Zirconia lattice

Electrocatalytic reactions, such as the transformation of O2 from the zirconia lattice to oxygen adsorbed on the film at or near the three-phase-boundaries, which we denote by 0(a), have been found to take place primarily at these three phase boundaries.5 8 This electrocatalytic reaction will be denoted by ... 

As discussed below, the porosity and surface area of the catalyst film is controllable to a large extent by the sintering temperature during catalyst preparation. This, however, affects not only the catalytically active surface area but also the length / of the tpb between the solid electrolyte, the catalyst film, and the gas phase (Figure 8). Elec-trocatalytic reactions, such as the transformation of from the zirconia lattice to oxygen adsorbed on the film at or near the tpb, which we denote by 0(a), (Equation [11]), have been found to take place primarily at these There is some experimental... 

Figure 7.19 Replacement of Zr ions by Ca ions in the zirconia lattice creating vacancies in the oxygen lattice.

Yttrium is used in SOFC cells to stabilize the zirconia lattice in electrolyte materials and used within a range of 3-10 mol% (3YSZ, 8YSZ, lOYSZ, etc.). 

A series of samples such as CuO-stabilized zirconia (CuO-Zr02 with a CuO content of 1-33 mol%) were prepared by sol-gel procedure. XPS study of this sample showed that Cu is essentially in the Cu " oxidation state and is incorporated into the zirconia lattice up to 5 mol% [60]. Impedance measurements indicate that the conduction mechanism is not altered by the incorporation of CuO in the Zr02 lattice. The conductivity changes (increases) up to 10mol% of CuO... 

Zirconium oxide is used in the production of ceramic colors or stains for ceramic tile and sanitary wares. Zirconia and siHca are fired together to form zircon in the presence of small amounts of other elements which are trapped in the zircon lattice to form colors such as tin—vanadium yellow, praseodymium—zircon yellow [68187-15-5] vanadium—zircon blue [12067-91 -3] iron—zircon pink [68412-79-3] indium—vanadium orange (105—108). 

Voltage Cell Type Oxygen Sensor The operation of the zirconia oxygen sensor utilizes the conduction of oxygen ions by virtue of anion or oxygen ion vacancies in the crystalline lattice. " The anion vacancies are created when the... 

To avoid this phase change, zirconia is stabilized in the cubic phase by the addition of a small amount of a divalent or trivalent oxide of cubic symmetry, such as MgO, CaO, or Y2O3. The additive oxide cation enters the crystal lattice and increases the ionic character of the metal-oxygen bonds. The cubic phase is not thermodynamically stable below approximately 1400°C for MgO additions, 1140°C for CaO additions, and below 750°C for Y2O3 additions. However, the diffusion rates for the cations are so low at Xhtstsubsolidus temperatures that the cubic phase can easily be quenched and retained as a metastable phase. Zirconia is commercially applied by thermal spray. It is also readily produced by CVD, mostly on an experimental basis. Its characteristics and properties are summarized in Table 11.8. 

We can introduce vacancies into a crystal by doping it with a selected impurity. For instance, if we add CaCl2 to a NaCl crystal, each Ca ion replaces fwoNa ions in order to preserve electrical neutrality, and so one cation vacancy is created. Such created vacancies are known as extrinsic. An important example that you will meet later in the chapter is that of zirconia, ZrOz. This structure can be stabilised by doping with CaO, where the Ca ions replace the Zr(IV) atoms in the lattice. The charge compensation here is achieved by the production of anion vacancies on the oxide sublattice. 

Conductivity maximizes at relatively low concentrations of dopant, but not at the 50% one might expect this is because there is an elastic interaction between the substituted ion and the vacancy created. The best conductivity seems to be achieved when the crystal lattice is distorted as little as possible (i.e., when the dopant ion is similar in size to the cation it is replacing). Consequently, two of the best oxygen-ion conductors are zirconia... 

Zirconium Hydride. ZrH2 ( ) mw 93.24 ( ) grey-blk pdr, does not form a well defined -compd it exists in five cryst phases, the e phase is a face-centered tetragonal cryst lattice that approximates the formula closely mp, air auto-ign temp of 270° d 5.6g/cc. V si sol in HF or coned acids. Prepn is either by heating Zr with H2, forming the metal in the presence of H2, reduction of zirconia with Ca hydride in the presence of H2 at 600—1000°, or by the com-bstn of Zr in H2... 

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