Hydrogen absorption-desorption characteristics of mischmetal-nickel-aluminum alloys

• Published in: Journal of the less-common metals 1979-01, Vol.66 (1), p.67-75
• Main Authors: Osumi, Y, Kato, A, Suzuki, H, Nakane, M, Miyake, Y
• Format: Article
• Language: English
• ISSN: 0022-5088
• DOI: 10.1016/0022-5088(79)90196-6

The hydrogen absorption and desorption characteristics of mischmetal (Mm)-nickel-aluminum alloys were investigated. MmNi 5− x Al x ( x = 0.25 −0.5) have been found to have the same hexagonal structure as LaNi 5 and MmNi 5, and they reacted readily with hydrogen to form the hydrides MmNi 4.75 Al 0.25H 5.4, MmNi 4.65Al 0.35H 5.3H 5.3 and MmNi 4.5Al 0.5H 4.9 (hydrogen content: 1.3,1.2 and 1.2 wt.%, respectively) under 60 atm hydrogen pressure at room temperature. The dissociation pressures of these hydrides were dependent on the aluminum content (aluminum partially substitutes for nickel) and the value of log Pbecame lower than the value for MmNi 5 hydride as x increased. The enthalpy change on hydride formation as determined from the dissociation isotherms for the MmNi 4.5Al 0.5-H system was − 5.5 kcal (mol H 2) −1; this value was smaller than those for LaNi 5 and MmNi 5. The dissociation pressure at 30 °C was 3 atm and was nearly the same as that of LaNi 5. The desorption rate of hydrogen for MmNi 4.5Al 0.5 was larger than those for LaNi 5 and MmNi 5) and a value of 2.1 – 4.3 kcal mol −1 was obtained for the apparent activation energy of hydrogen desorption. For MmNi 4.5Al 0.5 the hydrogen absorption-desorption cycle was repeated 30 times, but no variation in the hydrogen absorption-desorption capacity was observed. The hydride of MmNi 4.5A1 0.5 proved to be suitable for use as a stationary hydrogen storage material.