Corrosion-resistant erbium oxide coatings by organometallic chemical vapor deposition

An oganometallic chemical vapor deposition (OMCVD) process was developed for the preparation of protective erbium oxide coatings resistant to corrosion by liquid plutonium. The coatings were deposited from the precursor compound Er(tmhd)(3) using a standard hot-wall reactor. The substrates used for process development were 304 stainless-steel flats; coatings were subsequently deposited on the internal surfaces of high-aspect-ratio tubular parts, as well as a variety of curved samples. The coatings have the correct oxygen/erbium ratio, and small concentrations of carbon and hydrogen impurities. The impurities are present in the form of unreacted or partially-reacted precursor molecules, presumably concentrated at the grain boundaries of the material. The films are polycrystalline with a grain size of 40-50 nm, and exhibit excellent adhesion and mechanical toughness. The small grain size and the resultant favorable mechanical properties may be attributable in part to the presence of the organic fragments at the grain boundaries. Coatings deposited on stainless-steel hats are resistant to corrosion by liquid plutonium, although an erbia-thickness threshold is observed. The failure mechanism for samples with thicknesses below the threshold value is most likely related to flaws in the film morphology, for example large pinholes, rather than grain-boundary attack. (C) 2000 Elsevier Science S.A. All rights reserved.