Institute of Solid State Chemistry and Mechanochemistry of Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia:

E. G. Avvakumov, Chief Researcher, e-mail: avvakumov@solid.nsc.ru

O. B. Vinokurova, Leading Engineer

Institute of Geology and Mineralogy of Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia:
G. G. Lepezin, Leading Researcher

“KDS-Lipetsk” LLC, Lipetsk, Russia:
D. V. Gorbachev, Chief Technologist

Researches of synthesis, structural and chemical properties of cordierites are being intensively developed with the aim of preparation of materials with predetermined properties on their base. These materials should be distinguished by low thermal expansion coefficients, which will make possible to use them in various areas of technology. Cordierite is usually prepared in industry by sintering of mixtures of talc (3MgO·4SiO₂·H₂O), kaolin (Al₂O₃·2SiO₂·2H₂O) and aluminum oxide Al₂O₃, in the temperature range of 1400–1500 ^oC during 20–60 hours. In this way, synthesized products contain cordierite and 20% of other phases, including spinel, mullite and clinoenstatite, which worsen the performance properties of ceramics. For this reason, new methods are developed for decreasing of energy expenses and improvement of final products' quality. Such methods include a method of mechanical activation of mixtures with subsequent thermal treatment. Application of this method to the considered mixture made it possible to decrease the temperature, increase the cordierite formation rate and reduce the quantity of by-products (undesirable and harmful phases). Talc, kaolin and alumina are not the only materials for obtaining of cordierite. It is also possible to make a cordierite synthesis from mixtures of other minerals. In particular, sillimanite group minerals (andalusite, sillimanite, kyanite) can be used as alumosilicate raw materials for cordierite synthesis. There was found that mechanical activation of mixtures of sillimanite group minerals with talc and silicon additives in periodic and flow grinding-activating devices provides the significant acceleration of their interaction with formation of cordierite at subsequent high-temperature treatment. It is shown that cordierite yield depends on mineral nature: it is considerably higher in mixture with sillimanite, than in mixture with andalusite and kyanite, while the mullitization rate of these minerals has opposite nature. It means that formation of mullite during thermal treatment is not a limiting stage in cordierite synthesis. It is shown that the rate of reaction is determined by the difference in acidbase properties of these minerals, which depend on coordination of aluminum cations by oxygen ions, different for each modification.

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