| Hydriding rate data of FeTi with minimum heat effect, which had been obtained by applying thermal ballast in a Cu tube reactor, were analysed by both the rate equations developed under the assumption of continuous moving boundary and the Johnson-Mehl-Avrami equation. The rate was directly proportional to (pH₂-Peq) at high temperature and low reacted fraction, and to (√pH₂√Peq) at low temperature and high reacted fraction, which illustrates the change of the rate controlling step from a surface reaction to a reaction in the bulk, the diffusion or the interface reaction, as the temperature is decreased and as the reaction proceeds. The dependence of the rate on the reacted fraction showed the characteristic feature of the nucleation and growth process. A model which relates the surface reaction and the nucleation and growth process is proposed. The apparent activation energy of the surface reaction is estimated to be about 1500㎈/mole, and that of the reaction in the bulk about 8000㎈/mole. |
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