TiO_2纳米材料的制备方法与应用进展

介绍了纳米TiO2材料主要制备方法,包括液相法、气相法等。液相法主要有水热法,钛醇盐水解法,W/O微乳法等,气相法主要有四氯化钛气相法,钛醇盐气相水解法,低压气体蒸发法等。液相法中的几种方法由于工艺简单、条件温和,气相法反应速度快,过程易放大,容易实现连续生产。     

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。     

超细氧化镁粉体的制备方法探讨

超细氧化镁粉体属于新型高功能精细无机材料。着重介绍了超细氧化镁粉体的制备方法(包括气相法、金属醇盐水解法、液相法、固相法、硬脂酸法)，对各方法的原理及优缺点作了详细的阐述。最后提出了硬脂酸法这一有前景的新工艺。     

金属醇盐的合成(Ⅱ)

简要介绍了金属醇盐合成的发展概况，单金属醇盐和多金属（双金属、三金属及四金属）醇盐等的合成分法。     

金属醇盐的合成(Ⅰ)

简要介绍了金属醇盐合成的发展概况，单金属醇盐和多金属（双金属、三金属及四金属）醇盐等的合成方法。     

金属醇盐的合成（1）

简要介绍了金属醇盐合成的发展概况，单金属醇盐和多金属（双金属、三金属及四金属）醇盐等的合成方法。     

由碳酸二甲酯合成芳香醚的绿色工艺

综述了酚类化合物与碳酸二甲酯(DMC)甲基化反应合成芳香醚的绿色工艺。气相连续流动法和液相间歇法是2种有效的由DMC合成芳香醚的方法。在气液相转移催化和液固相转移催化的条件下,酚与DMC甲基化反应的产率和选择性均很高。酚与DMC甲基化反应的均相催化剂一般选择叔胺、叔膦、季铵盐及Schiff碱等有机碱,多相催化剂为碱金属碳酸盐、沸石、氧化铝及附载有金属盐的氧化铝和煅烧的Mg-Al水滑石。     

金属醇盐的合成（II）

简要介绍了金属醇盐合成的发展概况，单金属醇盐和多金属（双金属，三金属及四金属）醇盐等的合成方法。     

制备氢氟烃中的氟化催化剂的研究进展

氟化催化剂是制备氢氟烃的核心技术。目前,主要包括气相氟化催化剂和液相氟化催化剂,活性金属包括铬、钙、铝等,活性高、寿命长、环境友好等综合性能优异的氟化催化剂是该领域的研究重点。文章对气相法和液相法合成氢氟烃中的氟化催化剂的种类、制备方法以及再生手段进行了综述。     

由草酸二甲酯加氢制乙二醇及乙二醇单甲醚的铜基催化剂及其制备方法

<正>本发明属于化工技术领域,具体是一种用于草酸二甲酯气相催化加氢合成乙二醇及乙二醇单甲醚的铜基催化剂及其制备方法。该催化剂以改性后的氧化锆为载体,负载有铜和其他助剂金属。其制备方法为:先采用改善的硬模板法制备氧化锆;对氧化锆进行酸化改性处理;在上述悬浊液中加入可溶性铜盐和可溶性助剂金属盐,使用蒸氨法进行金属     

Influence of ambient flow conditions on the droplet atomization characteristics of dimethyl ether (DME)

This paper describes the effects of ambient flow conditions on the droplet atomization characteristics of dimethyl ether (DME) both experimentally and numerically.In this investigation, the droplet atomization of DME fuel affected by ambient flow conditions was studied in terms of droplet mean size and detected droplet percentage under elevated ambient pressures and temperatures. In order to predict the DME spray atomization, the hybrid breakup model combined with KH-RT (Kelvin-Helmholtz and Rayleigh-Taylor) and KH-DDB (Kelvin-Helmholtz and Drop Deformation Breakup) models was applied in this study.It was revealed that the spray arrival time of DME fuel under a high ambient pressure increased in accordance with the increase in ambient pressure in the spray chamber. It can be seen that more small droplets are distributed at high ambient flow pressure conditions than at atmospheric conditions. This is a consequence of enhanced atomization of DME fuel. On the other hand, when the ambient pressure increases to 2 MPa, the Sauter mean diameter (SMD) increases only slightly compared with that at 1 MPa of pressure. The SMD value of droplets is increased as ambient temperature is increased. Under the high temperature condition in the chamber, the small droplets of DME fuel evaporate quickly and mix with the ambient air. As a result, it promotes the air-fuel mixing in a combustion chamber.     

Design optimization of twin-fluid atomizers with an internal mixing chamber for heavy fuel oils

The present work is devoted to determine the magnitude of the main parameters that yield the optimum results for twin-fluid nozzles with an internal mixing chamber. The focus is placed on the study of the interaction of both air and liquid flows at the internal chamber and its effects on the resulting spray. To this end, some experiments have been performed for different air central channel diameters and liquid ports, as well as for several experimental conditions (air and liquid mass flow rates), in order to understand the influence of the flow conditions at the mixing chamber on the size of the droplets produced. It has been demonstrated that under certain experimental conditions the atomizing fluid discharged to the internal chamber is choked. The sonic condition is achieved for different air and liquid mass flow rates as a function of the air central channel diameter. It has also been obtained that to achieve the best results with moderate atomizing fluid flow rates, it is convenient to operate in choked conditions. This is an important result that will help in the optimum design of this type of nozzles.     

INFLUENCE OF BATCH MIXING TIME AND BATCH GRAIN SIZE ON HOMOGENEITY OF A SODA-LIME-SILICA GLASS*

Density-spread determinations were made on a series of melts of a soda-lime-silica glass employing batches compounded from raw materials varying in particle size from 20- to 60-mesh to minus 200-mesh, which had been mixed by tumbling for one, ten, or thirty minutes. The two melting techniques employed were (1) melting for sixteen hours in a stationary platinum crucible at 1400°C. under conditions of even temperature distribution and consequently a minimum of convection mixing and (2) melting for four hours at 1400°C. in a rotating tilted crucible; this condition was intended to simulate convection mixing Under the experimental conditions employed, it was found that (1) batch mixing time has relatively little effect on the homogenizing rate, (2) homogenization increases rapidly with decrease in grain size, and (3) in all cases the 4-hour melting treatment with moderate mixing gives better homogeneity than sixteen hours melting time in a stationary crucible, this effect increasing with decrease in grain size. No significant difference in glass homogeneity resulted from three different methods of mixing, namely, tumbling, ball milling, and mixing in a muller-type mixer, although the homogenizing influence imposed probably was sufficient to mask any differences in uniformity of mixing that might have existed.     

受限空间内空心锥形喷雾-横流掺混规律

在自建的冷态横流-旋流喷雾两相掺混系统实验台上,采用PIV测量了掺混通道内气液两相掺混过程中液滴群的运动特性,获得了掺混流场中不同位置的液滴分布图像与流场结构特性。实验段结构为方腔（横截面尺寸为95 mm×95 mm）,喷嘴采用空心锥形雾化喷嘴。对影响掺混效果的主要参数（横流速度、喷嘴雾化压力、喷嘴雾化粒径）进行了详细研究,绘出了最佳掺混效果下各参数关系曲线。掺混过程主要受不同尺度的旋涡结构影响,液滴多富集于旋涡边缘,稳定的大尺度涡不利于掺混。提高掺混效果的途径即是避免流场中出现稳定的大尺度旋涡结构,采用喷嘴前倾布置、增加喷嘴个数、确定合适的横流速度均是提高掺混效果的有效途径。分析方法与研究结果为工程实际应用中掺混室结构的设计及掺混性能的改进提供了依据和参考。     

LEAFLASH SPRAY DRYER: INVESTIGATION OF THE ATOMIZATION PROCESS

The atomization process of the LEAFLASH spray dryer has been investigated by laser diffractometry and video imaging. The LEAFLASH atomizer is a particular pneumatic nozzle where the pressurized gas is the hot drying air. The drying and the atomization processes are interrelated in the spray dryer. Consequently the mixing of the liquid droplets and the drying medium is very efficient, permitting to work with short drying duration and reduced chamber volume. The mean diameter and the drop size distribution are measured at the outlet of the nozzle by laser diffraction. We studied the coupling effects of the air temperature (150 to 300° C) and pressure (1.20 to 1.50 bars abs) and of the dry matter content of the liquid feed (aqueous maltodextrin solution, 20 to 55% w/ w) on the droplets/ size distribution and on the general pattern of the spray. Analyses of video images of the generated spray give the general pattern of the spray and an estimation of the liquid velocity     

Homogeneous Nucleation by Continuous Mixing of High Temperature Vapor with Room Temperature Gas

The formation of aerosol particles by homogeneous nucleation in a supersaturated vapor has been studied experimentally and theoretically. In the laboratory, a particle-free gas at room temperature is continuously mixed with a high-temperature gas containing dibutylphthalate vapor in a new device for the study of aerosol nucleation called a particle size magnifier. A highly supersaturated vapor is rapidly formed in the mixing zone of the particle size magnifier, and the resulting number concentrations of aerosol particles are measured under various temperatures, mixing ratios, and mixing methods. Measured number concentrations are compared with those predicted by the classical and Lothe-Pound nucleation theories. The measured concentrations lie between the predictions of the two theories, and the trends with temperature and saturation ratio are consistent with either nucleation theory, provided vapor depletion is considered.     

Nucleation of Ethylene Glycol Vapor and Growth of Sub-10-nm Particles in Nanoparticle Size Magnifier

We investigated the rates of heterogeneous and homogeneous nucleation of ethylene glycol vapor onto sub-10-nm particles in a newly developed condensation device called nanoparticle size magnifier (NanoPSM). The saturation ratio in the NanoPSM is precisely controlled by vapor-feeding system and mixing section, which are designed based on an earlier particle size magnifier (PSM) developed by Okuyama et al. (1984). Size-classified NaCl nanoparticles smaller than 10 nm in mobility diameter are used as heterogeneous nuclei for the condensation of ethylene glycol vapor. The activation efficiency and growth rate of the activated nuclei are determined by a pulse height analysis using an optical particle counter (OPC). A computer fluid dynamics (CFD) simulation is employed to calculate the profiles of the gas velocity, temperature, vapor concentration, and resulting supersaturation in the NanoPSM. Annular high-supersaturation region is generated around the mixing boundary between cold aerosol and hot vapor. The experimental activation efficiency is 50% for 4.5-nm and 0.8% for 2 nm NaCl particles, through the subsequent growth of droplets to 2 μm in diameter. The experimental data are in fairly good agreement with the predicted activation efficiencies based on the classical Kelvin-Thomson theory when the local profiles of supersaturation are taken into account.     

Internal mixing: A practical investigation of the influence of intermeshing rotor configuration and operating variables on mixing characteristics and flow dynamics

This paper deals with the measurement and interpretation of pressures and temperatures produced by the mixing of a rubber compound in the chamber of an internal mixer equipped with interlocking rotors. Pressure transducers and infrared/fiber optic temperature sensors were sited flush with the inner surface of the mixing chamber of a Francis Shaw KO Intermix of 2 L chamber volume. The variation of pressure with transducer position In the chamber wall and with rotor position was measured for selected fill factors and rotor speeds at “equilibrium” conditions (quasi-static power requirement for the mixer) and at intervals during a complete mixing cycle. Two rotor designs were studied. Interpretation of the results was carried out with reference to biconical rotor rheometer measurements on the mixed rubber compounds and by reference to four regimes of viscoelastic behavior identified for two-roll mill mixing. A basic flow analysis was carried out by use of the lubrication approximation in conjunction with an isothermal power-law model.     

Hygroscopic Growth of an (NH 4 ) 2 SO 4 Aqueous Solution Droplet Measured Using an Environmental Scanning Electron Microscope (ESEM)

The contact angle, θ, and volume equivalent diameter of an (NH₄)₂SO₄ aqueous droplet was measured using an environmental scanning electric microscope (ESEM), showing the hygroscopic growth of the solution droplet as the relative humidity (RH) increased from 80% to 98%. (NH₄)₂SO₄ particles with diameters in the range 1–2 μ m were produced by an atomization technique, and collected onto a copper substrate that had been treated with polytetrafluoroethylene. To observe the hygroscope growth, the sample chamber of the ESEM was filled with water vapor at a pressure of 600 Pa, and the sample temperature was adjusted using a cooling stage to control the relative humidity inside the chamber. Before the observation of the hygroscopic growth, we determined the value of θ from overhead views of droplets on the stage at a tilted angle of 45°. The average value of θ was 96 ± 10°, and this value was used to estimate the droplet diameter. We measured the diameter of the (NH₄)₂SO₄ droplets at different RH, and observed that the growth factor, G, increased with increasing RH. The experimental value of G was consistent with the theoretically estimated value. This shows that our method for determining the value of θ was valid, and that the ESEM technique can be used to measure the diameters of droplets of aqueous solutions.     

A study on the effects of chaotic mixer design and operating conditions on morphology development in immiscible polymer systems

Self‐similar mixing structures, a novel feature of chaotic mixing, were generated in this study as precursor to an array of mixing microstructures, such as nested layers, elongated fibrils, droplets and their combinations in the blending of two immiscible polymers, polypropylene (PP) and polyamide‐6 (PA6). Simulations based on Newtonian flow model were used to compute Poincaré maps and stretching distribution as the tools for investigation of the effect of shear gap and chaotic mixing parameter, such as angular displacement per period (θ) of rotors, on the degree of mixing and morphology development in a batch chaotic mixing device. It was found that a value of θ = 1440° provided the conditions for fastest conversion of the PP‐phase into droplets for the same total strain. A 25% reduction in shear gap from 0.0127 m to 0.0095 m gave rise to much more uniform mixing of the components and led to faster conversion of the PP‐phase into droplets for the same value of θ and the same total strain. A very large fraction (>90%) of the droplets generated fell below the equilibrium size and were found to be much smaller than those produced by twin‐screw extrusion method. Polym. Eng. Sci. 44:407–422, 2004. © 2004 Society of Plastics Engineers.