Of cordierite

The object was an auto exhaust catalyst, a monolith cylinder 25 mm in length and 38 mm in diameter. The outside wall was broken away so that one of the 1 ram-wide channels became accessible to the IR and probe laser beams, and a portion of one channel was studied in the manner shown schematically in the insert of Fig. 8. The sample was examined in air, because a cell large enough to contain the monolith was not available. The spectrum shows the features of cordierite [20], the material from which honeycomb monoliths are usually made, a broad absorption in... 

Hensen B. J. and Green D. H. (1973). Experimental study of the stability of cordierite and garnet in pelitic compositions at high pressures and temperatures. Contrib. Mineral Petrol, 38 151-166. 

DPFs are important aftertreatment devices, enabling significant reduction in the emissions of PM. Typically, the filters are made of cordierite or silicon carbide materials, and can be either coated with a catalyst or left uncoated. The exhaust stream is forced to flow from one channel of the filter to an adjacent channel (see Fig. 37) the PM is filtered out by the wall of the filter. 

The Crystal Structures of Cordierite and Indialite [Mg2Al3(AlSis0i8) H20]... 

Farrell, E. F. Newnham, R. E. (1967) Electronic and vibrational absorption spectra of cordierite. Amer. Mineral., 52, 380-8. 

For three-way catalysts in converters for Otto engines Pt/Rh supported on La-stabilized alumina are used. Promoters are present e.g., Ce02. The alumina is usually situated as a washcoat layer in a monolith (typically with a cell density of 400 cells/in2) consisting of cordierite. In practice, the catalysts appear to be very stable. In fact, the durability of the electronic control system (for the regulation of the X value in the converter) is more critical than the catalyst itself. 

In industry, cordierite is usually obtained by calcination of the mixtures containing talc, kaolinite and silica at 1300-1450°C for 20-60 h. The product contains the impurity phases spinel, mullite, clinoenstatite, etc., that worsen the exploitation characteristics of cordierite. Since the mentioned minerals contain structural water, chemical interaction between them during mechanical activation can be considered from the viewpoint of soft mechanochemical synthesis. Mechanical activation of this mixture does simplifies the interaction between its components. It is sufficient to heat this mixture for 2 h at a temperature of 1260°C to obtain practically homogeneous cordierite without impurity phases (Fig. 7.2) [2-9]. 

Prokofyev V.Yu., Kunin A.V., Ilyin A.P. et al. Application of mechanochemical methods to the synthesis of cordierite catalyts supports. Zhurn. Prikl. Khimii 1997 79 1655-60. 

Filio J.M., Sugiyama K., Kassi N. et. al. Effect of dry mixed grinding of talk, kaolinite and gibbsite on preparation of cordierite ceramics, J. Chem. Ing. Japan 1994 26 565-69. 

Avvakumov EG., Devyatkina E.T., Kosova N.V. et al. Novel mechanochemical method of the preparation of cordierite and support based on it. Kinetika i Kataliz 1998 39 722-25. 

FIGURE 13.2 Scaiming electron micrographs of fractnre snrfaces of cordierite composition gels sintered at 1300°C for 2 h (a) nanocomposite and (b) homogeneons (single phase). (Reprinted with permission from Kazakos, A.M., Komameni, S., and Roy, R., J. Mater. Res., 5, 1095, 1990.)... 

Figure 7 Average CTE values of cordierite crystallite along its three axes (25-800 C).

The importance of transparent glass-ceramics doped by Cr as potential new materials for luminescent solar concentrators and tunable lasers is considerable It has been shown that Cr(III) exhibits exceptionally high quantum efficiency of luminescence in these materials as compared to glasses of the same compositions . Cr is also used as a probe for nucleation of and crystallization of cordierite into glass-ceramics . ... 

Cordierite, 2 MgO. 2 AI2O3. 5 Si02, is a compound with an extraordinarily low expansion coefficient. The content of this phase is responsible for thermal expansion of cordierite ceramics and for its resistance to thermal shocks. Linear thermal expansion coefficient of about 15 x 10 (20-300 °C) is attainable. However, difficulties are again encountered on firing, because of the large amounts of melt formed at the liquidus temperature. A difference of only several degrees may have the result that a small fired object contains both porous (insufficiently fired) as well as fused (excessively fired) zones. 

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