Hydrogenation of FeSi and FeS alloys at high pressure and high temperature

Hydrogenation of iron-light element alloys, such as Fe-Si and Fe-S, under high pressure is important to understand the composition and the thermal structure of the planetary cores. Here, we report the hydrogenation pressures of FeSi and FeS, hydrogen solubilities into these alloys and the effect of hydrogen on their phase relations based on in situ X-ray diffraction experiment of FeSi-H and FeS-H systems up to 17 GPa and 2123 K. Hydrogenation of FeSi and FeS occurs at the pressures more than 10 GPa and 3 GPa, respectively. The H solubilities (x) are estimated to be x~0.2-0.3, which are well below compared to the H solubility into pure iron (x~1.0). This small amount of H solubility into the alloys causes only small depressions (150-250 K) of their melting temperaure whereas dissolution of H into Fe decreases its melting temperature significantly.