Ellipsometric study of passive films on the stainless steel SS304

Four surface treatments were given to AISI 304 SS in the cold-worked and he at-treated condition. The surface treatments were : exposure to laboratory air, exposure to 20% HNO3, anodization in H2SO4 with and without dissolved oxygen. Passive films thus obtained were characterised ellipsometrically an d the refractive index and thickness values were measured. It was seen that the refractive index of films obtained in all cases except one was around 2.52, while in the case of the film obtained after anodizat ion in H2SO4 with dissolved oxygen, it was seen to be 2.46. The thickness o f films varied from 46 to 129 Angstrom depending on the surface treatment. Heat-treatment appeared to have little effect on the type of film formed.