Monolayer dispersion of oxide additives on SnO2 and their promoting effects on thermal stability of SnO2 ultrafine particles

The dispersion behavior of some oxides on the surface of SnO₂ and the effects on the thermal stability of SnO₂ have been studied. The results show that many oxides such as NiO, CuO, ZnO, Bi₂O₃, MoO₃, Cr₂O₃ and Sb₂O₃ can disperse onto the surface of SnO₂ by impregnation method or dry method—mixing a compound with the support thoroughly, followed by calcination at an appropriate temperature. The utmost dispersion capacities of these oxides on the surface of SnO₂ are measured and they are all in good agreement with those estimated by a close-packed monolayer model. These oxides dispersed on the surface of SnO₂ can retard the decrease in the specific surface areas of the samples and the increase in the crystallite size of SnO₂ during calcination. In numerous effect factors, the surface coverage is a key factor. It is easy to stabilize the size of SnO₂ grains to be 6 nm by this means, and the higher the valence of the cation of oxide, the stronger the stabilizing effects.     

超声雾化热分解法制备超细SnO2粉体及其形貌和粒度控制

以SnCl4·5H2O为原料,采用喷雾热分解法制备超细SnO2粉体,结果表明,通过控制反应炉温、前驱体溶液浓度、载气流量,选择合适的添加剂可以有效调控粉体的粒度与形貌.当反应条件为温度600℃、前驱体盐溶液浓度0.4mol/L、载气流量124L/h和柠檬酸浓度0.004mol/L,得到的SnO2颗粒大小在1.4μm左右,粒度分布均匀,结晶度高,球形度好.     

On the thermal stability of pure and doped SnO2 ultrafine particles

Pure and doped SnO₂ ultrafine particles were prepared by thermal decomposition of nitrates, then samples were heated at various temperatures. The results indicated that Li₂O helped the growth of SnO₂ particles; NiO had no significant influence; Fe₂O₃ (below 600°C, Al₂O₃, Cr₂O₃, ZrO₂ (below 800°C) hindered the growth of SnO₂ particles. At higher temperature, as the impurity phases crystallized, they no longer held back the growth of SnO₂ particles.     

Microstructure development in SnO2 with and without additives

The microstructure development in pure and ZnO-, Nb₂O₅- or (ZnO + Nb₂O₅)-containing SnO₂ has been studied. Sintering of pure SnO₂ proceeds by an evaporation-condensation mechanism and grain and pore sizes increase without densification. The pores are open with no closed pores developed. Grain and pore structures become homogeneous with sintering time. Sintered pure SnO₂ is porous and has large grains. Nb₂O₅ suppresses particle coarsening and pore growth but does not promote densification, leading to porous sintered bodies with small grains. ZnO and (ZnO + Nb₂O₅) promote densification but do not suppress particle and grain coarsening. The sintered body is composed of large grains with pores located on grain boundaries.     

SnO2纳米颗粒制备及其对溶胶-凝胶Sb:SnO2薄膜性能的影响

以Sn(OEt)2为起始原料,采用水热晶化法合成了分散性良好的金红石结构的SnO2纳米颗粒.采用X射线衍射对其进行了表征,表明SnO2纳米颗粒的结晶性良好,颗粒尺寸小于10nm.将合成的SnO2纳米颗粒均匀分散到Sb:SnO2镀膜液中,经陈化后制成镀膜溶胶,以溶胶-凝胶浸渍镀膜工艺制备纳米颗粒掺杂Sb:SnO2薄膜.分别采用范德堡(Van Der Pauw)法、UV/VIS分光光度计和FTIR中红外分析仪测量并分析膜层的导电性能、光学性能及结构特征,研究了导电纳米颗粒添加对Sb:SnO2薄膜电性能、光学性能和结构的影响.     

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.     

厨房油烟超细颗粒排放特征

利用快速迁移率粒径谱仪(fast mobility particle sizer,FMPS3091)对烧菜时产生的超细油烟颗粒进行测量.结果表明,在食用油加热阶段产生的颗粒物数量浓度成对数单峰分布,峰值在60~70nm之间.放入菜后测量得到颗粒物数浓度成对数双峰分布,其中青菜产生的颗粒物浓度最高,并且其平均粒径和几何标准差最大,分别为83.84nm和2.62nm;鱼丸产生的颗粒物中位径和几何平均粒径最大,分别为80.6nm和57.98nm,汽车尾气的各个参数普遍比较小.通过对炒、煎和炸三种炒菜方式的测量,得出炸产生的颗粒物浓度最高,炒次之,煎最低,在炒菜过程中翻滚对颗粒物的产生影响最大.     

Synthesis of ultrafine particles of barium ferrite by chemical coprecipitation

A new method to synthesize barium hexaferrite by chemical coprecipitation is described. A mixed precursor was precipitated by addition of a barium salt to a strongly alkaline ferrate (VI) solution. The precursor yielded barium hexaferrite on heating for 6 h at 800 °C; partial transformation was evident even at lower temperatures, from X-ray patterns and Mossbauer spectra. Scanning electron microscopy of the powders fired at 800 °C, showed that the particles were less than 0.5 μm in diameter. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis of ultrafine glass particles by laser ablation of microspheres

We describe a new method for producing ultrafine glass particles that employs pulsed-laser ablation of microspheres. Experiments were conducted using pulsed laser wave-lengths from 248 to 1064 nm with ≈ 10 ns pulses and with initial microsphere diameters from 8 to 60 μm. The ejected nanoparticles were collected on silicon substrates for analysis by computer-aided image processing of SEM micrographs to determine the effect of experimental parameters on the particle size distribution. Results showed mean particle diameters were as small as 59 nm and generally inversely proportional to laser fluence. The particle size distributions were closely log-normal with small geometric standard deviations.     

Effect of Sn precursor on the synthesis of SnO2 and Sb-doped SnO2 particles via polymeric precursor method

SnO2 and Sb-doped SnO2 particles were synthesized using the polymeric precursor method with different Sn salt precursors： SnCl2.2H2O, SnCl4.5H20, or Sn citrate. Sb2O3 was used as the precursor of Sb, and the molar ratio of nsn：nsb was held constant. FTIR and TGA/DTA were used to examine the influence of the Sn precursor on the formation and thermal decomposition of the Sn and Sn-Sb complexes. The calcination products obtained from heating the Sn and Sn-Sb complexes at 500℃ in air were analyzed using XRD and TEM analysis. The results revealed that the SnO2 and Sb-doped SnO2 formation temperatures depended on the nature of the Sn precursor. The calcination products were found to be SnO2 and Sb-doped SnO2 particles, which crystallized in a tetragonal cassiterite structure with a highly preferred （110） planar orientation. The Sn precursor and the presence of Sb in the SnO2 matrix strongly influenced the crystallinity and lattice parameters.     

Synthesis of ultrafine single-component oxide particles by the spray-ICP technique

Ultrafine oxide particles were synthesized by introducing aqueous solutions of metal salts into a high-temperature r.f. inductively coupled plasma (the spray-ICP technique). The particles synthesized were spherical for ZrO₂, Y₂O₃, Sm₂O₃, La₂O₃, δ-Al₂O₃, TiO₂ (anatase), β-Bi₂O₃ and CuO, plate-like for Nd₃O₂, Cr₂O₃ and Pr₂O₃, polyhedral for PrO₂, CeO₂ and γ-Fe₂O₃, cubical for NiO, MgO, CaO, Co₃O₄ and Mn₃O₄, bar-like for SnO₂ and ZnO, and foil-like for β-PbO and MoO₃. The products of the alkaline earth group except for magnesium, were hydroxides and/or carbonates, spoiled by atmospheric H₂O and/or CO₂. The particle morphology suggests that particle growth is controlled predominantly by the gas-solid reaction occurring on the surface of nuclei condensed from the gas phase. Some of the oxides revealed a particle morphology characteristic of their crystal structures.     

Preparation of BaTiO3 ultrafine particles by micro-emulsion charring method

Ultrafine BaTiO₃ particles were prepared by a micro-emulsion charring (MEC) method. The MEC method consisted of two steps. The first step is the preparation of a water/oil micro-emulsion with BaTiO₃ elements, and the second is a low temperature firing process in N₂ atmosphere, which includes charring of oil in an emulsion and powdering BaTiO₃ particles with the char. The char formed around BaTiO₃ particles prevents an agglomeration of BaTiO₃ particles during firing. In the present experiment, the W/O ratio and the amount of emulsifier greatly influenced the size of droplets of the emulsion. The charring temperature was another important experimental factor in order to obtain the desired BaTiO₃ particles. The finally obtained BaTiO₃ charring powders were monodispersed spherical particles and the particle size was 0.1 m to 0.5 m.     

Surface characterizations of ultrafine Ni particles

Ultrafine Ni particles have been obtained by evaporating pure Ni in methane gas atmosphere of 100 Torr, and in a mixture of H₂ and Ar of 760 Torr, respectively. The distinct characterization of the layers on two kinds of Ni particle surfaces were investigated by X-ray photoelectron spectroscopy (XPS) and oxygen determination. The morphology and mean particle size were determined by transmission electron spectroscopy (TEM) and subsequent image analysis. The structure of ultrafine Ni particles were identified by X-ray diffraction (XRD). The effect of oxide and carbon layers on magnetization of the particles were studied by vibrating sample magnetometer (VSM). It was observed that a carbon-rich and an oxide of Ni₂O₃ layers were formed on the surface of Ni particles obtained in methane gas, and in a mixture of H₂ and A_r gas atmosphere, respectively. It was shown that the methane gas makes resistance to oxidization during evaporating Ni in this gas atmosphere and no nickel carbides or Ni-C solid solutionformed.     

超细碳酸钡粒子的合成

采用共沉淀法合成了碳酸钡粒子。通过添加合适的晶形控制剂,合成了球状和哑铃状的碳酸钡粉体,利用扫描电子显微镜(SEM)和X射线衍射仪(XRD)进行了表征,并对不同晶形碳酸钡的形成机理进行了初步的探讨。     

超细粒子氧化铝的制备

本文讨论了用超临界流体干燥混凝胶制备氧化铝超细粒子的影响因素；一类为超临界流体的影响因素．其甲温度和压力具有明显的影响，有一较台适的超临界温度达最大比表面积；但超临界压力越低，比表面积越大。加热速率几乎没有影响。另一类为制备混凝胶的影响因素，包括水解温度、加水比例．异丙醇铝固体浓度等均有一最佳制备条件。     

Light scattering of ultrafine silica particles by VUV synchrotron radiation

Vacuum ultraviolet (VUV) light scattering from ultrafine silica particles is studied with an aerosol instrument recently established at the Advanced Light Source (ALS) in Berkeley. Silica particles, size-selected by a differential mobility analyzer, are introduced into vacuum through a set of aerodynamic lenses to form a particle beam. The scattered photons from the crossing area of the VUV synchrotron beam and particle beam are detected with a rotatable VUV photon detector. The angular distributions of scattered photons (ADSP) originating from 70, 100, 200 nm diameter silica particles are measured with 145.9 and 118.1 nm synchrotron radiation. These angular distributions show strong forward scattering. The measured ADSPs are consistent with simulation of Mie scattering. The refractive indices of silica particles, 2.6 + 1.1i and 1.6 + 0.0001i for 118.1 and 145.9 nm, respectively, are obtained by fitting the measured ADSPs; the least average percentage deviations are 18% and 6%, respectively. The scattered fluxes at widely different wavelengths (visible versus VUV) also exhibit clear size sensitivity. Under comparable experimental conditions of photon fluxes and detection efficiencies, limits of particle size detection of 70 and 250 nm are obtained, respectively, when using 118.1 and 532 nm illumination. As anticipated, VUV scattering is a more sensitive probe for ultrafine particles, which will find application in detection of these ubiquitous species beyond the confines of a laboratory.