CAS OpenIR
水热法合成钛酸锶工艺优化及其机理研究
张娜
Subtype硕士
Thesis Advisor钟莉
2019-07-01
Degree Grantor中国科学院大学
Degree Discipline化学工程
KeywordSrtio3纳米粒子,锐钛矿tio2,一步水热合成,油酸辅助,工艺优化
Abstract

钛酸锶不溶于水,室温时为白色立方晶体的钙钛矿型(Perovskite)氧化物,在电子陶瓷等领域用途广泛,具有介电常数高和损耗低以及热稳定性好的优点,有优异压电与铁电性能,在电子和陶瓷及机械领域有广泛的应用;且SrTiO3禁带宽度为3.2 eV,禁带宽度高、光催化活性好,具有优异的氧化还原催化活性,在光催化领域受到了广泛关注。钛酸锶的常规合成方法是通过碳酸锶和二氧化钛之间的高温固相反应,需要经过高温煅烧。然而,用这种方法得到的粉末通常团聚现象严重、杂质多且颗粒形貌不规则,既不适用于光催化领域,也不适合用于加工具有亚微米或纳米颗粒的致密陶瓷。由此产生了很多湿化学方法,比如溶胶-凝胶法,燃烧法,溶解-沉淀法、微波合成法、溶剂热法、化学共沉淀法和水热法等。其中,水热合成不需要退火处理以改善结晶度,具有流程短、操作易、产品指标可调控等优点。本论文采用一步水热法,以廉价易得的锐钛矿二氧化钛(TiO2)为钛源,以八水合氢氧化锶(Sr(OH)2?8H2O)为锶源合成钛酸锶纳米粉体。通过单因素实验和多因素正交试验,系统考察反应温度、反应时间、碱性介质浓度、反应物浓度、Sr/Ti摩尔比、油酸添加浓度等工艺参数,产品粒度、晶体结构、形貌、晶粒尺寸、产率、纯度及团聚的影响,合成出了形貌规整、粒度分布窄、纯度高及分散性好的产品;并对合成机理进行探究。得到如下主要结论:(1)产品形貌调控:产品存在团聚现象,油酸的加入可减弱SrTiO3纳米颗粒之间的团聚现象、增加分散,在油酸浓度为3%时颗粒为形貌规则尺寸均匀的立方体且分散性好。(2)产品纯度调控:反应温度和碱性介质浓度增大,产物纯度随之增加;反应物浓度对产物纯度影响不明显;Sr/Ti摩尔比为1.25和1.00时,产物中存在TiO2杂质峰;Sr/Ti摩尔比为0.75和0.5时,产物中无杂质峰,为纯净的SrTiO3,但在Sr/Ti=0.5时结晶度变差。优化的制备工艺条件为油酸浓度3%、摩尔比Sr/Ti=0.75。(3)产品粒度调控:通过探究不同反应物浓度、不同Sr/Ti摩尔比、不同浓度氢氧化钠溶液、不同反应温度、不同反应时间及不同油酸浓度下的实验,可以看出,随着反应物浓度的增加、随着物料Sr/Ti摩尔比增加、随着反应时间的延长、随着碱性介质浓度增加和反应温度升高时,钛酸锶纳米颗粒的粒度均增加。激光粒度分析仪测得的粒度主要分布在0.1-1 μm左右(4)产品微观结构调控:在实验范围内,随反应时间和Sr/Ti摩尔比增加,SrTiO3纳米粒子的晶粒尺寸呈增加趋势,通过谢乐公式结算得颗粒的晶粒尺寸主要分布在35-65 nm之间;合成出的产品为尺寸均匀、形貌规则的钙钛矿相立方SrTiO3纳米粒子。(5)合成机理研究:油酸、反应时间和Sr/Ti摩尔比对SrTiO3纳米粒子微观结构的影响分别可以用颗粒间作用力、奥斯特瓦尔德熟化和晶体成核来解释。该实验的反应机理符合溶解-沉淀反应机理。;Strontium titanate is a perovskite oxide insoluble in water with white cubic crystal at room temperature. It is widely used in electronic ceramics and other fields. It has the advantages of high dielectric constant, low loss and good thermal stability. Because of its excellent piezoelectric, ferroelectric properties and is widely used in the fields of electronic, ceramic and mechanical industries. Moreover, band gap of SrTiO3 is 3.2 eV, high band gap, good photocatalytic activity and excellent redox catalytic activity, SrTiO3 has attracted extensive attention in the field of photocatalysis.The conventional synthesis of SrTiO3 is by solid-state reaction between SrCO3 and TiO2 at high temperature, which requires high temperature calcination. However, the powders obtained with this method usually have serious agglomeration, large particle size, considerable impurity, and irregular particle morphologies,which are not suitable for neither photocatalytic applications nor the processing of dense ceramics with submicron or nanoparticles. In recent years, many wet-chemical methods to synthesize SrTiO3 perovskite ceramic materials,including sol-gel method, combustion method, solution-precipitation method, solvothermal method, hydrothermal routes and mechanochemical method. Among them, hydrothermal synthesis does not require annealing treatment to improve crystallinity, and it has the advantages of short process, easy operation, and controllable product specifications.In this paper, SrTiO3 nanopowders were synthesized by one-step hydrothermal method using cheap and readily available anatase titanium dioxide (TiO2) as titanium source and strontium hydroxide octahydrate (Sr(OH)2?8H2O) as strontium source. Through single factor and multi-factor orthogonal experiments, the effects of process parameters such as reaction temperature, reaction time, alkaline medium concentration, reactant concentration, Sr/Ti molar ratio and oleic acid addition concentration on product size, crystal structure, morphology, grain size, yield, purity and agglomeration were systematically investigated. The products with regular morphology, narrow particle size distribution, high purity and good dispersion were synthesized. The mechanism of synthesis was explored. The main conclusions are as follows:(1) Regulation of product morphology: the products showed agglomeration, the agglomeration of SrTiO3 nanoparticles are weakened by the addition of oleic acid and dispersion increased. When oleic acid concentration is 3%, the particles are cubic with regular shape, uniform size and good dispersion.(2) Regulation of product purity: with the increase of reaction temperature and alkaline medium concentration, the purity of the SrTiO3 products are increased, and the concentration of the reactants has little effect on the purity of the product. when the molar ratio of Sr/Ti is 1.25 and 1.00, the peak of TiO2 is present in the product; When the molar ratio of /Ti is 0.75 and 0.5, there is no impurity peak in the product, which is pure SrTiO3, but the crystallinity deteriorates under Sr/Ti molar ratio is 0.5. The optimized preparation process conditions are oleic acid concentration 3% and Sr/Ti molar ratio as 0.75.(3) Regulation of product granularity: By investigating the experiments under different reactant concentration, different Sr/Ti molar ratios, different concentration of sodium hydroxide solution, different reaction temperature, different reaction time and different oleic acid concentration. It can be seen that the particle size of SrTiO3 nanoparticles increase with the increasing of reactant concentration, Sr/Ti molar ratio, reaction time, alkaline medium concentration and reaction temperature. The particle size measured by laser particle size analyzer mainly distributes in the range of 0.1-1 μm.(4) Regulation of microstructure: within the experimental range, with the increase of reaction time and Sr/Ti molar ratio, the grain size of SrTiO3 nanoparticles tends to increase. The grain size of SrTiO3 nanoparticles is mainly distributed between 35-65 nm calculated by Scherrer formula. The products synthesized are perovskite cubic SrTiO3 nanoparticles with uniform size and regular morphology.(5) Synthesis mechanism research: the influence of oleic acid, reaction time and Sr/Ti mole ratio on microstructures of SrTiO3 nanoparticles can be explained by interparticle force, Ostwald Ripening and crystal nucleation, respectively. The reaction mechanism of this experiment is consistent with the dissolution-precipitation reaction mechanism

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/40698
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
张娜. 水热法合成钛酸锶工艺优化及其机理研究[D]. 中国科学院大学,2019.
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