Oxidation of Micro-Sized Aluminium Particles: Hollow Alumina Spheres

Oxidized aluminium microparticles have recently been proposed for manufacturing new, environmentally-friendly, protective coatings on stainless-steels and Ni-base alloys. The oxidation mechanisms of spherical aluminium microparticles of an average particle size of 3.5 mu m were studied. Accordingly, simultaneous differential thermal analysis-thermogravimetry tests were carried out in air at different temperatures, always above aluminium melting temperature. Scanning electron microscopy and XRD were also used for the interpretation of results. Weight gain and energy results were explained in terms of the different structural changes taking place in aluminium particles. Dehydroxylation process was identified. The transformation of amorphous alumina to gamma-Al2O3 was numerically evaluated and the alumina phase transformation (gamma-Al2O3 -> I +/--Al2O3) was also studied. The temperature ranges revealed the appearance of metastable phases (theta-Al2O3). Complete oxidation of particles can be obtained at 1,300 A degrees C in < 1 h, although this also takes place at lower temperatures if enough oxidation time is used. Activation energy of oxidation process at high temperature was also estimated, taking a value of 334 kJ/mol. High temperature oxidation causes the formation of hollow alumina spheres, without any aluminium left inside them.

Oxidation of Micro-Sized Aluminium Particles: Hollow Alumina Spheres Articles