Cordierites

5 Crystal field spectra of transition metal ions 

Mineral Site or symmetry absorption bands (cm-1) A (cm-1) CFSE (cm-1) Sources of data 

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Corbel Corcat Cordarone Corderoite [53237-82-4] Cordials Cordierite... 

Corning 9606 cordierite, 2 MgO-2 A12 03-5 Si02 spinel, Mg0Al203 MgO-stuffed P-quart2 quart2, Si02 low expansion, high transparency to radar missile radomes... 

Oo, and Sr ferrites mixed sulfides such as Zn—OdS and Pb—OdS and coated particles such as Ee O with Al(OH)2 or Or(OH)2. OontroUed hydrolysis of alkoxides has also been used to produce submicrometer Ti02, doped Ti02, Zr02, doped Zr02, doped Si02, SrTiO, and even cordierite powders (1,3). 

Ceramics. In ceramics, talc is widely used in wall tile and hobbyware bodies, in electrical porcelains, and in cordierite formulations. Wall tile and hobbyware ate talc—clay bodies that ate pressed and fast-fired to a high porosity (bisque) and then glazed and tefired to produce the final product. Talc containing tremolite and carbonate is preferred to ensure good porosity. 

Cordierite [12182-53-5] Mg Al Si O g, is a ceramic made from talc (25%), kaolin (65%), and Al O (10%). It has the lowest thermal expansion coefficient of any commercial ceramic and thus tremendous thermal shock resistance. It has traditionally been used for kiln furniture and mote recently for automotive exhaust catalyst substrates. In the latter, the cordierite taw materials ate mixed as a wet paste, extmded into the honeycomb shape, then dried and fired. The finished part is coated with transition-metal catalysts in a separate process. 

K. Pattas and co-workers, Cordierite Filter Durability with Cerium Fuel Additive 100,000 km of Revenue Service in Athens, SAE Technical Paper 920363, Society of Automotive Engineers, Warrendale, Pa., 1992 U.S. Pat. 4,522,631 (June 11, 1985), A. M. Mourao and C. H. Falst. 

Idiochromatic examples of this are black magnetite [1309-38-2] Fe O otherwise written as Fe(II)0 Fe2(111)02 and the analogous red Mn O and the pigments Pmssian blue [14038-43-8] and Turnbull s blue [25869-98-17, both Fe4(III)[Fe(II)(CN)2]2. Allochromatic examples are widespread in the mineral field, with Fe + + Fe + being involved in blue and green tourmaline [1317-93-7] blue iolite (cordierite) [12182-53-5] etc. 

Cera.mic, The ceramic substrate is made from a mixture of siUcon dioxide, talc, and kaolin to make the compound cordierite [12182-53-5]. Cordierite possesses a very low coefficient of thermal expansion and is thermal-shock resistant. The manufacturing process involves extmding the starting mixture (which is mixed with water and kneaded into a sort of dough) through a complex die to form the honeycomb stmcture. The extmded piece is dried and fired in a kiln to form the cordierite. The outside or circumferential dimension is formed by the die, and the length is cut later with a ceramic saw. 

A ceramic monolith catalyst support, cordierite, consisting of silica, alumina and magnesium oxide. The purpose of this is to provide support, strength and stability over a wide temperature range. 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

While the discovery of the catalytic properties of zeolites was driven by the desire to improve industrial prcKessing, the development of emission control catalysts was necessitated by governmental fiat. The first requirement was for 90+% removal of CO and of hydrocarbons, a goal which could not be met by oxidation with base metal oxides. To achieve the required spedfications during automobile operations, it was necessary to develop supported platinum catalysts. Originally the support was alumina in pellet form. Later platinum on cordierite was used in honeycomb form, containing 200-400 square channels per square inch. 

Two ways to reduce the diffusion length in TBRs are 1) use of smaller catalyst particles, or 2) use of an egg-shell catalyst. The first remedy, however, will increase pressure drop until it becomes unacceptable, and the second reduces the catalyst load in the reaction zone, making the loads of the TBR and the MR comparable. For instance, the volumetric catalyst load for a bed of 1 mm spherical particles with a 0.1 mm thick layer of active material is 0.27. The corresponding load for a monolithic catalyst made from a commercial cordierite structure (square cells, 400 cpsi, wall thickness 0.15 mm), also with a 0.1 mm thick layer of active material, is 0.25. 

Table 9.1. Preparation of V205/W03—Si02— Ti02 SCR catalysts coated on metal and cordierite substrates...

Kleemann, M. (1999) Beschichtung von Cordierit-Wabenkorpern fur die Selektive Katalytis-che Reduktion von Stickoxiden, Ph.D. Thesis No. 13401, ETH Zurich. 

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