Phase transformations in LaNi5−xCox–H2 system

The interaction in LaNi5−xCox–H2 (x=0.6, 1.0, 1.5, and 2.0) system was studied at 20–955°C and pressure up to 6.2 MPa by means of differential thermal analysis (DTA), X-ray diffraction (XRD) analysis and thermodesorption of hydrogen in vacuum. The LaNi3.5Co1.5 and LaNi3.0Co2.0 (after heating at P H 2 = 5 – 6.2 MPa to 880–955°C) compounds transform into an amorphous state. The heating of LaNi3.0Co2.0 compound at P H 2 = 5 MPa to 810°C with holding for 1.5 h leads to a partial amorphization and partial decomposition (disproportionation) into LaHx and Co. The heating of LaNi3.5Co1.5 amorphous products in vacuum to 225 and 285°C results in both a partial and complete recrystallization into a phase with CaCu5-type structure and pure Co, respectively, but at 940°C they again are partial amorphous. The LaNi3.0Co2.0 amorphous products are completely recrystallized into a textured phase with CaCu5-type structure in vacuum at 880°C.