Zirconia unstabilized

Unstabilized zirconia is deposited by the reaction of the metal halide with CO2 and hydrogen (the water-gas reaction) at 900-1200°C 01... 

Figure 3.11 Comparison of predicted Young s mt ulus for alumina-zirconia composites with experimental data. The agreement is good if zirco-nia is retained in the tetragonal phase (by stabilization with yttria) but is poor for the unstabilized zirconia at higher volume fractions.

Commercial zirconia grades. Usually unstabilized zirconia (i.e., fully monoclinic), partially stabilized zirconia, and stabilized zirconia (i.e., completely cubic) grades exist commercially and are available among advanced ceramic producers worldwide (e.g., Zircoa, Vesuvius, and Degussa), and they are briefly described below. 

Preparation of unstabilized zirconia. Zirconia is usually produced from zircon flour. Although the carbochlorination of zircon produces zirconium tetrachloride that can be oxidized to yield zirconia, such a method is only restricted to the production of zirconium metal (see Zirconium and Zirconium alloys). Therefore, to produce zirconia from zircon, the first step is to convert zircon to zirconyl chloride dihydrate. The process starts with the preparation of disodium metazirconate (Na ZrOj) by digesting zircon into molten sodium hydroxide as follows ... 

Duplex Ceramics. Spherical pressure zones 10-50pm diameter are homogenously dispersed in a ceramic matrix, to toughen it and to enhance its thermal shock resistance. The zones contain a high proportion of unstabilized zirconia. Spontaneous or stress-induced tetragonal/monoclinic transformation of the zirconia produces compressive stresses in the zones, and radial compressive and tensile hoop stresses in the nearby matrix. (H.E. Lutz and N. Claussen, J. Ear. Ceram. Soc. 7 (1991) 209)... 

The measured V — Ki diagrams of alumina and the composites prepared with the colloidal route and different volume fraction of unstabilized zirconia are plotted in Fig.l4 AI2O3, A7.5Z, AIOZ and A15Z correspond to nanocomposites with 0, 7.5, 10 and 15 vol % ZrOi respectively and A7.5Z-2Y is a composite with 7.5 vol % Zr02, stabilized by 2 mol % Y2O3. Subcritical crack growth laws were measured using the double torsion technique and the relaxation method. 

Sintered density of the three series of composite powders containing 15 vol% of Zr02, calcined at 950°C for 3 h and sintered at 1530°C for 3 h is shown in Table 6-15. Sintered bulk density of the AlaOa/stabilized Zr02-Zr02 composites increased to >99% when the Zr02 vol% was increased to 15%. Relative density of the sintered composite containing unstabilized zirconia decreased considerably with increase in the ZrOz content in the composites. 

Pure Zirconia. Pure, or unstabilized zirconia, has many uses despite the phase-transformation phenomenon described. Its density, 6.05 g/cm, makes it valuable as a grinding medium. Added to alumina or magnesia it promotes sinterability and enhances strength and other properties, as discussed above under Toughened alumina. It is an important constituent of ceramic colors, and a component of lead-zirconia-titanate-based electronic ceramic devices such as capacitors. But its uses increase dramatically as a result of a process known as stabilization, which is discussed in the following sections. 

In particular, the evolution of radiation-induced defects in fully stabilized cubic zirconia (FSZ) (Y, Ca, and Er dopants acting as stabilizing agents) and a pure unstabilized monoclinic zirconia was investigated [60],... 

In the past, zirconia has been added routinely to a variety of ceramic materials in order to increase their toughness. Zirconia-toughened alumina was first developed by Claussen, who demonstrated a significant toughening effect of unstabilized, but transformable, tetragonal zirconia particles within the alumina matrix [214]. 

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