The electrodeposition of metals from their trifluoroacetate-amide baths

This paper will deal with the electrodeposition of copper and nickel from the Cu(CF₃COO)₂-HCONH₂ bath, Ni(CF₃COO)₂-HCONH₂ bath, Cu(CF₃COO)₂-HCON(CH₃)₂ bath and Ni(CF₃COO)₂-HCON(CH₃)₂ bath. The properties of these baths and the mechanism of the electrodeposition of copper and nickel from these baths were studied. While solvolysis occurs in the HCONH₂ bath, it does not occur in the HCON(CH₃)₂ bath. A complex is formed in each bath. Since the bond between the metallic ion and the solvent in the HCON(CH₃)₂ bath is stronger than that in the HCONH₂ bath, and since the dielectric constant of the solvent in the former is also lower than in the latter, is difficult to electrodeposit metal and Cu₂O is formed at cathode in the Cu(CF₃COO)₂-HCON(CH₃)₂ bath. The specific conductance in the HCON(CH₃)₂ bath is lower than that in the HCONH₂ bath. It is possible to obtain a better copper electrodeposit over a wider range of current density in the Cu(CF₃COO)₂- HCON(CH₃)₂ bath containing citric acid than in the same bath containing no citric acid. This range almost coincides with that in the Cu(CF₃COO)₂-HCONH₂ bath. While it is possible to obtain better nickel electrodeposit in Ni(CF₃COO)₂-HCONH₂ and Ni(CF₃COO)₂-HCON(CH₃)₂ baths containing appropriate additives, the range of current density which permits one to obtain a superior electrodeposit in the latter bath is narrow. The electrodeposit of nickel or copper obtained from the HCONH₂ and HCON(CH₃)₂ baths has a granular structure. The values of η_cE_c, and b_c in the copper electrodeposition reaction from the Cu(CF₃COO)₂-HCON(CH₃)₂-200 g/l citric acid bath are higher than those in the same reaction from the Cu(CF₃COO)₂-HCONH₂ bath, while the values of i_oc and α_c are lower, so the electrodeposition of copper from the former can be said to be more difficult. On the other hand, the value of n is always about 1 for both the baths. It may be concluded in view of this fact that the deposition of copper from HCONH₂ and HCON(CH₃)₂ baths takes place through Cu⁺ and that the deposition of nickel from HCONH₂ bath takes place through Ni⁺.     

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.     

Activation effect of halides on chromium electrodeposition from chromic acid baths

The current efficiency of chromium electrodeposition and cathodic polarization curves were determined in halide-chromic acid-sulphuric acid systems. The composition of the cathodic films formed was determined by XPS and AES. The results show that sulphate is an effective catalyst for the deposition of bright chromium and that the current efficiency of the chromium deposition increases remarkably when F^– and Cl^– are added to the bath, and also that F^– and Cl^– participate in the formation of the films. The depth profile curves of the film show that halide is distributed in the inner layer of the film, and SO₄ ^2– in the surface layer. It is deduced that F^– and Cl^– form a bridged complex, [C^III-X^–-Cr^III], in which electron transition is easily carried out.     

Model of nickel electrodeposition from acidic medium

A step-wise computer model is presented for simultaneous deposition of nickel and nickel hydroxide in aqueous solutions. In acidic solutions ({pH} 1), the potentiostatic current-time transient response on glassy carbon or titanium was analysed with respect to nucleation and radial growth mechanism. pH changes influence the current-time response greatly. A marked maximum in the current transient appears for slightly acidic solutions ({pH} 4.5) and a consecutive decrease in the deposition current density at long times is obtained. This behaviour is attributed to early precipitation of nickel hydroxide due to a local pH increase at the cathode surface.     

Investigations on electrodeposition of nickel from dimethylsulfoxide

Process of cathodic deposition of nickel mainly from Ni(BF₄)₂ solution in DMSO has been investigated using various experimental techniques. It has been found that this process is complicated. The collected experimental data indicate that passivation of fresh cathodic layer of Ni by chemisorption of DMSO molecules takes place. By basing on the rde methods the values of αn_m = 0.4 (± 0.05) and k_fh = f(E_c) have been estimated.     

Effect of temperature on nickel electrodeposition from a nickel sulfamate electrolyte

The effect of temperature on nickel electrodeposition from a nickel sulfamate electrolyte has been investigated. All the experimental points in a plot of nickel film thickness vs. current density collapse onto a single straight line irrespective of deposition temperature. A relation derived from the Butler–Volmer equation is successful in predicting cathode potential shifts caused by change of deposition temperature. Moreover, an interface width, which characterizes the roughness of the surface and is defined by the root mean square of fluctuation in the height, is shown to have a saturated value that is related to the deposition temperature. Thus, two kinds of activation energies for the charge transfer reaction and for grain growth are estimated from the temperature dependence of the cathode potential shift and the grain size.     

Inhibition effect of some aromatic amines on copper electrodeposition from acidic baths

To improve the quality requirements for copper deposits, the influence of some inhibition agents added to the acidic copper bath has been studied. Several aromatic nitrogen compounds have been tested as inhibition agents, such as aniline, N-methylaniline, N-ethylaniline, N,N-dimethylaniline (DMA), and N,N-diethylaniline (DEA). The electrochemical behavior of these organic additives and the most relevant aspects of the electrochemical behavior of copper in acid solutions have been analyzed by cyclic voltammetry. At the same time, a correlation between voltammetric data and molecular properties of protonated amines obtained by molecular modeling has been performed. The morphology of the copper deposits obtained in the absence and presence of organic compounds has been studied by scanning electron microscopy. An improvement of the roughness degree and crystallite size upon addition of aromatic amine has been found. Best results were obtained for DMA and DEA working at room temperature (25 ± 0.1 °C) and 200 A m⁻² current density, in 1 mol L⁻¹ sulfuric acid solution with 50 g L⁻¹ Cu²⁺.     

化学镀镍老化液再生技术研究现状

介绍了国内外化学镀镍老化液再生技术研究现状。     

Initial stages of tin electrodeposition from sulfate baths in the presence of gluconate

Tin electrodeposition in its initial stages in acid sulfate/gluconate baths was studied with varying tin and gluconate concentrations using potential-controlled electrochemical techniques. The deposit morphology was observed by scanning electron microscopy (SEM). A comparison with tin electrodeposition from acid sulfate baths in the absence of gluconate was also carried out. Use of a highly acidic bath leads to nonuniform deposits, even in the presence of gluconate; at pH 4 deposits are uniform, brilliant and suitable for finishing applications. Tin crystallites have a well defined morphology which depends on bath agitation conditions. In the absence of agitation, the crystallites have the same tetragonal shape as in a sulfate bath without gluconate.     

Black nickel electrodeposition from a modified Watts bath

Black nickel coatings were electrodeposited on to steel substrates from a Watts bath containing potassium nitrate. The best operating conditions necessary to produce smooth and highly adherent black nickel were found to be NiSO₄ · 6H₂O 0.63 M, NiCl₂ · 6H₂O 0.09 M, H₃BO₃ 0.3 M and KNO₃ 0.2 M at pH of 4.6, i=0.5 A dm⁻², T=25 °C and t=10 min. The modified Watts bath has a throwing power (TP) of 61%, which is higher than that reported, not only for nickel, but also for many other metals electrodeposited from different baths. The potentiostatic current–time transients indicate instantaneous nucleation. X-ray diffraction (XRD) analysis shows that the black nickel deposit is pure metallic nickel with Ni(111) preferred orientation.     

Induced electrodeposition of tungsten with nickel from acidic citrate electrolyte

Induced electrodeposition of Ni–W alloys was carried out onto steel substrates from acidic citrate baths (pH 4.5) under different conditions of concentration of electrolyte, current density and temperature. Bright and highly adherent Ni–W deposits were successfully obtained with a relatively high cathodic current efficiency CCE (80–85%). The CCE increases greatly with increasing pH and Ni²⁺ ion content in the bath. The W% in the alloy deposits is in the range of 4–20 wt% depending on the operating condition. The W content in the deposit was found to increase with an increase in Ni²⁺ ion content, pH and temperature. The surface morphology was examined by scanning electron microscopy while the structure of the alloy was examined by X-ray diffraction analysis.     

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.     

ZnNi alloy electrodeposition from acid baths containing sorbitol or glycerol and characterization of ZnNi deposits

The influence of sorbitol or glycerol on the electrodeposition of ZnNi alloys and on the morphology, composition and structure of the ZnNi deposits was investigated. The highest current efficiency (CE), around 90%, was obtained in the presence of glycerol in the potential range from approximately −1.30 V to −1.40 V, while in the presence of sorbitol or absence of either polyalcohol the CE was 82–85%, for the same potential range. Scanning electron microscopy (SEM) analysis showed that ZnNi deposition at −1.26 V or −1.40 V from a bath with sorbitol led to the formation of more compact deposits than with glycerol. Energy dispersive X-ray spectroscopy (EDS) analysis showed that the Ni content in the deposit obtained in the presence of sorbitol remained in the range of 7–9.5 wt% Ni, over a large range of deposition conditions. On the other hand, ZnNi deposits with variable Ni content (5.5–19.5 wt% Ni) were obtained from baths with glycerol or without either polyalcohol, by shifting the deposition potential. All ZnNi deposits showed uniform distribution of the elements Zn and Ni. X-ray analysis of ZnNi deposits obtained from plating baths with and without polyalcohol’s at −1.26 and −1.40 V presented the γ, γ¹ and Pt₃–Zn phases.     

Voltammetric study of plating baths for electrodeposition of Co-W amorphous alloys

Cyclic voltammetry and chronoamperometry at glassy carbon and platinum microdisc electrodes have been used to study the electrodeposition of Co–W amorphous alloys. Voltammetric results show that cathodic deposition of Co–W alloy is accompanied by hydrogen evolution and the efficiency of Co–W electrodeposition does not exceed 20%. Voltammetric behaviour of cobalt (II) and tungstate in ammonium citrate solution depend strongly on composition of the plating bath. The concentration of Co(II) ions can be monitoredin situ during electroplating by means of anodic stripping voltammetry at a platinum microelectrode. The deposit of the alloy on the microelectrode is stable in the atmosphere and thus can be stored for subsequent comparison with a deposit obtained later in the life of the working bath.     

Surface pH measurements during nickel electrodeposition

To better understand the electrochemistry of nickel electrowinning from nickel chloride solutions at the cathode-electrolyte interface, the cathode surface pH was measured using a flat-bottom combination glass pH electrode and a 500 mesh nickel-plated gold gauze as cathode. The cell was a modification of that designed by Romankiw and coworkers. The pH electrode was positioned at the back of, and in direct contact with, the gauze cathode. As expected, the cathode surface pH was always higher than the pH in the bulk electrolyte, and if the current density was sufficiently large, it could cause the precipitation of insoluble Ni(OH)₂₍₅₎ on the cathode surface. Lower bulk pH, higher nickel concentration, higher temperature, and the additions of H₃BO₃ and NH₄Cl effectively suppressed the rise of the cathode surface pH. The results provide further evidence of the buffering action of H₃BO₃ and NH₄Cl and of the enhancement of nickel deposition by H₃BO₃. At current densities less than 240 A m^–2 additions of NaCl and Na₂SO₄ suppressed the rise of the cathode surface pH but to a much smaller degree.     

The electrodepositions of copper and nickel from trifluoroacetate-H2O baths

In the present study, the electrodepositions of copper from the Cu(CF₃COO)₂CF₃COOHH₂O bath and nickel from the Ni(CF₃COO)₂NH₄ClH₂O bath, were studied.In the copper electrodeposition from Cu(CF₃COO)₂ (100 g/l)CF₃COOH(0.1 N)H₂O bath, the cathode current efficiency showed about 100% and the anode current efficiency showed over 100% at low cd. In the nickel electrodeposition from Ni(CF₃COO)₂ (200 g/lH₄Cl(15.0 g/l)H₂O bath, the efficiencies of the cathode and anode were about 100%. The range of current density to obtain bright and smooth copper and nickel deposits were 4.0 ～ 24 A/dm², 5.0 ～ 16 A/dm² respectively, and the cross-section of the electrodeposits showed a granular structure.The rates of the electrodeposition of copper and nickel from the above-mentioned baths were controlled by the charge-transfer reaction in the same way as in the reaction in non-aqueous solution[1, 2].     

方波伏安法快速测定镀镍液中的镍含量

由于利用传统度镍液中的镍含量时共存离子的干扰不易消除,在此采用方波伏安法进行测定。阐述了该方法的原理,探讨了试验条件,共存离子对测量结果的影响。结果发现,在ＰＨ＝１０．０的ＮＨ３．ＨＯ２－ＮＨ４ＣＩ缓冲液中以三乙醇胺为掩蔽剂,镍（Ⅱ）于－１．１２Ｖ（ｖｓＳＣＥ）出现极谱峰,在镍（Ⅱ）浓度为２～２０ｇ／Ｌ范围内镍（Ⅱ）浓度成线性关,镍（Ⅱ）检出限为０．５ｍｇ／Ｌ。该方法简单、快速、准确度和灵敏度高,     

分光光度法测定光亮镍及珍珠镍镀液中的镍含量

光亮镍和珍珠镍镀中镍的测定定通常采用EDTM滴定法,该法选择性低,易造成环境污染,本文采用分光光度法进行分析,探讨了测量波长,硫酸浓度及干扰元素等的影响,该法在镍含量为0－200mg范围内遵守比耳定律,测量结果准确,能满足实际生产的要求。     

Effect of nickel impurities on zinc electrodeposition

The kinetics of nickel-zinc co-deposition and the effect of nickel on zinc morphology have been studied by means of chemical analysis, X-ray diffraction and SEM observations of cathodic deposits obtained in various experimental conditions, including acid and alkaline baths. It has been shown that nickel ions, even if present in the electrolyte at very low concentrations (1 ppm), do not deposit under mass transport controlled conditions but are dragged by zinc ions whose concentration influences the nickel current. With regard to zinc morphology, it has been observed that nickel reduces the grain size of the zinc crystals formed during the electrodeposition.     

化学镀镍废液的处理及回收利用

化学镀镍废液的处理方法主要有化学沉淀法、催化还原法、电解法、离子交换法等。综述了这几种方法国内外的研究现状,并对其工艺原理及优缺点进行了介绍。综合考虑多方面认为,采用多种方法综合处理化学镀镍废液是一种综合利用资源、有利于环境保护、较为合理的处理方法。