Oxidation of nano-sized aluminum powders

Abstract

Oxidation of aluminum nanopowders obtained by electro-exploded wires is studied. Particle size distributions are obtained from transmission electron microscopy (TEM) images. Thermo-gravimetric (TG) experiments are complemented by TEM and XRD studies of partially oxidized particles. Qualitatively, oxidation follows the mechanism developed for coarser aluminum powder and resulting in formation of hollow oxide shells. Sintering of particles is also observed. The TG results are processed to account explicitly for the particle size distribution and spherical shapes, so that oxidation of particles of different sizes is characterized. The apparent activation energy is obtained as a function of the reaction progress using model-free isoconversion processing of experimental data. A complete phenomenological oxidation model is then proposed assuming a spherically symmetric geometry. The oxidation kinetics of aluminum powder is shown to be unaffected by particle sizes reduced down to tens of nm. The apparent activation energy describing growth of amorphous alumina is increasing at the very early stages of oxidation. The higher activation energy is likely associated with an increasing homogeneity in the growing amorphous oxide layer, initially containing multiple defects and imperfections. The trends describing changes in both activation energy and pre-exponent of the growing amorphous oxide are useful for predicting ignition delays of aluminum particles. The kinetic trends describing activation energies and pre-exponents in a broader range of the oxide thicknesses are useful for prediction of aging behavior of aluminum powders.

Identification of kinetic triplets by results of derivatographic analysis

“…This explains long and sustained interest in studying the features of metal nanopowder, in particular the kinetics of oxidation [3]. The proceeding heterogeneous reaction can be in full measure characterized by the so-called "kinetic triplet" -the frequency factor A, the activation energy and the mathematical description of the reaction mechanism f(α) [4,5,6].…”

Effect of Heating Rate on Ignition Characteristics of Newly Prepared and Aged Aluminum Nanoparticles

“…Puri et al [28] obtained similar results for the melting mechanism of nano aluminum. Noor et al [29] and Vorozhtsov et al [30] presented the staged oxidation process at low heating rates below 30 K/min. Sundaram et al [31] summarized the oxidation process of Al nanoparticles during combustion, including three stages: particle heating to core melting point, phase transformations and ignition, and surface combustion.…”

Adsorption behaviors of ether and aluminum surface: A molecular dynamics study

“…Issues like affecting the aging and ignition phenomenon are both associated with the oxidation of ANPs. 7 For overcoming such drawbacks, one solution is to coat ANPs by a protection layer. 6 In this study, an Al slab is investigated as a simplified model to study adsorption processes.…”