Optimising chemical vapour deposition
Magnesium (Mg) alloys are highly susceptible to corrosion and abrasion. Surface treatments do exist, but concerns regarding the associated environmental hazards have limited the use of Mg components in the automotive and aviation industries. The GROWTH Programme funded research into new, environmentally friendlier coating technologies. One such project, entitled NANOMAG, brought together experts from seven different countries, including materials scientists from the University of Bari in Italy. Their task was to optimise the deposition of a very thin layer of silicon oxide (SiOx) on the Mg surface that was capable of protecting against corrosion, tarnishing and other threats. They turned to Plasma-enhanced chemical vapour deposition (PECVD), specifically a Radio-frequency (RF) plasma with hexamethyldisiloxane, oxygen and argon as feed gases. Several experiments were performed during the three-year project. The best results were obtained when the substrate was first introduced to an RF plasma fed with hydrogen operated at high pressure but at a lower power density. The research team with the University of Bari has therefore recommended the inclusion of this pre-treatment step in order to facilitate adhesion of the SiOx.
