Crystalline Phase Analysis and Thermal Expansion Coefficient Calculation of Quartz-Sand/Corundum Composites

Quartz-sand/corundum composites have been successfully produced by a simple solid-state reaction approach. The composites with corundum weight fractions of 10%, 20%, and 30% were prepared through grinding mixtures of purified Indonesian quartz sand and commercial high purity corundum for a half-hour with an addition of 3% polyvinyl alcohol. The composites were shaped into discs and pressed prior to the sintering at 950 °C and 1050 °C to form compact ceramic composites. The crystalline phase verification within the samples was conducted by means of X-ray diffraction (XRD). The coefficient of thermal expansion (CTE) of the composites was semi-theoretically evaluated, after being taken into consideration the XRD data analysis results, by means of Halpin-Tsai formula. The detected major crystalline phases within the sintered samples, based on the XRD profiles analysis, were quartz-SiO₂ and corundum-Al₂O₃. Meanwhile, the minor crystalline phases were wollastonite-CaSiO₃ (below 7%) for all samples and cristobalite-SiO₂ (around 1%) for the composite with 1050 °C sintering temperature. Generally, the addition of corundum into the quartz-sand/corundum composites reduced the CTE, having the value from 10.5 to 11.5 ppm/°C.