Oxidized barrier thin film from plasma grown polysiloxane coating over austenitic stainless steel

Polysiloxane films were deposited on an AISI316L stainless steel by remote plasma assisted chemical vapour deposition from 1.1.3.3-tetramethyldisiloxane. Thicknesses up to 5 μm were developed at a max growth rate of 400 nm min-1. The organosilicon films were then treated by remote plasma assisted oxidation and thermal treatment under air. The remote plasma assisted oxidation modified the surface composition of the coatings but let the bulk properties unchanged. The thermal treatment allowed a full mineralization of the coatings. Below 450°C the mineralization was partial and oxygen could not reach the coating core. This oxygen diffusion limitation was removed only for temperature of circa 600°C. The final surface composition appeared to be SiO1.8 which might represent a structure close to amorphous silica. After the most severe thermal treatment (600°C), neither desquamation nor cracking of the deposit occurred. The final composite is a steel substrate covered by a coherent layer of silica glass material. The steel underneath remained non-oxidized which testified of a strong diffusion barrier role vs. O2.