Studying aluminum hydride by means of thermal analysis

Abstract

Chemical reactions and physical transformations that occur upon heating aluminum hydride (AlH₃, alane), stored for 25 years, in the temperature range of 50–1200°C in an atmosphere of nitrogen, argon, and air are studied by means of thermogravimetric analysis and differential scanning calorimetry. The heat of thermal decomposition and the hydrogen content are determined for the AlH₃ samples and are found to be 318 ± 25 J/g and 9.32 ± 0.24 wt %, respectively. It is established that the estimated enthalpy of formation of AlH₃ in stoichiometric composition (Δ_f H ≈ −10.3 kJ/mol) agrees with the literature data. After the release of hydrogen, the mass of the precipitate increases by 0.5 ± 0.3%, relative to the initial mass of the AlH₃ samples; the most likely reason for this effect is the adsorption of nitrogen (argon) in the micropores and mesopores that form. Thermal phenomena associated with the crystallization of the amorphous aluminum that forms after hydrogen is released from the alane particles are analyzed. It is established that the aluminum contained in initial AlH₃ samples is almost completely transformed into aluminum nitride and oxide (AlN and Al₃O₃) upon heating to 1200°C in nitrogen and air, respectively.