SHRINKING CORE MODEL TO DESCRIBE METAL PARTICLE OXIDATION FROM THERMAL ANALYSIS DATA

摘要

The oxidation of metals has widespread applications ranging from microelectronics to surface sciences, corrosion, and oxygen storage. High energetic materials mainly embody active metal particles, in addition to oxidizers and organic materials. Pyrotechnic compositions are based on metallic particles as well as thermites, which consist of metal-metal oxide combinations with differing metals. During various applications, the metal particles are subjected to reacting atmospheres, the oxidation being the most important result. For example, the conversion of solid energetic material starts with the phase transition and decomposition to build an oxidizing atmosphere in order to convert the metallic particles to metal oxide particles. The most important metals form solid oxides even at low temperatures. In this case, diffusion dominates the reaction in most reaction domains. In addition, diffusion and reaction may occur simultaneously. The shrinking core model describes a combined model based on a quasi-steady-state approximation, which assumes a uniform temperature distribution of the particle that is undergoing reaction. The approach starts with the equation for the static profile of diffusing oxygen from the surface into a sphere to the reaction front with the metallic fuel under quasi-static conditions. The conversion of the diffusing oxygen occurs in a first-order reaction and consumes the oxygen flux completely. A new and more correct method to solve the resulting equation has been applied to thermogravimetric measurements of aluminum oxidation. Reaction models are verified by the oxidation to γ- or θ-alumina and α-alumina and the kinetic parameters derived and discussed. A nonlinear, least-squares fit of the calculated curves to the measured data resulted in very good agreement.