A study of the hydriding kinetics of TiFe and its alloys

Abstract

A kinetic study of the hydriding reaction of TiFe and TiFe0.8Mn0.2 was performed by the pressure sweep method. A new method of analysing the pressure sweep data was developed by converting pressure versus time into the reacted fraction F versus time. At the initial stage of the reaction the rate-controlling step is chemisorption on the metal surface, and the rate equations for TiFe and TiFe0.8Mn0.2 at constant temperature T and constant pressure P0 are F = 3.5 × 10 exp {- 800(cal mol) RT} P0-Peq Tt and F=5.0 × 10 exp {- 1000(cal mol) RT} P0-Peq Tt respectively. At a later stage (0.35 < F < 0.55) the sorption rate is controlled by the chemical reaction at the metal-hydride interface. The rate equations for TiFe and TiFe0.8Mn0.2 are (1-F)=5.6 × 10 exp {- 1000(cal(mol H)) RT} × (P0-Peq)(t-t) and (1-F)-(1-F)=9.0 × 10 exp{- 1500(cal(mol H)) RT} × (P0-Peq(t-t) respectively where t is time required to reach F and t is the time required to reach the initial stage. The rate increases with increasing pressure at constant temperature and with decreasing temperature at constant pressure. The addition of manganese to TiFe increases the hydryding rate as well as promoting activation (see Fig 13).As mangaanese is added the plateau pressure Peq is lowered resulting in a large driving force. © 1982.