Processing map for touch-free flash sintering of a whiteware ceramic

Flash sintering has evolved into touch-free sintering, where free-standing workpieces can be sintered without attaching electrodes. Instead, the flash is transmitted from the surface of a reactor into the workpiece with superimposition of a magnetic field. Thus, sintering now depends on two independent parameters: the current used to sustain the flash in the reactor and the current flowing through the induction coil. We present a first report on the influence of these two parameters on the quality of the sintered workpiece. The specimens were made from whiteware, consisting of aggregates of ceramic particles interspersed with particles of a glass phase. The results are presented in a map with the reactor current and the induction current as the control variables. Three regimes are identified: insufficient sintering, good sintering, and the formation of defects. The reactor current emerges as an important variable: densification is poor if it is too low, and defects form if it is too high, with high density achieved in the intermediate regime. High induction currents are needed to achieve good sintering. Touch-free flash sintering has also been shown to sinter and at the same time transform powders of elemental oxides into a single-phase multicomponent ceramic.