Experimental investigation and thermodynamic reassessment of La–Ni and LaNi5–H systems

In this study, the La–Ni and LaNi5–H systems were thermodynamically reassessed while taking into consideration the La5Ni19 phase. High-resolution X-ray diffraction and differential scanning calorimetry showed that the La5Ni19 phase was formed from the liquid and LaNi5 phases through a peritectic reaction, L+LaNi5→La5Ni19, at 1276 K, and existed stably down to the room temperature. The phase equilibrium relationships in the La–Ni system were thermodynamically optimized, and a good agreement was obtained between the experimental and calculated results. Additionally, the thermodynamically assessed LaNi5–H vertical section showed a satisfactory agreement with the experimental data of the literatures, and the present results of pressure–composition–temperature, X-ray diffraction, and high pressure differential scanning calorimetry. Finally, the decomposition temperatures of LaNi5H7 at different pressures ranging from 0.1 to 3 MPa were calculated, and a good agreement with the experimental data was obtained. These results are meaningful for further studies on the La–Ni–H system.