Promotional effect of H2O on the activity of In2O3‐doped Ga2O3–Al2O3 for the selective reduction of nitrogen monoxide

Effect of metal oxide additives on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by the sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. Of several metal oxide additives, the addition of In₂O₃ enhanced drastically the activity of Ga₂O₃–Al₂O₃ for NO reduction by propene in the presence of H₂O. In addition, the activity of In₂O₃‐doped Ga₂O₃–Al₂O₃ catalyst was extremely intensified by the presence of H₂O below 350°C. The promotional effect of H₂O was interpreted by the suppression of undesirable propene oxidation and the removal of carbonaceous materials deposited on the catalyst surface. We also found that close interaction of In₂O₃ and Ga₂O₃ is necessary for the enhancement of activity by H₂O. A lot of hydrocarbons except methane and oxygenated compounds served as good reducing agents, among which propene and 2‐propanol were the most efficient ones. In₂O₃‐doped Ga₂O₃–Al₂O₃ catalyst was capable of reducing NO into N₂ quite efficiently in the presence of H₂O at a very high space velocity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sintering behavior of Cr2O3–Al2O3 ceramics

We investigated the sintering behavior of Cr₂O₃–Al₂O₃ ceramic materials. In our observation of the isothermal shrinkage behavior of Cr₂O₃–Al₂O₃ ceramic, the activation energy of sintering reaction was measured to be 102 kJ/mol, that is, the near value of the activation energy of diffusion of Al ions in Al₂O₃ single crystal. Therefore the diffusion of cations is believed to control the sintering behavior of this material. With the addition of TiO₂, (the compound chosen to accelerate the diffusion of cations) to Cr₂O₃–Al₂O₃, the sintering behavior was accelerated.     

Effect of Tungsten Oxide on the Crystallization Properties of Glasses of the B2O3–La2O3–Nb2O5 System

Glass Physics and Chemistry - The effect of tungsten oxide on the crystallization properties of glasses of the 37.5B2O3 22.5La2O3 (40 – x)Nb2O5 xWO3 (where x = 10, 15, 20, 30, 40 mol %)...     

Effect of P2O5 on evolution of microstructure of MgO–Al2O3–SiO2 glass ceramics

Abstract

MgO–Al₂O₃–SiO₂ (MAS) cordierite based glass ceramics were prepared by volume crystallisation. X-ray diffraction, Scanning electron microscopy and Energy diffraction scanning were used to investigate crystallisation behaviour and the influence of P₂O₅ on microstructure MAS based glass ceramics. The results showed that P⁵⁺ could promote the phase separation of MAS glass and that the glass was divided into two areas, such as Mg₄Al₂Ti₉O₂₅ and the containing P⁵⁺ area at <900°C. Mg₄Al₂Ti₉O₂₅ and Mg₃(PO₄)₂ in the area were both advantageous to the precipitation of μ cordierite, which further transformed to α cordierite due to P⁵⁺ in the residual glassy phase. However, P⁵⁺ inhibited the presence of cordierite when the heat treatment temperature was >900°C.     

Degradation of orange G by H2O2、S2O82－、S2O82－-H2O2with ferrous ion

以偶氮染料橙黄G（OG）为目标污染物,研究Fe2+分别催化H2O2、S2O82－、H2O2-S2O82－降解0.1 mmol/L OG Fe2+/H2O2体系,[Fe2+]=1 mmol/L, pH=3, [H2O2]0=10 mmol/L,降解30 min OG脱色率为96%,随着pH值增大和[H2O2]0＞10 mmol/L,OG脱色率减小,呈线性变化。Fe2+/S2O82－体系,随着S2O82－初始浓度增加OG脱色率增大,随着pH值增大OG脱色率减小,呈非线性变化。Fe2+/H2O2-S2O82－体系,pH=3, [H2O2]0=2 mmol/L, [S2O82－]0＞10 mmol/L时OG脱色率持续增大。Fe2+/H2O2-S2O82－体系矿化率最高。利用乙醇和硝基苯作为分子探针,采用分子探针竞争实验鉴定该体系中产生的SO4?和OH?。     

Effect of CeO2 and La2O3 on the Activity of CeO2−La2O3/Al2O3-Supported Pd Catalysts for Steam Reforming of Methane

The effect of the addition of CeO₂ or La₂O₃ on the surface properties and catalytic behaviors of Al₂O₃-supported Pd catalysts was studied in the steam reforming of methane. The FTIR spectroscopy of adsorbed CO and the Pd dispersion suggest the partial coverage of Pd⁰ by ceria or lanthana species. This could lead to the formation of an adduct MPd _x O (M = Ce or La) at the surface of the metal crystallites. The addition of ceria or lanthana resulted in an increase of the turnover rate and specific rate for steam reforming of methane. One possible explanation if that the Pd⁰*Pd^δ+O–M interfacial species (M = Ce or La) are oxidized by H₂O or CO₂, promoting the O* transfer to the metal surface. This could facilitate the removal of C* species from the metal surface, resulting in the increase of specific reaction rate and increase of the accessibility of CH₄ to metal active sites.     

Catalytic behavior of V2O5 in rechargeable Li–O2 batteries

The possibility of using vanadium pentoxide (V₂O₅) as a catalyst in rechargeable lithium–oxygen (Li–O₂) batteries was studied. A V₂O₅-carbon composite was cast onto Ni foam to form a cathode. Electrochemical cells designed based on the flat cell manufactured by Hohsen Corporation were fabricated. The initial discharge capacity was 715 mA?h?g^?1, and the maximum discharge capacity reached 2,260 mA?h?g^?1 during the twelfth cycle. The cell had high capacity retention during cycling (1.24?% during cycles 2–8). V₂O₅ acted as a catalyst as well as an active material, improving the specific capacity and capacity retention of the non-aqueous Li–O₂ cell more effectively than do other materials.     

On the Possibility of Forming Complexes with the Participation of O2– Ions in Melts and Glasses of the Na2O–SiO2–Cu2O System

The structural role of copper ions in melts (glasses) of the Na₂O–SiO₂–Cu₂O–CuO system is analyzed in the framework of the acid–base concept with due regard for the geometric (the radius ratio for Cu²⁽¹⁾⁺ and O^2– ions) and energy (the mean enthalpies of the Cu²⁽¹⁾⁺–O bonds) factors. It is demonstrated that copper ions in the structure fulfill the function of modifier cations. In these melts, the Cu¹⁺–Cu²⁺ redox equilibrium can be described without regard for the formation of [Cu²⁽¹⁾⁺O_4/2]^2(3)– ionic complexes (which could be incorporated into the structure of silicon–oxygen anions) and [Cu²⁺O _b/k ]^{2 – b/k} polyhedra providing the interaction between Cu²⁺ ions and anions. The influence of the formation of these polyhedra on the redox equilibrium is considered within the formalism of chemical thermodynamics. The composition dependence of the oxygen ion exponent pO is measured by an electromotive force (emf) technique. The ratio between the numbers of copper atoms with different valences is determined by chemical analysis. The experimental data obtained are in agreement with the theoretical inferences.     

Rh–Sr/Al2O3 Catalyst for N2O Decomposition in the Presence of O2

The improving effect of Sr in the catalytic activity of Rh for N₂O decomposition has been studied under 1,000 ppm N₂O/He and 1,000 ppm N₂O/5% O₂/He (GHSV = 10,000 h^?1). Different techniques have been used for catalysts characterization: TEM, SEM-EDX, XRD, N₂ adsorption at ?196 °C and in situ XPS. Sr favours the Rh dispersion and reduction under reaction conditions, and allows the low temperature removal of N₂O in the presence of O₂ (100% decomposition at 350 °C).     

Influence of annealing treatment on magnetic properties of Fe2O3/SiO2 and formation of ε-Fe2O3 phase

Magnetic properties of Fe₂O₃/SiO₂ samples were studied after being produced by sol-gel synthesis and formation of ε-Fe₂O₃ polymorph. Samples were thermally treated, using different annealing temperatures and annealing times. The size and morphological characteristics of the iron oxide nanoparticles were examined using a TEM microscope. We used the “ellipticity of shapes”, which is a measure of how much the shape of a nanoparticle differs from a perfect ellipse, in order to quantitatively describe morphological properties of nanoparticles. Coercivity measurements were used to identify and monitor the formation of the epsilon-iron oxide phase during the thermal treatments (annealing). Coercivity values were in the range from 1.2 to 15.4 kOe, which is in accordance with previous experience regarding the existence of ε-Fe₂O₃. We have determined the optimal formation conditions for the ε-Fe₂O₃ polymorph (t=1050 °C for 7 h, H_C=15.4 kOe), as well as the narrow temperature interval (1050–1060 °C) in which the polymorph abruptly vanished (H_C=2300 Oe), on the basis of results of the magnetic properties. The threshold temperature for the ε-Fe₂O₃ phase transformation was measured as 1060 °C. We found that different annealing temperatures and annealing times significantly affected magnetic properties of the examined samples.     

Effect of adding Y2O3 on structural and mechanical properties of Al2O3–ZrO2 ceramics

The effects of adding 1–8 wt% Y₂O₃ on phase formation and fracture toughness of Al₂O₃–xZrO₂–Y₂O₃(AZY) ceramics were studied. Phase formations of the samples were characterized by the X-ray diffraction (XRD) technique. It was found that the major phase was rhombohedral-Al₂O₃, while the minor phase consisted of the monoclinic-ZrO₂, tetragonal-ZrO₂ and monoclinic-Y₂O₃. It was found that Y₂O₃ contents did not clearly influence grain shape of AZY ceramics. The results obtained from the microhardness test could be used to evaluate the fracture toughness. It was found that the smaller grains had high fracture toughness. The maximum fracture toughness of 4.827 MPa m^1/2 was obtained from 4 wt% Y₂O₃. Refinement of lattice parameters using Rietveld analysis revealed the quantitative phases of AZY ceramics. This shows that under adding Y₂O₃ conditions the proportion of tetragonal-ZrO₂ phase plays an important role for the mechanical properties of AZY ceramics.     

The characteristics of ZnO–Bi2O3-based varistor ceramics doped with Y2O3 and varying amounts of Sb2O3

ZnO–Bi₂O₃-based varistor samples doped with 0.45 mol% of Y₂O₃ and varying amounts of Sb₂O₃ in the range from 1.8 to 0.0 mol% were fired at 1230 °C. Only in the samples co-doped with Sb₂O₃ did doping with Y₂O₃ resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase (the Y₂O₃-containing phase) at the grain boundaries, which very effectively hinders the grain growth. Despite of a decrease in the amount of added Sb₂O₃ from 1.8 to 0.45 mol% and a significant decrease in the amount of spinel phase the samples had a similar ZnO grain size and a threshold voltage of 200 V/mm. The results confirmed that doping with Y₂O₃ is a very promising route for the production of fine-grained high-voltage ZnO–Bi₂O₃-based varistor ceramics, and determining the proper amounts of added Sb₂O₃ and Y₂O₃ is of great importance.     

A Significant Role of Tb2O3 on the Optical Properties and Radiation Shielding Performance of Ga2O3–B2O3–Al2O3–GeO2 Glasses

Journal of Inorganic and Organometallic Polymers and Materials - This research article focuses on the significant role of Tb2O3 content on the optical properties and radiation shielding performance...     

Effect of Sb_2O_3 Replace V_2O_5 on the Electronic Property of V2O5–P2O5–Sb2O3–Bi2O3 Glass System

采用体积电阻率法、红外光谱、X射线衍射研究了V2O5–P2O5–Sb2O3–Bi2O3体系玻璃的电性能、结构和析晶状况。结果表明：随着Sb2O3取代部分V2O5,玻璃的体积电阻率显著升高,电子分别以V4＋和V5＋为中心不停地进行电子跃迁的电子导电特征得到明显抑制,15%Sb2O3、20%Sb2O3玻璃的体积电阻率可以达到实用水平。当Sb2O3取代V2O5进入钒酸盐玻璃中,玻璃结构得到增强,析晶状况得到改善,削弱了玻璃的导电能力。     

Crystallization of Glasses in the K2O–Nb2O5–SiO2System

The changes in the structure and phase composition of glasses in the K₂O–Nb₂O₅–SiO₂system upon their heat treatment in the temperature range 700–800°C are studied by the small-angle X-ray scattering (SAXS) technique and X-ray powder diffraction. It is demonstrated that the crystallization is the primary process giving rise to microinhomogeneities in glasses due to heat treatment. Nanocrystals of an unidentified niobium-containing phase precipitate in glasses with the formation of regions with a decreased content of potassium and niobium oxides. An increase in the duration of heat treatment at the studied temperatures results in an increase in the size of nanocrystals without change in their phase composition. This is accompanied by the disappearance of diffusion zones, which leads to a decrease in the SAXS intensity in the range of small scattering angles and, correspondingly, to a decrease in the light scattering intensity.     

Pixelated sintering of α-Al2O3

The sintering of α-alumina by a brand new and innovative technique, called pixelated sintering (PS), is here studied. Densification and grain growth by PS of perfectly controlled granular compacts are analysed and compared to results obtained using Spark Plasma Sintering (SPS) and Pressure-Less SPS (PL-SPS). Materials are exposed to the same temperature profiles whatever the sintering technique used in order to assess the potential of PS in terms of microstructure control. It is shown that PS can be used as an alternative technique to SPS for fast sintering with the advantages of a much simpler and cost-effective set-up, as well as a better control of the localised heat input. PS also appears to be a very modular technology in the way it controls the temperature gradients allowing its implementation for multi-step sintering approaches, as well as for the fabrication of large and complex parts.     

Melt extraction processing of structural Y2O3–Al2O3 fibers

Compounds in the system Y₂O₃-Al₂O₃ are promising materials for optical, electronic and structural applications. In this study, a melt extraction process with a new approach to making ceramic fibers was used to produce amorphous fibers in the Y₂O₃–Al₂O₃ system within the 20–30-micron size range. Smooth and uniform cross section fibers with relatively high tensile strength were obtained depending on the wheel velocity. X-ray diffraction of as-extracted fibers revealed the non-crystalline nature of the yttria-alumina compositions. The crystallization and glass transition temperatures of non-crystalline fibers were determined using differential thermal analysis (DTA). Crystalline phases were identified by X-ray diffraction in the fibers after heat treatment.     

Sintering of α-Al2O3-seeded nanocrystalline γ-Al2O3 powders

This paper demonstrates that seeding nanocrystalline transition alumina powders is a viable option for producing high quality, alumina-based ceramics. By using α-Al₂O₃ concentrations of ⩾1.25 wt.% α-Al₂O₃ seed particles (equivalent to 5 ×10¹⁴ seeds/cm³ of γ-Al₂O₃) the sintering temperature is reduced from 1600°C for unseeded γ-Al₂O₃ to 1300–1400°C in dry pressed powders. The scale of the sintered microstructure is related to N_v^−1/3 and thus a 100-nm grain size is obtained. It is apparent that seeding is necessary for producing dense, alumina-based ceramics from nanocrystalline transition alumina powders.