Thermal conductivity of highly porous ceramic foams with different agar concentrations

• Highly porous ceramic foams were firstly prepared by combining the direct foaming method and agar consolidation method, using fly ash as the raw material, which is economical, practical, environment friendly.
• Meanwhile, the production of ceramic foams is a useful way of recycling large amounts of fly ash, which could efficiently resolve the disposal problem of fly ash.
• Additionally, the change of thermal conductivity of highly porous ceramic foams along with different amounts of agar gelation agents was systematically researched.

The ceramic foams with low thermal conductivity (0.0579–0.0826 W m−1 K−1) were successfully prepared by using fly ash as main raw material, combining direct foaming method and agar consolidation method. Additionally, the change of thermal conductivity of highly porous ceramic foams along with different amounts of agar gelation agents was systematically researched. The experimental results show that the samples with different amounts of agar gelation agents exhibit similar pore morphology. As the content of agar increased the pore size decreased first and then increased, but the porosity continued to decrease. Meanwhile, lower thermal conductivity was achieved with higher porosity, smaller pore size and more small pores of sintered product, but the porosity dominated.