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 effec t of electric fields on self-sustaining combustion synthesis reactions. It was shown that the field plays a major role in these reactions. By overcomi ng thermodynamic and kinetic limitations, the imposition of a field makes s uch reactions possible in systems which cannot otherwise sustain them. This makes possible the synthesis of a large number of ceramic, metallic, and c omposite materials. Modeling studies, based on the Fourier heat balance equ ation, 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 lo w conductivity products, the current is localized in the narrow (approximat e to 1 mm thick) reaction front. The effect of electrical and thermal condu ctivities, as well as porosity was investigated. A major finding with pract ical implications is the effect of the field on the mechanism of the synthe sis reactions. It was demonstrated that the field influences the nature of the product phases, their composition, and uniformity. The field, in this r egard, can be considered as a processing parameter in the synthesis of mate rials. (C) 2000 Elsevier Science S.A. All rights reserved.