Microstructure and mechanical properties of high strength porous ceramics with high sewage sludge content

Sewage sludge is a by-product produced in the process of sewage treatment, which has characteristics of large yield, wide source, high pollution and strong harmfulness. The resource and harmless treatment of sewage sludge has attracted extensive attention all over the world. This research successfully produced environmentally clean porous ceramics using sewage sludge (SS) and kaoline (KE) as the main raw materials. The effects of sintering temperature on the crystalline phase, microstructure and mechanical properties of porous ceramics were also discussed. The results showed that all sintered porous ceramics contained various crystalline phases, such as mullite (3Al2O3·2SiO2), sillimanite (Al2SiO5) and hematite (Fe2O3), which laid a foundation for the development of mechanical properties. When sintered at 1250 °C–1400 °C, porous ceramics presented smooth surface, typical void structure and excellent mechanical properties due to the formation of liquid phase. And the porous ceramics gradually shrank and densified with the raising of sintering temperature, resulting in smoother surface and larger internal pores, so the density and shrinkage presented a continuous increasing trend, while the porosity continued to decrease. The maximum bulk density, sintering shrinkage and apparent porosity were 2.02 g/cm3, 20.34% and 34.74%, respectively. Also, the mechanical strength of porous ceramics reached the maximum value when the sintering temperature was 1350 °C, the compressive strength and flexural strength were 90 and 53 MPa, respectively.