扩散火焰燃烧法合成纳米二氧化钛

以TiCl4为原料,采用空气和液化石油气(LPG)气相燃烧法,在扩散火焰中合成纳米TiO2粉体,研究了反应气体的流量、火焰温度、火焰形状等条件对产物的粒径、晶型及其粒径分布的影响.实验中发现,随着空气流量的增加,颗粒的粒径明显增大;随着LPG流量的增加,粒径略有增加.在最佳条件下,纳米TiO2的平均粒径小于20 nm.产物以锐钛型的晶型为主,随着火焰温度的升高,金红石型的含量增加.火焰的长度是影响粒径大小的重要因素.     

火焰法合成纳米TiO2颗粒生长过程

在新型火焰反应器生产纳米TiO2的过程中使用TEM微栅在不同火焰高度位置处进行原位取样分析,得到生长过程中纳米TiO2颗粒的粒径和形态. TiO2颗粒经历了成核、生长、聚并、烧结的过程. 调节反应物浓度为7.9×10-5~5.7×10-3 mol/L,研究了不同反应物浓度对纳米颗粒生长过程的影响,高前驱体浓度形成较高的单体浓度,使颗粒间碰撞几率增加,从而得到粒径较大的颗粒,产物粒径17~85 nm. 调节CH4和O2流量,改变温度场,研究温度对颗粒生长过程的影响,在相同反应物浓度条件下,较高的温度下形成分散性好、一次粒径为63 nm的颗粒,而在较低的温度下形成的颗粒一次粒径为35 nm,但颈部烧结严重;增加喷嘴气流速度减小了反应停留时间,颗粒粒径从63 nm减小到36 nm.     

气相结晶技术模型在合成氟化氢铵工艺中的应用

研究了氟化氢铵气相合成新工艺,应用气相结晶理论验证了气相结晶过程,拟舍得到了适合于该过程的气相结晶模型,确定了颗粒平均粒径和流体流速之间的关系。并通过实验来验证了该气相结晶技术模型的正确性。通过实验确定了优化反应条件：反应温度为250℃,冷却器温度控制在80℃,反应物进料配比为NH3：HF=0．75：2,氨气流量为0．04m^3/h载气流量为0．6m^3/h。氟化氢铵含量达99．5％。     

幻彩型人工氟金云母钛珠光颜料制备工艺的研究

利用液相沉积法对不同粒径的氟金云母钛珠光颜料制备工艺进行了研究。探讨了反应温度、TiCl4浓度、TiCl4加料速度对幻彩系列颜料珠光效果的影响以及TiCl4用量与颜料幻彩颜色的对应关系。采用扫描电子显微镜(SEM)观察云母钛珠光颜料的表面TiO2膜形貌。研究结果表明:在反应温度为78℃、TiCl4浓度为1.5～2.0 mol/L时得到珠光颜料光泽好,其表面包覆的TiO2膜平整、连续、致密、粒径在40 nm左右。氟金云母的平均粒径越小,TiCl4的最佳加料速度越快。制备同一色彩珠光颜料时,不同粒径的氟金云母所需包覆的TiO2量以单位比表面积计基本相同,所以在颜料色彩相同情况下,只要测得氟金云母的比表面积,即可推算出不同粒径云母所需包覆的TiO2量。     

基于OpenFOAM的竖直管内气-液-水合物流动特性研究

针对天然气水合物开采过程中涉及的复杂气液固三相流动问题，基于群体平衡模型，提出了新的水合物颗粒聚并破碎模型组合，同时考虑了气泡的聚并破碎行为，运用开源CFD软件OpenFOAM对建立的模型进行求解验证。考察了入口流速、气相和水合物颗粒体积分数对竖直管内气-液-水合物流动特性的影响。结果表明：所建立的模型准确有效，各相的浓度分布、气泡的平均粒径径向分布和水合物颗粒平均粒径大小受水合物颗粒体积分数的影响很大，压力损失梯度随着流速的增加先减小后增大，存在特定工况下的最优流速，气相体积分数的增加会让管内流体的压力损失梯度明显减小。     

氢氧焰燃烧制备纳米Al2O3颗粒及其分散性能

利用多重射流氢氧燃烧反应器,以AlCl3为前驱体制备了具有不同形貌和晶型结构的Al2O3纳米颗粒,表征了其形貌、晶型结构、比表面积、粒径分布等性能,考察了火焰燃烧形式和反应区最高温度等因素对颗粒性能的影响规律. 结果表明,随反应温度升高,Al2O3粒径不断长大,形貌从具有链状结构的不规则颗粒逐渐转变为分散性良好的球形颗粒;同时随反应温度升高和在高温火焰中停留时间延长,晶型由单纯g相逐渐转变为d和d*相. 产品纳米Al2O3颗粒具有较强亲水性,其分散液具有较好的稳定性. 探讨了高温快速反应过程中颗粒和团聚体的生长机理,最终产物的粒径和团聚体形貌取决于各主要影响条件的相互竞争.     

纳米金红石型TiO2的制备研究

以TiCl4为原料,通过低温水热处理和高温煅烧两步法得到了金红石型TiO2纳米晶。利用XRD、TEM、BET和紫外一可见光光谱对不同反应条件下制得的样品进行了表征。结果表明,水热温度较高时所得到的前体煅烧后更有利于形成小粒径和高分散的TiO2纳米晶,并且有较高的比表面积。     

四氯化钛制备中加碳氯化反应的研究

为了进一步了解四氯化钛制备中加碳氯化反应,通过计算对二氧化钛加碳氯化的CO与CO2摩尔比值、配碳比等进行了研究,发现它们对加碳氯化反应产生重要影响,低温下加碳氯化反应主要生成CO2,高温下主要生成CO。当配碳比较高时,碳的反应不完全,存在过量;较低时,不利于TiO2的完全反应。对工业TiCl4生产的CO与CO2摩尔比值进行了详细阐述。同时对低价钛氧化物的生成进行了探讨,认为不会生成低价钛氧化物。通过实验讨论了TiO2与TiCl4间的反应,发现TiO2与TiCl4间的反应能够发生,并随温度的升高而加强。研究结果为进一步优化加碳氯化反应提供了依据。     

多喷嘴对置式气化炉内颗粒挥发分火焰可视化研究

基于实验室规模多喷嘴对置式水煤浆气化炉及其可视化装置,研究了气化炉喷嘴平面非射流区颗粒挥发分燃烧过程。结合图像处理技术,在气化条件下对粒径小于300 μm颗粒挥发分火焰尾迹形态及变化过程进行分析。研究结果表明,颗粒挥发分火焰非典型包络型火焰,而是形成挥发分火焰尾迹。颗粒挥发分尾迹形态受颗粒脱挥发分所处阶段和颗粒相对于气流的运动状态的影响,随时间不断变化。颗粒挥发分最大火焰尺寸随颗粒粒径增加而增加。气流床气化还原性气氛条件下颗粒挥发分燃烧时间较颗粒在富氧气氛中燃烧时间显著增加。     

以TiCl4为原料制备纳米TiO2的研究进展——气相法

介绍了以TiCl4为原料,用气相法制备纳米TiO2的几种方法;详述了制备纳米TiO2的原理、工艺、产品的形态和结构、影响产品质量的因素等.     

Preparation of Nano-titanium Dioxide in Propane/Air Diffusion Flame

Titanium dioxide (TiO2) nanoparticles were synthesized by the oxidation of titanium tetrachloride (TiCl4), in propane/air diffusion flame. The propane/air diffusion flame is generated using a multi-port diffusion type burner composed of 4 concentric tubes. Flow rates of TiCl4 and combustion gases such as air, industrial propane and carrier gas were chosen as key experimental variables for the control of the particle size and morphology. Effects of propane/air mole ratio and precursor flow rate on particle size, morphology, structure and carbon dots of titanium dioxide particles were studied.     

Comparison of Titania Particles Between Oxidation of Titanium Tetrachloride and Thermal Decomposition of Titanium Tetraisopropoxide

Thermal decomposition of TTIP was compared with oxidation of TiCl 4 in morphology and primary particle size of produced TiO 2 particles in a tubular reactor 2.7 cm in diameter and 54 cm in length under equal rate constants. The reactor temperature was varied from 850 to 1000°C for TiCl 4 oxidation and from 492 to 579°C for TTIP decomposition. The lower and upper limits of decomposition temperature for TTIP were determined so that the rate constants become equal, at corresponding limits, between TiCl 4 oxidation and TTIP decomposition. In order to maintain constant concentration with variation of reactor temperature, the flow rate of dilution gas was adjusted to compensate for the volume change of gas with temperature. The precursor concentration at the reaction condition was in the range of 1.09 2 10 m 6 to 1.09 2 10 m 5 mol/L, and the residence time of 3.1 to 10.8 s was based on the reactor set temperature. Particles from TTIP were spherical, while those from TiCl 4 were polyhedral. A considerable fraction of the precursor admitted to the reactor was consumed on the tube wall by surface reaction to form a zone coated with TiO 2 . The loss of precursor to the wall was greater with TiCl 4 oxidation. The particle size was, however, larger by 20% with TiCl 4 oxidation. By replacing the straight reaction tube with a concentric tube, the loss could be reduced, thereby increasing the amount of TiCl 4 available for particle formation significantly; the particle size was similar, however. With the straight tube a mixture of TiCl 4 and oxygen entered the reactor and the reaction occurred over the gradual increase from 650°C to a reactor set temperature of 900°C. With the concentric tube, the reactants had been preheated separately and then brought into contact right at the set temperature. The difference in the history of temperature for reaction may have brought about a difference in nucleation rate and consequently yielded particles of similar size. By analyses of BET surface area, X-ray diffraction patterns, and thermogravimetric data, TiO 2 particles from both routes were nearly nonporous, showed anatase peaks in majority, and contained no appreciable volatiles.     

掺铝对气相合成TiO2超细粒子形态的影响

管式电加热气溶胶反应器中,利用ＴｉＣｌ４气相氧化制备ＴｉＯ２超细粒子。研究掺铝量和反应温度对粒子形态的影响,结果表明粒子中金红石相质量分数随掺铝量增加而增大,粒径随掺铝量增加而减小;当反应温度为１２００℃时,粒子中金红石质量分数出现最大值,粒径随温度升高而增     

TiCl_4-AlCl_3-O_2高温反应合成TiO_2-Al_2O_3纳米复合颗粒

引　言纳米粉体制备是获得纳米陶瓷的重要前提[1] .ＴｉＯ2 和Ａｌ2 Ｏ3 复合陶瓷热膨胀系数小、熔点高、抗震性好 ,是很有发展前途的高温结构材料[2 ] .通常采用球磨法[3] 实现ＴｉＯ2 和Ａｌ2 Ｏ3 粉共混 ,但往往得不到微观均匀混合的纳米粉体 .Ｗｏｉｇｎｉｅｒ等[4 ] 采用醇盐共水解Ｓｏｌ -Ｇｅｌ法 ,成本高、反应时间长 ;Ｏｋｕｍｕｒａ等[5] 利用烷氧基钛水解反应在Ａｌ2 Ｏ3颗粒表面包覆ＴｉＯ2 ,该法均匀性差 ,且需严格控制原料滴加速度、反应时间较长 .气相反应法快速高效 ,能直接获得金属氧化物晶体 ,产物纯度较高 ,已用于制备Ｔ…     

纳米二氧化钛的气相合成

综述了TiCl4氢氧焰水解法、TiCl4气相氧化法、钛醇盐气相氧化法、钛醇盐气相水解法和钛醇盐气相热解法合成纳米二氧化钛的技术进展。气相法合成纳米二氧化钛的研究热点是工艺参数、反应物的混合方式、添加剂、外加电场和反应器型式对纳米二氧化钛的微结构和性能的影响,用计算流体力学、反应动力学与气相颗粒形成模型相结合来模拟过程和改进反应器设计也是一个令人关注的研究领域。TiCl4气相氧化法由于其具有经济、环保和生产工艺的柔性等优点而最具竞争力。控制纳米二氧化钛粒子的形态、粒径分布、比表面积和晶型组成以及防止反应器壁二氧化钛结疤是气相法规模化生产纳米二氧化钛需重点解决的问题。     

Numerical simulation of nanoparticle synthesis in diffusion flame reactor

A computational model combining the fluid dynamics with the particle kinetics was employed to study TiO₂ nanoparticle synthesis in a diffusion flame reactor. A one-step chemical kinetics approach was used to model titanium tetraisopropoxide (TTIP) decomposition that leads to homogeneous nucleation and particle formation. The momentum, heat, and mass transfer, Brownian coagulation and diffusion, surface growth, coalescence and thermophoresis have been taken into account. Based on the particle size distributions, an efficient quadrature method of moments was allowed to approximate the general dynamics equation of particle, and the eddy dissipation concept (EDC) combustion model was used to estimate the flame temperature field. Excellent agreements between the model predictions and experimental data, with respect to the flame temperature distribution and particle kinetics, are reached. By taking the particle size and surface area as independent variables, the full distributions of volume equivalent diameters, evolution of the agglomerate number, the geometric standard deviation based on volume and agglomerate fractal nature, mean primary particle size and the number of primary particles per agglomerate are revealed. The variation of oxygen flow rate has an important influence on the temperature distribution and hence on the particle kinetics accordingly.     

机械法制备纳米二氧化钛粉体及其光学性能

用一种高能搅拌磨研磨锐钛矿型TiO2粉体,用氮气吸附法测量不同研磨时间TiO2粉体的比表面积,用声发射粒度仪和扫描电镜测量和观察了颗粒的粒径和形貌.结果表明:经研磨7h得到的TiO2粉体的平均粒径为50nm,比表面积大于70m2/g.经X射线衍射仪测试表明:研磨后TiO2粉体的晶型发生变化,随着研磨时间增加,TiO2结晶度会明显降低.另外,用分光光度计测量了甲基橙在TiO2光催化前后的吸光率,用紫外吸收光谱仪测量了TiO2在研磨前后的紫外漫反射吸收光谱,从而表征了TiO2粉体的光学性能.机械法制备的纳米TiO2粉体在紫外线的照射下能够产生光催化作用,并且具有吸收紫外线的能力.     

Generation of Silica Nanoparticles from Tetraethylorthosilicate (TEOS) Vapor in a Diffusion Flame

Silica (SiO2) nanoparticles were synthesized by the gas phase thermal oxidation of tetraethylorthosilicate (TEOS) in a laminar diffusion flame reactor. Characteristics of the formation of silica nanoparticles along the axial distance above the burner outlet were investigated. Effects of maximum flame temperature, TEOS concentration, residence time, and water vapor on the particle size were also investigated. Silica nanoparticles less than 20 nm in average particle diameter were synthesized in all of the experiments. Morphological changes of particles were found along axial distance above the burner outlet; many small aggregates of particles (dp = ～ 7 nm) were found up to 2 cm, isolated smaller particles ( dp = ～ 5 nm) at 4 cm, and aggregates of bigger particles (dp = ～ 10 nm) at 10 cm. Larger particles at higher TEOS concentrations are generated in the flame synthesis. As the maximum flame temperature increased, the average particle size of silica also increased. Smaller particles were produced with decrease of the residence time of TEOS vapor in the flame. The average particle size decreased with the injection of water vapor to the flame.