COMPOSITE PTCR THERMISTORS UTILIZING CONDUCTING BORIDES, SILICIDES, AND CARBIDE POWDERS

Ceramic-polymer composite thermistors using conducting boride, silicide, and carbide powders that include TiB2, ZrB2, NbB2, NbSi2, WSi2, MoSi2, and TiC have been fabricated. Percolation and subsequent PTCR effects were observed for all the powders in both semi-crystalline (polyethylene) and amorphous (epoxy) polymer matrix materials, however, as found for carbon black and metal fillers, both niobate powders did not exhibit a PTCR effect in the amorphous polymer. Results indicate that percolation and PTCR behaviour are related to the powder characteristics (size/distribution), composite microstructure and ceramic-polymer interface. Composite thermistors with room temperature resistivities as low as 1-OMEGA-cm and a nine-order of magnitude change (DELTA-rho) at 1 kHz (12-DELTA-rho at d.c.) were achieved.