Sol-gel processing of spirosilicates and their polymers

Abstract

The sol-gel transition of tetra-coordinated spirosilicate via hydrolysis and condensation under acidic and basic condition is examined to study the effect of catalyst, time dependence, temperature and the properties of obtained gel. The main advantage of this process is the low temperature employed, giving the formation of solid network with a high specific surface area. FTIR spectroscopy and TGA analysis were used to characterize the formation of siloxane bonds (Si-O-Si). It is found that spirosilicate can be hydrolyzed under both acid and base catalyzed conditions, and the condensation rate to silicates is shown to be at a minimum at 1% HC1 of 1M, which is the iso-electric point of silica. The prepared xerogel has a low-density and is amorphous material with surface area of 538 m2/g. Besides the catalyst media, the type of precursor also has a strong influence on the gel formation. The aminospirosilicate, six-membered ring, containing methylene and amino groups as substituents, was chosen for this study. The resulting xerogel determined by the fact that to obtain the Si-O-Si bonds, a higher concentration of solvent and higher temperature are more favorable, due to the length and branching of alkyl portion.