Novel ‘inorganic gel casting’ process for the manufacturing of glass foams

A new technique for the production of glass foams was developed, based on alkali activation and gel casting. The alkali activation of soda-lime waste glass powders allowed for the obtainment of well-dispersed concentrated suspensions, undergoing gelification by treatment at low temperature (75 °C). An extensive direct foaming was achieved by mechanical stirring of partially gelified suspensions, comprising also a surfactant. The suspensions were carefully studied in terms of rheological behavior, so that the final microstructure (total amount of porosity, cell size) can be directly correlated with the degree of gelification. A sintering treatment, at 700–800 °C, was finally applied to stabilize the foams, in terms of leaching of alkaline ions. Considering the high overall porosity (88–93%), the newly obtained foams exhibited a remarkable compressive strength, in the range of 1.7–4.8 MPa.