Determination of Thermal Effusivity of Lunar Regolith Simulant Particle Using Thermal Microscopy

This study aimed to measure the thermal effusivity distribution on a lunar regolith simulant (FJS-1) using a thermal microscope and to calculate the average thermal effusivity and thermal conductivity using density and specific heat. Moreover, discussions were conducted based on the results of the microstructural analysis of the sample. The FJS-1 particles were embedded in an epoxy resin and polished to a mirror finish. The samples were analyzed using scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM–EDS). X-ray diffraction (XRD) was performed to identify the mineral phases in FJS-1. The results of SEM–EDS and XRD showed that a single sand particle was composed of several minerals, such as anorthite and olivine. Then, the thermal microscope was used to obtain the distribution of the thermal effusivity of a particle from the mirror-finished sample in a 1 × 1 mm² area with intervals of 10 μm. The measured thermal effusivity correlates with the SEM image of the sample. Anorthite has a small thermal effusivity of 1.99 ± 0.31 kJ·s^−0.5·m⁻²·K⁻¹, while olivine has a large thermal effusivity of 2.73 ± 0.35 kJ·s^−0.5·m⁻²·K⁻¹. In both cases, the thermal effusivity was found to be of the same order of magnitude as the reported values. The average thermal effusivity and conductivity of a single particle were determined to be 2.4 ± 0.6 kJ·s^−0.5·m⁻²·K⁻¹ and 2.6 ± 1.3 W m⁻¹·K⁻¹, respectively, based on the proportion of existing phases.