The use of polarized light microscopy in examining the structure of carbon fibres*

Summary The structure of carbon fibres has been examined using the optical microscope. Three types of fibre structure have been identified which differ in the orientation of the graphite crystallites within the transverse plane, the type of precursor can be identified by the shape of the carbonized fibre. The particular type of structure is determined by the process conditions which the fibre has undergone. Subsequent heat treatment merely enhances the crystallite alignment of the structure without altering the direction of preferred orientation.