Electrodeposition of Amorphous Ni-Mo Alloys from Ammonia Citrate Bath and Their Corrosion Resisitance.

Abstract

The preparation of amorphous Ni-Mo alloy films by electrodeposition from ammonia citrate baths with the addition of ammonia as a complexing agent was studied, and their corrosion resistance was determined.Amorphous Ni-Mo alloy films were deposited from baths of a pH of 9.0 containing nickel sulfate (0.13∼0.18mol/L) and sodium molybdate (0.08∼0.13mol/L) such that total metallic (Ni2++Mo6+) ion concentration was a constant 0.26mol/L with 0.32mol/L of sodium citrate and 0.53mol/L of ammonia as a complexing agent at a pH of 9.0 and current densities of 8∼20A/dm2.Electrolytic aging produced an increase in the molybdenum content of the electrodeposited film to 37wt% as well as arise in cathodic current efficiency. Peeling of the films was reduced, and no cracking occurred. Films with a molybdenum content of about 28wt% or more exhibited an amorphous structure. Electrochemical measurements and immersion tests were curried out at 30°C in both 1N H2SO4 and 1N HCl solutions, and the results indicated that amorphous Ni-Mo alloys had greater self-passivation ability and lower corrosion rates than did crystalline alloys, and showed better corrosion resistance than SUS 304 stainless steel in the above mentioned solutions.