A Study of the Pressure-Composition-Temperature Curve of Mg(BH4)2 by Sievert’s Type Apparatus

Abstract

The Pressure-Composition-Temperature(PCT) curve of Mg(BH4)2 was studied by Sievert`` type apparatus. In order to understand the slope of the first plateau pressure, a thermal analysis technique was introduced. The PCT curves of the dehydriding reaction for Mg(BH4)2 are measured at 573, 598, 623, and 653 K, respectively. Under every temperature measured, the first plateau pressure shows slope but the second plateau pressure of MgH2 is clearly observed. The apparent enthalpy for the first plateau pressure from Mg(BH4)2 to MgH2 is roughly estimated. The equilibrium pressure at each temperature is determined to be the first plateau pressure where the hydrogen content is -5wt%. The apparent enthalpy for the first reaction from Mg(BH4)2 was estimated to be △H = 51.1 kJ mol-1 H2, and the apparent enthalpy for the dehydriding reaction from MgH2 was estimated to be △H = 90.0 kJ mol-1H2. The result of the thermal analysis shows three peaks. This means that it decomposes at least through the pathway of three reactions.