Peter M. A. Sherwood

Surface analysis of carbon and carbon fibers for composites

Abstract 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 authors 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.

X-ray photoelectron spectroscopic studies of carbon fiber surfaces VIII—A comparison of type I and type II fibers and their interaction with thin resin films

Abstract Type I (high-modulus HM) and Type II (high-strength HT) carbon fibers electrochemically treated in a variety of electrolytes have been analyzed using X-ray photoelectron spectroscopy. A comparison of the differences in surface functionality and the possible interaction of treated fibers with epoxy resin is reported. The amount of carbon/oxygen functionality is greater for type II for the untreated and electrochemically treated fibers. Carboxylic/ester groups are produced at edge sites in the fiber surface whereas keto-enol groups are produced on the basal planes. Conclusive evidence for a chemical reaction between the fiber surface and 828-resin for fibers polarized in acidic electrolyte is given. It is not possible to conclude whether chemical bonding is responsible for the increased interlaminar shear strength of composites produced from treated fibers.

X-ray photoelectron spectroscopic studies of carbon-fibre surfaces. Part 4.—The effect of electrochemical treatment in nitric acid

Carbon fibres, electrochemically treated using nitric acid, have been analysed using X.p.s., F.t.i.r. and s.e.m. Substantial quantities of surface oxide (mainly carbonyl-type oxides) could be produced leading to large topographical changes on the fibre surfaces. The nature of the surface oxide depended upon the potential, the reaction time in solution and the electrolyte concentration. No nitrogen-containing species were found on the surface.

X-ray photoelectron-spectroscopic studies of carbon-fibre surfaces. Part 5.—The effect of pH on surface oxidation

Carbon fibres, electrochemically treated in a variety of different electrolytes, have been analysed using X.p.s. and s.e.m. The amount and type of surface oxide varies considerably depending upon the pH of the electrolyte. Much more surface is produced in acidic environments. Carbon dioxide is evolved during treatment in acidic environments, and oxygen, together with clouding of the solution, in basic environments. Different oxidation mechanisms are suggested at different pH values.

X-ray photoelectron spectroscopic studies of oxide films on platinum and gold electrodes

The oxide films produced by anodic oxidation of gold and platinum have been studied by X-ray photoelectron spectroscopy. The change in the amount of each species present, with electrode potential, has been investigated. It is demonstrated that X-ray reduction occurs for these systems but that it can be minimised by a suitable choice of experimental conditions.A study of the intensities of the photoelectron peaks demonstrates how the thickness of an oxide layer and the true surface area of the electrode may be determined.

X-Ray Photoelectron-Spectroscopic Studies of Carbon Fiber Surfaces. Part IX: The Effect of Microwave Plasma Treatment on Carbon Fiber Surfaces

X-ray photoelectron spectroscopy has been used to monitor the surface chemical changes occurring on type II carbon fibers exposed to air, oxygen, and nitrogen plasmas. In all cases the plasmas caused changes in surface functionality, in terms of both C-O and C-N functionality. Prolonged exposure to the plasmas caused loss of surface functionality for air and oxygen plasmas, and extended treatment caused fiber damage. Plasma treatment of fibers promises to be an effective method of fiber treatment.

Quantitative use of the angular variation technique in studies of tin by X-ray photoelectron spectroscopy

Abstract The relative photoionisation cross-sections of the tin 3 d and 4 d electrons are determined and combined with angular variation studies to establ

Valence band x-ray photoelectron spectroscopic studies to distinguish between oxidized aluminum species

The determination of the detailed chemical nature of oxidized aluminum species is an essential requirement for the study of many important practical aspects associated with aluminum metal and its compounds. While thick oxidized films of aluminum metal can be easily characterized by x-ray powder diffraction when the films are crystalline, thin amorphous films are very difficult to characterize. In this article, a study of the valence band x-ray photoelectron spectrum of aluminum oxides, hydroxides, and oxyhydroxides is reported using monochromatic aluminum Kα X radiation. The valence band spectra obtained are shown to have significant differences for different oxidized aluminum species, and can be well understood by comparison with spectra generated from cluster and band structure calculations. This study compliments earlier published studies from this research group using achromatic radiation, and demonstrates how the use of monochromatic X radiation allows a more conclusive distinction to be made among o...

X-Ray Photoelectron-Spectroscopic Studies of Carbon Fiber Surfaces. Part XII: The Effect of Microwave Plasma Treatment on Pitch-Based Carbon Fiber Surfaces

X-ray photoelectron spectroscopy has been used to monitor the surface chemical changes on DuPont high-modulus pitch-based carbon fiber surfaces brought about by microwave air-plasma treatments for different periods of time. The air-plasma treatment increased the fiber surface functionalities, but extended treatment caused fiber damage. X-ray diffraction studies showed that the bulk structure was not affected by the air-plasma treatment. XPS valence band spectra proved a more sensitive probe of the surface chemistry of the carbon fibers than XPS core studies. Air-plasma treatment of fibers promises to be an effective method of fiber treatment.

Curve fitting in surface analysis and the effect of background inclusion in the fitting process

An overview is presented of data analysis methods that can be used in surface analysis, especially those that can be used in x‐ray photoelectron spectroscopy (XPS). The paper provides illustrations of the application of data analysis methods to real systems, and discusses practical problems that can arise when working with real data sets. The paper focuses upon curve fitting of core XPS data, and discusses the importance of combining curve fitting information with other supporting information and experiments. The effect of different backgrounds incorporated into the fitting process is discussed.