SOME HIGH-PRESSURE EXPERIMENTS ON THE FE-H SYSTEM

In situ X-ray diffraction measurements have been performed of the hydriding process of iron under high hydrogen pressure and temperatures, using a synchrotron radiation source. After hydrogenation, a sample of FeH(x) in equilibrium with approximately 6 GPa of fluid H-2 undergoes a sequence of phase transitions, dhcp --> fcc --> new phase --> melt, at 650 approximately 700-degrees-C, 800 approximately 900-degrees-C and 1200-degrees-C, respectively. The structure of the new high-temperature phase is tentatively identified as a defect-bcc structure in which many vacancies exist in one of the simple-cubic sublattices of bcc-Fe.