Abstract
High resolution phase contrast microscopy has been used to study the ultrafine structure of Morganite I and Thornel high modulus carbon fibers. Both are commercial fibers processed at 2800° to 3000°C, the former made from a polyacrylonitrile and the latter from an cellulose (rayon) precursor. Graphitizing is combined with stretching in order to align the basal planes parallel to the fiber axis to secure the high modulus. The ultrafine structures of these fibers have previously proved elusive.The fibers have been looked at in two ways. Since they are irregular in shape it was found possible to direct the electron beam normal to the fiber axis and image the basal planes viewed edge-on at the periphery of a fiber. The image disappears as one moves into the thicker region, so that only the structure near the surface is accessible. The second approach was to fracture the fiber by applying local bending stresses.
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