Passivity breakdown and stress corrosion cracking of α-brass in sodium nitrate solutions

The anodic behaviour and SCC susceptibility of pure copper and four α-brasses of different zinc alloy concentration in a 1 M NaNO3 solution was studied by means of potentiodynamic polarisation curves and constant potential slow strain rate experiments. SCC was exclusively observed when the potential was equal to or higher than a certain critical value (Ec) at which pitting initiated under slow dynamic straining. It is concluded that the same SCC mechanism should be operating during SCC of copper and α-brasses in sodium nitrate, sodium nitrite and copper (II) nitrate solutions.

Research highlights
► The anodic behaviour and SCC susceptibility of Cu–Zn alloys are studied in a 1 M NaNO3 solution.
► Cu–Zn alloys exhibit susceptibility to SCC in sodium nitrate solutions at potentials higher than the breakdown potential.
► The crack velocity measured for Cu–Zn alloys strained in a 1 M NaNO3 solution change with the copper alloy concentration in the same way as reported for Cu(II) nitrate and NaNO2 solutions.
► The SCC of Cu–Zn alloys in NaNO3, NaNO2 and Cu(II) nitrate solutions result from the same process.