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.