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

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 $\mathrm{1,100}°\mathrm{C}–\mathrm{1,200}°\mathrm{C}$, 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, $\beta$-cristobalite formed in desert sand and remained at room temperature; the content increased with increased sintering temperature. The quartz-anorthite ceramics were composed of $\alpha$-quartz, $\beta$-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 (${5.1\times 10}^{-6}·{\mathrm{K}}^{-1}$), the highest linear shrinkage (24.2%), and the highest bulk density (${2.5\mathrm{g}/\mathrm{cm}}^3$) 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.

Inexhaustible supplies of desert sand and huge reserves of industrial solid waste cause serious negative effects on the environment. In addition, the manufacturing of building materials consumes tremendous amounts of inorganic minerals. The use of idle desert sand and industrial solid waste to produce useful building materials is an effective route to reduce environmental problems and mineral consumption. Desert sand and fly ash contain quartz, feldspar, mullite, and amorphous phase—similar to the composition of silicate materials. Therefore, they can be used as sustainable raw materials for ceramic production through the use of new techniques. The present study introduces a new material—anorthite-based ceramic—and a method for synthesizing it using low-cost desert sand and fly ash as raw materials. The anorthite-based ceramic can be used in the construction and building fields—the largest consumer of silicate materials—in tiles, bricks, porcelain, lightweight filling materials, and insulation materials. This is of great significance to the economization of mineral resources, resource regeneration, and improvement to the environment.