Fabricating protective silica/PMDS composite films for Mg alloy: Correlating bulk silica reinforcement with barrier performance

Abstract Despite numerous innovative research ideas and advances in coating manufacturing and testing, the phenomenon surrounding cathodic blistering in primers and top-coats is still unclear, especially in hypersaline media. In this work, we have discussed a new silica/polydimethylsiloxane synthetic route for Mg coating, and have also probed the fate of ionic/molecular migration within coating variants with varying crosslink densities in saturated NaCl solution. Corrosion resistance is observed to increase with silica content, and the optimum amount of tetra alkoxide needed to prepare an efficient corrosion resistant coating has been established. Improved corrosion resistance is attributed to the compact coating network with reticulate internal ceramic structures as well as the hydrophobic character of their polydimethylsiloxane (PDMS) moiety. These protective silica-modified composite coating materials were synthesized using two end-capped PDMS molecules bearing reactive groups, epoxypropoxypropyl terminated PDMS and aminopropyl terminated PDMS, added in a fixed ratio, in combination with tetraethoxysilane. Their barrier properties on Mg alloy were examined by electrochemical impedance spectroscopy while the extent of coating degradation and blistering were probed using scanning electron microscopy after chloride-induced treatment.