Effects of flux components on the properties and pore structure of ceramic foams produced from coal bottom ash

Ceramic foams with low bulk density and uniform tiny pores were successfully prepared from coal bottom ash (CBA) by introducing only a small amount of sodium carbonate and magnesium oxide as fluxing agents. The effects were investigated of the Na2O and MgO contents on the bulk density, the crystalline phases, the pore structure and the compressive strength of the ceramic foams. The results indicated that, at firing temperature, an increase in Na2O content significantly improved the pore formation ability of CBA powder compacts. The samples that contained 8 wt% Na2O exhibited a low bulk density and large-sized pores but the Na2O caused a dramatic change in bulk density with firing temperature. Nevertheless, if MgO was introduced, the increasing MgO content resulted in a further decrease in bulk density as well as a decrease and homogenization of the pore size. The improved pore structure of samples that contained more than 4 wt% of MgO contributed to a relative increase in their compressive strength. It was concluded that MgO can be used as a foam stabilizer for ceramic foams produced from CBA powder. 4-6 wt% of MgO combined with 6 wt% of Na2O in the composition of CBA powder was determined to be the best proportions for preparing ceramic foams with an optimal pore structure and good mechanical properties.