Effect of pH on the Stress Corrosion Cracking of α-Brass in Chlorate Solution

Abstract

The stress corrosion cracking (SCC) behaviour of 72/28 brass has been studied in sodium chlorate solutions at ambient temperature over a pH range of 2 to 12, at the open-circuit potential and at controlled potentials, using the slow strain rate technique. A constant strain rate of 1·5 × 10–5 S⁻¹ was applied. Under free corrosion conditions, stress corrosion cracking was observedfor the specimens tested in the pH range 4–9. Application of cathodic potentials prevented SCC, while application of anodic potentials accelerated SCC in the whole range of pH studied. It was observed thatlhe severity of cracking increased with increase of potential, which was in the range, + 200 to + 400 mVH. It was also noticed that, at a fixed applied potential, the SCC severity increased with an increase in pH in the range of pH 2 – 6, stayed relatively constant up to pH 8 and decreased thereafter. Metallographic inspection revealed that, under open-circuit potential and up to a potential value of ≃200 mVH, the mode of cracking was predominantly intergranular, while at potentials > 200 mVH, transgranular cracking predominated. The results support the anodic dissolution mechanism of SCC.