Resistance measurements, zirconia

Kleitz, M. Bernard, H. Fernandez, E. Schouler, E. Impedance Spectroscopy and Electrical Resistance Measurements on Stabilized Zirconia in "Advances in Ceramics Vol. 3, SCIENCE AND TECHNOLOGY OF ZIRCONIA, ed. Hever, A. H., American Ceramic Society Columbus, Ohio, 1981. 

Kleitz, M., Bernard, H., Fernandez, E., andSchouler, E. (1981). Impedance spectroscopy and electrical resistance measurements on stabihzed zirconia. Advances in Ceramics. Science and Technology of Zirconia, Vol. 3,310-336, Heuer, A. H., and Hobbs, L. W., eds., Washington, DC The American Ceramic Society. 

It was hrst reported in 2001 [32] that the evaluation by impedance spectroscopy of a biased zirconia sensor with an attached LaFeOa-SE has shown that only the electrode resistance is a function of NO2 content. Consequently, impedance spectroscopy offers a method for directly probing the electrode reactions that are the basis for mixed-potential-type gas sensors [67]. As a result of further development by using impedance spectroscopy in zirconia-based gas sensors with oxide-SEs, a new type of YSZ-based sensor for detecting total NO and HCs at high temperatures has been proposed recently [2, 14, 21, 62, 74, 96-100]. In this case, the change in the complex impedance of the device attached with a specific oxide-SE was measured as a sensing signal. 

In order to examine how impurities affect the resistance of both single-crystal and polycrystalline zirconia, samples were prepared and resistance was measured. Samples of polycrystalline zirconia and the zirconia single aystal with the same concentration of Y2O3 were used at temperatures of 400-800 C. The results of testing are shown in Figure 4.8. Based on the fact that the higher the sintering conditions of polycrystalline zirconia, the less the resistance and porosity of solid electrolyte... 

FIGURE 4.8 Temperature dependence of the logarithm of resistance of the zirconia ( ) polycrystalline ceramic and ( ) single crystal. (From Zhuiykov, S., Zirconia single crystal analyser for low-temperature measurements, Proc. Control and Quality 11 (1998) 23-37. With permission.)... 

A majority of commonly used inorganic membranes are composites consisting of a thin separation barrier on porous support (e.g., Membralox zirconia and alumina membrane products). Inorganic MF and UF membranes are characterized by their narrow pore size distributions. This allows the description of their separative performance in terms of their true pore diameter rather than MW CO value which can vary with operating conditions. This can be advantageous in comparing the relative separation performance of two different membranes independent of the operating conditions. MF membranes, in addition, can be characterized by their bubble point pressures. Due to their superior mechanical resistance bubble point measurements can be extended to smaller diameter MF membranes (0.1 or 0.2 pm) which may have bubble point pressure in excess of 10 bar with water. 

For the preparation of aluminate coatings, the deionized water was preheated with an electric heater under constant stirring to the desired temperature, a zirconia disc was inserted and then the AIN powder added to the water. The pH and temperature were measured versus time using a combined glass-electrode/Pt 1000 thermometer pH meter (Metrohom 827). In addition, some of the prepared boehmite coatings on zirconia surface were thermally treated in the resistance oven in dry air, at 900 °C, for 1 hour, at a heating rate 10 °C/min. 

Fig.3 presents the temperature dependencies of relative elongation and total resistivity of the glass-ceramic materials. The total conductivity was found essentially independent of composition the impedance spectroscopy and e.m.f. measurements of oxygen concentration cells suggest that the role of electronic transport is predominant (Table 2 and Fig.4). Since excessive additions of YSZ increase the ionic conduction and oxygen permeability, zirconia amounts in sealants should be less than 30-35 wt%.

In 1963, an important development was the zirconia membrane electrode showing ionic conductivity due to oxide ion (10). This electrode, initially composed of calcium oxide and zirconia, later has appeared in other forms, notably zirconia-yttria and zirconia-thoria. It has proven effective for oxide ion activity measurements over an extremely wide range at temperature of 1000 or higher, but it is of limited use at temperatures below 500 because of excessive resistance. 

Sensors for measurements of oxygen in molten steel are the most important application in liquid metal sensing. As an electrolyte MgO partially stabilized, zirconia is used because of its high thermal shock resistance due to phase transformations. 

Barnett, Perry, and Kaufmann (75) found that fuel cells using 8 im thick yttria-stabiUzed zirconia (YSZ) electrolytes provide low ohmic loss. Furthermore, adding thin porous yttria-doped ceria (YDC) layers on either side of the YSZ yielded much-reduced interfacial resistance at both LSM cathodes and Ni-YSZ anodes. The cells provided higher power densities than previously reported below 700 °C, e g., 300 and 480 mW/cm at 600 and 650 °C, respectively (measured in 97 percent H2 and 3 percent H2O and air), and also provided high power densities at higher temperatures, e g., 760 mW/cm at 750 °C. Other data (Figure 7-25) from the University of Utah (73) show power densities of 1.75 W/cm with H2/air and 2.9 W/cm with H2/O2 at 800 °C for an anode-supported cell. However, no data is presented with regard to electrodes or electrolyte thickness or composition. 

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