Synthesis and microstructure of iridium coatings on carbon fibers

Abstract

Uniform, adherent, and non-bridging iridium coatings were applied to polyacrylonitrile-derived (ex-PAN) carbon fibers using low temperature metal organic chemical vapor deposition (MOCVD) from iridium (III) acetylacetonate. Composition, morphology, texture and topography of the iridium coated carbon fibers depending on MOCVD parameters have been studied by scanning electron microscopy/energy dispersive spectroscopy, atomic force microscopy, X-ray diffraction and extended X-ray absorption fine structure (EXAFS). For the MOCVD parameters studied, metallic iridium is the main phase of the coating. Together with iridium, a carbon-containing phase can be also present in the coating. The interatomic distances, corresponded coordination numbers and structural/microstructural parameters were established. The dependence of the microstructure of the Ir-coated carbon fibers on MOCVD parameters and possible structural models are discussed in detail. EXAFS showed that the Ir–O chemical bond on the boundary between the carbon fiber and the iridium coating is either absent or its contribution is too small to be detected by this method. Iridium appears to be bound to carbon fiber only by van der Waals forces. The data obtained by all methods are in a good agreement.