The phase stability of solid LiAlO2 used for the electrolyte matrix of molten carbonate fuel cells

LiAlO2 is used as a solid matrix for molten carbonate fuel cell (MCFC) electrolyte tiles. These devices operate within the temperature range of 870–970 K. The γ-crystallographic form of this compound is commonly used for fabrication of these matrix tiles. The thermodynamic stability of this phase within the above temperature range is not clear and it is reasonable to consider the γ→α transformation to take place in solid LiAlO2 in presence of molten alkali carbonates. In order to establish the crystallographic form of the compound that forms as a product of reaction between the liquid Li2CO3 and solid Al2O3, the kinetics of LiAlO2 formation has been investigated. Values of conversion factor as a function of the reaction time have been determined both for a stoichiometric reaction mixture and for mixtures with an excess of the liquid 0.53 Li2CO3 + 0.47 Na2CO3 eutectic. The simultaneous determination of the reaction conversion factor and the relative intensity of the characteristic x-ray peak for the α − LiAlO2 form in the reaction mixture have shown that, within 843–973 K, in experiments of ca 100–10 hours, respectively, only this phasev of LiAlO2 is formed. These results may explain the presence of some α − LiAlO2 amount in the MCFC electrolyte tiles after long run tests of these devices.