Combustion of Metallic Powders: A Phenomenological Model for the Initiation of Combustion

Abstract

A mathematical model which describes the process when a spherical metallic particle is exposed to an oxidizing atmosphere, has been formulated. We refer to the oxidation process in a generic sense, and the model can be used for the formation of oxides, nitrides and sulphides in general. The oxidation process is modeled for oxides which form n-type semiconductors with the defects in the form of interstitial cations and electrons (e.g., Al2O3) in terms of mass and energy transport phenomena.It accounts for the release of metal cations and electrons at the metal-oxide interface, the transport of these species through the oxide layer due to concentration and eleclric field gradients, and the formation of the metal oxide at the outer interface. As a result a hollow oxide sphere develops as the metal is converted 10 oxide. If the energy released by the oxidation reaction exceeds the heat losses, self-heating will occur. Such a rise in temperature accelerates the release of cations and electrons from the metal i...