ECS Proceedings Volumes

The optical basicities in some halide compounds and in oxide - halide systems such as CaO - CaF₂, CaO - CaCl₂ systems have been measured using photoacoustic spectroscopy in order to examine an application of the optical basicity concept for oxide - halide systems. The optical basicities measured in this study were compared with the values of the theoretical optical basicity based on the concept of the average electron density (D). The optical basicities mesured were in agreement with the theoretical optical basicities in CaO - CaF₂ and CaO - CaCl₂ systems. On the other hand, two values of the optical basicity were obtained from the sample in CaO - NaCl system. One of them was considered to correspond to the optical basicity of CaO.

The pinhole formation mechanism was studied with a variety of MEAs using ex-situ and in-situ methods. The ex-situ tests included the MEA aging in oxygen and MEA heat of ignition. In-situ durability tests were performed in fuel cells at different operating conditions with hydrogen and oxygen. After the in-situ failure, MEAs were analyzed with an Olympus BX 60 optical microscope and Cambridge 120 scanning electron microscope. MEA chemical analysis was performed with an IXRF EDS microanalysis system. The MEA failure analyses showed that pinholes and tears were the MEA failure modes. The pinholes appeared in MEA areas where the membrane thickness was drastically reduced. Their location coincided with the stress concentration points, indicating that membrane creep was responsible for their formation. Some of the pinholes detected had contaminant particles precipitated within the membrane. This mechanism of pinhole formation was correlated to the polymer blistering.

A thermodynamic database has been developed for the LiCl-NaCl-KCl-MgCl₂-CaCl₂-MnCl₂-FeCl₂-FeCl₃-CoCl₂-NiCl₂-AlCl₃ system. All binary subsystems (except AlCl₃-FeCl₃) as well as all higher order (mostly ternary) subsystems for which experimental data were available have been considered. A complete critical evaluation of all available phase diagram and thermodynamic data (enthalpy of mixing, emf and vapor pressure measurements) has been performed for all condensed phases (liquid, solid solutions, stoichiometric compounds) and relevant gaseous species, and optimized model parameters have been found which best reproduce all the data simultaneously. In this way the data have been rendered self-consistent, discrepancies among the data have been identified, and extrapolations and interpolations have been performed. The models can be used with Gibbs free energy minimization software to calculate phase diagram sections, vapor pressures, and all thermodynamic properties at all compositions over extended ranges of temperature and pressure. In this paper, the results obtained for the LiCl-NaCl-KCl-MgCl₂-AlCl₃ subsystem are presented.