Flash sintering as a nucleation phenomenon and a model thereof

Isothermal field-assisted sintering of two-phase, 50 vol% 3YSZ-alumina composites exhibit an incubation time for the onset of the flash event. Weaker applied fields and lower temperatures lengthen the incubation period. The effect is highly non-linear. For example at 1300 degrees C and 150 V cm(-1) the flash occurs nearly instantaneously (in 10 s), but extends to 2 h at 1275 degrees C and 65 V cm(-1). This behavior is reminiscent of nucleation and growth phenomena in chemically driven experiments involving phase transformations in the solid state. Here, a model for nucleation under electrical driving forces, based upon the growth of embryos of colossal permittivity is presented. Nucleation is the precursor to the onset of a flash. Therefore it occurs at the furnace temperature. Joule heating is a consequence of nucleation not the cause of it. (C) 2014 Elsevier Ltd. All rights reserved.