Temperature dependence of electrical resistivity, deformation, and fracture of polygranular graphite with different amounts of porosity

Synthetic polygranular graphites have a wide range of current and potential applications. Indeed, some are being considered as candidate moderator materials for the next generation of nuclear power plants, which are designed to operate at temperatures as high as 1000 degrees C. Detailed experimental work has been performed to investigate the electrical resistivity and mechanical behaviour of a synthetic graphite over a range of temperatures. An electrothermomechanical testing rig has been employed to conduct tensile tests to evaluate elastic modulus and fracture strength over the temperature range from room temperature to 700 degrees C for a near-isotropic synthetic polygranular graphite. A series of mm length scale 'dogbone' geometry specimens, containing varying levels of porosity between 8% and 18%, were used for testing. Acquired data revealed an average of 30% gain in material stiffness, occurring at temperatures above 400 degrees C. Tensile strength decreased linearly with increasing porosity at higher temperatures (700 degrees C). The accumulated percentage reduction of resistivity during the transition from room temperature to 700 degrees C reduced linearly with increasing amounts of porosity. The resistivity and mechanical property measurements are discussed, with particular attention given to the porosity of the synthetic graphite.