The thermodynamics of the LaNi 5-H 2 system by differential heat flow calorimetry II: The α and β single-phase regions

Abstract

Simultaneous pressure-composition isotherms and partial relative molar enthalpies of hydrogen for the single-phase portions of the system LaNi 5H x with 0 ⩽ x ⩽ 6.4 were obtained. In absorption the system exhibits chemisorption for 0 ⩽ x ⩽ 0.05 with ¦Δ H ̄ ∞ o¦ = 80 kJ ( mol H 2) −1 , followed by trapping for 0.05 ⩽ x ⩽ 0.23 with ¦ Δ H ̄ o¦ = 59 kJ ( mol H 2) −1 at x = 0.05 and then contains an α solid solution to the phase limit at x = 0.42. In desorption this phase limit is at x = 0.34. Both the α−(α + β) and the (α + β)−β phase boundaries exhibit discontinuous changes in Δ H ̄ with single-phase ¦ΔH̄¦ values of 26.5 kJ (mol H 2) −1 and 38.5 kJ (mol H 2) −1 respectively. The partil relative enthalpy for the β single phase for x > 6.05 decreases slowly with increasing x.