Zirconia monoliths

S. Wodiunig, F. Bokeloh, J. Nicole, and C. Comninellis, Electrochemical Promotion of R11O2 Catalyst Dispersed on an Yttria-Stabilized Zirconia Monolith, Electrochemical and Solid State Letters 2(6), 281-283 (1999). 

Randon et al. reported on an alternative approach for the preparation of zirconia monoliths [96]. The sol-gel process is initiated by hydrolysis of an ethanolic zirconium alkoxide solution, on addition... 

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... 

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). 

Figure 15. SCG in ZTA composites, compared to alumina and zirconia monoliths (for details, see ref. [35,39]).

Zirconia monoliths can be prepared from alkoxy precursors however, obtaining mechanically stable zirconia monolithic materials is a challenging task [8]. Zirconium alkoxides have faster hydrolysis rates compared with aluminiun or titanium alkoxides. This is due to larger positive partial charge of the zirconium atom, which enhances nucleophilic attacks on the zirconium atoms [52]. 

Wear properties of alumina, zirconia and alumina/zirconia nano-composite ceramics were investigated with two types of wear apparatus. An end face apparatus was used to measure wear between flat surfaces in distilled water. Results show that wear of alumina is lower than that of zirconia under poor lubrication conditions. According to the observed wear surfaces, adhesion and micro-ploughing are the major wear mechanism for zirconia. The wear rate under concentrated contact pressure was measured with a sphrae on flat apparatus in bovine serum solution. In contrast to the former test, alumina shows higher wear rate than zirconia due to micro-cracking. Wear of alumina/zirconia nano-composite ceramic is lower than alumina and zirconia monolithic ceramics during both tests. In other words, the nano-composite ceramics shows higher wear resistance irrespective of lubrication conditions and contact pressure. It is concluded that the alumina/zirconia nano-composite ceramics have excellent properties for ceramic/ceramic joint prostheses. 

Fig. 4 shows the wear factors of the ceramic plates for sliding with the alumina pins. In contrast to the previous case, excessive wear arises for alumina plate while wear of zirconia is lower than the case of alumina/alumina combination. Wear rates of alumina/zirconia nano-composite ceramics are much lower than those of alumina and zirconia monolithic ceramics. Fig. S shows that wear rate of the alumina pin is highest when sliding with zirconia disc. This figure also shows that the wear of alumina pin is vray low when sliding with alumina/zirconia nano-composite ceramics. 

According to the result of the wear test, alumina/zirconia nano-composite ceramics show lower wear rate than alumina and zirconia monoliths in the wide range of lubrication condition and contact pressure. As hardness and strength of the composite ceramics are higher than the values prediction by the monolithic ceramics, a joint prosthesis of the composite material seems to have longer life and higher reliability than the existing alumina/alumina total hip prostheses. 

This chapter deals with the properties of high-pressure liquid chromatography columns. It is divided into two sections column physics and column chemistry. In the section on column physics, we discuss the properties that influence column performance, such as particle size, column length and column diameter, together with the effect of instrumentation on the quality of a separation. In the section on column chemistry, we examine in depth the surfaces of modern packings, as well as the newer developments such as zirconia-hased packings, hybrid packings or monoliths. We have also included a short section on... 

For instance, dislocations have been shown to play a key role in the accommodation process in YTZP, justifying the threshold stress in YTZP, in contrast with the hypothesis that this threshold stress is due to the electric field created by impurity segregation. However, dislocations are not systematically observed in YTZP furthermore it was shown that in yttria-stabilized tetragonal zirconia single crystals, the stress necessary to activate dislocations at 1400°C was over 400 MPa, one order of magnitude higher than the stresses used during superplastic deformation of YTZP at the same temperature. It will be necessary to conduct a systematic study of the microstructure of the monolithic ceramics such as YTZP before and after deformation and to correlate their relationship with the superplastic features. 

Tonkovich et al. [81] compared the performance ofa commercial ruthenium/zirconia powder catalyst from Degussa with a laboratory-made ruthenium/zirconia catalyst prepared on a nickel foam monolith for the water-gas shift reaction. Methane formation occurred for the powder catalyst, which was much less pronounced for the monolith. The selectivity towards methane could be reduced at shorter residence times. However, the activity of the laboratory-made catalyst was lower, which was partially attributed to the lower catalyst mass (modified residence time). 

Fig. 13.22. The monolithic SOFC concept of Argonne National Laboratory. Anode nickel-yttria-stabilized zirconia. Cathode strontium-doped lanthanum manganite. Interconnect doped lanthanum chromite, a, Interconnection b, electron-ion path c, anode d, electrolyte e, cathode. (Reprinted from K. Kordesch,...

In addition to the initial work in the alumina and mullite matrix systems previously mentioned, SiC whiskers have also been used to reinforce other ceramic matrices such as silicon nitride,9-13 glass,14 15 magnesia-alumina spinel,16 cordierite,17 zirconia,18 alumina/zirconia,18 19 mullite/zirconia,18-21 and boron carbide.22 A summary of the effect of SiC whisker additions on the mechanical properties of various ceramics is given in Table 2.1. As shown, the addition of whiskers increases the fracture toughness of the ceramics in all cases as compared to the same monolithic materials. In many instances, improvements in the flexural strengths were also observed. Also important is the fact that these improvements over the monolithic materials are retained at elevated temperatures in many cases. 

The monoliths are prepared both from organic (mainly based not only on polystyrene, acrylamides, acrylates, or methacrylates but also on imprinted polymers) and inorganic materials (based on sUica, zirconia, titania, or aluminium oxide) as continuous... 

Supported, multilayered (as5onmetric) - dense oxide or metal - porous ceramic membranes alumina, zirconia, titania, carbon - composite ceramic-metal, ceramic-ceramic layers on porous support tube, disk multilayers on porous support plate, disk, tube, monolith... 

A variety of membrane materials has been investigated and reported [1,9] and an overview of commercially available systems has been given by Flsieh [9]. Alumina, zirconia and, more recently, titania membranes are used in large-scale applications. The more complex shapes, i.e. monolith and honeycomb, are almost exclusively based on a-alumina or cordierite. 

Carbosep membranes (Tech-Sep, France) are made of a zirconia layer attached to a porous carbon supporting tube assembled into modules containing up to 252 tubes. The same company produces Kerasep membranes of alumina or titania on a monolithic alumina-titania support containing 7-19 channels. 

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