Zirconia phases

Carr and co workers [77] studied the retention of different amines on PBD-Zirconia phases. On PBD zirconia, they found that steric hindrance has a much greater effect on retention of bases in comparison to silica ODS phases thus, quaternary amines have substantially less retention than the corresponding less hydrophobic primary amine. This result agreed with previous findings of Sokolowski and Wahlund [78]. Thus, secondary and tertiary amines such as dimethylbutylamine and TEA were less effective silanol blockers. Only ammonia and primary amines were able to improve the chromatographic properties of basic solutes on PBD-zirconia. It would be interesting to check the application of these results also to silica-ODS phases. 

FIGURE 5.11 Phase diagram of the pseudobinaiy CaO-ZrOz system. The cubic calcia-stabilized zirconia phase occupies the central band in the diagram and is stable to about 2400°C. 

Transformation of tetragonal zirconia phase to monoclinic phase has been studied in [53], Calcination of zirconium hydroxide ZrO(OH)2 at various temperatures produced three types of paramagnetic centers assigned to trapped electrons located in oxygen vacancies of Zr02 (g = 2.0018), to adsorbed 02"... 

J. Dai, X. Yang, and P. W. Carr, Comparison of chromatography of octadecyl silane bonded silica and polybntadiene-coated zirconia phases based on diverse set of cationic dmgs, J. Chromatogr. A 1005 (2003), 63-82. 

In addition, anode crystallographic information after PEVD was obtained with XRD. The XRD spectrum of the PEVD composite anode is presented in Eigure 33. Three phases exist in the XRD spectrum a yttria stabilized zirconia phase (cubic), a pure zirconia phase (monoclinic) and a metallic Pt phase. The Pt phase shows up in the spectrum because the PEVD product on top of the Pt is thin enough to allow x-rays to penetrate the product phase to reach the underlying Pt phase. Based on the relative peak intensity, yttria stabilized zirconia is the major phase in the PEVD product. However, a certain amount of pure zirconia is evident. Thus, the zirconia in the PEVD product... 

As an example of the application of the WH method. Figure 13.7 shows the diffraction pattern of a ceria stabilized-zirconia powder sample [with a 20 wt.% addition of standard silicon (SRM 640b distributed by the NIST)], together with the corresponding WH plot for the tetragonal zirconia phase. The WH plot points out the presence of both size and strain effects (respectively, non-zero intercept and slope), and the best fit of Equation (14) gives < L >v = 18(l)nm and e = 0.0024(3). ... 

Figure 13.7 XRD pattern of a ceria stabilized zirconia powder mixed with 20 wt.% of standard silicon (asterisks). Experimental data (O) profile fitting result (line) and difference between data and fit (residual, lower line) (a) WH plot for the stabilized zirconia phase, with indication of Miller indices, regression line and 95% confidence range (b). (Reprinted from ref. 38 with the permission of the International Union of Crystallography.)...

For samples prepared by using a mixture of solid crystalline hydrates with Me CA ratio equal to 1 2, deviations from the additivity are even bigger, though in this case, part of zirconium is segregated as a separate zirconia phase. 

Fig. 22 Zirconia-rich end of the yttria-zirconia phase equilibrium diagram [77] (reprinted with permission)...

Oblate crystallographically oriented spheroidal precipitates of the tetragonal zirconia phase within the matrix of monoclinic zirconia are shown in Figure 4.6. 

Low Temperature Preparation of the Ceria Stabilised Zirconia Phase... 

The XRD patterns of the in situ (PdZr-i, trace 2) and air-oxidized (PdZr-a, trace 3) alloys do not indicate significant bulk structural differences between these catalysts. After oxidation of the alloy imder reaction conditions in situ) as well as in air, a solid made up of PdO and monoclinic and tetragonal Zr02 was formed. After reduction in hydrogen only reflections due to metallic palladium and zirconia phases were detected by XRD (trace 4). 

The XRD pattern of the coprecipitated catalyst (PdZr-c, trace 5) show palladium reflections indicating the presence of palladium crystallites, while the reflections due to zirconia phases are greatly broadened, which suggests amorphous phases. XRD line broadening and electron microscopy indicated that the catalysts prepared by oxidation of the glassy alloy were made up of small poorly crystalline palladium domains of about 5-7 nm lateral dimension. These domains were flilly integrated in predominantly amorphous zirconia. Although the coprecipitated catalyst contained palladium particles of about similar size (8 nm). 

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