Changes in glossiness, electrical properties and hardness of red sandstone after thermal treatment

Abstract

The physical properties (glossiness, hardness, capacitance and electrical impedance) of red sandstone after thermal treatment at different temperature will be performed differently. The experiments show that the entire process can be divided into three stages. (1) 100–400 °C: as the temperature increases, the amount of water that exists as free water inside red sandstone is reduced, and micro-cracks begin to appear at the interior. (2) 400–800 °C: dehydroxylation of red sandstone occurs, and the thermal expansion rate of the quartz-based minerals reaches its maximum value at 600 °C. As a result, fractures develop in the sandstone and the surface becomes rougher. Meanwhile, changes in the color of red sandstone may be related to changes in iron. (3) 800–1300 °C: the quartz, feldspar and other minerals melt. Meanwhile, the high-temperature metamorphism of the red sandstone results in a complete color change. Smooth enamel crystals appear on the surface, which forms rocks similar to metamorphic rocks. The mineral composition and structure change before and after 800 °C, and the capacitance and electrical impedance change dramatically at this point.