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The stability of beta alumina in fully developed Zebra normalNa/FeCl2 cells under long‐term cycling has been proven. In the early stages of development of the normalNa/FeCl2 cell, some problems in the form of increased resistances were encountered under certain extreme conditions of temperature and voltage. While these difficulties have now been overcome in practical cells, the scientific investigation into the causes of the anomalous resistance behavior showed it to be related to the interaction of the beta alumina with constitutents of the positive electrode compartment. In particular, iron has been shown to enter beta alumina in the presence of an electric field when current is passing, if the cell is deliberately overheated. However, it was found that only the β (but not the β″) phase was modified by the incursion of iron. The resistance of the iron‐doped regions of the ceramic was very high. Chloroaluminate melts also irreversibly damage the beta alumina in the absence of an electric field, when FeCl3 or excess AlCl3 is present, by abstraction of Na+ ions, forming γ alumina.

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