Study of the suitability of silica based xerogels synthesized using ethyltrimethoxysilane and/or methyltrimethoxysilane precursors for aerospace applications

Abstract

Silica based materials were synthesized using ethyltrimethoxysilane (ETMS) and/or methyltrimethoxysilane (MTMS) precursors by sol–gel technology, in order to ascertain if their properties are suitable for aerospace applications. When ETMS was used alone and in equimolar ETMS/MTMS mixtures, no gel formation took place and a resin-like precipitate was observed. After drying, a compact tablet was formed. When mixtures of 25% ETMS/75% MTMS and MTMS alone were used, gel formation occurred and xerogels were produced upon drying. Chemical and structural characterization of the obtained materials was performed using Elemental Analysis, FTIR, XRD and SEM. Bulk density, specific surface area, contact angle and the thermal behavior were also evaluated. For materials from ETMS, the chemical structure grows preferentially in one direction and, in the case of MTMS the growth follows a 3D pattern. The use of ETMS precursor leads to a significant increase in the product density, accompanied by a decrease in the specific surface area. It also leads to a decrease in the thermal stability limit of the synthesized materials. Then, ETMS precursor is less appropriate than MTMS precursor for space applications. However, ETMS co-precursor in mixtures with MTMS contributes to the increase in the hydrophobic character of the synthesized materials.