Surface analysis of carbon and carbon fibers for composites

Carbon fibers are finding increasing application in making various composites with special properties. It is found that such composites have properties that can be markedly affected by the carbon fiber surface. The effects of surface modification by electrochemical and plasma oxidation are discussed and the surface chemical changes described with examples from the author's work. It is seen that the interaction of the matrix with the fiber surface is a subtle mixture of physical and chemical effects. Surface studies with core and valence band X-ray photoelectron spectroscopy (XPS) and other techniques are described. Valence band X-ray photoelectron spectroscopy is shown to have the ability to distinguish some subtle chemical differences, and the combination of XPS data from different regions is shown to indicate differences in chemical composition with depth into the surface. Examples are provided of interfacial chemical reactions between treated fibers and a coating of resin or polymer. A special cell for monitoring high temperature carbon oxidation is described, with examples of oxidation protection by aluminum oxide and magnesium oxide films.