Effect of early densification on foaming process of glass–calcium carbonate mixture

Abstract

The understanding of relationship between densification and foaming for preparation of foam glasses is still lacking. In this study, 128 powder compacts of glass-CaCO3 mixture were foamed isothermally for different time by varying glass particle size, foaming temperature and initial density of green compacts. The results showed that densification tends to take place in the early stage by viscous flow sintering prior to predominant foaming expansion. Therefore, there exists a critical time at which the maximum apparent density is reached, and it is correlated with both the densification rate and kinetics of CaCO3 decomposition. Such a densification has a minor effect on the minimum apparent density, however, it significantly impacts the evolution of pore structure including pore size and homogeneity, depending on glass particle size. Coarse-particle glass and high load applied on the green compacts, leading to higher green density, is favorable for slow development of pore structure with time. In this case, the foam glasses were endowed with small size of pores and homogeneity. This study provides an insight into how to obtain low apparent density and the optimum microstructure by the interplay between densification and foaming.