Contrasting effects of various factors upon the properties of foam ceramics and the mechanisms of crystalline phase reconstruction and microstructure regulation

The application prospects of foam ceramics are closely linked to their properties; however, the influence mechanism of the raw material composition and sintering parameters on the properties of foam ceramics remains obscure. In this study, the properties of SiO2–Al2O3–Na2O–K2O-based foam ceramics at various sintering temperatures and sintering times, and with different SiC contents, ratios of Al2O3 to SiO2, and fluxing agent contents were determined. Significant discrepancies in the variation trends and strengths of different influencing factors were observed. To interpret these phenomena, the crystalline phases and microstructure of the foam ceramics were analyzed, and the results indicated that their compressive strength was jointly controlled by their crystal phases and microstructure; however, other properties depended only on the microstructure. Furthermore, analysis of the phase diagram and sintering process revealed that the chemical reactions between the basic materials varied, as the ratio of Al2O3 to SiO2 and the fluxing agent contents were varied, resulting in differences in the phase transition temperature, liquid phase content, and crystalline phases. Moreover, the sintering temperature, sintering time, and SiC content affected the microstructure of the foam ceramics by changing the liquid viscosity, reaction time, and foaming amount, respectively. Overall, our findings provide a theoretical basis for preparing foam ceramics with excellent properties.