Preparation of homogeneous mullite fibrous porous ceramics consolidated by propylene oxide

Silica sol, one of the most commonly used binders in the fabrication of fibrous porous ceramics, can diffuse as the solvent evaporates during the drying stage, leading to an uneven structure of ceramics. To prevent the diffusion of silica particles and prepare homogeneous mullite fibrous porous ceramics, propylene oxide (PO) was introduced into the fabricating procedures. The effects of solid content of silica sol and the molar ratio of PO /silica phase (PO/SiO2) on the microstructure and physical properties of mullite fibrous porous ceramics were also investigated. The results demonstrated that PO addition strongly consolidated the mullite fibrous skeleton and helped to obtain a homogenous property, because silica phase had been consolidated in situ around the fibers during the gelation stage. Furthermore, the mullite fibrous ceramics prepared with PO addition showed an even microstructure and a much better compressive strength (1.489 MPa), compared with the ones prepared without PO addition (0.868 MPa). Finally, the solid content of silica sol showed a very strong relevance to the properties of the ceramics: the compressive strength raised from 0.731 MPa to 1.715 MPa with the solid content of silica sols increasing from 9 wt% to 18 wt%; while the molar ratio of PO/SiO2 had little: the compressive strength was around 1.480 MPa, with the corresponding molar ratios of PO/SiO2 ranging from 0.43 to 1.72.