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

The intrinsic and mechanically modified thermal stabilities of the alpha-, beta-, and gamma-phases of AlH3 have been experimentally determined. The thermogravimetric profiles of the alpha- and gamma-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 beta-phase shows the continuous dehydriding reactions, which differs from the other two phases. The values of the enthalpy of dehydriding reactions Delta H-dehyd. are determined to be 6.0 +/- 1.5, -3 similar to -5 and 1.0 +/- 0.5 kJ/mol H-2 for the alpha-, beta- and gamma-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 alpha- and gamma-phases during milling, but there is no drastic change in the beta-phase.