The Thermal Expansion of Various Carbons, its Thermal Dependence, and Carbons having Negative Expansion Coefficient

Abstract

Thermal expansion of various carbons brerared at 1200°C or graphitized, have been measured over the temperature range frome room temperature (20°C) to about 600°C by using a dilatometer, shown in Fig 1.
The mean thermal expansion coefficient “α” of various carbons are found to differ largely with each other in its kind. Some of these as anthracite and Ceylon graphite was anisotropic in α. Particulary, pitch coke which is anisotropic in its bubble pore and is heated at 1200°C or graphitized, and anthracite which is graphitized, have showed a “negative α”, up to certain temperature along its layer direction. A specimen, molded with mixed powder of Ceylon graphite and pitch, showed also a negative α in a direction perpendicular to the molding pressure. Expansion of most carbons and contraction of anisotropic pitch cokes with increasing temperature is seen in Fig 2. The α values of these specimens showed a linear increase with increasing temperature in these temperature range as is seen in Fig 3. The coefficient of the temperature dependence of α was 1.8×10^-9 for petroleum or pitch cokes and this is not affected whether it is block of raw material or formed article and it is graphitized or not. Other carbons such as metallurgical coke have different cofficient of thermal dependence of α respectively.