Phase composition of sintered lime refractories with TiO2 additions
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A study of mixtures of CaO and TiO2 fired at 1770 K with various heating rates confirmed the presence of three binary compounds in the system CaO-TiO2: CaTiO3, Ca3Ti2O7, and Ca4Ti3O10.
Mixtures of CaO and TiO2 of the same composition but fired at different rates develop calcium titanates that are stoichiometrically different: with a heating rate of 50 K/h Ca3TiO7 and Ca4Ti3O10 are formed; and at 300 K/h — -mainly calcium monotitanate CaTiO3, with a small amount of Ca3Ti2O7.
The features of the crystallochemical structure of calcium titanate indicating that the structure of Ca3Ti2O7 and Ca4Ti3O10 can be perceived as alternating layers of CaTiO3 and CaO mean that we can assume that the first crystal phase developing in the solid-phase sintering in mixtures CaO-TiO2 is CaTiO3. Subsequently, during slow heating gradual ordering of the structure of calcium titanates occurs, leading to the formation of equilibrium with a high concentration of CaO (> 88%) in the association of Ca3Ti2O7 and Ca4Ti3O10.
With increase in the CaO content in calcium titanate there should be an increase in the resistance of lime refractories to atmospheric hydrolysis. The sintering schedule of lime refractories and especially lime clinker should therefore ensure the formation of titanates and solid solutions most highly enriched with CaO.
KeywordsCalcium TiO2 Hydrolysis Solid Solution Titanate
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