Surface composition of ordered intermetallic compounds PtBi and PtPb

The surface composition of bulk electrodes made from the ordered intermetallic phases PtBi and PtPb has been studied by ex-situ X-ray photoelectron spectroscopy (XPS) after being subjected to various electrochemical treatments. Analysis of the freshly polished surfaces showed that in the surface and near surface regions the less-noble metals; Bi and Pb are oxidized to a significant extent (28% and 41%, respectively). Upon cycling to increasingly positive potentials, the fraction of oxidized to metallic forms of Bi and Pb decreased gradually to reach the minimal values of 7% and 6% at +400 mV vs. Ag/AgCl (saturated KCl). The observed decrements are due to leaching of surface oxides; Bi₂O₃ on PtBi and PbCO₃ or Pb(OH)₂ on PtPb. When the potential sweep was extended to more positive values, there was a linear decrease in the surface concentration of the less-noble metal, along with a slight increase in the amount of the species in their oxidized state (Bi₂O₃ for PtBi and PbSO₄ for PtPb). Leaching of Bi from the electrode surface occurs in accordance to the Pourbaix diagram for elemental bismuth, indicating no significant increase in stability arising from the formation of an intermetallic phase with platinum. In the case of PtPb, however, the Pb starts to dissolve away at potentials significantly more positive (+800 mV) than what was anticipated from the Pourbaix diagram. The results obtained here are in accord with our previous observations on the effects of electrochemical pre-treatment on these intermetallic phases for the electrocatalytic oxidation of formic acid and other potential fuel cell fuels.     

Persistent local chemical bonds in intermetallic phase formation

We found a direct evidence for the existence of the local chemical Bi–In bonds in the BiIn₂ melt. These bonds are strong and prevail, dominating the structure evolution of the intermetallic clusters. From the local structure of the melt-quenched BiIn₂ ribbon, the chemical Bi–In bonds strengthen compared with those in the equilibrium solidified alloy. The chemical bonds in BiIn₂ melt retain to solid during a rapid quenching process. The results suggest that the intermetallic clusters in the melt evolve into the as-quenched intermetallic phase, and the intermetallic phase originates from the chemical bonds between unlike atoms in the melt. The chemical bonds preserve the chemical ordered clusters and dominate the clusters evolution.     

Decomposition behavior and properties for tin–antimony alloy with bismuth content

The peritectic alloy Sn–10Sb, was chosen as one of the lead-free solder alloys to be subjected to many studies. Bi atoms were added to this alloy in the range of 1–3 wt%. The experimental results obtained from this study show a complete solubility of Bi atoms when added by 2 wt%. More additions of Bi tend to increase the formation of the intermetallic compound SnSb by reducing the precipitations of Sb as a single phase. This intermetallic compound with the precipitation of Bi as a third phase tends to improve the mechanical properties of this alloy.     

Microstructure and tribological properties of TiCu2Al intermetallic compound coating

TiCu₂Al ternary intermetallic compound coating has been in situ synthesized successfully on pure Ti substrate by laser cladding. Tribological properties of the prepared TiCu₂Al intermetallic compound coating were systematically evaluated. It was found that the friction coefficient and wear rate was closely related to the normal load and sliding speed, i.e., the friction coefficient of the prepared TiCu₂Al intermetallic compound coating decreased with increasing normal load and sliding speed. The wear rate of the TiCu₂Al intermetallic compound coating decreased rapidly with increasing sliding speed, while the wear rate first increased and then decreased at normal load from 5 to 15 N.     

Structure Studies of Platinothioneins by Using Extended X-Ray Absorption Fine Structure Spectroscopy

The metal binding sites in the two Pt containing metallothioneins (Pt₇MT and Pt₁₄MT) were examined by means of Pt(II) L₃-edge extended X-ray absorption fine structure (EXAFS) spectroscopy. Comparisons between the phase and amplitude functions derived from the isolated shells to those of Pt…Pt, Pt-S and Pt-N model components showed that each platinum in Pt₇MT was coordinated by four sulfur atoms at a distance of 2.31±0.01 Å. Analysis of the outer shell data of platinum atom in Pt⁷MT indicated backscattering platinum atom at approximate 4.29 Å. Strikingly different structural parameters had been obtained for the Pt¹⁴MT species, fitting of the first shell revealed that each platinum was coordinated by two sulfurs at the distance of 2.30±0.02 Å and two nitrogens at 2.02±0.02 Å. The results of the work provided the detailed information concerning the local environments of the coordinated Pt(II) in these two platinothioneins.     

铂纳米立方体的合成及其SERS活性研究

本文用氢气还原氯亚铂酸钾,以聚丙烯酸钠作表面活性剂合成了铂纳米立方体,得到的铂纳米立方体的边长约为15nm。将铂纳米立方体组装到玻碳电极表面上可以作为SERS基底。以SCN-作为探针分子,初步研究铂纳米立方体的SERS效应。从铂纳米立方体上得到的SERS信号强度比粗糙的铂电极强,这表明铂纳米立方体具有更高的SERS活性。     

Influence of argon ion bombardment on the formation of intermetallic compounds in the nickel-aluminum system

The formation of Ni _x Al _y intermetallic compounds in two-layer (Ni/Al) structures (nickel films deposited on aluminum substrates in vacuum) under bombardment by Ar⁺ ions has been studied experimentally. The method based on Rutherford backscattering of He⁺ ions is used to demonstrate that argon ion bombardment causes the formation of intermetallic compounds in the near-surface layer. The thickness of the intermetallic layer formed in the near-surface region substantially exceeds the projective ion path. The composition and thickness of the intermetallic layer depend mainly on the implantation dose and the substrate temperature, rather than on the ion current density. In the intermetallic layer, the content of nickel increases with increasing temperature. It has been established that, in the absence of bombardment, intermetallic phases are not observed at temperatures lower than T = 400°C and that, in the presence of bombardment, the Ni₃Al intermetallic layer arises at a temperature of 320°C.     

Chemisorption of alkyl thiols and S-alkyl thiosulfates on Pt(1 1 1) and polycrystalline platinum surfaces

The self-assembled monolayers prepared from 1-dodecanethiol (C₁₂SH) or S-dodecylthiosulfate (Bunte salt, C₁₂SSO₃Na) have been characterised on polycrystalline gold and platinum surfaces and on Pt(1 1 1). Contact angle and impedance measurements show that the film quality decreases in the order Au/C₁₂SH > Pt/C₁₂SH ∼ Au/C₁₂SSO₃Na > Pt/C₁₂S SO₃Na. XPS measurements show that the S-SO₃ bond of organic thiosulfates is broken on platinum surfaces and the state of the surface-bound sulfur is indistinguishable from that of thiolate. On platinum three sulfur species are formed upon SAM formation and we suggest that the catalytic activity of platinum is responsible for their existence in pristine monolayers.     

Muonium emission andreaction on platinum and gold powder surfaces revealed by MuSR

Muonium has been observed in powdered platinum (30 nm diameter) andgold (100 nm diameter), respectively, placed in vacuum by the muonium spin rotation (MuSR) technique at ambient temperature. Upon introducing gaseous oxygen up to 23 Torr into platinum powder, the muonium signal was eliminated, indicating that the observed muonium stays outside the platinum particles. The result on the platinum surface treated by hydrogen but exposed to oxygen gas suggests a reactive collision between muonium andoxygen adsorbed atomically on the surface.     

Microstructure and tribological properties of TiAg intermetallic compound coating

TiAg intermetallic compound coating has been in situ synthesized successfully on pure Ti substrate by laser cladding using Ag powder as the precursor. It has been found that the prepared coating mainly comprised TiAg and Ti phases. The high resolution transmission electron microscopy results further conform the existence of TiAg intermetallic compound in the prepared coating. The magnified high resolution transmission electron microscopy images shown that the laser cladding coating contains TiAg nanocrystalline with the size of about 4 nm. Tribological properties of the prepared TiAg intermetallic compound coating were systematically evaluated. It was found that the friction coefficient and wear rate was closely related to the normal load and sliding speed, i.e., the friction coefficient of the prepared TiAg intermetallic compound coating decreased with increasing normal load and sliding speed. The wear rate of the TiAg intermetallic compound coating decreased rapidly with increasing sliding speed, while the wear rate increased as the normal load increased.     

Gd-Cu二元系合金相图

本文用X射线粉末照相法和差热分析法测定了Gd-Cu二元系合金相图,发现GdCu₆在735℃发生同素异构转变。此合金系中共存在着四种金属互化物,即GdCu,GdCu₂,GdCu₅和GdCu₆,金属互化物GdCu,在932℃同成份熔化;而GdCu,GdCu₂和GdCu₆分别在759℃,870℃和884℃由包晶反应形成,存在两个共晶反应,分别发生在32at％Cu668℃和92at％Cu875℃,无论是Gd在Cu中或是Cu在Gd中都没有可觉察的固溶度。 关键词：     

Structure and orientation of an intermetallic phase in a W-Ni-Co alloy

The aim of this investigation is crystal structure determination of an intermetallic phase formed in a W-Ni-Co alloy during a heat-treatment carried out at a temperature of 800°C. This intermetallic phase is expected to play a critical role on the final microstructure (fine tungsten particles in an FCC matrix that is present in between large tungsten grains) and thereby, on the properties of the alloy. 92W-5.3Ni-2.7Co alloy was prepared through powder metallurgy route (liquid phase sintering) followed by heat-treatment at 800°C for 5?h. The intermetallic phase formed at this temperature was characterised using transmission and scanning electron microscopes. The intermetallic phase was found to have orthorhombic crystal structure with Pnam (62) space group as determined using automated diffraction tomography along with precession electron diffraction. Chemical analysis in TEM suggested that the intermetallic phase is based on stoichiometry (Co,Ni)₂W. Orientation imaging of the phase was also carried out in TEM and EBSD to understand its evolution. Equiaxed or lath morphology of the intermetallic phase was found to depend on the crystallographic orientation relationship of the phase with the tungsten grains and the matrix phase.     

Hydrogenation properties of catalyzed and non-catalyzed magnesium films

The hydrogenation properties of 400 Å thick magnesium films, grown under ultra-high vacuum conditions, have been studied under conditions relevant for hydrogen storage, i.e., elevated temperatures and pressures. The hydrogen uptake of films modified by deposition of platinum on the magnesium surface was also investigated. A realistic hydrogen storage system is modeled by studying the combined effect on hydrogen sorption by a platinum catalyst and magnesium oxide, the latter a common impurity in magnesium-based hydrogen storage systems. Magnesium and platinum are found to inter-diffuse readily at room temperature. However, a partially oxidized magnesium layer stabilizes platinum on the surface, while still being permeable to hydrogen.     

Structural Behavior of Pt–Sn Supported on MgO

Pt–Sn supported on magnesia and alumina were characterized, before and after treatment with hydrogen, by Mössbauer spectroscopy and X-ray diffraction. For the calcined samples on both supports tin is present as SnO₂ and platinum as metal. After reduction with hydrogen, platinum and tin diffuse into the magnesia lattice to form a solid solution. On alumina Sn(IV), Sn(II), Sn(0), Pt, Pt₃Sn, PtSn and PtSn₂ alloys are formed. The SnO interacts strongly with the alumina support. The catalytic activity of both Pt–Sn catalysts is strongly affected by the support. On alumina the dehydrogenation of cyclohexane is very high, whereas that on magnesia is almost non-active.     

A Mössbauer study on the ion-beam-induced phases in the Fe/Al thin film bilayer

Conversion Electron Mössbauer Spectroscopy, (CEMS), has been used to study ion-beam-induced mass transport and phase formation in the Fe/Al bilayer system. In a previous work it was shown that ion irradiation in the same system with noble gases (Ar⁺, Kr²⁺, and Xe³⁺) leaded to the formation of non intermetallic phases when the samples were kept at 77 and 300 K during the bombardments. On the other hand, intermetallic phases were observed for irradiations at substrate temperature of 500 K. The last experimental condition for phase formation corresponds to a lower temperature than conventional thermal treatment needs to reach the same phase. Here, the irradiation conditions were devised to account intermediate substrate temperatures, namely 200 and 400 K, in order to identify the effect of the implantation dose in the phase formation. The intermetallic phases observed in the samples submitted to irradiations at substrate temperature of 500 K, are now formed by even lower temperature-400 K. The results also show a threshold dose of irradiation above which the intermetallic phases are formed. These observations are discussed in terms of a superposition of collision cascades.     

Study of the Microstructure,Crystallographic Structure and Thermal Stability of Al–Ti–Nb Alloys Produced by Selective Electron Beam Alloying

This paper aims an investigation of the microstructure and crystallographic structure as well as the thermal stability of Al–Ti–Nb formed by selective electron beam surface alloying. The fabrication of the samples has been carried out using circular sweep mode, as two velocities of the sample movement have been chosen: V₁ = 1 cm/s and V₂ = 0.5 cm/s. The studied microstructure and crystallographic structure have been investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM) respectively. The thermal behavior of the obtained surface alloys are evaluated by the coefficient of thermal expansion (CTE) which has been evaluated by neutron diffraction measurements at high temperature. The results show that in the earlier stages of formation, the microstructure of the intermetallic phase is mainly in the form of coarse fractions, but at the following moments they dissolve, forming separated alloyed zone and base Al substrate as the alloyed zone consists of fine (Ti,Nb)Al₃ particles dispersed in the Al matrix with small amount of undissolved intermetallic fractions. Formation of preferred crystallographic orientation as a function of the speed of specimen motion has not been observed. The performed neutron diffraction measurements show that the lattice parameters of the obtained intermetallic (Ti,Nb)Al₃ are less upshifted in comparison to pure Al. It has been found that the aluminium lattice is much more unstable at high temperatures than that of the intermetallic phase. The CTE for the intermetallic phase is 8.70 ppm/K for a axis and 7.75 ppm/K for c axis respectively while considering Al it is 12.95 ppm/K.     

X-ray photoelectron spectroscopy and Raman microscopy of a ferroan platinum crystal from the Kondyor Massif,Russian Far East

X-ray Photoelectron Spectroscopy was used to study a ferroan platinum crystal from the Kondyor Massif, Russian Far East. Prior to the X-ray Photoelectron Spectroscopic analyses, the nature of the crystal was confirmed by X-ray diffraction. The survey scan showed mainly the presence of Pt and Fe, with smaller amounts of O and Si. The high resolutions spectra of the Pt 4f and Fe 2p showed 18.3 atom% Fe in the crystal, which puts the composition on the lower boundary for ferroan platinum and confirms earlier analyses using other methods such as Scanning Electron Microscopy-Energy Dispersive X-ray analysis/microprobe. The binding energy of the Pt 4f5/2 was 74.0?eV and Pt 4f7/2 70.5?eV, while the Fe 2p3/2 for metallic Fe was observed at 707.2?eV. The Fe 2p3/2 for metallic Fe was significantly sharper than that of Fe 2p3/2 at 710.7?eV associated with surface material. The Raman spectrum was dominated by the Pt–Pt stretching mode at 253?cm^?1. Changed orientation resulted in the observation of two bands at 127 and 139?cm^?1, interpreted as being due to stretching modes of two Pt–Pt bonds with the third bond to Fe and Pt fixed. The presence of Ca-Fe-Al-Mg-Si-O on the surface was probably associated with the presence of a clinopyroxene. These minerals can be expected since the crystal came originally from a clinopyroxenite-dunite matrix. The spectra showed a variety of interferences, e.g. Al 2p with Pt 4f, Mg 2p with Fe 3p, and Ca 2p1/2 with Mg Auger, making exact determinations of the ratios of these elements difficult.     

First-principles study of structural, electronic and elastic properties of single crystal CuZr

Investigations into the structural, electronic and elastic properties of intermetallic CuZr compound had been conducted by the plane-wave pseudopotential method. The calculated lattice constant was consistent well with the experimental value. The absence of band gap and finite value of the density of states (DOS) at the Fermi level reveal the metallic behavior of CuZr crystal, and Zr 4d states give rise to the electrical conductivity. The calculated elastic constants for single crystal CuZr at zero pressure obey the cubic mechanical stability condition, which indicates that the cubic CuZr crystal is mechanical stable at zero pressure. By analyzing the ratio between the bulk and shear moduli, we conclude that CuZr crystal is ductile in nature. The present theoretical investigations might give prediction to polycrystalline CuZr system.     

Nd-Cu二元系合金相图

本文用X射线粉末衍射法,微差热分析法和金相显微观察,测定了Nd-Cu二元系合金相图。此合金系中共存在着五种金属间化合物,它们是:NdCu,NdCu₂,NdCu₄,NdCu₅和NdCu₆,化合物NdCu₂,NdCu₆分别在830℃,962℃同成份熔化;化合物NdCu,NdCu₄,NdCu₅,分别在602℃,853℃,916℃由包晶反应形成,有三个共晶反应,共晶点成份及其共晶反应温度分别为33at%Cu,478℃;74at%Cu,760℃;91at％Cu,874℃无论是Nd在Cu中或是Cu在Nd中都不存在可觉察到的固溶度,金属间化合物之间也不存在可觉察到的固溶度。 关键词：     

Adsorption d'hydrogène entre 300 et 873 K sur un catalyseur Pt/MgO

Hydrogen adsorption on MgO-supported platinum was studied by thermal desorption and infrared spectroscopy at 300 and 800 K. For both temperatures, reversibly and irreversibly adsorbed species have been detected. At 300 K, reversible adsorption leads to the appearance of infrared bands at 2120 and 2060 cm^?1, attributed to terminal Pt-H species. Irreversibly adsorbed hydrogen has been detected by thermal desorption, whereas no infrared band was detected in the spectral range 4000–4750 cm^?1 for Pt/MgO sample. For hydrogen adsorption at 800 K, reversibly adsorbed hydrogen gave the same picture as for the 300 K adsorption. An additional form of irreversibly adsorbed hydrogen has been evidenced both by thermal desorption and infrared spectroscopy. This form corresponds to hydrogen strongly adsorbed on platinum and gives an infrared band at 950 cm^?1 which is characteristic of an hydrogen atom in interaction with more than one platinum atom (multicentered) species.