Reactive flash sintering in a bilayer of zirconia and lanthana: measurement of the diffusion coefficient in real time

Reactive flash sintering is a process where off-the-shelf powders of elemental oxides can be simultaneously sintered and reacted to form a multicomponent oxide in a matter of seconds at low furnace temperatures. The fact that several cation species, each residing within their own particles, can migrate over distances of several micrometers, and mix on the atomic scale to form multicomponent oxides, so quickly, is quite remarkable. The question arises as to the rate of this solid-state diffusion phenomenon. In this paper, we present measurements of this diffusion coefficient from live flash experiments. The results are obtained from millimeter scale bilayers of yttria-stabilized zirconia and lanthana where the flash initiates in the zirconia layer and then migrates into the lanthana layer, forming lanthanum zirconates. The velocities of migration of the flash-front, coupled with measurements of the length scale of the profile of zirconium and lanthanum interdiffusion, across the bilayer interface, provide an estimate of the effective diffusion coefficient. These measurements give a value for the cation diffusion to lie in the range of 2.5 x 10(-10) m(2) s(-1) at 1380 degrees C, with an activation energy of 200-250 kJ mol(-1). In comparison, the cation diffusion coefficient in yttria-stabilized zirconia, at 1350 degrees C, is stated to be 1.1 x 10(-20) m(2) s(-1) with an activation energy of similar to 550 kJ mol(-1). A pause for reflection.