Low reactivity of stoichiometric FeS with hydrogen at high-pressure and high-temperature conditions

Abstract

Hydrogenation of iron sulfide (FeS) under high-pressure and high-temperature conditions has attracted attention because hydrogen and sulfur are promising candidates as light elements in the cores of the Earth and other terrestrial planets. In earlier reports describing the hydrogenation of FeS, the chemical compositions of starting materials were not fully clarified. This study reports in-situ neutron and X-ray diffraction measurements under high-pressure and high-temperature conditions of an Fe-S-H system using a stochiometric Fe1.000S (troilite) as a starting material. The site occupancies of hydrogen atoms in FeS, estimated by Rietveld refinement of neutron diffraction patterns collected at about 5 GPa, were 0.014(2) at 700 K and 0.024(2) at 1000 K. The hydrogen occupancy at 900 K and 18.2 GPa was estimated as 0.067(6) from the unit-cell volume determined by X-ray diffraction using the hydrogen-induced volume expansion calculated from firstprinciples calculations. These occupancies were significantly lower than those reported from earlier studies, indicating that the hydrogenation of FeS can be affected strongly by the stoichiometry of iron sulfide.