Heat Transfer during Heat-treatment of Carbon Fibers by Direct Currenting

Abstract

A polyacrylonitrile-based carbon fiber tow was heat-treated by directly passing electric current through the tow. The relation between the surface temperature of the tow and supplied electric power was analyzed by an energy balance equation. The rediation became the dominant factor for the heat-loss at high temperatures. The apparent heatconductivity of tow increased with increasing temperature. Temperature distribution in the crosssection of tow was analyzed by considering the temperature dependences of heat-conductivity and specific resistivity. The calculated temperature difference between the center and the surface of the tow increased with increasing surface temperature. The temperature distribution was reduced by installing a reflector around the tow. It is expected that the temperature distribution in a tow gives rise to a certain distribution of the structure of carbon fibers. This subject was also studied by analysing the intensity profiles of wide-angle x-ray diffraction. The integral width of 002 reflection for the tow heat-treated by direct currenting was calculated by using the analyzed temperature distribution and the heat-treatment temperature versus layer thickness relation obtained for the carbon fibers heat-treated with a conventional furnace. The estimated values agreed well with the experimental ones.