Effect of pH Value on Electrochemical Performance of Passive Films Formed on Brass in Boracic Acid Buffer Solutions

The passive films on brass in boracic acid buffer solutions with different pH values were studied by electrochemical methods and Mott-Schottky analysis. The results showed that under different pH conditions, the brass showed obvious passivation state in special potential range. When pH was at 8, 8.8 and 9.5, the passive films were porous, while pH was at 10.5 and 12.5 the passive films were compact. The Mott-Schottky plots for the passive films on the brass surface were linear with a negative slop and indicated the behavior of p-type semiconductor. With the increase of pH, the film impedance increased firstly, and then decreased. When pH value was at 10.5, the film possessed the maximum impedance, the minimum acceptor density(NA) and the best corrosion resistance.