Influencing factors for the preparation of Fe0 in lunar soil simulant using high-temperature carbothermic reduction

Abstract

Metallic iron (Fe0) within lunar soil grains can affect their visual and near-infrared spectra, adhesion, biological toxicity, and electrostatic migration characteristics. The Fe0 particle therefore is an important component of lunar soil. This study devised a high-temperature carbothermic reduction method for preparing Fe0 via graphite reduction of Chinese Lunar Regolith Simulant (CLRS-2) in an argon atmosphere, which is similar to the Fe0 in the agglutinitic glass of lunar samples. The X-ray diffraction and electron microscopy data show that the mixture of lunar soil simulants and graphite heated at high temperature rapidly quenched to form a glassy phase with dispersed Fe0 particles, the microstructure of which is consistent with the α-Fe (bcc) in lunar soil. This paper also discusses the main influencing factors for preparing Fe0, such as the ratio of raw materials, heating temperature, and holding time. The optimal experimental conditions are a graphite-to-CLRS-2 mass ratio of 1.0: 27.0 (Fe/C = 2.0: 2.6), reduction temperature of ∼1600 °C, and holding time of ∼4 h, which produce single-phase α-Fe with an average particle size of ∼180 ± 10 nm and no residual impurities (e.g., graphite).