Study On Hydrothermal Synthesis Of Barium Titanate Powder And Its Properties

Barium titanate (BT) is an important fundamental material of electrical ceramic because of its excellent performance, such as high dielectric constant, good ferroelectric and piezoelectric properties, withstanding voltage and insulation, etc. BT powders are widely used in the manufacture of electronic components such as multilayer ceramic capacitors(MLCC), thermistors, piezoelectric ceramic and a variety of optoelectronic devices. Increasing requirement of MLCC with the fast development of 3C (Computer, Communication, Consumer Electronics) industry promotes the market demand of BT powders. Meanwhile, with the recent tendency of MLCC industry to miniaturization and high capacitance, reducing the thickness of each layer and increasing the number of layers are necessary. The key challenge is that the BT powders are supposed to have high purity, a narrow particle size distribution and superfine particle size.The main preparation of BT powders are introduced in the paper. The hydrothermal method is chosen upon the compare of various techniques. Then, the effects of reaction temperature, reactant concentration, reactant Ba/Ti, reaction time and different sources of titanium, three kinds of surfactant (sodium dodecyl benzene sulphonate, SDBS; dodecyl trimethyl ammonium chloride, DTAC; polyethylene glycol 2000, PEG) and two organic solvents (ethanol and isopropanol) are studied on the BT powders'nature in hydrothermal synthesis process. The powders'morphology, phase composition, particle size, the specific surface area, the Ba/Ti of powder and its ceramic properties have been measured using transmission electron microscopy (TEM), laser particle size analyzer, the specific surface area measurement instrument, the X-ray diffraction (XRD), and X-ray Fluorescence Spectrometer (XRF). The research results are as followed:The effects of reaction temperature, reactant concentration, reactant Ba/Ti, reaction time and different sources of titanium to powders'properties are investigated. With increased reaction temperatures, the growth rate of BT crystal is improved and the particle size increases. With increasing reactant concentration and reactant Ba/Ti, smaller particles would be synthesized because of faster nucleation rate brought on by higher supersaturation. With prolonged reaction time, particle size would be larger due to more sufficient growth of crystal. More BaCO3 will form if the original Ba/Ti of the powder is too low. Furthermore, grey correlation analysis on the effect of the above-mentioned reaction conditions to particle size is done using the software programmed by Visual Basic and Matlab. The result shows the order of these factors: reaction temperature > reactant Ba/Ti> reactant concentration > reaction time. Besides, it's considered that TiCl4 is more suitable as the source of titanium than nano-TiO2.For restraining the influence of coalescence and aggregation to particle size, particle size distribution and morphology and improving dispersibility, the effect and acting mechanism of different additives to BT powders'properties are studied. The results are as followed: The addition of SDBS will increase the specific surface area and decrease the mean particle size of BT powder. But when the addition is too much, it leads to the formation of BaSO4. DTAC and PEG have little influence on the particle size. When these surfactants are added properly, they will improve the dispersity of the BT powder obviously. Isopropanol and ethanol can give much better influence than surfactants to decrease the average particle size and to get better dispersity. When the concentration of additive is 25%, particle size is 50 nm, the BT powder shows the best dispersity. The range of particle size distribution (d90-d10) is only 100nm. When Increasing temperature to 240℃, the mean particle size becomes 84nm, but d90 and d10 are smaller, and AF(50) is only equal to 1, which means that the aggregation is almost neglectable.The proper sintering temperature of BT powders by hydrothermal synthesis is at about 1250℃and the dielectric constant of all BT ceramics can achieve the maximum. These powders with the molar ratio of barium to titanium approaching to 1 have higher dielectric constant. Doping of Nb2O5 and Nd2O3 will strongly influence the dielectric constant and dielectric loss of BT ceramics. When the content of Nb2O5 and Nd2O3 are 0.3mol% and 0.1mol% respectively, the dielectric constant and dielectric lose all be up to maximum.