Zirconia calcia

An example of the use of the zirconia + calcia electrolyte for the investigation of liquid alloys is provided by Fruehan who determined the activity of chromium in molten chromium + nickel alloys at 1875 K by measuring the e.m.f. of the galvanic cell ... 

At 1875 K, the dissociation pressure of chromic oxide is about 10 atm, whereas Fruehan demonstrated that zirconia + calcia exhibits insignificant electronic conductivity down to about 3 x 10 atm at that temperature. 

It has been mentioned above that zirconia + calcia solutions exhibit predominantly ionic conductivity at oxygen pressures of 10 atm. At lower oxygen pressures, however, electronic conductivity begins to limit the usefulness of the electrolyte. In other words, the electrolyte cannot be employed reliably in the usual cell arrangement with metals the affinity of... 

Measurements of the conductivity of zirconia-calcia solutions [5,12,13,17—20] or zirconia-yttria solutions [20, 21] when plotted [22] as a function of the concentration of CaO or Y2O3 at 1000°C show a conductivity maximum between 10 and 15 % CaO or between 5 and 10% Y2O3 respectively. The maximum conductivity occurs close to the concentration of CaO or Y2O3 which is the lower limit for the cubic phase stabilization of zirconia. It is likely that the conductivity maximum is correlated to the number and distribution of vacancies. Plots of the logarithm of the resistivity versus 1/T at constant composition are linear for CaO contents between 12 and 15 % and for Y2O3 between 9 and 30% in the range between 800°C and 1400°C. Resistivities of about 25ficm... 

Figure 12.24 A portion of the zirconia-calcia phase diagram ss denotes solid solution.

Similarly, fusion of milled zircon with dolomite or lime forms CaSiO and MgZrO [12032-31 -4] CaZrO [12013-47-7] and CaO Ca2SiO or CaSiO and Zr02, and is used to prepare zirconium oxide, usually as calcia-stabiUzed cubic zirconia because of the calcia left in soHd solution in the zirconia (27-29). 

The diffusion coefficient of oxygen in solid silver was measured with a rod of silver initially containing oxygen at a conceim ation cq placed end-on in contact with a calcia-zirconia electrolyte and an Fe/FeO electrode. A constant potential was applied across dre resulting cell... 

The same principles apply when two solids react, as can be illustrated by the reaction of a crystal of zirconia, Zr02, with a small amount of calcia, CaO, to produce a crystal of calcia-stabilized zirconia. There are two principal ways that this reaction can be imagined to occur either the Ca atoms occupy Zr sites or they occupy interstitial sites. 

M. J. Radler, J. B. Cohen, and J. B. Faber, J. Phys. Chem. Solids, 51, 217-228 (1990). References to calcia-stabilized zirconia ... 

Each added Cd2+ ion generates one cation vacancy. Similarly, each added Ca2+ ion into Zr02, as in calcia-stabilized zirconia (Section 1.11.6), generates a compensating anion vacancy ... 

The stabilized zirconia family of oxides, especially calcia-stabilized zirconia, are solids in which oxide ion conductivity has been increased to the extent that they are widely used solid electrolytes (Section 1.11.6, Section 4.4.5, and Section 6.8). 

CALCIA-STABILIZED ZIRCONIA AND RELATED FAST OXYGEN ION CONDUCTORS... 

A number of oxides with the fluorite structure are used in solid-state electrochemical systems. They have formulas A02 xCaO or A02 xM203, where A is typically Zr, Hf, and Th, and M is usually La, Sm, Y, Yb, or Sc. Calcia-stabilized zirconia, ZrC)2.xCaO, typifies the group. The technological importance of these materials lies in the fact that they are fast ion conductors for oxygen ions at moderate temperatures and are stable to high temperatures. This property is enhanced by the fact that there is negligible cation diffusion or electronic conductivity in these materials, which makes them ideal for use in a diverse variety of batteries and sensors. 

The parent phase is a stoichiometric oxide M02 with the fluorite structure. Substitution of a lower valence cation for Zr4+ is compensated by oxygen vacancies (Section 1.11.6 and Section 4.4.5). Taking calcia-stabilized zirconia as an example, addition of CaO drops the metal to oxygen ratio to below 2.0, and the formula of the oxide becomes Ca Zrj -x02-x. 

Calcia or yttria or magnesia stabilized zirconia tube externally coated with a film Zr Y Ti (87 12 1 mol%) using ECVD technique (in double pipe configuration), film thickness 2-10 /inner diameter 1 cm, length 15 cm. 

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