Development of Ultra High-Temperature Oxide Proton Conductive Solid Electrolyte

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The defect structure of the conventional proton conductor CaZrO3(+In) in the high temperature region was studied in detail at first. According to the results, a new method to compensate the effect of the oxide ion conduction, which become remarkable in higher temperature range, was developed. The prototype hydrogen sensor system designed adopting this method was made and tested in the laboratory and the practical plant. The high performance of the system as the monitoring tool for the metal melting process was confirmed.In order to find the proton conductor usable in higher temperatures, the behavior of hydrogen in the single crystal of magnesium aluminate spinel was studied. From the existence of OH stretching vibration observed in the IR absorption spectrum, the dissolution of hydrogen into the alumina-rich spinel as the type of proton was ascertained. The chemical diffusion coefficient of hydrogen determined from the dissolution rate was found far smaller than those of conventional … More perobskite-type proton conductors. As the H/D isotope effect in the electrical conductivity was not observed, it was confirmed that the contribution of the movement of the dissolved proton to the electrical conduction was very small.From the consideration on the curious phenomena observed concerning the extra high hydrogen solubility of molten aluminum, the possibility of alumina-base proton.conductor was suggested. Therefore, the hydrogen dissolution into the single crystal of Mg-doped alpha alumina was studied extensively. From the result of IR absorption, hydrogen was confirmed to dissolve as a movable proton. A clear H/D isotope effect was observed in the electrical conductivity measurement. And the predominancy of the proton conduction was ascertained. Using Mg doped sintered polycrystalline alumina, the proton transport number was determined by EMF method. The determined value in hydrogen atmosphere was more than 0.5 even at the temperature l473K.It was found that Mg-doped alpha alumina was the best material as a proton conducting solid electrolyte for high temperature use. The performance of the hydrogen sensor using this electrolyte was also tested and good results were obtained. Less