Cold foaming of cellular glass

logo_smallThis sounds like energy by cold fusion, but in this case it is real.  Prof. Enrico Bernardo from the Engineering University of Padua invented a new process to foam glass below 80°C. The motivation for this invention is quite clear.

enricoEnrico does not want to limit him self to the foaming of “easy” soda lime glass but he wants also foam glasses which are eager to crystallize. Such glasses are already crystallizing during sintering and does not foam due to the crystallization. Glasses obtained from waste incinerators (bottom ash, fly ash) are a typical example. In fact, all the efforts are based on the philosophy to recycle any waste.

The full process is described in a paper. The alkali-activation method (geopolymers) is used to create a gel. Air is introduced in this gel (foaming) by mechanical stirring. The resulting foams are hardened at 75°C. After this step, the foam has already all its properties like compressive strength, thermal conductivity, ….. To eliminate leaching out or to make the foam chemically stable, a temperature step at 700°C (firing) is needed. Because the foam is formed, crystallization in this last step is not a problem anymore.

The foams are open celled, which opens a new market for cellular glass, based on “real” waste and as a consequence at very low cost. I think now on a cheap alternative of low and high density gas concrete. But if the foam can be evacuated to low pressures (0.1 Torr) and packed, a low thermal conductivity of the order of 0.025 W/mK can be reached.

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