Effect of addition agents on the properties of aluminum deposited from an aluminum chloride-sodium chloride melt

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1953
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Virginia Polytechnic Institute
Abstract

It was the purpose of this investigation to study the effect of addition agents on the electrodeposition of aluminum on copper from a fused bath of 80 per cent aluminum chloride and 20 per cent sodium chloride. The agents added and the concentrations studied were lead chloride, 0.5 and 1.0 per cent; aluminum thiocyanate, 0.5 and 1.0 per cent; chromic oxide, 0.5 per cent; sodium cyanide, 0.1 and 0.5 per cent; and vanadium pentoxide, 0.1 per cent.

The electrolysis was carried out in a 1000-millimeter beaker in a furnace heated by a 1000-watt element. The plating cell was fitted with a tight lid through which the electrodes could be adjusted.

The optimum current density range while plating from a bath of 80 per cent aluminum chloride and 20 per cent sodium chloride was 8.2 to 21.0 amperes per square foot. When aluminum was electroplated from a bath of 75 per cent aluminum chloride, 20 per cent sodium chloride, and 5 per cent lithium chloride, the plates did not adhere to the base metal. Also, the plates corroded to the base metal in a few days. The optimum temperature was found to be 356 °F.

Lead chloride, when added at a concentration of 0.5 and 1.0 per cent, produced a smoothening effect. The plates obtained at the former concentration were smoothest. However, the plates were rather easily corroded by the atmosphere. In contrast, chronic oxide at 0.5 per cent did not improve the smoothness of the plate but did improve considerably the corrosion resistance of the plate. Addition of aluminum thiocyanate caused formation of a black powder which was non-adherent. Sodium cyanide at 0.1 and 0.5 per cent did not improve the ductility and corrosive resistance of the plate to any extent. Vanadium pentoxide gave corrosive resistance and ductility to the deposit at lower current densities of 10 to 100 amperes per square foot and thin mirror plates at current densities between 100 and 500 amperes per square foot. The vanadium pentoxide was used at a concentration of 0.1 weight per cent.

In attempts to protect the plates from corrosion, applications of chemical treatment to the aluminum plate failed, as also did an application of lacquer.

The results obtained with the addition of lead chloride, chromic oxide, and vanadium pentoxide warrant further study to determine optimum operating conditions and limits.

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