High-Temperature Corrosion of Surfaces and Protection Schemes
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When alloys are exposed to various environments at elevated temperatures, the thermodynamic conditions are usually such that reactions take place between the alloys and the environments. While a great variety of reactions are possible, those of most technical importance are the ones which can be used to inhibit subsequent reactions between the alloys and the environments. The science of protecting the surfaces of high temperature alloys requires consideration of the thermodynamics and kinetics of surface reactions as well as the factors that influence the properties of the resulting reaction product barriers. The protection scheme usually consists of forming the most protective reaction product barrier possible on the surfaces of the alloys. Of course the barriers which can be used are limited to some extent by the environments and by the structural requirements that must be satisfied by the alloys. Most often it is not practical to attempt to modify the environment. Most environments encountered in practice, however, contain some oxygen and oxides are the most protective reaction product barriers. The combined requirements of high temperature corrosion resistance and most structural properties are very frequently not compatible with each other in a given alloy system. This complication can be overcome to a large degree by using coatings on the structural alloys. The coating is designed for corrosion resistance and need satisfy only greatly reduced mechanican property requirements.
KeywordsOxide Scale Continuous Layer Structural Alloy Parabolic Rate Constant Oxide Barrier
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