Zirconia body

Figure 10. Ionic conductivity of jully and partially stabilized zirconia bodies...

Figure 11. Optical micrograph of high silica content (> 1%) yttria fully stabilized zirconia body (bar = 37 microns)...

As can be seen, the mechanical strength of the partially stabilized body is approximately twice that of the fully stabilized and the thermal expansion is approximately 30% lower. Because of this, the thermal shock resistance of the PSZ body is greatly improved. The ionic conductivity of the PSZ body is lower but is still adequate for automotive applications. Figure 10 compares the conductivity of a yttria partially stabilized zirconia body with several fully stabilized bodies. 

The tetragonal-monoclinic phase transformation is further responsible for compressive surface layers formed during the processing of stabilised zirconia owing to the absence of a hydrostatic pressure near the free surface of a zirconia body (Figure 4.10). 

Schey04] Scheying G, Wuhrl I, Eisele U, Riedel R (2004) Monoclinic zirconia bodies by thermoplastic ceramic extrusion. J Am Ceram Soc vol 87 No 3 pp 358-364... 

Infiltration (67) provides a unique means of fabricating ceramic composites. A ceramic compact is partially sintered to produce a porous body that is subsequently infiltrated with a low viscosity ceramic precursor solution. Advanced ceramic matrix composites such as alumina dispersed in zirconia [1314-23-4] Zr02, can be fabricated using this technique. Complete infiltration produces a homogeneous composite partial infiltration produces a surface modified ceramic composite. 

Other types of refractory that find use are forsterite, zirconia, and zircon. Acid-resisting bricks consisting of a dense body like stoneware... 

Other types of refractory that find use are forsterite, zirconia, and zircon. Acid-resisting bricks consisting of a dense body like stoneware are used for lining tanks and conduits in the chemical industry. Carbon blocks are used as linings for the crucibles of blast furnaces, very extensively in a number of countries and to a limited extent in the United States. Fusion-cast bricks of mullite or alumina are largely used to line glass tanks. 

Uchida, M., Kim, H.-M.Miyaji, F. Kokubo, T. and Nakamura, T. (2001) Bonelike apatite formation induced on zirconia gel in a simulated body fluid and its modified solutions. Journal of the American Ceramic Society, 84, 2041-2044. 

The following table contrasts the properties of a typical partially stabilized zirconia (PSZ) body as used in this application with a typical fully stabilized (Y2O3) body. 

It should be noted that it is possible to produce fully stabilized bodies with much higher fracture strengths than listed here but this requires the use of fine particle size, chemically prepared powders (3). The use of this type of material involves a number of penalties both in cost and processability that may be prohibitive for a high volume automotive application. In addition to the type of partially stabilized body described here, two other basic types of partially stabilized bodies have been reported (4, ). Both are classified as transformation toughened partially stabilized zirconias and involve different processing techniques to obtain a body with various amounts of a metastable tetragonal phase. While the mechanical properties of these materials have been studied extensively, little has been reported about their electrical properties or their stability under the thermal, mechanical and chemical conditions of an automotive exhaust system. 

Hydroxyapatite (HAP), with basically the same crystal structure as Ca-deficient, carbonate-containing hydroxyapatite, is compatible with and reactive in a live human body. However, sintered HAP prepared by treating fine HAP particles under elevated temperature and pressure has insufficient mechanical properties, in particular fracture toughness, which greatly limits its commercial applicability. It is rarely implanted alone. On the other hand, zirconia, particularly partially stabilized zirconia (PSZ),... 

As mentioned previously, the main body of research on whisker-reinforced composites was concerned with alumina, mullite, and silicon nitride matrix materials. None the less, selected work examined zirconia, cordierite, and spinel as matrix materials.16-18 The high temperature strength behavior reported for these composites is summarized in Table 2.5. As shown, the zirconia matrix composites exhibited decreases in room temperature strength with the addition of SiC whiskers. However, the retained strength at 1000°C, was significantly improved for the whisker composites over the monolithic. Claussen and co-workers attributed this behavior to loss of transformation toughening at elevated temperatures for the zirconia monolith, whereas the whisker-reinforcement contribution did not decrease at the higher temperature.17,18... 

Considerable development has occurred on sintered ceramics as bone substitutes. Sintered ceramics, such as alumina-based ones, are uru eactive materials as compared to CBPCs. CBPCs, because they are chemically synthesized, should perform much better as biomaterials. Sintered ceramics are fabricated by heat treatment, which makes it difficult to manipulate their microstructure, size, and shape as compared to CBPCs. Sintered ceramics may be implanted in place but cannot be used as an adhesive that will set in situ and form a joint, or as a material to fill cavities of complicated shapes. CBPCs, on the other hand, are formed out of a paste by chemical reaction and thus have distinct advantages, such as easy delivery of the CBPC paste that fills cavities. Because CBPCs expand during hardening, albeit slightly, they take the shape of those cavities. Furthermore, some CBPCs may be resorbed by the body, due to their high solubility in the biological environment, which can be useful in some applications. CBPCs are more easily manufactured and have a relatively low cost compared to sintered ceramics such as alumina and zirconia. Of the dental cements reviewed in Chapter 2 and Ref. [1], plaster of paris and zinc phosphate... 

Hydrothermal homogeneous precipitation is one of the best ways to produce zirconia powders. The process, properties of the powders, and microstructure of the sintered body are shown in Table 1.5 and Figure 1.8, Figure 1.9, and Figure 1.10. ° ... 

Some ceramics exhibit biocompatibility in the human body. Alumina and zirconia are employed as the ball for hip replacements. Hydroxyapatite (Caio(P04)6(OH)2) is used as bone replacements, as ocular implants, and as a coating for metallic implants. Ceramics also find application in dentistry for restorative work. 

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