Estimation of formation mechanism of spherical fine ZrO2-SiO2 particles by ultrasonic spray pyrolysis

Spherical fine ZrO₂-SiO₂ (11) particles were synthesized from a hydrolysed mix-solution of Si(OC₂H₅)₄ and ZrOCI₂ · 8H₂O by ultrasonic spray pyrolysis, and the formation mechanism of the particles discussed. All of the resultant particles identified as t-ZrO₂ and amorphous SiO₂ with an atomic order dispersion were spherical, and mainly of diameter 0.8 to 1.0m. It was estimated that the three-dimensional ladder siloxane chains containing an equimolar Zr⁴⁺ homogeneously dispersed were formed by hydrolysis, and an atomized droplet itself converted into an isolated ZrO₂-SiO₂ (11) particle without aggregation.     

超声喷雾热解法制备ZnO薄膜及性能研究

以醋酸锌水溶液为前驱体溶液,使用自制的超声喷雾热解系统在玻璃基板上制备得到了ZnO薄膜.经X射线衍射(XRD),扫描电镜(SEM)分析得到ZnO薄膜的晶体结构和微观形貌.测试结果表明,ZnO薄膜为六角纤锌矿结构,在450～500℃下制备的薄膜显示出良好的结晶性能,并且沿(002)晶面择优取向生长,薄膜具有优良的均匀性和致密性.同时,制备得到的薄膜在可见光区也表现出80%以上的高透过率.     

Preparation of dense spherical Ni particles and hollow NiO particles by spray pyrolysis

Dense spherical Ni particles were prepared from nitrate solution by spray pyrolysis in a H2–N2 atmosphere. Hollow NiO particles with rough surfaces were formed first at low temperature and then reduced to Ni by H2 above 300°C. Subsequent intraparticle sintering of the Ni crystallites gave rise to densification of Ni particles as the temperature was raised; most Ni particles became dense above the pyrolysis temperature of 1000°C. However, when a N2 atmosphere was used, hollow NiO particles were formed, which did not densify even at 1200°C due to the lack of sintering. The dense Ni particles obtained were of good crystallinity and good oxidation resistance, especially for those formed at higher pyrolysis temperatures and longer residence times.     

Characterization of submicro-sized Ag/ZnO particles generated using the spray pyrolysis method

Environmental issues caused by the rapid industrialization and urbanization of modern society are a serious problem. For example, conventional wastewater treatment technologies such as adsorption, coagulation, and filtration are expensive and cannot completely treat the discharge of organic pollutants in industrial wastewater. A promising alternative is the decomposition treatment of organic pollutants using an eco-friendly metal oxide photocatalyst. However, the rapid recombination of excited electron-holes limits the photolytic activity of semiconductor photocatalysts. This study investigates the inhibition of electron-hole recombination by supporting Ag nanoparticles on a ZnO photocatalyst. Ag/ZnO particles are generated under various conditions using ultrasonic spray pyrolysis. XRD analysis confirms the presence of Ag and ZnO crystal peaks in the generated particles. EDX mapping and STEM images show that Ag nanoparticles are well dispersed in ZnO. The photolysis rate of organic dye (rhodamine-B) is faster than that of ZnO in all Ag/ZnO particles, and particles with a 0.2 mass% silver nitrate supported on ZnO particles exhibit twice the photolysis activity of P25. Additionally, the optimal photolysis activity in 100 mL of 5 mg/L rhodamine-B aqueous solution with 10 mg of Ag/ZnO particles are confirmed and had excellent persistence and stability even during 7 reuses.     

Growth of thin ZnO films by ultrasonic spray pyrolysis

We report the growth of high-quality thin ZnO films with controlled microstructure on Si(111) substrates by ultrasonic spray pyrolysis of Zn-containing solutions.     

Preparation of spherical Zr0.8Sn0.2TiO4 powder by ultrasonic spray pyrolysis

Fine, spherical Zr_0.8Sn_0.2Tio₄ powders were prepared by spray pyrolysis, using an ultrasonic transducer, from an aqueous solution of metal chlorides. The synthesized powders had a spherical morphology and many shell fragments. The observed shell fragments were attributed to the impermeable surface crust formed during thermal decomposition of the droplets. The raw materials for the preparation of Zr_0.8Sn_0.2TiO₄ were analysed prior to any treatments because the properties of the surface crust could be related to those of the raw materials. ZrOCl₂·8H₂O was supposed to affect the shell fragments as well. Spherical Zr_0.8Sn_0.2TiO₄ powders without shell fragments could be prepared using ZrO(CH₃COO)₂ in place of ZrOCl₂·8H₂O.     

Synthesis of mullite nanostructured spherical powder by ultrasonic spray pyrolysis

In this paper the synthesis of nanostructured spherical particles of mullite powders by ultrasonic spray pyrolysis is presented. The mullite crystallization and the nanostructure development during heating were examined by infrared spectroscopy, X-ray diffraction, scanning and transmission electron microscope analysis. Comparative analysis of experimentally determined and theoretically calculated particle size distribution, obtained on the basis of three-dimensional (3D) model of spherical/ellipsoidal waves generated by incident ultrasonic field, confirmed that the process of aerosol/powder particle synthesis can be regarded as deterministic process.     

Synthesis of nanosized spherical cobalt powder by ultrasonic spray pyrolysis

The ultrasonic spray pyrolysis (USP) method has been used to prepare nanosized powders of metallic, intermetallic compounds and ceramic materials. Spherical nanosized cobalt powders were obtained by USP of aqueous solutions of cobalt nitrate followed by thermal decomposition of generated aerosols in hydrogen atmosphere. Particle sizes of the produced cobalt powder can be controlled by the change of the concentration of an initial solution. Non-agglomerated spherical nanosized cobalt particles in the range of 158–1001 nm were obtained at 800 °C. A decrease of the concentration of cobalt nitrate decreases the mean particle diameter from 596 to 480 nm. The discrepancy between the experimentally and theoretically obtained values indicates that the partial coalescence of the droplets occur during the formation of aerosol.     

Modification of titania particles by ultrasonic spray pyrolysis of colloid

Composite fine particles such as ZnO-TiO₂, CdS-TiO₂, ZnS-TiO₂ and Ag-TiO₂ were prepared by ultrasonic spray pyrolysis of metal salt aqueous solution in which TiO₂ (Degussa P25) particles were suspended. The crystallinity, chemical compositions, and morphologies of the produced particles were investigated by XRD, centrifugal particle size analyzer, and SEM/EDAX. The photocatalytic activity of the modified particles was investigated for the decomposition of trichloroethylene (TCE). The prepared particles were micro-porous and had spherical shapes of 0.3–1.5 m in diameter. The size and size distribution of the prepared particles were not significantly changed by the type and loading of modifier. The crystallinity and crystallite size of TiO₂ was not changed by these modifications. The photocatalytic activities of modified particles was slightly higher than pure titania when the loading was low. However, as the loading was further increased, the photocatalytic activity was sharply decreased and became almost constant.     

Preparation of spherical Pb(Zr,Ti)O3 powders by ultrasonic spray pyrolysis

Spherical Pb(Zr,Ti)O₃ powders were prepared from the aqueous acetate-base solution by ultrasonic spray pyrolysis. The raw materials were Pb(C₂H₃O₂)-3H₂O, ZrO(C₂H₃O₂)₂ and a mixture of Ti(C₃H₇O)₄ and C₅H₇O₂. A single-phase PZT was formed at 900 C in air and at 700 C in O₂ atmosphere. The PbTiO₃ phase, as an intermediate product, was observed in the formation of PZT and no PbZrO₃ phase was detected under our experimental conditions. The intensity of the PbTiO₃ peak decreased with increasing reaction temperature in air, while the reverse effect of reaction temperature was observed in O₂. Spherical and irregular-shaped particles coexisted in the powder containing the minor PbTiO₃ phase, while the particles of a single-phase PZT have spherical morphology with little evidence of irregular-shaped particle formation.     

Synthesis and sintering of barium titanate fine powders by ultrasonic spray pyrolysis

Crystalline, spherical barium titanate fine powders with a narrow particle size distribution were prepared by ultrasonic spray pyrolysis. The stability of the starting solution was influenced by type of barium source and peptizer. The particle structure was influenced by the pyrolysis temperature of the barium source. The particle structure derived from barium acetate was dense, while powders derived from barium nitrate involved a lot of hollow particles. As-prepared powders were crystallized to a perovskite structure. Inductively coupled plasma analysis showed that the BaO/TiO₂ molar ratio of as-prepared powders was 50.5:49.5. The effects of the concentration of the starting fluid, pyrolysis temperature and flow rate of carrier air through the furnace on powder characteristics such as particle size, size distribution and crystal phase were investigated. The particle size depended on the concentration of starting solution and the flow rate of carrier air, but the particle size distribution was independent of these variables. Single-phase BaTiO₃ was obtained at more than 700°C. The relative density of barium titanate sintered at 1200°C was 98%. The hollow particles in the powders resulted in a low sintering density and a large grain size. The dielectric constant and tan δ of barium titanate at 25°C were 4500 and 0.02, respectively.     

Preparation of spherical TiO2/SnO2 powders by ultrasonic spray pyrolysis and its spinodal decomposition

Spherical TiO₂/SnO₂ powders were prepared from the TiCl₄-SnCl₄ aqueous solution by ultrasonic spray pyrolysis. The particle size, particle-size distribution and morphology of the powders were studied in relation to concentration of source solutions and reaction temperatures. The width of the compositional undulation induced by spinodal decomposition in the sintered bodies increased with increasing starting particle sizes, which resulted from micro-compositional heterogeneity in the form of a solid solution within a TiO₂/SnO₂ secondary sphere.     

Synthesis of optical quality ZnO nanowires utilizing ultrasonic spray pyrolysis

ZnO nanowires were grown by an ultrasonic spray pyrolysis technique. The aspect ratio and size of the wire were dependent mainly on the pH value of a precursor solution and the growth temperature. By high-resolution transmission electron microscopic analysis and photoluminescence measurements, it was confirmed that the nanowires are monocrystalline with good optical quality.     

Synthesis and formation mechanism of submicrometre spherical cordierite powders by ultrasonic spray pyrolysis

Cordierite powders containing very pure submicrometre spherical particles have been synthesized by the ultrasonic spray pyrolysis. Aqueous solutions of silicic acid, Al(NO3)3·9H2O and MgCl2·6H2O were used as precursors. Scanning electron micrographs have shown that particle surfaces were smooth and the mean particle diameter was 0.834 m. For the estimation of chemical and phase composition and phase transformation temperatures, differential thermal analysis, thermogravimetric analysis, X-ray diffraction, energy dispersive spectroscopy and infrared analysis have been applied. It was found that during spray pyrolysis, the condensation of silicic acid mostly occurred while aluminium and magnesium ion remained incorported between Si–O–Si chains. By subsequent heating to over 800°C, Si–O–M bonds (M=Al, Mg) were formed. The synthesis of cordierite occurred by the crystallization of -cordierite from the amorphous phase at 900°C followed by the phase transformation of - into -cordierite in the temperature range 1100–1200°C.     

Synthesis of submicron carbon spheres by the ultrasonic spray pyrolysis method

Submicron carbon spherical particles were obtained by polycondensation of resorcinol and formaldehyde in a solution and subsequent ultrasonic spray pyrolysis of the prepared sol. Microscopic characterization indicates the regular spherical shape of the obtained particles and sphere diameters in 200-700 nm range. The carbon spheres are amorphous as confirmed by electron diffraction, EELS, XRD and HREM characterization. Activation procedure was performed with H₂O in a nitrogen flow for 15 and 30 min at 800 °C. The activation procedure preserved the initial spherical shapes of the particles while the particle porosity and specific surface area were increased. The amount of surface oxygen functionalities was also increased by activation procedure as indicated by FTIR analysis.     

Preparation of ceria films by spray pyrolysis method

The deposition of CeO₂ films on fused-silica substrates by spray pyrolysis of a water–ethanol solution of a cerium nitrate precursor has been studied. Polycrystalline films have been obtained at a substrate temperature of 300–450°C after annealing of the deposit in air at temperatures in the range 350–500°C. It has been established that the best uniform ceria films with nanometric scale grains are prepared at a substrate temperature of 400°C with 0.5 h annealing of the deposit at 500°C. At lower spraying temperatures large CeO₂ crystallites have been observed on the film surface along with the fine grains. When the substrate temperature exceeds 400°C, numerous cracks caused by thermal stresses appear in the films.     

Evaluation of photocatalysis of Au supported ZnO prepared by the spray pyrolysis method

Environmental pollution by organic dyes used in industry is a serious problem in developing countries. Environmentally friendly treatment methods are being studied because conventional methods require chemical or additional decomposition treatment. In particular, oxidation via a photocatalyst is a promising alternative due to its chemical and physical stabilities and low cost. However, electron-hole recombination limits the photocatalytic activity in semiconductor photocatalysts such as ZnO and TiO₂. This study investigates control of electron-hole recombination of the photocatalyst by loading Au on ZnO (Au/ZnO). Using the Ultrasonic Spray Pyrolysis (USP) method, Au/ZnO particle generation is easily achieved under various conditions. XRD analysis confirms the crystal peaks of ZnO and Au. The EDX mapping and STEM images of the particles show that the Au crystals are well dispersed in the inner and outer portions of ZnO. The photocatalytic decomposition rate of organic dye (Rhodamine-B) is faster than that of ZnO in all Au/ZnO particles, and the best photocatalytic activity occurs in particles with 0.1 mass% Au supported on ZnO particles. In addition, optimal photolysis activity occurs in 100 mL of 5 mg/L RhB aqueous solution and 10 mg dose of Au/ZnO particles.