Etching of SiOC ceramic foams

Polymer derived SiOC microcellular foams were etched by means of a 20 vol.-%HF solution. An increase in one order of magnitude in specific surface area (SSA) values compared to the unetched samples was observed. This SSA increase was accompanied by micro- and mesopores formation. The limited increase in the specific surface area was attributed to several factors: the smaller dimension of the etchable SiO2 nanodomains and the more amorphous nanostructure of these polymer derived ceramics compared to the sol-gel derived ones. Moreover a possible role of the carbon residue deriving from polymethylmetacrylate (PMMA) microbeads used as porosity source was supposed. Higher SSA values (up to 65 m(2) g(-1)) were reached by inducing a slight phase separation, accompanied by a growth of the nanodomains size, and by an oxidative treatment that partly removed the residual carbon. Microcellular ceramic foams with a bimodal pore size distribution were produced.