Effect of the calcium halides, CaCl₂ and CaBr₂, on hydrogen desorption in the Li–Mg–N–H system

Calcium-halide-doped lithium amide–magnesium hydride samples were prepared both by hand-grinding and ball-milling 2LiNH₂–MgH₂–xCaX₂ (x = 0, 0.1, and 0.15; X = Cl or Br). The addition of calcium halides reduced the hydrogen desorption temperature in all samples. The ball-milled undoped sample (2LiNH₂–MgH₂) began to desorb hydrogen at around 125 °C and peaked at 170 °C. Hydrogen desorption from the 0.15 mol CaCl₂-containing sample began ca 30 °C lower than that of the undoped sample and peaked at 150 °C. Both the onset and peak temperatures of the CaBr₂ sample (x = 0.15) were reduced by 15 °C compared to the chloride. Kissinger’s method was used to calculate the effective activation energy (Ea) for the systems: Ea for the 0.15 mol CaCl2-containing sample was found to be 91.8 kJ mol^-1 and the value for the 0.15 mol CaBr₂-containing sample was 78.8 kJ mol^-1.