Koichi Kanno

Effects of carbon black addition on the carbonization of mesophase pitch

Abstract Carbonization of a mesophase pitch produced catalytically from naphthalene with HF/BF3 was examined by blending carbon black particles to suppress its severe expansion just before the resolidification that was its major disadvantage for the application as a composite binding substance. The carbon blacks were found effective to suppress the expansion of the mesophase pitch, the particle of large surface area or high oil absorption ability in the pitch such as Ketjen Black (KB) being most effective. The KB particles were found well dispersed in the whole area of the pitch, extending the chain structure, breaking the molecular stacking into smaller optical units (fine mozaic), and hindering the graphitization at the calcined and graphitized stages of the mesophase pitch. Such dispersed particles are expected to release the evolved gases from the molten mesophase pitch along their surface. It is noted that the slurry of the mesophase pitch with carbon blacks maintained the viscosity low enough for smooth impregnation before the carbonization, although the blending certainly increased apparent viscosity.

Evaluation of naphthalene-derived mesophase pitches as a binder for carbon-carbon composites

Binding properties of the mesophase pitches produced catalytically from naphthalene with HF/BF3 were examined in terms of their carbon value, fluidity, thermal stability and oxidative stabilization reactivity. The present pitches with 100% anisotrophy and low softening points of 207–275°C provided very high coke yields of 80–88 wt% under atmospheric pressure and 90–95 wt% under 30 atm. Pitches with softening points of 207 and 224°C exhibited strikingly low viscosity below 1 Pa♦s at 350°C. It is noted that viscosity-temperature profiles of a series of the present pitches cover the complete area of the processing window for the manufacture of carbon-carbon composites, whose processes typically include impregnation of mesophase pitch into a two-dimensional carbon fiber preform, oxidative stabilization and successive carbonizations. The pitches were thermally stable under nitrogen at 300°C, keeping the melt viscosity constant for longer than 100 h to assure easy handling. At the same time, they were very reactive for the oxidation in air at 200°C for rapid stabilization.

Mesophase pitch and phenolic resin blends as binders for magnesia–graphite bricks

Abstract Naphthalene-derived mesophase pitch (NMP) and phenolic resins of novolac type and resol type were applied for the binder of MgO–C brick. NMP provided a brick of high strength at over 1000°C and high oxidative resistivity, however, the apparent porosity of the brick was high because of NMPs expansion at the carbonization. Both types of resins provided bricks of high strength and low apparent porosity at low temperature, the strength seriously decreasing over 1000°C. A blend of NMP and the resins provided bricks of excellent performance with high strength and low apparent porosity in a wide temperature range and high oxidative resistivity. The thermosetting resin bound MgO around 100°C and surrounded the dispersed NMP particles to prevent expansion at the latter carbonization, while NMP-originating carbon moderated the strong shrinkage of the resin over 1000°C, maintaining the high strength and density of the brick in a wide temperature range.

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 (DBF) 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. Airand CO2-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 CO2-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.

Self-adhesive carbon grains oxidatively prepared from naphthalene-derived mesophase pitch for mould of high density

Self-adhesive carbonaceous grains for binderless mould were prepared through the oxidation treatment of the ground mesophase pitches catalytically synthesized from naphthalene with HF/BF3. The oxidation conditions strongly influenced the carbonization behaviors of the mesophase pitch grains and the strength of the resultant carbon artifacts (diameter: 20 mm, thickness: 4 mm). The oxidation at 493 K for 1–2 h in air flow was optimum to balance the fusibility and the thermosetting property of the mesophase pitch grains. The properly oxidized grains were proven to show self-adhesive ability, shape stability, and higher carbon yield, providing a carbon artifact of strikingly high density, 1.88 g/cm3, high compressive strength, 2.9–2.6 tf/cm2, and large shrinkage ratio, 33–42 vol% by the calcination at 1573 K. The observation using a polarized light optical microscope and SEM indicated fine-mosaic texture, dense packing, and sufficient adhesion of the grains in the carbonized artifact.

Densification of carbons prepared from mesophase pitch and phenolic resin blend

Co-carbonization of naphthalene-derived mesophase pitch (NMP) and novolac-type phenolic resin (NV) was investigated to densify the carbon derived from the mesophase pitch. Blending both types of phenolic resin to NMP suppressed the expansion during carbonization to densify the resultant carbon. Thermosetting NV before the carbonization of NMP fixed the molten pitch in the crosslinked network, suppressing the expansion of NMP. Blending in THF before the carbonization was effective in making the region of NMP smaller, leading to higher bulk density and finer mosaic texture of the resultant carbon. The carbon yields of the blend were lower than those expected from the additivity line. A large amount of naphthenic hydrogen of NMP is released to react with phenolic OH to prevent crosslinking and decompose phenolic resin. The air blowing of NMP drastically decreased its aliphatic hydrogens, increasing the carbon yields and the bulk density of the blend.