Fundamental Study on Electrodeposition of Co and Co-P Films

Co and Co-P alloy films were electrodeposited on a rotating disk electrode. The experimental results suggested that the ratio of partial current density consumed by phosphorus deposition to the total current density was relatively small and 2+ that the competit ion of eleetrodeposition of Co ion and H2 gas evolution determined the phosphorus content in the Co-P film. The addition of phosphorus acid to electrolyte solution was also found to depress the preferential g rowth of the (i 00) plane, wh ich was observed in the electrodeposition of Co film, and induced the growth of (002) plane. A further addition of phosphorus acid resulted in the formation of amorphous- l ike film. The diffusion model, taking into account the dissoci-ation of H3PO3 molecules, was applied to calculate the pH value at the cathode surface. The surface concentrations of Co 2§ and H3PO3 were also estimated f rom the partial current densities. The phosphorus content of the electrodeposited film has been correlated to the surface concentration of H3PO3 based on a concept of adsorption equil ibrium of H3PO 3. Adsorbed H3PQ molecules may hinder the surface diffusion of Co atoms, wh ich causes the formation of the amorphous- l ike structure of the electrodeposited film. Various kinds of amorphous metal films have been inten-sively studied f rom the standpoint of their resistance to corrosion and abrasion and also their excellent magnet i