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    题名: 製備參數對水熱法製備球形奈米鈦酸鋇粉體之影響研究;Effects of Solvents on the Formation and Morphology of Nanocrystalline Barium Titanae Powders in Hydrothermal Method
    作者: 陳坤源;Kun-Yuan Chen
    贡献者: 化學工程與材料工程研究所
    关键词: 金紅石;銳鈦礦;二氧化鈦;水熱合成法;鈦酸鋇;barium titanate;hydrothermal method;rutile;anatase;colloid sol;titania;thermal hydrolysis
    日期: 2004-05-19
    上传时间: 2009-09-21 12:21:34 (UTC+8)
    出版者: 國立中央大學圖書館
    摘要: 摘 要 本研究主要利用低介電常數之醇類與水混合,調整溶液之介電常數及無機酸與水之混合,藉由酸為觸媒以増加溶液中鹽類之水解速率及粒子之結晶速度;以控制二氧化鈦(TiO2)粉體之成長機構,進而控制其外形、粒徑及晶形。其次再利用此二氧化鈦粉體為原料於低溫下(<100℃)經水熱反應製備外形與粒徑和起始二氧化鈦粉體相同且具正方晶形(tetragonal)之鈦酸鋇(BaTiO3)粉體。本研究分兩步驟:(1)直接加熱水解含有機醇或無機酸之四氯化鈦水溶液,製備球形及菱形TiO2粉體。TiO2粉體之外形、粒徑及晶相可由溶液中之醇水體積比(RH ratio)或氫鈦莫耳比(H/Ti)控制。(2)將TiO2及Ba(OH)2置於高壓反應器中,水熱合成BaTiO3粉體。BaTiO3粉體之外形、粒徑及晶相可由起始之TiO2粉體控制。 在醇-水溶液中,以丙酮或正丙醇調整溶液之介電常數,最適宜製備球形鈦酸鋇粉體。當RH=3時,以70℃熱處理30min以上,可製得分散之球形TiO2粉體。當熱處理溫度高於70℃會破壞球形粉體之外形。四氯化鈦(TiCl4)濃度低於0.2 M,均可製備球形之TiO2粉體,唯濃度増加時粒徑變大,粒徑與濃度約略成正比關係。為減少粉體之聚集,加入0.001 g/cm3之丙羥基纖維素(HPC)為立體分散劑。球形TiO2粉體於Ba(OH)2水溶液中水熱反應合成BaTiO3粉體,水熱合成之BaTiO3粉體具立方晶系,其粒徑與外形均和起始TiO2粉體相同,反應機構應為In-situ Transformation。水熱反應之溫度及時間並不影響粉體之外形及粒徑;但稍為影響其晶格大小;鋇鈦比(Ba/Ti)則會影響粉體粒徑大小,但不影響粉體之晶格及外形。球形BaTiO3粉體熱處理至900℃時仍維持立方晶相,熱處理至1150℃時晶相轉變為正方晶系(tetragonal)其晶格比(c/a)=1.0110。此球形BaTiO3粉體之燒結體的體密度為5.86 g/cm3;其緻密度可達理論密度之97.34 %。 在無機酸-水溶液中,無機酸的種類及濃度影響TiO2粉體的外形、粒徑及晶形甚大。其中以過氯酸為介質製備之TiO2粉體粒徑為最小;當H/Ti比為1時TiO2粉體之外形為長軸為80nm;短軸為10nm之菱形狀且具金紅石(rutile)之晶形。此奈米TiO2粉體於Ba(OH)2水溶液中水熱反應合成BaTiO3粉體,水熱合成之BaTiO3粉體具立方晶系,其粒徑與外形均和起始TiO2粉體不同,外形由菱形(TiO2)變為球形(BaTiO3),粒徑由50 nm(TiO2)變為20~50 nm(BaTiO3);此反應機構應為Dissolution- precipitation Reaction。水熱反應之溫度及時間並不影響粉體之外形及粒徑;但稍為影響其晶格大小。而不同之Ba/Ti比會影響粉體粒徑大小,但不影響粉體之晶格及外形。奈米BaTiO3粉體熱處理至900℃時仍維持立方晶相,熱處理至1150℃時晶相轉變為正方晶系(tetragonal)其晶格比(c/a)=1.0165。此奈米BaTiO3粉體其燒結體之體密度為5.92 g/cm3;其緻密度可達理論密度之98.33 %。 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.
    显示于类别:[化學工程與材料工程研究所] 博碩士論文

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