MODIFICATION OF SOLUTION COMPOSITION IN THE ELECTROCHEMICAL DEPOSITION OF NI-FE ALLOY-FILMS

Modifications of commonly used sulphate-chloride solutions for electrodeposition of thin Ni-Fe alloy films on cylindrical electrodes were investigated. The introduction of Fe3+ ions increases the cathode polarization, reduces the current efficiency of the Ni-Fe deposition process and gives uncontrolled film composition. Spontaneous oxidation of Fe2+ to Fe3+ can be inhibited by the addition of l-ascorbic acid. This agent does not reduce the process efficiency. No significant changes in the alloy composition occur. It seems that the replacement of saccharin by thiourea changes the deposition of the iron in the Ni-Fe alloy from a diffusion-controlled process to a discharge-controlled process. It was established that hydrogen evolution is highly dependent on the thiourea concentration in the solution. In the case of higher thiourea concentrations (above 2 mM) the current efficiency of the process decreases considerably. This can be attributed to thiourea's taking part in the electrode processes. The Ni-Fe films obtained contained sulphur inclusions and had become less corrosion resistant. The application of sulphamate solutions for depositing thin cylindrical Ni-Fe films is recommended provided that the sulphamic acid is of high purity. Solutions prepared from technical grade sulphamic acid had low current efficiencies of the order of 30-50%. © 1979.