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 N ₂ 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.