A novel way of enhancing the electrical and thermal stability of conductive epoxy resin-carbon black composites via the joule heating effect for heating-element applications

The influence of Joule heating treatments and carbon black (CB) on the electrical and thermal behavior of epoxy resin composites is well described in this article. The effect of CB and Joule heating on network structure characteristics, such as shrinkability, interparticle distance between conductive particles, crosslinking density, hardness, thermoelectric power, thermal conductivity, the thermal expansion coefficient, and scanning electron microscopy, of epoxy composites was investigated. The electrical conductivity (sigma) of epoxy resin correlated with the volume fraction of CB and Joule heating treatment. sigma, increased continuously with increasing CB content, and Joule heating increased the level of sigma, which makes it attractive for electronic utilization. The sigma, for fresh and Joule heating samples was recorded during heating-cooling cycles. The conduction mechanism of sigma, for epoxy composites was identified. The activation energy and hopping energy for two batches of epoxy as a function of CB content were estimated. The hopping distance, the state density at the Fermi level, and the radius of localized wave function versus CB content were evaluated. The current-voltage-temperature characteristics of fresh and Joule heating samples of epoxy composites were demonstrated. The thermal reliability was tested by means of temperature-time characteristics when certain applied power was on and off for several cycles. The specific heat and amount of heat transfer by radiation and convection were calculated based on the energy balance model for two batches. The results indicate that the Joule heating effect is a very effective and prospective way of enhancing the electrical and thermal stability of epoxy-CB composites for consumer use as heaters and in other electronic areas such as electromagnetic shielding effectiveness. (C) 2002 Wiley Periodicals, Inc.