Synthesis of zirconium oxide by hydrolysis of zirconium alkoxide

Submicrometre particles have been prepared from hydrolysis-polycondensation of zirconium alkoxide [Zr(n-C₃H₇O)₄] in ethanolic solution. The properties of these particles (morphology, specific surface area, S _BET, crystal phase and size distribution) after calcination at 450 °C for 5 h were found to depend on the conditions of synthesis, i.e. alkoxide concentration and mole ratio water/alkoxide.     

Features of the procedures to obtain ultrafine zirconium dioxide by mechanochemical method

The results of investigation of mechanochemical reactions in the mixtures of hydroxides and carbonates of alkaline and alkaline earth metals with zirconium oxychloride and oxynitrate are presented. It is shown that one of the features of interaction between the components is the formation of the salts of alkaline and alkaline earth metals along with X-ray amorphous zirconium-containing compound. It is demonstrated that the mechanical activation of the mixture of yttrium carbonate and zirconium oxynitrate, followed by thermal treatment of this mechanically activated mixture, results in the formation of solid solution ZrO₂-Y₂O₃ in cubic modification.     

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。     

Preparation of spherical zirconium salt particles by homogeneous precipitation

Spherical basic zirconium sulphate particles were prepared by homogeneous precipitation in mixed solutions of zirconium sulphate and urea. Values of [SO ₄ ^2– ]/[Zr⁴⁺] and [urea]/[Zr⁴⁺] in starting mixed solutions and cooling rate may affect the formation of spherical particles. Complexes such as [Zr(OH)_n]^4–n could prevent the formation and thus lead to gel precipitation. In addition, spherical particles could only be obtained in the presence of SO ₄ ^2– ; for NO^3– and Cl^–, only gel precipitation occurred.     

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.     

FeBP非晶态合金超细微粒的合成及其对PH3分解的催化作用

用化学还原法合成了FeBP非晶态合金超细微粒，用电感耦合等离子体光谱（ICP）、X射线粉末衍射（XRD）、透射电子显微镜（TEM）和差热分析（DSC）等手段对其进行了物性表征，并用微型催化反应装置考察了其对PH3分解的催化作用，结果表明，非晶态合金FeBP对PH3的分解具有良好的催化作用，能使PH3的分解温度从800℃以上降到500℃左右。490℃时分解率超过90％，540℃时达100％。     

NO decomposition by ultrafine noble metals dispersed on the rare earth phosphate hollow particles

Novel fine polymer particles containing ultrafine Pd, Pt or Rh metal dispersed on the core-shell [core, poly(styrene-co-acrylamide) or poly(styrene-co-acrylic acid); shell, LnPO₄(Ln = Ce, Nd, Pr, Sm, La)] type microsphere were prepared by the emulsifier-free emulsion polymerization of styrene with acrylamide or acrylic acid followed by the addition of PdCl₂, HPtCl₆, or RhCl₃ and finally by the addition of a mixture of Ln(NO₃)₃ and NaH₂PO₄. Pyrolysis of the resulting polymer particles at 700–900°C provides polymer-free hollow particles (diameter 450–550 nm) composed of noble metals and LnPO₄. The excellent catalytic reduction of NO gas into N₂ and O₂ was observed at 500–700°C using the rersulting particles as catalyst.     

Chemical vapour deposition of epitaxial Ni-Zn ferrite films by thermal decomposition of acetylacetonato complexes

Epitaxial (Ni, Zn)Fe₂O₄ films were prepared on (100) MgO single crystal substrate by lowpressure chemical vapour deposition using a thermal decomposition of acetylacetonatocomplexes, Ni(acac)₂, Zn(acac)₂ and Fe(acac)₃. These complexes were evaporated at 157, 79 and 146° C, respectively, and transported with nitrogen carrier gas (flow rate 100 ml min⁻¹) to the deposition furnace. Polycrystalline and epitaxial films were grown at 500 to 600 and 600 to 650° C, respectively, under a pressure of 12 torr. The epitaxial film of Ni_1−xZn_xFe₂O₄ (x⋍0.4) treated at 600° C for 60 min, showed the saturation magnetization of 67 e.m.u. g⁻¹ and the coercive force of 20 to 30 Oe.     

Hydrolysis of zirconium alkoxide under an uncontrolled atmosphere

The laboratory prepared zirconium n-butoxide was hydrolysed under an uncontrolled atmosphere by exposing it to air moisture (natural hydrolysis) or adding water solutions at various pH (accelerated hydrolysis) to the alkoxide solutions. Investigations were performed on the effects of the different processes and the pH of the water solutions on the products morphology, crystallinity and phase transformation. XRD, SEM, TEM and SAD were used for these investigations. A strong correlation between crystallite size, calculated with Scherrer formula, and phase transformation was observed in the present work.     

Preparation of ultrafine particles of silicon base intermetallic compound by arc plasma method

The purpose of this paper was to prepare ultrafine particles of Si-based intermetallic compounds, TiSi₂, MoSi₂ and VSi₂, by an arc plasma method with hydrogen addition. The properties of the prepared particles were affected by the vapor pressure ratio (Ti/Si, V/Si: 10⁻¹; Mo/Si: 10⁻³) of the constituent metals. The vaporization and condensation rates of the constituent metals should be controlled to prepare intermetallic compound particles in the case of large different vapor pressures. The vaporization rate can be controlled by H₂ concentration in the arc; for example, an increase in H₂ concentration leads to an increase in Ti fraction in the prepared particles in a Si---Ti system. The preparation of ultrafine particles of TiSi₂ was most successful from the 60-wt.% Ti raw material with the 50%-H₂ arc. MoSi₂ particles were prepared from the 85-wt.% Mo raw material with the 50%-H₂ arc. A single phase of VSi₂ particles was prepared successfully from the 60-wt.% V raw material with the 50%-H₂ arc. Another purpose was to investigate the mechanism of vaporization enhancement of particular metals from a metal mixture by hydrogen in arc plasmas. The vaporization enhancement was mainly attributed to the formation of intermediate products such as hydride and/or activity modification by hydrogen in molten metals.     

Manganese dioxide structural effects on its thermal decomposition

In this work, the influence of the structure, composition and morphology on the amount of mass lost from γ-MnO₂ during heat treatment, and the activation energy for this process (from iso-conversional kinetic analysis), was determined using a statistical approach. It was found that the differential thermogravimetric (DTG) data for electrolytic manganese dioxide (EMD) samples typically show two regions of mass loss; water bound to surface sites and structural water at or near the surface removed between ∼120 and 200 °C, and bulk hydroxyl groups lost in the range ∼200-400 °C. The composition and morphology had the greatest effect on the amount of mass lost; namely, BET surface area and percentage Mn(III) for the first process (r² = 0.92) and percentage Mn(IV), percentage Mn(III) and cation vacancy fraction for the second (r² = 0.89). The activation energy for the first processes was most affected by BET surface area, c₀ and crystallite size in the (2 2 1) direction (r² = 0.89). Relatively poor correlations were found between the amount of water lost and the activation energy for the second process and the material properties measured in this work. This likely relates to the slow kinetics of the first mass loss which complicates the relationships existing for the second.     

Preparation of ZnO nanoparticles by thermal decomposition of zinc alginate

A new method to produce zinc oxide nanocrystals is presented. The method is based on the thermal decomposition of zinc alginate gels. The gels were produced in the form of beads by ionic gelation between a zinc solution and sodium alginate. The wet beads were heated at 800 and 450 °C for 24 h and the products were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission electron microscopy (TEM) and micro-Raman spectroscopy. XRD analysis showed that all obtained samples are of wurtzite structure. TEM analysis combined with electron diffraction also showed the presence of single crystals indexed as ZnO hexagonal phase. Crystal size was determined by measuring individual crystals from SEM pictures. It was found that heating temperature and the kind of zinc agent influence the crystal size. Raman scattering revealed the existence of defects in the structure of nanoparticles whose cringing was discussed in the context of recent studies in this field.