Fluorination of carbon blacks:: an X-ray photoelectron spectroscopy study IV.: Reactivity of different carbon blacks in CF4 radiofrequency plasma

The effect of CF4-plasma enhanced fluorination on the surface modification of carbon blacks has been examined using XPS. Three different types of carbon blacks have been studied: a thermal black, a furnace black and a high electrical conducting black. The analysis of the XPS spectra of fluorinated carbon black samples indicates that all fluorine atoms, fixed at the surface and in a subsuperficial zone of the particles, are covalently linked to carbon atoms. The influence of the physicochemical properties and morphology of these three types of carbon blacks on the fluorination reaction has also been investigated. The proportion of different types of fluorinated carbon atoms, i.e. on one hand CFx surface and border groups of graphitic bulk domains for which the planar configuration of the graphene layers is preserved together with the sp(2) character of C, i.e. structures of type I, on the other hand polyalicyclic perfluorinated structures in which sp(3)C form puckered layers similar to those of covalent fluorographites, i.e. structures of type II, and also the F/C ratio of the fluorinated groups are related to the surface morphology and depend on the microstructural organization of particles. When the microstructure ordering and graphitic character of the carbon increase, the size of the ordered graphitic domain also increases. At the same time the density, the size of defects and proportion of protonated sp(3)C entities bridging the graphene layers decrease. As a consequence, the proportion of carbon atoms, potentially able to form perfluorinated CF2 and CF3 groups, decreases. The relative contribution of those groups is appreciably higher in fluorinated compounds which are derived from carbon blacks with a lower structural order. (C) 1999 Elsevier Science Ltd. All rights reserved.