Effect of high vacuum environment on the microwave melting behavior of lunar regolith simulant

The high vacuum environment is one of the most prominent characteristics of the extreme conditions on the lunar surface. It has a significant influence on the application of in situ lunar construction technologies. This study comparatively investigates the microwave melting behavior of lunar regolith simulant under high vacuum and atmospheric environment. Particular attention is paid to differences in temperature evolution and melt pool expansion during the melting process. In addition, the morphology, macro- and microstructural characteristics, mineralogical and elemental compositions, as well as the macro- and micromechanical properties of the melted samples are systematically analyzed. The results show that, during microwave melting of the lunar regolith simulant, the high vacuum environment accelerated the melting rate, with an average increase of 1.7–3 times. In addition, the high vacuum environment promoted melt pool expansion and prolonged the cooling and solidification processes. The melted samples under high vacuum exhibited greater quality and volume but lower density. Among these, the average quality and volume increased by 2.4 and 4.0 times, respectively, whereas the average density decreased by 1.7 times due to gas escape and related effects. Moreover, the high vacuum environment favored mineral crystal growth and effectively reduced glass phase formation, with the glass content decreasing by an average of 10.6%–34.8%. In terms of mechanical properties, the pronounced variation in micromechanical properties is mainly attributed to the heterogeneity of mineral crystals. Their uniaxial compressive strength was also significantly lower than that of the melted samples under atmospheric environment, with an average decrease of 9.7 times. The findings of this study provide a theoretical foundation for the development of lunar in situ construction technologies.