Mechanical activation of the synthesis reaction of BaTiO3 from a mixture of BaCO3 and TiO2 powders

The influence of long term milling in an attritor of a mixture of BaCO3 and TiO2 powders on the reaction synthesis of BaTiO3 was studied. Thermal analysis (TG and DTA) of the unmilled and milled powders and X-ray diffraction of powders calcined at different temperatures were undertaken. Milling does not change the reaction sequence between BaCO3 and TiO2. BaTiO3 and Ba2TiO3 are produced in both kinds of powders. However, milling reduces the formation temperature and accelerates the formation rate of these two phases. The production of final BaTiO3 is incomplete in the milled powder, probably because of the formation of big crystals of Ba2TiO4. As a consequence, the milled powder contains large amounts of Ba2TiO4 after calcination at 1200 degrees C. Milling produces allotropic transformations in TiO2 from anatase phase, to alpha-PbO2-like phase and finally to rutile structure. (C) 2000 Elsevier Science Ltd and Techna S.r.l. All rights reserved.