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Magnesium silicide (Mg 2 Si) is a promising intermetallic compound for applications such as light-weight composite materials and thermoelectricenergy conversion.It is difficult, however, to synthesize high-quality Mg 2 Si on a large scale. Self-propagating high-temperature synthesis (SHS) is an attractive pathway, but it is difficult to ignite the low-exothermic Mg/Si mixtureand achieve a self-sustained propagation of the combustion wave. In the present paper, mechanical activation was used to facilitate the ignition. Magnesium and silicon powders were mixed and then milled in a planetary ball mill in an argon environment. The mixtures were compacted into pellets and ignited at the top in a reaction chamber filled with argon. Depending on the pellet dimensions and diameter-to-height ratio, two modes of combustion synthesis, viz.,thermal explosion and SHS, were observed. In both modes, Mg 2 Si product was obtained. Thermocouple measurements have revealed that the exothermic reaction stages include two self-heating events separated by a long period of relatively slow interaction. To clarify the reaction mechanisms, differential scanning calorimetry was used, which also revealed two peaks of exothermic reaction in the milled Mg/Si mixture. The first peak is explained by the effect of mechanical activation. Explosive-based shockwave consolidation was used to increase the product density. Thermophysical properties of the obtained material were determined using a laser flash apparatus.

It has been shown recently that mixtures of JSC-1A lunar regolith simulant with magnesium are combustible. Thermite-type reactions in these mixtures could be used for in situ production of construction materials on the Moon. Because of complex composition of lunar regolith, however, the mechanisms of these reactions are not well understood. Also, for Mars mission applications, it is important to explore the possibility of using Martian regolith in such mixtures. In the present paper, combustion of two Martian regolith simulants (JSC-Mars-1A and Mojave Mars) with magnesium is studied using thermodynamic calculations and combustion experiments. To understand the reaction mechanisms in these mixtures as well as in the mixtures of JSC-1A lunar regolith simulant with magnesium, thermoanalytical experiments are also conducted. It has been shown that the Martian regolith simulants form combustible mixtures with magnesium. The measured combustion temperatures and identified product compositions are in reasonable agreement with thermodynamic predictions. The mixtures of JSC-Mars-1A with magnesium at 20-30 wt% Mg exhibit higher temperatures and burn more vigorously than mixtures based on Mojave Mars, which is explained by the higher content of iron oxide in JSC-Mars-1A. For Mojave Mars, combustion is accompanied by oscillations in the front motion and by the formation of a layered structure of the product. This effect is more significant at lower concentrations of Mg. Thermoanalytical studies have shown that iron oxide plays a dominant role in the combustion of JSC-Mars-1A simulant with magnesium. However, Mg/SiO 2 mixture ignites at a temperature lower by approximately 100°C than for Mg/Fe 2 O 3 . For Mojave Mars material and JSC-1A lunar regolith simulant, which include more silica and less iron oxide, silica exhibits a significant effect on the combustion, promoting reactions at lower temperatures.

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