A TRANSMISSION ELECTRON-MICROSCOPY AND DIFFERENTIAL THERMAL-ANALYSIS STUDY OF THE ZRCO-H SYSTEM

ZrCo has been suggested as a storage medium with rather low equilibrium pressures for hydrogen and its isotopes. Here, the system ZrCo-H was investigated with conventional transmission electron microscopy and differential thermal analysis techniques. Hydrogen charging of ZrCo samples was mainly achieved by exposure to orthophosphoric acid. The beta-hydride phase of composition ZrCoH3 was found to precipitate on {100}. The orientation relationship of 6 with the matrix was established. The selected area diffraction results confirm the reciprocal lattice derived from the structure proposed by Irodova et al. in 1978. Low temperature phase transitions were not detected. DTA curves obtained from ZrCoH3 powder produced from the gas phase display an endothermic peak between 320 and 340-degrees-C which is due to an outgassing reaction. Bulk samples display another peak near 490-degrees-C which is tentatively ascribed to the phase transition: ordered beta-phase --> disordered alpha-phase. A phase diagram for the pseudo binary phase ZrCo-H is proposed.