Hydrogen-induced disproportionation of Zr2Co

The kinetics of hydrogen-induced disproportionation of Zr 2 Co was studied by the conventional constant volume method in a temperature range of 773 to 873 K. It was found that Zr 2 Co disproportionated as 2Zr 2 Co + 3H 2 → 3ZrH 2 + ZrCo 2 through a two-step mechanism as 1) Zr 2 Co + H 2 → ZrH 2 + ZrCo and 2) 2ZrCo + H 2 → ZrH 2 + ZrCo 2 . The first step was very fast and completed within only 100 s at 773 K. The rate, however, decreased with increases in temperature The apparent rate constant for the first step disproportionation was determined to be k = 2.0 × 10 -2 exp[15.0 × 10 3 (J/mol)/RT], where the kinetics could be explained by nucleation and one-dimensional growth model. The kinetics of the second step disproportionation could be explained by nucleation and three-dimensional growth model.