Solid-state diffusion during the selective dissolution of brass: chronoamperometry and positron annihilation study

The anodic dissolution of α-brass was investigated by chronoamperometry in the solutions containing Na 2 SO 4 , NaCl, H 2 SO 4 and CuCl 2 , respectively, at 30 °C. The transient currents were caused by the sole dissolution of zinc from brass at the appropriate potential. The results show that the current-time behavior follows the Cottrell law in the initial period of alloy dissolution. The diffusion coefficients obtained for zinc in α-brass are of the order of 10 −15 −10 −13 cm 2 s −1 , depending on the solution composition. Positron Lifetime Spectra have been measured for α-, β-, γ- and ε-brass specimens before and after corroding in 1% CuCl 2 solution. It was found that their dezincification rate depended on the rate of production of the excess (di)vacancies in the dezincification layer. It indicates that the solid-state diffusion of zinc atoms occurs via (di)vacancies created on the alloy surface during corrosion. Thus, the divacancy diffusion mechanism was supported experimentally. The inhibition of dezincification by traces of arsenic in the alloy and the effects of certain medium components on the value of the diffusion coefficient can be well explained in terms of the divacancy diffusion mechanism.