Foaming of borosilicate glasses by chemical reactions in the temperature range 950-1150sup(o)C

Sintering experiments with glass powders showed, that silicon carbide and silicon nitride are very effective foaming agents for borosilicate glasses over a wide range of temperatures. They allow control of the pore size and pore structure of the foamed products by variation of their concentration and by admixture of transition metal oxides. The pronounced crystallization tendency of the glass powders to cristobalite can be inhibited by addition of alumina-containing materials. The reactions of SiC and Si3N4 with the atmosphere, with constituents of the glass and with the mineral components are rather complex. Depending on the foaming agents used, the gas present in the closed pores is composed of CO, CO2, N2 and H2. (orig.)