A comparative study of the passivation and localized corrosion of α-brass and β-brass in borate buffer solutions containing sodium chloride:: III.: The effect of temperature

The passivation and localized corrosion of a-brass and P-brass in an aqueous borate-boric acid buffer (pH 9) containing different concentrations of NaCl (c(NaCl)) in the temperature range 5 degrees C less than or equal to T less than or equal to 45 degrees C were studied comparatively by potential sweeping at 2x10(-2)Vs(-1) and 2x10(-4)Vs(-1) and de-alloying measurements. The passivation of alpha-brass and beta-brass was related to the electroformation of a complex ZnO . xH(2)O/Cu2O layer, its thickness and compactness presumably increasing with temperature. For both alpha-brass and beta-brass immersed in an aqueous NaCl-containing buffer, pitting corrosion was observed as the value of the breakdown potential (E-b) was exceeded. At constant temperature, the value of E-b shifted negatively as either c(NaCl) or the zinc content in the alloy was increased. For beta-brass, the value of E-b decreased slightly with increasing temperature in the range 5 degrees C less than or equal to T less than or equal to 45 degrees C. In the range 5 degrees C less than or equal to T less than or equal to 25 degrees C, for alpha-brass the Value of E-b was close to that reported For copper, whereas for T > 25 degrees C it approached those values measured for beta-brass. De-alloying measurements in aqueous 0.5 M NaCl indicate that zinc surface enrichment of alpha-brass was responsible for the decrease in pitting corrosion resistance at T > 45 degrees C. (C) 1998 Elsevier Science Ltd. All rights reserved.