Theoretical Investigation on Heat Conduction of Multi-Sized Powders Sintered-Ceramic Based on Monte-Carlo Method

Thermophysical property prediction of sintered lunar regolith plays a crucial role in developing extraterrestrial thermal processing techniques for In-situ Resource Utilization (ISRU) on the lunar surface since the Moon has been regarded as an outpost of deep space exploration. It is widely established that well-designed heat treatments can improve the mechanical and thermal characteristics of powdered material for industrial applications. Varying particle sizes and compositions significantly impact the sintering neck formation and heat transfer between solid particles. Previous studies have developed several parametric expressions for thermal conductance between sintered mono-sized metallic or oxide particles, whilst only a few concentrated on evaluating the thermal conductivity of sintered bodies with multi-sized powders. In this study, we aim to establish an analytical model for predicting Effective Thermal Conductivity (ETC) of sintered ceramic samples fabricated using bi-sized particles. The sintering contact between grains was simulated by an algorithm that couples the Monte-Carlo method to neck formation theory. Here, samples of two oxides, alumina and silica, with different granularity fractions were prepared to simulate the lunar regolith. Volume ratios of small (radius of 5μm) to large (radius of 22.5μm) were 4:1, 2:1, and 1:2, respectively. The presented model was validated by ETC values obtained from a special-designed ETC measurement device and specific surface area within porous media measured by the BET technique. The simulated results agree well with the measured data of samples with single chemical component (RMSE=6.9%). However, the predicted ETC value for the mixture of two oxides (50/50 Vol.%) was about 50% higher than the measured. The formation of mullite, verified by X-Ray Diffraction (XRD) analysis, was probably the main reason for the overvalued modeling ETC. Besides, the presented model was applied to analyze the sensitivity of ETC to multiple factors. It can be concluded that sintering neck between multi-sized particles negatively influences the heat transport, resulting from the curvature deficiency at their junctions.