Preparation and characterization of coal slime-based porous ceramics for thermal insulation

Coal slime is a solid waste generated during coal washing and is rich in aluminosilicate minerals and carbonaceous components, making it a promising precursor for porous ceramics. In this study, coal slime was used as the main raw material to prepare porous thermal-insulating ceramics by a combined freeze-drying and sintering process. The effects of sintering temperature, water addition, and carbonaceous component content in coal slime on the microstructure, porosity, and thermal conductivity of the resulting materials were systematically investigated. The results showed that, compared with conventional oven drying, freeze-drying significantly suppressed green-body shrinkage and improved pore-structure retention, increasing the final ceramic porosity by approximately 14%. Under the optimum conditions of a sintering temperature of 1050°C, a water addition of 15%, and a carbonaceous component content of 55%, the obtained sample exhibited a porosity of 63.81% and good thermal-insulation performance, with thermal conductivities of 0.13 W·m−1·K−1 at 25°C and 0.17 W·m−1·K−1 at 700°C. These results demonstrate that the freeze-drying – sintering route can effectively construct a highly porous coal-slime-based ceramic structure and provide a new technical pathway for the resource utilization of coal slime in the preparation of porous thermal-insulating materials.