Study on dehydrogenation and oxidation kinetics mechanisms of micron α-AlH3 in an oxidative atmosphere

Aluminum hydride (AlH3) exhibits attractive properties, such as high hydrogen/energy storage, relatively good stability, and low dehydrogenation temperature. Thus, AlH3 has appreciable prospects as a component in solid propellant for promoting the specific impulse of rocket engines and for effectively reducing the erosion of engine nozzles. The TGMS, SEM, XRD, XPS, and EDS results show that the thermal reaction of AlH3 is divided into three stages: (1) Dehydrogenation (below 210 degrees C, 2AlH(3)-> 2Al+3H(2)) starts from the inherent defects on the surface with an incomplete decomposition due to the passivation reaction in which an amorphous Al2O3 layer is formed to encapsulate the contained hydrogen. This is accompanied by nucleation and growth of Al nuclei from the outer particles to the inner particles and the formation of H2O via oxidation of the generated hydrogen. (2) The primary oxidation of Al (210-650 degrees C, 4Al+3O(2)-> 2 gamma-Al2O3) is attributed to a discontinuous layer of gamma-Al2O3, which is transformed from amorphous Al2O3 that results in the reaction of naked residual Al and O-2. (3) The secondary oxidation of residual Al (above 650 degrees C, 4Al+3O(2)-> 2 alpha-Al2O3) occurs because of the crystal conversion from gamma-Al2O3 to alpha-Al2O3, which leads to the shrinkage of the oxide shell and to the formation of cracks. Also, melting of residual Al