Crystallinity dependence of thermal and mechanical properties of glass-ceramic foams

Glass foams and glass-ceramic foams exhibit great potential in thermal insulation of buildings, consequently reducing the necessity for heating or cooling, and ultimately contributing to energy saving. In this study, we prepared glass-ceramic foams utilizing silicate glass as starting material and CaCO3 as foaming agent through a thermochemical process. Foams with varying degrees of relative crystallinity were produced by controlling temperature and duration of isothermal heat treatment. The foaming mechanism in the glass-ceramics was discussed by analyzing how the heat flow, mass, and volume evolve within the powder mixture during dynamic heating. The crystallization in glass did not show any clear trend on the compressive strength of glass foams. On the other hand, the thermal conductivity of the glass-ceramic foams increases with increasing relative crystallinity. The calculated solid thermal conductivity exhibited a minimum at low relative crystallinity (<20 %). These findings are crucial for designing high performance glass-ceramic foams for thermal insulation, potentially also for fabricating glass-ceramic foams using waste glasses.