Cross-Banding of Hollow Carbon Fibres

Abstract

Hollow gas-phase carbon fibres have been examined by electron microscopy using bright-field, dark-field and selected-area diffraction modes. It is shown that viewed under (002) dark-field mode the cross-banding is not caused by the presence of twist and tilt boundaries along the microfibril and also diffraction from individual microfibril or micro-crystallite, but is a Moiré pattern produced by basal planes overlapping and lying at near-Bragg angle. The alternation of dark and bright bands is due to the twisting of basal planes as they progress along the line parallel to the fibre axis. The twisting is random, therefore the bands are arranged chaotically. There are Moiré fringes with a period of 0.5 – 0.8 nM in small areas (3 – 4 nM) of some bright bands. Correlations have been observed between the absence of bright bands on some areas of (002) dark-field image of fibre wall and appearance of holes in this wall after fibre oxidation. The assumption has, thus, been made that the cross-banding is related to the local wall strength of hollow carbon fibre.