¹Shiori Inada, ^1,2Shogo Tachibana
Geochimica et Cosmochimica Acta (in Press) Open Source Link to Article [DOI: 10.1016/j.gca.2026.07.046]
¹Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan
²UTokyo Organization for Planetary and Space Science, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan
Copyright Elsevier

Effects of ambient gas are important for understanding evaporation of planetary materials in the protosolar disk. In this study, we experimentally investigated the evaporation kinetics of forsterite in H₂-H₂O gas mixtures to elucidate the dependences on H₂O abundance at  of 10⁻⁴–10⁻², temperatures of 1400–1600 K, and a total pressure of 1 Pa. We found that the evaporation rate decreases with increasing  with a reaction order of −1.02 ± 0.12 only above certain  (10⁻³–10⁻² depending on temperature). The activation energy increased when the evaporation is suppressed by H₂O (497 ± 11 kJ mol⁻¹, while 359 ± 1 kJ mol⁻¹ without the effect of H₂O). The  dependence of the evaporation rate is consistent with the previously proposed model based on the chemical equilibrium consideration and the Hertz-Knudsen equation. This consistency can be explained in terms of a reaction mechanism. Based on the experimentally determined evaporation kinetics, we evaluated conditions of the protosolar disk where H₂O affects evaporation of forsterite dust. This showed that H₂O suppresses the evaporation at 1300 K at  of the Solar abundance and 1600 K under H₂O-enriched conditions, which possibly affected moderate-temperature thermal processing of silicate dust and evaporation of chondrule melt under oxidizing conditions.