Synthesis of in-situ mullite foam using waste rice husk ash derived sol by slip-casting route

In this study, mullite foam ceramic is synthesized via a simple slip-casting method without using any pore producing additive or agent, in order to avoid the emission of greenhouse gases (mainly CO2) from the matrix. Waste rice husk ash (RHA) extracted sol (solid contain similar to 7.5 wt%) as an alternative of conventional silica sources along with active alumina is used for the preparation of slip-casting slurry. About 22 wt% solid containing slurry is casted in the plaster of paris (POP) mold. The casting mass is dried at 110 degrees C and fired at 1100 degrees C, 1200 degrees C, 1250 degrees C, 1300 degrees C, 1350 degrees C, and 1400 degrees C. Several properties like phases, microstructure, porosity, density, mechanical strength, and thermal conductivity are comprehensively investigated with the foam samples. At 1250 degrees C fired sample is retained mullite dominating phase in the matrix. The single-phase mullite is formed at 1300 degrees C fired sample with 75.99% total porosity, 11.07 MPa compressive strength, and thermal conductivity of 0.153 W/m.k. Furthermore, the strength value and thermal conductivity are increased and porosity is reduced with the increasing firing temperature. The obtained results exhibit that the waste RHA derived sol is capable to produce low-temperature in-situ mullite foam through slip-casting route without generating the pollutants (mainly CO2 up arrow).