Numerical model for sparking and plasma formation during spark plasma sintering of ceramic compacts

The conditions for spark discharge and plasma formation in non-conducting ceramic granular compacts subjected to spark plasma sintering (SPS) were analyzed. The SPS plungers-die-powder assembly was modeled, whereby a compact of spherical YAG nanoparticles was considered. Electric resistance of the simulated SPS assembly versus temperature was comparable to that of the experimental SPS system. The conditions for particle surface charging and discharge were determined with respect to the applied current, the SPS temperature, and duration. Sudden increase in the electric current through the simulated granular compact was observed around 1200 A degrees C, confirming the percolative nature of the current. This finding is in agreement with the experimental densification start at 1250 A degrees C. Moreover, the electric current percolation was simulated by passing a DC current through a modeled granular compact box, comprised of resistors and capacitors which resembled the particle's surface resistivity and the inter-particle gaps, respectively. Spark discharge and plasma formation depend on connectivity within the granular compact and cease with the formation of a close-packed system.