Synthesis of nano-sized ceria powders by two-emulsion method using sodium hydroxide

In the present study, nano-sized ceria powders were prepared by the two-emulsion method in the presence of aqueous sodium hydroxide. The effect of the ceria precursor concentration and the addition of an aqueous sodium hydroxide on the crystallite size, the size distribution and the morphology of the synthesized powders were investigated. The precipitates were obtained by mixing two water-in-oil emulsions with kerosene containing cerium nitrate aqueous solution and sodium hydroxide aqueous solution. The synthesized ceria powders were characterized by XRD and TEM. The synthesized ceria powders had nearly spherical shape and a uniform crystallite size in a range of 10 to 20 nm depending on the concentration of precursor solution and an addition amount of mineralizer.     

Synthesis and microstructure of calcia doped ceria as UV filters

Fine particles of calcium oxide doped cerium dioxide, 2–4 nm in diameter, were prepared by the chemical reaction of CeCl₃-CaCl₂ mixed aqueous solution and NaOH aqueous solution at pH 6–12 and 40°C followed by the oxidation with hydrogen peroxide. Doping of CaO with CeO₂ resulted in decreasing the particle size and consequently, increasing UV shielding efficiency and transparency to visible light. The particle shape of ceria changed significantly depending on the reaction condition, i.e., rod-like particles and spherical particles were formed by the H₂O₂ oxidation of cerium trihydroxide pH above 8 and below 7, respectively.     

TiOCl2 溶液低温水解合成金红石型氧化钛纳米粉

由TiOCl2均相溶液采用低温（室温－60℃）陈化直接制备了纳米氧化钛针形聚集体颗粒。研究了搅拌和陈化温度对产物形貌及尺寸的影响。结果表明,在搅拌的条件下,产物的形貌为准球形;陈化温度（室温－60℃）对产物形貌无影响。利用透射电镜（TEM）和X射线衍射（XRD）对产物进行了表征,结果表明,产物形貌为针形聚集体,晶型为金红石型。     

Preparation and characterization of submicron-cerium oxide by hypergravity coprecipitation method

Submicron-cerium oxide particles were synthesized by applying hypergravity using ammonium bicarbonate (precipitant) and cerium nitrate hexahydrate (precursor). The influence of the concentration, pH, dispersant loading, flow rate, rotation speed of the hypergravity rotating bed, calcination temperature, and time on the cerium oxide particle size were examined by zeta potential, solid–liquid contact angle, thermo-gravimetry–differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The cerium oxide particles were highly dispersed, with an average particle size of 200 nm. Calcining at 650 °C for 1.5 h afforded the smallest particles. The crystallite size and fraction crystallinity increased with prolonged calcination. Crystalline cerium dioxide grew along three crystal planes, forming a complete face-centered cube, affording high hardness and activity of the polishing powder. The optimal conditions were: cerium nitrate concentration: 0.7 mol/L, cerium nitrate/ammonium bicarbonate molar ratio: 1:3, dispersant mass fraction: 3%, cerium nitrate initial pH: 4–5; the precursor solution was adjusted to pH 9 with ammonia water. Hypergravity coprecipitation with 1.5 h calcination afforded submicron-sized cerium oxide with a uniform size distribution using ammonium bicarbonate in an industrially viable process. The simple and low-cost manufacturing process may enable the development of hypergravity-assisted chemical synthesis technology.     

Morphology control and luminescence properties of YAG:Eu phosphors prepared by spray pyrolysis

Starting from nitrate aqueous solutions with citric acid and polyethylene glycol (PEG) as additives, Y₃Al₅O₁₂:Eu (YAG:Eu) phosphors were prepared by a two-step spray pyrolysis (SP) method. The obtained YAG:Eu phosphor particles have spherical shape, submicron size and smooth surface. The effects of process conditions of the spray pyrolysis on the crystallinity, morphology and luminescence properties of phosphor particles were investigated. The emission intensity of the phosphors increased with increasing of sintering temperature and solution concentration due to the increase of the crystallinity and particles size, respectively. Adequate amount of PEG was necessary for obtaining spherical particles, and the optimum emission intensity could be obtained when the concentration of PEG was 0.10 g/ml in the precursor solution. Compared with the YAG:Eu phosphor prepared by citrate-gel (CG) method with non-spherical morphology, spherical YAG:Eu phosphor particles showed a higher emission intensity.     

Novel synthesis of nanocrystalline CeO2 by mechanochemical and water-in-oil microemulsion methods

Nanocrystalline cerium dioxide (CeO₂) had been synthesized by two different methods which were mechanochemical and water-in-oil microemulsion. Effects of synthesis conditions on properties of nanocrystalline cerium dioxide were investigated. X-ray diffraction (XRD) was used to characterize the phase and crystallite size of synthesized cerium dioxide nanoparticles. XRD results showed that face centered cubic CeO₂ nanoparticles with crystallite size in nanometer scale were formed. The crystallinity increased with increasing annealing temperature. The average specific surface area of the particles was probed using gas adsorption-desorption measurements. The average particles size was calculated from the specific surface area and was determined to be 5.2 nm for microemulsion samples and 6.9 nm for mechanochemical samples. These results showed that properties of synthesized cerium dioxide could be tailored by adjusting the synthesis conditions.     

Synthesis of nanocrystalline materials through reverse micelles: A versatile methodology for synthesis of complex metal oxides

We have been successful in obtaining monophasic nanosized oxides with varying chemical compositions using the reverse micellar method. Here we describe our methodology to obtain important metal oxides like ceria, zirconia and zinc oxide. The oxalate of cerium, zirconium and zinc were synthesized using the reverse micellar route. While nanorods of zinc oxalate with dimension, 120 nm in diameter and 600 nm in length, could be obtained, whereas spherical particles of size, 4–6 nm, were obtained for cerium oxalate. These precursors were heated to form their respective oxides. Mixture of nanorods and nanoparticles of cerium oxide was obtained. ZrO₂ nanoparticles of 3–4 nm size were obtained by the thermal decomposition of zirconium oxalate precursor. ZnO nanoparticles (55 nm) were obtained by the decomposition of zinc oxalate nanorods. Photoluminescence (PL) studies at 20 K shows the presence of three peaks corresponding to free excitonic emission, free to bound and donor-acceptor transitions. We also synthesized nanoparticles corresponding to Ba_1−x Pb _x ZrO₃ using the reverse micellar route. The dielectric constant and loss were stable with frequency and temperature for the solid solution.     

Investigation of CaLa2S4 powder prepared by sulphurization of coprecipitated carbonates

Factors, including pH, coprecipitating medium, and temperature, for preparing CaLa₂S₄ powder were investigated. The precursors obtained by rapid precipitation in an aqueous solution at 25 °C had a homogeneous morphology of minute dentrites, and showed little or no CaS in the X-ray diffraction (XRD) patterns after sulphurization at 950 °C for 24 h. The particle size of the precursors or sulphides obtained in the vicinity of isoelectric point of pH=7.8 had a broad distribution, while that obtained at pH>9.24 had a narrow distribution. The precursors obtained in hydrous ethanol were a mixture of spherical, flaky and acicular particles in morphology, but all showed calcium deficiency. Interconnected particles were obtained in anhydrous ethanol at pH=6.81 and 25 °C with a highly homogeneous composition. No CaS phase was determined by XRD after sulphurization at 950 °C for 24 h. The CaLa₂S₄ powders obtained in both aqueous and anhydrous ethanol solutions were sintered, and a translucent pellet was obtained.     

Preparation of microstructured hydroxyapatite microspheres using oil in water emulsions

Hydroxyapatite (HAP) microspheres with peculiar spheres-in-sphere morphology were prepared by using oil-in-water emulsions and solvent evaporation technique. Ethylene vinyl acetate co-polymer (EVA) was used as the binder material. Preparation of HAP/EVA microspheres was followed by the thermal debinding and sintering at 1150°C for 3 h to obtain HAP microspheres. Each microsphere of 100–1000 μm was in turn composed of spherical hydroxyapatite granules of 2–15 (μm size which were obtained by spray drying the precipitated HAP. The parameters such as percentage of initial HAP loading, type of stabilizer, concentration of stabilizer, stirring speed and temperature of microsphere preparation were varied to study their effect on the particle size and geometry of the microspheres obtained. It was observed that these parameters do have an effect on the size and shape of the microspheres obtained, which in turn will affect the sintered HAP microstructure. Of the three stabilizers used viz. polyoxyethylene(20) sorbitan monopalmitate (Tween-40), sodium laurate and polyvinyl alcohol (PVA), only PVA with a concentration not less than 0.1 wt% showed controlled stabilization of HAP granules resulting in spherical microspheres of required size. Morphologically better spherical microspheres were obtained at 20°C. Increasing the stirring speed produced smaller microspheres. Smaller microspheres having size < 50 μm were obtained at a stirring speed of 1500 ±50 rpm. A gradual decrease in pore size was observed in the sintered microspheres with increase in HAP loading.     

Preparation of spherical SnO2 particles by W/O type emulsion method

An attempt to prepare spherical particles was made using a W/O type emulsion as a reaction field. The effects of surfactant content, W/O ratio and stirring conditions for the preparation of emulsions, which determined the size of water drops in the emulsions, were investigated on the size and morphology of the obtained SnO₂ particles. The size and morphology of the obtained particles were largely influenced by a water/surfactant molar ratio (R-value) for the preparation of the emulsions. Particles having relatively high sphericity were obtained at an R-value below 1500. In order to obtain mono-sized SnO₂ particles with narrow distributions, R-value should be adjusted to the narrow range from 250 to 500. Spherical SnO₂ particles showing narrow particle size distributions were obtained at W/O ratio of 1/1 and surfactant content of 11.2 × 10^–2 mol/l or 22.4 × 10^–2 mol/l. Furthermore, the particle size and morphology of SnO₂ depended on the revolution rate of an emulsifier for emulsification. Mono-dispersed spherical particles having narrow size distributions formed at revolution rates of 3000 and 4000 rpm. At extremely low and high revolution rate of the emulsifier, particles showing high sphericity were not obtained, but agglomerates of un-spherical fine particles. The interfacial reaction time determined the internal structures of spherical particles. The reaction for short time yielded hollow spherical SnO₂ particles, and the internal structure of the particles became denser with increasing reaction time.     

单分散双功能化复合二氧化硅微球的可控合成

在水溶液中,以硫氰基丙基三乙氧基硅烷(TCPTES)为前驱体,氨水为催化剂,合成了TC-SiO_2聚倍半硅氧烷微球。进一步以TC-SiO_2微球为核,用脲丙基三乙氧基硅烷(UDPTES)在其表面进行溶胶-凝胶反应,制备了TC-SiO_2@U-SiO_2双功能化核壳结构复合微球。通过扫描电子显微镜(SEM)、傅里叶变换红外光谱(FTIR)、热重(TG)对所得微球的形貌、结构及性能进行了表征。实验结果表明,十六烷基三甲基溴化铵(CTAB)的用量和包覆时间对所得双功能化微球TC-SiO_2@U-SiO_2的粒径和形貌有着重要影响。当CTAB为30mg,水、乙醇分别为20mL和7mL,TC-SiO_2球为40mg,氨水为0.3mL,UDPTES为0.6mL时,室温下反应20h,可制得粒径630~690nm且分散性良好的TC-SiO_2@U-SiO_2微球。     

碳酸铅纳米粉体的制备及其表征

在溶液结晶体系中加入适当的添加剂可改变晶体的生长环境,影响晶体的生长、团聚行为,从而得到理想的晶形及晶粒尺寸。本研究在化学沉淀法制备碳酸铅的反应体系中加入适量表面活性剂,通过表面活性剂对晶粒生长和团聚的抑制作用,制备了疏松的碳酸铅纳米粉体。XRD和TEM分析表明,反应体系中加入表面活性剂后,制备的碳酸铅纳米粉体的晶形发生了改变,纳米碳酸铅颗粒呈球形,粒度均匀,为60 nm左右。     

Cobalt nanoparticles prepared by three different methods

This work aimed to study cobalt nanoparticles (Co-NPs) preparation using three different methods in order to evaluate the effect of synthesis variables that can influence the nanoparticle size distribution and particle shape. The synthesised nanoparticles were characterised by Transmission Electron Microscopy. The first synthesis employed decomposition of Co₂(CO)₈, at high temperatures. This procedure resulted in spherical nanoparticles with low size distribution. The size of Co-NPs could be tuned by modification of precursor/surfactant, nevertheless the stirring and injection time influenced the size distribution. Using polyol process, at high temperatures, it was produced undefined-shape nanoparticles. This result suggests that the solution composition, i.e. the amount of trioctylphosphine and oleic acid was not suitable to control both size and shape of nanoparticles. Finally, the method based on reduction with NaBH₄ resulted spherical nanoparticles with tiny sizes, indicating that in this case a variation on amount of reductant would be more efficient on the particle size control than a variation in concentration of oleic acid. These results indicated that, for each method, a different variable exists for the control of the distribution size and the shape of the formed particles.     

Morphology control and luminescent property of Y3Al5O12:Tb particles prepared by spray pyrolysis

A spray pyrolysis process was used to prepare spherical yttrium aluminum garnet (Y₃Al₅O₁₂:Tb) phosphor particles with enhanced luminescence properties. The aim of the process was to improve the morphology and luminescent intensity of the Y₃Al₅O₁₂:Tb phosphor particles by modifying the precursor solution. The particles produced from a nitrate aqueous solution were spherical with a hollow structure that was deformed by the post treatment at 1400 °C. To avoid the hollowness, the nitrate solution was modified by the addition of an NH₄OH solution so that a polycation solution could be obtained. Compared with the hollow particles prepared from the nitrate aqueous solution, the Y₃Al₅O₁₂:Tb particles with the spherical morphology and nonaggregated structure, even after the post treatment, were successfully prepared and found to have an improved photoluminescence and cathodoluminescence intensity.     

Synthesis of zeolite NaA at room temperature: The effect of synthesis parameters on crystal size and its size distribution

Zeolite NaA crystals were prepared by hydrothermal synthesis under room-temperature conditions. The products were characterized by XRD, SEM, IR and particle size analysis. Some influence parameters such as crystallization time, aging time, stirring speed, different sources of silicon and aluminum on the crystalline end products were studied. The results showed that crystallization time was a crucial factor for the final products, well-shaped crystals could be obtained at the crystallization time of 72 h. While further prolonging the crystallization time more, crystals continued to grow, along with the changes of crystal size distributions. The crystals obtained with the aging time of 1, 1.5, 2 and 3 h show the mean particle sizes of 368, 356, 338 and 314 nm, with the crystal size distribution ranges of 82–435, 70–441, 54–450 and 40–476 nm, respectively. Longer aging time leads to the mean particle size of crystal decrease. Whilst, the stirring speed affects the particle size distribution only slightly. Moreover, the aluminum source has much more obviously influence on the crystal phase of final product than the silicon source does in this system.     

Effect of fuel type on the aminolysis synthesis of CrN powders from combustion synthesis precursors

CrN nanopowders were synthesized by the aminolysis method by using the low temperature combustion synthesis (LCS) precursor derived from the mixed solution of chromium nitrate and alanine, or urea, or glycine, or citric acid. Effects of fuel type on the particle size and morphology of precursors and their corresponding aminolysis powders were studied in detail. It was found that the use of different types of fuel in solution, had a significant effect on the particle size and morphology of precursors and their corresponding aminolysis powders. Moreover, the optimized fuel type (glycine) yielded the precursor with high specific surface area and reactivity. The characteristics of aminolysis powders were found similar to those of their corresponding precursor. The CrN powders derived from glycine and synthesized at 750?°C for 6?h were comprised of well-distributed spherical particles, exhibiting high specific surface area (32.5?m²/g) with an average size of 30–50?nm.     

Highly (100)-oriented CeO2 films prepared on amorphous substrates by laser chemical vapor deposition

CeO₂ films were prepared on amorphous silica substrates by laser chemical vapor deposition using cerium dipivaloylmethanate precursor and a semiconductor InGaAlAs (808 nm in wavelength) laser system. The laser spot size was about 20 mm, which was sufficient to cover the whole substrate. Highly (100)-oriented CeO₂ films were obtained at extraordinary high deposition rates ranging from 60 to 132 μm/h. Films exhibited a columnar feather-like structure with a large number of nano-sized voids, and a surface morphology consisting of either nearly flat or pyramidal top-ending columns depending on the laser power. Nearly flat top-ending columns could be fairly (100)-oriented at the top and (111)-oriented laterally.     

Nano-precipitate and its aging behavior in a B2-NiAl strengthened ferritic ODS alloy

The effect of aging on a mechanical alloyed (MA) ferritic oxide dispersion strengthened (ODS) alloy was investigated focusing on the B2-NiAl nano-precipitates. The matrix of the alloy is decorated with a high volume fraction of B2-NiAl precipitates and dispersed nano-oxide particles. Due to the coarsening effect of Al on oxides and the changed Zener drag effect on grain growth, the bimodal grain structure was formed. With the extension of the aging time, the size of nano-precipitate increases and its morphology changed from near spherical to rodlike. The temporal evolution of nano-precipitates upon aging treatment is consistent with the modified Lifshitz–Slyozov–Wangner (LSW) theory. In addition, the quantitative calculation reveals the weakening effect caused by nano-precipitates coarsening during aging is the main reason for the decrease in alloy strength.

     

单分散球形MoS2超细粉体材料的制备

采用液相沉淀-高温氢还原两步合成新方法制备单分散球形MoS2超细粉体材料,利用透射能谱、X射线衍射仪(XRD)、冷场扫描电子显微镜(SEM)和马尔文激光粒度仪等研究了反应条件对产物化学组成、晶型的影响以及酸浓度、熟化时间和反应温度对前驱体MoS3平均粒径的影响.研究结果表明:反应条件对 前驱体MoS3的晶型没有影响;M...     

中孔炭的水玻璃模板法制备、结构调控及球形功能化

以廉价水玻璃为原料, 通过控制水解条件, 合成出具有不同尺寸的SiO₂溶胶, 并与间苯二酚-甲醛(RF)溶胶形成均相的凝胶复合物, 经常压干燥、炭化、酸洗, 得到具有可控结构的中孔炭材料。考察了水解温度、水解时间和反应物组成对孔结构的影响, 并通过氮气吸附、扫描电镜和透射电镜对材料的微观结构进行了表征。结果表明: 中孔炭的孔隙反相复制于SiO₂凝胶网络, 其平均孔径随水解时间的延长或水解温度的升高而增大, 并在6~12 nm范围内精细调控, 而其总孔隙率可以通过改变炭、SiO₂前驱体比例调节。对液相复合溶胶通过悬浮聚合法和喷雾干燥法处理, 分别制备出毫米级和微米级的中孔炭球, 进而实现了中孔炭在宏观形貌上的调控。本工作为中孔炭的低成本制备、精细结构调控以及球形功能化提供了重要参考。