Role of acid-base interactions in synthesis of cordierite from talc and sillimanite group minerals

It has been found that the mechanical activation of mixtures of sillimanite group minerals with talc and silica additives in grinding-activating devices with periodic and flow action provides significant acceleration of their interaction with formation of cordierite at the subsequent high-temperature treatment. It is shown that the output of cordierite depends on nature of mineral: in mixture with a sillimanite it is considerably higher, than with an andalusite and kyanite, while the rate of mullitization of these minerals has opposite character. It means that the formation of mullite during heat treatment is not a limiting step in synthesis of cordierite. It is shown that the rate of reaction is determined by the difference in the acid-base properties of these minerals, which depend on the coordination of aluminum cations by oxygen ions, different for each of the modifications

Chemistry for Sustainable Development 20 (2012) 297301 Effect of Mechanical Activation on the Kinetics of Kyanite Mullitization

Abstract The kinetics of mullitization of kyanite samples, both initial and mechanically activated in high-energy grinding devices within temperature range 12731573 K was investigated. It was shown that the kinetics of kyanite mullitization formally corresponds to the equation of monomolecular decomposition. The activation energy of this transformation is (630±10) kJ/mol. It was established that mechanical activation of kyanite accelerates mullitization processes during subsequent thermal treatment. The yield of mullite per unit surface area is almost two times higher for mechanically activated sample than for non-activated one. Possible mechanism of mullitization process and technological aspects of the implementation of this process in industry are discussed