Transformation Characteristics of Gucheng Quartzite and Assessment of Its Application Prospects

ABSTRACT: With the aim to well understand the relationship between the composition and properties of quartzite in Gucheng, three types of quartzite from a mining area in Gucheng have been investigated. This paper focused on the phase composition evolution and thermal expansion behavior of them under different thermal histories in the temperature range of 1200 °C to 1500 °C, and subsequently, the true density and microstructure were also measured and analyzed. In addition, inclusion analysis was conducted. The results indicate that black quartzite has a higher Fe content, white quartzite has relatively higher Al and K contents, and gray quartzite has a higher Ca content. Furthermore, all three types of quartzite almost completely transform into cristobalite after heat treatment at 1500 °C, although the transformation rates vary slightly with increasing temperature. The thermal expansion of the three types of quartzite exhibits similar trends, but gray quartzite exhibits greater residual expansion. It is believed that the phase transformation plays a dominant role in the total expansion, together with the sintering effect accelerated by the glass phase. At the same time, the microstructure of quartzite was also significantly influenced by the phase transformation process. The gas/liquid inclusion analysis revealed that all three types of quartzite have high inclusion content. The black quartzite contained only 5% transparent particles, the lowest among the three specimens, none of the three quartzite types are suitable for direct use in high-purity quartz applications.