Temperature effects of electrical resistivity of conductive silicone rubber filled with carbon blacks

The temperature effects of electrical resistivity of conductive silicone rubber filled with widely varying concentrations of carbon blacks (CBs: GPF 660 carbon black, HAF N-330 carbon black, VXC-72 conductive carbon black, and BP2000 superconductive carbon black) were studied from 30 to 200degreesC. Both low positive temperature coefficient (L-PTC) and negative temperature coefficient (NTC) phenomena were observed, whose intensity and temperature range depend on the type and the concentration of CBs. A stronger temperature dependency of resistivity was observed when the CB concentration was in the percolation region. Unlike crystalline polymers/CBs composites, the high positive temperature coefficient (H-PTC) phenomenon was not observed in CB-filled silicone rubber when the CB concentration was near the percolation threshold. Generally, pronounced the NTC phenomenon appears in composites with small particles of CBs at concentrations near the percolation threshold, whereas a pronounced PTC phenomenon appears in composites with large CB particles of at concentrations exceeding the percolation region. If both PTC and NTC phenomena were in the same sample of conductive silicone rubber, the PTC phenomenon always appeared at relatively low temperatures and NTC at relatively high temperatures. The results were discussed. (C) 2003 Wiley Periodicals, Inc.