G. Bhatia

Effect of sintering temperature on the characteristics of carbons based on mesocarbon microbeads

A study was conducted to determine the effect of sintering temperature, ranging between 350 and 2700°C, on the characteristics of carbons made from mesocarbon microbeads (MCMB) of size 4–16 μm, formed in a coal tar pitch by heat treatment at 420 °C for 2.5 h, and separated by solvent extraction using a tar oil. It was found that the MCMB-based carbon plates heat treated to 1000 and 2700°C possess, respectively, an apparent density of 1.64 and 1.78 g cm-3, a weight loss of 11.5% and 15.3%, a volume shrinkage of 32.4% and 45.0%, an open porosity of 7.6% and 14.0%, a bending strength of 72 and 50 MPa, and an atomic C/H ratio of 30 and 417. The 2700°C heat-treated plates revealed homogeneity and fine isotropic structure.

Formation of mesophase spherules in low-Ql coal tar pitches and development of monolithic carbons therefrom

Three coal tar pitches having different and low contents of primary quinoline insolubles (Ql) were subjected to a series of thermal treatments at a predetermined temperature for different periods of soaking. The development of mesophase, in terms of its size and content in the heat-treated pitches, was studied as a function of the soaking time and content of primary quinoline insolubles in the original pitches. Mesophase spherules, with an average size of about 5 μm, formed in one of the coal tar pitches were separated using solvent extraction employing a suitable tar oil. These spherules, also called “mesocarbon microbeads (MCMB)”, after being moulded into small rectangular plates, were carbonized at temperatures of 950 and 2700 °C to obtain fine textured monolithic carbons possessing apparent densities of 1.66 and 1.85 g cm−3, respectively, at these heat-treatment temperatures.

Conversion of phenol formaldehyde resin to glass-like carbon

Glass-like carbons have been produced for many years by the careful carbonization of a variety of starting materials such as cellulose, phenol formaldehyde, polyfurfuryl alcohol, acetone furfuryldehyde and other suitable thermosetting resins. A number of publications have appeared in the literature concerning their characteristics and applications. However, little is known about the preparation procedure and its influence on the development of this form of carbon. The present paper incorporates the studies on the carbonization behaviour of a suitable phenol formaldehyde resin and on the optimization of the phenol to formaldehyde molar ratio in the resin, carried out with respect to the various physical characteristics of the resins and the resulting carbons. The implications of these studies have been disucussed in detail.

Rheological characteristics of coal tar and petroleum pitches with and without additives

Abstract An extensive study of rheological characteristics of coal tar and petroleum pitches with and without additives, namely, petroleum coke, natural graphite and carbon black has been made. It is found that all pitches, pure or mixed with a carbon additive are not Newtonian as reported in the literature, but behave Theologically as Bingham plastics with certain yield stress and plastic viscosity at all temperatures of measurement between 85–180°C. The yield stress and plastic viscosity both decrease with increase in temperature of the pitch. A pure petroleum pitch having the same softening point as that of a coal tar pitch is found to have a lower viscosity compared to that of the latter at all temperatures of measurement. This suggests that the criterion of softening point as a measure of suitability of a coal tar pitch binder in the manufacture of artificial carbon is not sufficient for petroleum pitches. Addition of ten parts of carbon black by weight of pitch results in a considerable decrease in viscosity change with temperature of the coal tar pitch compared to almost insignificant change in the case of the petroleum pitch of the same softening point. However, the addition of petroleum coke or natural graphite makes the pitch more viscous but does not change the temperature dependence of viscosity of either of the two types of pitches. The implications are discussed.

Effect of calcination conditions of self-sintering mesocarbon microbeads on the characteristics of resulting graphite

Mesocarbon microbeads are now-a-days used as a prominent self-sintering precursor for the production of high density monolithic graphite. The quality of this graphite is highly dependent on the characteristics of these microbeads, such as the quinoline and toluene insoluble contents, β-resins content and volatile matter content, which in turn, can be controlled to desired values by suitable treatments of their extraction and calcination. In the present paper, the authors give an account of the study conducted to see the effect of calcination conditions of mesocarbon microbeads on the characteristics of the resulting graphite. A calcination at a temperature in the range of 280–320 °C for 30 min. under an ambient pressure of nitrogen, or at a temperature of 245–310 °C for 10 min. under a reduced pressure (5 cm Hg) of nitrogen, results in mesocarbon microbeads having a quinoline insoluble content of 83.6–89.8%, toluene insoluble content of 94.4–99.7%, β-resins content of 6.8–11.9% and a volatile matter content of 10.2–13.5%. Such microbeads have been found to lead to a monolithic graphite possessing a bulk density 1.91–2.02 g cm−3, bending strength of 62–70 MPa, Shore hardness of 58–69, electrical resistivity of 2.1–2.6 mΩ cm and a degree of anisotropy of 1.02–1.05.

A relationship for the evaluation o coking values of coal tar pitches from their physical characteristics

A relationship has been proposed to evaluate the coking values of coal tar pitches from the knowledge of their three other characteristics, namely, softening point, benzene insolubles content and quinoline insolubles content. It has been tried on 44 self-prepared coal tar pitches and 18 others obtained from the literature, possessing widely-ranging characteristics, and is found to give coking values comparable to those obtained experimentally. The coefficients of correlation between the theoretical (obtained using the relationship) and experimentally determined coking values for the two lots of pitches have been calculated to be 0.98 and 8.94 respectively, which indicate an excellent validity of the proposed relationship for the evaluation of coking values of coal tar pitches.

Development of glass-like carbon from phenol formaldehyde resins employing monohydric and dihydric phenols

A study on the development of glass-like carbon from phenol formaldehyde resins employing monohydric (simple) and dihydric phenols (resorcinol and catechol) has been made. It is revealed that to obtain a good glass-like carbon, the optimum molar ratio of formaldehyde to resorcinol in the resorcinol formaldehyde resin is 1.5, as was found earlier in the case of a simple phenol formaldehyde resin, whereas for catechol formaldehyde resin, the optimum molar ratio of formaldehyde to catechol is found to be 2.0. Further, it is observed that the three types of resins lead to glass-like carbons of essentially the similar characteristics, except that the catechol formaldehyde based carbons possess the highest strength of 326 M Pa. A mechanism has been proposed on the basis of three types of phenolic rings designated as attached, bridging and cross-linking, in the structure of the three cured phenol formaldehyde resins to explain the respective optimum molar ratio of formaldehyde to type of phenol.

Physical characteristics of baked carbon mixes employing coal tar and petroleum pitches

A study of the physical characteristics of baked carbon mixes employing coal tar and petroleum pitches as the binder has been made to explore their relative suitability in the fabrication of carbon products. The study reveals that coal tar pitch is the most suitable binder and a petroleum pitch of the same softening point leads to a carbon product of much inferior characteristics. Raising the softening point of the petroleum pitch from 78 to 150° C or adding 10 parts of carbon black in the lower softening point pitch, increases the density, strength and also the electrical resistivity of the baked carbons. The addition of 10 parts of carbon black to the higher softening point petroleum pitch leads to a carbon product with further improved values of density and strength, which are comparable to those obtained with the coal tar pitch. However, the electrical resistivity also is marginally increased. It appears that a petroleum pitch of high aromaticity may fulfill the requirements expected of a good binder.

A comparative study of the characteristics of baked carbon mixes employing different filler materials

A study of the physical characteristics of baked carbon mixes employing calcined petroleum coke, coal-tar pitch coke, metallurgical coke and anthracite coal has been made to explore their relative suitability and area of application. It is revealed that petroleum coke and pitch coke lead to a carbon product of almost the same density and electrical resistivity. However, the crushing strength of the product employing pitch coke is 1 1/2 times that of the one employing petroleum coke. The carbon product produced from the metallurgical coke is found to be slightly inferior in respect of density and electrical resistivity and slightly superior in respect of crushing strength when compared with that made from petroleum coke. The use of anthracite coal results in a carbon product of significantly lower density and much higher electrical resistivity than that of the product using the petroleum coke. However, the strength of the anthracite coal-based carbons is found to be nearly double that of the petroleum coke-based carbons. Thus, the significance of the present study lies in the fact that the above findings help one to estimate a possible filler composition for a carbon product possessing the desirable critical characteristics.

Development of preforming pitch for carbon-carbon composites from coal-based precursors

Preforming pitch, a special type of pitch, used for the matrix formation of carbon-carbon composites, has been developed from suitable coal-based precursors, using the techniques of distillation, condensation and polymerization. The effects of various processing parameters, namely the temperature and period of heat treatment, and the atmosphere (inert or partial vacuum) during the heat treatment, on the characteristics of the resulting pitch have been studied. Some of the pitches were subjected to field trials from which the characteristics of a good preforming pitch leading to a carbon-carbon composite of density around 1.8 g cm−3 have been identified.