Ryuji Fujiura

Carbon disc of high density and strength prepared from heat-treated mesophase pitch grains

Abstract Carbonaceous grains for binderless moulding were prepared by control of the preheat-treatment of the naphthalene-derived mesophase pitch. The carbonized and graphitized discs were evaluated in terms of physical properties and textures. Carbon disc of strikingly high bulk density, 2.04 g/cm3, high compressive strength, 1.94 tf/cm2, and large shrinkage ratio, 15.9%, was obtained through the grinding of the pitch preheat-treated at 753 K, their cold moulding, carbonization at a heating rate of 12 K/h, and successive graphitization at 2173 K. A homogeneous fine-mosaic texture of optical anisotropy was observed over the whole region in the artifact, indicative of sufficient adhesion among grains during the carbonization. X-ray analyses suggested a graphitizing nature of the grains in their moulds. Grains preheat-treated under 753 K exhibited excess fusibility for adhesion, leading to partial flow texture, where many cracks were easily induced during the calcination, decreasing the strength of the disc. In contrast, preheat-treatment over 753 K caused insufficient adhesion among grains, decreasing markedly both density and strength of the disc. A slight but significant presence of the pyridine-insoluble/quinoline-soluble fraction in the preheattreated pitch system is indicated to play a major role in adhesive ability of the grains preheat-treated at 753 K.

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.

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.

Hanical properties of binderless carbon mould prepared from heat-treated mesophase pitch of controlled grain size

Abstract The mechanical properties of binderless carbon moulds produced from the preheat-treated mesophase pitch of controlled grain sizes were investigated. The particular mesophase pitch catalytically synthesized from pure naphthalene with HF/BF 3 was properly preheat-treated at 753 K for 2 hours and then ground by a jet-mill into grains of different sizes. These grains were moulded at room temperature under 170 MPa into a rectangular plate (35 mm × 40 mm × 5 mm) carbonized, calcined, and graphitized up to 2773 K to examine its texture and mechanical properties. The finest grains (average particle size: 2.4 μ m) provided a high-performance graphite artifact of the bending strength: 100 MPa, the compressive strength: 190 MPa. the total pore volume: 17 mm 3 /g, and the bulk density: 2.0 g/cm 3 , with extremely high carbon yield of 92% by large shrinkage ratio of 15%. The graphitized plate from the smallest grains exhibited a highly homogeneous tine-mosaic texture of optically anisotropic units μ m, which were randomly oriented. No boundary among grains was distinguishable after the carbonization, indicating that the whole grains in their mould firmly adhered to each other. A crack was not detectable over the entire region in the mould even after the graphitization. corresponding to the excellent mechanical properties. In contrast, the largest grains (average particle size: 8.0 μ m) provided a graphite plate of coarse-mosaic texture, where some cracks were induced by calcination at 1573 K. The graphitization developed the cracks, decreasing the mechanical strength. The density, homogeneous isotropy, and random orientation in the packing of mesophase pitch grains depending on the grain size appear to be key factors to achieve the high performance of the graphite artifact.