TOPOGRAPHY OF CARBON-FIBER SURFACES

Scanning tunnelling microscopy (STM) has been used to study topographic features on carbon fibre surfaces. Operating at a resolution of several nanometres, STM has shown a systematic change in surface profile as a function of oxidative fibre surface treatment. The surface of the polyacrylonitrile-based carbon fibre can be seen to consist of graphitic platelets of dimensions 30 x 20 x 100 nm. The platelets protrude from, rather than lie parallel to, the fibre surface. Maximum exposure of the edge of the platelets occurs at a level of treatment known to give high chemical activity and peak interfacial shear strength. Superimposed on the platelets are slit-like pores lying transverse to the fibre longitudinal axis. At high levels of treatment average surface roughness increases dramatically, coinciding with a decline in interface bond strength.