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

The passivation and localized corrosion of alpha-, beta-, and (alpha + beta)-brass in borate-boric acid buffer solutions (pH 9) containing different NaCl concentrations (c(NaCl)) were studied comparatively using conventional electrochemical techniques at 25 degrees C. The passivation of brass in borate-boric acid buffer was due to the electroformation 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 passive layer occurs Leading to pitting corrosion when the applied potential 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 increases in the following order (alpha + beta)-brass congruent to beta-brass < alpha-brass. For all brass the localized corrosion resistance was lower than that of polycrystalline Cu, but considerably greater than that of polycrystalline Zn. Passive film composition and de-alloying can account for the localized corrosion resistance of these alloys.