The effect of external electric fields on the nature and properties of materials synthesized by self-propagating combustion

Experimental and modeling studies were carried out to investigate the effect of electric fields on self-sustaining combustion synthesis reactions. It was shown that the field plays a major role in these reactions. By overcoming thermodynamic and kinetic limitations, the imposition of a field makes such reactions possible in systems which cannot otherwise sustain them. This makes possible the synthesis of a large number of ceramic, metallic, and composite materials. Modeling studies, based on the Fourier heat balance equation, showed that the effect of the field is primarily thermal, with Joule heating imparted to the system in a distribution which is dependent on the electrical conductivities of the participating phases. For systems with low conductivity products, the current is localized in the narrow (approximate to 1 mm thick) reaction front. The effect of electrical and thermal conductivities, as well as porosity was investigated. A major finding with practical implications is the effect of the field on the mechanism of the synthesis reactions. It was demonstrated that the field influences the nature of the product phases, their composition, and uniformity. The field, in this regard, can be considered as a processing parameter in the synthesis of materials. (C) 2000 Elsevier Science S.A. All rights reserved.