Studies On Dispersibility And Mechanism Of Ultrafine BaTiO₃ Fine Used In Functional Ceramics

Barium titanate (BaTiO₃) is one of the most important materials in electronics because of unique perovskite structure. It is extensively used in multilayer ceramics capacitors (MLCCs), grain boundary barrier layer capacitors, positive temperature coeffection resistivity (PTCR), gas sensors, actuators and other electronic devices. The miniaturization trend of electronic elements makes progress of research and development of functional ceramic materials on nanometer level. It is necessary to study the nucleation and growth mechanism of barium titanate for controling its particle size, distribution and agglomeration. Agglomeration problems of ultrafine particles are universal in wet chemical methods, which have bad influence on its fine property, thus it is important to study the dispersion of barium titanate by direct precipitation method.The nucleation and growth mechanism of barium titanate by direct precipitation method were discussed. It was thought that barium titanate was obtained by absorption or co-precipitation, diffusion and exchange. System acidity and a certain energy field (radiant heat, ultrasonic field or microwave field) are essential conditions for the formation of barium titanate prepared by direct precipitation. Hydrolysis of TiCl4 almost controlled the whole reaction nucleation, which followed homogeneous nucleation mechanism and induced formation of Ba(OH)₂ crystal nucleus. There were two possible growth mechanism. Several possible mechanism models for barium titanate by direct precipitation weres proposed.Based on the nucleation, growth and formation mechanism, surfactants were studied to search for the rule of BaTiO₃ powders prepared by the direct precipitation method, which had good absorption and dispersion effect. The microstructure of BaTiO₃ nanocrystals was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), BET, fourier transform infrared spectroscopy (FT-IR) and sedimentograph. Influence of surfactants (different surfactants, concentration, adding time and applying methods) on aggregated particle size and dispersion of barium titanate were studied. The results indicated that different surfactants with proper concentration could reduced the agglomeration and improve the dispersibility of BaTiO₃ powders in some degree. Comparatively speaking, with 0.5wt% APG2065 adding into TiCl4 solution before reaction, uniform and superfine BaTiO₃ nanopowders could be obtained, which could improve the dispersibility of BaTiO₃ powders and prevent the formation of hard agglomerates.Ultrasonication was added into the precipitation of BaTiO₃ powders, for its cavitation effect could improve the physical properties of BaTiO₃. Influence of ultrasonication (ultrasonic frequency, power, time temperature and water bath time) on aggregated particle size and dispersion of barium titanate were studied. The results indicated that ultrasonication with proper conditions could decrease the particle size, distribution and improve the dispersibility of BaTiO₃ powders. The comparatively most optimizatic ultrasonic route of synthesizing the nanometer powders of BaTiO₃ was ultrasonic frequency 45kHz, ultrasonic power 100W, ultrasonic temperature 60℃, ultrasonic time 1h, and water bath time 2h. BaTiO₃ with low particle size and good dispersibility could be obtained under these conditions.