Current Isolation in Spark Plasma Sintering of Conductive and Nonconductive Ceramics

Abstract

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.

A methodology to investigate the intrinsic effect of the pulsed electric current during the spark plasma sintering of electrically conductive powders

“…A voltage of about 10 V was measured but no current could be detected under the above simulated experimental conditions. Similar theoretical and experimental results were obtained by Carney and Mah when attempting to restrict the electric current to flowing through alumina samples [20]. Thus, we may conclude that the electrical contact resistances in ensemble C may affect the total current flowing through the system, but its distribution among the different elements should not be affected.…”

“…In fact, an intrinsic effect of the application of a pulsed electric current have been experimentally observed only on the solid-state diffusion during steel plates boriding [21] and on reactivity during diffusion couples experiments [22][23][24]. On the other hand, by imposing the same temperature and mechanical pressure, similar densities and microstructures were observed in electrically conductive ceramic samples heated by either restricting the current to flow only through the powder or with current allowed to pass through both the graphite die and the powder [20]. Further experimental investigations conducted following the proposed approach may shed light on the behavior of aluminum powder under different operating conditions or of other electrically conductive powder.…”

Electric Field-Assisted Sintering and Hot Pressing of Semiconductive Zinc Oxide: A Comparative Study

“…Only a few articles have been published on the specific mechanisms involved during FAST, induced thermally, electrically, or mechanically, but the number of such investigations grows. In the case of FAST sintering, a crucial point is the possibility for an electrical current to flow through the specimen 6–9 . If the electrical conductivity of the material is high enough, a current can pass through the powder compact and the local temperature at the contact points between particles may be increased by several hundreds of degrees centigrade 2 .…”

Microstructure and tribological properties of pulsed electric current sintered alumina–zirconia nanocomposites with different solid lubricants

“…The pulsed current is applied through the mould/powder system. If the powder is conductive, it is heated by its specific resistance; when powder is an insulator, the heating is conductive and occurs by the rapidly increasing temperature of the mould [35]. The heating rates can be even a thousand degrees per minute, though usually it is kept around 50-200 1C/min.…”