Up-cycling of ‘unrecyclable’ glasses in glass-based foams by weak alkali-activation, gel casting and low-temperature sintering

A significant amount of glasses is landfilled because mainstream recycling solutions do not address the articles of specific chemical compositions, including opal glass and glass fibers residues. This manuscript suggests the up-cycling of these glasses through the production of highly porous glass foams. Fine glass powders were dispersed in weakly alkaline solutions, which were foamed by the combination of surfactant addition and intensive mechanical stirring. The cellular structures were stabilized first by the gelation of suspensions, upon drying, then by viscous flow sintering at 700–800 °C, for 10–60 min. The foams based on glass fibers reached an excellent strength-to-density ratio, due to the formation of closed cells and partial crystallization. The foams made from opal glass maintained a particularly uniform open porosity, and importantly, also retained the volatile and toxic fluorine due to the rapid, low-temperature sintering.