High-Performance Ceramics III

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Authors: C.E. Cao, Ying Jun Wang, N.Z. Zheng, C.H. Xiong, H.R. Shen
Abstract: Calcium borate used for non-pollution flux of ceramic decoration materials is synthesized by using boric acid and calcium carbonate as raw materials. The effects of reaction temperature, concentration, time, pH value and additive agent on synthesis of calcium borate are studied. The synthesized products are characterized by using DTA, XRD, TEM and SEM. The results show that the better conditions are: synthesis temperature is 80-100°C, the proportion of boric acid and water is0.26 ~ 0.42 to 1(mol), the proportion of calcium carbonate and boric acid is 0.09-0.15 to 1(mol), the pH value is 5 ~ 7, reaction time is 3hs. The synthetic calcium borate is non-crystalline with particle size of 0.1 ~ 0.2 µm, when being calcinated at 300°C, the main crystal phase isCaO·3B2O3·4H2O.
605
Authors: Hao Sheng, Zhen Xing Yue, Zhi Lun Gui, Long Tu Li
Abstract: BiFeO3-PbTiO3 powders were synthesized by a novel sol-gel auto-combustion method. The gels, transformed from the aqueous solutions of metal nitrate and citric acid, undergo a selfpropagatingcombustion process when being ignited and yield voluminous ashes. These ashes are single phase perovskite BiFeO3-PbTiO3 powders. The redox behaviors of the dried gels were studied by DTA-TG technique and IR spectra. The synthesized powders were characterized in terms of XRD, SEM and BET techniques.
609
Authors: Qing Zhi Yan, Xin Tai Su, Wen Feng Zhang, Chang Chun Ge
Abstract: Non-agglomerated nano-sized BaTiO3 powders were prepared by a 3 step decomposition of barium titanyl citric acid chelate derived from Ba(NO3)2-TiO(NO3)2-citric acid-NH4NO3 based complex compound system. The 1st step was the thermal treatment of chelate wet gel at 150°C for 40min to remove water and non-bridging hydroxyl groups and to form expanded gel intermediate. The 2nd step was the decomposition of the organic fuel by igniting expanded gel intermediate at 300°C. The 3rd step was the formation of the high purity BaTiO3 by calcining the decomposed powders at 700°C for 2 hours. The most expanded gel intermediate was found to be a decisive factor for the elimination of hard agglomerate. In addition, the initial oxidant/fuel molar ratio was shown to strongly influence the characteristics of the powders thus obtained. The optimum oxidant/fuel value was 3 for obtaining non-agglomerated pure BaTiO3 powders with a particle size of 50 nm. The agglomerate degree of BaTiO3 powders was determined by particle morphology and uniformity of the green compact microstructure observed by field emission scanning electron microscopy and scanning electron microscope.
613
Authors: Ya Lu Ma, Hong Long Zhu, Jian Lin Li
Abstract: The clear and transparent sols of BaTi acetate were prepared from tetrabutyltitanate, barium acetate aqueous solution, ethanol and acetic acid. The BaTi acetate sols were transferred into gels by sol-gel process, and the gels were dried and calcined to nanostructured BaTiO3 powders. Pure barium titanate powders added in mixtures of acetone and iodine and water or acetylacetone (Acac) and ethanol (EtOH) as suspension systems, the aim of this study was to use the electrophoretic deposition technique (EPD) to fabrication the BaTiO3 ferroelectric films with high dielectric constant. During sol-gel transition process, it is found that the initial PH value of sol affected not only the sol-gel transition, but also the particles size of the final calcined BaTiO3 powders. The effects of the EPD process parameters such as the suspension, powder concentration, electrical field strength on the specific EPD deposited weight were investigated. The films sintered at 1050°C for 2h were crystallized into the tetragonal phase at room temperature, which were sufficiently dense and had uniform microstructure and excellent dielectric properties.
617
Authors: Qing Song Peng, Wan Jiang, Jing Feng Li
Abstract: Lanthanum-modified lead zirconate-titanate (PLZT5/54/46) powders were prepared from the commercial PbO, La2O3, TiO2 and ZrO2 powders by high-energy ball milling process. The synthesized powders milled for different hours were characterized using XRD and SEM. Thedesigned PLZT perovskite phase was formed from the mixture of the starting materials after milling for 20 hours. PLZT(5/54/46) ceramics were obtained using the produced powders milled for 20 h followed by sintering at temperatures ranging from 1000 to1200°C. Ferroelectric property of the PLZT ceramics was also measured.
623
Authors: Gang Xu, Zhao Hui Ren, Wen Jian Weng, Pi Yi Du, Gao Rong Han
Abstract: Lead zirconate titanate (PZT) ceramics are of great technological interest due to their excellent piezoelectric and ferroelectric properties. In the present work, a modified coprecipitation method for PZT phase preparation was proposed by combining the advantages of partial oxalate method and coprecipitation method. Firstly, the zirconium and titanium hydroxides were coprecipitated to form the precipitate of (Zr,Ti)O(OH)2. Then, the lead hydroxide was precipitated into a ammonia solution in which the precipitate of (Zr,Ti)O(OH)2 obtained above was well dispersed. The single perovskite PZT phase was directly synthesized without any intermediate phase appearing by calcinations the precursor at 500oC-800oC. The method proposed in the paper is an effective route for the synthesis of PZT powders.
627
Authors: Xin Tai Su, Qing Zhi Yan, Chang Chun Ge
Abstract: Ba3(Ca1.18Nb1.82)O9-d (BCN18) powder was synthesized using a wet chemical method from mixtures of all water-soluble compounds including Ba, Ca and Nb-citrate. It has been found that NH4NO3 in the initial solutions plays an important role in controlling the enthalpy of low temperature combustion process as well as the gel decomposition temperature. Further steps include evaporating, drying and calcinating. The obtained gels were characterized by TG-DSC, and the powder was characterized with XRD, TEM and BET. The experimental results have indicated that the heating temperature was only 800°C for synthesizing the powder and the average particle size was only about 40-50 nm. Furthermore it was found that a pure BCN18 phase with complexperovskite structure was formed at 800°C, which was about 800°C lower than that of the traditional solid-reaction method. So it is more practical and more superior to the traditional solid-reaction method and the present wet-chemical method in alcohol salt system reported in literature.
631
Authors: Zh.J. Xu, Rui Qing Chu, Bao Shan Li, Guo Rong Li, Qing Rui Yin
Abstract: Pb(Mn1/3Nb2/3)O3-Pb(Ti,Zr)O3 (PMnN-PZT) powders were synthesized by a hybrid method of sol-gel and ultrasonic atomization. The study shows that the resulting powder is pure, homogeneous and possesses a reasonably fine particle size. It is also believed to be applicable to other materials that can be processed via the technique.
635
Authors: Shi Kao Shi, Ji Ye Wang, Jun Min Li, Rui Long Zong, Ji Zhou
Abstract: The precursor powder of Sr2CeO4 was prepared from a nitrate starting solution by a combustion route with urea as a fuel. Sintering the precursor powder at different temperatures for 6h, a blue-white emission phosphor was synthesized. The microstructure and photoluminescence studies of Sr2CeO4 compound are reported. The particle sizes of the powder phosphor are around 0.5-2 µm when heat treated between 9500C to 11500C and the emission spectrum exhibits a broad band maximum at about 470 nm. The chemical purity and photoluminescence intensity of Sr2CeO4 powder phosphor strongly depend on the post-heat-treated temperature.
639
Authors: Yi Kun Liao, Dan Yu Jiang, Ya Ming Ji, Jian Lin Shi
Abstract: Y2Hf2O7 and Lu2Hf2O7 precursor powders are prepared by nitrate solution combustion method with various fuels at 450°C, respectively. Phase evolution of the synthesized powders was determined by X-ray diffraction (XRD) techniques. Single-phase cubic Y2Hf2O7 and Lu2Hf2O7 crystalline powders were obtained by calcining the resultant combustion ash at 800°C for 2h. By controlling the pH of the nitrate solution, the type of fuel and the ratio of fuel/nitrate, nanosized powders can be obtained. The crystallite size of resultant powders is much related to the combustion flame temperature, which can be controlled by controlling the type of fuel and adjusting the fuel-to-oxidizer ratio. The influence of the ratio of reactants and the type of fuel on the properties of the final products was investigated. The crystal size and morphology were analyzed by TEM.
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