Foam glass

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Foam glass is a porous glass foam material. Its advantages as a building material include its light weight, high strength, and thermal and acoustic insulating properties. It is made by heating a mixture of crushed or granulated glass and a blowing agent (chemical foaming agent) such as carbon or limestone. Near the melting point of the glass, the blowing agent releases a gas, producing a foaming effect in the glass. After cooling the mixture hardens into a rigid material with gas-filled closed-cell pores comprising a large portion of its volume.

As to chemical foaming agents, there are several additives that facilitate the release of the gaseous phase upon heat treatment.^[1][2][3][4] In general, these additives are categorized into two categories: a) redox and neutralization agents, and b) decomposing agents. Redox and neutralization agents include nonoxide materials, e.g. carbides or nitrides. Decomposing agents include sulfates, e.g. CaSO₄•nH₂O,^{[citation needed]} organic compounds, and carbonates, e.g. CaCO₃. These materials release gas following decomposition and/or burning.