| dc.description.abstract | ABSTRACT
Spherical barium titanate particles with cubic phase were synthesized by a low-temperature hydrothermal reaction. Firstly, the method of hydrolysis of titanium tetrachloride was used for producing spherical or rhombus TiO2 particles in alcoholic or acidic solution with various concentrations of TiCl4 in the range of 0.05 and 0.2 M. These TiO2 particles were converted to barium titanate particles by a hydrothermal method in a barium hydroxide solution. It was attempted to control the size and morphology of the BaTiO3 particles by the original TiO2 particles.
In alcoholic solution, the size and morphology of the TiO2 particles was greatly influenced by the volume ratios of alcohol/water, temperature, concentration of titanium and surfactant (hydroxyl propyl cellulose, HPC). Using acetone or 1-propanol as the alcohol source, spherical TiO2 particles in the colloid sol with approximately 0.5-1.4 μm in diameter were synthesized at various concentrations of titanium with alcohol/water (RH) ratio of 3 at 70 ℃.These TiO2 particles were in the anatase phase and were converted to the rutile phase when the calcination temperature increased to 700℃ and above. Uniform and spherical barium titanate particles were synthesized from the as-prepared TiO2 particles by using a hydrothermal reaction in a barium hydroxide solution. The Ba/Ti ratios, reaction temperature, and reaction time did not influence the size and morphology of BaTiO3 particles, but increase the concentration of unfavorable salts such as Ba(OH)2 and BaCO3. The high purity BaTiO3 particles could be obtained by washing with formic acid to remove the undesired salts. The size and morphology of the BaTiO3 particles remained the same as those of the TiO2 particles, confirming the in-situ transformation mechanism for the conversion of TiO2 to BaTiO3. The as-synthesized particles were cubic phase and transformed to tetragonal phase after calcinations at 1150 ℃ for 2 h. The mean density of the pellets sintered at 1250℃ for 2 h was 5.86 g/cm3 and accounted for 97.34% of the theoretical density.
In acidic solution, the nanosized TiO2 sol was successfully synthesized by the directly thermal-hydrolysis of TiCl4 solution with various acids. The size and morphology of the TiO2 particles was greatly influenced by the mole ratios of H/Ti, temperature, and concentration of titanium. Nanosized TiO2 powders with rutile phase, which have small particle size, ca.50 nm and narrow particle size distribution, were prepared at 100 ℃ for 24 h by using HCl or HClO4 acid. These nanosized TiO2 particles maintained the rutile phase when the calcination temperature increased to 700 ℃ or above. Nanosized barium titanate particles with cubic phase were synthesized from the as-prepared TiO2 particles by using a hydrothermal reaction in a barium hydroxide solution. The Ba/Ti ratios slightly influenced the particles size but did not influence the morphology and lattice constant of BaTiO3 particles. The reaction temperature and reaction time slightly influenced the lattice constant and did not influence the size and morphology of BaTiO3 particles. The high purity BaTiO3 particles could be obtained by washing with formic acid to remove the undesired salts. The size and morphology of the BaTiO3 particles were different from those of the original TiO2 particles, indicating the dissolution-precipitation reaction mechanism for the conversion of TiO2 to BaTiO3. The as-synthesized BaTiO3 particles were cubic phase and transformed to tetragonal phase after calcinations at 1150℃ for 2 h. The mean density of the pellets sintered at 1250 ℃ for 2 h was 5.92 g/cm3 and accounted for 98.33% of the theoretical density. | en_US |