Preparation and properties of lithium aluminate supported electrolytic tiles for electrochemical concentrators
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"An electrochemical gas concentrator effects the removal of a specified gas (such as carbon dioxide or sulfur dioxide) by an electrochemical process. This electrochemical transfer takes place across the electrode electrolyte-electrode interfaces in an electrochemical cell. The advent of a viable gas concentration process effecting removal by electrochemical transfer requires the development of a reliable, cost-effective system. Examination and optimization of cell ccmponents, processing parameters of said components, and cell operation variables are an essential portion of this development. In aqueous electrochemical concentrators, the electrolyte is dispersed in a solvent, water. However, in molten salt concentration cells (and fuel cells), the electrolyte is contained in a ceramic matrix struc ture. The stability, both physical and chemical, of this matrix-electrolyte combination, called the electrolytic tile, is extremely important to (1) the operation and performance of the cell. Currently, there is a fundamental need to understand the factors which determine the stability of the electrolytic tile in the operating environment. Processing techniques need to be developed for preparing the tile and its components which will consistently yield tiles with sufficient physical and chemical stability to achieve high performance and long endurance. The suitability of a chemical compound to act as a support matrix for an electrolyte is governed by its physical and chemical character in the operating system. Magnesium oxide was used as the electrolyte support (1) medium in early developmental work of the molten carbonate fuel cell. The magnesium oxide-alkali carbonate (electrolyte) mixture formed a (2) stiff paste at cell operating temperatures. However, it was soon determined that magnesium oxide is chemically active in the molten carbonate environment (3). Thus, effort was directed towards finding a support material that is both chemically inert and physically stable in the molten carbonate environment of a fuel cell. Broers and co-workers determined that lithium aluminate possessed these requirements and suggested its use as the support medium for molten carbonate electrolytes (1). A mixture of lithium aluminate and dilithium oxide is commercially available (Alfa Division, Ventron Corp., chemical analysis: 78.6% LiA102/21.4% Li20). However, due to the lack of a supply of relatively pure lithium aluminate, there is a need to develop a process for its formation and to understand the relationship between process variables and final product characteristics. Much of the developmental work in this area has been concerned with the optimization of a procedure to manufacture tile powder containing both lithium aluminate and the binary alkali carbonate eutectic used as the electrolyte in the molten carbonate fuel cell. Due to the dual function of lithium aluminate as the support medium for electrolytes for both the carbon dioxide and sulfur dioxide molten salt concentrators, it is necessary to obtain and optimize an electrolyte-free lithium aluminate production method. The final product characteristics produced in such a method play an important role in determining the properties of the electrolytic tile and thus, have sane important effects on the performance and long-term stability of the tile in the operating environment of a molten salt electrochemical concentrator."--Introduction.
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M.S.