Intermetallic hydrides .1. Investigation of the rate of phase transformation

By using a new experimental procedure, reproducible isotherms were obtained for LaNi5-H-2 systems in the temperature range 278-300 K. This was a necessary step before conducting a comprehensive study of the rate of phase transformation. Analysis of the time variation of the pressure above the sample during gas transfer revealed that the rate of the phase transformation could be expressed by a general rate equation. Experimental data were fitted by adjusting only two parameters. The first is a rate constant whose value depends on the operating temperature, and the second can be related to the morphological growth of the hydride. An excellent correlation was found between experimental and calculated data under various conditions of operating temperature and hydrogen mass flow. In this preliminary investigation, it was also found that the same rate law can be used on the range 1 < H/M < 3. Results obtained are discussed with regard to hydride phase growth and the phase transformation mechanism.