Abstract
The original flash sintering experiment was carried out by applying an electric field, and switching to current control at the onset of the flash, signaled by a rise in conductivity. Here, we consider experiments where the experiment is controlled from the very start, by injecting current, which is increased at a constant rate. The current rates are varied from 50聽mA/min to 5000聽mA/min. The experiment is continued until, in all cases, the current density reaches 100聽mA/mm2. The total duration of the experiment ranged from approximately 7聽seconds to 700聽seconds. The following comparisons to the earlier voltage鈥恡o鈥恈urrent experiments are noted: (a) in both instances, the onset of the flash is signaled by an unusual rise in conductivity; however, since the power supply remains in the current control mode, the increase in conductivity is manifested by a drop in the voltage generated across the specimen; (b) the blackbody radiation model is modified to include the energy absorbed in specific heat, in order to determine the time鈥恉ependent change in temperature as the current is increased鈥攖his correction is particularly significant at the very high current rates; (c) sintering occurs continuously, reaching full density, in all instances, when the current density reaches ~100聽mA/mm2; and (d) these early experiments suggest that the current鈥恟ate experiments yield fine鈥恎rained microstructure across the entire gauge section of the dog鈥恇one specimen, presumably because the highly transient conditions of voltage鈥恡o鈥恈urrent flash experiments are sidestepped. The experiments were carried out on 3 mol% yttria鈥恠tabilized zirconia.