Preparation of anorthite-based porous ceramics using high-alumina fly ash microbeads and steel slag

Abstract High-alumina fly ash microbeads and steel slag were used as main raw materials to synthesize feldspar porous ceramics via high-temperature solid phase sintering by adding pulverized coal as a pore-forming agent. The effects of the steel slag and pore-forming agent on the apparent porosity and flexural strength of porous ceramics were investigated. The phase composition and microstructure of porous ceramics were characterized using X-ray diffraction and scanning electron microscopy, and the results indicated that the added amount of steel slag was only related to the amount of liquid phase formed in porous ceramics. The higher the amount of steel slag added, the more the liquid phase formed. At the same sintering temperature, the higher the pore former content, the higher the porosity of the porous ceramics and the lower the bending strength. When porous ceramics were sintered at 1160 °C steel slag melted and fly ash microsphere structures were formed. When the porous ceramics were sintered at 1190 °C, the fly ash microsphere structure disappeared. After the internal liquid phase of the ceramic was formed, the lower the sintering temperature, the larger the porous ceramic structure factor, the more sensitive the flexural strength to changes in porosity and the higher the theoretical strength of ceramic densification. Moreover, as the sintering temperature decreased, the network structure formed during the reaction of fly ash microbeads with CaO greatly increased the flexural strength of fly ash ceramics. When the sintering temperature, sintering time and pore former content were 1170 °C, 120 min, and 10%, respectively, the obtained porous ceramics presented superior apparent porosity and flexural strength (49.21% and 12.88 MPa, respectively), and the main crystalline phase of porous ceramics was anorthite featuring pore size ranging from 5 to 50 μm.