An analysis of heat effect on the hydriding and dehydriding kinetics of FeTi intermetallic compound

Abstract

Reaction rates and temperature changes in the reactor were measured during the hydriding and dehydriding reactions of FeTi while the heat effect was reduced progressively by applying a thermal ballast technique and using a highly heat conductive copper tube reactor with the ballasts. When FeTi 1.04, mixed with ballast material (manganese in this work), was hydrided in the copper reactor, the heat effect was reduced significantly so that the assumption of isothermal conditions was possible; from the results an empirical rate equation was obtained. The heat effect on the rates is analysed with the aid of the empirical rate equation, which is proved to be a powerful tool for understanding the intrinsic hydriding kinetics of FeTi. Hydriding rate data, which were obtained by applying thermal ballast in the copper reactor, show parabolic dependence on the applied hydrogen pressure at low temperature and high hydrogen concentration and linear dependence at high temperature and low hydrogen concentration, indicating a transition of the kinetic mechanism with temperature and hydrogen concentration. The heat effect is more pronounced during the dehydriding reaction than the hydriding reaction. Dehydriding rate data with minimum heat effect are also presented.