Electrical Properties of Zinc-Kaolin Composites below its Percolation Threshold
In this paper, we present some electrical properties of the zinc-kaolin cermet resistors with zinc metal fillers below the percolation threshold. Rectangular cermet rods of dimensions 65 mm by 6.5 mm by 3.2 mm were produced in a mould with semi-dry the zinc/kaolin powder mixture which is compressed with a force of about 1.32 x 105 N. Percolation threshold was found to be both a function of the metal-kaolin ceramic mixture and the annealing temperature. The percolation threshold for cermets annealed at 300and 4000C is between 70 and 80% (vol.) while the cermets annealed at temperatures between 500 and 9000C is between 15 and 20% (vol.). The electrical conduction mechanism of the zinc-kaolin cermet below the percolation threshold is a mixture of both the hopping and the tunneling model with the hopping mechanism dominating. The temperature coefficient of resistance (TCR) is predominantly positive and large (30000-45000 ppmK-1) when cermet temperature is below 1000C. It is observed that changes in the measurement of TCR can be used to determine percolation threshold in cermets.
Keywords: Cermet, Percolation threshold, Electrical properties, Composite, Hopping and Tunneling.