Exhaust ceramic materials

Available results on the preparation, characterization, and utilization of metallic and catalytic particles (Sect. 3), semiconductor particles and particulate films (Sect. 4), conductors and superconductors (Sect. 5), magnetism and magnetic particles and particulate films (Sect. 6), and advanced ceramic materials (Sect. 7) will constitute the main body of the monograph. An attempt will be made to cover these materials exhaustively. 

The particle injection studies also indicated that lead sulfate alone was more harmful than lead oxide or lead chloride, suggesting that in the absence of catalytic activity on carbon combustion, higher melting compounds are more harmful than materials of lower melting point. Flakes of iron oxide from a corroded exhaust valve and bits of ceramic material from a broken spark plug insulator are very potent sources of surface ignition... 

This equation indicates that electrons are withdrawn from the material and oxygen ions are formed as the partial pressure of the surrounding oxygen increases. A reduction in the number of electrons results in a decrease in conductivity. Because the outside air and the exhaust fumes have different P(02) values there are different amounts of electrons per volume unit present in the parts of the ceramic material which are adjacent to these gases and that causes the difference in voltage. 

X HE USE OF CHEMICAL APPROACHES to improve the processing, properties, and performance of advanced ceramic materials is a rapidly growing area of research and development. One approach involves the preparation of organometallic polymer precursors and their controlled pyrolysis to ceramic materials. This chapter will review the preparation and application of silicon-, carbon-, and nitrogen-containing polymer systems. However, the discussion is not exhaustive the focus is on systems with historical significance or that demonstrate key technological advances. 

This is by no means an exhaustive review of all ceramic materials deposited by CVD. The materials discussed were chosen to illustrate the chemistry of CVD, and articles and reviews that indicate the current direction of research are presented. 

Miura, N. et al., Zirconia-based gas sensors using oxide sensing electrode for monitoring NOj in car exhaust, Proc. of 29th Int. Conf. Adv. Ceram. Comp., Advances in Ceramic Materials, American Ceramic Society, 26 (2005) 3-13. 

Supported metal clusters play an important role in nanoscience and nanotechnology for a variety of reasons [1-6]. Yet, the most immediate applications are related to catalysis. The heterogeneous catalyst, installed in automobiles to reduce the amount of harmful car exhaust, is quite typical it consists of a monolithic backbone covered internally with a porous ceramic material like alumina. Small particles of noble metals such as palladium, platinum, and rhodium are deposited on the surface of the ceramic. Other pertinent examples are transition metal clusters and atomic species in zeolites which may react even with such inert compounds as saturated hydrocarbons activating their catalytic transformations [7-9]. Dehydrogenation of alkanes to the alkenes is an important initial step in the transformation of ethane or propane to aromatics [8-11]. This conversion via nonoxidative routes augments the type of feedstocks available for the synthesis of these valuable products. 

Catalytic Combustor - The catalytic combustor section is shown in Figure 6. At full load conditions, the temperature in the catalytic section is increased from inlet 1208 K to the exhaust 1623 K. Therefore, structural components in the hot section are made of ceramic materials. The catalytic combustor includes the following components ... 

Typical ceramic materials produced on a co-rotating twin screw extruder are for example catalyst carriers. They are commonly shaped into granules for use as bulk material in reactors in the chemical industry or into honeycombs for catalytic converters in automobiles exhaust systems (Fig. 12). After extrusion, the catalyst carriers are cut oversized in the lineal direction, dried and then cut to the proper length. Afterwards the binder is removed and the carriers are calcinated or sintered. Finally, to provide them with catalytic properties, they are impregnated with an active film in a bath [Fri76]. 

Heterogeneous catalysis has a role in the atmospheric chemistry of ozone in the troposphere as well. Catalytic converters in automobiles are filled with a porous ceramic material, which provides a surface that catalyzes the removal of CO and NO (nitrogen oxides) ftom the exhaust. (Nitrogen oxides initiate the formation of ozone and other lung irritants in photochemical smog. We will examine this process in detail in Section 11.8.) The process by which catalytic converters operate is shown in Figure 11.14. The types of steps shown there are found in most examples of heterogeneous catalysis. 

Since exhaust gas temperature changes rapidly during engine operation, ceramic honeycomb substrates must have thermal shock resistance. Thermal shock resistance of ceramic honeycombs is determined by electric furnace or gas burner testing. Thermal shock resistance of ceramic material is generally represented by the following equation [8]. As the coefficient of thermal expansion of extruded cordierite is extremely low, high thermal shock resistance is expected. 

Nishibori M, Shin W, Tajima K, Houlet LF, Izu N, Itoh T, Matsubara I (2008) Long-term stability of Pt/alumina catalyst combustors for micro-gas sensor application. J Eur Ceram Soc 28 2183-2190 Nowotny J (1988) Surface segregation of defects in oxide ceramic materials. Solid State Ion 28-30 1235-1243 Oudet F, Vejux A, Courtine P (1989) Evolution during thermal treatment of pure and lanthanum-doped Pt/Al O, and Pt-Rh/AljO, automotive exhaust catalysts transmission electron microscopy studies on model samples. Appl Catal 50 79-86... 

Assume that in a certain automobile the exhaust gas has a carbon monoxide mole fraction of 0.0140 and a temperature of 500 K when it reaches the catalytic converter, which contains a solid platinum catalyst coated on a ceramic material with a large surface area. Calculate the number of carbon monoxide molecules and the amount of carbon monoxide in moles that strikes 50.00 m of catalyst surface in 1.000 minute. 

It would be a misstatement to claim that this title provides an exhaustiveness coverage of the world of ceramic materials, if only because this subject covers such a wide area that only one book would not be able to do it justice - even if it is supplemented by a book dedicated to ceramic composites and by several volumes devoted to the cousins of ceramics, namely glasses, cements and concretes, and geomaterials. However, we believe that this problem can also be an advantage, because it resulted in the production of a concise woik that provides the essence of the subject. In fact, initially this book was written for non-ceramists - students and engineers - interested in an introduction to the knowledge of this vast family of materials, in other words, for readers whose interests are not limited only to ceramics but for those who are aware that ceramics can act as a support (often) or as a rival (sometimes) to other materials. 

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