Current Isolation in Spark Plasma Sintering of Conductive and Nonconductive Ceramics

A systematic study of current path in spark plasma sintering was conducted to determine its effect on the sintering of an insulating material. The current, voltage, temperature, and densification characteristics of Al2O3 held under constant pressure in a graphite die were determined. A comparison was made between samples in a graphite die with and without a BN coating. The BN coating prevented the current from flowing through the graphite punches and into the die body so that no indirect heating could occur. When no BN coating was used, the sample densified as expected; however, when a BN coating was used, no heating of the sample was observed. A brief comparison between the use of a BN coating with insulating and conductive samples is made using powders of HfB2-24 vol% SiC as an example.