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Mechanical properties such as strength, modulus and strain to break, and coefficients of thermal expansion of mesophase-pitch-based carbon fibers were measured using the fibers with four different microtextures heat-treated at two different temperatures. The textures were radial with wedge, radial, random and onion. In strain to break of the fibers, there were not so much difference with different microtextures. Young's moduli, however, were different with microtextures, especially in graphitized fibers. The modulus cor-respond to the orientation function, and to crystallographical parameters. The fiber with higher modulus seemed to be stronger. Coefficients of thermal expansion of the carbonized fibers were able to be classified into two groups; those of the fibers with radial with wedge/random and with radial/onion, but those of graphitized ones were in the same level. The coefficients were smaller than those of PAN-based fibers with the same Young's moduli.

The changes of X-ray parameters, c0, Lc (00l), La (110), and Lc (112), with heat-treatment temperature (HHT) were investigated on three types of meso-carbon microbeads (MC) and also on the cokes obtained from each raw pitches by carbonization at 430°C for 40hr. The values of c0 and La (110) for the MC were similar to those for the cokes above 1600°C. The (112) diffraction profile of the MC appeared above 2200°C (c0=6.85A). This temperature was higher than that for the cokes, but the MC and the cokes showed similar relation between c0 and Lc (112). On the relation between c0 and Lc (112) On the relation between c0 and lattice strain (ec) which was calculated from the slope of the plot of 1/Lc (00l) vs. l, ec of three types of MC was 0.015 when c0 was about 6.75A, being larger than that of the cokes. The differences of X-ray parameters between the MC and the cokes were explained from the shape of the sphere which was preserved during heat treatment of MC.

It is attempted to produce high density, high strength and isotropic carbon solids made of meso-carbon microbeads.This paper describes relation between processing conditions for production of carbon solids and these mechanical strength.The meso-carbon microbeads used were Type M and Type P, these microbeads were done the molding without binder pitch under the pressures of 500-3000kg/cm2 at a room temperature. The molding was heattreated at final temperature of 1000-2800°C. Density, weight loss, shrinkage and strength of the obtained carbon solids were measured. The following results were obtained.1) Carbon solids made of Type M had larger compressive and bending strength than those from Type P which were produced under the same condition. This reason is suggested that the molding made of Type P was given about duplicate weight loss comparing with that of Type M below 1600°C.2) Bulk density and strength of carbon solids changed with the molding pressure. These values increased with increasing of the molding pressure of 500 to 1500kg/cm2, but were constant above 1500kg/cm2.3) In the molding made of Type P, the rate of heating up to 1000°C was most suitable within the range of 120 to 180°C/min.4) Bulk density and strength of carbon solid made of Type M heat-treated at 2800°C were 1.92g/cm3 and 1700kg/cm2 (compressive strength), 700kg/cm2 (bending strength). From this result, it is confirmed that the isotropic carbon solids had high density and high strength were prepared from the meso-carbon microbeads.

The carbon fibers, the surface of which was hydrogenated and oxidized, were sub-mitted to be examined concerning the effect of the surface structure of carbon fiber on the strength of C/C composite. After the sizing agent on carbon fiber surface was first removed by boiling with ethyl methyl ketone, the surface was hydrogenated with H2 at 1000°C and further the surface hydrogenated was oxidized with aqueous H2O2 solution at the boiling temperature for various hours respectively. The amount of surface oxides, in this case, was measured by means of alkali titration, on the assumption that the surface oxides belong to the acidic groups such as hydroxyls, carboxyls and so on. The tensile strength of carbon fibers barely changed through such chemical surface modifications. It was found that the bending strength of C/C composites, in which the carbon fibers had been used as a reinforcing filler, linearly increased with an increase in the amount of surface acidity, that is, the surface acidic sites played a major role in the increase of the bending strength of C/C composite.Such effects of surface oxides could be ascribed to the strong adhesion between the fiber surface and the binder in the first stage and the following formation of C-C bond between the fiber surface and the binder the pyrolysis of surface oxides, during the molding of composite by means of hot-pressing.

Binder pitch for the production of carbon materials was prepared by adding meso-carbon microbeads (Type-M) to straight coal-tar pitch.The straight coal-tar pitch containing 0-20 wt% Type-M microbeads was heat-treated at temperatures between 300 and 400°C. The amounts of fixed carbon (FC), benzene insolubles (BI) and quinoline insolubles (QI), and softening Point (SP) of the pitch were measured. Then, the capability in using the pitch as bmder for carbon materials was examined by measuring compressive strength of the carbon blocks prepared by using the pitch.Values of FC, BI, QI and SP of the pitch increased linearly with increasing of additional amounts of Type-M microbeads and could be estimated from its additional amounts. The compressive strength of carbon blocks prepared from the mixture of the 35 wt% pitch with 65 wt% coke powder was measured. The compressive strength of carbon blocks had high values when the pitch containing 3-10 wt% Type-M microbeads were used, and these values were higher than those of the carbon blocks produced by using commercial binder pitch.These results show that the characteristics of pitches can be controlled easily by additional amounts of meso-carbon microbeads and that the carbon blocks in which these pitches are used as a binder have high compressive strength.

Chemical structure was investigated of a commercial coal tar pitch and the pitches produced in our laboratory from petroleum residues.The pitches were divided into three fractions;the benzene insoluble (BI), the benzene soluble and n-heptane insoluble (BS-HI) and the n-heptane soluble (HS), each fraction being examined by elementary analysis, MW and N.M.R.experiments.Discussion was given on the relation between the structural parameters of pitches derived from these experiments and such a property as compressive strength of baked carbon blocks containing the pitch as a binder.

Interaction between Carbon fiber surface and binders such as phenol resin and mesophase coal tar pitch, that is, the delamination at the interface in the cross section of thin plate composites from these materials were mainly examined by SEM-observation. The composites were heat-treated at 1000°C. The starting carbon fibers were prepared from PAN and mesophase coal tar pitch, followed by oxidation in air. These carbon fibers were heat-treated at various temperature under an inert atmosphere.The heats of immersion of carbon fibers into benzene at 25°C and phenol at 50°C were also measured to be concerned with the adhesion.In every cases, the higher the heat-treatment temperature of carbon fiber was, the higher the delamination frequency at the interface was.In contrast with the frequency, the heats of immersion into benzene or phenol decreased with a rise in the pretreatment temperature.Such tendencies could be ascribed to the structure change of the carbon fiber with the progress of carbonization by heat-treatment.The delamination frequency in pitch-based carbon fiber was higher than that of PAN-based one. The heats of immersion of pitch-based carbon fiber in to benzene or phenol were smaller than those of PAN-based one.

Meso-carbon microbeads were added in various pitches; coal-tar pitch, quinoline soluble coal-tar pitch (QS coal-tar pitch) and asphalt pitch, and these pitches were heat-treated at 400-430°C. A correlation between the microbeads added and the mesophase formed in pitch was investigated by using a polarized light microscope.The obtained results are follows;(1) In the case of addition of the microbeads of Type-M in QS coal-tar pitch, the growth of Type-M is observed but new mesophase is not formed in the pitch. For Type-P in QS coal-tar pitch, new mesophase spherules are formed in the pitch and their growth is predominant rather than the growth of Type-P . This is similar to the case of addition of Type-C and Type-M in asphalt pitch. From these results, it is considered that the growth of the added microbeads as well as the coalescence of new mesophase and the added microbeads requires similarity in molecular structure between pitch and meso-carbon microbeads.(2) In the case of addition of the microbeads of Type-C, Type-P and Type-M in coal-tar pitch containing metaphase, the microbeads added do not grow, and new mesophase spherules surrounded with metaphase are nucleated and grown. Thus the metaphase in pitch plays an important role in the formation of mesophase . In particular, the formation of mesophase spherules at the surface of metaphase in pitch is predominant than at the surface of microbeads themselves or of metaphase on Type-M. From these results, it is suggested that the metaphase in pitch has active site on itself for the formation of mesophase.(3) In the case of addition of Type-P in coal-tar pitch or addition of Type-C and Type-M in asphalt pitch, the microbeads added are dispersed in the pitch over the wide range, and coalesced with new mesophase formed in the pitch. It seems that coal-tar pitch is able to mix and melt homogeneously with asphalt pitch through the medium of mesophase.

Quinoline-soluble coal-tar pitch, coal-tar pitch containing 3.4% free-carbon (quinolineinsoluble particles) and petroleum asphalt containing 5.4% sulphur were heat-treated for 120 min., 90 min. and 60 min. at 430°C respectively. Formation of mesophase spherules was observed by using a polarized-light microscope.The mesophase spherules were separated by solvent extraction from heat-treated pitches. The separated mesophase spherules were named meso-carbon microbeads and classified into type C, type M and type P according to above mentioned raw pitches. The shapes of meso-carbon microbeads were studied with a scanning electron microscope.The shapes of type C and type P can be divided into two classes, that is, the shapes of meso-carbon microbeads having larger size than about 5μm are approximately true spheres and those having smaller size than about 3μm are lemon-like spheroid. It is not obvious that the meso-carbon microbeads showing lemon-like shapes have the same lamellae structure as those larger than about 5μm, because the sensitive-tint technique can not be used for the meso-carbon microbeads smaller than about 3μm according to the resolving power of optical microscope.The shapes of type M are irregular, although their sizes are almost the same, and the free-carbon smaller than about 1μm are retained over the surface of mesophase.

The behavior of meso-carbon microbeads in the boiling quinoline was investigated. The meso-carbon microbeads used were of three kinds; Type C, Type M and Type P. These were treated in quinoline at 238°C for 30 min. and the insoluble part was filtered out. This procedure was repeated five times. The amount of quinoline soluble part was measured and the structural characteristics of quinoline insoluble part were examined by IR spectroscopy, X-ray diffraction and scanning electron microscopy. The following results were obtained.(1) Almost all amount of quinoline soluble part in the three types of the meso-carbon microbeads was extracted after the first treatment. Among the three types, the amount of quinoline soluble part was highest in type P.(2) The characteristics of the quinoline insoluble part in the meso-carbon microbeads determined by IR and X-ray analyses were not altered from those in the non-treated microbeads. However, the meso-carbon microbeads were found to have several cracks after treatment in quinoline. The cracks developed in three or four directions starting from the point corresponding to the position of pole in the mesophase spherule proposed by Taylor et al. From these results, it was suggested that the formation of cracks in the microbeads by the treatment in quinoline is due to the release of internal strain of lamellae near the pole.