Abstract
The influence of hydrogen pressure and reaction temperature on the initiation of uranium hydride sites has been determined in the ranges 60–1000mbar and 75-130°C, respectively. In order to study the influence of these reaction conditions independently of other possible experimental influences, it was necessary to develop a standard sample preparation (wet abrasion) and a drying pre-treatment (16h, 75°C, in-vacuo) methodology. It is shown that, under constant pressure and temperature conditions, the number of hydride sites varies as a power-like function of time. A power-like function may also be used to describe the relationship between the inverse of the time for the nth hydride site to appear (for n=1, 5, 10, 20 and 50) and the applied hydrogen pressure, with an exponent value of 1.3 and an associated activation energy of 57kJmol−1. These observations are broadly consistent with existing hydride initiation models in which the uranium surface oxide layer is considered to act as a barrier to hydrogen diffusion to the oxide–metal interface.
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