High modulus, high strength carbon fibers produced from mesophase pitch

A carbon fiber capable of being converted thermally to a fiber having a structure possessing the three-dimensional order characteristic of polycrystalline graphite, said carbon fiber having a diameter no greater than 30 microns;

• a preferred orientation of carbon crystallites parallel to the fiber axis such that the preferred orientation parameter for the fiber is less than 45.degree. (determined by microdensitometer scanning of the (002) band of the exposed X-ray film of the fiber and expressed as the full width at half maximum of the azimuthal intensity distribution);
• and containing at least 40 per cent of oriented elongated domains preferentially aligned parallel to the fiber axis, said domains characteristically being greater than 5000 A in diameter and visible under polarized light at a magnification of 1000 X.

A carbonaceous pitch fiber capable of being thermoset and converted thermally to a fiber having a structure possessing the three-dimensional order characteristic of polycrystalline graphite, said pitch fiber having a mesophase content of from 40 per cent by weight to 90 per cent by weight, a diameter no greater than 30 microns, a preferred orientation of pitch molecules parallel to the fiber axis such that the preferred orientation parameter for the fiber is from 20.degree. to 35.degree. (determined by microdensitometer scanning of the (002) band of the exposed X-ray film of the fiber and expressed as the full width at half maximum of the azimuthal intensity distribution), and containing elongated domains of oriented molecules preferentially aligned parallel to the fiber axis, said domains characteristically being greater than 5000 A in diameter and visible under polarized light at a magnification of 1000 X.

A process for producing a carbon fiber capable of being converted thermally to a fiber having a structure possessing the three-dimensional order characteristic of polycrystalline graphite, said carbon fiber having a diameter no greater than 30 microns and a preferred orientation of carbon crystallites parallel to the fiber axis such that the preferred orientation parameter for the fiber is less than 45.degree. (determined by microdensitometer scanning of the (002) band of the exposed X-ray film of the fiber and expressed as the full width at half maximum of the azimuthal intensity distribution), which comprises spinning a carbonaceous fiber having a diameter no greater than 30 microns from a carbonaceous pitch containing from 40 per cent by weight to 90 per cent by weight mesophase, which mesophase, under quiescent conditions, forms a homogeneous bulk mesophase which when examined under polarized light exhibits large coalesced domains in excess of 200 microns in size, said pitch being nonthixotropic and having a viscosity of 10 poises to 200 poises at the temperature of spinning;

• heating the spun fiber in an oxygen-containing atmosphere at a temperature of from 250.degree. C. to 400.degree. C. for a time sufficient to render it infusible;
• and then heating the infusible fiber so produced in an inert atmosphere to a temperature of at least 1000.degree. C.

A process for producing a fiber having a structure possessing the three-dimensional order characteristic of polycrystalline graphite, said fiber having a diameter no greater than 30 microns and a preferred orientation of carbon crystallites parallel to the fiber axis such that the preferred orientation parameter for the fiber is no greater than 10.degree. (determined by microdensitometer scanning of the (002) band of the exposed X-ray film of the fiber and expressed as the full width at half maximum of the azimuthal intensity distribution), which comprises spinning a carbonaceous fiber having a diameter no greater than 30 microns from a carbonaceous pitch containing from 40 per cent by weight to 90 per cent by weight mesophase, which mesophase, under quiescent conditions, forms a homogeneous bulk mesophase which when examined under polarized light exhibits large coalesced domains in excess of 200 microns in size, said pitch being nonthixotropic and having a viscosity of 10 poises to 200 poises at the temperature of spinning;

• heating the spun fiber in an oxygen-containing atmosphere at a temperature of from 250.degree. C. to 400.degree. C. for a time sufficient to render it infusible;
• and then heating the infusible fiber so produced in an inert atmosphere first to a temperature of at least 1000.degree. C., and then to a higher temperature of at least 2500.degree. C.