EFFECT OF PRODUCT CONDUCTIVITY ON FIELD-ACTIVATED COMBUSTION SYNTHESIS

Experimental and modeling results on the field-activated combustion sy nthesis (FACS) of Nb5Si3 are reported. In the absence of an electric f ield and without reactant preheating, Nb5Si3 cannot be prepared by sel f-propagating high-temperature synthesis (SHS). Under the influence of a field a self-sustaining combustion wave is established whose rate o f propagation decreases with traveled distance. For relatively low; he ld values, the wave propagation mode changes from a continuous (smooth ) to a spin mode. The product of synthesis depends on the mode of prop agation. Synthesis during continuous wave propagation results in the f ormation of Nb5Si3, primarily in the alpha-modification. In contrast, when the wave propagates in a spin mode, the product is NbSi2 with unr eacted niobium. The present observations demonstrate a case where the field effect is not localized, as was the case in previous studies. Th e difference in behavior is attributed to differences in the electrica l conductivities of the product phases.