IN-SITU X-RAY POWDER DIFFRACTION INVESTIGATION OF QUARTZ LOW TO HIGH PHASE TRANSITION

Quartz (SiO₂) is the most common and abundant mineral which undergoes significant phase transitions under varying temperature and pressure conditions. The phase transitions involve structural changes, accompanied by volume and thermal expansions. These structural changes may impact the physical properties of quartz, such as its thermal stability, density, mechanical strength, piezoelectricity, and optical properties. Understanding these phase transitions is essential for applications in geoscience, materials science, and various industrial processes such as glassware, electronics, and ceramics where quartz is applied as a critical raw material.

High-temperature X-ray diffraction (HT-XRD) is an analytical technique used to study the behavior of materials under varying temperature conditions. In this study, phase transformations in a quartz sample from Arkansas, AR (USA) were observed. The goal was to monitor the quartz structural transformations in real-time as the temperature gradually increased from 25 °C to 1595 °C using HT-XRD. High-temperature experiments revealed the α ↔ β phase transition in quartz at 500 °C with substantial anisotropic changes in the unit cell volume, followed by the formation of cristobalite at 750 °C and tridymite at 1450 °C. Crystallite size significantly impacts a material reactivity. The crystallite size of the sample was calculated using the Scherrer equation. Temperature increases generally lead to the formation of larger crystallite domains. The mean crystallite size as calculated using Scherrer equation increased from 158 to 192 nm when the temperature increased from 25 to 1250 °C. However, the crystallite size decreased from 192 to 150 nm in the temperature range 1250–1595 °C. Since the melting point is inversely proportional to the average crystallite size, raising the temperature above annealing point (1215 °C) and close to the melting point can enhance lattice disorder, leading to the observed reduction in crystallite size.