The inhibition of the stress corrosion cracking of 70/30 brass in nitrite solution with additions of alloying arsenic and arsenic anions

Abstract

The inhibitive effect of arsenic (As) on stress corrosion cracking (SCC) of 70/30 brass in 1 N NaNO 2 solution has been investigated using slow-strain rate tests (SSRT) at a strain rate of 3 × 10 −6 l/s. The effectiveness of inhibition with additions of arsenic alloying element to brass and arsenic anions (AsO 2 − and H AsO 4 2−) into solution has been evaluated. The results showed that the inhibitive effect of alloyed As was limited. Appreciable inhibitive effect was observed only in the brass containing 0.03–0.1% As at free corrosion potential and at applied potentials greater than 0 mV. The alloyed As content up to 0.45% caused a deleterious effect. The additions of arsenic anions into solution were effective in inhibiting the SCC. The effectiveness increased with the decrease of potential and increase of As concentration: 1 g/l As added as arsenite (AsO 2 −) completely eliminated the SCC of brass at −100 mV (SCE). For a given As concentration, the addition with arsenite was more effective than the addition with arsenate (H AsO 4 2−) at −100 mV; this order of inhibitive effect reversed at potentials greater than −50 mV. It was observed that arsenic had the effect of inhibiting both crack initiation and crack propagation. Supplementary tests revealed that arsenic anions also inhibit the SCC of pure copper in 1 N NaNO 2. The measurements of polarization behaviour demonstrated that arsenic anions significantly suppressed the anodic dissolution of both brass and copper in the nitrite solution. The results are discussed based on the chemisorption mechanism for the inhibitive effect of arsenic.