Porous mullite templated from hard mullite beads

Porous mullite bodies were developed by spark plasma sintering (SPS) amorphous mullite beads of about ∼30 μm in diameter at two temperatures, 950 and 1300 °C. Materials showed a close random stacking of solid spheres that retained their original packing but slightly flattened at the contacts in some cases. Depending on the thermal history, the beads were partially or fully crystallized. The thermal conductivity of the different porous mullite materials was analyzed as a function of the microstructure. Owing to the particular porous network, high gas permeability and very low thermal conductivities (1–2 W m−1 K−1) were achieved, among the lowest reported for sintered mullite materials.