Analysis of the Metal hydride Decomposition Temperatures of Zn(BH4)2 – MgH2 – Tm (Tm = Ni, Ti or Fe) Using a Sievert’s Type Volumetric Apparatus
In this work, Zn(BH4)2, Ni, or Ti were selected as additives to improve the hydriding and dehydriding rates of magnesium. Zn(BH4)2 was prepared by milling ZnCl2 and NaBH4 in a planetary ball mill under an Ar atmosphere. The prepared Zn(BH4)2 sample contained NaCl. 13.6 wt% MgH2+49.1 wt% Zn(BH4)2+30.2 wt% NaCl+7.0 wt% Ni (named 14MgH2+49Zn(BH4)2+30NaCl+7Ni) and 13.6 wt% MgH2+49.1 wt% Zn(BH4)2+30.2 wt% NaCl+7.0 wt% Ti (named 14MgH2+49Zn(BH4)2+30NaCl+7Ti) samples were prepared by horizontal ball milling. The gas release properties, especially the metal hydride decomposition temperatures (the onset temperature of the metal hydride decomposition and the maximum rate of released gas quantity change with temperature change), of the prepared samples were investigated using a Sievert’s type volumetric apparatus. The quantity of the gas released under 1.0 bar H2 was measured as the temperature was increased and the variation in the rate of released gas quantity Gr change with temperature T change, dGr/dT, as a function of temperature was obtained. This analysis method can be used instead of thermal analysis methods such as thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and differential thermal analysis (DTA). The investigated properties of the samples were then compared. In the as-milled 14MgH2 +49Zn(BH4)2+30NaCl+7Ni, it is believed that Zn(BH4)2 begins to decompose at about 350 K and the rate of Gr change with T change, dGr/dT, reaches its peak at about 390 K, and that MgH2 begins to decompose at about 670 K and dGr/dT reaches its peak at about 698 K.
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