In situ scanning force microscopy (SFM) study of the electrochemical activation of carbon fibres

Abstract

Electrochemical activation of the polyacrylonitrile (PAN) based high-tensile-strength HTA carbon fibres in ammonium bicarbonate solution has been examined for the first time in situ by the method of scanning force microscopy (SFM). Special sample holders have been constructed and specific procedures developed to simulate industrial treatments and hence characterise, by SFM, the changes of surface morphology of fibres occurring during electrochemical activation. To improve the resolution of the SFM images new high-aspect ratio silicon tips instead of standard low-aspect ratio Si 3N 4 tips have been utilised for the first time to study carbon fibres. The influences of the experimental conditions and activation time on the morphology and porous structure of the fibre surface have been investigated and changes in the surface texture and 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 the edge planes to the fibre surface. Further electrochemical treatment followed by additional etching of the fibre surface results in the formation and development of etch pits reducing the mechanical strength of the fibres. Quantitative results of the in situ experiments are compared with the SFM measurements accomplished for carbon fibres after commercial treatments and good correlation between the outcome of the in situ and ex situ studies is demonstrated.