Fine-sized LiCoO2 particles prepared by spray pyrolysis from polymeric precursor solution

Fine-sized LiCoO₂ particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from a spray solution with citric acid and ethylene glycol. The precursor particles obtained from the spray solution with citric acid and ethylene glycol transformed into fine-sized LiCoO₂ particles with regular morphology after post-treatment at temperatures between 700 and 900 °C. The mean size and aggregation degree of the primary particles were affected by the concentrations of polymeric precursors added into spray solutions. The LiCoO₂ particles obtained from the spray solution without polymeric precursors had irregular and aggregated morphology. The discharge capacities of the LiCoO₂ particles changed from 132 to 151 mAh/g when the concentrations of the citric acid and ethylene glycol changed from 0 to 1 M. The particles prepared from the spray solution containing 0.3 M each of citric acid and ethylene glycol had the maximum discharge intensity.     

Morphologies and crystal structures of nano-sized Ba1−xSrxTiO3 primary particles prepared by flame spray pyrolysis

Nano-sized Ba_1−xSr_xTiO₃ (BST) powder was prepared by flame spray pyrolysis using “CA-assisted” spray solution. The effects of the mole ratios of Ba to Sr components on the mean sizes, morphologies, and crystal structures of the BST powder prepared by flame spray pyrolysis were investigated. The precursor powders obtained by flame spray pyrolysis had large size, fractured and hollow structures irrespective of the mole ratios of Ba to Sr components. The post-treated BST powders had slightly aggregated morphology of the primary particles with nanometer sizes. The slightly aggregated BST powders turned to nano-sized primary particles by a simple milling process. The milled BaTiO₃ particles post-treated at temperature of 1000 °C had spherical-like shape. On the other hand, the milled Ba_0.5Sr_0.5TiO₃ and SrTiO₃ particles had square shape. The mean sizes of the milled BaTiO₃, Ba_0.5Sr_0.5TiO₃ and SrTiO₃ particles were each 110, 32, and 48 nm. Phase pure BST powder was obtained at a post-treatment temperature of 1000 °C irrespective of the mole ratios of Ba to Sr components. The BaTiO₃ powder had tetragonal crystal structure. On the other hand, the BST except for the BaTiO₃ composition had cubic crystal structures at post-treatment temperature of 1000 °C. The mean crystallite sizes of the milled Ba_1−xSr_xTiO₃ primary particles were changed from 29 to 37 nm according to the mole ratios of Ba to Sr components.     

Direct synthesis of strontium titanate phosphor particles with high luminescence by flame spray pyrolysis

SrTiO₃:Pr, Al phosphor particles with high luminescence intensities were directly prepared by flame spray pyrolysis without post-treatment. They had better crystallinity than those prepared by general spray pyrolysis with post-treatment and solid-state reaction methods. In addition, they had complete spherical shape and narrow size distribution. On the other hand, the particles prepared by general spray pyrolysis had irregular shape, and poorer brightness than those prepared by solid-state reaction method, while the particles prepared by flame spray pyrolysis had comparable photoluminescence and cathodoluminescence intensities with those of particles prepared by solid-state reaction method. The photoluminescence intensity of SrTiO₃:Pr, Al particles prepared by flame spray pyrolysis was as much as 4.7 times higher than that of particles prepared by general spray pyrolysis.     

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.     

Preparation of size-controlled tungsten oxide nanoparticles and evaluation of their adsorption performance

The present study investigated the effects of particle size on the adsorption performance of tungsten oxide nanoparticles. Nanoparticles 18-73 nm in diameter were prepared by evaporation of bulk tungsten oxide particles using a flame spray process. Annealing plasma-made tungsten oxide nanoparticles produced particles with diameters of 7-19 nm. The mechanism of nanoparticle formation for each synthetic route was examined. The low-cost, solid-fed flame process readily produced highly crystalline tungsten oxide nanoparticles with controllable size and a remarkably high adsorption capability. These nanoparticles are comparable to those prepared using the more expensive plasma process.     

Gd2O3:Eu phosphor powders prepared using a size-controllable droplet generator

Gd₂O₃:Eu phosphor powders were prepared by a filter expansion aerosol generator (FEAG) process capable of changing the mean size of droplets. The change in the mean size of the Gd₂O₃:Eu phosphor powders according to the concentrations of polyethylene glycol added to spray solutions was caused by the difference in the mean size of the droplets produced via the FEAG process. The mean sizes of droplets produced by the FEAG process were affected by the surface tension and viscosity of the spray solutions. The mean sizes of the Gd₂O₃:Eu phosphor powders obtained from the spray solutions with the same concentration of metal salts changed from 1.5 to 4.2 μm according to the concentrations of polyethylene glycol and citric acid added to the spray solutions. The maximum photoluminescent intensity of the phosphor powders obtained from the spray solutions with polymeric precursors and boric acid flux was 144% of that of the phosphor powders obtained from the aqueous spray solutions without flux.     

Y3Al5O12:Tb phosphor particles prepared by spray pyrolysis from spray solution with polymeric precursors and ammonium fluoride flux

High brightness Y₃Al₅O₁₂:Tb phosphor particles with spherical shape and fine size were prepared by spray pyrolysis from spray solution with polymeric precursors and ammonium fluoride flux. The effect of ammonium fluoride flux on the characteristics of the Y₃Al₅O₁₂:Tb phosphor particles prepared by spray pyrolysis was investigated. Ammonium fluoride flux dissolved into spray solution improved the photoluminescence intensity of the Y₃Al₅O₁₂:Tb phosphor particles prepared by spray pyrolysis. The optimum addition amount of ammonium fluoride flux to produce the maximum photoluminescence intensity was 1 wt.% of the Y₃Al₅O₁₂:Tb phosphor particles. The spherical shape of the as-prepared particles obtained by spray pyrolysis from spray solution with polymeric precursors and small amount of ammonium fluoride flux had maintained after post-treatment below 1300 °C. The optimum photoluminescence intensity of the Y₃Al₅O₁₂:Tb phosphor particles prepared from polymeric precursors and ammonium fluoride flux was 156% of that of the phosphor particles prepared from pure aqueous solution.     

Size-controlled synthesis of alumina nanoparticles from aluminum alkoxides

Aluminum oxide nanoparticles were prepared by the hydrolysis of aluminum oxide alkoxides followed by calcinations, in the presence of surface stabilizing agents, such as Na(AOT) molecules. The size of alumina precursors (bohemite) was 20-30 nm, yielding aluminum oxide particles with an average size of 80 nm after calcinations at 1200 °C. The shape of the α-alumina nanoparticles was mainly spherical and the high temperature inhibited the formation of the hexagonal crystals. The introduction of Na(AOT) during the appropriate processing step, had the effect of controlling the size of the particles, the degree of aggregation and the particles shapes.     

Controllable fabrication of various ZnO micro/nanostructures from a wire-like Zn-EG-AC precursor via a facile solution-based route

In this paper, ZnO particles with various morphologies were prepared though a facile solution-based route. The complexes Zn-EG-AC (EG: ethylene glycol; AC: CH₃COO⁻ groups) obtained by reaction of anhydrous zinc acetate and EG were used as precursors. It is found that the precursor could transform into ZnO in water with no need of assistant of additional alkali as it is sensitive to water. At the same time, it is well dispersed in reaction medium (water and ethanol). Experimental results showed that ZnO particles with various morphologies, such as the hexagonal rings, the hexagonal plates, the tubes, the prisms, and some interesting hierarchical structures, could be obtained by controlling hydrolysis of precursor in water and water/ethanol medium through finely tuning the experimental parameters. The success of shape-controllable fabrication was related intimately with the Zn-EG-AC precursor used in our synthesis.     

Effect of preparation temperature on the characteristics of Eu-doped borate phosphor particles in the spray pyrolysis

Eu-doped gadolinium borate (GdBO₃:Eu) phosphor particles with fine size and uniform morphology were prepared by spray pyrolysis. The effects of the preparation temperatures on the characteristics of the GdBO₃:Eu phosphor particles prepared by spray pyrolysis were analyzed. The precursor particles obtained at preparation temperatures below 1400 °C had hollow and porous inner structures. On the other hand, the precursor particles obtained at preparation temperature of 1600 °C had dense structure and uniform morphologies. The precursor particles with glass phases were formed at high-preparation temperatures above 1400 °C. The precursor particles prepared at preparation temperature of 1400 °C turned into GdBO₃:Eu phosphor particles with fine size and regular morphology after post-treatment. The GdBO₃:Eu phosphor particles prepared from the precursor particles obtained at a preparation temperature of 1400 °C had the maximum photoluminescence intensity, which was similar to that of the commercial (Y,Gd)BO₃:Eu phosphor particles.     

Floating combustion synthesis of spherical vitreous silica nano-powder

Vitreous silica nano-powder, with spherical particles of 50-300 nm in size, was successfully produced via floating combustion synthesis. Mechano-chemically activated and spray-dried Si-powder was oxidized in fluidized bed between 900 °C and 1550 °C in air. After 10 min, rapid removal of powder from the furnace and quenching maintained silica's vitreous nature. The process comprises sequential cycles of the following stages until nano-sized particles of silica are obtained. Superficial melting of Si-particles initially occurs and the particles obtain a spherical shape. The surface of the particles is oxidized. The stress at silica/silicon interface causes collapse of particles to smaller ones.     

Hydrogen evolution from aqueous methanol solution on mesoporous titania prepared by a process combining evaporation induced self-assembly and spray pyrolysis

Mesoporous TiO₂ powders were prepared in 1 min from an aqueous mixture of chelated complex titanium precursor and tri-block copolymer by using a process combining evaporation induced self-assembly (EISA) and spray pyrolysis. Photocatalytic activity was evaluated by measuring the rate of hydrogen evolution from methanol solution. The prepared powders were mainly anatase phase and had worm-like pores. Crystallite size was in the range from 7.8 to 18.6 nm in diameter. The mesoporous TiO₂ powders calcined at 823 K had surface area of 144 m² g⁻¹ and high pore volume of 0.33 cm³ g⁻¹. Pore size distribution was also narrow. In addition, it had high light absorption intensity below 350 nm. The rate of hydrogen evolution was by a factor of six higher than the rate measured with commercial nano-sized TiO₂ powder (Degussa P-25). Unique structural and optical properties, which were mainly originated from our new combined process of EISA and spray pyrolysis, contributed to the enhanced rate of hydrogen evolution.     

Preparation and characterization of CdS hollow spheres

CdS hollow spherical particles with average diameter of 800 and 850 nm have been prepared using core/shell fabrication method with poly-(styrene-acrylic acid) (PSA) latex particles as template. TEM images show that smoothly coated core/shell composite particles have been fabricated by multicycles of coating in optimum concentration of reactants. CdS hollow spheres were obtained after removing the template by dissolving the polymer in the organic solvent, and the wall thickness is about 40-100 nm.     

有机前驱体法BN纤维的制备和表征

以聚合环硼氮烷前驱体(PBN)为原料, 通过熔融纺丝、不熔化处理、高温热解陶瓷化等工艺制备了BN中空陶瓷纤维. 利用XRD、SEM、TEM等对BN中空纤维的物相、结构和形貌进行了分析和表征, 同时测量了BN中空纤维的抗氧化性能及介电性能. 研究表明, 升温速率和热解温度是影响BN中空纤维的结构及介电性能的重要因素. 在优化工艺条件下, 制备BN中空纤维介电性能优异, 介电常数ε′和介电损耗正切值tanδ分别小于3.30和0.00064(室温, 7~18 GHz), 在氧化气氛中的使用温度高达950℃.     

Preparation of nanometre size oxide particles using filter expansion aerosol generator

Crystalline zinc oxide particles of nanometre size (< 20 nm) particles were produced from a zinc acetate solution by using a filter expansion aerosol generator (FEAG). The FEAG is an aerosol generator that is operated at 60 torr reactor pressure and produces droplets of around 2 m. The shape of the particles produced by the FEAG were distinctively different from those produced by the ultrasonic spray source (USS). Results from scanning electron microscopy (SEM) and X-ray diffractometry (XRD) indicated that crystalline zinc oxide particles of nanometre size were produced at 600 °C in 0.02 s residence time. Weight loss of these particles, determined by thermogravimetric analysis (TGA), was 3 wt%. Based on the morphology change as a function of the reactor temperature and solute concentration, we proposed that the nanometre particles were formed by uniform precipitation at the drying stage and decomposition followed by disintegration into nanometre particles. It was also shown that exothermic decomposition of the solute was not required for the disintegration of the primary particles in the FEAG process. This result opened up an opportunity for producing carbon-free nanometre particles from nitrate salts by using the FEAG.     

Preparation of CaO as OLED getter material through control of crystal growth of CaCO3 by block copolymers in aqueous solution

As the starting materials of organic light-emitting diode (OLED) getter, calcium carbonate (CaCO₃) particles with various shapes and crystal structures have been successfully prepared with additives (L64 or PEGPG), which contain blocks of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO). These CaCO₃ particles were calcinated into highly crystalline calcium oxide (CaO) nanoparticles with high capacity of water adsorption up to 14.23 wt.%. The CaCO₃ and CaO particles prepared at various conditions were characterized using the field emission scanning electron microscopy (FE-SEM), Fourier transform infrared microscopy (FT-IR), X-ray powder diffraction (XRD), and dynamic vapor sorption (DVS) method.     

Effects of the size of nano-copper catalysts and reaction temperature on the morphology of carbon fibers

In this study, carbon fibers with different morphologies, including coiled carbon nanofibers and straight carbon fibers, were obtained by the chemical vapor deposition using a Cu-catalytic pyrolysis of acetylene at 250 °C. The influences of nano-copper catalyst particle size and the reaction temperature on the morphology of carbon fibers were investigated. Under the same reaction condition, coiled carbon nanofibers generally were synthesized using nano-copper catalyst with smaller particles size, and bigger copper particles are apt to produce straight carbon fibers. With decreasing of reaction temperature to 200 °C, straight carbon fibers were obtained, instead of coiled carbon nanofibers at 250 °C. The product was characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and X-ray powder diffraction (XRD).     

Phase content and particle morphology of Bi-Mo-V-O powders produced by aerosol pyrolysis

Aerosol pyrolysis was utilized to synthesize spherical submicron Bi-Mo-V-O powders over a wide range of reactor temperatures (500-1000 °C) and elemental compositions. Evaporative loss of Mo from particles was significant at temperatures of 800 °C or higher; however, this could be compensated by adjustment of the solution composition. The crystalline phase content for powders produced at 800 °C over a wide range of compositions was largely consistent with previously reported binary oxide and ternary solid solution phases. Powder colors ranged from bright yellow to reddish or greenish yellow, and were characterized by the Munsell color parameters. Particle morphology ranged from spherical to faceted and partially hollow particles, and could be largely explained by proximity to the composition-dependent solidus or liquidus temperature. Particle morphology and phase content can also be influenced by the addition of ethanol to the precursor solution.     

Morphologies and properties of NiO particles prepared from NiSO<Subscript>4</Subscript>·6H<Subscript>2</Subscript>O and Ni(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O by spray pyrolysis

Nickel oxide particles were prepared by spray pyrolysis of aqueous solutions of NiSO₄·6H₂O and Ni(NO₃)₂·6H₂O. In spray pyrolysis reactor hollow salt particles initially formed were collapsed by decomposition to reduce their size. For NiSO₄·6H₂O less hollowness of the primitive particles and its higher decomposition temperature made the oxide particles highly spherical with very smooth surface. On the other hand the particles prepared from Ni(NO₃)₂·6H₂O were so hollow and fragile with rough surface since they were formed on the liquid pool of the salt melt. The particle size decreased with the furnace set temperature while increased with the initial salt concentration. Single oxide particle was composed of many small nuclei without sintering whose size varied with the rate of decomposition. The crystallinity of the particles increased with both temperature and the initial salt concentration. Preliminary drying in diffusion dryer fixed the size of the oxide particles from NiSO₄·6H₂O at that of the primitive particles, independent of the temperature. However, by the preliminary drying the particles from Ni(NO₃)₂·6H₂O became more hollow and fragile, whose sizes decreased with the temperature.     

Characteristics of Eu-doped Ca-α-SiAlON phosphor powders prepared by spray pyrolysis process

Eu²⁺-doped Ca-α-SiAlON phosphor powders with fine size and regular morphology were prepared by combining spray pyrolysis and the carbothermal reduction and nitridation processes. The precursor powders were prepared by spray pyrolysis from the spray solution with ethylenediaminetetraacetic acid, citric acid, and sucrose; they had large sizes, were hollow, and had thin wall structures. The precursor powders containing a carbon component turned into Ca-α-SiAlON phosphor powders after firing at 1450 °C under a H₂/N₂ mixture gas. The mean size of the phosphor powders was 5.1 μm. The phosphor powders had a broad excitation spectra range of 250-500 nm; this consisted of two broadbands centered at 305 and 400 nm. When excited by a 455-nm blue light, the emission spectra of the phosphor powders displayed a broadband in the range of 500-700 nm, which resulted in a yellow emission. The wavelength of the emission spectrum showing the maximum intensity was 576 nm.