A monophase mullite fibrous porous ceramic produced by a gel-casting method

Monophase mullite fibrous porous ceramics were successfully fabricated by a simple aqueous gel-casting method with mullite fibers as raw material, ρ-Al₂O_3, and microsilica as gelling agents, and the precursor of mullite. The effects of the ratio of powder (ρ-Al₂O₃ powder and microsilica) to mullite fiber on the phase composition, microstructure, sintering behavior, mechanical and thermal properties, and permeability of porous ceramics were investigated. The results showed that mullite fibers were bonded by in-situ formed mullite via the reaction of ρ-Al₂O₃ and microsilica to create a bird's nest structure. As the ratio of powder to mullite fibers was varied from 2:1 to 1:3, the porosity was increased, the bulk density was decreased, the pore size was enlarged, the fractal dimension of the pores was decreased, and the compressive strength of the porous ceramics was decreased accordingly. Due to increased porosity, pore size, and decreased fractal dimension, the prepared porous ceramics have good permeability (the Darcy permeability is up to 4.8 × 10⁻¹² m²). At the same time, the thermal conductivity of the porous ceramics was increased because of the increased thermal transfer in the fiber and pores.