High-temperature oxidation of a metal particle: Nonisothermal model



A transient electric voltage of the order of 1 V may form during the combustion of a metal particle. The electrical field may form due to the different diffusion rate of the positive and negative charge carriers through a growing mixed-ionic-electronic conducting oxide shell. Unlike previous models, the effect of ambient gaseous oxygen transport to the particle surface is accounted for and steady-state and charge neutrality in the oxide layer is not a priori assumed. Four key parameters affect the voltage-temperature formation. The ratio between charge carries diffusion coefficients determines the surface electric potential amplitude, polarization and the time delay between the maximums of particle potential and temperature. The larger the difference between the diffusion coefficients, the greater is the voltage and the longer is the combustion time and the shorter is the time delay. The convection and radiation heat-transfer coefficients exert a major impact on the time delay between the maximum of the surface electric potential and that of the temperature. The maximum electric potential and temperature are achieved almost at the same time when the transport coefficients are sufficiently large. This time difference decreases as either the heat-transfer coefficients or the difference between the diffusion coefficients increase. Increasing the activation energy of the adsorption strongly decreased the oxidation, temperature and surface electric potential rate of rise during the early stage of the oxidation. Increasing the activation energy of the desorption increased the duration of the temperature and the potential drop in the later stage of the reaction. © 2005 American Institute of Chemical Engineers AIChE J, 2005