Preparation of foam ceramics from solid wastes: a study on the relationship between firing regime and properties by grey system theory

Foam ceramics were prepared by using 80 wt.% sand shale, 8 wt.% coal fly ash, 8 wt.% steel slag and 4 wt.% magnesite as raw materials and 0.3 wt.% SiC as foam agent. Effects of firing temperature and holding time on performance and phases of foam ceramics were investigated. Grey system theory was used to explore the correlation between pore structure parameters and thermal conductivity. The foam ceramics sintered at 1160 °C for 50 min exhibit the optimal comprehensive properties: bulk density of 0.651 g/cm3, flexural strength of 4.75 MPa, total porosity of 73.58%, closed porosity of 54.16%, and thermal conductivity of 0.081 W/(m·K). The Micro-CT results show that the pores with the average pore volume of 1.083 mm3 are relatively independent and uniform; and the pore wall thickness presents a normal distribution, which is conducive to improving the properties. Among the pore structure parameters, the fractal dimension has the greatest correlation with the thermal conductivity of foam ceramics.