Hollow carbon fibers and carbon fibers having a generally C-shaped transverse cross-sectional area are produced by extruding a carbonaceous anisotropic liquid precursor through a spinneret having a capillary with a generally C-shaped cross-sectional area, into a fiber filament, controlling the viscosity...http://www.google.com/patents/US5156831?utm_source=gb-gplus-sharePatent US5156831 - Method for producing high strength, melt spun carbon fibers
