High-Pressure Chemistry of Hydrogen in Metals: In Situ Study of Iron Hydride

• DOI: 10.1126/science.253.5018.421
• Publication Date: 2006-10-05T22:10:16Z
• Authors: J. V. Badding; R. J. Hemley; H. K. Mao
• Keywords: 0303 health sciences; 03 medical and health sciences; 7. Clean energy

Optical observations and x-ray diffraction measurements of the reaction between iron and hydrogen at high pressure to form iron hydride are described. The reaction is associated with a sudden pressure-induced expansion at 3.5 gigapascals of iron samples immersed in fluid hydrogen. Synchrotron x-ray diffraction measurements carried out to 62 gigapascals demonstrate that iron hydride has a double hexagonal close-packed structure, a cell volume up to 17% larger than pure iron, and a stoichiometry close to FeH. These results greatly extend the pressure range over which the technologically important iron-hydrogen phase diagram has been characterized and have implications for problems ranging from hydrogen degradation and embrittlement of ferrous metals to the presence of hydrogen in Earth's metallic core.