Tailoring of Grain Boundary Chemistry of Alumina Ceramics for Corrosion Resistance

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9625354 Levi-Setti Commercial ceramics that are presently available are generally unsuitable for highly corrosive applications because they contain corrodible glassy grain boundary phases. Such phases result from the commercial use of liquid- phase sintering additives or from poor control of powder purity and processing. In this project, we are interested particularly in alumina ceramics and their corrosion properties in hydrogen fluoride (HF) ambients, with a view to developing improved materials of construction in the fluorochemical manufacturing. Corrosion research at DuPont has led to the discovery that a small amount of MgO (0.05%), a classic solid-solution sintering aid, improves the corrosion rate of alumina in HF, even in the presence of glass-forming impurities. The atomistic mechanism by which MgO functions is not understood, mainly because its influence on other cation impurities is not known. The goal of the proposed collaboration between the University of Chicago and DuPont is to improve our understanding of the grain boundary chemistry and its effect on corrosion behavior, with a view to designing corrosion-resistant ceramics. The approach will be to develop fabrication strategies that eliminate or adjust the nature of glassy grain boundaries. The distributions of trace dopants and impurities in a number of systematically designed alumina compositions will be studied by high resolution imaging secondary ion mass spectrometry (SIMS). %%% The principal focus of this study is to correlate the grain boundary chemistry of aluminum oxide to the corrosion behavior of the bulk material. This information will aid in the design of commercial ceramic materials that are resistant to corrosion by a variety of materials. ***