Phase transformations of titanium hydride in thermal desorption process with different heating rates

• The mechanism of TiH2 decomposition was studied by simultaneous TG-TDS technique.
• The activation energies of the observed three peaks were from 94 to 166 kJ/mol.
• Phase transformation was considered as the rate limiting step.
• Equilibrium hydrogen pressures were considered as the origins of the observed peaks.
• Heating rate can affect the phase transformation sequence.

Thermal desorption behaviors of titanium hydride powders were studied using simultaneous TG-TDS accompanied with TG-DSC measurements at the heating rate of 1.5, 2.5, 5, 10, 15, 20 °C/min, respectively. Phase transformation was considered as the rate limiting step and the phase transformation sequences were established by correlating the observed peaks of H2 release, mass loss and heat absorption. The origins of the peaks were described as the equilibrium hydrogen pressures of a number of consecutive phase regions that decomposition reaction passed through. Effect of heating rate on the thermal desorption behavior was taken into consideration, which was shown to be essential for the phase transformation sequence during TiH2 decomposition. For heating at lower than 10 °C/min, the phase transformation sequence can be schematized as: δ → β + δ → β → α + β → α while for heating rate equivalent to or higher than 10 °C/min the sequence can be expressed as: δ → β + δ → β.