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Applied Surface Science (v.257, #19)

Editorial Board (pp. ii).

E-MRS2010 Fall Meeting Symposium F: “10th International Symposium on Electrochemical/Chemical Reactivity of Metastable Materials” 13–17 September 2010, Warsaw (Poland) by Hiroki Habazaki; Maria Janik Czachor; Paweł Kulesza (pp. 8139-8140).

What we have learned from studies on chemical properties of amorphous alloys? by Koji Hashimoto (pp. 8141-8150).

► Superior characteristics of amorphous alloys are based on the homogeneous single-phase nature.► No corrosion of amorphous alloys with corrosion-resistant elements in 12M HCl. ► Corrosion resistance is due to spontaneous passivation. ► The homogeneous single-phase nature is useful as the catalyst precursor.Amorphous alloys have many attractive characteristics including extremely high corrosion resistance if the sufficient amounts of corrosion-resistant elements are added. The superiority of amorphous alloys is based on the homogeneous single phase nature without any chemical and physical heterogeneities. Although there are processing limitations to avoid the formation of heterogeneous crystalline structure in addition to no welding technology without crystallization, the application of corrosion-resistant amorphous alloys is expected particularly to the very aggressive environments, where any conventional crystalline metallic materials cannot be used. Some amorphous bulk alloys showed zero corrosion mass loss due to spontaneous passivation even in 12M HCl. Production of amorphous bulk alloys became possible for selected compositions. The homogeneous single phase nature is also effective to form useful catalysts with unique composition and structure. An example of catalysts is for carbon dioxide methanation useful for supply of renewable energy in the form of methane.

Keywords: Homogeneous alloy; 12; M HCl; Spontaneous passivation; Amorphous bulk alloy; Catalyst; CO; ₂; methanation

Catalytic applications of amorphous alloys: Expectations, achievements, and disappointments by Árpád Molnár (pp. 8151-8164).

► In situ activation of amorphous metallic alloy precursors. ► Characterization of formed materials by varied experimental techniques. ► Application of formed catalyst systems in organic transformations. ► High specific activities achieved in varied reactions.This review intends to summarize the major achievements in the application of amorphous alloys as precursors of catalyst materials. This non-traditional catalyst preparation method may provide supported catalysts with novel chemical and structural properties. Selected examples for both glassy alloy precursors and those fabricated by mechanochemistry include CO oxidation over binary and ternary alloys, dehydrogenation over Cu–M (M=Ti, Zr or Hf), one-step synthesis of methyl isobutyl ketone, and selective hydrogenation of unsaturated carbonyl compounds. Ni alloys for methanation developed for the project to solve global warming by recycling carbon dioxide are also discussed.

Keywords: Amorphous alloys; Crystallization; Catalytic applications; Hydrogenation; Dehydrogenation; Electrocatalysis

Hydrogenation of carbon monoxide over nanostructured systems: A mechanochemical approach by Gabriele Mulas; Renato Campesi; Sebastiano Garroni; Francesco Delogu; Chiara Milanese (pp. 8165-8170).

► We investigated the mechanochemical hydrogenation of CO over nanostructured FeCo- and Mg₂Ni-based catalysts. ► We developed a methodology to evaluate the activity of the solid catalysts on an absolute basis. ► Conversion data were, indeed, expressed as turnover frequency, TOF. ► Conversion was related to the ball to powder collisions events through the mechanochemical turnover frequency parameter, MTOF.In this study we investigated the mechanochemical hydrogenation of carbon monoxide over nanostructured FeCo- and Mg₂Ni-based catalysts. To this aim powdered materials, prepared by mechanical alloying, were subjected to mechanical treatment under CO+H₂ atmosphere. A methodology to evaluate the activity of the solid catalysts on an absolute basis was developed. Conversion data were, indeed, expressed as turnover frequency, TOF, and related to the occurrence of ball to powder collision events through the mechanochemical turnover frequency parameter, MTOF. Differences in the catalytic activity and selectivity were observed for the two FeCo-based studied systems, the solid solution Fe₅₀Co₅₀ and its dispersion on TiO₂ support. As for the Mg₂Ni system, we explored the possibility to estimate the specific role of hydrogen pre-activation step. The catalytic properties of the mechanically alloyed Mg₂Ni system were compared with the conversion data shown by the same system pre-hydrogenated and subsequently milled under CO atmosphere.

Keywords: Mechanochemical process; Nanostructured catalysts; Carbon monoxide hydrogenation

The effect of heat treatment on the performance of the Ni/(Zr-Sm oxide) catalysts for carbon dioxide methanation by Hiroyuki Takano; Koichi Izumiya; Naokazu Kumagai; Koji Hashimoto (pp. 8171-8176).

► CO₂ methanation on the catalyst prepared from an aqueous ZrO₂ sol with Sm(NO₃)₃ and Ni(NO₃)₂. ► Rapid methanation with almost 100% methane selectivity and no CO formation. ► The active catalyst is Ni supported on tetragonal ZrO₂ stabilized by inclusion of Sm³⁺. ► The activity increase with Sm³⁺ content, that is, oxygen vacancies in tetragonal ZrO₂ lattice.The active catalysts for methane formation from the gas mixture of CO₂+4H₂ with almost 100% methane selectivity were prepared by reduction of the oxide mixture of NiO and ZrO₂ prepared by calcination of aqueous ZrO₂ sol with Sm(NO₃)₃ and Ni(NO₃)₂. The 50at%Ni-50at%(Zr-Sm oxide) catalyst consisting of 50at%Ni-50at%(Zr+Sm) with Zr/Sm=5 calcined at 650 or 800°C showed the highest activity for methanation. The active catalysts were Ni supported on tetragonal ZrO₂, and the activity for methanation increased by an increase in inclusion of Sm³⁺ ions substituting Zr⁴⁺ ions in the tetragonal ZrO₂ lattice as a result of an increase in calcination temperature. However, the increase in calcination temperature decreased BET surface area, metal dispersion and hydrogen uptake due to grain growth. Thus, the optimum calcination temperature existed.

Keywords: CO; ₂; methanation; Nearly 100% methane selectivity; Ni/tetragonal ZrO; ₂; catalyst; Stabilization of tetragonal ZrO; ₂; Oxygen vacancy

From anodic TiO₂ nanotubes to hexagonally ordered TiO₂ nanocolumns by T. Ruff; R. Hahn; P. Schmuki (pp. 8177-8181).

► A new hexagonally shaped TiO₂ nanocolumnar morphology is obtained by anodisation. ► Key parameters are the controlled substrate temperature and the applied potential. ► Transition from nanocolumns to nanotubular morphology can be established.We report on the formation of hexagonally ordered TiO₂ nanocolumnar layers by electrochemical oxidation in a fluoride containing electrolyte, using self-organizing nanotube formation conditions at elevated potentials and low temperatures. The influence of the substrate temperature on the nanocolumn morphology and composition is investigated and characterized by FE-SEM and EDX. The origin of these nanocolumns can be attributed to a thickening of the inner tube wall of the double wall structure of self-organized TiO₂ nanotubes. Furthermore, a transition from nanocolumnar to nanotubular structure can be established by changing the applied voltage or applying a post-immersion treatment.

Keywords: TiO; ₂; Nanotubes; Temperature; Diameter; Nanocolumns

Surface-enhanced Raman scattering (SERS) activity of Ag, Au and Cu nanoclusters on TiO₂-nanotubes/Ti substrate by Agata Roguska; Andrzej Kudelski; Marcin Pisarek; Magdalena Opara; Maria Janik-Czachor (pp. 8182-8189).

▶ Ag, Au or Cu loaded TiO2 nanotubes as active and reproducible SERS substrate. ▶ SERS activity of the composites is strongly dependent on the amount of metal deposit. ▶ The SERS activity of Au or Cu loaded composites is distinctly lower than those with Ag. ▶ High activity of Ag loaded composites is mainly a result of their specific morphology.Tubular arrays of TiO₂ nanotubes (ranging in diameter from 40 to 110nm) on a Ti substrate were used as a support for Ag, Au or Cu deposits obtained by the sputter deposition technique, where the amount of metal varied from 0.01 to 0.2mg/cm². Those composite supports were intended for surface-enhanced Raman scattering (SERS) investigations. Composite samples were studied with the aid of scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) to reveal their characteristic morphological and chemical features. Raman spectra of pyridine (as a probe molecule) were measured at different cathodic potentials ranging from −0.2 down to −1.2V after the pyridine had been adsorbed on the metal-covered TiO₂ nanotube/Ti substrates. In addition, SERS spectra on a bulk standard activated Ag, Au and Cu substrates were also measured. The SERS activity of the composite samples was strongly dependent on the amount of metal deposit, e.g. at and above 0.06mg Ag/cm², the intensity of SERS signal was even higher than that for the Ag reference substrate. The high activity of these composites is mainly a result of their specific morphology. The high SERS sensitivity on the surface morphology of the substrate made it possible to monitor very small temporal changes in the Ag metal clusters. This rearrangement was not detectable with microscopic (SEM) or microanalytical (AES) methods. The SERS activity of Au or Cu clusters was distinctly lower than those of Ag. The spectral differences exhibited by the three kinds of composites as compared to the reference metal samples are discussed.

Keywords: Ag, Au or Cu clusters; TiO; ₂; nanotubes; Surface-enhanced Raman scattering (SERS); SEM morphological examinations; AES surface analysis

Effect of electrolyte temperature on the formation of self-organized anodic niobium oxide microcones in hot phosphate–glycerol electrolyte by S. Yang; Y. Aoki; H. Habazaki (pp. 8190-8195).

► Nanoporous niobium oxide microcones were formed by anodizing in phosphate-glycerol electrolyte. ► The size and shape of microcones were independent of electrolyte temperature. ► However, the required anodizing time to form microcones became shorter at higher temperatures.Nanoporous niobium oxide films with microcone-type surface morphology were formed by anodizing at 10V in glycerol electrolyte containing 0.6moldm⁻³ K₂HPO₄ and 0.2moldm⁻³ K₃PO₄ in a temperature range of 428–453K. The microcones appeared after prolonged anodizing, but the required time was largely reduced by increasing electrolyte temperature. The anodic oxide was initially amorphous at all temperatures, but crystalline oxide nucleated during anodizing. The anodic oxide microcones, which were crystalline, appeared on surface as a consequence of preferential chemical dissolution of initially formed amorphous oxide. The chemical dissolution of an initially formed amorphous layer was accelerated by increasing the electrolyte temperature, with negligible influence of the temperature on the morphology of microcones up to 448K.

Keywords: Anodizing; Anodic oxide; Nanoporous film; Self-organization; Organic electrolyte

Effect of two-step functionalization of Ti by chemical processes on protein adsorption by M. Pisarek; A. Roguska; M. Andrzejczuk; L. Marcon; S. Szunerits; M. Lewandowska; M. Janik-Czachor (pp. 8196-8204).

► The chemical treatment of a Ti surface resulted in significant changes in morphology. ► Ti(H₂O₂+H₃PO₄) treatment led to the incorporation of phosphates into the oxide film. ► Calcium phosphate coatings can be uniformly grown on a chemically treated Ti surface. ► Ti(H₂O₂+H₃PO₄) surface adsorb more albumin than does the Ti(NaOH) or reference Ti.Titanium and its alloys are widely used for orthopedic and dental implants because of their superior mechanical properties, low modulus, excellent corrosion resistance and good biocompatibility. However, it takes several months for titanium implants and bone tissue to reach integration. Hence, there is growing interest in shortening the process of osseointegration and thereby reducing surgical restrictions. Various surface modifications have been applied to form a bioactive titanium oxide layer on the metal surface, which is known to accelerate osseointegration.The present work shows that titanium dioxide (TiO₂) layers formed on titanium substrates by etching in a solution of sodium hydroxide (NaOH) or hydrogen peroxide/phosphoric acid (H₃PO₄/H₂O₂, with a volume ratio of 1:1) are highly suitable pre-treatments for apatite-like coating deposition. Using a two-step procedure (etching in an alkaline or acidic solution followed by soaking in Hanks’ medium), biomimetic calcium phosphate coatings were deposited on porous TiO₂ layers. The combined effects of surface topography and chemistry on the formation of the calcium phosphate layer are presented. The topography of the TiO₂ layers was characterized using HR-SEM and AFM techniques. The nucleation and growth of calcium phosphate (Ca–P) coatings deposited on TiO₂ porous layers from Hanks’ solution was investigated using HR-SEM microscopy. AES, XPS and FTIR surface analytical techniques were used to characterize the titanium dioxide layers before and after deposition of the calcium phosphate coatings, as well as after the process of protein adsorption. To evaluate the potential use of such materials for biomedical applications, the adsorption of serum albumin, the most abundant protein in the blood, was studied on such surfaces.

Keywords: Titanium dioxide (TiO; ₂; ); Chemical treatment; EDS and surface analysis (AES, XPS, FTIR); Biomaterials; Hanks’ solution; Calcium phosphate coatings

Enhancement of activity of platinum towards oxidation of ethanol by supporting on titanium dioxide containing phosphomolybdate-modified gold nanoparticles by Sylwia Zoladek; Iwona A. Rutkowska; Pawel J. Kulesza (pp. 8205-8210).

► Phosphododecamolybdate adsorbates are capable of stabilizing Au nanoparticles. ► Pt black dispersed over Au-containing TiO₂ is the ethanol oxidation electrocatalyst. ► Specific Pt–TiO₂ or Pt–Au electronic interactions are postulated. ► TiO₂ and phoshomolybdates provide active OH groups in the vicinity of Pt sites.A new concept of utilization of titanium dioxide matrix in electrocatalysis by admixing it with polyoxometallate modified gold nanoparticles is described here. The approach utilizes Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻) adsorbates capable of modifying, activating and stabilizing Au nanoparticles of the sizes of 30–40nm. Ultra-thin films of phosphomolybdates on nanostructured gold are characterized by well-defined fast (reversible) multi-electron electrochemical reactions. By dispersing platinum black over the Au-containing TiO₂, the electrocatalytic activity of Pt nanoparticles towards oxidation of ethanol has been enhanced. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account improvement of overall conductivity (due to the presence of nanostructured gold) at the electrocatalytic interface (including TiO₂-support), as well as and possibility of specific Pt–TiO₂ or Pt–Au electronic interactions and existence of active hydroxyl groups (on titanium dioxide or polyoxometallate surfaces) in the vicinity of catalytic Pt sites.

Keywords: Electrocatalysis; Ethanol oxidation; Titanium dioxide; Gold nanoparticles; Polyoxometallate; Platinum black

Deactivation of carbon supported palladium catalyst in direct formic acid fuel cell by A. Mikołajczuk; A. Borodzinski; P. Kedzierzawski; L. Stobinski; B. Mierzwa; R. Dziura (pp. 8211-8214).

► Carbon black supported palladium catalyst. ► Catalyst for direct formic acid fuel cell comparable to commercial. ► In very pure formic acid accumulation of CO₂ gas bubbles deactivate the anode. ► In pure for analysis formic acid CO from fuel impurities deactivate the anode.A new carbon black supported palladium catalyst for direct formic acid fuel cell applications has been prepared and characterized by X-ray diffraction. Bi-modal distribution of Pd crystallite sizes was observed. The average Pd size for crystallites in small size and large size ranges were about 2.7nm and 11.2nm, respectively. The initial activity of the catalyst in the oxidation of formic acid tested in a fuel cell was similar to a commercial well dispersed 20wt.% Pd/Vulcan. The rates of the fuel cell power decay were measured for formic acid of two purities for various current loadings. The results showed that various mechanisms contribute to the decrease of cell power with time. In direct formic acid fuel cell (DFAFC) fed with a very pure HCOOH accumulation of CO₂ gas bubbles in anode catalyst layer is responsible for observed power decay. In DFAFC fed with a pure for analysis (p.a.) grade formic acid the formation of CO_ads poison from the formic acid impurities is the main deactivation reason.

Keywords: Pd catalyst; Deactivation; Formic acid fuel cell; Electrocatalysis; Highlights

Application of Black Pearl carbon-supported WO₃ nanostructures as hybrid carriers for electrocatalytic RuSe_x nanoparticles by Krzysztof Miecznikowski; Pawel J. Kulesza; Sebastian Fiechter (pp. 8215-8222).

► RuSex catalyst was deposited onto hybrid carriers Black Pearl carbon-supported WO₃. ► WO₃-utilizing and RuSex nanoparticle was investigated during oxygen reduction reaction. ► A bifunctional mechanism, where RuSex induce electroreduction of O₂ and WO₃ reduce H₂O₂.RuSe_x electrocatalytic nanoparticles were deposited onto hybrid carriers composed of Black Pearl carbon-supported tungsten oxide; and the resulting system's electrochemical activity was investigated during oxygen reduction reaction. The tungsten oxide-utilizing and RuSe_x nanoparticle-containing materials were characterized using transmission electron microscopy, X-ray diffraction and electrochemical diagnostic techniques such as cyclic voltammetry and rotating ring-disk voltammetry. Application of Black Pearl carbon carriers modified with ultra-thin films of WO₃ as matrices (supports) for RuSe_x catalytic centers results during electroreduction of oxygen in 0.5moldm⁻³ H₂SO₄ (under rotating disk voltammetric conditions) in the potential shift of ca. 70mV towards more positive values relative to the behavior of the analogous WO₃-free system. Also the percent formation (at ring in the rotating ring-disk voltammetry) of the undesirable hydrogen peroxide has been decreased approximately twice by utilizing WO₃-modified carbon carriers. The results are consistent with the bifunctional mechanism in which oxygen reduction is initiated at RuSe_x centers and the hydrogen peroxide intermediate is reductively decomposed at reactive WO₃-modified Black Pearl supports. The electrocatalytic activity of the system utilizing WO₃-modified Black Pearl supports has been basically unchanged upon addition of acetic acid, formic acid or methyl formate to the sulfuric acid supporting electrolyte.

Keywords: Oxygen reduction; Hydrogen peroxide reduction; Ruthenium chalcogenide; Carbon black support; Tungsten oxide matrix; Rotating ring disk voltammetry

Hexagonal nanorods of tungsten trioxide: Synthesis, structure, electrochemical properties and activity as supporting material in electrocatalysis by Samiha Salmaoui; Faouzi Sediri; Néji Gharbi; Christian Perruchot; Salah Aeiyach; Iwona A. Rutkowska; Pawel J. Kulesza; Mohamed Jouini (pp. 8223-8229).

► Hydrothermal preparation of hexagonal WO₃ nanorods. ► Reversible electroactive hexagonal WO₃ nanorods. ► Structure-electroactivity relationship in hexagonal WO₃ nanorods. ► Hexagonal WO₃ nanorods as active support for Pt–Ru nanoparticles catalysis of ethanol electrooxidation.Tungsten trioxide, unhydrated with hexagonal structure (h-WO₃), has been prepared by hydrothermal method at a temperature of 180°C in acidified sodium tungstate solution. Thus prepared h-WO₃ has been characterized by X-ray diffraction (XRD) method and using electrochemical techniques. The morphology has been examined by scanning and transmission electron microscopies (SEM and TEM) and it is consistent with existence of nanorods of 50–70nm diameter and up to 5μm length. Cyclic voltammetric characterization of thin films of h-WO₃ nanorods has revealed reversible redox behaviour with charge–discharge cycling corresponding to the reversible lithium intercalation/deintercalation into the crystal lattice of the h-WO₃ nanorods. In propylene carbonate containing LiClO₄, two successive redox processes of hexagonal WO₃ nanorods are observed at the scan rate of 50mV/s. Such behaviour shall be attributed to the presence of at least two W atoms of different surroundings in the lattice structure of h-WO₃ nanorods. On the other hand, in aqueous LiClO₄ solution, only one redox process is observed at the scan rate of 10mV/s. The above observations can be explained in terms of differences in the diffusion of ions inside two types of channel cavities existing in the structure of the h-WO₃ nanorods. Moreover, the material can be applied as active support for the catalytic bi-metallic Pt–Ru nanoparticles during electrooxidation of ethanol in acid medium (0.5moldm⁻³ H₂SO₄).

Keywords: Keyword; Tungsten trioxide

Durability enhancement and degradation of oxygen evolution anodes in seawater electrolysis for hydrogen production by Zenta Kato; Jagadeesh Bhattarai; Naokazu Kumagai; Koichi Izumiya; Koji Hashimoto (pp. 8230-8236).

▶ Oxygen evolution anode in seawater electrolysis for hydrogen production. ▶ Sn1−_xIr_xO₂ intermediate layer effective in preventing oxidation of titanium substrate. ▶ Unevenness of the intermediate layer is responsible for localized growth of titanium oxide bumps. ▶ Localized titanium oxide growth results in destruction of electrocatalyst. ▶ Exposure of intermediate layer active for chlorine formation to NaCl solution determines the life of anode.For the anode composed of electrocatalyst oxide, intermediate layer and titanium substrate, the substitution of a certain amount of iridium with tin in the IrO₂ intermediate layer was remarkably effective in elongating the life of the anode in preventing oxidation of the substrate titanium during oxygen evolution. The longest life was realized by preparation of intermediate layer with uniform thickness by brush-coating of H₂IrCl₆–SnCl₄ butanol solution and subsequent calcination. The anode with the intermediate layer prepared from 0.04M H₂IrCl₆–0.06M SnCl₄ butanol solution showed the best performance, that is, the oxygen evolution efficiency higher than 99.8% for more than 4300h in the electrolysis of 0.5M NaCl solution of pH 1 at the current density of 1000Am⁻². An increase in SnCl₄ concentration decreased the viscosity of the coating solution with a consequent enhancement of uniformity of the intermediate layer but decreased the thickness of the intermediate layer acting as a barrier to prevent oxidation of titanium. Thus, the best performance was attained at an intermediate SnCl₄ concentration. The growth of an oxide layer on titanium during electrolysis occurred and was found by the potential increase.

Keywords: Oxygen evolution anode; Seawater electrolysis; Life elongation; Mn-Mo-Sn triple oxide electrocatalyst; Sn–Ir double oxide intermediate layer

ZrNi5-based hydrogenated phases formed under high hydrogen pressure conditions by Stanisław M. Filipek; Valerie Paul-Boncour; Ru-Shi Liu (pp. 8237-8240).

► ZrNi₅ treated under high hydrogen pressure transformed into two hydrides with different hydrogen content. ► Both hydrides were very unstable at normal conditions. ► Structural changes during the desorption process were registered by using the Position Sensitive Detector technique.Formation of novel hydrides from ZrNi₅ alloy has been confirmed experimentally. After exposure of ZrNi₅ at 0.9 GPa(H₂) and 100°C for 6days the alloy transformed into two hydrogenated phases α and β containing initially more than 0.38 and 0.86 hydrogen atoms per formula unit respectively. At ambient conditions both hydrides were extremely unstable. Major part of hydrogen desorbed within few minutes. During this desorption the lattice parameters of both hydrides were continuously reduced what confirms their solid solution character.

Keywords: Zr–Ni intermetallic compounds; ZrNi; ₅; based hydrides; High hydrogen pressure

Surface and bulk phenomena in the process of hydride formation in thin films of rare earth metals: Comparison between terbium and europium by M. Knor; R. Nowakowski; R. Duś (pp. 8241-8245).

► Two rare earth metals, europium and terbium, have been compared in hydride formation. ► Hydrogen interaction with Eu or Tb films at 298K leads to metal–semiconductor transition. ► Different resistance courses of Eu and Tb hydride films versus hydrogen content are noticeable. ► The inversion of polarization of the hydrogen adspecies is noted for both metals. ► Low temperature ordered surface phase of hydride for Tb (<100K) and Eu (<160K) is suggested.Work function changes Δ Φ caused by H₂ interaction with thin terbium and europium films deposited on glass under UHV conditions were correlated with hydrogen uptake and electrical resistance R, measured in situ. For both metals, the course of Δ Φ(H/Me) at room temperature confirms the change in charge-transfer direction on the surface during hydride formation. As a result, the hydrogen adsorbate's nature is changed from positively polarized (precursor state) to negatively polarized adspecies. The hydrogen behavior is significantly different at low temperature due to the formation of the surface ordered low-temperature phase (α′) with positively polarized hydrogen adspecies. This phase, strongly inhibiting penetration of hydrogen into the bulk, is stable up to 100K for terbium and 160K for europium. Increasing temperature above these values resulted in additional large absorption of hydrogen. Moreover, differences in the course of R(H/Me) are clearly noticeable between the investigated metals. The resistance of thin TbH_x ( x∼3) films in our experiments did not exceed 1kΩ, however transition of thin metallic europium film into EuH_y ( y∼2) increased the resistance up to 10MΩ. This dissimilarity in electrical behavior can be explained by the coexistence of two factors which are different for the two metals in question: the phase relation of hydrides and the response of thin film to stress generated during hydride formation.

Keywords: Terbium hydride; Europium hydride; Hydrogen adsorption; Metal–semiconductor transition

Surface-enhanced Raman scattering studies on bombesin, its selected fragments and related peptides adsorbed at the silver colloidal surface by Edyta Podstawka-Proniewicz; Yukihiro Ozaki; Younkyoo Kim; Yizhuang Xu; Leonard M. Proniewicz (pp. 8246-8252).

► We show that investigated molecules bind to a colloidal silver surface mainly through Trp⁸ and Met¹⁴. ► Trp⁸ adsorbs at the surface almost perpendicularly. ► Met¹⁴ appears on the surface mainly as a P_C-G conformer. ► His¹² practically does not take part in the adsorption process. ► Substitution of Leu¹³ by Phe does not change substantially the pattern of the adsorption mechanism. ► Modification such Phe¹² and Tyr⁶ cause changes in the SERS spectra.SERS studies presented in this work onBN^8–14, [d-Phe⁶,β-Ala¹¹,Phe¹³,Nle¹⁴]BN^6–14, [d-Tyr⁶,β-Ala¹¹,Phe¹³,Nle¹⁴]BN^6–14, BN and its modified analogues, as well asNMB,NMC, andPG-L show that these molecules at pH 8.3 bind to a colloidal silver surface mainly through Trp⁸ and Met¹⁴ residues. Trp⁸ adsorbs at the surface almost perpendicularly. Met¹⁴ appears on the surface mainly as a P_C-G conformer. His¹², as is evident from the spectra, practically does not take part in the adsorption process. Substitution ofl-leucine at the 13 position of amino acid sequence withl-phenylalanine does not change substantially the pattern of the adsorption mechanism; however, substitution of phenylalanine at the 12 position (instead ofl-histidine) causes changes in the SERS spectra that show that Phe¹² takes parallel orientation to the surface upon adsorption of[d-Phe¹²]BN, while in the case of[Tyr⁴,d-Phe¹²]BN this residue is perpendicular to the surface and influences the orientation of the bound Trp⁸. On the other hand, substitution of Asn with Tyr in the 6 position in nonapeptide fragment causes changes in the adsorption mechanism. In this case, the discussed fragment binds to the silver colloidal surface by Tyr⁶, Trp⁸, and Met¹⁴. The SERS spectrum ofNMC is very similar to that ofBN; although it differs by the binding orientation of the amide bond towards the surface. Appearance of Phe¹³ inNMB andPG-L causes that this residue competes successfully with Trp⁸ forcing it to take tilted orientation. As seen from the enhancement of the characteristic Phe vibrations this moiety inNMB andPG-L adsorbs on the silver surface in a tilted fashion. This arrangements cause that the 8–14 peptide chain in all these studied compounds takes almost a parallel orientation to the surface while the 1–5 fragment of the peptide chain is removed from the silver surface vicinity.

Keywords: Surface-enhanced Raman scattering; SERS; Colloidal silver surface; Bombesin; BN; BN-related peptides

Growth mechanism of hydroxyapatite-coatings formed on pure magnesium and corrosion behavior of the coated magnesium by Masanari Tomozawa; Sachiko Hiromoto (pp. 8253-8257).

► HAp coatings were formed on Mg surface by a hydrothermal treatment. ► At the initial stage of treatment, dome-shape HAp precipitates were formed. ► With an increase in the treatment time, the dome-shape precipitates formed layer. ► Protectiveness of the HAp coating increased with its growth.Hydroxyapatite (HAp) coatings were uniformly formed on pure Mg by a hydrothermal treatment using a C₁₀H₁₂N₂O₈Na₂Ca (Ca-EDTA) solution. The growth mechanism of the HAp coating was investigated with XRD, SEM and TEM. At the initial stage, dome-shape HAp precipitates were formed on the Mg. Subsequently, the precipitates grew and the coating became a dual-layer consisting of an inner dense HAp layer and outer course layer consisting of rod-like HAp crystals. The protectiveness of the coatings with different treatment times was investigated by a polarization test in a 3.5wt.% NaCl solution. The corrosion current density decreased with the growth of the HAp coating.

Keywords: Magnesium; Hydroxyapatite; Hydrothermal treatment; Corrosion resistant coatings; Bioabsorbable metals

Corrosion and passivation behavior of Mg–Zn–Y–Al alloys prepared by cooling rate-controlled solidification by Michiaki Yamasaki; Shogo Izumi; Yoshihito Kawamura; Hiroki Habazaki (pp. 8258-8267).

► Highly corrosion-resistant Mg alloys are prepared by cooling rate-controlled solidification. ► Corrosion behavior of Mg–Zn–Y–Al alloys are investigated by SIT and electrochemical measurements. ► Rapid solidification brings about the grain refinement and an increase in the solid solubility. ► Enhancing microstructural and electrochemical homogeneity improves corrosion resistance.Highly corrosion-resistant nanocrystalline Mg–Zn–Y–Al multi-phase alloys have been prepared by consolidation of rapidly solidified (RS) ribbons. The relation between corrosion behavior and microstructure evolution of Mg–Zn–Y–Al alloys with a long period stacking ordered phase has been investigated. In order to clarify the influence of rapid solidification on the occurrence of localized corrosion such as filiform corrosion, several Mg_96.75Zn_0.75Y₂Al_0.5 (at.%) alloys with different cooling rates are fabricated by the gravity casting, copper mould injection casting and melt-spinning techniques and their corrosion behavior and microstructures are examined by the salt water immersion test, electrochemical measurements, GDOES, XRD, SEM and TEM. To clarify the effect of aluminium addition on the improvement in corrosion resistance of the alloys, several Mg97.25−_xZn_0.75Y₂Al_x alloys with different aluminium contents are fabricated by consolidating RS ribbons and the formation of corroded films on the Mg–Zn–Y–Al alloys have been investigated. Rapid solidification brings about the grain refinement and an increase in the solid solubility of zinc, yttrium and aluminium into the magnesium matrix, enhancing microstructural and electrochemical homogeneity, which in turn enhanced corrosion resistance. The addition of aluminium to magnesium can modify the structure and chemical composition of surface films and improves the resistance to local breakdown of the films.

Keywords: Magnesium alloy; Yttrium; Aluminium; Cooling rate; Filiform corrosion; Passivation

The corrosion behavior of intermetallic compounds Ni₃(Si,Ti) and Ni₃(Si,Ti)+2Mo in acidic solutions by Gadang Priyotomo; Kenji Okitsu; Akihiro Iwase; Yasuyuki Kaneno; Rokuro Nishimura; Takayuki Takasugi (pp. 8268-8274).

► The intergranular attack was observed for Ni₃(Si,Ti) in acidic solutions. ► Ni₃(Si,Ti)+2Mo had the preferential dissolution of L1₂ compared to L1₂+Ni_ss phase in acidic solutions. ► Ni₃(Si,Ti)+2Mo had the lowest corrosion resistance in acidic solutions. ► The intermetallic compounds were difficult to form a stable film in the H₂SO₄ solution as well as in the HCl solution.The corrosion behavior of the intermetallic compounds homogenized, Ni₃(Si,Ti) (L1₂: single phase) and Ni₃(Si,Ti)+2Mo (L1₂ and (L1₂+Ni_ss) mixture region), has been investigated using an immersion test, electrochemical method and surface analytical method (SEM; scanning electron microscope and EPMA: electron probe microanalysis) in 0.5kmol/m³ H₂SO₄ and 0.5kmol/m³ HCl solutions at 303K. In addition, the corrosion behavior of a solution annealed austenitic stainless steel type 304 was studied under the same experimental conditions as a reference. It was found that the intergranular attack was observed for Ni₃(Si,Ti) at an initial stage of the immersion test, but not Ni₃(Si,Ti)+2Mo, while Ni₃(Si,Ti)+2Mo had the preferential dissolution of L1₂ with a lower Mo concentration compared to (L1₂+Ni_ss) mixture region. From the immersion test and polarization curves, Ni₃(Si,Ti)+2Mo showed the lowest corrosion resistance in both solutions and Ni₃(Si,Ti) had the highest corrosion resistance in the HCl solution, but not in the H₂SO₄ solution. For instance, it was found that unlike type 304 stainless steel, these intermetallic compounds were difficult to form a stable passive film in the H₂SO₄ solution. The results obtained were explained in terms of boron segregation at grain boundaries, Mo enrichment and film stability (or strength).

Keywords: Intermetallic compound; Ni; ₃; (Si,Ti); Ni; ₃; (Si,Ti); +; 2Mo; Intergranular corrosion; Preferential dissolution

Constant-load delayed fracture test of atmospherically corroded high strength steels by Eiji Akiyama; Katsuhiro Matsukado; Songjie Li; Kaneaki Tsuzaki (pp. 8275-8281).

► Constant load test of corroded specimen is useful for evaluating delayed fracture. ► Delayed fracture is controlled by diffusible hydrogen concentration. ► Hydrogen entry is enhanced with progress of atmospheric corrosion.Constant load tests of circumferentially notched round bar specimens of high strength steels after cyclic corrosion test and outdoor exposure have been performed to demonstrate that delayed fracture occurs when the hydrogen content from the environment, H_E, exceeds the critical hydrogen content for delayed fracture, H_C. During the constant load tests the humidity around the specimen was increased in stepwise manner to increase hydrogen entry. After fracture the specimen was kept at the humidity long enough to homogenize hydrogen in the specimen and to obtain more quantitative hydrogen content by thermal desorption analysis. H_E of the fractured specimens was higher than H_C, and H_E of the specimens not fractured was lower than H_C. This result confirms that the balance between H_C and H_E determines the occurrence of delayed fracture and that hydrogen-content-based evaluation of susceptibility to delayed fracture is reasonable. To certify the increase of H_E with increase in humidity, electrochemical hydrogen permeation test was carried out. The hydrogen permeation current density was increased especially at 98%RH. Enhancement of hydrogen entry with increase in CCT number was also shown by the test.

Keywords: Hydrogen embrittlement; Delayed fracture; Atmospheric corrosion; High strength steel

Superhydrophobic hierarchical surfaces fabricated by anodizing of oblique angle deposited Al–Nb alloy columnar films by Takashi Fujii; Yoshitaka Aoki; Hiroki Habazaki (pp. 8282-8288).

► The authors developed a combined process of oblique angle magnetron sputtering and anodizing to fabricate submicron-/nano-dual scale porous structures. ► By utilizing such dual scale porous surface structure, superhydrophobic surface has been realized after coating the oxide surface with a fluoroalkyl phosphate layer.A combined process of oblique angle magnetron sputtering and anodizing has been developed to tailor superhydrophobic surfaces with hierarchical morphology. Isolated submicron columns of single-phase Al–Nb alloys are deposited by magnetron sputtering at several oblique deposition angles on a scalloped substrate surface, with the gaps between columns increasing with an increase in the deposition angle from 70° to 110°. Then, the columnar films have been anodized in hot phosphate–glycerol electrolyte to form a nanoporous anodic oxide layer on each column. Such surfaces with submicron-/nano-porous structure have been coated with a fluoroalkyl phosphate layer to reduce the surface energy. The porous surface before coating is superhydrophilic with a contact angle for water is less than 10°, while after coating the contact angles are larger than 150°, being superhydrophobic. The beneficial effect of dual-scale porosity to enhance the water repellency is found from the comparison of the contact angles of the submicron columnar films with and without nanoporous oxide layers. The larger submicron gaps between columns are also preferable to increase the water repellency.

Keywords: Sputter deposition; Oblique angle deposition; Anodizing; Dual scale pore structure; Superhydrophobic

Simple heat treatment for fabrication of carbonaceous layer-coated microelectrodes and conductive stainless steels by K. Fushimi; A. Ono; K. Matsushita; H. Kumagai; H. Konno (pp. 8289-8294).

► We fabricate carbonaceous layer-coated electrodes: needle-type micro-ring electrode with a representative length of ∼1μm and conductive and corrosion resistant stainless steel, by a simple heat treatment of petroleum pitch in flowing inert gas. ► We improved specific conductivity of the layer formed on quartz substrate by increases in temperature and period of the heating. ► We also improved conductivity of the layer on type-316 stainless steel and corrosion resistance of the steel by pre-treatment of nickel electroplating before the heating.A simple heat treatment was used to fabricate carbonaceous layer-coated electrodes: micro-ring electrodes and conductive stainless steel. Substrates of sharpened quartz capillaries or type-316 stainless steel plates were put in an alumina boat with powder of petroleum pitch A240F separately and heated at 1073–1273K in a flow of nitrogen or argon. By this treatment, both of the substrates were coated with a uniform carbonaceous layer of several hundred nano-meters in thickness. The electric conductivity of the layer was improved by increases in temperature and period of the heating. The quartz glass-capillary covered with the conductive layer was modified to a needle-type microelectrode by coating with an insulating polymer and baring the tip. At least a dozen carbon micro-ring electrodes with an outer radius of about 1μm were successfully prepared by the simple heat treatment. On the other hand, the carbonaceous layer formed on type-316 stainless steel showed relatively poor conductivity due to the formation of oxides in the layer. However, the conductivity was improved by electroplating of nickel on the substrate before the heating. The carbonaceous layer-coated stainless steel showed good corrosion resistance in sulphuric acid.

Keywords: Carbonaceous layer; Heat treatment; Microelectrode; Conductivity; Stainless steel

Dielectric properties of anodic films on sputter-deposited Ti–Si porous columnar films by M. Tauseef Tanvir; T. Fujii; Y. Aoki; K. Fushimi; H. Habazaki (pp. 8295-8300).

► Isolated columnar Ti and Ti–7at% Si films were successfully prepared by oblique angle magnetron sputtering. ► A uniform amorphous anodic oxide film is grown on the porous Ti–Si, but is limited to less than 6V on the porous titanium. ► Electric properties of anodic oxide films are improved markedly by the addition of silicon due to suppression of crystallization.For electrolytic capacitor application of the single-phase Ti alloys containing supersaturated silicon, which form anodic oxide films with superior dielectric properties, porous Ti–7at% Si columnar films, as well as Ti columnar films, have been prepared by oblique angle magnetron sputtering on to aluminum substrate with a concave cell structure to enhance the surface area and hence capacitance. The deposited films of both Ti and Ti–7at% Si have isolated columnar morphology with each column revealing nanogranular texture. The distances between columns are ∼500nm, corresponding to the cell size of the textured substrate and the gaps between columns are 100–200nm. When the porous Ti–7at% Si film is anodized at a constant current density in ammonium pentaborate electrolyte, the growth of a uniform amorphous oxide film continues to ∼35V, while it is limited to less than 6V on the porous Ti film. The maximum voltage of the growth of uniform amorphous oxide films on the Ti–7at% Si films is similar for both the flat and porous columnar films, suggesting little influence of surface roughness on the amorphous-to-crystalline transition of growing anodic oxide under the high electric field. Due to the suppression of crystallization to sufficiently high voltages, the anodic oxide films formed on the porous Ti–7at% Si film shows markedly improved dielectric properties, in comparison with those on the porous Ti film.

Keywords: Porous deposits; Non-equilibrium alloy; Oblique angle deposition; Anodic oxide; Dielectric

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Applied Surface Science (v.257, #19)