ALBERT

Notes: Abstract The effect of the aluminium cathode microstructure on zinc nucleation has been investigated through surface examination by SEM and cyclic voltammetry. Zinc nucleation is strongly affected by the surface preparation and impurities present in the aluminium. For chemically pure aluminium, the oxide film on the surface plays an important role during zinc nucleation and crystal growth. Thickening the barrier oxide film inhibits nucleation while a reverse effect can be obtained by thinning or removing the oxide film. In the case of a dilute aluminium with iron alloy, following anodization, the Al−Fe intermetallic phases provide conductive paths through the oxide film resulting in zinc nucleation.

Notes: Abstract The effect of fluoride ions on the corrosion of aluminium in sulphuric acid and zinc electrolyte has been investigated through thermodynamic analysis and corrosion experiments. The solution chemistry of aluminium, zinc, and iron in aqueous solution in the absence and in the presence of fluoride ions was studied with the construction of the Eh-pH diagrams for the Al−F−H2O, Zn−F−H2O and Fe−F−H2O systems at 25°C. In the presence of fluoride ions, aluminium can form a series of aluminium-fluoride complexes depending on the fluoride concentration and pH whereas zinc and iron can form soluble or insoluble metal-fluoride complex species only at relatively high fluoride concentration and at higher pH values. Experimental results show that in the presence of fluoride ions, the corrosion of pure aluminium in sulphuric acid is due to uniform dissolution and the reaction rate depends on the fluoride concentration. In zinc electrolyte containing fluoride ions, zinc deposits onto the pure aluminium substrate spontaneously and the amount of deposited zinc also depends on the fluoride concentration. On the other hand, the presence of iron in the Al−Fe alloy accelerates the corrosion of aluminium in H2SO4 and zinc electrolyte significantly and prevents the deposition of zinc on the aluminium surface. The effect of fluoride ions on zinc adherence to the aluminium is also discussed.

Notes: Abstract Practical electrosynthesis of cuprous oxide powder was carried out on a laboratory scale in a cell specially constructed both with and without a diaphragm under the various operating conditions guided by the authors' previous research. The electrolysis was appraised in terms of the quality of the cuprous oxide product, the electrodissolution of the copper anode, and the SEM microstructure of the cuprous oxide powder. In a cell having a diaphragm, of which nylon fabric is the best, the optimal electrolysis operating conditions are: 250gl−1 NaCl, 0.1–1.0gl−1 NaOH, 500–1500Am−2, 80°C, perforated titanium sheet as the cathode, and around 3% cell volume of electrolyte circulation per minute. Under these conditions a product containing more than 97% cuprous oxide can easily be produced with very stable electrolysis and quite uniform dissolution of the copper anode. To eliminate the use of a diaphragm in the cell, the addition of sodium chromate, sodium dichromate, or calcium gluconate is effective in a sense, depending upon the requirements of the cuprous oxide product. For a product in which more than 95% cuprous oxide and no copper powder are required but a slightly higher content of chloride is allowable, sodium chromate and dichromate can be proposed for use with the former around 0.03–0.05gl−1 and the latter around 0.020–0.025gl−1, although the copper anode will not be perfectly evenly dissolved. For a product in which more than 97% cuprous oxide is demanded and a very small amount of copper powder is tolerated, calcium gluconate would be acceptable at around 4.5gl−1 with quite even dissolution of the copper anode. As to the auxiliary additives, hydrazine hydrate has a negative effect on the quality of the cuprous oxide product. Sucrose can cause a small increase in the chloride content but can make the particles of cuprous oxide more compact thereby increasing sharply its apparent density. Hydroxylamine hydrochloride is the best auxiliary additive which has a positive effect on the purity of the cuprous oxide product but produces no obvious change in the microstructure on the cuprous oxide particles. Even though most work has been concentrated on the electrolytic process, the subsequent processes are equally important: 65–70°C, distilled water for washing, benzotriazole in ethanol solution for stabilization of the cuprous oxide, and 100°C at a vacuum of less than 20mm Hg for drying seem to be satisfactory. A vacuum drying temperature of 55–60°C may be more appropriate to ensure against any oxidation of the product.

Notes: Abstract The preferred process for the production of cuprous oxide powder is by the anodic dissolution of copper in an alkaline solution of sodium chloride. The purpose of the present investigation was to develop a cuprous oxide process suitable for use on an industrial scale usiing the anode-support system, i.e. an anode comprising a titanium mesh basket loaded with small pieces of high-grade copper scrap. Laboratory investigations with this type of anode together with a titanium mesh cathode were conducted using cells having capacities up to 400 dm3. The recommended operating conditions based on 120 h runs using the 400 dm3 cell are as follows: NaCl: 250 g dm−3; c.d.: 6 A dm−2; CI: 0.37 A dm−3; temperature: 80°C; pH 10. Of particular importance, especially as regards the quality of the product and cell scale-up, is the relationship between the current and the volume of the electrolyte, denoted as Cl and expressed as A dm−3. The use of anode and cathode diaphragms of polypropylene obviated the need for additives to counteract copper redox reactions in the cell. The power yield was 0.8–0.9 kWh kg−1. The product was well within ASTM specification D912-65 for Cu2O for use in antifouling paints.

Notes: Abstract The preferred process for the production of cuprous oxide powder is via the anodic dissolution of copper in alkaline solution of sodium chloride. The principal reactions are as follows: $$\begin{gathered} Cu + nCl^ - = CuCl_n^{1 - n} (n = 2, 3) \hfill \\ 2H_2 O + 2e = H_2 \uparrow + 2OH^ - \hfill \\ 2CuCl_n^{1 - n} + 2OH^ - = Cu_2 O \downarrow + 2nCl^ - + H_2 O \hfill \\ \end{gathered} $$ In the present investigation the basic electrode processes were studied systematically under a broad range of conditions using linear sweep voltammetry. Variables studied include the concentration of sodium chloride and sodium hydroxide (i.e., alkalinity), temperature of the solution, two categories of additives (an inhibitor for preventing the deposition of spongy metallic copper powder on the cathodes, and a chemical reducing agent for reducing the cupric ions to the cuprous state), and the effect of carbonate ions (resulting from the spontaneous absorption of carbon dioxide from the air by sodium hydroxide). Useful guidelines concerning the electrolysis conditions, additives, and the concentration limit of carbonate ions have been established. The proper operating conditions can be considered to be as follows: 80–85°C, NaCl 240–260 gl−1, NaOH below 1 gl−1. Conditions pertaining to the use of additives are the following: calcium gluconate 0–5 gl−1, Na2CrO4 below 0.5 gl−1, Na2Cr2O7 below 0.25 gl−1, NH2OH·HCl below 2.5 gl−1, N2H4·H2O below 2.5 gl−1, sucrose 0–5 gl−1. Special attention must be given to eliminate or reduce the presence of carbonate ions in the electrolyte below 0.25 gl−1 Na2CO3.

Notes: Abstract 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.