Quantifying the time-dependent contributions of volumetric microwave energy deposition and conductive heat redistribution inside rock materials

Microwave treatment can reduce the strength of hard rock to improve the efficiency of breakage and mining, which is regarded as a highly promising green measure. This weakening process relies on the conversion of electromagnetic energy into thermal energy within the rock, which triggers thermal stress concentration and microcrack propagation. The thermal field capable of causing fracture is caused by a combined effect of electromagnetic energy deposition and conductive heat transfer. However, the lack of quantitative separation between these two contributions makes it difficult to identify the actual heating mechanism and the effective microwave-affected depth. Here, we developed a thermal-contribution quantification analysis by combining a thermal-conduction barrier experiment with coupled electromagnetic–thermal modelling. To comprehensively explore the heat contribution, this study was conducted from three aspects: rock depth, exposure time, and rock heterogeneity effects. The analysis revealed that electromagnetic heating contributes the most to the thermal fields across all rock depths and irradiation periods, even though heat conduction plays an increasingly important role as irradiation time increases. The minimum contribution rate of electromagnetic heating was 85.51% at 3 cm rock depth under 3 kW microwave irradiation for 2 min. From the rock depth perspective, the contribution rates of outward heat conduction remained high, range between 22% and 24.5% at depths of 2 to 7 cm within the rock, while the contribution rate for inward heat conduction presented high absolute values around 15% at 1 to 3 cm depths. For time scale, the contribution rate of inward and outward conductive heat transfer as well as electromagnetic heating raise with the increasing irradiation time. In terms of rock heterogeneity, it redistributes both contributions by creating mineral-controlled hotspots, and its effect on temperature and heat contribution at a certain position in the rock can be amplified by irradiation time. This work provides a heat-source quantitative separation framework which not only offers a clearer basis for interpreting the thermal field and mechanism, but also provides a pathway for exploring the heating mechanism in other materials that are hard to observe the interiors under external heat source treatment.