Porous acicular mullite obtained by controlled oxidation of waste molybdenum disilicide

Highlights: • Waste MoSi₂ heating elements were used as starting material for fabrication of porous acicular mullite. • Calcined MoSi₂ powder was source of SiO₂ and pore former at the same time. • Porous acicular mullite is promising material for filtration of diesel engine exhaust. • Samples with decent mechanical integrity and porosity of more than 60% were fabricated. - Abstract: Porous acicular mullite was fabricated by using waste MoSi₂ heating element and Al₂O₃. Careful calcination of the pulverized heating element led to the formation of a mixture of MoO₃ and amorphous SiO₂. This mixture was employed as both SiO₂ precursor and pore former. The oxidation of MoSi₂ and mullite formation were studied. The effect of fabrication temperature on phase composition, porosity, grain morphology, and compressive strength of sintered mullite was examined. Pure mullite with porosity of more than 60% and compressive strength of ∼20 MPa was obtained at temperature as low as 1300 °C. The microstructure consisted of elongated, rectangular, prism-like grains which are known to be effective in filtration of diesel engine exhaust. The increase in sintering temperature caused the change of grain morphology and reduction in compressive strength