Alumina zirconia composites

Pratapa, S. Low, I.M. (1998) Infiltration-processed functionally-graded AT/alumina-zirconia composites II, Mechanical properties. J. Mater Sci. 33, 3047-3053. 

Moon, R.J., Hoffman, M., Hilden, J., Bowman, K., Trumble, K., Roedel, J. Weight function analysis on the 7 -curve behavior of multilayered alumina-zirconia composites, J. Am. Ceram. Soc. 85(6), 1505-1510, 2002. 

The high temperature, short-term properties of alumina and alumina/ zirconia composites have been examined in a number of studies.18,19,24-32 Typical fracture strength and toughness at elevated temperatures are summarized in Figs. 2.2 and 2.3. 

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.

Figure8.76 Lenticular void that acted as a fracture origin in an alumina-zirconia composite scanning electron micrograph. (From Green et ai, 1989, reproduced courtesy of CRC Press, Boca Raton, FL.)...

For orthopedic applications, alumina-zirconia composites have a higher reliability than single-phase ceramics, due to the combined advantages of both the alumina and the zirconia. With the same pre-existing defects, these composites can work at loads two times higher than monolithic alumina without delayed failure and are not susceptible to the hydrothermal instability (low temperature degradation) observed in the case of stabilized—zirconia bioceramics. 

Morita Y, Nakata K, Kim Y H, Sekino T, Niihara K, Ikeuchi K (2004) Wear properties of alumina/ zirconia composite ceramics for joint prostheses measured with an end-face apparams. Bio-Med Mater Eng 14 263-270... 

Bu ko M (2000) Ionic conductivity of alumina-zirconia composites. Pol Ceram Bull 61 95-102... 

This latest trend in load-bearing materials for arthroplastic applications involves the development of highly fracture-resistant alumina/zirconia composites, as an alternative choice to alumina and zirconia monolithic ceramics. Composite materials are designed from both chemical and microstructural viewpoints in order to prevent environmental degradation and fracture events in vivo. Based on the experimental determination of an activation energy value for an environmentally driven tetragonal to monoclinic transformation, the long-term in vivo environmental resistance of prostheses made from these composite materials can be predicted (Chevalier et al., 2009). 

The alumina zirconia composites processed by the colloidal route present a narrow distribution that is roughly between Dc and D. This leads to a more efficient transformation toughening in the ceramics processed by the colloidal route and to a shift of the crack velocity versus stress intensity factor curve towards higher Ki values for the composites obtained by the colloidal route compared to the composites obtained by a powder-mixing technique [35]. 

Kazakov AI, Rubtsov Yul, Lempert DB, Manelis GB (2003) Kinetics of oxidation of organic acids by ammonium nitrate. Russ J Appl Chem 76 1214-1220 Behera SK, Barpanda R Prathar SK, Bhattacharyya S (2004) Synthesis of magnesium-aluminium spinel from autoignition of citrate-nitrate gel. Mater Lett 58 1451-1455 Chandradass J, Kim K, Ki H (2004) Effect of activity on the citrate-nitrate combustion synthesis of alumina-zirconia composite powder. Metals Mater Int 15 2039-2043 Purohit RD, Saha S, Tyagi AK (2006) Nanocrystalline ceria powders through citrate-nitrate combustion. J Nanosci Nanotech 6 209-214... 

S. K. Malhotra is Chief Design Engineer and Head ofthe Composites Technology Centre at the Indian Institute of Technology, Madras. He has pubhshed over 100 journal and proceedings papers on polymer and alumina-zirconia composites. 

Although - as is evident from these considerations - it should not be concealed that some microstructural targets probably carmot be achieved with ceramic materials and some of the earlier expectations have turned out to be too optimistic, for many of the above applications alumina, ziiconia and alumina-zirconia composite ceramics are quite suitable. Without doubt, during the second half of the 20 century alumina has developed into the most frequently... 

This is possible because the elastieitj standard relations must hold for all isotropic continua, whether heterogeneous on the mieroscale or not [Torquato 2002]. It will be shown below, that in the case of the dense alumina-zirconia composite ceramics (Poisson ratios 0.23 and 0.31 for alumina and zirconia, respectively) the deviation of the Voigt bound Ey... 

Effective Elastic Moduli of Alumina, Zirconia and Alumina-Zirconia Composite Ceramics... 

Figure 3. Effective tensile modulus of dense alumina-zirconia composite ceramics Voigt bound (crosses slightly above the upper solid line calculated from the Voigt values of the effective shear and bulk moduli), approximate Voigt bound (according to the mixture rule, upper solid line), Reuss boimd (results of both calculations identical, crosses and lower solid curve), upper and lower Hashin-Shtrikman bounds (dashed curves) and values measured by the resonant frequency method for dense (porosity < 3 %) alumina-zirconia composite ceramics prepared by slip casting.

For the calculation of the effective Poisson ratio the mixture rule is usually recommended. In the case of alumina-zirconia composite ceramics it takes the form (dimensionless)... 

All the above formulae allow the direct and easy calculation of the effective elastic moduli and Poisson ratios of dense alumina-zirconia composites for a given zirconia volume fraction (f). Since usually the composition of alumina-zirconia composites (in the sequel abbreviated as AZ composites ) is given in weight percent (weight fractions ) the volume fraetions usually to be ealculated via the (theoretical) density. In the... 

Figure 4. Voigt bound (solid straight line) and Hashin-Shtrikman upper bound (solid curve) for the relative tensile modulus of porous ceramics (e.g. alumina, zirconia or alumina-zirconia composites) the Reuss bound and the lower Hashin-Shtrikman bound (dashed lines along the axes) degenerate to zero...

Fig. 7 shows the porosity dependence of the tensile moduli experimentally measured (by the resonant frequency technique) for alumina, zirconia and alumina-zirconia composites (ZTA and ATZ) prepared from submicron oxide powders using starch as a pore-forming agent (com starch with a median size of approx. 14 micrometers and potato starch with a median size of approx. 50 micrometers). The processing method is starch consolidation casting, cf. the details given and references cited in [Pabst et al. 2004b, 2005],... 

In this chapter we have treated the effective elastic moduli of alumina, zirconia and alumina-zirconia composite ceramics. We have invoked the theory of linear elasticity [Gurtin 1972], which is the appropriate framework for the macroscopic mechanical behavior of alumina and... 

All micromechanical relations presented in this chapter are based on the volume fraetions of the constituent phases (i.e. one-point correlation fimctions and a special part of the two-point correlation functions) as the only input information. If complete two-point and three-point information would be available (e.g. from stereological analysis or 3D tomography), the Hashin-Shtrikman bounds (i.e. the two-point bounds) could be improved in principle, whieh leads to the three-point bounds due to [Beran Molyneux 1966] and [Milton Phan-Thien 1982], cf. also [Jeulin 2001, 2002, Markov 2000, Milton 2002, Sobczyk Kirkner 2001, Torquato 2000, 2002]. Of course, in the case of dense alumina-zirconia composites it is quite... 

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