Surface acidity of the La2O3/Al2O3 system

Surface acidity of aluminium oxide containing 5 wt. % lanthanum oxide has been determined by IR spectroscopy. Strength of Lewis sites of the La₂O₃/Al₂O₃ system was lower than that of pure aluminium oxide. However, the presence of La₂O₃ in aluminium oxide increased the thermostability of these sites in the mixed system.     

p区金属氧化物Ga2O3和Sb2O3光催化降解盐酸四环素性能差异

对沉淀法合成的p区金属氧化物Ga₂O₃和Sb₂O₃紫外光光催化降解盐酸四环素的性能进行了研究,讨论了制备条件对光催化性能的影响。最佳制备条件下得到的Ga₂O₃-900和Sb₂O₃-500样品光催化性能存在巨大差异,通过X射线粉末衍射、傅里叶红外光谱、N₂吸附-脱附测试、荧光光谱、拉曼光谱、电化学分析及活性物种捕获实验等对样品进行分析,研究二者光催化降解盐酸四环素的机理,揭示影响光催化性能差异的本质因素。结果表明,Ga₂O₃和Sb₂O₃光催化性能差异主要归结于二者不同的电子和晶体结构、表面所含羟基数量及光催化降解机理。     

p区金属氧化物Ga2O3和Sb2O3光催化降解盐酸四环素性能差异

对沉淀法合成的p区金属氧化物Ga₂O₃和Sb₂O₃紫外光光催化降解盐酸四环素的性能进行了研究,讨论了制备条件对光催化性能的影响。最佳制备条件下得到的Ga₂O₃-900和Sb₂O₃-500样品光催化性能存在巨大差异,通过X射线粉末衍射、傅里叶红外光谱、N2吸附-脱附测试、荧光光谱、拉曼光谱、电化学分析及活性物种捕获实验等对样品进行分析,研究二者光催化降解盐酸四环素的机理,揭示影响光催化性能差异的本质因素。结果表明,Ga₂O₃和Sb₂O₃光催化性能差异主要归结于二者不同的电子和晶体结构、表面所含羟基数量及光催化降解机理。     

Sm2O3Ga2O3 and Gd2O3Ga2O3 phase diagrams

Four definite compounds exist in the Sm₂O₃Ga₂O₃ binary phase diagram, namely: Sm₃GaO₆, Sm₄Ga₂O₉, SmGaO₃, and Sm₃Ga₅O₁₂. The $\text{3}\text{1}$ compound is orthorhombic (space group Pnna - Z.4) with the cell parameters: a = 11.40₀Å, b = 5.51₅Å, c = 9.07Å and belongs to the oxysel family. Sm₃GaO₆ and SmGaO₃ melt incongruently at 1715 and 1565°C; Sm₄Ga₂O₉ and Sm₃Ga₅O₁₂ have a congruent melting point at 1710 and 1655°C. With regard to the Gd₂O₃Ga₂O₃ system three definite compounds have been identified: Gd₃GaO₆, Gd₄Ga₂O₉, and Gd₃Ga₅O₁₂. Only the garnet melts congruently at 1740°C with the following composition: Gd_3.12Ga_4.88O₁₂. Gd₃GaO₆, and Gd₄Ga₂O₉ melt incongruently at 1760 and 1700°C. GdGaO₃ is only obtained by melt overheating which may yield an equilibrium or a metastable phase diagram.     

TPR studies on steam reforming of 2-propanol on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3

Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al₂O₃, Ru/Al₂O₃ and Pd/Al₂O₃ have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of TPRs suggest that that of IPA on Rh/Al₂O₃ and Ru/Al₂O₃ proceeds via acetone, while the steam reforming of IPA on Pd/Al₂O₃ takes place via propene from acetone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Garnet-perovskite transformations in the Sm2O3Ga2O3 and Gd2O3Ga2O3 systems

The effect of heating garnet melts to various temperatures has been investigated. The previously reported decomposition of the garnet phase due to loss of Ga₂O₃ was corroborated. However, it was also observed that when gallium oxide loss is prevented and the maximum temperature of the melt exceeds a critical value, phase separation of garnet to perovskite and β-gallium oxide occurs:

$\text{RE}{}_3\text{Ga}{}_5\text{O}{}_{12}\text{?3RE}\text{GaO}{}_3\text{+}\text{Ga}{}_2\text{O}{}_3$

.The reverse reaction will occur by reheating the two-phase mixture to the garnet melting point.     

Hydrothermal synthesis of antimony oxychloride and oxide nanocrystals: Sb4O5Cl2, Sb8O11Cl2, and Sb2O3

We described herein a facile solution-phase route to three nanocrystals of antimony oxychlorides and oxides (Sb₄O₅Cl₂, Sb₈O₁₁Cl₂, and Sb₂O₃), whose morphologies and phases were varied with the pH value of a reaction mixture or composition of a mixed solvent. In particular, the solvent composition controlled the selective preparation of cubic Sb₂O₃ (senarmontite) and orthorhombic Sb₂O₃ (valentinite). Both cubic and orthorhombic Sb₂O₃ samples exhibited strong emission properties.     

Contribution from the solid-phase interactions of activating oxides to their nonlinear joint effect on the thermal oxidation of GaAs

The contribution from the solid-phase interactions in the PbO + Sb₂O₃ and PbO + Bi₂O₃ activating compositions to the multichannel process of GaAs thermal oxidation has been determined by spatial separation of the oxides. The solid-phase interactions make a positive contribution to the overall negative nonlinear effect in the dependence of the oxide film thickness on the GaAs surface on the activator batch composition. The contributions from the oxide interactions on the semiconductor surface and in the gas phase have been evaluated for the PbO + Sb₂O₃ composition.     

Selective catalytic reduction of NO over metal oxide or noble metal-doped In2O3/Al2O3 catalysts by propene in the presence of oxygen

The activities of metal oxide CuO, SnO₂, CoO, Ag₂O, ZnO or noble metal Pt, Pd, Rh-doped In₂O₃/Al₂O₃ catalysts for selective catalytic reduction of NO by propene were investigated. The temperature windows for NO reduction over noble metal-doped In₂O₃/Al₂O₃ catalysts were shifted and broaden slightly compared with single component catalyst alone. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nonadditive Linearity in the Chemostimulating Effect of Activator Oxides + Dlient Compositions on GaAs Thermal Oxidation

The chemostimulation efficiency of the activators Sb₂O₃ and Bi₂O₃ in compositions with a diluent (Al₂O₃) is a linear function of activator percentage over a wide range of temperatures. This function is not, however, additive to the thicknesses achieved in the presence of individual components. The percentage of the activator elements in the resulting oxide layers coincides with that in the initial compositions in the linear region and differs from it in the nonadditivity region. Thermal analysis in combination with X-ray powder diffraction showed that Al₂O₃ alters the temperature range and character of the intrinsic transformations of activator oxides.     

Study of the acid-base properties of Ga2O3/Al2O3 by using test reactions

Two test reactions: conversions of propan-2-ol and 2-methyl-3-butyn-2-ol were applied for the investigation of the acid-base properties of Ga₂O₃-Al₂O₃ materials. Both test reactions lead to consistent conclusions on the overall acid-base properties of the materials studied. It has been found that the deposition of gallium oxide on the surface of γ-Al₂O₃ enhances the overall basicity.     

Cathodic electrochemiluminescence at double barrier Al/Al2O3/Al/Al2O3 tunnel emission electrodes

Double insulating barrier tunnel emission electrodes were fabricated by adding a new pure aluminum layer upon oxidized aluminum electrodes by vacuum evaporation and thermally oxidizing the new aluminum layer in air at room temperature. Resulting Al/Al₂O₃/Al/Al₂O₃ electrodes allow the use of various aluminum alloys in the electrode body necessary for hardness or shaping ability of the electrode while obtaining the luminescence properties of pure aluminum oxide. During electrical excitation of luminescent labels by cathodic hot electron injection into aqueous electrolyte solution, the background noise is mainly based on high-field-induced solid-state electroluminescence and F-center luminescence of the outer aluminum oxide film. The more defect states and/or impurity centers the outer oxide film contains, the higher is the background emission intensity. The present electrode fabrication method provides a considerable improvement in signal-to-noise ratio for time-resolved electrochemiluminescence (TR-ECL) measurements when the original native oxide film of the electrode body contains luminescence centers displaying long-lived luminescence. The excellent performance of the present electrodes is demonstrated by extremely low-level detection of Tb(III) chelates, luminol, Pt(II) coproporphyrin and Tb(III) labels in an immunometric immunoassay by time-resolved electrochemiluminescence.     

AES investigation of thermally sprayed Al2O3 coatings on steel

Summary The investigation of plasma sprayed steel/Al₂O₃ composites by means of Auger Electron Spectroscopy (AES) combined with depth profile analysis is described. Incomplete sprayed Al₂O₃ layers permit analysis of single sprayed particles and of surrounding uncovered steel substrate regions. More complete coatings are separated from the substrates, so that contact surfaces of substrates and Al₂O₃ layers can be analyzed. In order to determine the influence of preheating the substrates on the interface widths between steel substrate and Al₂O₃ coating and therefore on the adherence mechanism, both procedures are carried out for two preheating temperatures. It is shown that preheating hardly effects the interface widths beneath single sprayed particles but it causes laterally constant widths for complete layer fragments. Additionally, a comprehensive view about oxide layer thicknesses on the steel substrates before and after plasma spraying is offered.     

Catalytic Combustion of Ethyl Acetate over Al2O3- Ce0.5Zr0.5O2 Supported Metal Oxide Catalysts

The catalysts for the combustion of ethyl acetate were prepared using Fe, Co, Cu, Cr, and Mn metal oxide as active components supported on Al₂O₃-Ce_0.5Zr_0.5O₂ mixed oxides and characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), oxygen storage capacity measurement, BET surface area, XPS measurement, and activity test. According to the results of characterization, it was found that Cu/Al₂O₃-Ce_0.5Zr_0.5O₂ (1:2, mass ratio) and Mn/Al₂O₃-Ce_0.5Zr_0.5O₂ (1:2) catalysts presented excellent activity for the catalytic combustion of ethyl acetate, because of the more reducible species and high reducibility of the catalysts. For ethyl acetate oxidation, more than 99% conversion was achieved at 245 °C over catalysts Cu/Al₂O₃-Ce_0.5Zr_0.5O₂ (1:2) and Mn/Al₂O₃-Ce_0.5Zr_0.5O₂ (1:2, mass ratio), indicating that the catalysts had great potential for wide use.     

AES investigations of plasma sprayed Al2O3 coatings on Ni

Summary The system of plasma sprayed Al₂O₃ on Ni substrates is investigated by means of AES/depth profiling. The influence of two process parameters — preoxidation procedure and spraying temperature — is examined. Rupture between substrate and ceramic layer occurs between a residual — or, in the case of excessive preoxidation, a superfluous — NiO layer on Ni, the thickness of the former depending on preoxidation conditions and the Al₂O₃ layer, the back side of which being partially covered with NiO. The thickness of this NiO layer increases up to about 1 m with the thickness of the initial NiO layer on the substrate, until this layer is about 1.3 m thick, and remains constant thereafter. The same dependence is observed for the width (0.1–1 m range) of the mixed oxide interface between the sprayed Al₂O₃ layer and the NiO layer below. These results represent the chemical contribution to adherence. Contrary to excessive preoxidation, an increase of the spraying temperature from 300°C to 500°C effects broader interfaces.This poster was awarded the First Prize in Poster Section C by the Deutscher Arbeitskreis für Spektroskopie (DASp)     

Zur Kinetik der Spinellbildung von β-Ga2O3 mit zweiwertigen Oxiden. I. Die Festkörperreaktion von β-Ga2O3 mit NiO

The solid state reaction in a sandwich type diffusion couple of NiO and β-Ga₂O₃ has been investigated between 1240 and 1550°C in air and inert gas atmosphere.Optical microscope and X-ray methods are used to identify the reaction product, which is a singlephased spinel of the general formula $\text{Ni}{}_{\mathrm{1?y}}\text{Ga}{}_{\mathrm{<mtext>2+</mtext><mtext>2y</mtext><mtext>3</mtext>}}\text{O}{}_4$. The homogeneity range of the spinel phase was investigated by X-ray methods; there is a high solubility of β-Ga₂O₃ in the spinel lattice.The growth of the thickness of the reaction layer follows a parabolic rate law, and therefore a diffusion process must be rate determining. The activation energy of the rate controlling step is 82 kcal/mole.Pt-marker experiments are not sufficient for determining the reaction mechanism. Investigations with an electron-probe microanalyzer, an connection with a modified marker technique, resulted in a Wagner-mechanism of counterdiffusion of cations for formation of nickel-gallium spinel; the total amount in Ga³⁺ ions is lost for spinel formation before there is an appreciable solubility of gallium in NiO.     

Micro-sized Sb2O3 octahedra fabricated via a PEG-1000 polymer-assisted hydrothermal route

The micro-sized Sb₂O₃ octahedra can be synthesized on a large scale via a simple PEG-1000 polymer-assisted hydrothermal route (PAHR) in the temperature range of 160-180 °C for 10-14 h. The structures, compositions, and morphologies of the as-synthesized products are derived from X-ray power diffraction pattern, X-ray photoelectron spectra, and field emission scanning electronic microscope. Meanwhile, the optical properties of the micro-sized Sb₂O₃ octahedra are studied by their photoluminescene spectroscopy and Raman spectrum. Furthermore, the possible growth mechanism of the micro-metered Sb₂O₃ octahedra is discussed on the basis of a series of supplementary experiments. And it has been found that PEG-1000, sodium tartrate, the reaction temperature, and the reaction time have considerable effects on the final morphology of Sb₂O₃, while the pH value has an influence on the formation of the Sb₂O₃ crystals.     

Survey of the phase formation in the Yb2O3Ga2O3MO and Yb2O3Cr2O3MO systems in air at high temperatures (M: Co,Ni, Cu,and Zn)

The phase relations in the Yb₂O₃Ga₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Ga₂O₃CuO system at 1000°C and the Yb₂O₃Ga₂O₃ZnO system at 1350 and 1200°C, the Yb₂O₃Cr₂O₃CoO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃NiO system at 1300 and 1200°C, the Yb₂O₃Cr₂O₃CuO system at 1000°C, and the Yb₂O₃Cr₂O₃ZnO system at 1300 and 1200°C were determined in air by means of a classical quenching method. YbGaCoO₄ (a = 3.4165(1) and c = 25.081(2) Å), YbGaCuO₄ (a = 3.4601(4) and c = 24.172(6) Å), and YbGaZnO₄ (a = 3.4153(5) and c = 25.093(7) Å), which are isostructural with YbFe₂O₄ (space group: $\text{R}\text{3}\text{m, a = 3.455(1)}$ and c = 25.109(2) Å, were obtained as stable phases. In the Yb₂O₃Ga₂O₃NiO system and the Yb₂O₃Cr₂O₃MO system (M: Co, Ni, Cu, and Zn), no ternary stable phases existed.     

Sub-nanometer-thick Al2O3 Overcoat Remarkably Enhancing Thermal Stability of Supported Gold Catalysts

Supported gold nanoparticle catalysts show extraordinarily high activity in many reactions. While the relative poor thermal stability of Au nanoparticles against sintering at elevated temperatures severely limits their practical applications. Here atomic layer deposition (ALD) of TiO₂ and Al₂O₃ was performed to deposit an Au/TiO₂ catalyst with precise thickness con-trol, and the thermal stability was investigated. We surprisingly found that sub-nanometer-thick Al₂O₃ overcoat can su ciently inhibit the aggregation of Au particles up to 600 C in oxygen. On the other hand, the enhancement of Au nanoparticle stability by TiO₂ overcoat is very limited. Di use reffectance infrared Fourier transform spectroscopy (DRIFTS) of CO chemisorption and X-ray photoelectron spectroscopy measurements both con rmed the ALD overcoat on Au particles surface and suggested that the presence of TiO₂ and Al₂O₃ ALD overcoat on Au nanoparticles does not considerably change the electronic properties of Au nanoparticles. The catalytic activities of the Al₂O₃ overcoated Au/TiO₂ catalysts in CO oxidation increased as increasing calcination temperature, which suggests that the embed-ded Au nanoparticles become more accessible for catalytic function after high temperature treatment, consistent with our DRIFTS CO chemisorption results.     

Phase relations in the pseudobinary system TiO2Ga2O3

Phase relations and microstructures in the TiO₂-rich part of the TiO₂Ga₂O₃ pseudobinary system have been determined at temperatures between 1373 and 1623°K using X-ray diffraction and electron and optical microscopy. The phases occurring in the system are TiO₂ (rutile), β-Ga₂O₃, a series of oxides Ga₄Ti_m?4O_2m?2 (m odd) which exist above 1463°K, and Ga₂TiO₅, which exists above 1598°K. The width of the phase region occupied by the Ga₄Ti_m?4O_2m?2 phases varies with temperature. At 1473°K it is narrow, and has limits of Ga₄Ti₂₅O₅₆ to Ga₄Ti₂₁O₄₈ while at higher temperatures it broadens to limits of from Ga₄Ti₂₇O₆₀ to Ga₄Ti₁₁O₂₈ at 1623°K. These phases are often disordered and crystals frequently contain partially ordered intergrowths of oxides with various values of m. On the TiO₂-rich side of the phase region there is a continuous change in texture from rutile to the end members of the Ga₄Ti_m?4O_2m?2 structures. The findings are summarized on a phase diagram.