Oxidation Mechanism of Aluminum Nanopowders

Aluminum 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 °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 alu...