Development of YSZ pH sensor for Use in High Temperature Solutions

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A solid-electrolyte pH sensor using a yittria-stabilized zirconia (YSZ) has been developed for pH measurements in high temperature aqueous solutions. A thin film of Ni-NiO mixture, which was deposited on one side of the YSZ plate by ion-beam-sputtering, was used as a solid-state internal reference electrode. The pH response of the sensor was examined at temperatures in the range of 368-523K.It was found that at every temperatures examined, the potential of the pH sensor decreases linearly with increasing pH.The gradient of the potential vs. pH relationship increased with increasing temperatures, and it almost agreed with the predicted Nernstian value when the temperature exceeded 423K.The response potentials at pH0, which were estimated by extrapolation of the potential vs. pH relationships, were close to those calculated thermodymanically for a Ni-NiO reference electrode. The pH response of the sensor was slow at temperatures lower than 473K,but became faster when the temperature exceeded 473K ; the stationary potentials of the sensor were reached within one hour at 523K.