Experiments revealed that a transient electric voltage of the order of 1 V may form during the combustion of a single metal particle. We present a model showing that such an electrical field may form as a result of the different diffusion rates of the positive and negative charge carriers through a growing mixed-ionic-electronic-conducting oxide shell. Simulations of the evolution of the electric charge carriers and temporal potential distribution reveal that three key parameters affect the voltage formation. The ratio of the characteristic oxygen ion diffusion rate within the particle to the maximum oxygen transport rate to the particle surface affects the formation of a diffusion layer and the carrier distributions inside the oxide shell. The ratio between the thickness of an exterior oxide layer, formed before the reaction has started, and the Debye screening length has a strong impact on the amplitude and temporal evolution of the voltage. The thinner this initial oxide shell is, the larger is the voltage amplitude. The ratio between the diffusion coefficients of the positive and negative charge carriers determines the sign of the excess electrical charge on the surface. (C) 2004 American Institute of Chemical Engineers.