Hydrogen-induced disproportionation of Zr₂Co

The kinetics of hydrogen-induced disproportionation of Zr₂Co was studied by the conventional constant volume method in a temperature range of 773 to 873 K. It was found that Zr₂Co disproportionated as 2Zr₂Co+3H₂→3ZrH₂+ZrCo₂ through a two-step mechanism as 1) Zr₂Co+H₂→ZrH₂+ZrCo and 2) 2ZrCo+H₂→ZrH₂+ZrCo₂. 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^-2exp[15.0×10³ (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.