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Journal of Materials Science: Full Set - Includes `Journal of Materials Science Letters' (v.44, #20)
Negative thermal expansion: a review by W. Miller; C. W. Smith; D. S. Mackenzie; K. E. Evans (pp. 5441-5451).
Most materials demonstrate an expansion upon heating, however a few are known to contract, i.e. exhibit a negative coefficient of thermal expansivity (NTE). This naturally occurring phenomenon has been shown to occur in a range of solids including complex metal oxides, polymers and zeolites, and opens the door to composites with a coefficient of thermal expansion (CTE) of zero. The state of the art in NTE solids is reviewed, and understanding of the driving mechanisms of the effect is considered along with experimental and theoretical evidence. The various categories of solids with NTE are explored, and experimental methods for their experimental characterisation and applications for such solids are proposed. An abstraction for an underlying mechanism for NTE at the supramolecular level and its applicability at the molecular level is discussed.
Effect of abnormal grain growth on tensile strength of Al–Cu–Mg alloy friction stir welded joints by M. A. Safarkhanian; M. Goodarzi; S. M. A. Boutorabi (pp. 5452-5458).
An Al-4.5%Cu-1.5%Mg aluminum alloy with a T4 temper was friction stir welded, and the effect of the abnormal grain growth on the tensile strength of joints was investigated. Abnormal grain growth usually happens during post weld heat treatment. It is found that the tensile strength and elongation of the heat-treated joint will increase significantly if this phenomenon completely happens in stir zone. On the other hand stable grains in the stir zone have no effect on the mechanical properties of heat-treated joint.
Kinetic study of controlled release of VPA and DPH antiepileptic drugs using biocompatible nanostructured sol–gel TiO2 by T. López; R. Alexander-Katz; P. Castillo; M. González; J. Manjarrez; R. D. Gonzalez; L. Ilharco; A. Fidalgo; J. Rieumont (pp. 5459-5468).
Sol–gel TiO2 porous matrix was used to host valproic acid (VPA) and phenytoin (DPH), which are commonly used as antiepileptic drugs. The addition of these drugs was carried out during the synthesis in the hydrolysis stage. In vitro short term kinetic studies on drug liberation showed that almost all samples followed a first order kinetics with the exception of one sample which had a linear behavior. High resolution electron microscopy revealed the existence of nanocrystalinity in all samples, however, electron diffraction patterns showed that some were predominantly amorphous while in others suggested a greater density of nanocrystals. NMR studies demonstrated that VPA was less mobile in a more crystalline TiO2 matrix than when the TiO2 is mainly amorphous. Some features of the kinetics of drug liberation are explained in terms of the competition between nanocrystallinity and drug content. The reservoirs were implanted by means of stereotactic surgery in Wistar rats in which epilepsy was previously induced following the Kindling model of epilepsy. The efficiency of the reservoirs was follow by electroencephalography (EEGs). In vivo studies revealed that a more crystalline sample was more effective in preventing further epileptic events than samples with a higher content of VPA but predominantly amorphous.
Electrical characterization of LiTaO3:P(VDF–TrFE) composites by Padmaja Guggilla; A. K. Batra; M. E. Edwards (pp. 5469-5474).
Composites of pyroelectric ceramics and polymers are very important as their unique features and properties can be easily tailored for various specific applications. Lithium tantalatum oxide (LiTaO3, LT), the pyroelectric ceramic powder has been incorporated into a polyvinylidene fluoride–trifluoroethylene [P(VDF–TrFE) 70/30 mol%] copolymer matrix to form 0–3 composites. The composite films were prepared using ‘solvent casting’ (SC) method to disperse the ceramic powder homogeneously in the P(VDF–TrFE) copolymer matrix with various wt% of LT powder. In order to derive high pyroelectric performance, the samples were poled. Electric properties, such as the dielectric constant, dielectric loss, and pyroelectric coefficient, have been measured as a function of temperature and frequency. In addition, material figures-of-merit, very important factors for assessing many sensor applications have also been calculated. The results show that the fabricated lead free lithium tantalite: P(VDF–TrFE) composite materials have a good potential for pyroelectric infrared sensor applications.
Effect of hot compression and annealing on microstructure evolution of ZK60 magnesium alloys by Shouren Wang; Suk Bong Kang; JaeHyung Cho (pp. 5475-5484).
Microstructural evolution of ZK60 magnesium alloys, during twin roll cast (TRC) and hot compression (HC) with a strain rate of 0.1 s−1 at 350 °C and subsequent annealing at temperatures of 250–400 °C for 102−5 × 105 s, has been observed by optical microscopy (OM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The distribution of average grain size and recrystallized grain size at different annealing conditions were calculated. Activation energy and recrystallized volume fractions during annealing were discussed using analysis of static recrystallization (SRX) kinetics. Based on examination of microstructure evolution during annealing, it was found that several SRX mechanisms were co-activated. Subgrains with high misorientation angles to surrounding grains were formed by dislocation rearrangement, and they seemed to evolve into newly recrystallized grains.
The fabrication of a MWNTs–polymer composite chemoresistive sensor array to discriminate between chemical toxic agents by Chang-Pin Chang; Chun-Lung Yuan (pp. 5485-5493).
In this study, a chemoresistive sensor was fabricated by the chemical polymerization and coating of either polyaniline (PANI), poly[2-methoxy-5-(2-ethyloxy)-p-phenylenevinylene], or commercial poly(methyl methacrylate) on MWNTs. We investigated the resistance responsiveness of the multilayer samples to simulated chemical warfare agents, including dimethyl methyl phosphonate (DMMP) and dichloromethane (DCM), as well as to organic agents, such as chloroform, tetrahydrofuran, methyl-ethyl ketone, and xylene. The MWNTs–PANI film was characterized by SEM and FT-IR, and the resistivity values for the six solvents were measured at different temperatures. We observed that the MWNTs-PANI sensing film exhibited a high sensitivity, excellent selectivity, and good reproducibility to the detection of all of the aforementioned agent vapors. In addition, we used atomic force microscopy to demonstrate the MWNTs–PANI absorption of DMMP vapor, wherein the sensing film exhibited a swelling phenomenon, such that the film thickness increased from 0.8 to 1.3 μm. In addition, we used principal component analysis to evaluate the performance of the sensor in detecting DMMP, DCM, and the aforementioned organic agent vapors.
Powder metallurgical fabrication of zirconium matrix cermet nuclear fuels by Aaron R. Totemeier; Sean M. McDeavitt (pp. 5494-5500).
Two powder metallurgical fabrication methods for a zirconium-based cermet nuclear dispersion fuel with oxide microspheres have been demonstrated. A multi-pass, cold-drawing process is shown to have excellent capability to control the final matrix density, though it requires several high-temperature anneals during fabrication to relieve strain hardening and increase matrix–particle bonding. Severe oxide particle damage was observed in the cold-drawn fuel pin and was likely a result of high matrix deformation resistance at room temperature. A single-pass, hot-extrusion process has been demonstrated and was shown to be capable of providing a dense matrix phase with less particle damage. Both processes were shown to be effective fabrication methods for a zirconium-based cermet, and the process variables may be controlled to create the desired fuel properties.
Three-jet electrospinning using a flat spinneret by Feng-Lei Zhou; Rong-Hua Gong; Isaac Porat (pp. 5501-5508).
Electrospinning is a simple but highly versatile technology to produce nanofibers from solutions or melts mostly of polymers using electrostatic forces. A primary challenge facing electrospinning is its low productivity mainly limited by flow rate. In this work, a custom-made three-hole spinneret instead of conventional needles was adopted to enhance the flow rate of electrospinning. Three-jet formation, nanofiber deposition, nanofiber morphology and size were characterized by digital camera and scanning electron microscopy (SEM) as the effects of several governing parameters in electrospinning, including applied voltage from 19.8 to 21.0 kV, working distance from 15.2 to 16.8 cm and flow rate from 6.0 to 9.0 mL/h. It was found that three simultaneous stable jets were ejected from the three-hole spinneret under suitable operating conditions. Moreover, it was found that the fibers collected from the jets from each hole deposited separately in circular spots on a stationary collector. The resultant fibers mostly have an average diameter of less than 300 nm. It has been proved that simple holes on a flat surface can be used to electrospin nanofibers. The three-hole spinneret produces nanofibers at flow rates greater than that in single needle electrospinning. Flow rate has the potential to be easily scaled up by increasing the spinneret diameter and the number of holes.
Thermal properties and microstructure of bulk nanocrystalline Gd material by Hong Zeng; Chunjiang Kuang; Jiuxing Zhang; Ming Yue (pp. 5509-5514).
Bulk nanocrystalline gadolinium (Gd) material has been consolidated from Gd nanoparticles using spark plasma sintering (SPS). High density (>99.5%) bulk nanocrystalline material was achieved after sintering at a temperature of 280 °C with a pressure of 500 MPa. Microstructure analysis shows that the consolidated bulk material exhibits a single phase with hexagonal close packed structure and a fine grain microstructure with a mean grain size of about 15 nm. The structural transformation from hexagonal condensed packed to face centered cubic was not observed, and the second-order magnetic transition remained in the nanocrystalline Gd sample. The Curie temperature of the nanocrystalline Gd decreased by more than 10.7 K below that of the coarse-grained. The activation energies for the coarse-grained and the as-consolidated Gd materials are 2.7702 and 1.0130 eV, respectively.
Magnetoelectric and electrical properties of WO3-doped (Ni0.8Zn0.1Cu0.1)Fe2O4/[Pb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3] composites by Renbing Sun; Bijun Fang; Xinwei Dong; Junming Liu (pp. 5515-5523).
A total of 5 mol% WO3-doped (1−x)(Ni0.8Zn0.1Cu0.1)Fe2O4/xPb(Ni1/3Nb2/3)O3–Pb(Zn1/3Nb2/3)O3–PbTiO3 ((1−x)NZCF/xPNN-PZN-PT) magnetoelectric particulate ceramic composites were prepared by conventional solid-state reaction method via low-temperature sintering process. X-ray diffraction (XRD) measurement and scanning electron microscopy (SEM) observation indicate that piezoelectric phase and ferrite phase coexist in the sintered particulate ceramic composites. Dielectric property of the (1−x)NZCF/x0.53PNN–0.02PZN–0.05Pb(Ni1/2W1/2)O3–0.40PT ((1−x)NZCF/xPNN-PZN-PNW-PT, nominal composition) composites is improved greatly as compared to that of the undoped (1−x)NZCF/xPNN-PZN-PT composites. The WO3-doped (1−x)NZCF/xPNN-PZN-PT composites exhibit typical P–E hysteresis loops at room temperature accompanied by the decrease of saturation polarization (P s) and remnant polarization (P r). At the same time, piezoelectric property of the composites deteriorates greatly with the increase of ferrite content. The (1−x)NZCF/xPNN-PZN-PNW-PT composites can be electrically and magnetically poled and exhibit apparent magnetoelectric (ME) effect. A maximum ME voltage coefficient of 13.1 mV/(cm Oe) is obtained in the 0.1NZCF/0.9PNN-PZN-PNW-PT composite at 400 Oe d.c. magnetic bias field superimposed 1 kHz a.c. magnetic field with 5 Oe amplitude. The addition of WO3 in the piezoelectric phase decreases sintering temperature greatly from 1180 °C to 950 °C and decreases dielectric loss sharply of the composites, thus the ME voltage coefficient increases. Such ceramic processing is valuable for the preparation of magnetoelectric particulate ceramic composites with excellent ME effect.
A combined synchrotron powder diffraction and vibrational study of the thermal treatment of palygorskite–indigo to produce Maya blue by Manuel Sánchez del Río; Enrico Boccaleri; Marco Milanesio; Gianluca Croce; Wouter van Beek; Constantinos Tsiantos; Georgios D. Chyssikos; Vassilis Gionis; George H. Kacandes; Mercedes Suárez; Emilia García-Romero (pp. 5524-5536).
The heating process (30–200 °C) of a palygorskite-indigo mixture has been monitored in situ and simultaneously by synchrotron powder diffraction and Raman spectroscopy. During this process, the dye and the clay interact to form Maya blue (MB), a pigment highly resistant to degradation. It is shown that the formation of a very stable pigment occurs in the 70–130 °C interval; i.e., when palygorskite starts to loose zeolitic water, and is accompanied by a reduction of the crystallographic a parameter, as well as by alterations in the C=C and C=O bonds of indigo. Mid- and near-infrared spectroscopic work and microporosity measurements, employed to study the rehydration process after the complex formation, provide evidence for the inhibition of the rehydration of MB as compared with palygorskite. These results are consistent with the blocking of the palygorskite tunnel entrance by indigo molecules with a possible partial penetration inside the tunnels. The surface silanols of palygorskite are not perturbed by indigo, suggesting that MB is not a surface complex.
On the essential work of fracture in polymer–metal multilayers by Géraldine Garnier; Béchir Chehab; Bernard Yrieix; Yves Bréchet; Lionel Flandin (pp. 5537-5543).
Polyethylene terephtalate (PET) metallized with aluminium by physical vapour deposition was investigated through classical physical chemistry techniques and mechanical characterization. The amount of aluminium altered the amount of crystallinity of the PET substrate, but appeared unrelated to the mechanical properties obtained with regular tensile test. In contrast, the essential work of fracture (EWF), as obtained with Cotterell tests, permitted to better discriminate the perforation resistance. It is shown that increasing the amount of crystallinity within the PET linearly reduced the EWF.
Mechanical characterization of anti-infectious, anti-allergic, and bioactive coatings on orthopedic implant surfaces by Andreas Fritsche; Maximilian Haenle; Carmen Zietz; Wolfram Mittelmeier; Hans-Georg Neumann; Frank Heidenau; Birgit Finke; Rainer Bader (pp. 5544-5551).
In total joint replacement much effort has been made to reduce implant loosening. We investigated different implant coatings (copper integrated titanium dioxide (TiO2–Cu), titanium nitride (TiN), plasma polymerized allylamine (PPAAm), and calcium phosphate (CaP)) regarding the adhesion strength and wear resistance. Standardized scratch and adhesive tests were applied. Abrasive wear was measured with artificial bone and bone cement using a special testing machine. All tested coatings have higher bonding strengths than the 22 N/mm2 required for medical implant surface coatings by ASTM standard 4711-F. Using bone cement, wear testing revealed higher wear rates in most cases. Polished surfaces reduce the amount of wear, whereas rough surfaces highly increase the wear rate due to three-body wear, especially ceramic surfaces. In general, the application of bone cement in conjunction with modified implant surfaces can lead to an increase in wear rate.
Compression properties of cellular AlCu5Mn alloy foams with wide range of porosity by Dong-Hui Yang; Shang-Run Yang; Ai-Bin Ma; Jin-Hua Jiang (pp. 5552-5556).
Cellular AlCu5Mn foams with porosity of 91.2–45.8% were fabricated by melt-foaming method. The measured compression properties show that both strength and energy absorption capacity of cellular AlCu5Mn foams are better than those of the other Al-based foams. The highest values of strength and energy absorption capacity of cellular AlCu5Mn foams are 82.7 MPa and 72.22 MJ m−3, respectively, which implies that cellular AlCu5Mn foams should be attractive in practical applications.
Electrical conductivity, relaxation, and scaling analysis studies of lithium alumino phosphate glasses and glass ceramics by M. V. N. V. D. Sharma; A. V. Sarma; R. Balaji Rao (pp. 5557-5562).
Different compositions of lithium aluminum phosphate glasses were prepared by melt quenching technique. The best bulk conductivity achieved by the sample G3, (28 mol% of lithium oxide). Further, the investigation extended by crystallizing the G3 sample at different temperatures, 200 °C (GC200), 300 °C(GC300), 400 °C (GC400), and 500 °C (GC500). The electrical measurements for all the glasses and glass ceramics were carried out in the frequency range of 1–105 Hz and at a temperature range of 393–513 K by the impedance spectroscopy. The variation of conductivity with frequency of the samples was explained in the light of different valency states of aluminum ions. AC conductivity data are fitted to a power law equation. Scaled spectra for ac conductivity and modulus data suggested that the present glass samples follow temperature independent conductivity distribution relaxation mechanism.
Synthesis and characterization of BaTiO3-based X9R ceramics by Ling-xia Li; Ye-mei Han; Ping Zhang; Cui Ming; Xue Wei (pp. 5563-5568).
The effects of (Na0.5Bi0.5)TiO3 (NBT) and MgO addition on the dielectric properties and microstructures of BaTiO3 (BT) ceramics were investigated. NBT was first added to Nb2O5-doped BT system. As NBT content increases from 0 to 0.2 mol, the Curie temperature of the systems shifts to high temperatures and dielectric constant peak at T c is suppressed evidently. The variation of capacity (ΔC/C 20 °C (%)) of the system at 200 °C decreases with increasing NBT content from 0.1 to 0.2 mol, but that of −55 and 125 °C increases monotonously. The stable temperature characteristics of the dielectric properties improved by NBT doping would be connected with the distortion and deformation of the structure induced by substitution of Na+ and Bi3+ into Ba sites. MgO was employed to further flatten the ΔC/C 20 °C–T curve. It is very helpful for this ceramic system to satisfy the requirement of EIA-X9R specification on ΔC/C 20 °C and still keep a satisfied dielectric constant. The addition of MgO improved effectively the temperature stability of the dielectric properties. Changes of the crystalline structure and microstructure induced by MgO doping might contribute to these improvements.
Interfacial study of Crofer 22 APU interconnect-SABS-0 seal glass for solid oxide fuel/electrolyzer cells by M. K. Mahapatra; K. Lu (pp. 5569-5578).
In planar solid oxide fuel and electrolyzer cells, compatibility and thermochemical stability of interconnect-seal glass interface is essential in order to avoid mixing and leakage of different gases and degradation of cell performances. In the present work, interfacial compatibility and thermochemical stability are studied for an alkaline earth silicate based glass (SABS-0) and Crofer 22 APU interconnect system with respect to thermal treatment temperature (700–850 °C) and time (0–100 h). The study has been carried out in argon to avoid complications from oxidation. Even though pore and crack-free interface is obtained and maintained for all the thermal treatment conditions, there are simultaneous diffusion of the Crofer 22 APU and the SABS-0 glass elements, chemical reaction at the Crofer 22 APU/SABS-0 interface, and devitrification of the SABS-0 glass itself.
Structural study of Li2MnO3 by electron microscopy by C. H. Lei; J. G. Wen; M. Sardela; J. Bareño; I. Petrov; S.-H. Kang; D. P. Abraham (pp. 5579-5587).
Detailed crystallographic data on high-quality Li2MnO3 material has been obtained using a combination of X-ray diffraction (XRD), selected-area electron diffraction (SAED), high-resolution electron microscopy (HREM), and 0.1 nm probe high-angle annular dark-field imaging (HAADF) in a scanning transmission electron microscope. A high-purity Li2MnO3 powder was annealed at 950 °C for 3 days to obtain predominantly defect-free grains which average size was 3.0 ± 1.5 μm. Rietveld refinement indicated that the C2/m spacegroup provided the best fit for the XRD data. Electron diffraction patterns obtained along various zone axes, on defect-free oxide particles, could be uniquely indexed to the monoclinic structure. HREM and HAADF images of defect-free grains were consistent with a Li–Mn–Mn– arrangement, i.e., lithium ordering in the transition metal planes. Low-magnification TEM images occasionally revealed stacking defects within oxide particles. HREM images of sample areas containing defects revealed a low density of stacking faults within the monoclinic sequence, resulting in a trigonal P3 1 12 local arrangement.
Effect of fibre concentration, temperature and mould thickness on weldline integrity of short glass-fibre-reinforced polypropylene copolymer composites by S. Hashemi; P. Onishi (pp. 5588-5594).
The effect of fibre concentration, temperature and mould thickness on tensile strength of single- and double-gated injection-moulded polypropylene copolymer reinforced with 0, 10, 20, 30 and 40 wt% short glass fibre was studied at a fixed strain-rate of 7.58 × 10−3 s−1 between 23 and 100 °C. It was found that tensile strength of single-gated mouldings, σc, increased with increasing volume fraction of fibres, ϕf in a nonlinear manner and decreased with increasing temperature in a linear manner. However, for ϕf values in the range 0–10% a simple additive rule-of-mixtures adequately described the variation of σc with ϕf over the entire temperature range 23–100 °C studied here. Tensile strength of double-gated mouldings like their single-gated counterparts decreased linearly with increasing temperature. The presence of weldlines significantly reduced tensile strength of double-gated composite mouldings but had little effect on tensile strength of the matrix. Weldline integrity factor, F σ, defined as weldline strength divided by unweld strength, decreased with increasing ϕf but increased with increasing temperature. A linear dependence was found between F σ and temperature. Mould thickness had no significant effect upon weld and unweld tensile strengths and consequently had no significant effect upon weldline integrity factor.
Electromigration behaviors in Sb particle-reinforced composite eutectic SnAgCu solder joints by Fu Guo; Guangchen Xu; Hongwen He (pp. 5595-5601).
Due to the limited capacity of solder joints in microprocessors for the higher current density (usually 103–104 A/cm2), electromigration (EM), known as the mass movement resulting from imposition of high current density, has gained extensive attention during the last decades, specifically, the EM-induced damages in the eutectic 95.5Sn–3.8Ag–0.9Cu (e-SAC) that were heavily used in the electronic packaging industry. In order to conquer the instable physical properties of e-SAC in the severe service environment, composite approach was developed. One of the promising ways was intentionally incorporated metal-particles reinforcements. In this study, the e-SAC with 1 wt% Sb particles additive was investigated under the current density of 104 A/cm2 and 120 °C the ambient temperature. Unlike the non-composite solders that had obvious formation of hillock and valley at the anode side and cathode side, respectively. The crack initiated at the edge of the cathode interface and propagated to the center in the Sb particle-reinforced composite solder. The Sn–Sb phase, formed near the cathode interface after the first-reflow, blocked the movement of metal atoms/ions, but then induced the current crowding. In addition, synergistic influence of the compressive and tensile stress caused the fracturing of the Sn–Sb phase in the solder matrix due to its brittleness and immobility.
The effect of heat treatment on mechanical properties of carbon nanofiber reinforced copper matrix composites by Jianli Kang; Philip Nash; Jiajun Li; Chunsheng Shi; Naiqin Zhao; Sijie Gu (pp. 5602-5608).
The effect of heat treatment of carbon nanofibers (CNFs) on the mechanical properties of CNF (Ni/Y)–Cu composites was investigated. CNF (Ni/Y)–Cu composite powder mixtures were prepared by a combination of in situ chemical vapor deposition (CVD) and co-deposition processes. The in situ CNF (Ni/Y)–Cu powder synthesized by CVD was subject to heat treatment at temperatures ranging from 700 to 1,000 °C. The morphology and quality of CNFs were characterized by transmission electron microscope, scanning electron microscope, and Raman spectroscopy. Heat treatment can improve the CNFs by eliminating the amorphous carbon and disordered graphite. Bulk composites containing various fractions of CNFs were fabricated from the powder by cold pressing and sintering followed by repressing. With the same fraction of CNFs (2.5 wt%), the strengthening efficiency of the CNFs heat treated at 800 °C is 88% higher than that of as-synthesized CNFs. The strengthening mechanism of CNFs in the composites is discussed in detail.
Reaction progress of alkaline-activated metakaolin-ground granulated blast furnace slag blends by Anja Buchwald; R. Tatarin; D. Stephan (pp. 5609-5617).
Ground granulated blast furnace slag (ggbf slag) and metakaolin were blended and the combination was activated by sodium hydroxide solution. Two mix series were investigated, one with low NaOH concentration (9–16 wt%) and the other with a high NaOH concentration of 25 wt%. The reaction progress of the alkali-activated pastes was indirectly measured by isothermal calorimetry as well as by ultrasonic measurements. Both methods show an acceleration of the condensation reaction of the alkali-activated blends compared to both single phases. The acceleration effect is more considerable at the higher activator concentration related to a higher reaction degree of the metakaolin.
Pressure effects on elastic and thermodynamic properties of ZrB2 by Hongzhi Fu; Ying Lu; Wenfang Liu; Tao Gao (pp. 5618-5626).
A theoretical formalism to calculate the single crystal elastic constants for hexagonal crystals from first principle calculations is described. The calculated values compare favorably with recent experimental results. An expression to calculate the bulk modulus along crystallographic axes of single crystals, using elastic constants, has been derived. The calculated linear bulk moduli are found to be in good agreement with the experiments. The shear modulus, Young’s modulus, and Poisson’s ratio for ideal polycrystalline ZrB2 are also calculated and compared with corresponding experimental values. The shear anisotropic factors and anisotropy in the linear bulk modulus are obtained from the single crystal elastic constants. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal. The calculated elastic properties are found to be in good agreement with experimental values when the generalized gradient approximation is used for the exchange and correlation potential. It is found that the elastic constants and the Debye temperature of ZrB2 increase monotonically and the anisotropies weaken with pressure. The thermal properties including the equation of state, linear compressibility, ductility, and the heat capacity at various pressures and temperatures are estimated.
Precipitation hardening of Zr-modified Mg–Ca–Zn alloy by D. Shepelev; M. Bamberger; A. Katsman (pp. 5627-5635).
The microstructure and mechanical properties of Mg–Ca–Zn alloys with 1 wt.% Zr were investigated in as-cast and heat-treated conditions. A substantial decrease in grain size (from 65 µm for the Mg–Ca–Zn base alloy to 22 µm) was observed. The alloy was solution treated at 410 °C for up to 96 h followed by aging at 175 °C for up to 24 h. Conventional techniques, X-ray diffraction, EM + EDS, and TEM were used to characterize the microstructure of the alloy. The microstructure obtained after heat treatment had equiaxed grains with evenly distributed binary phase Zn2Zr. The binary Mg2Ca and ternary Mg2Ca6Zn3 phases were identified in the matrix and at grain boundaries surrounded by precipitate-depleted zones (PDZs). The thermal stability of the Zr-modified alloys was examined by microhardness measurements conducted after prolonged exposures of the alloys to elevated temperatures. It was found that Zr is a structure-stabilizing factor. Its influence was associated with the formation of Zn2Zr phase that does not undergo coarsening at the elevated temperatures used (due to the low diffusivity of Zr). The nanoscale mechanical properties of grain boundary PDZs were analyzed using combined nanoindentation and atomic force microscopy. These mechanical properties were then correlated to the composition and precipitate distribution in PDZs. An increase in the solution treatment duration from 10 to 96 h at 410 °C resulted in expansion of PDZs from ~0.75 to ~3 µm, while the following aging at 175 °C for up to 24 h did not lead to a detectable change in PDZs. The analysis indicates that the lowest hardness was found in the region where Zn2Zr precipitates density was low, regardless of the solute concentration.
Electron spin resonance study of Mo(V) ion species incorporated into aluminosilicate nanospheres with solid core/mesoporous shell structure by Gernho Back; Hyeyoung Lee; Minsik Kim; Jong-Sung Yu; Soobok Jeong; Young Bae Chae (pp. 5636-5643).
Silica spheres with sub-micrometer sized solid core and mesoporous shell (SCMS) structure were synthesized, and aluminum was incorporated into the mesoporous shell framework by impregnation method to generate SCMS aluminosilicate (AlSCMS) nanospheres. The impregnation of aluminum into the SCMS spheres generates the acid sites on the framework due to the presence of Al3+ ions. The AlSCMS was then used to support molybdenum ion species on the mesoporous shell framework. A solid-state reaction of MoO3 with AlSCMS followed by thermal reduction generated paramagnetic Mo(V) species. The dehydration produced a Mo(V) species that is characterized by electron spin resonance with g e > g ⊥ > g ||. The structural properties of active sites in the AlSCMS were characterized by means of XRD, UV–Vis, 27Al MAS NMR, FT-IR, and energy dispersive X-ray spectrometric measurements. Upon O2 adsorption, the Mo(V) ESR signal intensity decreased, and a new O2 − radical was generated. The Mo species in the dehydrated Mo-AlSCMS is found to exist as oxo-molybdenum species, (MoO2)+ or (MoO)3+. Since the AlSCMS has a low framework negative charge, the MoO2 + with a low positive charge can be easily stabilized and thus seems to be more probable in the AlSCMS framework.
Mold-filling characteristics and solidification behavior of magnesium alloy in vacuum suction casting process by Haitao Teng; Tingju Li; Xiaoli Zhang; Fudong Bai; Kai Qi (pp. 5644-5653).
A novel semi-solid processing technique, called new vacuum suction casting (NVSC), is used to manufacture high-quality components of AZ91D Mg alloy directly from a liquid metal. The resulting apparent morphologies and microstructures of castings are characterized in detail and linked to the corresponding mold-filling behavior and subsequent solidification behavior. It is revealed that the semi-solid metal (SSM) with higher viscosity can be caused to fill the mold with “solid-front fill”, as compared with the liquid metal “spraying” in the conventional vacuum suction casting (CVSC) process. The smooth filling achieved in the NVSC process diminishes some disadvantages inherent for the CVSC sheets, and generates castings with better surface finish and structures with high integrity. The microstructure of the CVSC sheet consists of the fine and homogeneous supersaturated α-Mg solid solution due to the extremely high cooling rate. In the NVSC microstructure, the “preexisting” primary solid particles, with the morphology of near-globules or rosettes, disperse in the homogeneous matrix consisting of fine near-equiaxed secondary α-Mg grains and fine precipitates of β-Mg17Al12 intermetallics. In addition, owing to rapid solidification, the volume fraction of the β phase in the sheets obtained by both the processes is much lower than that in the as-cast ingot.
Effect of combining plane-strain compression with equal channel angular pressing on mechanical properties and texture development in an Al alloy by Abdulhakim A. Almajid; Ehab A. El-Danaf; Mahmoud S. Soliman (pp. 5654-5661).
Commercial purity aluminum (1050) was processed via equal channel angular pressing (ECAP) to one, two, and four passes using route Bc in a 90° channel die, and subsequently compressed in plane strain in two different loading directions, and to two different strain levels. One of the plane-strain-loading directions is parallel to the ECAP forward direction, while the other is perpendicular to it. The flow response in plane-strain compression of the ECAP processed samples revealed an anisotropic behavior, one loading direction systematically gave higher flow stresses. A strain path change parameter was calculated for the two deformation schemes, to justify this anisotropic behavior. Texture evolution, of the plane-strain-compressed samples, was measured, and a transition to the rolling texture was always evidenced. The evolution of the main ideal rolling-texture components obtained from such a combination of deformation schemes, ECAP and plane-strain compression, is presented.
Preparation and characterization of composite materials obtained by pressure infiltration of aluminum in sintered SiC/kaolin preforms by N. Freitas; S. A. Pianaro; S. M. Tebcherani; F. N. Nadal; E. A. T. Berg (pp. 5662-5672).
The present work involved the preparation and characterization of SiC–Al composites containing kaolin concentrations varying from 10 to 50% in substitution of the major SiC phase. Ceramic preforms were produced, controlling the granulometric fraction of SiC/kaolin. After sintering at 1100 °C, these preforms were highly porous. XRD analyses revealed the existence of quartz and SiC phase. During the infiltration process, the molten aluminum reacted preferentially with the quartz and with other aluminosilicates in the preforms, reducing them and precipitating alumina and silica in the microstructure, which also showed excess aluminum that did not react in the process. The silica and silicates of the preform, by reacting preferentially with the aluminum, preventing the formation of Al4C3 phase. The SiC–kaolin–Al composites developed here can be used in applications that require high flexural strength (240–300 MPa), low density, and surface hardness of 180–380 kgf/mm2.
Oxidation resistance of hafnium diboride—silicon carbide from 1400 to 2000 °C by Carmen M. Carney (pp. 5673-5681).
Oxidation resistance tests were carried out on HfB2-20 vol.% SiC prepared by spark plasma sintering. The dense samples were exposed from 1400 to 2000 °C in an ambient atmosphere for 1 h. For comparison, the same material was tested using an arc jet to simulate an atmospheric reentry environment. The oxidation properties of the samples were determined by measuring the weight gain per unit surface area and the thicknesses of the oxide scale. The oxide scale consists of a SiO2 outer layer, porous HfO2 layers, and an HfB2 layer depleted in SiC. A transition in HfO2 morphology from equixed to columnar and a decrease in SiO2 viscosity between 1800 and 1900 °C accompanied a rapid increase in weight gain and scale thickness.
Study on the structure of SF fiber mats electrospun with HFIP and FA and cells behavior by Feng Zhang; Bao Q. Zuo; Lun Bai (pp. 5682-5687).
Bombyx mori silk fibroin (SF) fiber mats were prepared by electrospinning with the solvent of hexafluoroisopropanol (HFIP) and formic acid (FA). The average diameters of SF fiber mats observed by SEM were 2.0 and 0.3 μm when different solvent, HFIP and FA, were used. Fourier transform infrared and X-ray diffraction were employed to study the secondary structure of the SF fiber mats; the results showed that the electrospin solvent not only affect the secondary structure of as-spun SF fiber mats, but also indirectly affect the structure transition of SF fiber mats post-treatment with ethanol. And the SF fiber mats electrospun with FA showed more β-sheet structure before and after ethanol treatment. The differential thermal analysis curve indicated that the solvent of HFIP or FA had a weak effect on the thermal properties of SF fiber mats. To assay the cytocompatibility and cell behavior on the SF fiber mats, cell attachment, spreading, and proliferation of normal human epidermal fibroblasts (NHEF) seeded on the scaffolds was studied. The results indicated that the SF fiber mats support NHEF attachment and growth on SF fiber mats in vitro, and no difference between the SF fiber mats electrospun with HFIP and FA was observed. In this article, a desired morphology and secondary structure of SF fiber mats could be prepared by choosing different electrospinning solvent.
Preparation of polycrystalline bulk Mg2Si by using NaSi by Takahiro Yamada; Yusuke Oishi; Haruhiko Morito; Hisanori Yamane (pp. 5688-5691).
SIMS analysis of low content hydrogen in commercially pure titanium by Shigeru Hamada; Katsu Ohnishi; Hide-aki Nishikawa; Yasuji Oda; Hiroshi Noguchi (pp. 5692-5696).
Diameter variability and strength scatter of elementary flax fibers by E. Spārniņš; J. Andersons (pp. 5697-5699).