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

Abstract

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 G_r change with temperature T change, dG_r/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 G_r change with T change, dG_r/dT, reaches its peak at about 390 K, and that MgH₂ begins to decompose at about 670 K and dG_r/dT reaches its peak at about 698 K.

DOI: http://dx.doi.org/10.5755/j01.ms.23.1.14270