Gaseous Corrosion of Ceramics

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9870265 Readey The goal of the project is to gain a fundamental understanding of the active gas corrosion of ceramics. This research will study the high temperature corrosion of ceramics by halogen-containing gases, initially hydrogen chloride (HCl). There exist very few data on active gaseous corrosion of ceramics; that is, corrosion in which the products of the reaction are generally gaseous. However, those data that do exist show that gas diffusion of the product gases controls the rate of reaction at high temperature. As a result, the rate of corrosion can be predicted from thermodynamic data and the kinetic theory of gases. Hydrogen chloride will be used as the initial reactant gas since the equilibrium product gas pressures produced in reactions with it are predicted to be high over a large temperature range, and thus it should be possible to observe the transition from diffusion-controlled kinetics to surface reaction-controlled kinetics. Once the parameter space where a surface reaction is rate controlling is defined, then the mechanisms of the surface reaction can be studied. The reaction kinetics will be followed by weight loss measurements and grain boundary grooving as a function of temperature and gas composition. Single and multicomponent oxides, nitrides, and carbides will be studied. %%% The significance of the research is that halogen corrosion of ceramics has important technical implications in chemical processing, incinerators, chemical waste disposal, semiconductor processing, and high temperature heat engines. Understanding the kinetics can help materials engineers design materials that are less subject to degradation by these gases. ***