Carbon microcrystallites can become oriented in the carbonization process of coal tar pitch, which occurs with the characteristic where a mesophase is obtained, by using a magnetic field. An oriented film that has the ability to transmit visible light from 450 to 800 nm can be obtained by sandwiching an appropriate amount of coal pitch between two glass plates and heating in an inert atmosphere at 793 K under a magnetic field. This film can be used to obtain the same linearly polarized light as a commercially available polarizing element. The degree of orientation of the film prepared in a magnetic field of 3 T is not sufficient to use as a polarizer, but a magnetic field of 6 T is able to sufficiently suppress the passage of crossed polarized light. The electrical conductivity of the carbon film prepared at 793 K is improved by 10 times by the application of a magnetic field of 10 T. The electrical conductivity is sensitive to the magnetic field, and there is a possibility that it can be further improved by applying 10 T or more. Coal tar pitch is the residue after obtaining coke from coal, and the optical and electrical advantage of a material prepared in the magnetic field derived from such natural products is clarified.

The influence of an applied magnetic field on the formation of carbon materials from coal tar pitch is investigated. Under an applied magnetic field, crystallites in a mesophase resembling liquid crystals are magnetically oriented during the carbonization process. Compared with that under a nonmagnetic field, carbonized coal tar pitch under a strong magnetic field of 10 T, generated by a superconducting magnet, has a highly oriented structure of carbon crystallites. The orientation of samples prepared under 2 T, which can easily be supplied by an electromagnet, was insufficient. Activation by potassium hydroxide is effective for affording a precursor for activated carbon. The activated carbon obtained under a strong magnetic field has a unique adsorption ability, which arises from its increase in relative surface area and total pore volume compared with those of an activated carbon sample prepared from a precursor produced under zero magnetic field. The precursor carbonized under a magnetic field of 10 T contains a larger number of crystallites than that carbonized under a 0-T magnetic field, which leads to high-performance activated carbon.

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