Magnesium-based combustion synthesis of advanced materials for energy and space applications

As energy problems become more challenging, interest in low-energy-consuming methods for the fabrication of materials increases. Combustion synthesis is one such method because it is sustained by reaction heat release instead of external energy input. In the present work, combustion synthesis approaches are applied to the production of construction materials from lunar and Martian regolith and to the fabrication of magnesium silicide (Mg2Si), a promising thermoelectric material for high-temperature applications. In both cases, magnesium (Mg) was used as one of the main reactants and similar experimental approaches were employed. Recently, it has been proposed to use combustion of lunar regolith with Mg for the production of construction materials on the Moon. Although self-sustained combustion of JSC-1A lunar regolith simulant with Mg has been demonstrated, the reaction mechanisms are not well understood. Also, for Mars missions, it would be important to study combustion of Martian regolith with Mg. In the present work, thermoanalytical studies were conducted for mixtures of Mg with JSC-1A, JSC-Mars-1A, and Mojave Mars regolith simulants as well as with main reacting components of these materials – iron oxide and silica. Combustion of the two Martian simulants with Mg was also studied by thermodynamic calculations and combustion experiments. The mixtures based on JSC-Mars-1A exhibited higher temperatures than mixtures based on Mojave Mars, which correlates with iron oxide concentrations in the simulants. Thermoanalytical studies have shown that iron oxide plays a dominant role in the combustion of JSC-Mars-1A with Mg. However, for Mojave Mars and JSC-1A, which include more silica and less iron oxide, silica promotes reactions at lower temperatures. In previous attempts to fabricate Mg2Si via combustion synthesis, the thermal explosion mode was used, which required significant energy input and made it difficult to control the process and product quality. In the present work, for the first time Mg2Si was obtained in the SHS mode of combustion synthesis, which requires much less energy and facilitates control of the process. To enable SHS of Mg2Si, mechanical activation of Mg/Si mixtures was employed. Combustion experiments and thermoanalytical studies revealed that the reaction between Mg and Si includes two stages of self-accelerating reaction, separated by a long period of a relatively slow diffusion of Mg and Si ions through the layer of formed Mg2Si product. Explosive-based shockwave consolidation was used to increase the product density, and thermophysical properties of the obtained material were determined