Recent advances in aerogel manufacturing

Abstract

In this lecture we would like to present some interesting new developments made recently at DLR, which might have some interesting application not only as superinsulating materials. Aerogels from biopolymers like cellulose and -carrageenan can be manufactured by dissolution of the polysaccharides in salt-hydrate melts at around 100°C yielding a highly viscous solution. Casting into molds or extruding through dies allows to prepare monoliths or fibres. Regeneration by alcohols and supercritical drying leads to very light aerogels with interesting structure, namely a nanofibrillar felt, and fascinating mechanical properties. We recently observed during experimentation with a classical resorcinol-formaldehyde aerogel solution, that suitable small modifications of chemistry (dilution, pH-value) and drying processes allows to vary the mechanical properties drastically, namely from hard and brittle, to brittle and corky, to semi-flexible and ultimately to a rubber elastic behavior. It looks as if these properties can be preserved even after conversion to carbon aerogels. Combining aerogels with honeycombs allows manufacturing big pieces of quasi-monolithic character with a non-linear superposition of the properties of both ingredients. Some examples of honeycombs filled with aerogels are presented. Finally, combining two types of aerogels allows to prepare new composites with interesting properties. Finally, if time allows, we would like to present an application of aerogels being close to industrial utilization: the usage of carbon and silica aerogels granulates in foundries to improve drastically sand cast products.