A COMPARATIVE-STUDY ON THE PASSIVATION AND LOCALIZED CORROSION OF ALPHA-BRASS, BETA-BRASS AND ALPHA-BRASS IN BORATE BUFFER SOLUTIONS CONTAINING SODIUM-CHLORIDE .1. ELECTROCHEMICAL DATA(BETA)

The passivation and localized corrosion of alpha-, beta-, and (alpha beta)-brass in borate-boric acid buffer solutions (pH 9) containing d ifferent NaCl concentrations (c(NaCl)) were studied comparatively usin g conventional electrochemical techniques at 25 degrees C. The passiva tion of brass in borate-boric acid buffer was due to the electroformat ion of a complex passive layer consisting of ZnO.xH(2)O and Cu-2 O-CuO . In NaCl-containing borate-boric acid buffer the breakdown of the pas sive layer occurs Leading to pitting corrosion when the applied potent ial exceeds a certain critical value, E(b). For a given type of brass, the value of E(b) is shifted negatively as c(NaCl) is increased. At a constant c(NaCl) the localized corrosion resistance of brass increase s in the following order (alpha + beta)-brass congruent to beta-brass < alpha-brass. For all brass the localized corrosion resistance was lo wer than that of polycrystalline Cu, but considerably greater than tha t of polycrystalline Zn. Passive film composition and de-alloying can account for the localized corrosion resistance of these alloys.