Changes in the yield and size distribution of mesophase spheres on suppressing convective motion in a fused coal tar pitch

Upon heating of a coal tar pitch at 703 K, vaporization of the tar was promoted to a degree of 15–20 wt.%, either by increasing the free surface of the fused pitch exposed to a N2 atmosphere or by jetting N2 onto the surface. Enhanced viscosity of the pitch matrix by removing tar combined with restricted convection of the matrix prevented mesophase spheres from frequent coalescence and maintained a high interfacial area between the spheres and the matrix. The high interfacial area allowed a rapid increase in yield and sphere size. Sphere yields were up to 30 vol.% of the residual pitch, which lacked a bulk mesophase, and in which the average sphere radius was 2–4 μm.