Ceramic Structures

Some porous ceramic structures of oxides on titanium (CT2O3, RuOj, MnOj, VOJ obtained by baking films of metal complexes like acetylacetonates on titanium surfaces can also be regarded as chemically modified electrodes Applications... 

Scientists from Politecnico di Milano and Ineos Vinyls UK developed a tubular fixed-bed reactor comprising a metallic monolith [30]. The walls were coated with catalytically active material and the monolith pieces were loaded lengthwise. Corning, the world leader in ceramic structured supports, developed metallic supports with straight channels, zig-zag channels, and wall-flow channels. They were produced by extrusion of metal powders, for example, copper, fin, zinc, aluminum, iron, silver, nickel, and mixtures and alloys [31]. An alternative method is extrusion of softened bulk metal feed, for example, aluminum, copper, and their alloys. The metal surface can be covered with carbon, carbides, and alumina, using a CVD technique [32]. For metal monoliths, it is to be expected that the main resistance lies at the interface between reactor wall and monolith. Corning... 

Moser M., 1980, Microstructure of Ceramics, Structure and Properties of Grinding Tods, Akademiai Kiado, Budapest. 

Hnlayson-Dutton. G. Tinkering with Glass and Ceramic Structures, Science. 627 (August 10, 1900). 

Let us concentrate a little longer on ceramics. Here micro-analysis only slowly won ground and the application of solid state physics lagged behind. Very slowly the relationship between the properties of a material and its microstructure was being discovered. Metallurgy had already been characterized by a theoretical approach for some time and consequently metals were about 15 times as important as ceramic materials in 1960 (see Ashby s graph). This was of course influenced by the fact that metals have relatively simple structures which, in their turn, simplify theoretical comtemplations. Ceramic structures are very often complex and are characterized by multiphase systems. However, at present ceramic materials are approached much differently than for instance in 1900. 

Initially, packed beds were also used. They, however, were no success, and at present monoliths are applied exclusively. This should not be misunderstood. Monolith means literally a single stone. However, metal-based analogues are also included in the definition of monolith. In fact, for catalytic converters in cars, in addition to ceramics, metal-based monoliths have been and still are used. A major advantage of metal was the thin wall thickness that could be achieved. Later, industry succeeded in manufacturing ceramic structures of comparable wall thickness. In view of their higher resistance against corrosion, ceramic monoliths are now more generally applied than metal ones. 

The use of proven catalyst recipes would greatly curtail development times, and the absence of extraneous material avoids unwanted catalytic effects and enhances thermal stability. The fixation of catalyst on ceramic substrates such as washcoats is a well-known, reliable, and relatively straightforward procedure. The fabrication of complex small-scale ceramic structures is, however, more awkward than for metals or plastics, and they exhibit relatively poor mechanical strength. Furthermore, the porous ceramic nanostructure must be sealed to prevent contact between the reaction medium and coolant. 

It should be noted that this review concentrates on thermal shock (i.e. a single thermal cycle) and no attempt is made to incorporate and describe the effects of cyclic thermal loading (cyclic thermal shock, thermal shock fatigue, etc.) on the behaviour of CMCs. For information regarding cyclic thermal loading of ceramics and CMCs the reader is advised to consult the extensive review of Case (2002). Additionally, recent studies have shown that laminated ceramic-metal systems (Sherman, 2001) and layered ceramic-structures (Vandeperre etal, 2001) exhibit better resistance to thermal shock compared with monolithic materials. However, such systems are also beyond the scope of this contribution. 

Vandeperre, L.J., Kristofferson, A., Carlstrom, E., Clegg, W.J. (2001), Thermal shock of layered ceramic structures with crack-deflecting interfaces , J. Am. Ceram. Soc., 84( 1), 104-110. 

The hysteresis loop of a ceramic varies according to composition and ceramic structure but is typically of the form shown in Fig. 2.46(b). The coercive field is higher and the remanent polarization is lower than for a single crystal. Changes in both 180° and 90° domain configurations take place during a cycle and are impeded by the defects and internal strains within the crystallites. 

Many different filter designs have been the subject of experimental studies on diesel soot combustion. In the early investigations, structured honeycomb filters made from cordierite, such as those applied for the three-way catalyst for the reduction of spark ignition engine gas emissions, were the focus of the experimental studies [29-39]. The experimental results with these filters were not promising, because the cordierite honeycomb filter did not withstand the thermal stress. Temperature peaks of almost 1200 °C were measured, after which the ceramic structure was partly melted or totally destroyed [29, 40],... 

The ceramizing capacity of polyboroxosiloxane elastomer provides a new P-free intumescent mechanism [57], The combustion of PP-polyboroxosiloxane 3 1 blend filled with 1.25% organo-modified SEP (OSEP, Pangel B40 product of Tolsa Ltd.) and 1.25% melamine borate lead to the formation of white foamed ceramic structure shown in Figure 13.15. 

Muntere and Eurofortn, and a ceramic structured packing, Impulse packing, have also been reported (3,41). 

In spite of its developing state, dynamic fracture must be dealt with in designing ceramic structural components, such as heat engine components, ceramic armor and ceramic cutting tools. Shattering, which is characteristic of a... 

We give a brief description of the general principles of the sol-gel technique, with special emphasis on fiber making via this technique. Essentially the sol-gel route of making any glass or ceramic involves the formation of the appropriate glass or ceramic structure by chemical polymerization of suitable compounds in... 

But even though crystallographers have pulled the ceramic structure apart, can track the path of a current along their chains and planes, and can speculate as to where superconductivity actually takes place, this doesn t yet tell... 

---