Synthesis and characterization of low specific resistance alumina-clay–carbon composites by colloidal processing using sucrose as a soluble carbon source for electrical applications
Switching resistors in high voltage circuit breakers require the use of materials with low specific resistance which can sustain high temperatures for short durations, have high thermal conductivity and thermal shock resistance. Materials that satisfy these requirements can be produced by dispersing a conducting phase such as carbon black, graphite, CNT, graphene in ceramic matrix. Dispersion of these ultrafine forms of carbon to obtain contiguity at lower volume fractions is a challenge. In this work, alumina-clay–carbon composites were fabricated by using alumina-clay slurries with addition of sucrose as a soluble carbon source. Sucrose is converted into conducting carbon with heat treatment at high temperatures. Alumina-clay–carbon composites made using a soluble source (sucrose) sintered at 1400 °C showed resistor behaviour even at carbon contents less than 1 wt% produced by graphitization of sucrose at high temperature. Raman spectroscopic scans over a wide area of the samples confirmed uniform distribution of carbon within the ceramic matrix. Resistivity of the alumina-clay–carbon composites varied between 30 ohm cm to 2 ohm cm for sucrose additions (equivalent to carbon content) of 2–9 wt%. The resistivity of the composite samples produced with the use of sucrose was significantly lower than that of samples produced by dispersing carbon black as the conducting phase.