The oxidation of Al-particles down to nano-scale was investigated by TG, SEM and in-situ X-ray diffraction. Al particles are usually coated by a 2 ± 4 nm layer of Al 2 O 3 which can be derived from the degree of weight increase on complete oxidation by TGcurves. The low temperature oxidation of Al particles occurs at least in two steps. The first step builds a layer of 6 to 10 nm thickness composed of crystallites of the same size independent on the initial particle size. This reaction is dominated by chemical kinetics and converts a substantial fraction of the particle if the particle sizes decrease below 1 mm, an effect carefully to be taken into account for nano-particles because of safety reasons. The second step combines diffusion and chemical reaction and proceeds therefore slowly, the slower the bigger the particles are. The kinetic parameters of these two steps can be obtained by a model taking into account both reaction steps, chemical kinetics and diffusion for spherical particles when fitting it to TG-curves. X-ray diffraction shows that particles smaller than 1 mm build gand q-Al 2 O 3 in the first step with nano-crystalline structures which are then transformed to a-Al 2 O 3 .

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Aluminum hydride is a promising candidate for application in energetic materials and hydrogen storages. E.g. an AP/HTPB rocket propellant filled with alane was calculated for a 100 N s kg À1 higher specific impulse compared to the same concentration of aluminum. Different investigations on a-AlH 3 polyhedra using thermoanalytical methods and X-ray diffraction were performed to receive a better understanding of dehydration at about 450 K, passivation of the remaining porous aluminum particles and further oxidation. A modeling approach to describe these conversions including diffusion processes, Avrami-Erofeev mechanism and Arrhenius type reaction steps of n-th order were introduced. Results were discussed in comparison to experimental investigations under pressure with model propellants on the base of gelled pure nitromethane and also filled with alane or pure aluminum in concentrations of 5%, 10% and 15%. Both alane and aluminum increase the burning rate on a factor of two correlated with a temperature increase up to 500 K and more. A mesa burning effect at 6 to 10 MPa was indicated by the mixtures with alane.

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