Large-diameter ceramic room-temperature flash sintering technology based on new carbon electrodes

Room-temperature flash sintering (FS) for ceramics is a highly efficient and energy-saving new ceramic sintering technique. Addressing the current challenges in room-temperature flash sintering research, such as small product sizes, shape limitations, and high power requirements, limits their real application in the FS industry. In particular, for dog bone shape and small size, which are usually smaller than 10 mm, no records of sizes larger than 20 mm have been reported. In this study, a novel flash sintering device based on a composite layered carbon electrode structure was developed to conduct large-diameter sample flash sintering at room temperature (RT) in an air atmosphere under a direct current (DC) voltage below 100 V. Specifically, room-temperature flash sintering was achieved for ZnO ceramic disks with diameters of 40.0 mm and thicknesses of 1.80 mm, achieving a maximum relative density of 96.02%. Furthermore, room-temperature flash sintering was achieved for ZnO varistor ceramic disks with a diameter of 40.0 mm and a thickness of 1.93 mm, reaching a maximum relative density of 99.27%, a maximum voltage gradient of 330.5 V·mm⁻¹, and the highest nonlinearity coefficient (α) of 23.0. Room-temperature flash sintering was also achieved for 3 mol% yttrium-doped zirconia (3YSZ) ceramic disks, achieving a maximum relative density of 98.48%. The proposed flash sintering device and corresponding process demonstrate broad applicability for the ceramics industry.