International audienceAluminum nanopowders, oxidized at different temperatures using thermogravimetric analyses performed in high resolution mode, are characterized in terms of morphology, structure and microstructure. The particle structure is modeled via geometrical considerations that enable the calculation of the variation of specific surface area during oxidation. A two-step oxidation scenario is proposed. In the early oxidation stage, that is, for temperatures up to 650 degrees C where a pseudoplateau is reached, the oxidation, which occurs by diffusion of oxygen or aluminum through the alumina layer, leads to a core shell structure. At higher temperatures, that is, above the melting point of aluminum, outward diffusion of aluminum through the oxide shell is controlling the reaction rate. The reaction interface is then located at the external surface and voids are formed inside the particles. This result is confirmed by energy filtered electron micrographs that allow distinguishing a thin metallic aluminum layer outside the alumina shell. This suggests that the migration of aluminum toward the surface of the particles is faster than the oxidation. Some insights on the nucleation process during the crystallization of liquid aluminum are also proposed which are related to the particle microstructure: heterogeneous nucleation is proposed to govern the crystallization of liquid aluminum and to give a signature of the alumina layer structural state

International audienceHigh-energy ball-milling is proven to be an effective technique for manufacturing reactive aluminum nanopowders. The procedure of milling presented in this work allows the elaboration of aluminum powders with specific surface areas around 20 m 2 /g. The particles have platelet morphology and are constituted by a nanocrystalline aluminum core surrounded by a thick amorphous alumina layer of 4.57 0.5 nm. The reactivity of the powders is enhanced as compared to nanopowders elaborated with techniques involving vapor phase condensation. The morphology, the microstructure and the initial thickness of the alumina layer are shown to be important parameters that influence the reactivity. The method could be extended to any other ductile metal, provided a hard surface layer is continuously formed during milling

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