Hydrogenation Reactions in Iron-Light Element Systems at High Temperature and High Pressure

The Earth’s core contains nonnegligible concentrations of light elements, reducing the density of the iron core. The hydrogen-induced volume expansion of iron and related materials is key to clarify the chemical composition of the core. This article reviews recent advances on the hydrogenation reactions of Si-bearing iron and FeS through in-situ X-ray diffraction and neutron diffraction measurements at high-pressure and high-temperature conditions. The hydrogen-induced volume expansion of hcp Fe0.95Si0.05 is 10 % greater than the pure iron and the estimated hydrogen content in the core is about a half of that without the effect of silicon. Stoichiometric FeS (troilite) was hardly hydrogenated, suggesting that the hydrogenation reactions of FeS strongly depend on the stoichiometry of FeS.