Influences of Reaction Parameters on the Product of a Geothermite Reaction: A Multi-Component Oxidation-Reduction Reaction Study

This study investigated an oxidation-reduction reaction involving a mixture of minerals, glass, and aluminum that exhibited thermite-type reaction behavior. Thermite reactions are a class of Self-propagating High-temperature Synthesis (SHS) reactions. Chemical reactions between raw minerals and a reducing agent, which exhibit thermite-type reaction behavior, are termed geothermite reactions by the author. Geothermite reactions have the potential for use in In-Situ Resource Utilization (ISRU) applications on the Earth, the Moon, Mars, and beyond.

A geothermite reaction was shown to occur between two particle size distributions of lunar regolith simulant. Regolith simulant is a naturally occurring mixture of minerals and glass mined from a volcanic ash deposit. The chemical composition of the simulant is similar to actual lunar regolith found on the Moon. The product of the reaction was a ceramic-composite material. The effect of reactant stoichiometry, regolith simulant particle size, and reaction environment on phase formation, microstructure, and compressive strength of the reaction product was investigated. Reaction environments used in this study included a standard atmosphere and a vacuum environment of 0.600 Torr. In addition, the energy required to initiate each reaction using various reaction parameters was measured.

X-ray diffraction (XRD) analysis of reaction products synthesized in a standard atmosphere and in vacuum typically indicated the presence of the chemical species: silicon, corundum (α -Al₂O₃), spinel (MgAl₂O₄), and grossite (CaAl₄O₇). Many additional chemical species were present; their occurrence depended on reaction parameters used during synthesis. Diffraction peaks were observed for phases of aluminum nitride within all reaction products formed in a standard atmosphere. Scanning Electron Microscopy (SEM) showed the presence of whisker networks throughout the microstructure for all reactions conducted in a standard atmosphere. Energy Dispersive Spectroscopy (EDS) indicated the presence of aluminum and nitrogen within many of the whiskers. It was hypothesized that many of the whisker networks were composed of phases of aluminum nitride. No whisker networks were observed in the vacuum synthesized reaction products. Maximum mean compressive strengths were found to be ~ 18 MPa and occurred in the coarse particle size distribution of simulant using the smallest quantity of aluminum. Reactant mixtures using a coarse particle size distribution of regolith simulant were found to require substantially more energy to initiate the reaction than the simulant with the fine particle size distribution.