Intrinsic and mechanically modified thermal stabilities of α-, β- and γ-aluminum trihydrides AlH₃

The intrinsic and mechanically modified thermal stabilities of the α-, β-, and γ-phases of AlH₃ have been experimentally determined. The thermogravimetric profiles of the α- and γ-phases exhibit dehydriding reactions in the temperature range of 370-450 K. The amounts of hydrogen released are nearly 9 mass∈%. The profile of the β-phase shows the continuous dehydriding reactions, which differs from the other two phases. The values of the enthalpy of dehydriding reactions ΔH_dehyd. are determined to be 6.0±1.5, -3∼-5 and 1.0±0.5 kJ/mol∈H₂ for the α-, β- and γ-phases, respectively. The milling-time dependences of the powder X-ray diffraction measurement and thermal analyses indicate the occurrence of the dehydriding reactions both in the α- and γ-phases during milling, but there is no drastic change in the β-phase.