Evaporation kinetics of forsterite in H2-H2O gas mixtures

This is the authors' abstract. We don't add key points for this paper.

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 H 2 -H 2 O gas mixtures to elucidate the dependences on H 2 O abundance at P H 2 O / P H 2 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 P H 2 O / P H 2 with a reaction order of −1.02 ± 0.12 only above certain P H 2 O / P H 2 (10 −3 –10 −2 depending on temperature). The activation energy increased when the evaporation is suppressed by H 2 O (497 ± 11 kJ mol −1 , while 359 ± 1 kJ mol −1 without the effect of H 2 O). The P H 2 O / P H 2 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 H 2 O affects evaporation of forsterite dust. This showed that H 2 O suppresses the evaporation at ≲ 1300 K at P H 2 O / P H 2 of the Solar abundance and ≲ 1600 K under H 2 O-enriched conditions, which possibly affected moderate-temperature thermal processing of silicate dust and evaporation of chondrule melt under oxidizing conditions.