Experimental determination of dust cloud combustion parameters of α-AlH3 powder in its charged and fully discharged states for H2 storage applications

Abstract

This study discusses results of an experimental program for determination of dust cloud combustion parameters of charged and fully discharged states of metastable alane (aluminum hydride, α-AlH3 polymorph) powder in air. The measured characterization parameters include: maximum deflagration pressure rise (ΔPMAX), maximum rate of pressure rise (dP/dt)MAX, minimum ignition temperature (TC), minimum explosible concentration (MEC), and minimum ignition energy (MIE). These measured values are used for calculating the associated explosion severity (ES) index, and volume-normalized maximum rate of pressure rise (KSt). The experimental results show values of MEC and TC of fully discharged alane to be greater than those of the charged alane but measured MIE values are about the same. Moreover, the results show higher reactivity of fully discharged alane dust cloud in air compared to its charged state. For example, ES and KSt of discharged alane dust cloud in air are about 300% and 35% greater, respectively, than ES and KSt of charged alane dust. The higher air reactivity of fully-discharged (primarily Al powder) dust cloud compared to its charged state can be attributed to the higher surface energy (J/m2) of Al compared to that of α-AlH3. These experimental insights have safety implications in postulated risk scenarios involving light-duty vehicles powered by PEM fuel cells. The core insights and critical data provided by this contribution are useful for supporting development and promulgation of hydrogen safety standards and augmenting property databases of hydrogen storage materials.