The formation of high strength porous thermal insulating ceramics from silicothermal reduction of coal slime under various atmospheres

Porous thermal insulation ceramics are prepared by utilizing semi-solid waste coal slime as the primary material and adding small amount of silicon as reductant. The effects of silicon content and sintering atmosphere on the phase composition, micro-morphology, mechanical and thermal performance of the sintered samples are studied. The results indicate that the addition of silicon can contribute to the consumption of carbon and silica in the calcined coal slime, and obtain high performance porous SiC/mullite ceramics under argon atmosphere or Si₃N₄/Sialon under nitrogen atmosphere. The mechanical performance of porous ceramics is more significantly enhanced by the addition of silicon when sintering under argon atmosphere than nitrogen atmosphere. When sintered at 1400 °C with a silicon content of 15 wt% in argon atmosphere, the porous SiC/mullite ceramics exhibit a maximum flexural strength of 50.0 MPa at porosity of 29.5 %, due to the formation of large amount of SiC whiskers. Meanwhile, the high remained flexural strength of 30.1 MPa after quenching from 800 °C in air and low thermal conductivity of 0.184 W m⁻¹ K⁻¹, exhibit great potential for the effective utilization of coal slime waste in thermal insulation ceramic preparation.