Hybrid microwave sintering of a lunar soil simulant: Effects of processing parameters on microstructure characteristics and mechanical properties

Hybrid microwave sintering is considered a promising method to produce densified components using in-situ resources for lunar construction. This study aimed to examine the effects of primary microwave sintering parameters on the densification, microstructure evolution, and mechanical properties of a lunar soil simulant and analyzed the processing-microstructure-properties relationship. The experimental design was based on the Taguchi method, where temperature, dwell time, and heating rate were regarded as the primary design factors. Density measurements presented the porosity of microwave-sintered specimens ranging from 8.5 % to 11.5 %. Chemical and microstructural characterization was integrated and showed three identical mineral phases appeared at different sintering conditions. Nanoindentation was used to determine nanomechanical properties of microstructural components and subsequent effective stiffness via homogenization technique. Uniaxial compressive strength of sintered specimens was also measured. The sintering design parameters in the range attempted significantly affected microstructural characteristics, while no major changes in the chemical–mechanical properties of phases occurred. Taguchi analysis implied that microstructural evolution is predominantly affected by the sintering temperature, whereas the other two factors (i.e., dwell time and heating rate) were not significant. The fundamental understanding from this study can improve the design of hybrid microwave sintering to densify lunar soils for future lunar construction.