Review on the high-temperature resistance of graphite in inert atmospheres

Temperature dependence of electrical resistivity of graphite materials at high temperatures up to 3000 °C was discussed on the bases of the published results on the measurements of resistivity of graphite rods and resistance of graphite heaters in high temperature furnace in inert atmospheres, Ar, N2 and He, and in vacuum. After passing through its minimum at around 1000 °C, resistance of graphite materials for most experimental conditions increases monotonically with increasing temperature up to 3000 °C. Due to extrinsic factors at certain experimental conditions in Ar atmosphere, however, a marked reduction in resistivity of the graphite rod above 2200 °C and also in resistance of the graphite heater above 2500 °C have been reported, no such resistance reduction having observed on the graphite heaters made from the same graphite material in N2 and He atmospheres, and under vacuum. The resistance reduction in Ar atmosphere at around 2000-2500 °C was supposed to be due to the formation of a short circuit by ionized Ar, which could be accelerated by the coexisted vaporized gases from the carbon materials loaded in the furnace to be heat-treated. The resistance reduction could be avoided by mixing more than 32% He in Ar.

Resistance of graphite materials increases monotonically with increasing temperature up to 3000 °C after passing through its minimum at around 1000 °C. However, the resistance reduction at around 2000-2500 °C is often observed in Ar atmosphere due to ionization of Ar. The resistance reduction can be avoided by mixing more than 32% He in Ar, which is important for saving costs for the atmospheric gas and electricity for heating.50