Growth kinetics of anodic oxide layers on cobalt silicides in sulphuric acid solutions
The aim of this research was to study the growth kinetics of anodic oxide films on cobalt silicides in sulphuric acid solutions under potentiostatic conditions with various pretreatment of the electrode surface. For the study, we used low and high silicon silicides (Co<sub>2</sub>Si and CoSi<sub>2</sub>) in 0.05 and 0.5 M H<sub>2</sub>SO<sub>4</sub>. We obtained the chronoamperograms in the time interval t = 0.3-3000 s with the oxide formation potentials of E<sub>f</sub> = 0.2, 0.5, and 1.0 V (SHE). It was determined that the kinetics of the growth of oxide layers on cobalt silicides in acidic solutions greatly depends on the method of the silicide surface pretreatment (mechanical polishing; cathodic pre-polarisation in a H<sub>2</sub>SO<sub>4</sub> solution; exposure to H<sub>2</sub>SO<sub>4</sub> solution at the open circuit potential; exposure in a 2 M KOH solution; and exposure to 2% HF solution). In most cases, at low t (up to 30-50 s), the oxide films grew due to the ion migration in the strong electric field generated in the film during anodic polarisation. In some cases (Co<sub>2</sub>Si silicide with higher cobalt content; pretreatment of Co<sub>2</sub>Si in alkaline solution, further enriching the silicide surface with cobalt; and the region of high values of t), the point defect model seemed to be executed.