Synthesis of hybrid organic-inorganic sol-gel coatings for corrosion resistance

H-1-C-13 and H-1-Si-29 CP/MAS NMR spectroscopy has been used to characterize the structure of sol-gel derived hybrid materials prepared from 3-glycidoxypropyltrimethoxysilane (GLYMO) and tetraethylorthosilicate (TEOS) as a function of hydrolysis water ratio and organic content. H-1-C-13 CP/MAS NMR data indicate that the concentration of hydrolysis water (R value) has a fundamental effect on the nature of the acid-catalyzed hydrolysis and ring opening products. H-1-Si-29 CP/MAS NMR data suggest that for low R values, the ormosils are composed of a silica network with epoxide groups randomly dispersed throughout. At high R values, epoxide functionalities were found to coat the surfaces of dense silica particles. Salt spray analysis indicates that the corrosion resistance behavior of thin films derived from GLYMO-TEOS ormosils decreases as the concentration of hydrolysis water increases and improves as the organic content in the film increases. These observations can be related to the underlying thin film structure.