Exfoliation of carbon fibers through intercalation compounds synthesized electrochemically

Carbon fibers, mesophase-pitch-based, PAN-based and vapor-grown carbon fibers, were exfoliated through their intercalation compounds by rapid heating to 1000 degreesC. Intercalation into carbon fibers was electrochemically performed in concentrated nitric acid at 3 V for 15 min. Formation of intercalation compounds was confirmed from the fact that the interlayer spacing increased to about 0.78 nm, though a part of them was decomposed to the residual compounds after rinsing and drying. Textural and morphological changes in carbon fibers by exfoliation were studied by SEM and TEM. After rapid heating to 1000 degreesC, a marked morphological change was observed, a single fiber being converted to a bundle of thin filaments split along the original fiber axis. Each of these filaments was concluded to consist of well-oriented layer planes from TEM analysis. By the present procedure, even long fibers, as long as 50 cm, and carbon fiber fabrics could be exfoliated. On PAN-based carbon fibers with low crystallinity, the exfoliation was observed after rapid heating, though the formation of intercalation compounds was not proved from X-ray diffraction. (C) 2001 Elsevier Science Ltd. All rights reserved.