IN-SITU SCANNING FORCE MICROSCOPY (SFM) STUDY OF THE ELECTROCHEMICAL ACTIVATIONS OF CARBON-FIBERS

Electrochemical activation of the polyacrylonitrile (PAN) based high-t ensile-strength HTA carbon fibres in ammonium bicarbonate solution has been examined for the first time in situ by the method of scanning fo rce microscopy (SFM). Special sample holders have been constructed and specific procedures developed to simulate industrial treatments and h ence characterise, by SFM, the changes of surface morphology of fibres occurring during electrochemical activation. To improve the resolutio n of the SFM images new high-aspect ratio silicon tips instead of stan dard low-aspect ratio Si3N4 tips have been utilised for their st time to study carbon fibres. The influences of the experimental conditions and activation time on the morphology and porous structure of the fibr e surface have been investigated and changes in the surface texture an d in the microroughness of carbon fibres are presented and discussed. The optimum treatment results in removal of the weakly bonded graphite -like crystallites from the surface layer leading to outcropping of th e edge planes to the fibre surface. Further electrochemical treatment followed by additional etching of the fibre surface results in the for mation and development of etch pits reducing the mechanical strength o f the fibres. Quantitative results of the in situ experiments are comp ared with the SFM measurements accomplished for carbon fibres after co mmercial treatments and good correlation between the outcome of the in situ and ex situ studies is demonstrated (C) 1998 Published by Elsevi er Science Ltd. All rights reserved.