Effect of the CaO content and decomposition of calcium-containing minerals on properties and microstructure of ceramic foams from fly ash

Abstract

Abstract Ceramic foams were prepared using fly ash, sodium carbonate, magnesia and SiC powder by the powder foaming method. The influence of the CaO content and decomposition of calcium-containing minerals on the bulk density, pore structure, compressive strength, and crystalline structure of ceramic foams was systematically studied by adding calcium oxide, calcium carbonate, and gypsum. The results show that the sintering and foaming process is inhibited by the formation of anorthite at higher CaO contents. The bulk density increases gradually as the CaO content increases from 2.18 to 8.13 wt%, while the average pore size, apparent porosity, and homogeneity coefficient first come up and then down with the CaO content. On the other hand, a small CaO amount improves compressive strength due to a decrease in porosity and an increase in the crystalline phase with the CaO content. But when the CaO content becomes higher than 4.25 wt%, the pore structure deterioration results in a significant decrease in compressive strength. Moreover, due to the generation of large amounts of gas during the CaSO 4 decomposition in the foaming process, gypsum contained in fly ash has a significant effect on the foaming process and pore structure.