Modifications to carbonization of mesophase pitch by addition of carbon blacks

The addition of carbon blacks with large surface area or high oil absorption ability such as Ketjen Black (KB) was found very effective in suppress the swelling of mesophase pitch during carbonization. A good correlation between the swelling suppression and the dibutylphthalate (DBP) absorption ability indicates that a large effective volume of carbon black in the pitch system is a key factor in suppressing the swelling. The hollow structure and developed chain-like aggregate of carbon black particles are the origins of such large effective volume. Carbon black with large effective volume is well dispersed in mesophase pitch to initiate the pyrolysis of mesophase pitch at the lower temperature range, avoiding the intense pyrolysis and gas evolution in the narrow temperature range which leads to severe swelling of mesophase pitch. The carbon black dispersed in mesophase pitch is also effective to release the pyrolyzed gas smoothly from almost solidifying mesophase pitch of very high viscosity. Air- and CO(2)-gasification of a carbon black (MA600) improved its ability of swelling suppression comparable to that of KB. The air-gasification introduced a graphitic shell and hollow core in the particles of MA600 as observed with KB, significantly increasing the surface area at the low burn-off rate. The CO(2)-gasification decreased the nodule size, increasing the surface area proportionally with the burn-off rate. Such a structural change appeared to improve the ability for suppressing the swelling of mesophase pitch. (C) 1997 Elsevier Science Ltd.