Hydrogen-sorption and thermodynamic characteristics of mechanically grinded TiH19 as studied using thermal desorption spectroscopy

Isobaric thermal desorption spectroscopy and X-ray diffraction analysis were used to study the influence of mechanical dispersion during high-energy milling gamma-TiH1.9 hydride upon its hydrogen-sorption characteristics, temperature and enthalpy of the gamma -> beta (TiH1.9 -> Ti[H](beta)) phase transition at isobaric heating the sample under hydrogen atmosphere with speed 3 degrees/min. Isobars of hydrogen thermal desorption in the regions of the gamma and beta phases of the Ti-H-2 system at pressures of 0.1, 0.25, 0.315 and 0.45 MPa of hydrogen in the reactor have been derived. Experimental data obtained for initial titanium hydride and mechanically grinded for 20 min in a planetary ball mill have been used for construction of Van't Hoff plots and for determination of enthalpy of formation of gamma-hydride from solid solution of hydrogen in bcc titanium. Our experimental data reveal that 20 min high-energy influence on titanium hydride powder leads to increasing the specific surface of the samples from 0.13 to 8.58 m(2)/g and to significant (more than 250 degrees) decreasing the temperature of the beginning of hydrogen release when heating the sample (i.e., to a decrease of thermal stability of mechanically activated TiH1.9). However, mechanical dispersion does not change the temperature of the gamma -> beta phase transition. It has been established that high-energy milling TiH1.9 powder causes the effect of a decrease of enthalpy of the formation of gamma-hydride from 248 kJ/mole H-2 to 175 kJ/mole H-2. (C) 2010 Elsevier B.V. All rights reserved.