Zirconia electrodes

Normally, glass electrodes must be soaked in water for a few minutes to a few hours for the electrode to develop a pH response. This allows hydration of the outer surface to take place with the formation of the hydrogen ion-selective sites. Similarly, in 90°C pH tests at Pennsylvania State University, it has been found necessary to allow the zirconia electrodes to soak for several hours before a pH response was observed. 

Jimenez, R., Kloidt, T., Kleitz, M. Reaction-zone expansions and mechanism of the 0-2, Ag/ yttria-stabilized zirconia electrode reaction. J. Electrochem. Soc. 1997, 144, 582-5. 

Combes et al. (1980) used calcia-stabilized zirconia electrodes to determine the concentration in the MgCl2-NaCl-KCl mixtures at 1000 K with different BaO additions. They suggested that the following reactions take place in the melt ... 

M.L. Deanhardt and K.H. Stem, Solubility Products of Metal Oxides in Molten Salts by Coulometric Titration of Oxide Ion through Zirconia Electrode, J. Electrochem. Soc. 128... 

Comparison of Equation (26-10) with Equations (26-11 a) and (26-1 lb) shows that the reference electrode (hereafter often zirconia electrode ) functions as a platinum electrode in a melt with defined oxygen partial pressure, since Uo -, zr02(m) = o2-, zro w because of the uniform solid electrolyte [1]. This is also seen from Equation (26-12) for its galvanic potential ... 

A zirconia electrode with a particularly long lifetime is shown in Figure 26-6 [S, 7-9]. A zirconia electrolyte bridge, which is inserted into an alumina electrode shaft and whose position is fixed by an alumina bolt, connects the Pt,02 reference electrode and the melt. The... 

Figure 2/6-6. Dissolving zirconia electrode. (1) Zirconia bridge between (2) Pt,02 reference electrode and (3) melt (4) alumina electrode shaft (5) alumina bolt (6) zirconia grit (7) thermocouple (8) four-bore alumina tube (9) electrode head. T, reference electrode temperature temperature of measuring electrode in isothermal melt with T, .

The measurements were conducted by applying the cell in oxidic melts containing small and equal molar concentrations of antimonyflll) and antimonyfV) (or arsenic(lll) and arsenic(V)) oxide. The special arrangement used separated the melt essentially from the surrounding atmosphere and allowed electrochemical pumping of oxygen into, and out of, the melt by means of a platinum electrode and a zirconia electrode or the zirconia crucible, which contained the melt and served as the oxide ion-conducting wall [28]. The concentration ratio of the polyvalent ionic species could thus be well adjusted. 

Experimental arrangement for measuring thermoelectric emfs of glass-forming melts by means of zirconia microelectrodes. (1) Zirconia electrodes (2) melt (3) temperature gradient furnace (4) leads from PtiOj reference electrodes (5) leads from thermocouples (6) reference gas inlet (7) outlet. 

The zirconia electrode served as a reference electrode not only for the platinum electrode measuring the oxygen fugacity of the melt, but also for the platinum contact of the ZS crucible during the reaction between ZS and melt and was also short-circuited with the ZS contact in order to change the course of the reaction. The study resulted in an electrochromic-type... 

Experimental arrangement for studying a heterogeneous reaction between zirconium silicate (ZS) refractory (1) and oxidic melt (2). The zirconia electrode (3) is used as a reference electrode for the platinum electrode (4) measuring the oxygen fugacity of the melt, for the ZS crucible (1), and for a short-circuit with ZS, via platinum contact (3). 

The final example is concerned with standard Seebeck coefficients of glass melts, which were accessible after zirconia electrodes had been developed [12]. Continuously working glass melting units are characterized by nonisothermal operation, and metals, eg, platinum-type metals, contacting the melt and often short-circuited are subject to electrode reactions, eg, generation and consumption of oxygen, which can indirectly impair the production of the melters. Thermoelectric emfs of such nonisothermal cells. 

Figure 26-20. Practical signincance of thermoelectric potentials. The relative potentials, tRpt< of a platinum electrode in melts satisfying Equation (26-33) were obtained from standiud thermoelectric potentials, of a zirconia electrode and temperature-dependent emfs, E, of cell (VI) according to Equation (26-37). The temperature dependence of Pp, is determined by the standard Seebeck coefficients of the melts and is positive (a), negative (b), and, depending on the temperature, both negative and positive (c).

The sensor (a sensor) is designed to deliver measurements of the [O j in the exhaust gas. P(02) in the exhaust can be taken as a direct measure of the A/F ratio in the combustion chamber s inlet. The sensor is essentially a yttrium-stabilised zirconia electrode whose potential depends on P(02). This electrode (which is composed of the same material as the electrol)i e in a solid oxide fuel cell) transports as O " ions generating an electrical signal whose strength is proportional to P(02). The signal is sent to the fuel injection system which increases or decreases the A/F ratio as desired in order to keep the mixture stoichiometric [12]. 

Siebert, E., Hammouche, A., and Kleitz, M. (1993). Impedance spectroscopy analysis of Lai-xSrxMnOj yttria-stabilized zirconia electrode kinetics. Electrochim. Acta 40 1741-1753. 

At the present time research work is in progress in our laboratory on solid silver-zirconia electrodes to see whether such a model can be adequate and whether the second terms which appear in eq. (31) can account for the slant of the semi-circle impedance. 

Hauch A, Ebbesen SD, Jensen SH, Mogensen M (2008) Solid oxide electrolysis cells microstructure and degradation of the Ni/yttria-stabilized zirconia electrode. JElectrochem Soc 155(11) B1184—B1193... 

Spacil HS (1964) Electrical device including nickel-containing stabilized zirconia electrode. US Patent No. 3,503,809, filed October 30,1964... 

Although a number of the indicator electrodes have been tested for operation over a wide range of temperatures, only the platinum/hydrogen, Pt(H2), and yttria-stabilized zirconia electrodes, with a mercury/mercury oxide electrochemical couple, YSZ(Hg/HgO), were found to be capable of operating in a Nemstian manner at temperatures up to 400 °C. 

Zhi M, Chen X, Finldea H, Celik I, Wu NQ (2008) Electrochemical and microstructural analysis of nickel-yttria-stabilized zirconia electrode operated in phosphorus-containing syngas. J Power Somces 183 485 90... 

Wang, X.G., Nakagawa, N. Kato, K. Anodic polarization related to the ionic conductivity of zirconia at Ni-zirconia/zirconia electrodes. J. Electrochem. Soc. 148 (2001), pp. A565-A569. 

The basic composition of zirconia electrodes allows (and necessitates) the construction of several different types of electrodes. 

One of the disadvantages of more or less all zirconia electrodes is the rather strong corrosion (or solubility ) of the zirconia ceramics in oxidic melts. This fact prompted us to construct electrode units especially for application in industrial glass melting tanks, which are distinguished by rather long lifetimes despite the relatively high corrosion of the zirconia. 

Fig. 8.3 Arrangement for measuring thermoelectric emfs of doped zirconia rods used as zirconia electrolyte bridges. The specimen is clamped between two zirconia electrodes with equal oxygen partial pressure. The zirconia rod is kept in a temperature field due to the specially designed temperature gradient furnace...

The corrosion-protected zirconia electrode is protected from corrosion by a platinum tube around the alumina shaft, which protects the ceramics from condensing vapors of melt components with high vapor pressure. An additional... 

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