R.M. Khalil

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.

Electrodeposition of catalytically active nickel powders from electrolytes of various anionic compositions

The electrodeposition of nickel powders from different baths containing the same chemical constituents except for the anion was studied. The baths were based mainly on aqueous dilute solutions of nickel sulphate, chloride, iodide, nitrate and acetate. A detailed study was carried out to investigate the influence of these anions on the cathodic polarization curves, current efficiency, growth morphology and catalytic activity of the electrodeposited nickel powders. The characteristics tested were affected to different extents by the nature of the anion employed. X-ray diffraction studies proved that the deposited powders were very pure and had the face centered cubic structure with the orientations {111}, {200}, {220}, {222} and {311} respectively.

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%.

Electrodeposition of catalytically active Co-Ni-Tl alloy powders from dilute sulphate baths

Cobalt-nickel-thallium alloy powders were electrodeposited from dilute metal sulphate baths of composition: 0.007–0.0245 mol l−1 CoSO4·7H2O, 0.0245–0.007 mol l−1 NiSO4·6H2O, 0.001 mol l−1 TlCl, 0.5 mol l−1 (NH4)2SO4, 0.07 mol l−1 Na2SO4·10H2O and 0.4 mol l−1 H3BO3. The cathodic polarization curves were traced during electrodeposition and utilized in the discussion of a reaction mechanism for the electrolytic powder deposition. The alloy composition and the cathodic current efficiency were influenced to a great extent by the bath composition (I) and slightly by the deposition current density (II). Irrespective of variables (I) and (II), the electrodeposition of the alloy belonged to the anomalous type. The surface morphology and the catalytic activity, towards the decomposition of 0.4% H2O2 solution, of the as-deposited alloy powders were affected predominantly by the percentage of cobalt in the alloy. X-ray diffraction studies showed that the alloys consisted mainly of the face-centred cubic nickel phase either alone or with minor proportions of face-centred cubic cobalt phase and hexagonal close-packed α-cobalt phase. The occurrence of the latter phases was observed only in the alloys with a higher cobalt percentage than nickel.