Impact of temperature on chemical, thermo-physical, and mechanical properties of four rock materials for sensible thermal energy storage

The objective of this research study is to analyze the properties of four rock types, namely rhyolite, andesite, microdiorite, and granodiorite, as candidates for heat storage. These samples were collected from Oued Tensift near the city of Marrakech in Morocco, with the aim of selecting the most suitable aggregate for thermocline storage and determining the optimal temperature. We identified the chemical composition using techniques such as scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDX), X-ray fluorescence (XRF), as well as the structural characteristics of the rocks using X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). XRD and FTIR were applied to both raw samples and those subjected to five thermal cycles at temperatures of 300 degrees C and 600 degrees C. Furthermore, we determined the essential thermophysical and mechanical characteristics required for sensible thermal energy storage at temperatures ranging from ambient to high temperatures. To achieve this, techniques such as thermogravimetry-differential thermal analysis (TGA-DTA) were employed to assess mass stability at 1000 degrees C, dilatometry to observe changes in length during heating and cooling up to 600 degrees C, differential scanning calorimetry (DSC) to evaluate the variation in specific heat capacity for working temperature of 400 degrees C and hardness test to estimate mechanical properties. The study reveals that granodiorite experiences microcrack formation at high temperatures. In contrast, other rocks, especially rhyolite, confirm their potential for high-temperature energy storage applications.