The effect of storage time on the thermal behavior of nanocrystalline magnesium hydride with metal halide additives

•Release of water was observed during heating of all stored materials.•The emission of HF during decomposition of MgH2 with metal fluorides was observed.•The more water in the sample the less hydrogen is being released.•The more water in the sample the higher decomposition temperature.

This work presents results concerning the thermal stability of nanocrystalline magnesium hydride milled with 7 wt% of metal halide additives such as ZrF4, NbF5, TaF5, FeF2, FeF3, TiCl3 and VCl3 after one year of storage in a glovebox under a continuously purified argon atmosphere. The amounts of oxygen and water in the glovebox were below 0.1 ppm. The gases released from the materials during the thermal decomposition of all samples were analyzed using a quadrupole mass spectrometer. The oxidation of MgH2 at low oxygen and water vapor pressures leads to an increase in the hydride decomposition temperatures of the samples compared to their initial (as-prepared) counterparts, which are shown in Ref. [1]. The differences in the decomposition temperatures between the powders stored for one year in a glovebox and the initial as-prepared powders were greater than 60 °C for MgH2 with NbF5, ZrF4, TaF5, TiCl3 and VCl3. The release of water from all long-term-stored materials and the emission of hydrogen fluoride (HF) from MgH2 with metal fluorides were observed during heating. The observed results demonstrate that even a protective argon atmosphere did not prevent the degradation of the nanocrystalline MgH2 powders with various metal halide additives during their long-term storage in a professional glovebox, which is an important practical concern.