of SDS were rod like but their morphology was less oriented than anionic-rich region.Different morphologies of nano hydroxyapatite particles, Ca10(PO4)6(OH)2 (HAP) are prepared by precipitation method using CaCl2 and H3PO4 (water phase) and the mixture of cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and anionic one sodium dodecyl sulfate (SDS) as template. The mixture of these surfactants in two regions of cationic-rich and anionic-rich form the various aggregations as template. The results show that by changing the ratio of cationic to anionic surfactant in the mixture the morphology of the nano HAP can be controlled. The nano structure of products is studied by the means of X-ray diffraction (XRD), Fourier transmission infrared spectrometer (FT-IR) and scanning electron microscopy (SEM). With this system we could synthesize nano particles of hydroxyapatite with high crystallinity and least agglomeration.
Keywords: Nanostructures; Precipitation; Surface properties; Electron microscopy
Synthesis of monodisperse Ag–Au alloy nanoparticles with large size by a facile fabrication process
by Weiwei Zhang; Liqing Huang; Jian Zhu; You Liu; Jun Wang (pp. 136-141).
► A novel facile procedure for synthesizing Ag–Ag alloy nanoparticles was proposed. ► The monodisperse Ag–Au alloy nanoparticles with large size (>20nm) were synthesized. ► The formation mechanism is suggested by analyzing the characteristic results.The fairish monodisperse Ag–Au alloy nanoparticles (NPs) with various composition and size were synthesized by a facile fabrication procedure. UV–visible (UV–vis) spectroscopy and transmission electron microscopy (TEM) confirmed the formation of homogeneous alloy NPs. The diameters of the resultant monodisperse spherical Ag–Au alloy NPs are 21–32nm and the long-axis size of the resultant monodisperse nonspherical Ag–Au alloy NPs are about 28nm. The possible formation mechanism is suggested by analyzing the dynamic absorption spectra, TEM and energy dispersive X-ray (EDX) spectroscopy of the alloy nanoparticles at the different time. Ag–Au alloy NPs synthesis method developed in this paper has several advantages: (1) the synthesis process is very simple. Only sodium citrate was used as both reducing agent and stabilizing agent and only one step heating process was needed. (2) The resultant Ag–Au colloidal dispersion is free from AgCl deposition and (3) the fairish monodisperse and large size (>20nm) Ag–Au alloy NPs can be obtained.
Keywords: Alloys; Chemical synthesis; Energy dispersive analysis of X–rays; Electron microscopy; Optical properties
Specific heat and magnetic susceptibility of single-crystalline ZnCr2Se4 spinels doped with Ga, In and Ce
by E. Malicka; T. Groń; A. Ślebarski; A. Gągor; A.W. Pacyna; R. Sitko; J. Goraus; T. Mydlarz; J. Heimann (pp. 142-150).
Display Omitted► Ga, In and Ce substitutions do not affect the Cr3+ 3 d3 electronic configuration. ► The larger interatomic elongations, the lower saturation magnetic moment. ► Imaginary part of susceptibility reveals energy loss only in case of the HS state. ► In the LS state the second critical field is completely quenched. ► The spin wave propagation and lattice contribution weaken with increasing ionic radius.The crystal structure, X-ray photoelectron spectra (XPS), dc magnetic isotherm, ac magnetic susceptibility and specific heat measurements for antiferromagnetic and semiconducting ZnCr2Se4 spinel diluted with Ga, In and Ce are presented. For all the studied spinels the XPS spectra exhibit the Cr 2 p3/2 splitting of 1eV characteristic for the 3 d3 electron configuration of the chromium ions. A correlation between the second critical field Hc2 of the helix to paramagnetic transition and the magnetic specific heat C-peak was found in (Zn0.86Ce0.08)[Cr2]Se4. This correlation weakens for (Zn0.99)[Cr1.92Ga0.06]Se4 and disappears for (Zn0.83In0.11)[Cr1.73In0.14]Se4 as the saturation magnetic moment rapidly decreases in the sequence Ce, Ga and In. The magnetic contribution to the specific heat displays a sharp peak at TN and is maximal at the spin fluctuation temperature of 40K, which is related to the maximum of the magnetic susceptibility at the same temperature and at 50kOe in the spin fluctuation region, evidenced by the entropy exceeding 90% of the entropy calculated classically for the complete alignment of the Cr spins, Sm= Rln(2 S+1). These effects are considered within the cation–anion distances in octahedral sites, the cation deficiency and the spin state of 3 d Cr3+ ions in t2g orbital.
Keywords: Chalcogenides; X-ray photo-emission spectroscopy (XPS); Magnetic properties; Specific heat
Structural variations of MCF and SBA-15-like mesoporous materials as a result of differences in synthesis solution pH
by Ozge Aktas; Sena Yasyerli; Gulsen Dogu; Timur Dogu (pp. 151-159).
► Different structure/morphology of SBA-15 and MCF synthesized at pH 1.5 and pH ≪1.0. ► Distorted SBA-15 mesopore long range order and MCF cage-window structure at pH 1.5. ► Significant increase in micropore contribution and surface area at pH 1.5. ► Increased corona contribution and bridging of mesopores by secondary pores at pH 1.5. ► Complex interconnected pores with short range order at pH 1.5.This work illustrated the significance of synthesis solution pH on the structural characteristics of MCF and SBA-15-like mesoporous materials. SBA-15 and MCF-like materials synthesized at pH ≪1.0 and pH values higher than 1.0 showed highly different structural and morphological properties. XRD, TEM and nitrogen adsorption–desorption isotherms of the synthesized materials showed that the long range order of mesopores of SBA-15 and the cage-window structure of MCF were significantly distorted at higher synthesis solution pH values (all acidic). A totally amorphous material with no ordered pores was obtained at a pH value of 2.0. Surface area and micropore contribution to the total pore volume significantly increased, while average mesopore diameter was decreased by increasing the synthesis pH value to 1.5. This was considered to be due to the increased contribution of corona region and bridging of the mesopores by secondary pores at higher pH. Pore structures of the MCF and SBA-15-like materials prepared at pH 1.5 were rather complex and interconnected. SEM, FT-IR and pyridine adsorbed FT-IR analysis of the materials also showed the importance of synthesis solution pH on the morphology, structure and acidic characteristics of the synthesized materials.
Keywords: Mesoporous materials; SBA-15; MCF; Chemical synthesis; Microstructure
The impact of some factors on the inhibitory action of Radish seeds aqueous extract for mild steel corrosion in 1M H2SO4 solution
by Ehteram A. Noor (pp. 160-169).
► Corrosion inhibition of mild steel in acid solutions by aqueous extract of Radish seeds. ► The effect of some factors on the corrosion inhibition of mild steel in acid solutions. ► Electrochemical measurements were used in the present research. ► Correlation between the extract constituent and its inhibitive action was obtained.The impact of some factors (such as inhibitor concentration, solution temperature, I− ions addition, surface finishing and immersion time) on the inhibitory action of radish seeds aqueous extract (RSAE) for mild steel corrosion in 1M H2SO4 solution was investigated by using electrochemical measurements. The inhibition efficiency of RSAE increases with the increase of its concentration but decreases drastically at relatively high temperatures (50°C). The addition of I− ions synergistically increased the inhibition efficiency of RSAE and this synergistic effect depends on the concentration of both inhibitor and I− ions. It was found that the inhibition efficiency of RSAE increases with a surface roughness of up to 400 grits after which it decreases with additional increases in surface roughness. The data revealed that the inhibition efficiency of RSAE increases with increasing immersion time in the tested solution which may be attributed to a slow rate of adsorption process. The inhibitory action of RSAE is suggested to be due the synergistic effect of its constituents.
Keywords: Corrosion; Inhibition; Radish; Iodide ions; Surface finishing; Immersion time
Ultrasonic-assisted synthesis of magnetite based MRI contrast agent using cysteine as the biocapping coating
by Reza Ahmadi; Mahrooz Malek; Hamid Reza Madaah Hosseini; Mohammad Ali Shokrgozar; Mohammad Ali Oghabian; Afshin Masoudi; Ning Gu; Yu Zhang (pp. 170-177).
► We used cysteine as surfactant to synthesize stable magnetite-based ferrofluids. ► pH increase from 11 to 12 led to particle size decrease from 19.58 to 10.02nm. ► Cytotoxicity assay showed that synthesized particles were biocompatible. ► MRI results showed that magnetite particles were accumulated in lymph nodes.Magnetite nanoparticles (mean particle size ranging from 10 to 20nm) were prepared by a biomolecule-assisted solution-phase approach under ultrasonic irradiation. Cysteine was used as the capping agent in the solution. The results show that cysteine could be an efficient biocapping agent in producing Fe3O4 nanoparticles. The crystal structure and magnetic properties of the nanoparticles were characterized by XRD and VSM techniques, respectively. FT-IR was used to investigate the presence of cysteine on the nanoparticles surface. The influence of pH value of the solution on the size distribution and hydrodynamic size of nanoparticles were studied by TEM and DLS methods, respectively. The MTT assay performed by incubation of L929 cells, showed the good biocompability of synthesized ferrofluids. In vitro T1 and T2 relaxivity measurements along with in vivo studies, which were conducted on rats, demonstrate that synthesized nanoparticles are applicable as the contrast agents, especially for imaging of the lymphatic system.
Keywords: Magnetic materials; Nanostructures; Electron microscopy; Fourier transform infrared spectroscopy (FT-IR)
Chemical bond cleavage induced by electron heating
by Jun Fukushima; Keiichiro Kashimura; Motoyasu Sato (pp. 178-183).
Gas emissions from titanium-metalloid compounds (titanium nitride and oxide) have been investigated to understand the effects of a microwave field on chemical reactions. We employed a high vacuum system (PO2=10−6Pa) to observe in situ reductions. For titanium oxides, H-field heating significantly differed from conventional one in terms of oxygen emissions. For titanium nitride, the emissions were also induced by microwave heating. These tendencies were observed at temperatures above 1000°C. A quantum chemical interpretation is provided to explain the emissions of the gases, and the experimental data is in good agreement with results predicted using the electronic energy band structure.
Keywords: Microwave H-field; Titanium oxides; Titanium nitrides; Density of electron
Non-catalytic and template-free growth of single crystalline copper vanadate nanowires for field emission applications
by Muhammad Shahid; Imran Shakir; Hyoungwoo Yang; Padmnabh Rai; Dae Joon Kang (pp. 184-189).
► Single crystalline CuV2O6 nanowires were grown on Si by simple thermal annealing. ► Growth temperature play a vital role in controlling phase and diameter of nanowires. ► Field emission current density 1.2mAcm−2 with a turn-on field of 1.2Vμm−1 obtained.High quality single crystalline CuV2O6 (CVO) nanowires were successfully grown on the silicon substrates by simple thermal annealing of spin coated film in air. The synthesized nanowires have an average diameter of 100nm, and length ranges between 1 and 5μm, with growth direction along <201>. We found that growth temperature play a vital role in controlling the phase and the diameter of nanowires in this process. We propose a growth mechanism based on the experimental results. Field emission properties were revealed to be strongly morphology dependent. The nanowires in small diameter and high aspect ratio exhibited the best FE performance showing excellent field emission current densities 1.2mAcm−2 with a low turn-on field of ∼1.2Vμm−1. The experimental results show that CVO nanowires are promising candidate in realizing high performance field emission display.
Keywords: Field emission; Chemical solution deposition; Template–free growth; Nanowires
Coarsening mechanisms, texture evolution and size distribution of Cu6Sn5 between Cu and Sn-based solders
by H.F. Zou; H.J. Yang; Z.F. Zhang (pp. 190-198).
During the reflowing procedure, the Cu concentration in the solder affects the coarsening mechanisms of intermetallic compound (IMC) grains. For the Sn3Cu solder, the mean radius of the IMC grains was proportional to the cube root of the reflowing time; while it follows the square root relation with the reflowing time for the SnAgCu and Sn solders. It is proposed that the flux from the substrate was only consumed to coarsen the IMC grains for Sn3Cu solder, while it was separated into two fluxes for the SnAgCu and Sn solders at the reflowing initial procedure. For the Sn3.8Ag0.7Cu/Cu and Sn/Cu couples, the size distribution of the IMC grains well agrees with the modified flux driven ripening (FDR) model when the value of r/〈 r〉 is above 1; while it would closely match with Marqusee and Ross analysis when the value of r/〈 r〉 is below 1. For Sn3Cu/Cu couple, the size distribution of IMC grains shows good agreement with the FDR model. However, for SnPb/poly-Cu, during the solid-state aging procedure, the mean radius of the IMC grains was proportional to the cube root of the aging time. And the size distribution of IMC grains is well consistent with the FDR model.
Keywords: Intermetallic compounds; Nucleation; Interface; EBSD
Dielectric and magnetoelectric properties of Li0.5Ni0.75− x/2Zn x/2Fe2O4+Ba0.5Sr0.5TiO3 ME composites
by S.U. Durgadsimi; S.S. Chougule; B.K. Chougule; C.H. Bhosale; S.S. Bellad (pp. 199-203).
► The magnetoelectric composites Y[Li0.5Ni0.75− x/2Zn x/2Fe2O4]+(1− Y)[Ba0.5Sr0.5TiO3] are prepared by standard ceramic technique. ► The XRD patterns confirmed the coexistence of piezomagnetic and piezoelectric phases. ► Both dielectric constant ( ɛ′) and loss tangent (tan δ) decrease with increase in frequency. ► The linearity in the log σac vs. log ω2 plots confirmed small polaron hopping type of conduction mechanism. ► ME output showed direct relation with the resistivity of the composites.The magnetoelectric composites with the composition Y[Li0.5Ni0.75− x/2Zn x/2Fe2O4]+(1− Y)[Ba0.5Sr0.5TiO3] where x=0.1, 0.2. 0.3 and Y=0.1, 0.2, 0.3 were prepared by standard double sintering ceramic technique. The XRD patterns confirmed the coexistence of piezomagnetic and piezoelectric phases. Both dielectric constant ( ɛ′) and loss tangent (tan δ) decrease with increase in frequency exhibiting normal dielectric behaviour. The linearity in the log σac vs. log ω2 plots confirmed the small polaron hopping type of conduction mechanism in the composites studied. Flat curves in the ME output vs. dc magnetic field are obtained which may be due to the presence of strontium in the composites. ME output showed direct relation with the resistivity of the composites.
Keywords: ME effect; Composites; Ferrites; Dielectric constant; Resistivity
Thermal, structural and spectroscopic investigations on Eu3+ doped boro-tellurite glasses
by K. Selvaraju; K. Marimuthu; T.K. Seshagiri; S.V. Godbole (pp. 204-210).
► Fundamental O–H, (BO3)− vibrations and B–O–B linkages in borate network explored. ► The covalent nature of the Eu3+ ions with surrounding ligands have been confirmed. ► B3TMK glass is found to be the best optical candidate for laser working at 612nm.Eu3+ doped boro-tellurite glasses with the chemical composition (69− x)B2O3– xTeO2–15Mg2O–15K2O–1Eu2O3 (where x=0, 10, 20, 30 and 40wt%) have been synthesized and its thermal, structural and spectroscopic behavior were studied and reported. The thermal behavior of the Eu3+ doped boro-tellurite glasses were explored through DTA thermograms. The presence of varying tellurium dioxide results in structural and spectroscopic changes around Eu3+ ions and are explored through XRD, FTIR, UV–vis, Luminescence and lifetime measurements. The XRD pattern confirms the amorphous nature and the FTIR spectra reveal the formation of the local structural units BO3 and BO4 in the prepared glasses. The bonding parameters (̄ β and δ) have been calculated based on the observed band positions of the absorption spectra. The Judd–Ofelt (JO) parameters were determined from the absorption and luminescence spectra and the results are presented. The variation in the JO intensity parameters Ω λ ( λ=2, 4 and 6) and the hypersensitive band positions with the change in chemical composition have been discussed in detail. The JO parameters have been used to derive important radiative properties like transition probabilities ( A), branching ratios ( βR) and peak stimulated emission cross section ( σE/ P) for the5D0→7F J ( J=1, 2, 3 and 4) transitions of the Eu3+ ions. The varying optical properties of the prepared glasses with the change in tellurium dioxide have been studied and compared with similar results.
Keywords: Glasses; Annealing; FTIR; Luminescence; Optical properties
Reversible tuning of ZnO optical band gap by plasma treatment
by Szetsen Lee; Jr-Wei Peng; Ching-Yuan Ho (pp. 211-215).
► The ZnO optical band gap blue-shifts with hydrogen plasma treatment. ► The ZnO optical band gap red-shifts with oxygen plasma treatment. ► The ZnO optical band gap can be reversibly fine-tuned.Zinc oxide (ZnO) films synthesized by reacting zinc nitrate with hexamethylenetetramine were treated with hydrogen and oxygen plasmas. From UV–visible absorption and optical emission inspection, we have found that the optical band gap of ZnO films blue-shifted with hydrogen plasma treatment, but red-shifted with oxygen plasma treatment. By alternating the treatment sequence of hydrogen and oxygen plasmas, the ZnO optical band gap can be reversibly fine-tuned with the tunable range up to 80meV. Scanning electron microscopy characterization indicates that the variation of the optical band gap is attributed to the competition between amorphous and crystalline forms of ZnO. The mechanism of reversible optical band gap tuning is discussed.
Keywords: ZnO; UV–visible; Optical emission; Band gap
Thermoelectric properties of Ag-doped bismuth sulfide polycrystals prepared by mechanical alloying and spark plasma sintering
by Yi-Qiang Yu; Bo-Ping Zhang; Zhen-Hua Ge; Peng-Peng Shang; Yue-Xing Chen (pp. 216-222).
► The Bi2− xAg xS3 ( x=0–0.07) were prepared by mechanical alloying and spark plasma sintering. ► Ag entering into Bi2S3 lattice improves the electrical transport properties. ► The maximum ZT value of 0.25 is achieved at 573K for the Bi1.99Ag0.01S3 sample. ► The ZT value of 0.25 is the highest value in Bi2S3 system reported so far.Single orthorhombic phase Bi2− xAg xS3 ( x=0–0.07) bulk materials were prepared by combining mechanical alloying (MA) with spark plasma sintering (SPS) technique. The microstructure and electrical transport properties were investigated with a special emphasis on the influence of Ag content. All the samples have a high density (91.1–95.9%) and homogeneous grains of about 100–500nm. Optimizing the Ag content greatly improves the electrical conductivity and leads to a peak value of 2.8×103Sm−1 at 523K for the Bi1.99Ag0.01S3 composition. The absolute value of Seebeck coefficient shows an inversely varying trend to the electrical conductivity with Ag content, whereby a power factor at 523K by adjusting Ag content is enhanced from 91μWmK−2 for Bi2S3 to 235μWmK−2 for Bi1.99Ag0.01S3. The thermal conductivity of Bi2− xAg xS3 ranges from 0.48 to 0.73WmK−1, which is lower than the reported values of Bi2S3 compounds. An enhanced maximum ZT value 0.25 is achieved at 573K for the Bi1.99Ag0.01S3 sample, which is the highest value in Bi2S3 system in literature. The present work reveals that the non-toxic and cheap Bi2S3 based compound is a promising candidate for the thermoelectric applications.
Keywords: Semiconductors; Sintering; Electrical conductivity; Thermal conductivity
Synthesis and characterization of CdS/PVA nanocomposite thin films from a complexing agent free system
by D. Saikia; P.K. Saikia; P.K. Gogoi; M.R. Das; P. Sengupta; M.V. Shelke (pp. 223-229).
► Polymer–CdS nanocomposite thin films have been synthesized by in situ thermolysis of the precursors confined in polymer matrix. ► Thesynthetic method is free from complexing agent. ► The film was prepared within a short period (10–60min) compared to conventionalCBD method, which takes longer time. ► Our method can yield pinhole free, homogeneous and transparent films very well adhered to thesubstrate. ► The film is suitable for application as a window layer in solar cell.CdS/PVA nanocomposite thin films have been deposited on glass substrates by in situ thermolysis of precursors dispersed in polyvinyl alcohol (PVA). The synthetic technique reported in this study is free from complexing agent and hence no need to control the pH of the solution as in the case of conventional CBD. The as-prepared films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), UV–vis spectroscopy, and photoluminescence (PL) spectra. The XRD and SAED results indicated the formation of CdS nanoparticles with hexagonal phase in the PVA matrix. The photoluminescence and UV–vis spectroscopy revealed that CdS/PVA films showed quantum confinement effect. From the shift in optical band gap, particle sizes were calculated using effective mass approximation (EMA) method and it was found to be in agreement with the results obtained from TEM observations. The SEM results indicated that as grown films were homogeneous with no visible pinholes and cracks. The film prepared at100°C was found to be suitable for application as a window layer in solar cell.
Keywords: CdS/PVA; Nanocomposite; Thermolysis; Optical properties
Optical and magnetic behavior of Ag encapsulated β-Fe2O3 core–shell hollow nanotubes
by Anil Kumar; Aditi Singhal (pp. 230-240).
The addition of Ag functionalizes β-Fe2O3 to form Ag–β-Fe2O3 core–shell hollow tubular nanostructures depicting superparamagnetic behavior with relatively high Ms value.Display Omitted► Synthesis of colloidal Ag encapsulated β-Fe2O3 core–shell hollow nanotubes. ► A variation in [Ag] (0.23–0.76×10−4moldm−3) regularly blue shifts the excitonic band due to Fe2O3. ► Growth of β-Fe2O3 nanorods on Ag reduces their diameter with orientation in a particular direction. ► A typical [Ag] (0.58×10−4moldm−3) develops core–shell morphology, β-Fe2O3 as shell and Ag in core. ► At 7T and 5K magnetic behavior of Ag–β-Fe2O3 is transformed to superparamagnetic with enhanced Ms.This paper reports the synthesis of silver encapsulated β-Fe2O3 core–shell hollow nanotubes soluble in aqueous medium. Colloidal β-Fe2O3 nanoparticles produced by the hydrolysis of FeCl3 are grown on Ag nanoparticles in N2 environment to produce core–shell hollow tubular structure. A variation in the amount of silver (0.23×10−4moldm−3–0.76×10−4moldm−3) regularly blue shifts the excitonic band due to β-Fe2O3, and reduces the thickness of β-Fe2O3 in the shell besides changing the morphology of the nanostructures. A typical amount of silver (0.58×10−4moldm−3) leads to the development of core–shell hollow tubes (SC) in which the core consists of Ag nanoparticles with an average diameter of 3.5nm and the shell is made of β-Fe2O3 hollow nanotubes consisting of Cl− and NO3− ions with an average thickness and the inner diameter of 3nm and 9nm, respectively. Unlike pure β-Fe2O3 nanorods, SC at 7T exhibits superparamagnetic behavior at a relatively higher temperature (100K), whereas β-Fe2O3 under these conditions depicted paramagnetic behavior. However, at 7T and 5K both of the samples exhibited superparamagnetic behavior, but the magnetization for SC (0.4emucm−2) was about 5.6 times higher compared to that of pure β-Fe2O3. The presence of specific amount of Ag in SC possibly results in the observed change in morphology, decrease in dimension and the orientation of β-Fe2O3 nanorods in a particular direction, which contributes to the transformation in magnetic behavior associated with enhanced saturation magnetization.
Keywords: Optical; Magnetic; Semiconductors; Nanomaterials
A comparative study of ternary Al–Sn–Cu immiscible alloys prepared by conventional casting and casting under high-intensity ultrasonic irradiation
by H.R. Kotadia; A. Das; E. Doernberg; R. Schmid-Fetzer (pp. 241-249).
► Systematic investigation on the solidification microstructure of ternary Al–Sn–Cu immiscible system aided by computational thermodynamics calculations. ► Comparative study of conventional casting and casting under high-intensity ultrasonic irradiation. ► Demonstrated the high effectiveness of ultrasound exposure during solidification. ► Effect of cavitation on nucleation and the relative effects of cavitation and acoustic streaming on the dispersion of Sn-rich liquid phases have been explained from the experimental observation. Cavitation was found to promote fragmentation and dispersion of Sn-rich liquid leading to homogeneous dispersion of refined Sn phase. Microstructural modification was found to be contributed by cavitation and associated shockwave generation while bulk fluid flow under acoustic streaming was found to be less effective on the microstructure evolution. ► Globular and highly refined α-Al formed near the radiator through enhanced heterogeneous nucleation in contrast to dendritic α-Al observed in conventional solidification.A comparative study on the microstructure of four ternary Al–Sn–Cu immiscible alloys, guided by the recent thermodynamic assessment of the system, was carried out with specific focus on the soft Sn particulate distribution in hard Al-rich matrix in the presence and absence of ultrasonic irradiation during solidification. The results clearly demonstrate high effectiveness of ultrasonication in promoting significantly refined and homogeneously dispersed microstructure, probably aided by enhanced nucleation and droplet fragmentation under cavitation. While conventional solidification produced highly segregated Sn phase at the centre and bottom of Sn-rich alloy ingots, ultrasonic treatment produced effective dispersion irrespective of the alloy constitution in the region around the radiator. At distance >20mm from the radiator, presumably outside the region of active cavitation, any bulk fluid flow from acoustic streaming appears to be less efficient in preventing segregation of liquids even though still more effective than quiescent solidification conditions.
Keywords: Immiscible alloys; Al–Sn–Cu alloys; Solidification; Ultrasonic
Template Assisted Fabrication of Pt–Sn Core–Shell Nanospheres
by Chien Chon Chen; Chi Liang Chen; Yi-Sheng Lai (pp. 250-253).
► Pt–Sn core–shell nanospheres were formed on AAO through sputtering and thermal-reflowing methods. ► The thermo-reflowing process is shown to be a suitable method for fabricating nanospheres of uniform size. ► The quantity of spheres and surface area can be calculated easily.Sub-micron or nano-scale spheres are typically fabricated using conventional powder metallurgy processes; however, it is difficult to control the diameter and shape of each nanoparticle such that they are uniform. In this work, tin (Sn) was first sputtered on an anodic aluminum oxide (AAO) template. Then tin spheres were formed on the AAO by sinking tin-deposited AAO into silicone oil through the thermal-reflowing process. The size and quantity of the spheres were controlled with the sputtering time and power. The thermal-reflowed tin nanospheres were subsequently coated with thin platinum (Pt) film by DC sputtering, forming Pt–Sn core–shell nanospheres. The total surface area of the tin sphere on AAO and specific surface area of the Pt spherical shell were determined. The specific surface areas of Pt shell on the Sn nanospheres were 8.1–16.2, 10.3–20.6, and 12.8–25.6 (m2g−1) with wetting angles at 100°, 120°, and 150°, respectively between the Sn sphere an AAO.
Keywords: Nanostructure; Oxides; Thin films; Coatings; Solidification
The creep rate induced by interface diffusion in particulate composite materials
by Yinfeng Li; Zhonghua Li; Xi Wang; Jun Sun (pp. 254-257).
► An analytical solution for creep rate induced by interface diffusion in particulate reinforced composites is presented. ► The solution is applicable for the case of interface slip. ► The solution gives an upper bound of the creep rate for a composite of nonlinear matrix.A closed-form solution for creep rate induced by interface diffusion is developed for particulate reinforced composites. The driving force for diffusional mass transport along the interface is the normal stress acting on the interface, which is obtained from the Eshelby inclusion theory. For the application of the present solution to the realistic composites, the scale effect is taken into account by finite element analysis based on a three-dimensional unit cell under uniaxial tension. The closed-form solution is an explicit function of the applied stress, reinforcement volume fraction and size, as well as the modulus ratio between the reinforcement and the matrix. It is noted that although the present solution is derived under the assumptions of free interface slip and the composites of a linearly elastic matrix, it is approximately applicable for the case of interface slip, and gives an upper bound of the creep rate for a composite of nonlinear matrix.
Keywords: Composite materials; Creep; Diffusion
Negative differential resistance in ZnO nanowires induced by surface state modulation
by Qi Zhang; Junjie Qi; Yunhua Huang; Xin Li; Yue Zhang (pp. 258-261).
Display Omitted► Negative differential resistance (NDR) was observed by modulating ZnO NW surface. ► In the toluol environment, NDR was not observed, differing from the performance in ethanol. ► The conductance at the critical points is inversely proportional to the ethanol concentration. ► The released electrons at the surface created a potential perpendicular to the surface. ► The nonequilibrium occupation factor for electrons in the oxidation process saturates.Negative differential resistance was observed in current–voltage curves of ZnO nanowire embedded sensors in the ethanol environment and conductances at critical points are inversely proportional to the concentration, while this phenomenon was not observed in the toluol environment. Through individual ZnO nanowire experiments, we attribute negative differential resistance to the joint effect of electron transference in the oxidation process of hydroxyls and the nonequilibrium occupation factor for electrons in the process saturating with generation rate of carriers at the ZnO nanowire surface. The inverse variation is associated with the densities of donor and acceptor traps. These results indicate that surface depletion can be beneficial to nanodevices.
Keywords: Negative differential resistance; Surface state; Depletion layer; ZnO
Mechanism and characterizations studies of resistive switching effects on a thin FeO x-transition layer of the Ti/TiN/SiO2/FeO x/FePt structure by thermal annealing treatments
by Yao-Feng Chang; Li-Wei Feng; Ting-Chang Chang (pp. 262-267).
► Thermal annealing effects could change electrical and material properties in the transition iron-oxide layer of the Ti/TiN/SiO2/FeO x/FePt structure. ► Annealing effects could improve electrical characteristics, such as bipolar switching behaviors (set and reset process) and retention reliability. ► Statistics of the electrical parameters could be investigated to understand the mechanism and characterizations of iron-oxide resistive switching effect. ► The retention reliability of iron-oxide resistive switching memory could be improved by the optimized annealing condition.We investigated annealing effects on the bipolar resistive switching characteristics and mechanism of the thin FeO x transition layer in a Ti/TiN/SiO2/FeO x/FePt structure by depositing a plasma-enhanced tetraethyl orthosilicate oxide onto the Fe-contented electrode. The electrical results show that the values of operation voltage, variation of electrical parameters and retention properties could be improved with the increasing thermal treatment budget. Tunneling electron microscope, X-ray diffraction, Auger electron spectroscopy and X-ray photon-emission spectra depth profiles were examined for cross-section image, crystallinity and composition analyses of the transition layer. In order to investigate the resistive switching mechanism and characterizations in Ti/TiN/SiO2/FeO x/FePt structure, the electrical parameters were extracted during set and reset process. The retention property at room temperature and 85°C was improved after the thermal treatment and maintains both resistance states over 6×104s implies promising potential for future memory application.
Keywords: Resistive switching; Iron oxide; Annealing effect; Nonvolatile memory
Preparation of nanocrystalline VN by the melamine reduction of V2O5 xerogel and its supercapacitive behavior
by Fukui Cheng; Chun He; Dong Shu; Hongyu Chen; Jie Zhang; Shaoqing Tang; David E. Finlow (pp. 268-273).
► Organic nitridizing agent was employed for preparation of nanocrystalline VN. ► The supercapacitive behavior of VN was studied by electrochemical method. ► The supercapacitive behavior of VN was studied in three kinds of electrolyte. ► The specific capacitance of VN was determined as 273Fg−1 in 1.0M KOH. ► The supercapacitive mechanism and involved factor on capacitance were analyzed.An organic nitridizing reagent was employed in the preparation of nanocrystalline VN at 800°C under a N2 atmosphere. The prepared VN was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS), and its supercapacitive behavior was studied by cyclic voltammetry (CV) in three different types of aqueous electrolyte, 0.5M H2SO4, 2.0M NaNO3 and 1.0M KOH. The XRD results indicate that prepared VN has a cubic structure with space group Fm3m and a lattice parameter of 4.139Å. The nanocrystalline structure of VN with a low degree of crystallinity was confirmed by TEM imaging. The presence of oxygen on the VN surface was detected by FTIR and XPS, and its molecular composition was determined to be VN1.02O0.1. The specific capacitances of nanocrystalline VN were determined to be 114, 45.7 and 273Fg−1 in 0.5M H2SO4, 2.0M NaNO3 and 1.0M KOH, respectively. Thus, the KOH solution was considered the best aqueous electrolyte for the capacitive performance of VN. The supercapacitive mechanism and the factor that influenced the specific capacitance are also analyzed in this paper.
Keywords: Nanocrystalline VN; Melamine reduction; Cyclic voltammetry; Supercapacitor
In situ study on the structural transition in YBO3 through Raman spectroscopy
by G.X. Gu; D. Wang; X.S. Lv; S.M. Wan; J.L. You; Q.L. Zhang; S.T. Yin (pp. 274-277).
High temperature Raman spectroscopy has been used to investigate the conformational transition of YBO3. From the LT to HT phase, the B3O9 rings break into the isolated BO3 triangles.Display Omitted► High temperature Raman spectroscopy was used to study the conformational transition of YBO3. ► The characteristic Raman bands of the HT phase YBO3 were identified. ► A structural phase transition with a large thermal hysteresis was found.Raman spectroscopy is a powerful tool to judge the fundamental building units contained in crystal structure. In this work, it was used to investigate the basic structural groups involved in the low temperature (LT) and high temperature (HT) phase YBO3. The characteristic Raman vibrational bands of the LT and HT phases YBO3 were identified respectively. The characteristic vibrational peaks of the LT phase YBO3 locate around 410cm−1 and 500cm−1, both of them are attributed to the ring bending modes of B3O9 group. The strong characteristic vibrational band of the HT phase YBO3, arising from the symmetric stretching mode of BO3 group, locates around 940cm−1. A structural phase transition with a large thermal hysteresis was found. During the phase transition process, the B–O bonds of the BO4 groups break and the B3O9 rings cleave into the BO3 plane conjugated groups.
Keywords: Inorganic compounds; Phase transitions; Raman spectroscopy and scattering
Thermal evaluation of TiN/CN x multilayer films
by Mônica de Mesquita Lacerda; Júlio Miranda Pureza; José Fernando Fragalli; Ney Mattoso Filho; Yip-Wah Chung (pp. 278-283).
► Thermal analysis on TiN film shows multilayer better performance than single layer. ► Buckling at films follows continuous medium model in despite of multilayer structure. ► Crack resistance and propagation are dependent on bias voltage applied on samples.This work examines the thermal behavior and failure mechanisms of TiN/CN x multilayer coatings deposited by DC magnetron sputtering. The samples were examined by transmission electron microscopy before thermal analysis. During thermal analysis, the samples were heated up to 1070K at a constant rate of 10Kmin−1 in a N2 atmosphere and their thermal stability was evaluated by thermo gravimetric (TGA) and differential thermal analyses (DTA). These analyses indicate that the multilayer coating is thermally stable up to 950K, followed by stress relaxation when the temperature exceeds 950K. After this thermal treatment, coating surfaces were observed by scanning electron microscopy. Buckling and fractured surface were seen for multilayers deposited with and without substrate bias voltage applied during growth process, although samples deposited with substrate bias are more resistant to crack formation and propagation.
Keywords: Multilayer coating; Sputtering; DTA; Electron microscopy
Synthesis, conductivity and magnetic properties of poly(N-pyrrole phosphonic acid)–Fe3O4 nanocomposite
by Emine Temizel; Esra Ayan; Mehmet Şenel; Hamit Erdemi; Mustafa S. Yavuz; Hüseyin Kavas; Abdulhadi Baykal; Ramazan Öztürk (pp. 284-291).
► The preparation and characterization of poly(N-pyrrole phosphonic acid)–Fe3O4 nanocomposite. ► Structural characterizations and some physical properties. ► Analysis of conductivity and permittivity meausurements.The present study describes the preparation and characterization of poly(N-pyrrole phosphonic acid)–Fe3O4 (PPP/Fe3O4-NPs) nanocomposite. Structural characterizations and some physical properties such as magnetism, ac–dc conductivity performance and dielectric permittivity of the nanocomposite were performed by FT-IR, XRD, TGA, TEM and VSM (vibrating sample magnetometer). FT-IR measurements of the nanocomposite showed that the Fe3O4-NPs bound to the polymer chains via phosphonic acid moieties. From the XRD powder pattern, the crystallite size was estimated as 11±4nm which is consistent with the TEM micrographs and magnetic core size from VSM measurements. Analysis of conductivity and permittivity meausurements revealed the magnetic transition above 60 which gives rise to the maximum conductivity of 1.7×10−6Scm−1 at 100°C.
Keywords: Magnetic nanoparticles; Phosphonic acid; Conducting polymer; Electrical properties
Electrochemical properties of nano-sized Li3V2(PO4)3/C composite powders prepared by spray pyrolysis from spray solution with chelating agent
by Y.N. Ko; J.H. Kim; Y.J. Hong; Y.C. Kang (pp. 292-296).
Li3V2(PO4)3/C nanoparticles are prepared by spray pyrolysis introducing new concept. The precursor powders with hollow and thin wall structure formed from spray solution containing citric acid and ethylenediaminetetraacetic acid (EDTA) as chelating agents are easily pulverized into Li3V2(PO4)3/C nanoparticles by simple milling process. The Li3V2(PO4)3/C nanoparticles had high initial discharge capacity of 147mAhg−1 and good cycle property.Display Omitted► Li3V2(PO4)3/C nanoparticles are prepared by spray pyrolysis from spray solution containing chelating agents. ► The precursor powders with hollow structures are easily pulverized into nanoparticles by simple milling process. ► The Li3V2(PO4)3/C nanoparticles had high initial discharge capacity of 147mAhg−1 and good cycle property.Li3V2(PO4)3/C nanoparticles are prepared by spray pyrolysis. Particles formed from spray solutions containing citric acid and ethylenediaminetetraacetic acid (EDTA) as chelating agents are large and hollow with thin walls. The optimum concentrations of citric acid and EDTA are each 0.1M. Powders subsequently treated at 700°C under a reducing atmosphere have particles of single phase, monoclinic Li3V2(PO4)3. The Li3V2(PO4)3/C powders contains 14.9wt% carbon. The hollow structures are easily pulverized into nanoparticles by simple milling process. However, Li3V2(PO4)3 powder formed from spray solution without chelating agent has larger, aggregated structures. Both powders’ charge curves show four plateaus at ca. 3.62, 3.70, 4.08 and 4.55V. The initial discharge capacities of the Li3V2(PO4)3/C powders at constant current densities of 0.1, 1 and 3C were 147, 122 and 86mAhg−1, respectively. The capacity retention of the Li3V2(PO4)3/C nanoparticles at a high current density of 1C after 100th cycle was 78%.
Keywords: Composite materials; Electrochemical properties; Nanostructures; Chemical synthesis
Molecular dynamics for lateral surface adhesion and peeling behavior of single-walled carbon nanotubes on gold surfaces
by Pei-Hsing Huang (pp. 297-305).
► Adhesion and peeling behaviors of SWCNTs are investigated by detailed, fully atomistic MD simulations. ► Adhesion energy of SWCNTs are discussed. ► Dynamical behaviors of SWCNTs in low temperature adhesion are analyzed. ► Adhesion strengths of SWCNTs obtained from MD simulations are compared with the predictions of Hamaker theory and JKR model.Functional gecko-inspired adhesives have attracted a lot of research attention in the last decade. In this work, the lateral surface adhesion and normal peeling-off behavior of single-walled carbon nanotubes (SWCNTs) on gold substrates are investigated by performing detailed, fully atomistic molecular dynamics (MD) simulations. The effects of the diameter and adhered length of CNTs on the adhesive properties were systematically examined. The simulation results indicate that adhesion energies between the SWCNTs and the Au surface varied from 220 to 320mJm−2 over the reported chirality range. The adhesion forces on the lateral surface and the tip of the nanotubes obtained from MD simulations agree very well with the predictions of Hamaker theory and Johnson–Kendall–Roberts (JKR) model. The analyses of covalent bonds indicate that the SWCNTs exhibited excellent flexibility and extensibility when adhering at low temperatures (∼100K). This mechanism substantially increases adhesion time compared to that obtained at higher temperatures (300–700K), which makes SWCNTs promising for biomimetic adhesives in ultra-low temperature surroundings.
Keywords: C. Molecular dynamics; D. Adhesion; Carbon nanotubesPACS; 81.07.De; 68.35.Np; 87.10.Tf; 87.15.ap
Upconversion luminescence from Er3+ in nanocrystalline Y2Si2O7:Er3+ and Y2Si2O7:Yb3+,Er3+ phosphors
by Jerzy Sokolnicki (pp. 306-312).
► The synthesis of single phase of β polymorph of yttrium pyrosilicate (β-Y2Si2O7) nanoparticles at 1250°C is reported for the first time. ► In nanocrystalline β-Y2Si2O7 doped with Er3+ and codoped with Yb3+ an efficient green and red upconversion luminescence was observed. ► The superiority of the β-Y2Si2O7:Yb3+/Er3+ upconversion phosphor over the α-Y2Si2O7:Yb3+/Er3+ phosphor was shown and discussed. ► The mechanism of upconversion processes in β-Y2Si2O7:Yb3+/Er3+ phosphor was proposed.Nanocrystalline yttrium pyrosilicate Y2Si2O7 (YPS) doped with Er3+(YPS:Er) or Yb3+/Er3+(YPS:Yb,Er) was obtained by the reaction of nanostructured Y2O3 and colloidal SiO2. X-ray diffraction analysis confirmed the crystallization of a single phase of α-YPS at 1150°C and β-YPS at 1250°C. The luminescence and upconversion spectra of Yb3+/Er3+ codoped phosphors are reported. After direct excitation at 488nm the samples emitted mostly green radiation. Excitation at 980nm produced green and red upconversion luminescence both from Er3+ doped and Yb3+ co-doped samples. Using 804nm wavelength the green and red upconversion luminescences were observed for Yb3+ co-doped samples while Er3+ doped samples emitted exclusively in the green region. It was found that the Er3+ upconversion luminescence is more intense in β-YPS than in α-YPS. The dependence of upconversion luminescence intensity on the excitation power allows upconversion mechanisms for the investigated samples to be proposed.
Keywords: Nanocrystalline Y; 2; Si; 2; O; 7; Upconversion luminescence; Er; 3+; Yb; 3+
SiO2 mesoporous thin films containing Ag and NiO nanoparticles synthesized combining sol–gel and impregnation techniques
by Enrico Della Gaspera; Valentina Bello; Giovanni Mattei; Alessandro Martucci (pp. 313-319).
► Ag and NiO nanoparticles are embedded inside a porous SiO2 matrix. ► Combination of sol–gel and impregnation processes. ► High temperature annealing promotes nanoparticles crystallization and organic removal. ► Synthesis of high quality nanocomposite for optical detection of reducing gases. ► Procedure can be easily extended to other noble metal/metal oxide nanocomposites.SiO2 sol–gel mesoporous thin films containing NiO nanoparticles have been synthesized and successively impregnated with Ag ions. A subsequent thermal treatment induces the precipitation of Ag nanoparticles and the formation of Ag/NiO interfaces. Morphological, structural and optical characterizations are used to analyze the matrix evolution with thermal annealing and to investigate the Ag+ impregnation procedure and the Ag nanocrystals precipitation. NiO nanoparticles form upon annealing at 800°C while the SiO2 matrix is still highly porous due to the organic template removal. This porosity is useful for the impregnation process that is composed by a first pores functionalization with mercapto moieties and a second impregnation with Ag precursor solution followed by the thermal reduction of Ag ions. Optical gas sensing tests for CO and H2 detection are presented as one of the possible applications for these noble metal–metal oxides nanocomposites.
Keywords: Thin films; Nanostructures; Composite materials; Optical properties
Hot-pressed K0.48Na0.52Nb1− xBi xO3 ( x=0.05–0.15) lead-free ceramics for electro-optic applications
by Kun Li; Fa Liang Li; Yu Wang; Kin Wing Kwok; Helen Lai Wa Chan (pp. 320-324).
Bismuth-modified potassium sodium niobate K0.48Na0.52Nb1− xBi xO3 ( x=0.05–0.15) transparent lead-free ceramics were fabricated by a hot-pressing method. Both hot-pressing conditions (pressure, temperature and duration) and Bi-content were found to have strong influences on the density, transparency, electro-optical coefficient, and electrical properties of the ceramics. Under the typical hot-pressing conditions of 1060°C for 5h at 5.5MPa, the optimum Bi-content was found at 7.5at.% in the system under study. These ceramics display good optical transmission in the visible and particularly in the infrared regions. For visible light, the highest transmission value of a polished 0.5-mm thick plates is about 60% at a wavelength of 800nm; while for infrared, the transmission value is about 80% at 4000nm. The effective linear electro-optic coefficient of the ceramics was found to be 42pVm−1. The dielectric permittivity and loss tangent of the KNNB ( x=0.075) ceramics were found to be 716 and 0.031 at room temperature.
Keywords: Transparent ceramics; Lead-free; Electro-optic; Sodium potassium niobate; Hot-pressing
BiVO4–graphene catalyst and its high photocatalytic performance under visible light irradiation
by Yongsheng Fu; Xiaoqiang Sun; Xin Wang (pp. 325-330).
Display Omitted► A facile strategy is designed to deposit leaf-like BiVO4 lamellas on graphene sheet. ► Graphene oxide is reduced to graphene in the hydrothermal reaction process. ► BiVO4–graphene system shows high catalytic effects under visible light irradiation.A BiVO4–graphene photocatalyst was prepared by a facile one-step hydrothermal method and characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoelectron spectra (XPS), and transmission electron microscopy (TEM) techniques. The results show that the graphene sheets in this catalyst are exfoliated and decorated by leaf-like BiVO4 lamellas. In comparison with the pure BiVO4 catalyst, the BiVO4–graphene system reveals much higher photocatalytic activity for degradation of methyl orange (MO), methylene blue (MB), Rhodamine B (RhB) and active black BL-G in water under visible light irradiation due to the concerted effects of BiVO4 and graphene sheets or their integrated properties.
Keywords: Graphene; Leaf-like BiVO; 4; sheets; Photocatalysis; Visible light irradiation
Microwave synthesis of gold nanoparticles: Effect of applied microwave power and solution pH
by Seung Kwon Seol; Daeho Kim; Sunshin Jung; Yeukuang Hwu (pp. 331-335).
► We investigated the formation kinetics of microwave synthesis of colloidal AuNPs. ► Using higher microwave power at initial stage, homogeneous nucleation is facilitated and the size of the resultant nanoparticles is reduced while the uniformity is much improved. ► Adjusting solution pH to higher than 6.2 by the sodium citrate/HAuCl4 ratio could also have a positive effect on the quality of the nanosol. ► Therefore, we successfully produced uniform colloidal AuNPs with diameter of 12.04±1.35nm in a few minutes.We describe formation kinetics of gold nanoparticles (AuNPs) in microwave synthesis. Using high microwave power to increase the temperature ramping rate ( Rr) homogeneous nucleation is facilitated and the size of the resultant nanoparticles is reduced while the uniformity is much improved. Adjusting solution pH to higher than 6.2 could also have a positive effect on the quality of the nanosol. We therefore demonstrate that by adjusting these reaction parameters in microwave synthesis, we successfully produced uniform colloidal AuNPs with diameter of 12.04±1.35nm in a few minutes.
Keywords: Nanostructures; Chemical synthesis; Colloidal gold nanoparticles (AuNPs); Microwave synthesis, Microwave power; Solution pH; Homogenous formation; Scale up production
Ethylene glycol-mediated synthesis of PbO nanocrystal from PbSO4: A major component of lead paste in spent lead acid battery
by Jiakuan Yang; Xinfeng Zhu; R. Vasant Kumar (pp. 336-342).
► Nanostructured lead oxides were prepared by using PbSO4 as a starting material. ► The EG precursor showed the columnar-like morphology with the length of about 10μm. ► The EG precursor was completely different from the morphology of the CA precursor. ► The calcined products in the size of 50–100nm were prepared from the EG precursor.Lead sulfate (PbSO4) is a major component of lead paste of spent lead acid batteries, normally over 60%. In traditional pyrometallurgical process, the decomposition of PbSO4 requires a relatively high temperature and the use of coal as both the reducing agent and as the source of thermal energy, thereby causing emissions of SO x, lead particles and CO2. In this study, lead sulfate was desulfated by adding an aqueous solution comprising citric acid and tri-sodium citrate with the modulation of ethylene glycol (EG) in order to control the morphology. The treating agent reacted with lead sulfate to form an aqueous solution of sodium sulfate and a precipitated precursor of lead carboxylate crystals. The precursor was characterized by XRD, SEM, SDT and FTIR. The morphology of the EG-mediated precursor showed a regular columnar shape. On calcining at relatively low temperatures, EG-mediated precursor was transformed into fine particles of lead oxide. The characteristics of calcined products were investigated by XRD, SEM, and TEM. The results showed that nanostructured crystals of lead oxide could be easily prepared by combustion of EG-mediated precursor at 350°C with a lead recovery of about 98%. This paper has paved the way for obtaining nanostructured PbO from waste battery scrap.
Keywords: Nanostructures; Organometallic compounds; Electron microscopy; X-ray diffraction topography
Synthesis of poly(4-vinylphenol) (PVPh) and polyhedral oligomeric silsesquioxanes-poly(4-vinylphenol) (POSS-PVPh) with low surface energy and their surface properties
by Chun-Hsiung Liao; Fu-Ming Chien; Chen-Ming Chen; Lung-Chang Liu; Ming-Hua Chung; Feng-Chih Chang (pp. 343-347).
► PVPh and POSS-PVPh with low surface energies have been synthesized. ► The surface properties of PVPh and POSS-PVPh were manipulated. ► The surface energies of PVPh after thermal treatment of 180°C for 24h can be less than 20mJm−2. ► The surface energies of POSS-PVPh without thermal treatment can be less than 25mJm−2.In this paper, we have synthesized poly(4-vinylphenol) (PVPh) and polyhedral oligomeric silsesquioxanes-poly(4-vinylphenol) (POSS-PVPh) with low surface energies and investigated their surface properties. Experimental results reveal that the surface properties of PVPh and POSS-PVPh can be manipulated with the length of PVPh segment and POSS contents, respectively, resulting in the variation of intermolecular hydrogen bonding interactions. In addition, the surface energies of PVPh after thermal treatment of 180°C for 24h can be less than 20mJm−2 and those of POSS-PVPh without thermal treatment can be less than 25mJm−2 while those of poly(tetrafluoroethylene) (PTFE) are 22mJm−2.
Keywords: Polymers; Thin films; Chemical synthesis; Surface properties
Characterization of the effects of lignin and lignin complex particles as filler on a polystyrene film
by Waleed K. El-Zawawy; Maha M. Ibrahim; Mohamed Naceur Belgacem; Alain Dufresne (pp. 348-357).
► We have studied the use of Co(II) to form a complex with the lignin. We use first vanillin as the lignin model and we observed a change in color for the produced complex depending on the light wavelength. The use of other transition metals does not give the same observation. ► The use of the transition metal with the lignin precipitated from the black liquor after pulping of agricultural residues, gave a fluorescent color under fluorescent microscope. ► We applied the resulted lignin complex to prepare polymer film that can be used as special polymer packaging which can be color changed under different wavelengths.The work in this research outlines the use of lignin precipitated from lignocellulosic substrate as fillers after modified with transition metal cations, Fe(III), Ni(II) and Co(II), in the production of a polystyrene based composite for polymer packaging applications. Virgin polystyrene was compared with lignin and lignin complex filled composites with loading of 5% by weight prepared using twin screw extrusion. The lignin complexes were first characterized by the UV spectra to identify the new absorption bands occurred due to the complex formation. Moreover, lignin model, namely vanillin, was used to notify the geometric structure of the resulting complexes applying the GC mass spectra. Scanning electron microscopy was used to indicate the change in the morphological structure of the filler particles. On the other hand, the mechanical and thermal analysis for the resulting polymer composites was studied and it was noticed that the type of lignin or lignin complex plays a roll in the results. The inclusion of the Co(II)–lignin complex was observed to increase the tensile strength of the resulting polymer composite and a decrease of the glass transition temperature. Furthermore, light wave lengths and UV fluorescent microscope were used to identify the change of color for the resulting polymer film.
Keywords: A. Polymers; A. Thin films; C. Visible and ultraviolet spectrometers; C. Electron microscopy (SEM); C. Differential scanning calorimetry (DSC)
Surfactant-assisted facile synthesis of fluorescent zinc benzenedicarboxylate metal-organic framework nanorods with enhanced nitrobenzene explosives detection
by Yupeng Yuan; Wei Wang; Lingguang Qiu; Fumin Peng; Xia Jiang; Anjian Xie; Yuhua Shen; Xingyou Tian; Lide Zhang (pp. 358-361).
The present work describes a surfactant-assisted synthesis of nanoscale metal-organic framework (NMOF), and fluorescent sensing of nitrobenzene. The results suggest that the presence of the surfactant is crucial to the formation of NMOF with uniform size and shape, and significant quenching of fluorescent NMOFs may be monitored to detect nitroaromatic explosives.Display Omitted► Zn-BDC MOF (BDC=1,4-benzenedicarboxylate) nanorods were readily synthesized via a CTAB surfactant assisted methodology. ► CTAB surfactant plays an essential role in the formation of Zn-BDC MOF nanorods, while has no effect on its phase formation. ► Zn-BDC nanorods exhibit superior nitrobenzene sensing properties over its counter micro-scaled crystals obtained without the presence of CTAB surfactant.Zinc benzenedicarboxylate (Zn-BDC, BDC=1,4-benzenedicarboxylate) nanorods were synthesized via a novel cetyl trimethylammonium bromide (CTAB) surfactant-assisted technique and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and fluorescent sensing of nitrobenzene, respectively. The XRD analysis reveals that the products obtained with or without CTAB surfactant are both crystalline Zn-BDC MOF with a 2D layered structure. SEM images show that, in the presence of CTAB surfactant, Zn-BDC MOF nanosheets formed initially and were then transformed into Zn-BDC MOF nanorods with the increase of the reaction time. In contrast, micro-sized particles of Zn-BDC MOF with irregular shape formed in the absence of CTAB surfactant. It was found that Zn-BDC MOF nanorods exhibit superior nitrobenzene sensing properties over its counter part: micro-sized particles.
Keywords: A. Microporous materials; A. Nanostructure; B. Chemical synthesis
Small-angle X-ray scattering (SAXS) study of porous anodic alumina—A new approach
by Abdul Waheed; Mazhar Mehmood; Robert Benfield; Jamil Ahmad; Heinz Amenitsch; Muhammad Aslam; Abdur Rauf; Mujtabaul Hassan (pp. 362-369).
► The SAXS spectra clearly suggest that form factor has almost negligible role in the analysis of the SAXS response of alumite membranes and structure factor predominates. ► A sample may be characterized by SAXS at any orientation between face-on and edge-on. ► Based on the present methodology and analysis SAXS response can be successfully exploited to study the mutual variation in the axis of the cylindrical objects.Small angle X-ray scattering (SAXS) has been performed on porous anodic alumina prepared at 10, 20 and 30V. These were prepared by two-step anodizing to have uniform through-thickness structure. The thickness of the membranes was of the order of 100–200μm. The scattering has been explained on the basis of structure factor; the magnitude of scattering vectors (q) corresponding to well-established peaks being multiples of 2 π/ d, where d is the inter-pore distance. The usually studied form factor has not been found to play any profound role to determine the scattering response of anodic alumina. A large number of experiments have been performed with various geometries of the anodic alumina with respect to the incident beam. The scattering has been extremely anisotropic, whereq always lies at about 90° with respect to the sample's normal. A deviation from this angle which is limited to about ±2° has been due to scatter of the pore axis with respect to sample's normal, which is caused by occasional pore turning, branching and annihilation events. The analysis and methodology adopted in this study has also been suggested as extremely useful for determining the orientation of high-aspect ratio objects in an anisotropic sample along with assessing the degree of misalignment.
Keywords: Nanostructures; Porous alumina; Chemical synthesis; X-ray scattering
Refractive index depth profile and its relaxation in polydimethylsiloxane (PDMS) due to proton irradiation
by S.Z. Szilasi; J. Budai; Z. Pápa; R. Huszank; Z. Tóth; I. Rajta (pp. 370-374).
► The refractive index depth profile was determined in PDMS irradiated with 2MeV protons. ► The relaxation of the refractive index depth profile was investigated. ► The absorption was investigated in two different wavelengths. ► As a demonstration of the results above an integrated waveguide was created in PDMS.In this work the refractive index depth profile, its relaxation and the absorption were investigated in 2MeV proton irradiated PDMS. The above parameters were determined by the spectroscopic ellipsometry technique. The refractive index depth profile follows roughly the shape of the Bragg curve for the penetrating protons. It is shown that the observed difference between the refractive index of the surface ( dn=0.01) and deeper regions ( dn=0.08) is high enough to accomplish waveguiding that is also demonstrated in this paper. This work serves as basis for the production of integrated optical components, e.g. waveguides, gratings or other optical devices, which are planned to be produced by ion irradiation in PDMS.
Keywords: Polymers; Ion implantation; Optical properties; Radiation damage
Growth process conditions of tungsten oxide thin films using hot-wire chemical vapor deposition
by Z. Silvester Houweling; John W. Geus; Michiel de Jong; Peter-Paul R.M.L. Harks; Karine H.M. van der Werf; Ruud E.I. Schropp (pp. 375-386).
► Process parameters to control hot-wire CVD of WO3− x are categorized. ► Growth time, oxygen partial pressure, filament and substrate temperature are varied. ► Chemical and crystal structure, optical bandgap and morphology are determined. ► Oxygen partial pressure determines the deposition rate up to as high as 36μmmin−1. ► Nanostructures, viz. wires, crystallites and closed crystallite films, are controllably deposited.We report the growth conditions of nanostructured tungsten oxide (WO3− x) thin films using hot-wire chemical vapor deposition (HWCVD). Two tungsten filaments were resistively heated to various temperatures and exposed to an air flow at various subatmospheric pressures. The oxygen partial pressure was varied from 6.0×10−6 to 1.0mbar and the current through the filaments was varied from 4.0 to 9.0A, which constitutes a filament temperature of 1390–2340°C in vacuum.It is observed that the deposition rate of the films is predominantly determined by the oxygen partial pressure; it changes from about 1 to about 36,000nmmin−1 in the investigated range. Regardless of the oxygen partial pressure and filament temperature used, thin films with a nanogranular morphology are obtained, provided that the depositions last for 30min or shorter. The films consist either of amorphous or partially crystallized WO3− x with high averaged transparencies of over 70% and an indirect optical band gap of 3.3±0.1eV. A prolonged deposition time entails an extended exposure of the films to thermal radiation from the filaments, which causes crystallization to monoclinic WO3 with diffraction maxima due to the (002), (200) and (020) crystallographic planes, furthermore the nanograins sinter and the films exhibit a cone-shaped growth.By simultaneously influencing the surface mobility, by heating the substrates to Tsurface=700±100°C, and the deposition rate, a very good control of the morphology of the deposited films is obtained. Nanowire films, nanocrystallite films and closed crystallite films were thus deposited. These differently nanostructured c-WO3 films all possess an indirect optical band gap of 2.5±0.1eV.
Keywords: Tungsten oxide; Nanostructures; Chemical vapor deposition; Morphology; Electron microscopy
Microstructure, thermal and dielectric properties of homogeneous bismaleimide-triazine/barium titanate nanocomposite films
by Xiaoliang Zeng; Shuhui Yu; Rong Sun; Ruxu Du (pp. 387-392).
► The bismaleimide-triazine resin/BaTiO3 nanocomposite films were prepared. ► We examine the dielectric and thermal properties. ► Increasing BaTiO3 will increase the dielectric constant while the loss remains low. ► The highest glass transition temperature is 261°C.Bismaleimide-triazine resin/barium titanate (BT/BaTiO3) nanocomposite films were prepared by mixing the nano-BaTiO3 particles into BT resin, followed by films casting and thermal cure. The surface modification of BaTiO3 nanoparticles with silane coupling agent results in excellent dispersion and enhances the interaction between BaTiO3 and the BT matrix. The derived nanocomposite films exhibit improved dielectric constant, while the dielectric loss remains at a low level (<0.05). For the nanocomposite film containing 70wt% of BaTiO3, the effective dielectric constant at room temperature reaches 23.63, which is about 7 times larger than that of pure BT resin, and the dielectric loss is only 0.0212 at 100Hz. The dielectric properties of the nanocomposite films are nearly frequency-independent, which is attributed to the excellent dispersion of BaTiO3 nanoparticles in the BT matrix. The interaction between BaTiO3 and BT affects not only the phase transition of BaTiO3, but also the thermal behavior of BT. Moreover, the nanocomposite films exhibit improved thermal resistance. The highest glass transition temperature ( Tg) is 261°C, indicating good reliability as dielectric materials in applications.
Keywords: A. Composite materials; A. Thin films; D. Dielectric properties; D. Thermal properties
Photo-polymerization of photocurable resins containing polyhedral oligomeric silsesquioxane methacrylate
by Ho-May Lin; Shi-Yin Wu; Feng-Chih Chang; Ying-Chieh Yen (pp. 393-399).
Photocurable resins, bisphenol A propoxylate glycerolate diacrylate (BPA-PGDA, containing two hydroxyl) and bisphenol A propoxylate diacrylate (BPA-PDA), with fixed photoinitiator (Irgacure 907) concentration and various contents of methacrylisobutyl polyhedral oligomeric silsesquioxane (MI-POSS) were prepared and characterized by FTIR spectroscopy, scanning electron microscope and differential photocalorimetry. The MI-POSS molecules form crystals or aggregated particles in the cured resin matrix. The BPA-PGDA series photocurable resins show higher viscosity and lower photo-polymerization reactivity than the BPA-PDA series resins. The photo-polymerization rate and conversion of BPA-PGDA series are improved with increasing MI-POSS content. On the contrary, the photo-polymerization behavior of BPA-PDA series photocurable resins remains nearly unchanged by the addition of MI-POSS. Hydrogen-bonding interaction between the hydroxyl of BPA-PGDA and the siloxane of MI-POSS tends to attract and concentrate these acrylate double bonds around MI-POSS particles and thus enhances the photo-polymerization rate and conversion.
Keywords: Polyhedral oligomeric silsesquioxanes (POSSs); Photocurable resins; Hydrogen bonding; Acrylate monomer
Effects of compositional impurity on surface chemistry of TiO2 nanopowder and its chemical interactions with dispersants
by Chia-Chen Li; Shinn-Jen Chang; Ming-Yu Tai (pp. 400-405).
► Commercial TiO2 nanopowder is covered with a thick layer of SiO2 that is 2–3nm. ► Surface-treatment by HCl(aq) efficiently thins the SiO2 layer and decreases the acidity of TiO2. ► Both alkaline and acidic surfactants prefer to adsorb on the HCl-treated TiO2.We investigate the effects of a foreign substance, silica (SiO2), on surface chemistry of commercial titania (TiO2) nanopowder and its chemical interactions with dispersants. The surface of as-received TiO2 is covered with a 2–3-nm-thick layer of SiO2, which gives the nanopowder a low isoelectric point and makes it acidic. Treating the surface with an acidic solution thins the SiO2 layer to less than 0.5nm, which allows the TiO2 nanoparticles to exhibit surface properties similar to uncoated TiO2 nanoparticles. This variation of surface property of TiO2 due to acid-treatments results in a great impact on its interactions with dispersants. For as-received TiO2 nanoparticles, no competitive adsorption is observed between the acidic dispersant, oleic acid (OA), and the alkaline dispersant, oleylamine (OLA). However, for acid-treated TiO2 nanoparticles, OA competes readily with the adsorption of OLA.
Keywords: Ceramics; Oxides; Interfaces; Surface properties
Laser-induced grayscale patterning in TeO x thin films
by Aihuan Dun; Xiaoqing Ma; Jingsong Wei; Fuxi Gan (pp. 406-412).
Display Omitted► Grayscale patterns with precise grayscale changes are fabricated on TeO x thin film. ► Two obvious changes of grayscale level emerge as laser energy increases. ► The first change is from invisible to white-grayscale with low laser energy. ► The second change becomes darker and darker following the laser energy increases. ► The mechanism involves many reasons, different mechanism is dominant in each stage.Grayscale patterns have been widely studied and applied in many fields. In this paper, grayscale patterns with precise grayscale changes are fabricated on TeO x thin film by laser pulse with respective wavelengths of 635 and 405nm. Two obvious changes according to the different grayscale level emerge as laser energy increases. The first change is from invisible to white-grayscale with low laser pulse width between 2ns and 50ns. After a transient period with laser pulse width between 48ns and 55ns, the grayscale in the second change becomes darker and darker following the laser pulse width increases from 56ns to 250ns. The mechanism of the grayscale change is partly explained and verified by TEM, which involves the agglomeration and segregation of Te, crystallization and recrystallization after melting of Te and TeO2, and ablation of TeO x, wherein different mechanism is dominant in each stage. We can obtain grayscale patterns with precise grayscale changes to meet specific requirements by controlling the parameters precisely.
Keywords: PACS; 78.20.-e; 42.62.-b; 78.90. +tA. Chalcogenides; B. Sputtering; C. Electron microscopy (STEM; TEM and SEM); D. Optical properties
Structural and vibrational properties of Zn xMn1− xFe2O4 ( x=0.0, 0.25, 0.50, 0.75, 1.0) mixed ferrites
by Dinesh Varshney; Kavita Verma; Ashwini Kumar (pp. 413-419).
► XRD with Rietveld refinement reveals structure as single-phase of mixed ferrites. ► IR spectra correspond to the vibration of Fe2+–O2− bond at tetrahedral ( A) site. ► Raman spectroscopy shows the shifting of active modes toward higher frequency side. ► Mössbauer spectra (300K) reveal super paramagnetic nature of mixed ferrites.In this paper, we report the variations in the crystal structure, average crystallite size, Raman spectra and magnetic properties of Zn xMn1− xFe2O4 ( x=0.0, 0.25, 0.5, 0.75, 1.0) mixed ferrite samples synthesized by chemical co-precipitation method. The X-ray diffraction pattern confirms that the mixed ferrite samples are in cubic inverse spinel structure, which is further validated by Rietveld refinement. The oxygen position, the lattice parameter, and the cation distribution have been determined by means of Rietveld analysis, indicating the existence of mixed ferrites in all samples. The final structure was refined in space group Fd3 m. The structural studies identify the decrease of lattice parameter, whereas the crystallite size increases and porosity decreases on increasing the Zn concentration. IR spectra confirm vibration of Fe2+–O2− bond at tetrahedral ( A) site. The Raman spectrum reveals active phonon modes at room temperature and shifting of modes toward the higher frequency side on moving from MnFe2O4 to ZnFe2O4. The transmission Mössbauer spectroscopy determines the site preference of the substituted ions and their effect on the hyperfine magnetic fields. The results showed that all the samples are superparamagnetic in nature.
Keywords: Chemical synthesis; Powder diffraction; Raman spectroscopy and scattering; Mössbauer spectroscopy
Improved tribological properties of TiC with porous nanostructured TiO2 intermediate layer
by Ali Shanaghi; Shahrokh Ahangarani; Ali Reza Sabour Rouhaghdam; Paul K. Chu (pp. 420-424).
► The porous TiO2 nanoparticle coating is deposited as an intermediate layer on steel. ► A homogenous and low friction TiC nanostructure coating is deposited by plasma CVD. ► Intermediate layer can be determined the nucleation and growth of the TiC coating. ► The porous interlayer improves the friction and wear of the TiC nanostructure coating.The mismatch in the thermal expansion coefficients between TiC coatings and steel substrates and residual stress in the TiC degrade the tribological properties. In this work, a porous nanostructured TiO2 coating is deposited as an intermediate layer on hot-work steel (H11) before final deposition of the TiC film. This intermediate layer is expected to reduce the interfacial energy, decreases the thermal mismatch between TiC and steel, and improves the tribological properties. Grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), and pin-on-disk are used to study the structure as well as tribological properties such as friction, wear, and hardness. Our results reveal that the porous TiO2 interlayer improves the friction, wear, hardness, and elastic modulus of the system.
Keywords: Multilayers; Nanostructures; Plasma-assisted CVD; Surface properties; Tribology
Continuous synthesis of magnesium-hydroxide, zinc-oxide, and silver nanoparticles by microwave plasma in water
by Yoshiaki Hattori; Shinobu Mukasa; Hiromichi Toyota; Toru Inoue; Shinfuku Nomura (pp. 425-430).
Nanoparticles are continuously synthesized from submerged magnesium, zinc, and silver rods 1–2mm in diameter by microwave plasma in pure water at 20kPa. Magnesium-hydroxide nanoplates shaped as triangles, truncated triangles or hexagons with 25–125nm in size are synthesized with a production rate of 60gh−1. Zinc-oxide nanoparticles formed as sharp sticks with diameters of 50nm and lengths of 150–200nm are synthesized with a production rate of 14gh−1. Silver nanoparticles with a diameter of approximately 6nm are synthesized with a production rate of 0.8gh−1. The excitation temperature is estimated by applying the Boltzmann plot method in assumption of local thermodynamic equilibrium. The excitation temperatures obtained from hydrogen, magnesium, and zinc lines are 3300±100K, 4000±500K, and 3200±500K, respectively.
Keywords: Glow discharge; Nanostructures; Electron microscopy
Electrochemical properties of Li4Ti5−2 xNi xMn xO12 compounds synthesized by sol–gel process
by Wanmei Long; Xianyou Wang; Shunyi Yang; Hongbo Shu; Qiang Wu; Yansong Bai; Li Bai (pp. 431-435).
Ni and Mn co-doped spinel Li4Ti5O12 materials in the form of Li4Ti5−2 xNi xMn xO12 ( x=0.000, 0.050, 0.075, 0.100, 0.125) were prepared by sol–gel route and following calcination in an air atmosphere, and were used as anode materials of Li-ion battery. The structures, morphologies and electrochemical properties of the as-prepared materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), charge/discharge cycling, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that Ni and Mn co-doping did not change the electrochemical reaction mechanism of Li4Ti5O12, but can clearly influence its morphology and particle size. Besides, the Li4Ti5O12 samples co-doped with different molar fractions of Ni and Mn exhibited an enhanced electrochemical performance even at high current rate. It has been found that the spinel Li4Ti5−2 xNi xMn xO12 delivered a high reversible capacity and showed excellent cycling performance, especially Li4Ti4.8Ni0.1Mn0.1O12 exhibited a relatively good rate capability and excellent cycling stability. The initial discharge capacity of Li4Ti4.8Ni0.1Mn0.1O12 sample was 172.41mAhg−1 at a current of 0.5C, which was nearly close to the theoretic specific capacity of LiTi5O12; furthermore, a high discharge specific capacity of 142.53mAhg−1 was still kept after 100 cycles.
Keywords: Inorganic compounds; Chemical synthesis; Electrochemical techniques; Electrochemical properties
Modifications induced in poly (3-hexylthiophene) due to swift heavy ion beam of 100MeV silver (Ag8+)
by Amarjeet Kaur; Anju Dhillon; G.B.V.S. Lakshmi; Yogendra Mishra; D.K. Avasthi (pp. 436-442).
Display Omitted► Pristine samples of poly(3-hexyl thiophene) (P3HT) samples were irradiated with 100MeV silver (Ag8+) ions at fluences ranging from 1010 to 1012ionscm−2. ► The significant changes in FT-IR spectra, dc conductivity, and surface morphology observed in P3HT samples exposed to Ag8+ ion fluence of 1012ionscm−2 suggest the liberation of molecular fragments due to ion impact. ► The emission of gases during RGA suggests the probability of fragmentation of alkyl side chains rather than the breaking of thiophene ring. ► The obtained polymers can be applied as microstructures with defined conductivity for sensor applications.Pristine poly(3-hexylthiophene) (P3HT) samples were irradiated by 100MeV silver (Ag8+) ion at fluences ranging from 1010 to 1012ionscm−2. The modification in the structure of P3HT is explained in the light of a comparative study of samples before and after irradiation by using various techniques such as scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), residual gas analysis (RGA) and dc conductivity. Significant changes in FT-IR spectra and surface morphologies of irradiated samples have been observed at the ion fluence of 1012ionscm−2. Changes in FTIR spectra, conductivity and surface morphology of the irradiated samples are further explained by RGA investigations. The obtained micropatterned polymers can be applied as microstructures with defined conductivity for sensor applications.
Keywords: FT-IR; SEM; poly(3-hexylthiophene); RGA; Micropattern
Synthesis, structural characterization and ferroelectric properties of Pb0.76Ca0.24TiO3 nanotubes
by Satyendra Singh; S.B. Krupanidhi (pp. 443-448).
► First report on the synthesis and structural characterization of Pb0.76Ca0.24TiO3 nanotubes. ► Nanotubes made up of randomly aligned nanoparticles (5–8nm). ► Nanotube wall thickness of ∼20nm. ► Ferroelectric hysteresis loops demonstrate the ferroelectric characteristic of nanotubes.A capillary-enforced template-based method has been applied to fabricate Pb0.76Ca0.24TiO3 (PCT24) nanotubes via filling PCT24 precursor solution, prepared by modified sol–gel method, into nanochannels of anodic aluminum oxide templates. The morphology and structure of as-prepared PCT24 were examined by scanning electron microscopy, transmission electron microscopy (TEM) and X-ray diffraction techniques. The obtained PCT24 nanotubes with diameter of ∼200nm and wall thickness of ∼20nm exhibited a tetragonal perovskite structure. High resolution TEM (HRTEM) analysis confirmed that as-obtained PCT24 nanotubes made up of nanoparticles (5–8nm) which were randomly aligned in the nanotubes. Formation of some solid crystalline PCT24 nanorods, Y-junctions and multi-branches were observed. Interconnections in the pores of template are responsible for the growth of Y-junctions and multi-branches. The possible formation mechanism of PCT24 nanotubes/nanorods was discussed. Ferroelectric hysteresis loops of PCT24 nanotube arrays were measured, showing a room temperature ferroelectric characteristic of as-prepared PCT24 nanotubes.
Keywords: Nanostructures; Sol–gel growth; Ferroelectricity; Electron microscopy
Effect of zinc chloride and sodium hydroxide concentration on the optical property of chitosan–ZnO nanostructure prepared in chitin deacetylation
by S. Anandhavelu; S. Thambidurai (pp. 449-454).
► Micro addition of sodium hydroxide induced the nano particles crystallization. ► Nano crystals with maximum Zn/O ratio of 77:23 was prepared. ► Crystalline size with 16–53nm was estimated by XRD. ► In this study, nanocrystalline powders with band gap of 3.32eV was prepared.Chitosan–ZnO nanostructures are prepared by eco-friendly way of synthesis. With same amount of chitin, three different ratios of zinc chloride and sodium hydroxide concentrations are used for preparation. The hexagonal shape of chitosan–ZnO nanostructures with size range of 40–100nm are confirmed by transmission electron microscopy (TEM). Surface morphology is characterized by scanning electron microscopy. Maximum Zn/O atomic ratio of 77:23 is noticed by energy dispersive X-ray (EDAX) analysis. Presence of chitosan and ZnO structure are confirmed with FTIR spectra. Absorbance at 364nm in the UV–vis spectra indicates the presence of ZnO. X-ray diffraction pattern indicates the size of crystallites are in 16–53nm range. Optical studies revealed that chitosan–ZnO nanostructure with band gap of 3.4eV have been prepared by slow addition of 45% sodium hydroxide into 15% zinc chloride and chitin solution.
Keywords: Chitosan–ZnO; Nanostructures; Transmission electron microscopy; Optical properties
Oriented and non-oriented textures of nematic liquid crystals: Comparative peculiarities of the thermotropic behavior
by Arif Nesrullajev; Nejmettin Avcı (pp. 455-461).
► Studies of thermotropic behavior of various types of textures in nematic liquid crystals. ► Determination of temperatures of phase transition and widths of the heterophase regions for these transitions with high accuracy. ► Connection between type of texture and thermotropic behavior are found. ► Differences in transition temperatures and widths of heterophase regions are connected with differences in the anchoring energy for different textures.In this work the thermotropic behavior of various types of textures in monomorphic nematic liquid crystals has been investigated in detail. Thread-like, homeotropic oriented and planar oriented textures of MBBA, MBBA+EBBA and 5CB liquid crystals have been used. Temperatures of the direct nematic mesophase – isotropic liquid and reverse isotropic liquid – nematic mesophase phase transition, the thermal and linear widths of the heterophase regions for these transitions have been determined with high accuracy. Differences in temperatures of the direct and reverse phase transitions and differences in the thermal and linear widths of the heterophase regions of these transitions for non-oriented and oriented textures have been found. These differences are connected with differences in the anchoring energy between liquid crystalline molecules and reference surfaces for the non-oriented, homeotropic oriented and planar oriented textures.
Keywords: PACS; 42.70.Df; 61.30.Hn; 64.70.mfLiquid crystals; Hysteresis; Optical properties; Phase transitions
In vitro solubility and bioactivity of Sr and Mg co-doped calcium phosphate glass-ceramics derived from different heat-treatment temperatures
by Shu Cai; Jianxin Li; Guohua Xu; Xudong Li; Xiaojian Ye; Wei Jiang (pp. 462-470).
► Porous glass ceramics were prepared by controlled heat treatment process. ► A fast release of Mg ions has a great influence on the Ca/P ratio of the deposits. ► The chemical stability of the deposited apatite directly affects cell behavior. ► The glass ceramics heat-treated at 760°C and 780°C show less glass. ► The degradation rates are both compatible with cell growth and differentiation.CaO–P2O5–Na2O–SrO–MgO glass–ceramic system was prepared by controlled heat treatment process. Solubility and bioactivity of glass-ceramics were measured and evaluated in simulated body fluid (SBF) and cell culture medium respectively. The dissolution behavior of these glass-ceramics strongly depends on the amount and microstructure of the crystals precipitated by sintering treatment. Concerning the bioactivity, the onset of the apatite formation on the glass–ceramic system was directly dependent on the amount of bioactive glass amount which can be controlled using different temperatures of heat treatment. After immersing glass–ceramic in SBF, Mg ion as one of system composition can be released from residual glass and provides a high impact on the Ca/P ratio and chemical stability of the deposited apatite layer that directly affects cell attachment and proliferation in in vitro cell culture system. The glass ceramics heat-treated at 760°C and 780°C show less glass amount, and their degradation rates are both compatible with cell growth and differentiation.
Keywords: A. Glass-ceramics; B. Heat treatment; C. Corrosion test; D. Cell adhesion
1H,7Li, and23Na NMR study of the relaxation processes and molecular motions of Li2NaH(SO4)2·H2O single crystals
by Ae Ran Lim; Younkee Paik; Kye-Young Lim (pp. 471-476).
► The phase transition temperature of Li2NaH(SO4)2·H2O. ► The temperature dependences of the NMR resonance lines and spin–lattice relaxation times. ► The relaxation processes by reorientation motions. ► The activation energies of the molecular motions.Li2NaH(SO4)2·H2O single crystals were grown by using the slow evaporation method, and their phase transition temperatures were determined with differential scanning calorimetry (DSC). In addition, the temperature dependences of the NMR resonance lines and spin–lattice relaxation times, T1, of the1H,7Li, and23Na nuclei were obtained. Only one7Li resonance line is present in the spectrum above 390K, which means that at these temperatures the atoms surrounding Li+ are probably disrupted by the loss of H2O. The water protons were distinguished from the hydrogen-bond protons. From the variations with inverse temperature of the relaxation times of the hydrogen-bond protons, water protons, and7Li nuclei, we conclude that the relaxation processes in this crystal are affected by reorientation motions. We determined the activation energies of the molecular motions involving the7Li and23Na nuclei, the hydrogen-bond protons, and water protons from these results.
Keywords: PACS; 81.10.Dn; 76.60.−k; 77.80.BhB. Crystal growth; C. Nuclear magnetic resonance (NMR); D. Thermodynamic properties
Controlled synthesis of different morphologies of GdBO3:Eu3+ crystals and shape-dependent luminescence properties
by Lan Yang; Liqun Zhou; Ying Huang; Ziwei Tang (pp. 477-484).
► Novel structures GdBO3:Eu3+ have been synthesized by a hydrothermal process for first time. ► The effects of reaction temperature and pH value on the morphology of products have been studied. ► The formation mechanisms for different structures have been investigated in detail. ► The luminescence properties of GdBO3:Eu3+ with different morphologies have been studied in detail.Hexagonal GdBO3:Eu3+ with different morphologies, such as nanofibres, microspheres, microflowers and novel lotus leaf-like microstructures, have been successfully synthesized by complexing-agent-assisted hydrothermal process for the first time. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED), energy-dispersive spectra (EDS), and photoluminescence (PL) spectroscopy were employed to characterize the as-obtained products. It was found that the reaction temperature and the pH value have crucial influences on the formation and morphology of the resulting structures and morphologies. The possible formation mechanisms for different structures were put forward. A detailed investigation on the photoluminescence of GdBO3:Eu3+ different samples indicate that the luminescence properties of as-obtained GdBO3:Eu3+ phosphors are strongly dependent on the morphology, size and crystallinity. The microflower structure exhibits the strongest red emission.
Keywords: Inorganic compounds; Crystal growth; Crystal structure; Luminescence
Encapsulation of magnetic CoFe2O4 in SiO2 nanocomposites using hydroxyapatite as templates: A drug delivery system
by Weeraphat Pon-On; Narattaphol Charoenphandhu; I-Ming Tang; Prapaporn Jongwattanapisan; Nateetip Krishnamra; Rassmidara Hoonsawat (pp. 485-494).
► Composite nanomaterials of CoFSi show the core–shell structure. ► An inorganic silica based ordered meso-porous materials was used as a shell. ► The coercivity ( H c) of the uncoated CoF is lower than those of the coated CoFSi. ► Controlled release shown IMC rapidly released in initial following sustained release.This research focuses on the synthesis of composite CoFe2O4 (CoF) nanoparticles coated with SiO2 using hydroxyapatite (HAp) as a template (CoFSi) and the pH controlled release of indomethacin (IMC) drug from this nanocomposite. The formation of the CoFe2O4-HAp (CoFHAp) nanoparticles and of the CoFe2O4@SiO2 (CoFSi) nanoparticles were monitored using XRD, FT-IR, that TEM, SEM, and ED studies. The magnetic properties are measured with a VSM. The TEM images showed the CoFe2O4 to have a core–shell structure encapsulated by a silica coating with an average size of 50nm. BET showed the mean pore sizes of the silica shell to be approximately 10–20nm and the surface area to be 212.8m2g−1. Magnetization ( M s) and remnant ( M r) magnetic properties of CoFSi nanocomposite decreased upon silica coating (from ∼14 to 2emug−1 for M s of CoF and CoFSi, respectively). In contrast, the coercivity ( H c) of the uncoated CoFe2O4 (317Oe) is lower than that of the coated nanocomposites (1250Oe of CoFSi). In vitro drug loading of the CoFSi nanoparticles and its pH-responsive (pH=4.0 and 7.0) controlled release were investigated using IMC as a model drug. It was seen that the release of the IMC drug was significantly faster at a pH of 4.0 compared to that at a neutral pH 7.0. Furthermore, the lower concentration of ions release (iron and cobalt) from CoFSi was observed after aging for 50h.
Keywords: Hydroxyapatite; CoFe; 2; O; 4; Nanoparticles; Hyperthermia; Magnetic drug target (MDT)
DSC studies on the transformation kinetics of two separated crystallization peaks of Si12.5Te87.5 chalcogenide glass: An application of the theoretical method developed and isoconversional method
by M. Abu El-Oyoun (pp. 495-506).
► Thermal analysis using the DSC tool. ► The crystallization kinetics parameters. ► Theoretical method developed analysis. ► Isoconversional (model-free) methods. ► The transformation mechanisms.The transformation kinetics from glass to crystalline of two clearly separated crystallization peaks of Si12.5Te87.5 chalcogenide glass were studied using DSC technique. The kinetic parameters of these two separated crystallization peaks of the present chalcogenide glass under non-isothermal conditions are analyzed by the theoretical method developed (TMD) and the isoconversional (model-free) with the help of model-fitting method for the heating rates range of 5–90Kmin−1. The average values of the effective activation energies, E eff., are 133.27±5.29kJmol−1 for the first crystallization peak (FCP) and 198.99±4.81kJmol−1 for the second crystallization peak (SCP). The dependence of the transformed fraction, α P, corresponding to the maximum transformation rate, on impingement exponent, γi, indicated that the mode of impingement is due to “anisotropic growth”. The average value of kinetic exponent, n P, calculated using TMD method is 1.53±0.07 for FCP, while, the average value of n P for SCP is 5.55±0.52. The unexpected high value of the kinetic exponent for SCP could be explained as both nucleation frequency and crystal growth rate depend on the time as a power law. The effective activation energy of crystallization, E eff.( α), using the isoconversional method, shows a little variation throughout the entire interval of transformations for FCP compared to that for SCP. Whereas, the dependence of E eff.( α) for SCP shows a strong dependence on the degrees of transformation and temperature. The reaction model that may describe transformation process of Si12.5Te87.5 chalcogenide glass for FCP is Avrami–Erofeev model ( g( α)=[−ln(1− α)]1/ n) with n equal to 1.5 for all heating rates used (5–90Kmin−1). On the other hand, the reaction model that may describe transformation process of SCP is a power law model g( α)= α1/ ξ with ξ=0.25 for heating rate range of 5–35Kmin−1 and ξ=0.50 for the heating rate range of 40–90Kmin−1. Finally, the obtained results of transformation kinetic parameters using TMD analysis are in good agreement with that obtained according to the isoconversional one under non-isothermal regime. These results indicate that each method confirms and complements the other, and using the two methods for evaluating the transformation kinetic parameters to describe the glass-crystalline transformation process of Si12.5Te87.5 chalcogenide glass is helpful.
Keywords: PACS; 6470P; 6140; 6140DSi; 12.5; Te; 87.5; chalcogenide glass; Crystallization; Thermal properties; Differential scanning calorimetry (DSC)
Investigations on the effect of experimental parameters on the porosity features of silica aerogels synthesized at ambient drying conditions
by S. Smitha; P. Shajesh; K.G.K. Warrier (pp. 507-511).
Silica aerogels were synthesized through an ambient pressure drying technique, and the porosities of the aerogels were tailored over a wide range, by varying the experimental parameters such as hydrolysis temperature, gelation pH, aging pH and aging solvent. Pore size, pore volume and surface area could tailor between 6.2–18nm, 0.99–2.04ccg−1 and 452–635m2g−1 respectively by changing the hydrolysis–condensation conditions. By varying the aging pH from 3 to 11, pore size and pore volume was tailored in between 5.8–13.4nm and 0.88–1.45ccg−1 respectively. The investigation will be highly beneficial for the synthesis of tailor made silica aerogels at ambient conditions.
Keywords: Sol–gel growth; Amorphous materials; Microporous materials; Adsorption
Role of Ga2O3–In2O3–ZnO channel composition on the electrical performance of thin-film transistors
by A. Olziersky; P. Barquinha; A. Vilà; C. Magaña; E. Fortunato; J.R. Morante; R. Martins (pp. 512-518).
► How Ga2O3-In2O3-ZnO channel composition affects the electrical performance of TFTs. ► Zn sputtering deficiency affects the In/Ga atomic concentration ratios. ► Resistivity and mobility show a general trend against the measured In/Ga ratio. ► Increased In concentrations allow to obtain the best performances. ► A slightly lower In composition provides good performance, lowering material costs.In this work we present a study aiming to determine the role of Ga2O3–In2O3–ZnO (GIZO) channel layer composition on the electrical performance and stability exhibited by thin-film transistors (TFTs). The GIZO films were obtained by magnetron sputtering using ceramic targets of different compositions (Ga:In:Zn=2:2:1, 2:2:2, 2:4:1 and 2:4:2at.). Structural analysis corroborates the fully amorphous character of the GIZO deposited layers. For the target compositional range used we observe a Zn deficiency on the produced films, which affects the In/Ga atomic concentration ratios. Resistivity and mobility are found to show a general trend against the measured In/Ga ratio that reveals the role played by In and Ga cations on the transport mechanisms. Targets with increased In concentrations (2:4:1 and 2:4:2) allow to obtain the best TFT performances with field effect mobilities reaching values of 53.0 and 51.7cm2V−1s−1, respectively. In addition, the In-richer GIZO compositions result in considerably more stable TFTs, especially under positive gate bias stress conditions. Finally, it is verified that by using a target with a slightly lower In atomic composition (2:4:2 in comparison to 2:4:1), good stability and mobility can be achieved with potentially lower material costs.
Keywords: Oxides; Amorphous materials; Thin films; Electrical characterization
Near infrared electrochromic polymers based on phenazine moieties
by Elif Nazlı Esmer; Simge Tarkuc; Yasemin Arslan Udum; Levent Toppare (pp. 519-524).
► The polymers are multichromic which is rare in literature. ► Yet another one switches between green and gray/transparent regime. ► Green to transparent switching polymers only go back to 2007. ► One of the polymers reveals a switching time of less than 1s both in visible and near IR regions, quite an important feature for display applications.New fused-aromatic quinoxaline and thieno[3,4-b]pyrazine based monomers; 10,12-bis(4-hexylthiophen-2-yl)dibenzo[f,h]thieno[3,4-b]quinoxaline (HTBQ) and 10,13-bis(4-hexylthiophen-2-yl)dipyrido[3,2-a:2′,3′-c]phenazine (HTPP) were synthesized. Electrochemical polymerization of HTBQ and HTPP were performed in acetonitrile/dichloromethane (ACN/DCM) solution containing LiClO4/NaClO4. Spectroelectrochemical behavior and switching ability of PHTBQ and PHTPP films were investigated by UV–vis spectroscopy. The polymer films showed reversible electrochemical oxidation with high contrast ratios in the NIR region with low switching times. PHTBQ revealed color changes between brick color and green in the reduced and oxidized states. PHTPP changed color from green to gray when the polymer film was switched between its redox states.
Keywords: Polymers; Electrochemical techniques; Electrochemical properties; Optical properties
Spray pyrolytic deposition of polycrystalline Cu2S thin films
by Woo-Young Kim; Balasaheb M. Palve; Habib M. Pathan; Oh-Shim Joo (pp. 525-528).
► Synthesis of polycrystalline Cu2S films with band gap of 1.5eV which is truly useful for solar cell applications. ► Deposition has been carried out without any complexing agent. ► Films are compact.Polycrystalline copper sulfide (Cu2S) thin films were deposited by spray pyrolysis using aqueous solutions of copper nitrate and thiourea without any complexing agent at substrate (deposition) temperature of ∼200°C. The films were deposited onto glass and ITO-coated glass substrates. The deposited films were observed to be blackish brown in color, well adherent to the substrate, pin-hole free and uniform. The structural, surface morphological and optical properties of the films were carried out by means of X-ray diffraction, scanning electron microscopy and optical absorbance measurement techniques. XRD analysis showed that deposited films are chemically close to chalcocite, Cu2S. The optical band gap was calculated to be 1.5eV.
Keywords: Thin films; Chemical synthesis; Crystal structure; Electron microscopy
Characterisation of doped polypyrrole/manganese oxide nanocomposite for supercapacitor electrodes
by Ze Hua Dong; Yan Li Wei; Wei Shi; Guo An Zhang (pp. 529-534).
► MnO2 increases the specific capacitance of PPy. ► MnO2 retards the structural deterioration of PPy. ► MnO2 reduces the rate capability of PPy.P-toluenesulfonic acid (TSA) doped polypyrrole (PPy) binary nanocomposite and MnO2/PPy/TSA ternary nanocomposite were prepared by chemical oxidative polymerization. The chemical compositions of nanocomposites were characterised by infrared spectrometry and energy dispersive spectroscopy. Micrographs and BET isotherm measurements showed that the particle and the pore size of the ternary nanocomposite are much smaller than those of the binary one. Electrochemical measurements showed that the ternary nanocomposite electrode exhibited a higher specific capacitance of ∼376Fg−1 at 3mAcm−2 and better cycling stability in 0.5M Na2SO4 solution than the binary one, which is attributed to that the dispersed MnO2 particles adhered to PPy chains increase the specific surface area of the ternary nanocomposite and retard the structural deterioration of PPy backbones during charge–discharge cycling process. Long cyclic measurements showed that the specific capacitance of ternary composite can retain 90% of its initial value over 500 charge–discharge cycles in the potential range of −0.1 to 0.9V vs. SCE. Nevertheless, the dispersed MnO2 could reduce the rate capability and conductivity of the ternary composite.
Keywords: Polymers; Chemical synthesis; Electrochemical techniques; Supercapacitor
Structural, dielectric and electrical properties of BaFe0.5Nb0.5O3 ceramic prepared by solid-state reaction technique
by M. Ganguly; S. Parida; E. Sinha; S.K. Rout; A.K. Simanshu; A. Hussain; I.W. Kim (pp. 535-539).
► The BaFe0.5Nb0.5O3 ceramic prepared via solid state reaction route. ► The material found to be cubic symmetry over a wide temperature range (−100°C to 550°C). ► The temperature dependency dielectric study on materials showed a canonical type relaxor behavior. ► The present paper is going to make an end over the ambiguities reported on its structural behavior.Barium iron niobate (BaFe0.5Nb0.5O3) has been prepared by solid state reaction route through heat treatment at 1200°C for four hours in air. Structural properties have been investigated using X-ray diffraction (XRD), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy. Rietveld refinement technique has been employed to investigate the details of crystal structure and found to be cubic at room temperature with space group Pm-3m. The XRD patterns have been recorded from room temperature to 550°C did not show any phase transformation. Raman spectra recorded from −100°C to 550°C did not show any structural change as a function of temperature variation. Temperature dependent dielectric behavior and d.c. conductivity have been investigated from room temperature to 550°C. The dielectric study revealed two peaks; one for intrinsic and other for extrinsic type relaxation. Polarization study at various frequencies confirmed the hopping mechanism between Fe2+ and Fe3+ ions within the equivalent crystallographic sites of the sample. The material could be regarded as a canonical relaxor within 300°C.
Keywords: Ceramics; Fourier transform infrared spectroscopy; FT-Raman; Electrical property
Titanium–10wt% 45S5 Bioglass nanocomposite for biomedical applications
by K. Jurczyk; M.U. Jurczyk; K. Niespodziana; J. Jakubowicz; M. Jurczyk (pp. 540-546).
► High hardness, low E modulus, better corrosion resistance and good cytocompatibility. ► The cells penetrating the porous structure. ► On the polished surface, more spherical cells were observed. ► Ti–10wt% 45S5 Bioglass nanocomposite is a promising biomaterial.In the present study, titanium–10wt% 45S5 Bioglass nanocomposite was successfully synthesized by the combination of mechanical alloying and powder metallurgy process. The structure, mechanical and corrosion properties of this material were investigated. Microhardness test showed that the obtained material exhibits Vickers’ microhardness as high as 620HV0.2, which is two times higher than that of a conventional microcrystalline titanium (225HV0.2). Additionally, titanium–10wt% of 45S5 Bioglass nanocomposites ( ic=1.20×10−7Acm−2, Ec=−0.42V vs. SCE) were more corrosion resistant than microcrystalline titanium ( ic=2.27×10−6Acm−2, Ec=−0.36V vs. SCE). The electrochemical treatment in phosphoric acid electrolyte results in porous surface, attractive for tissue fixing and growth. In vitro cytocompatibility of these materials was evaluated and compared with a conventional microcrystalline titanium, where normal human osteoblast (NHOst) cells from Cambrex (CC-2538) were cultured on the discs of the materials and cell growth was examined. On porous surface, the cells adhered with their whole surface to the insert penetrating the porous structure, while on the polished surface, more spherical cells were observed with a smaller surface of adhesion. On the other hand, the morphology of the cell cultures obtained on Ti–10wt% 45S5 Bioglass nanocomposite was similar to those obtained on the microcrystalline titanium. The present study has demonstrated that porous titanium–10wt% 45S5 Bioglass nanocomposite is a promising biomaterial for bone tissue engineering due to its appropriate microstructure, high hardness, low E modulus, better corrosion resistance and good cytocompatibility.
Keywords: A. Biomaterials; A. Composite materials; B. Powder metallurgy; B. Sintering
The effects of surface modification on carbon felt electrodes for use in vanadium redox flow batteries
by Ki Jae Kim; Young-Jun Kim; Jae-Hun Kim; Min-Sik Park (pp. 547-553).
► We observed the physical and chemical changes on the surface of carbon felts after various surface modifications. ► The surface area and chemistry of functional groups formed on the surface of carbon felt are critical to determine the kinetics of the redox reactions of vanadium ions. ► By incorporation of the surface modifications into the electrode preparation, the electrochemical activity of carbon felts could be notably enhanced.The surface of carbon felt electrodes has been modified for improving energy efficiency of vanadium redox flow batteries. For comparative purposes, the effects of various surface modifications such as mild oxidation, plasma treatment, and gamma-ray irradiation on the electrochemical properties of carbon felt electrodes were investigated at optimized conditions. The cell energy efficiency was improved from 68 to 75% after the mild oxidation of the carbon felt at 500°C for 5h. This efficiency improvement could be attributed to the increased surface area of the carbon felt electrode and the formation of functional groups on its surface as a result of the modification. On the basis of various structural and electrochemical characterizations, a relationship between the surface nature and electrochemical activity of the carbon felt electrodes is discussed.
Keywords: Carbon felt; Electrochemistry; Redox flow batteries; Surface modification