Synthesis of [alpha]-Lithium Aluminate Fiber and Its Stability in Molten Carbonate Salt

The electrolyte matrix of Molten Carbonate Fuel Cells (MCFC) is generally reinforced with a mixture of alumina fibers to provide strength within the cell. However, alumina fibers corrode and are changed into lithium aluminate by reaction with lithium carbonate in molten carbonate. Lithium aluminate have two crystal structures in molten carbonate, α-phase and γ-phase. It is known that lithium aluminate undergo mutual crystal structure transformations between α- and γ-phase in molten carbonate. Therefore, the stability of electrolyte matrix is lowered. It is reported recently that α-lithium aluminate is more stable than γ-phase in molten carbonate. We have studied on α-lithium aluminate fiber instead of alumina fiber. We synthesized it at low temperature under CO2 atmosphere by the solid state reaction of γ-alumina fiber with lithium carbonate. Further, it was found that α-lithium aluminate fiber was synthesized with keeping fiber structure. The evaluation of stability of this fiber in molten carbonate were performed by comparing with alumina fiber. The mixture of α-lithium aluminate fiber and α-lithium aluminate powder was stable and the crystal structure of this mixture remained α-lithium aluminate. It can be expected that application of α-lithium aluminate fiber instead of alumina fiber improve the stability of the electrolyte matrix for MCFC.