Thermogravimetric research of hydrogen storage materials

During thermogravimetric research of metal hydrides we noticed mass growth of samples above 200°C even in an argon atmosphere. Further heating is leading to the growth of weight up to 2-7 weight% till 500°C. Second run of the same sample without taking out of DTA instrument gave only small mass changes, indicating that noticed mass increase during first run is permanent. Microscope and elemental analyses were made to determine the reason of mass growth. XRD inspection revealed the formation of new phase with bunsenite NiO structure with deformed cubic structure. The new phase is no more active to hydrogen sorption/desorption. Our results demonstrated that the usage of hydrogen storage alloys AB₅ must be taken with care - it is important not to exceed some critical temperature were irreversible structural, compositional and morphological changes will occur.