Structural changes of commercial TiH2 were studied using interrupted temperature desorption spectroscopy and X-ray diffraction techniques to understand the mechanism of its degradation under non-equilibrium conditions. Rapid cooling on different stages of temperature-programmed heating allowed to study the intermediate phase compositions that evolve upon cooling from the high-temperature phase beta Ti(H). The phase transformation sequence is described as a number of consecutive reactions corresponding to the observed desorption peaks. Phases delta TiH2-x, gamma TiH, and the solid solution alpha Ti(H) were found to be intermediates in the epsilon TiH2 --> alpha Ti transformation when the latter is interrupted. Additional evidence for the thermodynamic stability of gamma TiH is given. (C) 2009 Elsevier B.V. All rights reserved.