In the Mg-Ni system two intermetallic compounds are formed: Mg2Ni and MgNi2. MgNi2 did not react with H2 at pressures up to 400 psia and temperatures to 350°; however, Mg2Ni reacted readily with H2 at 300 psia and 325°. The product of the reaction was a new ternary hydride with the formula Mg2NiH4. The reaction was reversible and upon decomposition the original starting material was regenerated. The X-ray diffraction pattern of the product was indexed. Several pressure-composition isotherms were obtained. The dissociation pressure of the hydride was found to obey the relationship log Patm = (−3360/T) + 6.389 from which thermodynamic data were calculated. In the presence of excess Mg the pressure-composition isotherm exhibited two plateaus ; the lower plateau is attributed to the formation of MgH2 as evidenced by X-ray diffraction data and thermodynamic considerations. The presence of Mg2Ni appeared to have a catalytic effect on the formation of MgH2. © 1968, American Chemical Society. All rights reserved.
