SPS of conductor–insulator system close to percolation threshold based on Si3N4–ZrN

DOI: 10.62564/M4-BP1622

Bohdan Pokhylko, Valerii Kolesnichenko, Andrey Ragulya

Institute for Problems in Materials Science NAS of Ukraine


There is a difference in how conductive and insulating materials are heated during Spark Plasma Sintering (SPS) [1]. Conductive materials can be additionally heated by Joule heating, which may cause changes in shrinkage behaviour and structure evolution [2]–[3], and even thermal runaway [3]–[4]. It may be especially crucial for the conductor-insulator system which can drastically turn from insulator to conductor during SPS due to porosity reduction to a certain level called percolation threshold [5]. SPS of (Si3N4–30vZrN)–5vY2O3, SEM analysis of powders and sintered samples were carried out. To regulate the current density in the powder, combinations of die and powder were isolated from the current flow by applying an insulating coating (BN). A rapid rise in current indicators was observed when the die was isolated. It is assumed to be caused by the drop in powder resistivity after reaching the percolation threshold. In contrast, other isolation schemes with no applied isolation and isolation of both the powder and the die show nearly linear dependences. SPS with the isolated die appears to be more sensitive to the change in the powder conductivity due to concentrating most of the current in the powder instead of the die. The application of higher current density in the powder caused a lowering of the temperature at which shrinkage began up to 60 °C, and the shrinkage intensification at the final stage up to 2 times. The calculations of the resistance of the electric circuit of die and powder with different combinations of isolation of die and powder proved it. Displacement of punches, changes in height and conductivity of the powder sample were considered. The derived equation allows to evaluate the change in the powder conductivity during sintering. Therefore, SPS with the isolated die is quite a useful technique for the investigation of conductor-insulator systems with the percolation threshold.

Keywords
Spark Plasma Sintering, percolation, Si3N4, ZrN

Acknowledgments
Not provided

References
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