Change in grain size of disproportionation products of Zr2M (M = Co, Ni) with temperature and pressure

Zr2Co disproportionated to ZrH2 and ZrCo on a wide range of temperatures and pressures. The X-ray diffraction patterns of disproportionated Zr2Co were constructed broad peaks that meant to consist of fine crystallite. To evaluate the temperature and pressure dependence of nucleation of products, the grain size of ZrH2 was calculated on a half width of ZrH2 111 peak by using Sherrer equation. It was found that the grain size did not depend on disproportionation conditions such as temperature and pressure. Zr2Ni also disproportionated and the grain size was not affected by temperature and pressure. These results indicate that the probability of nucleation does not depend on temperature and pressure. The disproportionation rates of Zr2M are determined mainly by the crystal growth rate of products. However, Zr2NiH5 was formed under the condition of low hydrogen pressure. The appearance of disproportionation was affected by amount of absorbed hydrogen. (author)