Specific Features of Phase Transformations in Lanthanum–Nickel–Aluminum Alloys under the Action of Hydrogen

By the methods of differential thermal and X-ray phase diffraction analyses, we study the interactions in LaNi5 − xAl x –H2 systems with x = 1.0 and 1.5 at temperatures varying from the room temperature to 920°C under an initial pressure of hydrogen of up to ∼ 5.0 MPa. The temperature of disproportionation is equal to 555 and 535°C for the compounds with aluminum content x = 1.0 and 1.5, respectively. The original phase decomposes into LaH x and Ni3Al. At temperatures above 800°C, we observe the onset of recombination of the original phase leading to the formation of a compound with double-spaced structure. The products of disproportionation of the LaNi4Al compound, i.e., La(Ni, Al)5, LaH x , Ni3Al, and an unknown phase, recombine in a vacuum at 215°C with hydrogen release and the formation of one or several unknown phases. The products of disproportionation of the LaNi3.5Al1.5 compound, i.e., LaH x , Ni3Al, and an unknown phase, recombine in a vacuum at 150, 230, and 580°C with hydrogen release and the formation of the original phase.