Activation energy in the thermal decomposition of MgH2 powders by coupled TG–MS measurements. Part 1. Comparison among TG- and MS-data processing

The thermal desorption of hydrogen from commercial MgH2 powders was investigated by coupled thermogravimetry and mass spectroscopy (TG–MS). The analysis of the evolved gas species gives a detailed picture of the composition of the initial specimen and of its thermal decomposition: just before the H2 release from MgH2, additional H2O and CO2 are detected, sensing the presence of MgCO3 and Mg(OH)2 in the initial specimen. Measurements done at different heating rates allowed the determination of apparent activation energies for the whole thermal process. Moreover, by considering appropriate ion current signals of the MS data, the activation energies of the single chemical reactions, leading to the formation of H2O, CO2, and H2, were obtained. Differences coming from the choice of the (model-free isoconversion) method of analysis (Kissinger–Akahira–Sunose; Flynn–Wall–Ozawa; Starink; Friedman equations) are evidenced and discussed