Plasma CVD grown Al2O3 and MgAl2O4 coatings for corrosion protection applications

The development of active corrosion protection systems for metallic substrates is an issue of prime concern. The objective of this work was to demonstrate the applicability of plasma enhanced CVD (PECVD) in growing protective top oxide layers over sol-gel deposited organosiloxane (R-SiOx; water based inorganic-organic hybrid coating formulation containing 3-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane, crosslinked with hexamethylmethoxymelamine) coating to improve its thermal stability, chemical inertness and corrosion resistance. [MgAl2((OBu)-Bu-t)(4)H-4] and [AlH2((OBu)-Bu-t)](2) were used as single source precursors for depositing MgAl2O4 and Al2O3 thin films respectively. The coating systems namely, Al2O3/R-SiOx (ALSI) and MgAl2O4/R-SiOx (MALSI) were comparatively analyzed towards their corrosion protection behaviour. The post annealed PECVD deposited films were uniform, transparent and exhibited good adhesion as confirmed by focused ion beam scanning electron microscope (FIB-SEM) cross sectional analysis. ALSI and MALSI bilayer systems were found to be stable over temperatures as high as 600 degrees C. Corrosion performance of the coating systems effectively demonstrated the protective function of ALSI and MALSI bilayer system. However, it was observed that ALSI outperforms MALSI in this application.