Preparation and Properties of Quartz-Anorthite Ceramics Synthesized Using Desert Sand and Coal Fly Ash

Abstract

Low-cost desert sand and coal fly ash were used to synthesize high-quality quartz-anorthite composite ceramics. The effects of the addition of fly ash on the densification of green bodies, phase transformation, microstructure, and mechanical and thermal properties were investigated. The results showed that the densification of green bodies occurred when they were sintered from 1,100°C–1,200°C, and the phase transformation of anorthite mainly occurred in fly ash from 846.9°C to 982.7°C. Temperatures of densification and anorthite transformation increased with increased addition of fly ash. At 1,100°C, β-cristobalite formed in desert sand and remained at room temperature; the content increased with increased sintering temperature. The quartz-anorthite ceramics were composed of α-quartz, β-cristobalite, anorthite, and amorphous phase. Anorthite was formed by the solid-state reaction of quartz, mullite, and other phases in the desert sand and fly ash and was promoted by liquid-phase sintering at higher temperatures. The highest bending strength of 115.6 MPa and highest hardness of 668.3 Vickers hardness (HV) were produced for samples with 40% by weight fly ash sintered at 1,100°C. Samples with 100% by weight added fly ash had the lowest mean thermal expansion coefficient (5.1×10−6·K−1), the highest linear shrinkage (24.2%), and the highest bulk density (2.5 g/cm3) when sintered at 1,200°C. The samples with 0%–60%, 80%, and 100% by weight added fly ash exhibited a low water absorption of 0.8%–1.8% when sintered at 1,100°C, 1,150°C, and 1,200°C, respectively. This technique can be feasibly used to fabricate civil engineering materials such as decorative ceramics, roof tiles, wall bricks, and insulation and filling materials.