The effect of a.c. superimposed on d.c. and pulsating potential on the coercivity of electrodeposited Ni-Fe alloy thin films

The effect of d.c., a.c. superimposed on d.c. and constant and pulsating potentials on the coercivity of electrodeposited Ni-Fe alloy thin films obtained in a sulphate-tartrate bath has been investigated. It has been shown that the dependency of coercivity on current and potential parameters passes through a minimum. This phenomenon is related to the current efficiency of hydrogen production and to the alloy composition.     

Effect of some plating variables on the electrodeposition of Cu-Zn alloys from alkaline tartrate baths

The electrodeposition of copper, zinc and copper-zinc alloys from alkaline tartrate solutions has been investigated under different conditions of bath composition, added ammonium chloride, current density and temperature. A detailed study has been made of the effect of the variables on the cathode potentials and cathode efficiencies of copper, zinc and Cu-Zn alloys; the compositions of the alloys were determined. The results were consistent with the behaviour of a regular alloy plating system with zinc being the less noble metal.     

The effect of magnetic fields on the electrodeposition of CoFe alloys

The effect of a uniform magnetic field with a flux density up to 1 T and different configurations relative to the electrode surface, on the electrodeposition of Co, Fe and CoFe alloys from acidic sulphate electrolytes has been investigated. It was found that a magnetic field applied parallel to the electrode surface increases the limiting current density and deposition rate due to the magnetohydrodynamic (MHD)-effect caused by the Lorentz force. No significant changes of the limiting current density and deposition rate with a magnetic field applied in the perpendicular to electrode configuration were observed. But in this configuration desorption of hydrogen was found to be supported by a magnetic field. The chemical composition of the deposited alloys was found to be unaffected by the magnetic field. The deposition of CoFe at the highest applied potential (−1600 mV_MSE) was found to be anomalous. At this potential the increase of the interface pH value is sufficient for hydroxyl species formation.     

The electrodeposition of cobalt — molybdenum alloys

Previous studies have shown that cobalt-molybdenum alloys may be deposited with high efficiencies from a pyrophosphate bath using a specially designed plating cell incorporating cathode rotation, stirring and wiping. This investigation shows that it is possible to deposit bright and adherent alloys using a pulsed-potential method in the same bath, even without stirring, wiping or cathode rotation. The average content of the deposits was about 55 % molybdenum, 40 % cobalt and 5 % non-metallic material. The cathode current efficiency was about 47 %.     

Influence of a magnetic field on the electrodeposition of nickel-iron alloys

The electrodeposition of nickel-iron alloys is studied under the influence of a superimposed external static magnetic field. It is shown that the direction of the magnetic field with regard to the electric field affects the electrodeposition process (current efficiency, composition and morphology of the layers). Furthermore, the influence of the simultaneous action of natural and magnetically driven convection is discussed in function of the orientation of the working electrode. The electrochemical quartz crystal microbalance (EQCM) technique is used to determine the partial current due to the hydrogen evolution reaction (HER). It is observed that the magnetic field applied perpendicular to the electric field lines increases the rate of the HER, while no significant variation is observed in a magnetic field parallel to the electric field.     

某些有机添加剂对硫酸-酒石酸盐溶液中电沉积Cu-Zn合金的作用

研究了以酒石酸钾钠、柠檬酸三钠作为络合剂的酸性硫酸盐溶液中的Cu-Zn合金镀层。探讨了电流密度、pH、温度对镀液分散能力和镀层组成的影响。在本实验条件下,添加剂的加入可以使镀液具有较好的分散能力和较高的电流效率。实验发现,在所研究的各种添加剂中,糖精、苯酚是加速剂,而硫脲、甘油是阻化剂。采用动电位极化和电化学阻抗谱方法,测定了Cu-Zn合金镀层在NaCl(φ=3.5%)溶液中的耐蚀性能。采用扫描电镜研究了添加剂对控制沉积质量的微妙作用。X-射线衍射分析表明,合金镀层的相结构是正交晶。在上述研究的基础上,提出了Cu-Zn合金电沉积的最佳组成和工艺控制参数。     

Influence of substrate on the electrodeposition of nickel-molybdenum alloys

The electrodeposition of nickel-molybdenum alloy has been studied on various substrates, with the aim of determining the influence of hydrogen evolution on the formation of the deposit. Transient electrochemical methods were used. Three types of substrates were used. Glassy carbon in which hydrogen absorption cannot occur, palladium in which hydrogen diffusion is rapid, and nickel. Good and thick deposits were obtained on glassy carbon and annealed ultra pure nickel. On palladium no deposit was formed. The importance of hydrogen in the formation of the deposit was confirmed. Codeposition occurs in the same potential range as hydrogen evolution, and therefore hydrogen is trapped in the expanding lattice as seen by its oxidation during anodic polarization.     

The effect of d.c. glow discharge on hot filament chemical vapor deposition of diamond

The origin of bias-enhanced nucleation and growth of diamond has been investigated in hot filament chemical vapor deposition with two parallel W electrode wires inserted between filament and two floating Si substrates. An electrical voltage has been applied to the W electrodes to produce a glow discharge, which occurs in bias-enhanced deposition processes, during deposition. Substantial nucleation and growth enhancements occurred on the substrate near the negative glow of the d.c. discharge under the cathode wire. These observations indicate that the enhanced deposition of diamond in both positive and negative bias processes arises from chemically active species in the negative glow region rather than from electron or ion bombardment effects.     

The effect of oscillations superimposed upon a gas stream on mass transfer

The effect of progressive oscillations being superimposed upon laminar gas flow in a pipe on mass transfer between fluid and wall was experimentally investigated. Frequency and intensity of oscillations were varied between 580 to 1380 c.p.s., and 148 to 160 dB respectively. The increase of mass transfer which amounted up to 150% was attributed to the generation of acoustic turbulence close to the wall. This turbulence occured when the amplitude of oscillation reached the magnitude of the acoustic boundary layer thickness. To quantitatively describe the dependence of mass transfer increase on frequency and intensity of oscillation an empirical correlation was derived.     

电沉积梯度Ni-Co纳米合金镀层的研究

采用直流电沉积技术制备了梯度Ni-Co纳米合金厚镀层。测定了该镀层的内应力及显微硬度,采用X射线衍射仪及能谱仪分别对镀层的晶相结构与成分进行了分析,采用扫描电镜对镀层的表面形貌和磨痕进行了观察,并对其摩擦、磨损性能进行了研究。结果表明,该合金镀层具有较好的成分梯度和相应的结构梯度,具有优异的抗磨减摩性能。说明梯度化的设计可以有效降低合金镀层的内应力,提高镀层的抗磨和减摩性能。     

Thermal effects of a laser beam on the electrodeposition of Ni–P alloys

The paper deals with the effects of an incident laser beam on electrodeposition of Ni–P alloys from dilute acetate solutions. The kinetics of separate reductions of Ni2+ and H2PO–2 species were first investigated by linear sweep voltammetry, varying the hypophosphite concentration and the solution temperature: comparison of the kinetically limited current densities of the two reductions suggested that increasing temperature might reduce the significance of P codeposition. This tendency was confirmed by deposition runs carried out at controlled current. Deposition performance was discussed in terms of faradaic yield and deposit properties, namely P content together with the aspect and the structure of the alloys. Use of a continuous or pulsed laser beam was shown to reduce the P content in the deposit at high current densities; in some cases, amorphous structures were replaced by more crystalline forms with assistance of a laser beam.     

The effect of magnetic fields on the electrodeposition of cobalt

The effect of a magnetic field on the electrodeposition of Co has been investigated with respect to the strength and the orientation of the magnetic field (B). Two different effects of the magnetic field B on the electrodeposition of cobalt have been observed. The first is the magnetohydrodynamic (MHD) effect caused by the Lorentz force (). The second is an effect due to the paramagnetic force (), caused by the concentration gradient () and therefore the gradient of the molar susceptibility (). The limiting current density and the deposition rate of Co increases if the B-field is oriented parallel to the electrode surface. This is mainly due to the expected convection induced by . Both, the Co deposition and the reduction of hydrogen ions, are affected by this. At high cathodic potentials the contribution of the hydrogen reduction to the process changed, which led to homogeneous deposits. A decreasing deposition rate was measured for B-fields oriented parallel or antiparallel to the flow of ions. These results are attributed to the effect of on the electrochemical processes close to the surface.     

Ni-W纳米晶合金电沉积工艺条件的研究

纳米晶材料与常规晶体材料相比有许多优良的性能 ,已受到广泛关注。本文采用电沉积方法获得了Ni W纳米晶合金镀层。研究了镀液中钨酸钠含量、温度、pH值及电流密度对沉积速度的影响。测定了镀层的显微硬度 ,并用X -射线衍射仪对其微观结构进行了观察。结果表明 ,影响沉积速度最大的因素为pH值 ,其次是电流密度 ;镀层显微硬度最高可达 6 70 .3HV。通过正交试验得出适宜工艺条件范围为 :Na2 WO4·2H2 O 1 0～ 30g/L ,电流密度 1 0～1 5A/dm2 ,温度 6 0～ 70℃ ,pH值 6～ 7。     

Aqueous electrodeposition of iron group-vanadium binary alloys

Electrodeposition of binary iron group (IG)-vanadium (V) alloys from aqueous citrate solutions was investigated. Addition of NH₃(aq.) and increasing solution pH resulted in increased deposit V content, but non-metallic deposits were obtained at solution pH > 7. Increasing current density resulted in an almost linear decrease in V content and a sharp increase in hydrogen evolution (decreased current efficiency). In general, the amount of V deposited with the IG metal increased as follows: Ni < Fe ? Co. XRD spectra indicated that preferred orientations from 25 °C solutions were not displaced by elevated temperature deposits. Changes in orientation may contribute to the deposit magnetic properties; e.g., Co-V deposits with (1 0 0) planes exhibit harder magnetization than deposits with (0 0 2) planes.     

Electrodeposition of Cd-Ni alloys from acetate baths using a superimposed alternating current

The electrodeposition of Cd–Ni alloys from some selected acetate baths has been investigated. The influences of the proportions of Ni²⁺ and Cd²⁺ ions in the bath, the operating current density and superimposed alternating current on the electrodeposited alloys have been examined. The study includes the effect of these variables on the cathodic polarization curves, current efficiency, chemical composition and surface morphology of the alloys. Under all conditions the electrodeposition process is of the anomalous type. An explanation of this phenomenon with the help of a comparison between the experimental and the calculated polarization curves is given. X-ray diffraction studies show that the nickel-rich alloys consist of Ni and (Cd–Ni) phases, while the cadmium-rich alloys contain Cd, (Cd–Ni) and Ni phases. The optimum bath composition and operating conditions for the electrodeposition of sound, smooth and bright Cd–Ni alloys have been identified.     

The role of anion additives in the electrodeposition of nickel-cobalt alloys from sulfamate electrolyte

Nickel-cobalt alloys have been deposited from sulfamate electrolyte with acetate and citrate-anion additives and evaluated for structure and properties, such as microhardness, tensile strength, internal stress and high-temperature oxidation. XRD data show that at low Co content, the alloys exhibit face-centered cubic (fcc) growth orientations. Above 60% Co, the deposit is completely hexagonal close packed (hcp) with pronounced (100) and (110) lines. It seems likely that the Ni-Co deposits from typical sulfamate electrolyte at pH 5, as well as at current density higher than 5 A/dm², include metal hydroxides. This is followed by the formation of a more strained structure. The high-temperature oxidation rate of the Ni-Co coating from sulfamate electrolyte at pH 5 is twice that of the alloy deposited from the electrolyte with anion additives. We believe that, citrate complexes of Ni and Co, which are assumed to be involved in alloy deposition, eliminate the incorporation of hydroxides into the deposits and enable low-internal-stress coating. The anion-modified bath offers stability of structure and properties of the alloy over a wide range of acidity and current density.     

Cathodic inhibition and anomalous electrodeposition of Zn-Co alloys

The electrodeposition of Zn-Co alloys from chloride electrolytes was studied on steel substrate. Electrodeposition of Zn-Co alloys is usually divided into two potential regions, i.e. normal (positive to Zn deposition potential versus SCE) and anomalous (negative to ). In order to elucidate the deposition mechanism a complementary approach was used based on the combination of various electrochemical techniques. The morphology of the deposits and elemental composition analysis were determined by using SEM/EDX. It was found that the presence of Zn²⁺ in electrolyte inhibited Co²⁺ and H⁺ reductions in normal region. A critical potential was also noticed in the so-called normal deposition range above which a Co-enriched phase of Co-Zn alloy was favored and below that a severe mitigation to deposition occurred that was considered due to underpotential deposition (UPD) of Zn on the substrate and on active Co sites at either nucleation or growth stage. Beyond the deposition is considered anomalous due to the fact that Zn deposits preferentially compared to the more noble Co. This anomalism was explained by the faster deposition kinetics of Zn as compared to Co on steel and could be overcome by either increasing the Co²⁺/Zn²⁺ ratios in the electrolyte or by carrying out the deposition at higher temperature.     

Mass transport effects on the electrodeposition of iron-nickel alloys at the presence of additives

Iron-nickel (Fe-Ni) plating bath solution chemistry was studied by determining the Fe-Ni equilibrium concentrations at various pH levels. It was found that the alloy composition is determined by solution equilibria, mass transfer of the electroactive species within the diffusion layer and by the surface coverage of the additives on the electrode. The effect of the rotation speed of the disc electrode and the presence of organic additives on the deposition of Fe-Ni alloys are evaluated. Boric acid increases the absolute iron deposition rate, while it inhibits the rate of nickel reduction. Saccharin and ethylene diamine influence the metal deposition rate but are not as effective as boric acid.     

Structural effects during the electrodeposition of silver-antimony alloys from ferrocyanide-thiocyanate electrolytes

Self-organization phenomena are observed during electrodeposition of silver-antimony alloys. On increasing the current density, black regions (assumed to be an antimony-richer phase) appear on the electrode surface. Under certain conditions these black regions are shaped as spirals with different topological charges. The width of the black and white regions depends on the current density and the antimony content in the electrolyte. Quantitative characterization of the phase composition in the black regions is a problem which still remains to be solved.     

Recent developments in the electrodeposition of nickel and some nickel-based alloys

The numerous theoretical and practical studies of the electrodeposition of nickel and its binary and selected ternary alloys with copper and cobalt over the last 10–15 years are reviewed. The reported mechanisms of the electrodeposition processes and accompanying evolution of hydrogen are considered. The complex influence of different bath compositions, pHs, current densities or potential ranges and temperature on the formation of single or multiple deposition layers are compared. The determination of the structure and morphology of the deposits on different substrates, including solid surfaces and particulate materials, using a range of analytical techniques are reported.