Abstract
The kinetics of hafnium hydride formation were studied utilizing conventional rate measurements (Sieverts system) combined with metallographic examinations of partially hydrided samples. The rate measurements were performed at 700 TorrH 2 over a temperature range 200–550 °C. Two types of hafnium samples (polycrystalline and crystal bar) were compared. The progression of the massive stage of the reaction is characterized by a contracting-envelope morphology with a constant hydride front velocity. The anisotropy in the reaction front velocity regarding different crystalline orientations of the metal is small, resulting in similar results for the different types of hafnium. The temperature dependence of the front velocity obeys an Arrhenius-type relation over the temperature range 250–450 °C, with an apparent activation energy of 0.50 ± 0.05 eV. Considering a diffusion-controlled model, a diffusion activation barrier of about 0.4 eV is evaluated, which agrees with the average reported value for the diffusion of hydrogen in hafnium hydride. At temperatures above about 500 °C, deviations from the Arrhenius relation are displayed, possibly owing to a change of mechanism.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
