A process is presented for the preparation of the electrolyte matrix, a poorly bonded assemblage of LiAIO2 erystallites, based on the use of a fugitive reaction medium, a molten mixture of alkali chlorides. Data on the characteristics of both the reaction and the product are presented.The electrolyte structure, or tile, used in molten carbonate fuel cells consists of a mixture of liquid alkali metal carbonates retained by capillarity in the interstices of an array of chemically inert inorganic crystallites. At cell operating temperatures, the carbonates form an ionically conducting fluid held in place by capillarity. The selection of the carbonate composition is governed by consideration of, and balance between, proper liquid temperature range, ionic conductivity, reactant/product gas solubilities, volatility, etc. The most commonly used composition is 62 mole percent (m/o) Li2CO3-38 m/o K2CO3, having a liquidus temperature of ~764~ and represents a judicious balance of the critical factors (1). The present matrix material is lithium metaaluminate, LiA102, which may exist as one, or all, of three crystallographic modifications (2).The electrolyte-LiAIO2 matrix composite is most commonly prepared as an intimate mixture using either anhydrous techniques (3) or an initial aqueous solution/slurry of the components (4, 5). It is a characteristic of these preparations that either the electrolyte phase, or its precursor, is present throughout the synthetic sequence. The presence of the electrolyte phase precludes the presence of additional chemical species which could beneficially modify the matrix characteristics during its formation, since the matrix is not separated from these other species. The inclusion of the hygroscopic electrolyte also mandates that care be taken to maintain its chemical composition and purity throughout the required processing operations.The product of this preparation is a mixture of LiA102, average spherical equivalent crystallite size ranging from ~0.05 ~m to more than 1.0 ~m, and the mixed carbonates. It is generally recognized that minimization of the matrix crystallite size will maximize the volume fraction of molten electrolyte that can be properly retained, as well as produce matrix porosity which properly complements that of the fuel cell electrodes. However, the stability of small crystallites in the highly aggressive environment of the molten electrolyte is open to question, and will be more fully addressed in a companion paper.The electrolyte-matrix composite is fabricated into the electrolyte structure by hot-pressing at temperatures 5~176 below the electrolyte liquidus, and at pressures ranging up to 60 MPa (6). Densities ranging up to 99% of theoretical have been achieved in this fabrication process.An alternate preparation, the "chloride" synthesis, has been developed for the LiA102 matrix which does not involve the presence of the electrolyte or its precursors. This preparation involves the use of a fugitive molten ionic solvent to promote the formation of the product from the ...