Measurements and evaluations of the high-temperature physical properties of carbon and graphite products (Part Ⅰ): Thermal expansion

A device has been designed to measure the thermal expansion of artificial graphite products and a system developed for doing the same on carbon fibers. The device for the former evaluated the thermal expansion at temperatures > 2000 °C by using isotropic graphite in both its heater element and as a reference material in its measurement jigs. To measure thermal expansion at high temperatures, both a contact method using a push-rod, and non-contact methods with a laser dimensional measuring instrument were used. By measuring thermal expansion up to such ultra-high temperatures, it was possible to observe in-situ the dimensional shrinkage and/or expansion (i.e., puffing) of carbonized specimens during graphitization. In the measurement system for carbon fibers, small thermal strains in fibers heated by direct current were detected both in the fiber’s longitudinal direction and in its diameter using laser interferometry and diffraction methods, respectively. The temperature of the fiber sample was controlled not only by using a pyrometer but also by changing the voltage applied for heating. Each measurement device and system were verified using typical products, and some of the measurement results of temperature dependence of thermal expansion coefficient are presented.