Magnetic field alignment of the matrix in a carbon-carbon composite

Abstract The effect of a magnetic field on the alignment of the carbonaceous mesophase by itself, and as matrix between fiber bundles, within fiber bundles, and within a bidirectional fiber composite has been studied. Samples of A240 petroleum pitch and carbon-fiber bundles, and fabric impregnated with the pitch were pyrolyzed in a magnetic field of 5500 G. Spherules aligned with their polar axis in the plane perpendicular to the magnetic field. The bulk mesophase was oriented to the fibrous microstructure with all the molecular layers lying parallel to the magnetic field and thus, all the wedge disclinations aligned parallel to the magnetic field. The magnetic field did not have a significant effect on the alignment of the mesophase within a carbon-fiber bundle. The strong anchoring forces that align the disklike molecules parallel to the filament surfaces could not be overcome by the magnetic field. The magnetic coherence length of 7 μm permitted calculation of the elastic constant describing curvature of the molecular layers. The pyrolysis of a bidirectional fiber composite in the presence of the magnetic field has shown that the matrix between the fiber bundles was oriented perpendicular to the carbonfiber fabric plies when the magnetic field direction was perpendicular to the fabric plies.