Anodic dissolution of cobalt suicides in sulfuric acid solutions

Anodic dissolution of suicides Co2Si, CoSi, and CoSi2 in 0.5 M H2SO4 solutions with and without NaF is studied by polarization methods coupled with an atomic-absorption analysis. In the absence of NaF, anodic stability of cobalt silicides is higher than that of cobalt itself by 3–6 orders of magnitude and increases in the series Co2Si < CoSi < CoSi2. Cobalt selectively dissolves from the lattice of silicides, while silicon simultaneously oxidizes to SiO2. The process is controlled by the diffusion of elemental and oxidized cobalt in the suicide and the SiO2 surface layer, respectively. The anodic dissolution rate of silicides markedly increases in the presence of NaF, while their anodic stability becomes less different.