Flash Sintering of ZnO Ceramics at Room Temperature with Bisectional Electrode Distributions

Flash sintering was a fabulous method to sinter ceramics in several seconds with lower furnace temperature. By applying bisectional electrode distributions and the two-stage sintering method, dense zinc oxide (ZnO) specimens were sintered at room temperature under AC fields from 4,333 to 7,067 V/cm without sintering aids, achieving an average relative density of 93%. Besides the effect of Joule heating, the sintering processes could also be induced by flashover along specimen surfaces, which were both observed and verified by the experimental results. The method lowers the onset voltages and currents thus works as an ideal solution to physical fracture of specimens caused by large power surge when flash events occur. This method could also be adapted to flash sinter other long materials and functional gradient materials (FGMs).