Combustion of Lunar Regolith/Magnesium Mixtures for the Fabrication of Construction Materials

Abstract

Combustible mixtures of lunar regolith with magnesium could be used for the production of construction materials on the Moon. The present paper focuses on decreasing Mg content in these mixtures and increasing the density and strength of the combustion products. It has been shown that preheating to 100°C allows combustion of JSC-1A/Mg mixtures at 8 wt% Mg. Combustion of pellets submerged in silica led to a noticeable increase in the product strength. Significantly higher density and strength were achieved using SHS compaction. I. Introduction ELF-PROPAGATING high-temperature synthesis (SHS) has been envisioned for the production of construction materials on the Moon. This technique involves self-sustained propagation of the combustion wave over the mixture due to exothermic reactions between the mixture components. SHS has been used for synthesis of numerous ceramic compounds and other materials. Recently, SHS in the mixtures of JSC-1A lunar regolith simulant with magnesium has been investigated. 1-3 Thermodynamic calculations of the adiabatic flame temperatures and combustion products over a wide range of regolith/metal mixture ratios have shown that magnesium provides higher adiabatic temperatures as compared to aluminum. 1 Experiments on the combustion of Mg/JSC-1A mixture pellets in argon environment determined the combustion characteristics at under different conditions. 1-3 For stable combustion, the minimum concentration of magnesium was 13 wt%. 3 These experiments have shown, however, that the strength of the combustion products is not sufficiently high for using them as construction materials. The present paper focuses on two goals: to decrease the content of magnesium in the JSC-1A/Mg reaction and to obtain denser and stronger products. To minimize the magnesium content, a preheating step was added before ignition of the JSC-1A/Mg mixture. It is common in many SHS systems to raise the initial temperature of the green mixture for increasing the combustion temperature and front velocity. To produce dense and stronger materials, a technique called SHS compaction was used. In this method, the green mixture is located inside some inert powder (e.g., sand) placed under a hydraulic press. The mixture is ignited and after the combustion process, the product mixture is compacted by the press. This method allows for the production of denser products and items that have complicated shape and can be used with no subsequent treatment. As a preparation for SHS compaction, experiments with pellets submerged in silica powder were initially conducted. Next, an apparatus for quasi-isostatic pressing was constructed and SHS compaction tests with JSC1A/Mg mixtures were performed.