Interaction of intermetallic compounds of rare-earth metals, nickel, and aluminum with hydrogen

Abstract

AtT=293 K andpH2≤10 MPa. we synthesized hydridesR3Ni8Al-H7.2–15.2 (R=Nd. Sm. Gd. Tb. Dy, Ho, Er, Tm, and Lu). The X-ray analysis revealed an isotropic deformation of the original crystal lattice due to hydrogen penetration. For the hydrides obtained, the lattice constanta exceeds that of the original intermetallide by 3.9–6.0% and the constantc and the cell volumeV are increased by 6.0–12.6% and 15.6–26.4%, respectively. The volume expansion per absorbed hydrogen atom is (2.4–3.6)·10−3 nm−3. By construction of the isotherms of hydrogen desorption for the systemsR3Ni>8Al-H, we established the existence of the α-solid hydrogen solution and the region of its coexistence with β-hydride, the region of coexistence of β- and γ-hydrides, and the β- and γ-hydride phases. Heats of the phase transitions were determined as follows: ΔH=31.4±0.8 kJ/(mole H2) in the system Gd3Ni8Al-H for the transition γ→β, ΔH=39.8±1.1 kJ/(mole H2) in the system Tb3Ni8Al−H for the transition β→α. and ΔH=37.1±5.1 kJ/(mole H2) in the system Tm3Ni8Al−H for the transition γ→β. Among the products of hydrogenation, intermetallic compounds Lu3Ni8Al and Tm3Ni8Al. we revealed the β′- and γ-phases. We also found that, atpH2≤10 MPa andT=400–430 K, the phases of Sm3Ni8Al and Gd3Ni8Al decay into two hydridesRH2–3 andR(Ni.Al)5Hx.