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.     

Ultrafine particles of the ZrO2-SiO2 system prepared by the spray-ICP technique

Ultrafine powders of the ZrO₂-SiO₂ system prepared by spraying aqueous mixed solutions of ZrO(NO₃)₂·2H₂O and silicone oil into an ultrahigh temperature inductively coupled plasma (the spray-ICP technique) have been investigated in connection with particle growth and phase change caused by heat treatment. The prepared powders were composed of roundish ultrafine particles 10 to 20 nm in size, and their components were tetragonal ZrO₂ (t-ZrO₂) and amorphous SiO₂ (a-SiO₂).a-SiO₂ alone did not crystallize below 1400° C, though the particles grew above 900° C.t-ZrO₂ converted to monoclinic ZrO₂ (m-ZrO₂) above 400° C, also followed by particle growth. On the other hand composite powders oft-ZrO₂ anda-SiO₂ exhibited no particle growth below 1200° C. Above 1200° Ct-ZrO₂ converted tom-ZrO₂, and its amount decreased with an increase in SiO₂ content. At 1400° C particle growth occurred, and the round particles of ZrO₂ were dispersed in ana-SiO₂ glass medium. These results indicate that ZrO₂ and SiO₂ mutually block particle growth, and that SiO₂ contributes to the quenching oft-ZrO₂ by keeping the particles of ZrO₂ within the critical particle size oft-ZrO₂.     

Deposition of PbTiO3 film by the spray-ICP technique

PbTiO₃ thin films were prepared on various substrates by spraying an ultrasonically atomized aqueous solution of Pb(NO₃)₂ + TiO (NO₃)₂ into an inductively coupled plasma (ICP) under atmospheric pressure. Single-phase PbTiO₃ with perovskite structure was obtained at 500–650 °C. The perovskite obtained below 600 °C showed less tetragonality due to the effect of grain size. The PbTiO₃ films crystallized with preferred (1 1 1) and (0 0 1) orientations on sapphire (0 0 1) and MgO (1 0 0), respectively. Based on the analysis of ICP emission spectra, it is suggested that a reoxidation of titanium preceded that of lead in the plasma, and also that OH in the plasma played an important role in the deposition of PbTiO₃.     

Stabilization of SnO2 ultrafine particles by additives

In order to stabilize ultrafine particles of SnO₂ which is essential to obtain high gas sensitivity, a systematic investigation was undertaken regarding the stabilizing effects of 5 at% impregnated foreign additives, consisting of oxides or polyoxy compounds of 31 metals and 3 non-metals. The data of specific surface area, SA, as well as SnO₂ crystallite size, D, evaluated from X-ray diffraction showed that the additives could be classified into several groups according to the effectiveness. The most effective group, consisting of P-Ba, Sm, Ba, P, Mo, W, Ca, Sr, Cr and In, could keepD less than 10 nm even after calcination at 900°C, whereas pure SnO₂ underwent grain growth to haveD of 13 and 27 nm at 600 and 900°C, respectively. Electron microscopy revealed that neck sizes, X, between crystallites were fairly proportional toD(X/D = 0.80). A simple analysis of SA and D data based on a monosized sphere model suggested that each crystallite was coordinated with 3–4.5 neighbours through the necks. The existing state and stabilizing mechanism of additives are discussed in conjunction with the electrical resistance of porously sintered elements.     

Synthesis of PbTiO3 film on LaNiO3-coated substrate by the spray-ICP technique

In an attempt to utilize LaNiO₃ as a bottom electrode for PbTiO₃ ferroelectric film, PbTiO₃ and LaNiO₃ films were prepared by the spray-ICP technique under atmospheric pressure. The dense LaNiO₃ films crystallized with preferred (1 1 1) and (1 0 0) orientations on sapphire (0 0 1) and MgO (1 0 0), respectively. Resistivities of the LaNiO₃ films deposited above 600 °C were about 4 × 10^–6 m. The PbTiO₃ film with preferred (001) orientation was successfully prepared on LaNiO₃-coated MgO (1 0 0). Its dielectric constant and dissipation factor were about 200 and 0.02, respectively, at 1 kHz. The Curie temperature suggested that PbTiO₃ films were free from contamination by LaNiO₃.     

Trivalent Ce2O3 and CeO2−x intermediate oxides induced by laser irradiation of CeO2 powders

A strong non-stoichiometry of pure fcc CeO₂ was induced by laser irradiation. The increase of laser power and/or energy density had a saturable effect on particle size growth. The possibility of CeO₂ reduction to A-Ce₂O₃ by laser irradiation was demonstrated. Particles of stable Ce₇O₁₂ phase were observed in all specimens irradiated at low laser-power densities. An epitaxial relationship between triclinic Ce₁₁O₂₀ and cubic Ce₁₂O₂₂ phases was found. The controversial C-Ce₂O₃ phase was detected at the limits of a bcc particle. An unknown bcc phase of acicular morphology, strongly related to C-Ce₂O₃, was also registered. The dose dependence of CeO₂ structural modifications obtained by laser irradiation as a function of laser energy density variation could be explained by a simple defect aggregation model implying lattice defects (oxygen vacancies and Ce³⁺ ions).     

The formation of ultrafine Al2O3, ZrO2 and Fe2O3 by the spray-ICP technique

Ultrafine aluminium oxide, zirconium oxide and iron oxide have been prepared by spraying their corresponding nitrate solutions into an inductively coupled plasma (ICP) of ultra-high temperature (the spray-ICP technique). Their particles are roundish, 0.01–0.02 μm in diameter, and homogeneous both in size and in shape. Their major phases are γ-Al₂O₃, metastable tetragonal-ZrO₂ and γ-Fe₂O₃, respectively. These oxides appear to be formed through the following two reaction processes, (1) the complete decomposition of the droplets of the solution to their component atoms in the ICP flame, (2) the homogeneous nucleation and the successive crystal growth occurring outside the ICP flame. In the process (2), quenching is so rapid that the crystals grown after the nucleation do not transform to high temperature phases, which seems to cause the formation of the oxide of low temperature phase.     

Effect of a randomly oriented field on superparamagnetic ultrafine particles

The effect of a constant and a randomly oriented magnetic field H(ψ, ?), on the Néel relaxation time τ, of an assembly of ultrafine ferromagnetic particles with uniaxial anisotropy, is investigated. In this regard, the smallest non-vanishing eigenvalue of the Fokker-Planck equation is calculated as a function of ψ, ? and the parameter h = M_svH / k_BT, where M_s and v are denoting the saturation magnetization and the volume of a particle, respectively. The results obtained bring noticeable changes compared to previous calculations, and give satisfactory interpretation of the relaxation phenomenon in such systems.     

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.     

Characterization of CeO2 crystals synthesized with different amino acids

We investigated the relationship between the structures of the CeO₂ products (particle size, morphology and their characteristics) prepared using different amino acids. Cerium hydroxide carbonate precursors were initially prepared by a hydrothermal method and were subsequently converted to CeO₂ by its thermal decomposition. Various amino acids were used as structure-directing agents in the presence of cerium nitrate and urea as precursors. The results indicate morphology selectivity using different amino acids; CeO₂ structures, such as quasi-prism-sphere, straw-bundle, urchin-flower like and polyhedron prisms, indeed could be produced. Raman and photoluminescence studies indicate the presence of oxygen vacancies in the CeO₂ samples. Photoluminescence spectra of CeO₂ with l-Valine exhibit stronger emission compared with other amino acids utilized under this study, indicating the higher degree of defects in these particles. This study clearly indicates that the degree of defects varied in the presence of different amino acids. Improved precision to control the crystal morphology is important in various material applications and our study provides a novel method to achieve this specificity.     

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。     

Effect of current density on the microstructure and hardness of Ni-CeO2 nanocomposite coating synthesized by pulse electrodeposition technique

The Ni-CeO2 nanocomposite coatings have been synthesized by pulse electrodeposition technique with different current densities (0.10, 0.30, 0.40, 0.50, 0.70 and 0.90 A/cm2) from a Watts-type electrolyte containing nano-sized ceria particles. The Ni-CeO2 coatings produced with different current densities have been characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) coupled with an energy dispersive spectrometer (EDS). The hardness of the coatings has been measured by Vickers microhardness tester (VMHT). It has been found that the crystallite size decreases and hardness increases with the increasing current density. However, the co-deposition of ceria in the nickel matrix increases up to the current density of 0.5 A/cm2, beyond which it decreases.     

Synthesis and luminescence of Sr2CeO4 superfine particles by citrate-gel method

A strong blue-white emission phosphor Sr₂CeO₄ superfine particles, containing SrCe₄O₇, have been synthesized using a citrate-gel method. The crystalline phase and luminescence properties of superfine particles are reported. The results show that the strong blue-white emission is assigned to Ce⁴⁺–O²⁻ charge-transfer transition (CTT) of Sr₂CeO₄ and is not related to a lattice defect. The emission spectrum of post-heat-treated particles exhibits a broad band maximum at 470 nm, and the emission intensity is not affected by the existence of SeCe₄O₇.     

Effect of CeO2 on reaction-sintered mullite-ZrO2 ceramics

The effect of ceria on mullite formation and the sintering of zircon and alumina powders was investigated. Quantitative X-ray powder analysis was used to determine the formation of mullite and zirconia of both monoclinic and tetragonal forms. Scanning electron microscopy and electron-probe microanalysis were used for microstructural analysis. It was found that the addition of CeO₂ enhanced the formation of mullite and increased the fraction of tetragonal zirconia. The addition of CeO₂ caused the formation of mullite directly from reaction of zircon with alumina without decomposition of zircon into zirconia and silica. In addition to forming a liquid phase, the ceria essentially formed a solid solution with zirconia. The fracture toughness of the mullite-zirconia composites was about 5.5–6.0 MPa m^1/2.     

Preparation and characterization of the TiO2 ultrafine particles by detonation method

Utilizing the raw materials of TiOSO₄, NaOH, NH₄NO₃ and RDX, the TiO₂ ultrafine particles were prepared under high pressure and high temperature by detonation method. The structure, composition and size distribution of the TiO₂ ultrafine particles were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicated the as-prepared TiO₂ ultrafine particles exhibited spherical-like grains and that the average size of particles was 25 ± 5 nm. After being heated at 700 °C for 1 h, TiO₂ particles have entirely completed the anatase-rutile phase transition, which means that detonation method can effectively enhance the anatase-rutile phase transition by lowering the transition temperature. The size of TiO₂ nanoparticles can be effectively controlled because the as-prepared nanoparticles do not have enough time to grow to large and perfect crystallites during the detonation process.