Electrolytic nickel—molybdenum—vanadium alloy coatings as a material with a decreased hydrogen overvoltage

The process of electrodeposition of Ni-Mo-V alloys from an alkaline tartrate bath was studied. The effect of the cathodic current density on the chemical composition, phase composition and surface morphology of Ni-Mo-V alloy deposits, as well as on the current efficiency of the deposition process, was determined. Codeposition of molybdenum and vanadium with nickel and formation of the Ni-Mo-V alloy is possible due to the effects of depolarization and overpolarization occurring in the process of codischarge of the complex ions of these metals. It was observed that the use of cathodes electrodeposited with Ni-Mo-V alloy containing 9–12% Mo and 0.1–0.2% V for water electrolysis resulted in a decreased overpotential for hydrogen evolution.     

Influence of molybdenum on the anodic dissolution of iron in acidic solutions

The anodic dissolution of pure iron and binary iron-molybdenum alloys (10 and 20 wt% Mo) in molar H₂SO₄ and HCl solutions was studied by d.c. polarization and a.c. impedance techniques. Molybdenum additive influences both the steady state polarization curves and the impedance spectra in the two media, the impact being stronger for the Fe-20 wt % Mo alloy. In general, two-slope polarization curves are obtained for the alloys; impedance spectra exhibit two time constants in addition to the charge transfer one implying the existence of two reaction intermediates. Differences between spectra measured in H₂SO₄ and HCl are discussed. A kinetic model advanced on the basis of literature data for pure iron and molybdenum was able to reproduce quantitatively both the steady state and a.c. impedance results for both alloys in the two media. Kinetic parameters for the anodic dissolution of Fe-Mo alloys are thereby determined.     

Microstructural characterization and corrosion resistance of Ni–Zn–P alloys electrolessly deposited from a sulphate bath

Electroless Ni–Zn–P alloy coatings were obtained on an iron substrate from a sulfate bath at various pH values. The effects of changes in bath pH on alloy composition, morphology, microstructure and corrosion resistance were studied. Scanning electron microscopy was performed to observe the morphological change of the deposits with bath pH. Coating crystallinity was investigated by grazing incidence asymmetric Bragg X-ray diffraction and transmission electron microscopy. A transition from an amorphous to polycrystalline structure was observed on increasing the bath alkalinity, and thus decreasing the phosphorus content of the alloys. A single crystalline phase corresponding to face-centred-cubic nickel was identified in the alloys obtained from a strong alkaline solution. An increase in zinc percentage up to 23% in the deposits does not change the f.c.c. nickel crystalline structure. Corrosion potential and polarization resistance measurements indicated that the corrosion resistance of electroless Ni–Zn–P alloys depends strongly on the microstructure and chemical composition. The deposits obtained at pH 9.0–9.5 and with 11.4–12.5% zinc and 11.8–11.2% phosphorous exhibited the best corrosion resistance.     

Electrodeposition of amorphous/nanocrystalline and polycrystalline Ni-Mo alloys from pyrophosphate baths

Pyrophosphate plating bath was found to be a good alternative to citrate bath for deposition of Ni-Mo amorphous alloys. The addition of wetting agents such as 2-butyne-1,4-diol and rokafenol N-10 to the pyrophosphate bath resulted in the removal of bumps, spheres and cracks from the Ni-Mo alloy surface. The plated alloy layers adhered well to Cu-Zn brass and steel, were of thickness from a fraction to tens of micrometers and the molybdenum content was independent of the distance from the support. An increase in the concentration of the molybdate ion in the bath leads to an increase in the amount of Mo in the alloys up to 33-35 at.% and to a decrease in the deposition rate. These changes and the influence of pH are discussed in the paper. The atom arrangement in the alloys changes from (2 2 0) preferred for pure-nickel deposition to (1 1 1) for content of Mo higher than 15 at.%. For 20 and more at.% of Mo the structure of the alloy is amorphous like. An analysis of SEM and STM micrographs obtained indicates that contrary to the Ni-W alloy the “amorphous” phase is made of circa 10-50 nm in diameter objects and not by long needles perpendicular to the substrate.     

Electrodeposition of aluminium-copper alloys from alkyl benzene electrolytes

An experimental programme in which aluminium-copper alloys were electroplated from alkyl benzene/ AlBr₃ electrolytes is described. The investigation showed that Al-Cu alloys (0–3.5 wt% Cu) can be plated onto steel and that the resulting coatings are bright, adherent and less porous than equivalent coatings of pure aluminium. The composition of the cathode deposits can be readily controlled by using Al-Cu anodes of specified copper content. About half the copper dissolved from the anodes is transferred to the cathode, the remainder being precipitated from the electrolyte as CuBr. Coating composition varies with current density and this parameter can also be used to control the process. In a parallel investigation, potential differences between aluminium and a number of other metals (Zn, Pb, Cd, Sn, Cu, Ag) were measured. Potential differences in the alkyl benzene electrolytes were found to be 10–30 times less than in aqueous electrolytes which indicates that the alkyl benzenes should be useful for plating other alloys in addition to those of aluminium and copper.     

Electrodeposition of ternary nickel-iron-molybdenum alloys from an acetate bath

Ternary nickel-iron-molybdenum alloys containing 0.5–8.5% molybdenum, 18–48% iron and balance nickel were electrodeposited from an acetate bath under a variety of conditions. Satisfactory deposits were obtained from the bath containing 0.3394 M nickel acetate, 0.02878 M ferrous sulphate, 0.0015 M sodium molybdate at current density 2.0 A dm^–2, pH 5.0 and temperature 20°C without agitation for plating times up to 30min. The alloy deposits were examined for their crystal structure by X-ray diffraction and microstructure by metallography.Dedicated in honour of the late Dr D. Singh, Reader in Chemistry, Banaras Hindu University.     

Electrochemical investigation of the Ni–Cu–Mo electrodeposition system

The kinetics of Ni–Cu–Mo alloy deposition has been investigated by means of steady-state polarization measurements. Strong interactions between the three discharging metals occur: nickel induces molybdenum deposition but its discharge is markedly inhibited by molybdenum. Copper deposition has a depolarizing effect on Ni–Mo discharge. Hydrogen evolution is associated with molybdenum deposition. The electrocrystallization process is dominated by the Ni–Mo codischarge kinetics.     

深共融溶剂中电沉积Ni-Mo合金及其催化析氢性能

在深共融溶剂体系中电沉积制备了Ni-Mo合金.利用扫描电镜(SEM)、X射线衍射仪(XRD)及电化学测试对Ni-Mo合金形貌、结构及性能进行了表征.SEM、XRD测试结果表明,Ni-Mo合金为纳米晶结构,平均晶粒尺寸约为2.2 nm;镀层表面微观粗糙度较大,Mo的质量分数约为5%.阴极极化曲线测试结果表明,当电流密度为0.1 A·cm^-2时,深共融溶剂中制备的Ni-Mo合金电极析氢电位比水溶液中制备的Ni-Mo合金电极正移约100 mV,相比纯Ni电极正移近250 mV.     

Electrodeposition of Ni-Cu-Mo ternary alloys from citrate electrolytes

Conditions for the electrodeposition of Ni–Cu–Mo alloys from citrate electrolytes have been developed. The composition variations of the deposits with electrolyte pH and concentration have been investigated. A maximum molybdenum and nickel content is obtained for a pH of 7 and for low copper and large citrate concentrations. Molybdenum and copper are preferentially discharged at low current density whereas at high current density nickel becomes predominant. The deposits have a nodular morphology similar to that of the binary Ni–Mo layers     

高碳镍钼矿碱性还原熔炼-水浸分离与提取镍钼

在理论分析的基础上,以贵州遵义镍钼矿为原料,提出了镍钼矿碱性还原熔炼?水浸提钼的清洁冶金新工艺,考察了Na2CO3用量、温度、还原剂用量、反应时间对镍还原率及钼浸出率的影响,在最优条件下进行了扩大实验. 结果表明,在碱性介质及强还原气氛下,镍钼矿中的镍被还原成高品位镍铁合金,钼转化为可溶性的钼酸盐;最佳工艺条件为Na2CO3用量为理论量的2倍、熔炼温度1000℃、还原剂添加量为镍钼矿的5wt%、反应时间1.5 h. 最佳条件下扩大实验金属镍回收率为94.92%,金属钼挥发率为9.36%,浸出率为99.94%,固硫率接近100%,得到了高品位镍铁合金和含钼浸出液,镍钼有效分离.     

An EXAFS investigation of molybdate-based conversion coatings

The composition of molybdate-based conversion coatings on zinc–nickel alloy electrodeposits was examined by extended X-ray absorption fine structure (EXAFS). The absorption spectra from appropriate standards showed distinct differences between the Mo(IV) and Mo(VI) oxidation states. A pre-edge peak was apparent for the various molybdate species and molybdenum trioxide, with the energy and intensity dependent on the coordination of the molybdenum. A shift in the molybdenum K-edge spectra was also evident between Mo(IV) and Mo(VI) compounds. A qualitative analysis revealed that both Mo(IV) and Mo(VI) species were present within the molybdate-based conversion coating, with a significant prevalence of hexavalent molybdenum.     

A study of the kinetics of passive layer formation on CrMo alloys

Electrochemical measurements on alloys of the two pure metals chromium and molybdenum in the concentration range up to 20 wt% Mo were carried out. The investigations took place under stationary and non-stationary conditions.Stationary current-potential curves show that the behaviour in the active region is mainly determined by molybdenum. The active state, easily obtained for pure chromium, first appears in 5N HCl solution for the 10 wt% alloy; for the 20 wt% alloy it does not appear at all. This corresponds to the behaviour of pure molybdenum, for which an active region in aqueous electrolytes could not clearly be found.In contrast to this no specific influence of molybdenum could be found in the passive and transpassive region. The behaviour of the alloys is quite similar to that of pure chromium. This is indicated by galvanostatic switch-on and potentiostatic step experiments. As for pure chromium the results may be interpreted in terms of the simultaneous-place-exchange mechanism.     

Electrodeposition of Ni-Mo alloys with pulse reverse potentials

With the aim of improving the protective properties of Ni-Mo alloy layers, pulse reverse electro-deposition has been investigated. The anodic pulses were applied in the potential range where hydrogen desorption and oxidation occur. The alloy composition was shown to depend on the pulse parameters, especially on the anodic pulse duration. For long anodic pulses a preferential dissolution of molybdenum in the electrodeposited alloy occurs, while bulk Ni-Mo alloys do not undergo any dissolution. For anodic pulses longer than a certain threshold the electrocrystallization process becomes blocked. The morphology and microstructure of the layers are mainly determined by the molybdenum content rather than by the pulse parameters.     

Behaviour of multicomponent lead–tin alloys under cathodic polarization in a sodium hydroxide melt

The results of investigations of the electrochemical behaviour of multicomponent lead–tin alloys under cathodic polarization in a sodium hydroxide melt are presented. It has been shown that as a result of the formation of intermetallic compounds, such elements as antimony, tin, bismuth and arsenic are extracted from the cathode to the anode. The electrolysis product on the cathode is lead with a total percentage of the above impurities of 0.065–0.070%. The extraction kinetics have been studied, the dissolution rate constants for each of the alloy components have been determined and a mechanism of mass exchange between the electrodes has been proposed. The current consumption for the extraction of metals from the melt has been determined.     

Zinc–cobalt alloy electrodeposition from chloride baths

Electrodeposition of Zn–Co alloys on iron substrate from chloride baths under galvanostatic and potentiostatic conditions were carried out. Current density, temperature and cobalt percentage in the bath were found to strongly influence the composition of the deposits and their morphology. Changes in potentials, current efficiency and partial current densities were studied. The results show that the shift in potential and in the cobalt percentage of the deposits, for a particular current density during galvanostatic electrodeposition, does not always correspond to the transition from normal to anomalous codeposition. This shift is attributed to zinc ion discharge, which passes from underpotential to thermodynamic conditions. In the range of potentials for the underpotential deposition of zinc, the electrodeposition of zinc–cobalt alloys is discussed, emphasizing the influence of the electrode potential on the composition and microstructure of the deposits.     

Corrosion of alloys in tall oil distillation service

Plant corrosion tests of various metals and alloys in tall oil distillation streams present the effect of alloy composition on corrosion rate. Stream temperature, alloy composition and stream composition are correlated so as to provide a useful guide to material selection for tall oil distillation plants. Alloys exposed to corrosion test were iron or nickel base with chromium plus varying amounts of molybdenum. Molybdenum is the most important alloy addition in reducing the rate of corrosion attack, with corrosion attack at a very low rate, <.1 mil per year, at the 6% molybdenum level in the most aggressive stream tested, i.e., 85% fatty acids at 518F. The presence of chromium does not appear to be essential to obtaining good corrosion resistance to the more corrosive conditions. Corrosion rates increase with increasing temperature. The streams classed as high in fatty acids are much more corrosive than those which are classed as high in rosin acids. Vapor phase streams are more corrosive than liquid phase streams. Corrosion attack is normally from pitting. Most of the more corrosive conditions can be handled with an alloy containing 3% to 4% molybdenum (AISI Type 317), but some process conditions require higher molybdenum contents in order to obtain acceptable corrosion rates. Less corrosive streams can be handled with an alloy containing less than 3% molybdenum (AISI Type 316).     

电沉积钼合金及其电催化性能

通过正交实验得到La-Co-Mo合金电沉积的最佳工艺条件。以DSA为阳极分别在钛基体上电沉积La-Mo、Co-Mo、La-Co-Mo合金,采用AES、电子测厚仪、显微硬度计、划痕实验、盐雾实验等手段对镀层性能进行测试。所得钼合金镀层致密、结合力强、耐高温腐蚀性能好。极化曲线测定结果显示,钛基体电沉积La-Mo、Co-M0、La-Co-Mo合金层析氢过电势比钛电极低,电催化性能高。钛基体电沉积钼合金层可望作为新型氯碱工业用高活性阴极。     

Electrodeposition of Zn–Co alloy coatingsfrom sulfate–chloride electrolytes

The composition, surface morphology and appearance of Zn–Co alloy deposits as a function of current density, electrode potential and Co2+ concentration in the electrolyte was studied. It was found that coatings of good quality with low (1%) Co content are formed at a current density of 0.2Adm–2 and with high (6.5%) Co content at 2Adm–2 from electrolytes containing 1.0M Co2+ under galvanostatic conditions. The potentiodynamic dissolution of coatings with Co content of 6.5% indicates successive deposition of Co enriched phases and a pure Zn phase. The Zn–Co alloys are more corrosion resistant than zinc but are less resistant than cobalt.     

Effect of high temperature treatment on the properties of fe-mo oxide catalysts

In this study the structural and compositional changes that Fe-Mo oxide catalysts undergo during treatment at elevated temperatures were investigated. Commercial and laboratory prepared catalysts were examined. The changes in catalyst properties were determined by low temperature nitrogen adsorption, scanning electron microscopy, X-ray diffraction, X-ray fluorescence and thermogravimetric analysis. The activities of the catalysts for the oxidation of methanol in air to formaldehyde were measured using an integral bed reactor. The results showed that treatment at elevated temperatures resulted in the growth and segregation of Fe₂(Mo0₄)₃ and Mo0₃ crystals resulting in a loss of specific surface area. The changes in specific activity can be explained in terms of molybdenum depletion from a molybdenum rich iron molybdate phase.     

Physico-chemical properties of Zn-Fe alloy deposits from an alkaline sulphate bath containing triethanolamine

The composition, properties, structure and morphology of Zn-Fe alloy deposits obtained from an alkaline sulphate bath have been investigated. The bath containing triethanolamine produced smooth, uniform and bright Zn-Fe alloy deposits having the desired 15–25% Fe. The deposition potentials of Zn-Fe alloy lie between the potentials of the individual metals. Increased current density lowered the Fe percentage in the alloy deposit. The structure and morphology of the alloy deposits were found to depend on the Fe percentage in the alloy.