Chen-Feng Kao

Preparation of barium strontium titanate powder from citrate precursor

TiCl 4 or titanium isopropoxide reacted with citric acid to form a titanyl citrate precipitate. Barium strontium citrate solutions were then added to the titanyl citrate reaction to form gels. These gels were dried and calcined to (Ba,Sr)-TiO 3 powders. The gels and powders were characterized by DSC/TGA, IR, SEM and XRD analyses. These results showed that, at 500 °C, the gels decomposed to Ba,Sr carbonate and TiO 2 , followed by the formation of (Ba,Sr)-TiO 3 . The onset of perovskite formation occurred at 600 °C, and was nearly complete at 1000 °C. Traces of SrCO 3 were still present. The cation ratios of the titanate powder prepared in the pH range 5-6 were closest to the original stoichiometry. Only 0.1 mol% of the free cations remained in solution. The titanyl citrates were precipitated in either ethanol or acetone. The acetone-derived precipitates were always viscous, but those with a sufficient quantity of alcohol were powdery. The specific surface areas of the ceramic powders obtained by air-, vacuum- and freeze-drying methods were 8.3 × 10 3 , 10.2 × 10 3 and 12.5 × 10 3 m 2 kg -1 , respectively. The powder obtained by freeze-drying had the lowest degree of agglomeration. The precipitated powders of titanyl citrate which were freeze-dried and calcined at 1100°C were compacted and sintered at 1300 °C to obtain dense ceramic bodies with 95% of the theoretical density.

Preparation and electrical characterisation of strontium titanate ceramic from titanyl acylate precursor in strong alkaline solution

Abstract Strontium titanate powder can be obtained from titanyl acylate precursor by using acetic acid chelating with titanium isopropoxide in a strong alkaline solution (pH > 13) at room temperature. Infrared spectroscopy, differential scanning calorimetry/thermogravimetric analysis and X-ray diffraction were used to investigate the effects of the size and properties of the precipitated precursor on the properties of the powder and the sinterability for ceramics. It was found that the strontium ion diffused into the gel made by the hydrolysis of the titanyl acylate precursor to form strontium titanate powder. The reaction rate of forming powder at higher temperature such as 100 °C and higher water content (the ratio of water to titanium alkoxide is 20) or higher acetic acid (the ratio of acetic acid to titanium alkoxide is 10), is rapid and the particle size is less than 0.1 μm. Without adding any reagent the density of the sintered strontium titanate at 1300 °C from powder after freeze drying was over 95% of its theoretical density. The dielectric constant and dissipation factor of the strontium titanate body sintered at 1250, 1300, 1400 and 1450 °C, were also determined at a frequency of 1 kHz to 10 MHz at constant temperature.

Preparation and electrical properties of fine strontium titanate powder from titanium alkoxide in a strong alkaline solution

Abstract The particle size of the forming ceramic powder is related to the morphology of forming precipitated precursor. The rates of hydrolysis and condensation of titanyl acylate gel were slow because of the chelating action of acetic acid. Therefore, the particle size of the precursor gel was uniform and finer, and the formation rate of the powder was quicker. The powder obtained contained fine particles of size ∼ 0.04–0.05 μm and was readily sintered at 1423–1523 K. The dielectric constant and dissipation factor of strontium titanate were determined.

Preparation and electrical properties of barium titanate film by hydrothermal method

Abstract High concentration of the reactant is helpful to the uniformity of the grain, high reaction temperature is useful to the formation of the grain and longer reaction time affects the grain size clearly. The higher concentration of the reactant barium ion and the higher the pH value (0·25 N-pH 11·6→4 N-pH 13·8) and added hydroxide ion to increase the alkalinity make the uniformity of the grain very clearly. The bigger and more uniform of grain makes its dielectric constant larger. But the non-uniform grain having bigger size cannot increase its dielectric constant.

Liquid–liquid equilibria of alkane (C10–C14)+octylbenzene+sulfolane

Equilibrium tie line data have been determined at (323.15, 348.15, and 373.15) K for the ternary liquid–liquid equilibria (LLE) of three alkane + sec-butylbenzene + sulfolane systems, where the alkanes studied are decane, dodecane, and tetradecane. The relative mutual solubility of sec-butylbenzene is higher in decane + sulfolane than in dodecane + sulfolane or tetradecane + sulfolane mixtures. The tie line data were correlated with the UNIQUAC and NRTL models. The calculated values based on the UNIQUAC model were found to be better than those based on the NRTL model; the average root-mean-square deviation between the phase composition obtained from experiment and that from calculation was 0.00385 for UNIQUAC compared to 0.00566 for NRTL. The values of selectivity and distribution coefficients were derived from the equilibrium data.

Preparation and characterization of lanthanum nickel oxides by combined coprecipitation and molten salt reactions

This study deals with the preparation of the lanthanum nickel oxides by combined precipitation and molten salt reactions. The reagents such as LaCl3, NiCl2 and different alkali metal hydroxides were used to get the precursors in various compositions. They were reacted at 1073–1173 K to obtain the fine lanthanum nickel oxides (La2NiO4, LaNiO3) with a uniform particle size about 0.1 μm. LaNiO3 is unstable at high temperature and converted into La2NiO4. The powders coprecipitated with potassium hydroxide have good sinterability leading to less in electrical resistivity than those with sodium hydroxide or lithium hydroxide. These compounds with different compositions exhibit characteristics of Pauli paramagnetic materials. In correspondence with the change of phase ratios there are also changes in the mass susceptibility from 4.0×10−6 emu/(g-Gauss) for LaNiO3 to 1.25×10−6 emu/ (g-Gauss) for La2NiO4.

Liquid–liquid equilibria of alkane (C10/C12/C14)+1,4-diisopropylbenzene+sulfolane at 323.15, 348.15 and 373.15 K

Abstract Tie line data have been determined at 323.15, 348.15 and 373.15 K for the ternary liquid–liquid equilibria (LLE) of alkane (C10/C12/C14)+1,4-diisopropylbenzene+sulfolane systems. The addition of 1,4-diisopropylbenzene to sulfolane is found to increase the solubility of alkanes in the order of n-decane>n-dodecane>n-tetradecane and the relative mutual solubility of 1,4-diisopropylbenzene is higher in n-decane+sulfolane than in n-dodecane+sulfolane or n-tetradecane+sulfolane mixtures. The tie line data were correlated with the well-known UNIQUAC and NRTL models. The calculated equilibrium mole fractions based on the UNIQUAC model are better than those based on the NRTL model. The values of selectivity and distribution coefficient were derived from the equilibrium data.

Preparation and dielectric properties of semiconducting lanthanum-doped strontium titanate ceramics from titanyl citrate precursors

This study deals with the preparation of titanyl citrate precursors using the citrate method and titanium isopropoxide as a starting material. After drying and calcining, the titanyl citrate gels were converted into powders of lanthanum oxide doped strontium titanate. The cation ratios of the titanate powder prepared at pH 5–6 were very close to the original one. Only less than 0.1% of free cations remained in the solution. The titanyl citrates were precipitated using either ethanol or acetone. The precipitates obtained using acetone were always of a slimy consistency whereas those obtained using a sufficient quantity of alcohol were powdery. The powder obtained at pH 5–6 consisted of fine particle with a diameter of 0.3–0.5 μm and sintered readily between 1250 and 1350°C. The dielectric constants of the semiconducting La2O3-doped strontium titanates were determined.