The foaming mechanism and properties of SiO2–Al2O3–CaO-based foamed ceramics with varied foaming agents.

To select suitable high-temperature foaming agents, SiO 2 –Al 2 O 3 –CaO-based foam ceramics (SACFC) were successfully prepared with different foaming agents based on phosphorus tailings and coal gangue. The effects of high-temperature foaming agents (CaCO 3 , carbon black, MnO 2 and Fe 2 O 3) on the microstructure and compressive strength of the SACFC were investigated, and the corresponding foaming mechanism was revealed. The results indicated that CaCO 3 could increase the porosity of SACFC due to high-temperature decomposition. However, the precipitation of needle-like anorthite reduced the mechanical properties. Because the high-temperature oxidation temperature of carbon black was lower than the molten phase formation temperature, bubbles floated up and gathered on the surface of SACFC, leading to a decrease in strength. The continuous release of O 2 from MnO 2 during the sintering process promoted the growth and aggregation of large pores, which was detrimental to the strength. The CO 2 generated by the redox of Fe 2 O 3 by CO/C was the main factor for the foaming of SACFC. During the high-temperature foaming, the synergy effect of Fe2+ and Fe3+ promoted the formation of a uniformly distributed pore structure. When 2 wt.% Fe 2 O 3 was added, SACFC obtained the optimal comprehensive performance with bulk density and compressive strength of 0.78 g/cm3 and 3.50 MPa. [ABSTRACT FROM AUTHOR]