Ultrafine-grained isotropic graphite prepared from pitch-based carbon microbeads

In this work, ultrafine-grained pitch-based carbon microbeads (PCMBs) with a highly spherical structure were derived from the thermal polymerization of coal tar pitch at 350 degrees C for 4 h, followed by solvent extraction and drying processes. The PCMBs with average grain sizes of 6.00, 3.25, and 2.14 mu m were then obtained by ball milling, respectively. Three kinds of ultrafine-grained isotropic graphite (UGIG) were fabricated via isostatic pressing and sintering using the aforementioned PCMBs, and the effects of grain size on properties and microstructure were investigated. It was found that as the grain size decreased, their mechanical strength increased, accompanied by densification of the microstructure. The UGIG based on PCMB of 2.14 mu m possessed the highest density of 1.97 g/cm(3) and the lowest open porosity of 6.15 %. It featured a median pore diameter of 47.0 nm, with compressive and flexural strengths reaching 197.8 MPa and 91.5 MPa, respectively, as well as a high isotropy of 1.01.