Zirconia tetragonal polycrystals

Y-TZP = yttria-stabilized tetragonal zirconia polycrystal. LAS = lithium alurninosiUcate. 

Tetragonal structure, of ferroelectric crystals, 11 95, 96 Tetragonal symmetry, 8 114t Tetragonal zirconia polycrystals, 5 571 Tetrahedral... 

Nawa, M., Yamazaki, K., Sekino, T. et al, A new type of nanocomposite in tetragonal zirconia polycrystal-molybdenum system, Mater. Lett., 1994, 20(5-6) 299. 

The first observation of superplasticity in a 3 mol% yttria-stabilized tetragonal zirconia polycrystal ceramic (YTZP) with a grain size of 0.4 pm was reported by Wakai et al in 1986 (Fig. 16.1). Since then, a large number... 

Moreno, R., Requena, J., and Moya, J.S., Slip casting yttria-stabilized tetragonal zirconia polycrystals, J. Am. Ceram. Soc., 71,1036, 1988. 

A supersaturated bioinspired solution was used to coat alumina and zirconia substrates with a thin, poorly crystalline layer of OCP that after heat treatment at 1050 °C for 1 h was converted to hydroxyapatite with particle size of 300 nm (Pribosic, Beranic-Klopcic and Kosmac, 2010). Stefanic et al. (2012) applied a related method to rapidly deposit an OCP layer by a two-step process onto yttria-stabilised tetragonal zirconia polycrystal (Y-TZP). 80vol% Mg-PSZ/20 vol% alumina substrates were used by Nogiwa and Cortes (2006) to deposit biomimetically by immersion in 1.4 SBF a bone-like apatite coating of 15-30 pm thickness, using a bed of either wollastonite ceramics or bioactive glass as an additional source of Ca2+ ions. 

Tetragonal zirconia polycrystals (TZPs). These ceramics contain 100 percent tetragonal phase and small amounts of yttria and other rare-earth additives. With bend strength exceeding 2000 MPa, these ceramics are among the strongest known. 

Figure 12.12 Cyclic fatigue long-crack propagation data for several ceramics compared to those for some typical metals.TZPs are tetragonal zirconia polycrystals (see Chap. 11).

As a metal, zirconium is used in bone and muscle implant materials. The combination of mechanical properties and excellent biocompatibility makes tetragonal zirconia polycrystal (TZP) ceramics one of the best biomaterials for prosthetic joints. (Covacci et al. 1999). 

Fig. 51. (a) Temperature-pressure phase diagram of pure Zr02 [244] and (b) the zirconia-rich section of a Zr02-Y203 phase diagram [245]. Shaded areas indicate the ranges of compositions for partially stabilized zirconia (PSZ) and tetragonal zirconia polycrystals (TZP) [246]. 

Explain why tetragonal zirconia polycrystal (TZP) and Mg-partially stabilized zirconia (PSZ) ceramics have higher toughness than alumina ceramics. 

Yokota et al. [75] used SFD to produce the magnesium sulfate powders. Open pores were found at the dried powder surface. The porosity was about 87%-90% with pore size less than 100 nm. Fine powders of several other materials, e.g., calcium phosphate, tetragonal zirconia polycrystals, etc., can also be produced by SFD [55],... 

Hwang, S. L. and Chen, I.-W., Grain size control of tetragonal zirconia polycrystals using the spaee eharge eoncept, J. Am. Ceram. Soc., 73, 3269-77,1990. 

The addition of yttria to zirconia not only stabilizes the cubic or tetragonal form but also lowers the temperature ofthe t m transformation. The practical consequence of this is that larger zirconia particles can be retained in the metastable tetragonal form, thus considerably easing any problems associated with the fabrication of a toughened ceramic, such as ZTA. One important feature of this system is the solubility of yttria in zirconia up to a concentration of approximately 2.5 mol% which, in conjunction with a low eutectoid temperature, will facilitate the formation of fully tetragonal ceramics which are referred to as tetragonal zirconia polycrystals (see Section 1.6.4). 

Figure 15.1 As-received and tensile-deformed specimens of superplastic yttria tetragonal zirconia polycrystals (YTZP), as displayed by Wakai et al., in 1986. Illustration courtesy of Prof Wakai.

Dominguez-Rodriguez et al. have recently assessed the vahdity of a dislocation-driven model in yttria-tetragonal zirconia polycrystals [66], and concluded that such a mechanism would be quite unlikely to be operative in this system. 

Partially stabilized zirconia (PSZ) and tetragonal zirconia polycrystals (TZP)... 

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