XPS and AES analysis of passive films on Fe-25Cr-X (X = Mo,V, Si and Nb) model alloys

Corrosion resistance of stainless steel is due to the presence of a thin passive film of typically 1-2 nm thickness. The influence of ternary alloying elements on the composition of passive films on Fe-Cr alloys and their pitting corrosion resistance has been investigated. Iron-chromium alloys were analyzed by XPS and AES with model alloys (Fe-25Cr-X with X = at % Mo, Si, V and Nb) formed in sulphate solution in the presence and absence of chloride ions. All ternary alloying elements increase the pitting potential compared to the corresponding binary alloy. Films formed in chloride containing sulphate solution contain both electrolyte anions. Scanning Auger microscopy reveals that for a two phase system such as Fe-25Cr-11Nb, the dendritic phase is enriched with chromium, while essentially all of the niobium is located in the interdendritic eutectic.     

XPS and AES analysis of passive films on Fe-25Cr-X (X = Mo, V, Si and Nb) model alloys

Corrosion resistance of stainless steel is due to the presence of a thin passive film of typically 1–2 nm thickness. The influence of ternary alloying elements on the composition of passive films on Fe-Cr alloys and their pitting corrosion resistance has been investigated. Iron-chromium alloys were analyzed by XPS and AES with model alloys (Fe-25Cr-X with X = at % Mo, Si, V and Nb) formed in sulphate solution in the presence and absence of chloride ions. All ternary alloying elements increase the pitting potential compared to the corresponding binary alloy. Films formed in chloride containing sulphate solution contain both electrolyte anions. Scanning Auger microscopy reveals that for a two phase system such as Fe-25Cr-11Nb, the dendritic phase is enriched with chromium, while essentially all of the niobium is located in the interdendritic eutectic.     

Facetting of Fe-15% Cr-N, Fe-3% V-C and Fe-3% V-C,N (111) surfaces

Summary Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning electron microscopy (SEM) have been used to study the surface chemistry of crystallographically open bcc (111) surfaces of Fe-15% Cr-N, Fe-3% V-C and Fe-3% V-C,N alloys. The binary and ternary surface phases CrN, VC and V(C,N) were formed at temperatures ranging from 450 to 750°C depending on the alloy. On Fe-15% Cr-30ppmN (111) two-dimensional surface compounds CrN were formed at temperatures above 600°C according to the bulk phase diagram of the Fe-Cr-N system, whereas on Fe-15% Cr-N samples with nitrogen contents of more than about 100 ppm the precipitation of three-dimensional CrN took place at temperatures below 600°C. Optical and SEM micrographs as well as oxidation experiments at room temperature indicated that the substrate surfaces are inhomogeneously covered by the surface phases. Facetting of the bcc (111) surfaces induced both by cosegregation of the solutes and by surface precipitation was observed in real space (SEM) as well as in reciprocal space (LEED). It is shown that the surface phases are epitaxially arranged on (100) facets of the substrate.     

铈及混合稀土对Fe-36Ni低膨胀合金凝固组织的影响

研究了Ce及混合稀土对Fe-36Ni低膨胀合金凝固组织的影响,结果表明:加Ce或者混合稀土处理后,合金中分别形成了大量高熔点的Ce2O3颗粒和(Ce,La)2O2S复合第二相颗粒,错配度理论计算表明,Ce2O3,Ce2O2S和La2O2S的(0001)面与Fe-36Ni的(100)面分别具有6.21%,5.77%和5.42%的较低错配度,因此Ce2O3和(Ce,La)2O2S可以作为有效的非均质形核核心,使凝固组织的等轴晶比例增加,等轴晶尺寸减小,合金凝固组织得到显著细化。     

Phase transfer of oleic acid capped Ni(core)Ag(shell) nanoparticles assisted by the flexibility of oleic acid on the surface of silver

The phase transfer protocols in vogue for the oleic acid capped silver nanoparticles, viz., salt-induced precipitation and redispersion or phosphoric acid-induced method, are examined and compared thoroughly. A comprehensive evaluation with respect to the mechanistic aspects involved is made and the merits and demerits of the different procedures are delineated. It is found that the salt-induced precipitation and redispersion is more versatile in that the precipitate can actually be redispersed in both aqueous and organic media. However, in terms of mechanism both the routes seem to be very similar wherein the orientational change of oleic acid on the silver surface in the two different environments-organic and aqueous-plays a crucial role in the adaptability of the system to the different environments. Subsequently, this change of orientation of oleic acid on silver surface in aqueous and organic media has been utilized to phase transfer Ni-based nanoparticulate systems. The nascent oleic acid-capped Ni nanoparticles, which were synthesized by a foam-based protocol, were dispersible in water but not in nonpolar organic media such as cyclohexane or toluene. Then, just by coating a thin shell of silver on them we could achieve complete phase transfer of the Ni(core)Ag(shell) from aqueous to organic media following similar procedures used for oleic acid-capped silver nanoparticles. Here, the phase transfer seems to be facilitated by the orientational flexibility of oleic acid on the silver surface as opposed to other metal surfaces as evidenced from the infrared and thermogravimetric analyses of oleic acid-capped Ni and Ni(core)Ag(shell) nanoparticles. This orientation-assisted phase transfer method could be generalized and can be adapted to other systems where, if the nascent nanoparticles cannot be phase transferred as is, they can be coated by a silver shell and oleic acid making them suitable for dispersion in both aqueous and organic media.     

Corrosion,wear, and cell culture studies of oxygen ion implanted Ni–Ti alloy

To increase the biocompatibility of nickel–titanium (Ni–Ti) alloy substrates, oxygen ions have been implanted by the plasma immersion ion implantation (PIII–O) technique at low temperature without affecting the substrate properties. The implanted Ni–Ti surface is characterized for microhardness and composition. Energy‐dispersive spectroscopy and X‐ray photoelectron spectroscopy investigations show the replacement of native oxide on the alloy by a compact oxide during the implantation process. The corrosion behaviors of untreated substrate and PIII–O samples are investigated using potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid (Hanks' solution). Polarization and electrochemical impedance spectroscopy studies reveal nearly ideal capacitor behavior with better passivation characteristics for the oxygen‐implanted substrate. Sliding wear studies reveal lower friction of coefficient for the implanted layers as compared with the substrate. The bare and surface modified Ni–Ti alloy samples are evaluated for biocompatibility using osteoblast‐like cells (MG‐63). Cellular behavior in terms of cell morphology along with the viability and proliferations is evaluated by using scanning electron microscopy and in vitro cell culture assay, respectively. The results clearly show that oxygen implantation by PIII–O provides a better compatible surface for cell attachment and growth. The modified surface exhibits a higher percentage of cell viability demonstrating the enhanced biocompatibility of the oxygen‐implanted surface compared with bare Ni–Ti alloy. Copyright © 2017 John Wiley & Sons, Ltd.     

Surface cosegregation on Fe-3%V-C,Fe-3%V-C,N and Fe-15%Cr-N (110) single crystals

Surface cosegregation has been studied on (110) oriented Fe-3%V-C, Fe-3%V-C,N and Fe-15%Cr-N single crystals applying AES and LEED. The surface compounds VC,V(C,N) and CrN are formed upon annealing in the temperature range from 450 to 750 degrees C depending on the alloy. The stoichiometries of the binary surface compounds correspond to VC(1.2) and approximately CrN(0.8) as determined by quantitative evaluation of Auger peak height ratios. The composition of the V(C,N) surface compound varies between V(C(0.6)N(0.6)) at 450 degrees C and V(C(0.2)N(1.0)) at 640 degrees C. Three-dimensional precipitates are not formed as indicated by Ar(+) depth profiling. After short annealing times streaking LEED patterns are observed indicating partial disorder in one direction of the direct space. Upon sufficient annihilation of surface defects sharp (4 x 1) patterns appear. A missing and added row "model" is proposed for the surface compounds on bcc(110) substrate surfaces.     

Nanocomposite ta-C films prepared by the filtered vacuum arc process using nanosized Ni dots on a Si substrate

Recently, structural manipulation of tetrahedral amorphous carbon (ta-C) film at the nanometer scale has attracted much attention. We demonstrate a novel method to obtain a nanocomposite film where nanoscale columns of graphitic phase are embedded in a tetrahedral amorphous carbon matrix. When using a Si substrate with nanosized Ni dots on the surface, graphitic columns grew selectively on the Ni dots, while a dense ta-C film was deposited on the bare Si surface. The growth of the graphitic columns is closely related to the nanosized Ni dots that catalyze the graphitic-carbon formation in a filtered vacuum arc deposition condition.     

First‐Principles Study toward CO Adsorption on Au/Ni Surface Alloys

The introduction of a second metal, gold, into a nickel matrix can effectively improve the catalytic performance and thermal stability of the catalysts toward steam reforming of methane. To investigate the effect of Au on the adsorption properties and electronic structure of the Ni(111) surface, we chose CO as a probe molecule and examined CO adsorption on various Au/Ni surfaces. It was revealed that Au addition weakened the absorbate–substrate interactions on the Ni(111) surface. With increasing gold concentration, the binding energy declines further. The variation of the binding energies has been interpreted by exploring the electronic structure of surface nickel atoms. The effect of gold can be quantitatively characterized by the slopes of the fitting equations between the binding energy and the number of gold atoms surrounding the adsorption site. Our results show that the binding energy at top sites can be approximately estimated by counting the number of surrounding gold atoms. On one specific surface, the relative magnitude of the binding energy can be simply judged by the distance between gold and the geometrical center of the adsorption site. This empirical rule holds true for C, H, and O adsorption on the Au/Ni surface. It may be applicable to a system in which a doped atom of larger atomic size is incorporated into the host metal surface by forming a surface alloy.     

A Ti-V-based bcc phase alloy for use as metal hydride electrode with high discharge capacity

The electrochemical characteristics of single bcc phase Ti-30V-15Cr-15Mn alloy were investigated. It was demonstrated that the single bcc phase alloy has high electrochemical discharge performance at high temperature. Its discharge capacity is closely related with temperature and discharge current. The first discharge capacities of 580-814 mAh g(-1) of the alloy powder were obtained at discharge current of 45-10 mA g(-1) in 6 M KOH solution at 353 K. Although the electrochemical cycle life of the alloy is unsatisfactory at present, it opens up prospects for developing a new hydrogen storage alloy with high hydrogen capacity for use as high performance metal hydride electrodes in rechargeable Ni-MH battery.     

Gene transfection into adherent cells using electroporation on a dendrimer-modified gold electrode

Gene transfection into adherent cells from plasmid DNA (pDNA)-arrayed substrates known as gene transfection arrays appears to be a promising tool for the high-throughput analysis of gene functions and protein-protein interaction networks. We tested the ability of electric pulse-stimulated gene transfection from a substrate to overcome low expression efficiency and cross contamination between spots on arrays. We prepared the electrodes used for electric pulse-stimulated gene transfection by sequentially loading a gold thin layer, a self-assembled monolayer of a carboxylic acid-terminated alkanethiol (COOH-SAM), and poly(amidoamine) (PAMAM) dendrimers, either through electrostatic interactions or by covalent linkage to COOH-SAM and then to pDNA. When dendrimers were loaded onto the electrode using electrostatic interactions, the gene-expression efficiency of adherent cells increased as the generation numbers of the dendrimers that we used increased. Gene expression was rarely observed in adherent cells when dendrimers were covalently immobilized onto the electrode. Additionally, we successfully demonstrated site-specific gene transfer using a dendrimer-array electrode with no cross contamination between spots on the electrode.     

Exploration of electrodeposited platinum alloy catalysts for methanol electro-oxidation in 0.5 M H<Subscript>2</Subscript>SO<Subscript>4</Subscript>: Pt-Ni system

In this work, we examine the electrocatalytic activity of electrodeposited Platinum (Pt)-Nickel (Ni) alloy layers on an inert substrate electrode for methanol oxidation reaction. Analyses using energy-dispersive fluorescent X-ray analysis and powder X-ray diffractometry confirm alloying of Pt with Ni in a range of compositions. Steady-state polarisation measurements in 0.5 M methanol+0.5 M H₂SO₄ solutions clearly show that the onset of electro-oxidation shifts to less anodic potential values (approximately 160 mV), while also exhibiting current enhancements up to ~15 times the currents obtained for the pure Pt electrodeposit. A linear relationship between the cyclic voltammetric peak (oxidation) current and [MeOH] is observed at a scan rate of 50 mVs^–1, thus indicating reduced influence of adsorbed CO (CO_ads) surface poison. A critical composition, Pt (92%)/Ni (8%) [denoted Pt-Ni(3) alloy] is found to exhibit maximum electrocatalytic activity, beyond which the activity drops, whereas pure Ni does not catalyse the reaction. While the promotion of electro-oxidation is understood to be largely due to the alloy catalyst, surface redox species of Ni oxide formed during the electro-oxidation process may also contribute to the oxygenation of CO_ads, thereby enhancing the oxidation current. Plausible mechanisms of methanol oxidation on Pt/ transition metal alloy electrocatalysts are discussed in terms of electron transfer (in the alloy) and the role of Ni oxide species.     

电沉积制备的PtNi纳米粒子用于氧还原反应:成核和生长机理

质子交换膜燃料电池(PEMFCs)电堆中阴极Pt基催化剂的高用量造成其成本居高不下,成为阻碍燃料电池汽车商业化推进的重要原因,因此开发低Pt、高活性的Pt基催化剂势在必行.Pt合金催化剂能够有效地降低Pt用量,并通过对合金颗粒的元素比例、晶面、粒径等实行精确调控,显著提升氧还原(ORR)催化活性.然而,目前常用的制备方法由于原料与制备成本高昂、过程复杂大都难以适应规模化生产需求.电化学方法通过控制施加的电流或电位控制晶体生长.在水体系中该方法已得到验证,但由于Pt化合物的热力学标准电极电位与过渡金属元素之间相差较大,且对于过渡金属来说,电负性大多小于铂,因此还原电位通常负于析氢电位,使得二者难以实现共沉积.有机体系中电位窗口比水体系大得多,Pt与电位较负的过渡金属可实现共沉积,采用小分子有机溶剂也可避免溶剂清洗问题,具有应用潜力.本文提出了一种简单的一步电沉积方法,选择易溶于水的N,N-二甲基甲酰胺(DMF)作为溶剂,将碳载体滴涂到玻碳电极上作为工作电极,通过电化学方法直接将Pt-Ni合金沉积到碳载体上,并利用物化表征与密度泛函理论(DFT)理论计算来探究共沉积机理.透射电镜表征结果表明,在不同的沉积电位下均可得到分散均匀、粒径适当的催化剂;且随着电位值降低,催化剂颗粒分散得更均匀,颗粒粒径不断减小.元素分布和晶面结果表明,铂镍元素均匀分布于颗粒中.所有样品均表现出优异的ORR性能,最高的面积比活性达到商业催化剂的6.85倍.将材料表征、电化学表征与DFT计算结合,建立起了铂镍合金生长过程的模型,并发现了有机体系中独特的成核-生长机理.将体系中的DMF换成超纯水,用同样的方法进行沉积,得到的催化剂颗粒团聚严重,说明DMF的使用能够避免颗粒团聚.在单独铂的体系中沉积发现,负载量极小,表明体系中镍前驱体的添加对于催化剂的沉积过程起到重要作用.电化学表征结果表明,在所选用的DMF有机体系中,镍的还原电位与铂的十分接近,但还原动力学更慢,趋向于先形成吸附原子后快速还原.由此可以推测,在二者合金的形成过程中,镍在碳载体表面的缓慢还原而形成的吸附原子能够成为铂还原的活性位点,从而降低了铂还原成核所需的能量,使得载体上的成核位点大大增加,这与DFT模拟结果一致.DFT建立了碳上镍的位点和铂的位点,分别在上面进行铂的还原,发现镍位点上比铂位点上更容易实现铂沉积.本文提出了铂镍共沉积的机理:在过电位(即还原能量)下,铂的还原动力学较镍稍快,于是铂先还原形成晶核,但难以达到生长的临界半径,于是单独铂体系中的沉积负载量很少.载体上还原的镍为铂还原提供了大量的活性位点,促进了铂还原,并与镍共沉积.Pt-Ni表面则进一步促进了铂的沉积和颗粒的生长.综上,本文提出了一种用于制备铂合金催化剂的有机电沉积体系,实现了单分散的碳载铂镍合金催化剂的一步制备.随后,本文将材料表征、电化学表征与DFT计算相结合,建立起了有机体系中铂镍合金成核-生长过程的机理模型.     

电沉积制备的PtNi纳米粒子用于氧还原反应:成核和生长机理

质子交换膜燃料电池(PEMFCs)电堆中阴极Pt基催化剂的高用量造成其成本居高不下,成为阻碍燃料电池汽车商业化推进的重要原因,因此开发低Pt、高活性的Pt基催化剂势在必行.Pt合金催化剂能够有效地降低Pt用量,并通过对合金颗粒的元素比例、晶面、粒径等实行精确调控,显著提升氧还原(ORR)催化活性.然而,目前常用的制备方法由于原料与制备成本高昂、过程复杂大都难以适应规模化生产需求.电化学方法通过控制施加的电流或电位控制晶体生长.在水体系中该方法已得到验证,但由于Pt化合物的热力学标准电极电位与过渡金属元素之间相差较大,且对于过渡金属来说,电负性大多小于铂,因此还原电位通常负于析氢电位,使得二者难以实现共沉积.有机体系中电位窗口比水体系大得多,Pt与电位较负的过渡金属可实现共沉积,采用小分子有机溶剂也可避免溶剂清洗问题,具有应用潜力.本文提出了一种简单的一步电沉积方法,选择易溶于水的N,N-二甲基甲酰胺(DMF)作为溶剂,将碳载体滴涂到玻碳电极上作为工作电极,通过电化学方法直接将Pt-Ni合金沉积到碳载体上,并利用物化表征与密度泛函理论(DFT)理论计算来探究共沉积机理.透射电镜表征结果表明,在不同的沉积电位下均可得到分散均匀、粒径适当的催化剂;且随着电位值降低,催化剂颗粒分散得更均匀,颗粒粒径不断减小.元素分布和晶面结果表明,铂镍元素均匀分布于颗粒中.所有样品均表现出优异的ORR性能,最高的面积比活性达到商业催化剂的6.85倍.将材料表征、电化学表征与DFT计算结合,建立起了铂镍合金生长过程的模型,并发现了有机体系中独特的成核-生长机理.将体系中的DMF换成超纯水,用同样的方法进行沉积,得到的催化剂颗粒团聚严重,说明DMF的使用能够避免颗粒团聚.在单独铂的体系中沉积发现,负载量极小,表明体系中镍前驱体的添加对于催化剂的沉积过程起到重要作用.电化学表征结果表明,在所选用的DMF有机体系中,镍的还原电位与铂的十分接近,但还原动力学更慢,趋向于先形成吸附原子后快速还原.由此可以推测,在二者合金的形成过程中,镍在碳载体表面的缓慢还原而形成的吸附原子能够成为铂还原的活性位点,从而降低了铂还原成核所需的能量,使得载体上的成核位点大大增加,这与DFT模拟结果一致.DFT建立了碳上镍的位点和铂的位点,分别在上面进行铂的还原,发现镍位点上比铂位点上更容易实现铂沉积.本文提出了铂镍共沉积的机理:在过电位(即还原能量)下,铂的还原动力学较镍稍快,于是铂先还原形成晶核,但难以达到生长的临界半径,于是单独铂体系中的沉积负载量很少.载体上还原的镍为铂还原提供了大量的活性位点,促进了铂还原,并与镍共沉积.Pt-Ni表面则进一步促进了铂的沉积和颗粒的生长.综上,本文提出了一种用于制备铂合金催化剂的有机电沉积体系,实现了单分散的碳载铂镍合金催化剂的一步制备.随后,本文将材料表征、电化学表征与DFT计算相结合,建立起了有机体系中铂镍合金成核-生长过程的机理模型.     

化学镀镍诱发过程的研究 II.用电子能谱研究诱发过程

In the previous paper, it was reported that a sudden decrease down to -0.6V and lower in stationary potential was observed from the stationary potential-time curve and the reaction of electroless nickeling could be induced by metallic iron catalyst when it was in contact with substrate metallic copper. In this paper, AES and XPS surface analysis and depth profile technique was employed to investigate the surface and depth distribution of Ni, Cu, Fe and P in the nickel coating deposited on the substrate metal. The experimental results showed that there was a thin adsorption layer consisting of C, S and Cl. The pure electroless nickel deposition, its Ni/P ratio being about two, existed under the adsorption layer. A layer with rapidly changed Ni/P ratio occurred close to the surface of substrate metal, under this layer the substrate metal was alloyed with Ni and P, thus becoming Cu-Ni-P alloy. The ratio of components in this alloy was found to be Cu:Ni:P=56:36:5. This fact explained why the electroless nickel deposition can preferably adhered to the substrate metal. In inducing process, Fe was not detected by AES from the substrate metal and nickel deposition. Thus it showed that the inducing reaction takes place without the deposition of inducing metal.     

Influence de la distribution de potentiel électrochimique sur l'interprétation de la courbe courant-tension anodique d'une électrode tournante d'alliage Fe-31 % Ni en milieu sulfurique

Influence of the electrochemical potential distribution on the interpretation of the anodic current-voltage curve of a rotating electrode of a Fe-31 % Ni alloy in normal sulfuric acid solution. The anodic steady-state polarization curve of a Fe-31 % Ni rotating-ring electrode in normal sulfuric acid was studied, and the dissolution profiles obtained at different points of the curve were surveyed. We showed that the use of a rotating-ring electrode allowed to obtain the entire J(E) relationship between the current density J and the electrochemical potential E, whereas this relationship cannot be obtained from the polarization curve of the classical rotating-disk electrode because of the non-uniform potential distribution over the disk surface. With the ring electrode, additional information on the transitions between three different states of the metal (homogeneous dissolution, intergranular dissolution and passivity) could be obtained.     

Ni-Fe催化剂乙醇部分氧化制氢的研究

研究了Ni Fe催化剂对乙醇部分氧化制氢反应,系统地考察了不同O2/C2H5OH摩尔比及反应温度下催化剂的性能.发现Ni Fe催化剂对乙醇部分氧化制氢具有较好的催化活性,其中组成为Ni50Fe50催化剂最好,最佳的反应条件是O2/C2H5OH=1.0,T=573 K.XRD谱图表明催化剂主要由尖晶石结构的铁酸盐和FeNi3合金相组成. XPS结果说明,催化剂体相以还原态FeNi3合金相为主,表面以氧化态的铁酸盐为主.稳定性考察的结果表明,催化剂经40 h反应后,对氢的选择性明显下降,此时对应的FeNi3物相衍射峰强度也明显降低,表明催化剂对H2选择性的下降与FeNi3物相的转变有关.     

Study on the anodic reaction of Ni in an alkaline solution by transient pH detection based on scanning electrochemical microscopy (SECM)

The anodic reaction of Ni in an alkaline solution was studied by the tip–substrate voltammetry mode of scanning electrochemical microscopy (SECM) and cyclic voltammetry (CV). A platinum microdisc electrode was selected as the tip electrode, which functioned as a pH sensor with transient response capability. The pH value of the solution near the Ni electrode surface varied while the Ni substrate oxidation reaction occurred, and the pH variation could be detected by the tip faradic current. The cyclic voltammogram results showed that two types of hydroxides: i.e. α‐Ni(OH)₂ and β‐Ni(OH)₂ were formed during Ni oxidation in the lower potential region. In the proceedings of α‐Ni(OH)₂ → γ‐NiOOH and β‐Ni(OH)₂ → β‐NiOOH, the process of OH^? concentration decrease in the solution was ahead and behind of electron transfer in the solid phase, respectively. These results indicate that the OH^? adsorption process occurs as an elementary step in the former reaction and the H⁺ diffusion process from the inner to the outer layer of the solid phase occurs as a subsequent step in the latter reaction. The results also revealed that the oxide film on the Ni surface has a two‐layer structure. The real potential of the oxygen evolution reaction (OER) on the Ni surface with different cycles is also analyzed in the paper. Copyright © 2007 John Wiley & Sons, Ltd.     

Nanocrystalline structure and soft magnetic properties of nickel–molybdenum alloy thin films electrodeposited from acidic and alkaline aqueous solutions

Nanocrystalline nickel–molybdenum (Ni–Mo) alloy thin films were electrochemically synthesized in acidic and alkaline aqueous solutions. Transmission electron microscope bright-field images and electron diffraction patterns of the electrodeposits made it obvious that pure Ni consists of a submicron crystalline phase with the grain diameter of several hundred nanometers, while Ni–20 %Mo alloy was composed of a nanocrystalline phase with the grain diameter of a few nanometers. It was estimated that the nanocrystalline phase of electrodeposited Ni–Mo alloy thin films was introduced by the formation of supersaturated Ni–Mo solid solution phase with Mo content in the deposit more than 20 %. Submicron crystalline pure Ni thin films were hardly magnetized in perpendicular direction to the film plane while the nanocrystalline Ni–20 %Mo alloy thin films were isotropically magnetized. It was suggested that the isotropical magnetization behavior was caused by decreasing the demagnetizing field and the magneto crystalline anisotropy with a decrease in the magnetic moment and the average crystal grain size. Coercive force of a submicron crystalline pure Ni thin film electrodeposited from an acidic aqueous solution was ca. 100 Oe while that of a nanocrystalline Ni–20 %Mo alloy thin film electrodeposited from an alkaline aqueous solution was only 1～2 Oe. Soft magnetic properties of Ni–Mo alloy thin films electrodeposited from an alkaline aqueous solution were better than that from an acidic aqueous solution and it was improved with an increase in Mo content in the deposit. It was estimated that the electrodeposited Ni–Mo alloy catalysts could be easily recovered with magnetic field less than 1 kOe.     

Morphological study of supported thin Pd and Pd–25Ag membranes upon hydrogen permeation

Morphological change of Pd and Pd–25Ag membranes supported by V–15Ni alloy upon hydrogen permeation was investigated in the temperature range 423–673 K. The supported Pd–25Ag membrane exhibited higher resistance to hydrogen-induced cracking and grain growth than the supported Pd membrane. Long-term permeation of Pd–25Ag/V–15Ni composite membrane was carried out at 573 and 673 K for 200 h. There was no strong metallic interdiffusion between the Pd–25Ag membrane and the V–15Ni support after the long-term permeation at 573 K but small amounts of oxide had formed on the surface of Pd–25Ag membrane. Whisker and fissure-oxide morphologies were dominant on the exit and entrance side of the Pd–25Ag/V–15Ni composite membrane, respectively, accompanied by severe metallic interdiffusion after the long-term permeation at 673 K. AES and FE-SEM results revealed that metallic interdiffusion and selective oxidation of vanadium were responsible for the deterioration of Pd–25Ag membrane at 673 K. Hydrogenation–dehydrogenation of Pd and Pd–25Ag membranes supported by stainless steel and V–15Ni alloy were in situ examined by an optical microscope. The formation of hydride was uniform in the Pd/V–15Ni sample but localized in the Pd–25Ag/V–15Ni sample, suggesting that the hydrogen transfer through interface was strongly dependent on the composition of Pd alloy membranes. As for the stainless steel supported samples, both Pd and Pd–25Ag membranes had fractured.