A.M. Abd El-Halim

Effect of bath constituents and some plating variables on the electrodeposition of cadmium from acidic chloride baths

Abstract The electrodeposition of cadmium from acidic chloride electrolytes containing 0.3 M CdCl2·(5/2)H2O, 0.1 M HC1, 0.4 M H3BO3 and 2.0 M NH4Cl (bath I) was investigated. Electrodeposition in the presence of 0.5 M sodium potassium tartrate and 5 g gelatin 1−1 as organic additives (bath II) was also studied. The effects of the bath constituents, the plating current density i, the duration t and the pH on the cathodic polarization, the efficiency and the throwing power of cadmium electroplating from each bath, as well as on the morphology and the microhardness of the as-plated cadmium electrodeposits, are discussed. It was found that the additive-containing bath II yields more compact finer-grained brighter and harder plates than the additive-free bath I. The optimum conditions for cadmium electroplating from bath II at 25 °C are as follows: i, 1.0–1.6 A dm−2 5–15 min; pH 3.8–4.5.

The role played by the anions in cadmium electroplating from some acidic baths

Abstract The electrodeposition of cadmium from four selected baths with nearly the same composition except for the anion was examined. These baths were based mainly on acidic aqueous solutions of cadmium sulphate, cadmium chloride, cadmium bromide and cadmium iodide. It was found that the nature of the anion influenced to some extent the cathodic polarization and the throwing power of the cadmium electroplating from each bath; it also influenced the growth morphology and microhardness of the cadmium plates.

Electroplating of cadmium from acidic bromide baths

Earlier work on the electroplating of cadmium from acidic bromide solution containing 0.3M CdBr2·4H2O, 0.1M HC1, 0.4M H3BO3 and 2.0M KBr (Bath I) has been reviewed and extended to an examination of the influence of the organic additives 5g gelatin 1−1 and 2.5g melamine 1−1 (Bath II). The effects of the plating current density, plating time and pH on the cathodic polarization and the current efficiency of cadmium electroplating from Bath II, as well as on the morphology and the microhardness of the as-plated cadmium electrodeposits are discussed. It was observed that the additivecontaining Bath II yields more coherent, brighter and harder cadmium plates than the additive-free Bath I. The optimum operating conditions for obtaining satisfactory plates from Bath II at 25° C are:i=0.6–1.6 A dm−2;t=10–15 min and pH 3.6–1.9.Earlier work on the electroplating of cadmium from acidic bromide solution containing 0.3M CdBr2·4H2O, 0.1M HC1, 0.4M H3BO3 and 2.0M KBr (Bath I) has been reviewed and extended to an examination of the influence of the organic additives 5g gelatin 1−1 and 2.5g melamine 1−1 (Bath II). The effects of the plating current density, plating time and pH on the cathodic polarization and the current efficiency of cadmium electroplating from Bath II, as well as on the morphology and the microhardness of the as-plated cadmium electrodeposits are discussed. It was observed that the additivecontaining Bath II yields more coherent, brighter and harder cadmium plates than the additive-free Bath I. The optimum operating conditions for obtaining satisfactory plates from Bath II at 25° C are:i=0.6–1.6 A dm−2;t=10–15 min and pH 3.6–1.9.

Some characteristics of Ni-Co alloy powders electrodeposited from dilute sulphate baths

Abstract Electrodeposition of Ni-Co alloy powder was carried out utilizing dilute sulphate electrolytes containing concentrations of Ni 2+ and Co 2+ ions within the range found in some industrial effluents. The electrolytes examined had the composition 0.0125 – 0.0750 mol l -1 NiSO 4 ·6H 2 O, 0.0125 – 0.0500 mol l -1 CoSO 4 ·7H 2 O, 0.23 – 1.00 mol l -1 (NH 4 ) 2 SO 4 , 0.2 – 0.4 mol l -1 H 3 BO 3 and 0.07 mol l -1 Na 2 SO 4 ·10H 2 O. The effects of the bath constituents, pH and current density on some characteristics of the alloy were investigated. Increased concentration of NH + 4 ion in the bath was found to increase both the cathode potential and current efficiency and decrease the nickel content of the alloy. The cathode potential decreased with increasing concentration of either of the metal ions in the bath; a corresponding increase in the current efficiency and the metal content in the alloy were also observed. An increase in pH increased the cathode potential and current efficiency without appreciably affecting the alloy composition. The catalytic activity of the alloy powder towards the decomposition of 0.4% H 2 O 2 solution increased with increase in the concentrations of NH + 4 and/or CO 2+ ions in the bath and with raising the pH. The surface morphology of the alloy powder was greatly influenced by the above-mentioned variables. The structure of the alloy, as revealed by X-ray diffraction studies, was dependent on its composition.

Effect of some addition agents on the electrodeposition of cadmium from acidic chloride baths

Abstract In this paper a further development of a chloride-based cadmium plating bath containing 0.3 M CdCl2·( 5 2 )H2O, 0.1 M HCl, 0.4 M H3BO3 and 2.0 M NH4Cl (bath I) is described. The influences of the individual addition agents thiourea, coumarin, Ni2+ ions and I- ions on the characteristics of cadmium electrodeposition from acidic chloride electrolytes containing 0.3 M CdCl2·( 5 2 )H2O, 0.1 M HCl, 0.4 M H3BO3, 2.0 M NH4Cl, 0.5 M sodium potassium tartrate and 5 g gelatin 1-1 (bath II) were studied. Bath II including a combination of the four above-mentioned additives was denoted bath III. The additive-containing bath III produced a brighter but less hard cadmium deposit than the additive-free bath II. The individual effects of melamine, 3-methyl-4-p-methoxyphenylazopyrazol-5-one, dimethylformamide (DMF) and DMF with biacetyl-bis-(benzoylhydrazone) on the cathodic polarization and current efficiency of cadmium electrodeposition from baths II and III, as well as on the morphology and microhardness of the as-plated cadmium deposits, were investigated and discussed. However, each of the additives employed exerted, to a different extent, a polarization-increasing effect and a change in the growth morphology of the cadmium deposits from either bath II or bath III. The additives melamine, DMF and DMF with biacetyl-bis(benyzoylhydrazone) failed to achieve any improvement in the brightness of the cadmium deposits from either bath II or bath III but increased the hardness of those from bath III. 3-methyl-4-p-methoxyphenylazopyrazol-5-one led to the production of the brightest cadmium electrodeposits (from bath III) and the hardest cadmium electrodeposits (from bath II).

On the anomalous phenomenon of Co-Ni alloy electrodeposition

Abstract A study was carried out on the electrodeposition of cobalt, nickel and Co-Ni alloy from buffered (0.4 M H3BO3) simple sulphate baths containing 0.125 M CoSO4·7H2O, 0.875 M NiSO4·6H2O and 0.125 M CoSO4·7H2O with 0.875 M NiSO4·6H2O respectively. The cathodic polarization curves of the individual deposition of the parent metals and the alloy as well as the effects of the current density on the alloy composition and the partial current efficiencies of cobalt and nickel in the alloy were determined. The results were used for the calculation of the actual polarization curves for the codeposition of cobalt and nickel. A comparison between the calculated and the measured polarization curves indicated a marked decrease in the polarization of cobalt and an increase in that of nickel during codeposition. An explanation of the anomalous codeposition of Co-Ni alloy was provided on the basis of the changes in the overpotentials of the parent metals as a result of their codeposition in a solid solution.

Electrodeposition of catalytically active nickel powders from sulphate baths. I. Effect of bath constituents

Abstract A detailed study was made of the influence of the sulphate bath constituents: 0.3 - 0.0125 NiSO 4 ·7H 2 O (I), 0.05 – 0.23 (NH 4 ) 2 SO 4 (II), 0.1 – 0.4 H 3 BO 3 (III) and 0.07 – 0.35 mol l −1 Na 2 SO 4 ·10H 2 O (IV) on the electrodeposition of nickel powder. The cathodic polarization, current efficiency, growth morphology, crystallite size and catalytic activity of the electrodeposited nickel powders were affected to different extents by the bath constituents. A highly pure nickel powder characterized by a small crystallite size (776 A) and moderate catalytic activity was obtained from a bath containing: 0.0125 (I), 0.23 (II), 0.1 (III) and 0.07 mol l −1 (IV) at a current density of 10 A dm −2 and electrolysis time 60 min. at 25 °C. Structural studies with a scanning electron microscope are given and a reaction mechanism for the electrolytic powder deposition is discussed.

Electrodeposition of catalytically active nickel-thallium alloy powders from sulphate baths

The electrodeposition of nickel-thallium alloy powder was investigated from acidic sulphate baths containing 0.0125 NiSO4·6H2O, 0.005–0.020 Tl Cl, 0.05–0.23 (NH4)2SO4, 0.1 H3BO3 and 0.07 mol l−1 Na2SO4 · 10H2O. The polarization curves, the percentage composition and the current efficiency of the electrodeposited alloy powders were determined as a function of the bath composition. In addition, some properties of the deposits were examined such as the surface morphology, the structure as revealed by X-ray diffraction analysis and the catalytic activity towards the decomposition of 0.4% H2O2 solution. The results indicate that the characteristics of the alloy deposition and the properties of the alloy powder are affected to different extents by the bath composition.

Electrodeposition of thallium powder from sulphate baths

Abstract The characteristics of the electrodeposition of thallium powder from sulphate baths containing a relatively low Tl + ion content (0.005-0.020 mol 1 -1 ) were examined. The cathodic polarization curves for thallium electrodeposition were greatly affected by the bath composition and the pH. The percentage cathodic current efficiency was relatively low and increased with increasing concentration of Tl + ions in the bath to a maximum of 17%. According to the electrodeposition conditions, thallium powders were deposited in dendritic forms with different morphologies and grain sizes. X-ray diffraction analysis of the electrodeposited powders proved that the thallium was contaminated with Tl 2 O and Tl 2 O 3 .

Electrodeposition of catalytically active nickel powder from sulphate baths: Effect of some operating variables

Abstract Fine-grained nickel powder has been successfully electrodeposited from a very dilute all-sulphate bath of the composition 0.0125 moll −1 NiSO 4 · 7H 2 O, 0.23 moll −1 (NH 4 ) 2 SO 4 , 0.1 moll −1 H 3 BO 3 and 0.07moll −1 Na 2 SO 4 · 10H 2 O. The current efficiency of the deposition process and the surface morphology, as well as the catalytic activity of the electrodeposited nickel powder towards the decomposition of 0.4% H 2 O 2 solution, were found to be fundamentally influenced by the operating variables pH, current density and duration of the electrolysis. X-ray diffraction studies revealed that the nickel powder is free from oxide and hydroxide contaminations. Under the optimum operating conditions ( pH = 7.7 j = 13.3 A dm −2 and t = 10 min) the selected bath produced a nickel deposit characterized by catalytic activity approaching 100% with a deposition efficiency around 18%.