Decomposition of TiH2 studied in situ by synchrotron X-ray and neutron diffraction

Decomposition during constant heating of as-received and pre-oxidized titanium hydride (TiH2) powder under flowing and stationary Ar was studied in situ by synchrotron X-ray and neutron diffraction. Diffraction data were compared to corresponding thermoanalysis traces in order to relate peaks of H-2 release with individual phase transformations. We found that every peak of H-2 release is correlated with regimes of lattice parameter contraction. Core-shell models to describe the decomposition processes measured were found, and further verified by electron microscopy. The models show that a shell of the hexagonal close-packed hydrogen solid solution (alpha) around each particle core controls its dehydrogenation for as-received TiH2, while a TiO2 rutile shell controls the outgassing from the pre-oxidized powder. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.