Atmospheric Corrosion of Thin-film Recording Media in a Clean Environment and Its Evaluation

Abstract

Atmospheric corrosion of thin-film cobalt-based magnetic recording media was studied by surface analysis and by experimental deposition of dummy particles. Thin-film corrosion tends to be affected by adhering dust particles even in clean environments, and the incidence of corrosion depends on the size of dust particles. Surface corrosion is more conspicuous away from rather than directly under adhered dust. Corrosion in these areas involves water adsorption in the porous overcoat, cobalt dissolution from the magnetic layer, and migration of cobalt ions through the carbon overcoat. We propose the following thin-film corrosion model: atmospheric vapor condenses in the crevice between the carbon overcoat and adhered dust, this water penetrates and diffuses in the carbon overcoat, and a differential aeration cell is generated by the difference in dissolved oxygen concentration between the edge and center of the areas with diffused water. Furthermore, we propose a corrosion test method for thin-film recording media that uses uniform particles.