Synthesis and decomposition mechanisms of Mg2FeH6 studied by in-situ synchrotron X-ray diffraction and high-pressure DSC

Synthesis and decomposition mechanisms of ternary Mg₂FeH₆ were investigated using in-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and high-pressure differential scanning calorimetry (HP-DSC). Two routes for synthesis of Mg₂FeH₆ were studied. The first utilizes a ball-milled homogeneous MgH₂–Fe powder mixture and the second uses a mixture of Fe and Mg formed by decomposition of the ternary hydride, Mg₂FeH₆. In both cases the reaction mixture was sintered in a temperature range from RT to 500 °C under a hydrogen pressure of 100–120 bar. The reaction mechanisms were established using in-situ SR-PXD. The formation of Mg₂FeH₆ consists of two steps with MgH₂ as an intermediate compound, and the presence of magnesium was not observed. In contrast, the decomposition of Mg₂FeH₆ was found to be a single-step reaction. Additionally, both reactions were investigated using HP-DSC under similar conditions as in the SR-PXD experiments in order to estimate reaction enthalpies and temperatures. Mg₂FeH₆ was found to form from MgH₂ and Fe under hydrogen pressure regardless of whether the MgH₂ was introduced in the mixture or formed prior to creation of the ternary hydride.