Reaction barrier coating

Recent applications of e-beam and HF-plasma SNMS have been published in the following areas aerosol particles [3.77], X-ray mirrors [3.78, 3.79], ceramics and hard coatings [3.80-3.84], glasses [3.85], interface reactions [3.86], ion implantations [3.87], molecular beam epitaxy (MBE) layers [3.88], multilayer systems [3.89], ohmic contacts [3.90], organic additives [3.91], perovskite-type and superconducting layers [3.92], steel [3.93, 3.94], surface deposition [3.95], sub-surface diffusion [3.96], sensors [3.97-3.99], soil [3.100], and thermal barrier coatings [3.101]. 

Galvanized steel is a common example of galvanic coupling where steel (Fe), with a standard electrode potential of —0.440 V vs. SHE, is cathodicaUy protected by zinc, which has a more active standard electrode potential of —0.763 V. Obviously, zinc is not a corrosion-resistant metal and cannot be classified as a barrier coating. It protects steel from corrosion through its sacrificial properties. Because zinc is less noble than iron in terms of the standard electrode potentials, it acts as an anode. The sacrificial anode (zinc) is continuously consumed by anodic dissolution reaction and protects the underlying metal (iron in steel) from corrosion. In practice, sacrificial anodes are comprised of zinc, magnesium alloys, or aluminum. 

When ceramic fibers are in contact with metals at elevated temperatures (e.g., during fabrication of MMCs) an extensive reaction can occur that leads to interfacial cracking and degradation in the properties of the composite. These reactions are particularly severe for titanium matrices, which are of interest for high-temperature applications. Applying a protective coating (called a diffusion barrier) can reduce the extent of the reaction. These coatings must be... 

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