Abstract
The influence of vacuum thermal treatments on the hydrogenation kinetics of titanium sponge has been studied. The samples were annealed at 473 K in a rough vacuum (10 −1 Pa) for different time periods in order to clean and activate their surfaces. After this step they were hydrogenated at 623 K, 773 K and 1073 K. It has been found that the sample pretreatment has no influence on the Ti hydrogenation kinetics at 773 K and 1073 K where the process is controlled by hydrogen diffusion in the bulk Ti. On the other hand, samples hydrogenated at 623 K present an incubation time (no change in the chamber hydrogen pressure) that is followed by a linear pressure drop, corresponding to a surface controlled process, and a parabolic stage (hydrogen diffusion in the bulk). The incubation time at 623 K has been correlated to the activation time at 473 K. This correlation has been explained by considering two mechanisms operating during the cleaning stage: one in which the occluded gases are released from the Ti cavities leaving fresh titanium surfaces, and another one in which the fresh surfaces are oxidized.
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