Mechanical properties of silica aerogels measured by microindentation: influence of sol–gel processing parameters and carbon addition

The response to deformation of several types of silica aerogels is addressed. Samples were produced by sol–gel and hypercritical extraction of the solvent. The influence of the silicon alkoxide concentration, the solvent, the drying procedure and the addition of carbon on the sampleʹs mechanical behavior are studied. Continuous loads and displacements were recorded using a nanoindenter. The experimental equipment has extreme sensitivity and small loads and penetration depths are possible. Youngʹs moduli, hardness values and elastic parameters for all samples are reported. Initial conditions for the TMOS sol–gel polymerization process, such as the solvent and metal alkoxide molar ratio, have a pronounced influence on the density of the aerogels, which is reflected in their mechanical behavior. Solvent selection and details of the drying procedure cause variations in the aerogel hardness and Youngʹs modulus. Power function relationships have been found between these mechanical parameters and the aerogel densities. It is found that the addition of a small amount of activated carbon to the sol (2%) has a pronounced influence on the Youngʹs modulus.