Functional Carbon-Ceramic Composites for ElectronicsPart 2: The Study of Percolation Threshold in Carbon-Ceramic Composites

摘要

The percolation effects has been largely studied for different systems especially for bi-phase materials. Our studyconcerns three-phase composites materials over/under the percolation threshold. It is provided an investigation of carbonceramicmaterials obtained for a fixed ratio kaolin: α-Al2O3 of 1:1 with a variable content of graphite in the range of 10-20% wtas well as a comparison between materials containing graphite particles < 32μm and those containing graphite particles <63μm.Up to 12% wt graphite the composites show a dielectric behavior. Small pellets were investigated by Impedance Spectroscopyin the range of 10-3-107 Hz at 25℃. Using graphite <63μm, the electrical resistance is decreased up to one order of magnitudeshowing also a better stability over the entire range of frequencies compared with the former. For less than 14% wt graphite thepercolation threshold is attained. Through percolation threshold the electrical resistance dramatically decreases for about 108times. In the range of 14-20% wt graphite, the composites show a semimetallic conduction with a very good stability inalternating as well as continuos electrical fields. DC measurements in the temperature range of 25-220℃ shows a small andnegative temperature coefficient of variation of the electrical resistance. Optical and SEM investigations established therelationship electrical properties/microstructure over/under percolation threshold.