Glass–Ceramic Foams from Borosilicate Glass Waste

In this study, we reported the studies on a glass–ceramic foam with wollastonite and cristobalite micrometric crystals prepared by sintering a borosilicate glass waste with organic binder as foaming agent. The waste glass, coming from the dismantling of washing machine, was characterized by high CaO content and low-temperature sinterability. The effect of the temperature on the sinter-crystallization ability of the borosilicate glass waste was followed with thermal analysis, heating microscopy, and electron scanning microscopy (ESEM) observations. Additionally, the effect of temperature on the evolution of crystalline phases and density variation was monitored with XRD and density measurements. The softening started at 800°C and crystallization at 845°C to be completed at 900°C with a linear expansion of 38–40% in the range 850–900°C. Wollastonite and cristobalite were identified as crystalline phases in variable proportions dependently upon temperature. No crack evidence was found at high ESEM magnification even though cristobalite crystals were present. The final products showed a total porosity around 78–79% and an apparent density of about 0.5 g/cm3, in line with common porous closed-cell glass foams used for thermal insulation