Deposition of SiOx films from hexamethyldisiloxane/oxygen radiofrequency glow discharges: Process optimization by plasma diagnostics

This paper describes the preliminary results on the utilization of thin film deposited in Plasmas fed with hexamethyldisiloxane-oxygen (HMDSO-O-2) mixture for the corrosion protection of Mg alloys. The corrosion behavior of coated substrates has been evaluated by means of impedance measurements performed in aerated 0.1 M Na2SO4 solution. Interesting and promising results have been obtained when a suitable plasma pretreatment is performed both with hydrogen and CF4 fed plasmas and therefore when the extent of surface oxidation is reduced or when the magnesium surface is fluorinated. As a matter of fact, the charge transfer resistance, R-ct, increases from about 60Omegacm(2) for the uncoated alloy to more than 90 kOmegacm(2) after deposition of a 1300 nm thick SiOx film.