THE USE OF ELECTRODE FILMING IN ELECTRODEPOSITION OF METALS

It was demonstrated that the formation of insoluble films of compounds containing the metal to be deposited furnished a method of controlling the relative rates of competing electroreduction processes. It was shown that additives, such as halide and thiocyanate ions, that caused the precipitation of insoluble copper(I) films in the electrodeposition of copper would cause an increase in the current efficiency and would increase the relative amount of copper deposited in binary alloys. It was also shown that an insoluble adherent film [Pb6O5(NO3)2] was formed on the cathode during the deposition of lead from alkaline solutions. The formation of this film was aided by the introduction of a protective cationic surfactant. Therefore, addition of the surfactant caused increases in current efficiency an increases in the lead concentration in electrodeposited lead alloys. Deposition of thallium in the presence of oxygen leads to the formation of insoluble thallium (III) oxide at the cathode by the reaction of the metal with hydrogen peroxide formed by reduction of oxygen. However, this insoluble oxide did not adhere to the cathode, therefore the addition of oxygen did not cause increases in the relative concentration of thallium in binary electrodeposited alloys. Instead, since a corrosion process was involved, the current efficiency and relative amount of thallium in the alloy decreased upon addition of oxygen. Thus, in oxygen containing solutions, addition of sulfite ions which react with hydrogen peroxide cause increases in the current efficiency and increases in the relative amount of thallium in electrodeposited binary alloys.