Growth kinetics of anodic oxide layers on cobalt silicides in sulphuric acid solutions

Abstract

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 (Co2Si and CoSi2) in 0.05 and 0.5 M H2SO4. We obtained the chronoamperograms in the time interval t = 0.3–3000 s with the oxide formation potentials of Ef = 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 H2SO4 solution; exposure to H2SO4 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 (Co2Si silicide with higher cobalt content; pretreatment of Co2Si 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.

Keywords

• cobalt silicide
• passivity
• oxide film
• growth kinetics
• high field model
• point defect model