SPECIFIC FEATURES OF PHASE TRANSFORMATIONS IN LANTHANUM-NICKEL-ALUMINUM ALLOYS UNDER THE ACTION OF HYDROGEN

摘要

By the methods of differential thermal and X-ray phase diffraction analyses study the interactions in LaNi_(5-x)Al_x-H_2 systems with x = 1.0 and 1.5 at temperatures varying from the room temperature to 920 deg C under an initial pressure of hydrogen of up to approx 5.0 MPa. The temperature of disproportionation is equal to 555 and 535 deg C for the compounds with aluminum content x = 1.0 and 1.5, respectively. The original phase decomposes into LaH_x and Ni_3Al. At temperatures above 800 deg 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 LaNi_4Al compound, i.e., La(Ni, Al)_5, LaH_x, Ni_3Al, and an unknown phase, recombine in a vacuum at 215 deg C with hydrogen release and the formation of one or several unknown phases. The products of disproportionation of the LaNi_(3.5)Al_(1.5) compound, i.e., LaH_x, Ni_3Al, and an unknown phase, recombine in a vacuum at 150, 230, and 580 deg C with hydrogen release and the formation of the original phase.