Optimization of the self-propagating high-temperature process for the fabrication in situ of Lunar construction materials

The highly exothermic self-propagating thermite reduction of ilmenite (FeTiO3) is systematically investigated for the in situ fabrication of composite ceramics in Lunar environment. Because of its relatively lower volatility, Al is preferred to Mg as reducing agent. A self-propagating (SHS) behavior is displayed only if the Al/FeTiO3 molar ratio is higher than 0.9. In addition, when the amount of the reducing metal in the mixture is increased, the reactive process proceeds faster and the combustion temperature becomes higher, as a consequence of the increased system exothermicity. Correspondingly, the maximum amount of Lunar regolith (containing up to 20 wt.% ilmenite) to be possibly reacted with additional FeTiO3 and Al is identified. The obtained product, consisting of a complex mixture of various Al-, Ti-, Mg-, and Ca-oxides along with metallic and intermetallic phases, displays good compressive strength properties (25.8–27.2 MPa) that make it promising as construction material. Parabolic flight experiments evidenced that neither SHS process dynamics nor product characteristics are significantly affected by gravity. All the obtained findings allows us to conclude that the optimal conditions identified during terrestrial experiments are also valid for in situ applications in Lunar environment, with the only exception for the slight overpressure (few Torr) required for limiting Al vaporization during SHS.

► An SHS-based process for the fabrication of Lunar construction materials is optimized.
► The SHS reduction of ilmenite by Al takes place only if Al/FeTiO3 is higher than 0.9.
► Lunar regolith enriched in ilmenite can be suitably reacted with Al.
► The obtained composite material displays good compressive strength properties.
► The optimal conditions identified on the Earth are generally valid in Lunar environment.