Abstract: Functional filling of mine thermal storage has achieved the synergy of deep underground ore deposits and geothermal energy extraction. It is urgent to develop functional filling materials with suitable phase change parameters and excellent physicochemical properties. Aiming at the current situation that microencapsulated phase change materials (MicroPCM) lead to the decrease of compressive strength and thermal conductivity of the backfill, this study carries out pre-experiments to investigate the strength characteristics and thermal properties of the phase change backfill. After determining an optimal MicroPCM additive amount, the study further investigated the effects of various silicon carbide (SiC) additions (ranging from 0% to 8% by mass) on the compressive strength, thermal conductivity, and specific heat capacity of the phase change backfill. The density, water secretion rate, and fluidity of the backfill were also tested. At the same time, scanning electron microscope-energy dispersive spectrometer (SEM-EDS) was used to observe its micro-morphology, and energy spectrum analysis was carried out to explain the macro-experimental phenomena, to explore its thermal energy storage stability under alternating high and low temperature cycles. The following conclusions were obtained that the specific heat capacity of the phase change backfill reached a maximum of 1.75 MJ/(m³·K) at 5% MicroPCM addition. The maximum density of the backfill, 1.67 g/cm³, occurred at 2% SiC addition. As SiC content increases, both fluidity and water secretion of the backfill gradually rised. The compressive strength and thermal conductivity of the backfill increased continuously with the increase of SiC addition, and the increase was 10.1% and 21.7%, respectively, to 6.64 MPa and 1.12 W/(m·K) at 4% addition, and then the growth trend decelerated. The specific heat capacity of the phase change backfill exhibited a trend of initial growth followed by decay with increasing SiC addition. The fluctuation amplitude remained small. The maximum specific heat capacity of 2.32 MJ/(m³·K) is achieved at 4% SiC addition, making this the recommended SiC content. After 500 cycles of alternating high and low temperatures, the compressive strength of the phase change backfill increased, with a positive correlation to SiC content. Both the coefficient of thermal conductivity and specific heat capacity decreased, with the rate of decline gradually diminishing. This study offers data for reference in practical engineering applications of thermal storage filling.

Key words: mineral-thermal co-mining, phase change backfill, thermal energy storage, silicon carbide, alternating high and low temperature cycles