Zirconia based ceramics

Cheikh, A. et al., Ionic conductivity of zirconia based ceramics from single crystals to nanostructured polycrystals, J. Europ. Ceram. Soc. 21 (2001) 1837-1841. Hartmanova, M. et al., Correlation between microscopic and macroscopic properties of yttria stabilized zirconia 1. Single crystals. Solid State Ionics 136—137 (2000) 107-113. 

The volume changes associated with the r — m transformation around hardness impressions in zirconia-based ceramics have been monitored and quantified... 

Fig. 52. Raman spectra of various phases in zirconia-based ceramics (a) monoclinic (pure ZrOa) [255] (b) tetragonal (Zr02 + 2 mol% Y2O3) [256] and (c) cubic (Z1O2 + 9.5 mol% Y2O3) [257]. Gradual broadening of the spectral features upon increasing content of Y2O3 is due to the lattice mismatch caused by the differences in size between Zr and Y atoms.

Fig. 54. Schematic of indentation damage for (a) Vickers and (b) spherical indentations in zirconia-based ceramics. Dark areas comespond to higher microcrack density. Dashed lines show the elastic-plastic boundary. After Reference [251].

Adult orthodontics is recently gaining popularity due to its importance in esthetics, oral, and general health [182]. However, none of the currently available alumina- or zirconia-based ceramic orthodontic brackets meet the esthetic... 

In theory, heat in crystalline solids is transferred by three mechanisms (i) electrons (ii) lattice vibrations and (iii) radiation [44], Since zirconia is an electronic insulator (electrical conductivity occurring at high temperatures by oxygen ion diffusion), electrons play no part in the total thermal conductivity of the system. Hence, thermal conduction in zirconia-based ceramics is mainly by lattice vibrations (phonons) or by radiation (photons). 

One should note that transformation toughening is a possible method only in ceramics undergoing a transformation, for example in a zirconia-based ceramic in which tetragonal-monoclinic transformation might occur. One of the roles of... 

The data base now contains 5497 test results on over 320 different batches of ceramic materials. Approximately 46% of these are on zirconia-based ceramics, 9% are on silicon carbides, 21% are on silicon nitrides, 6.7% are on whisker-reinforced silicon nitrides, 16.3% are on alumina-based ceramics (including whisker-reinforced aluminas and mullites), and 2% are on other ceramics. Table 1 gives a detailed breakdown, by material class, of the data stored in the system, A list of materials within a material class Is available on request. 

Metal oxides and wide band semiconductors, such as SiC and GaN, with dielectric covering have a much better stability of surface and bulk properties in both oxygen and water environments in comparison with polymers and standard semiconductors (see Fig. 18.2), which prepares them for wide practical use in real devices of long-term use, available in the sensor market (Kerlau et al. 2006 Connolly et al. 2005). The results presented by Badwal (Badwal 1992 Badwal et al. 2000) show how stable metal oxides could be. Zirconia-based ceramics, which belong to the group of the most stable metal oxides, kept their electro-conductivity without considerable changes even at T> 1,000 °C. For comparison, the working temperature of polymer-based sensors is limited by 100-150 °C. 

In contrast to the above proposals, it is likely that other advanced ceramics-notably alumina, beryllia, sihcon carbide and sUicon nitride (see Chapter 11)-will demonstrate below-average growth rates owing to environmental concerns, competition from other ceramics (see Table 6.4), and an increasing reUance on slower-growing market segments such as cutting tools that are based on ceramic alloys (e.g., modified alumina and SiAlONs). In this situation, whilst alumina will surely remain the prominent material, its market share wiU be eroded by ferrites, and by beryllia- and zirconia-based ceramics. 

Hirvonen A. Nowak R. Yamamoto Y. (2006). Fabrication, Structure, Mechanical and Thermal Properties of Zirconia-based Ceramic Nanocomposites. Journal of the European Ceramic Society, Vol. 26, No. 8, May, pp. 1497-1505, ISSN 09552219... 

Kishimoto, A., Ayano, K., Teranishi, T., and Hayashi, H. (2014) The isothermal conductivity improvement in zirconia-based ceramics under 24GHz microwave heating. Mater. Chem. Phys., 143 (2), 486-489. 

The case of alumina is relatively simple since at least as first approximation, the reinforcement depends only on the crack length. Other cases are more complex, and the reinforcement can also depend on the applied stress. This is the case of the mechanisms acting at the crack front, such as microcracking and phase transformation toughening. A good example of the last case is the reinforcement in zirconia based ceramics. It is based on the tetragonal to monoclinic transformation of particles at the crack tip due to the local high stresses. The associated volume... 

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