Spectral analysis and temperature measurement during flash sintering under AC electric field

In-situ diffraction experiments were used to study the change in peak profiles of 8YSZ during conventional sintering and flash sintering under AC electric field. Using calibration from a conventionally heated standard, the lattice expansion of 8YSZ under flash conditions was correlated to actual specimen temperature, indicating temperature comparable to that required for conventional sintering. At higher current densities, a temperature rise greater than 2000 degrees C was reached, which resulted in abnormal grain growth and temperature instability. Microstructural analysis demonstrated that finer grain size can be achieved by limiting the current in order to avoid high specimen temperatures. Experiments varying the thickness of the green compact resulted in higher heat loss due to thermal conduction and corresponding reduction in final density. A replacement to the blackbody radiation model was successfully used to fit the data and explain all effects based on Joule heating as well as provide a flash sintering processing map incorporating furnace temperature, power dissipation, and sample geometry.