Foam glass

This article has an unclear citation style. The references used may be made clearer with a different or consistent style of citation and footnoting. (May 2017) (Learn how and when to remove this message)

Foam glass or expanded glass is a porous glass foam material. It is used as a light weight, moisture- and fireproof building material with thermal and acoustic insulating properties.

It is made by heating a mixture of crushed or granulated glass and a blowing agent (chemical foaming agent), often carbon or carbonates such as 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. Foam glass gravel is produced by letting the glass mass fracture during the cooling process. Often recycled glass, sometimes from disused CRTs, is used as a base material.^[1] Igneous rock such as obsidian and industrial waste slag may also be used.

While the term porous glass often indicates glass with pores in the nanometre- or micrometre-range the pore size of foam glass is usually within 0.5 to 5 mm, and the pores make up 80%~90% of the total volume.

Chemical foaming agents facilitate the release of the gaseous phase upon heat treatment.^[2][3][4][5] In general, these additives are either a) redox and neutralization agents, or 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.

Expanded glass is widely used in the building industry and for other industrial insulation applications as well as a filler in composite materials.^[6]