Study On The Preparation Of Titanate Powder Materials

BaTiO3, BaTi2O5, Bai-xSrxTiO3and ZnTiO3are all very important electronic ceramics. Each material has its own outstanding properties which cannot be simply substituted by other materials. All these materials are widely used in many kinds of electronic components. With the rapid development of electronic industry, high performances of these ceramic materials are required by people. Thus, much attention has been focused on the preparation of high purity, high uniformity and good dispersion of nanopowders. The traditional preparation methods cannot meet these requirements. Therefore, the thesis’work is focused on this topic, to find new ways to prepare these materials, to investigate every important factor influencing on the preparation of these materials and uncover the corresponding reaction mechanisms.First of all, on the basis of conditions preparing cubic BaTiO3at different Ti sources, different Ba sources, different mineralizers and different ratios of Ba/Ti, the conditions of low temperature preparation of tetragonal BaTiO3were investigated by means of different ways, such as multiple replacement of mother solution (MRMS), traditional hydrothermal synthesis (THS) and single replacement of mother solution (SRMS). The results show that enough crystallization time of MRMS has little influence on preparing tetragonal BaTiO3. With increasing the times of replacing mother solution, the amount of BaTiO3sample increases, too, but no apparent tetragonal BaTiO3can be found. Under some conditions, tetragonal BaTiO3can be successfully prepared by both THS and SRMS. At the same conditions, the similar crystallinity of tetragonal BaTiO3can be obtained by both SRMS for2-4days and THS for7days, respectively. When the crystallization time is fixed at7days, tetragonal BaTiO3can be obtained by both THS using4.0mol/L NaOH solution and SRMS only using0.5mol/L NaOH solution, respectively. The crystal size of tetragonal BaTiO3prepared by SRMS is not only small but also much even. In addition, the available cubic BaTiO3prepared by stearic acid gel (SAG) can be transformed into tetragonal BaTiO3by SRMS. As a result, SRMS has more outstanding advantages to prepare tetragonal BaTiO3than other methods.Then, thermal decomposition of SAG was employed to study the phase evolution of BaTiO3nanopowders. Some compulsory measures, such as continuous flow of air atmosphere, substantially shorting calcination time and quenching the obtained sample in air atmosphere, were employed to uncover the formation procedure of BaTiO3prepared by SAG. The intermediate phase of BaTi2O5was obtained directly and investigated. The influences of different atmosphere on the crystal phases of product obtained by thermal decomposition of SAG were studied to uncover the reaction mechanism of BaTiO3prepared by SAG which is as follows:(a) The intermediate phases of BaTi2O5and BaCO3are generated at first by calcining Ba-Ti gel at high temperature.(b) The solid state reaction between the intermediate phases of BaTi2O5and BaCO3cannot take place directly.(c) BaO and CO2are generated by the reversible reaction of BaCO3, and then the reaction between BaO and BaTi2O5takes place to generate BaTiO3.The phases of BaCO3, BaTiO3and BaTi2O5generated by calcining Ba-Ti gel in air atmosphere may affect each other and result in the low growth rate of BaTiO3crystallites.25-50nm BaTiO3crystallites were finally obtained at the calcination temperature700℃.In addition, the calcination methods have significant influence on preparing BaTiO3nanopowders by SAG. High purity BaTiO3nanopowders by SAG can be obtained at about550℃which is250℃lower than that of preparing BaTiO3by acetic acid gel method.Finally, on the basis of detail investigation of the phase evolution of BaTiO3prepared by SAG and its some important influence factors, Ba0.5Sr0.5TiO3, ZnTiO3and BaTi2O5were successfully synthesized by SAG. Using stearic acid as a solvent, high purity Ba0.5Sr0.5TiO3and ZnTiO3can be synthesized at substantially low temperature of550℃and600℃, respectively. The average crystalline size of Ba0.5Sr0.5TiO3synthesized at600℃is about50-80nm and almost ellipse in shape with a slight agglomeration. The average crystalline size of ZnTiO3synthesized at600℃is about20-50nm, and ZnTiO3crystallites aggregate to form large particles. BaTi2O5powders can be synthesized by SAG in a wide range of temperature (600-1100℃). Because of low calcination temperature and short calcination time, the as-prepared BaTi2O5is accompanied by some other generated phases of BaTiO3, BaCO3and TiO2. With increasing the calcination temperature, the diffraction peaks of other generated phases become weak quickly. The average crystalline size of BaTi2O5synthesized at900℃is about200nm and almost irregular in shape without serious agglomeration. The results show that Ba0.5Sr0.5TiO3, ZnTiO3and BaTi2O5can be synthesized conveniently by SAG method.