AGGREGATION PROCESS IN SILICA AEROGELS ON SINTERING

The ultrastructural evolution of aerogels on sintering into glass must be understood on the basis of a detailed description of a solid backb one and porosity. Silica aerogels from 'sonogels' have been studied ov er a wide length-scale range, using small-angle X-ray scattering and g as adsorption measurements. An aggregation model of a hierarchical nat ure can be formulated with a variable clustering index (N is the numbe r of elementary units inside a cluster) and hierarchical ratio (size o f a cluster in terms of the size of the elementary unit). The results reveal a change in the hierarchical level during the sintering process , which is ultrasonic dose-dependent.