Commercially fused mullite powder (crystallization, Maanshan Jinke Powder Engineering CO. LTD, P. R. China) with an average particle size of ~3 μm was used as the starting materials. The composition of the fused mullite powder is shown in Table 1. Acrylamide (AM) and N,N′-methylene-bis-acrylamide (MBAM) were used as organic monomers and cross linker. Initiator and catalyst for gelation reaction were ammonium presulfate (APS) and N,N,N,N-tetramethylethylenediamine (TEMED). Ammonium polyacrylate was used as dispersant. Foam agent and stabilizer for foaming were sodium dodecyl sulfate (SDS) and lauryl alcohol.