Kinetics and mechanism of the formation of hollandites in the BaO(Cs2O)-Al2O3-TiO2 system from initial mixtures prepared by different methods

Abstract

The mechanism and kinetics of formation of solid solutions based on hollandite in the BaO(Cs 2 O)-Al 2 O 3 -TiO 2 system are investigated using the initial mixtures prepared by two methods: (i) mechanical grinding and mixing of the initial components and (ii) coprecipitation from aqueous solutions of the salts. It is established that the mechanism of formation of hollandite in the system under investigation depends on the degree of dispersion of the initial mixtures used in the synthesis. When the synthesis is performed with the initial mixture prepared by mechanical grinding and mixing of the initial reactants (the particle size is equal to 50-300 nm), hollandite is formed at temperatures in the range 1100-1250 ° C in the presence of the accompanying phase Cs 2 Al 2 Ti 2 O 8 . When the synthesis is performed with the initial mixture prepared by coprecipitation from aqueous solutions of salts (the particle size is equal to 10-12 nm), hollandite is formed at temperatures in the range 850-1050 ° C. The investigation into the kinetics of formation of the hollandite phase from the above mixtures made it possible to determine the temperature-time conditions for the synthesis of this titanate in the form of a powder with a particle size of approximately 50 nm or in the form of a dense ceramic material with a particle size of ~200 nm.