η-Al_2O_3与γ-Al_2O_3在CS_2催化水解反应中的性能比较

通过制备高纯度的前驱体湃铝石获得了η-Al_2O_3材料,采用XRD验证了η-Al_2O_3与γ-Al_2O_3在晶相结构上的差异,比较了两者的表面形貌、织构及酸碱性能,结果显示,η-Al_2O_3与γ-Al_2O_3的比表面积相当,但η-Al_2O_3具有更弱的弱碱位和较少的强碱位,并拥有丰富的中等强度酸性位。将η-Al_2O_3与γ-Al_2O_3作为催化剂应用于CS_2水解反应,结果表明,在(200～450)℃测试温度范围内,η-Al_2O_3催化剂对CS_2的水解活性始终优于γ-Al_2O_3,两种催化剂上CS_2反应的浓度效应也明显不同,推测与它们的酸碱性质影响了对CS_2的吸附能力有关,导致两者催化CS_2水解反应遵循了不同的机制。     

Effect of Al_2O_3-SiC Composite Powder on Properties of Al_2O_3-SiC一C Bricks

Al2O3- SiC- C specimens were prepared using white fused corundum( 3- 1,≤1 and ≤0. 044 mm),Al2O3- SiC composite powders( d50≤5 μm),α-Al2O3micropowder( d50= 1. 2 μm),SiC powder( ≤0. 044mm),flake graphite( ≤0. 088 mm),Si powder( d50= 42. 8 μm) and B4C powder( d50≤10 μm) as main starting materials,and thermosetting phenolic resin as binder. 4%,8%,12% and 16%( in mass,the same hereinafter) of Al2O3- SiC composite powders substituted the same quantity of α-Al2O3micropowder + SiC powder.Effects of composite powder additions on apparent porosity,bulk density,cold modulus of rupture,cold crushing strength,hot modulus of rupture( 1 400 ℃),therma shock resistance( 1 100 ℃,water quenching) and oxidation resistance( 1 000 and 1 500 ℃) of Al2O3- SiC- C specimens after 180 ℃ curing,1 000 ℃ 3 h carbon-embedded firing and 1 500 ℃ 3 h carbon-embedded firing,respectively,were researched. The results indicate that:( 1) with the increase of Al2O3- SiC composite powder,cold strengths of the cured specimens decline,those of the specimens fired at 1 000 ℃ change a little,and those of the specimens fired at 1 500 ℃ change a little except for an obvious improvement of cold crushing strength;( 2) with the increase of Al2O3- SiC composite powder,hot modulus of rupture at 1 400 ℃ decreasesand thermal shock resistance enhances significantly;( 3) when Al2O3- SiC composite powder addition is4%,the oxidation resistance at 1 500 ℃ is the best,and the reason may be the composite powder is finer and more active,which is beneficial to form dense mullite protective layer to retard the O2diffusion into the specimens.     

Phase Formation and Process Analysis of SiC-Al_2O_3-Al_6Si_2O_(13) Composite Powder via Carbothermal Reduction of Fly Ash at 1 550 ℃

Silicon carbide(SiC)-alumina(Al_2O_3)-mullite(Al_6Si_2O_(13)) composite powder was successfully synthesized at 1 550 ℃ for 5 h via carbothermal reduction reaction,and the effects of various mass ratios of active carbon to fly ash(0.38,0.44 and 0.58) on the phase composition and microstructure of products were investigated,and the formation process of the powder was also analyzed in detail.The products mainly consist ofβ-SiC,α-Al_2O_3,Al_6Si_2O_(13) and FeSi.Increasing carbon content favors the decomposition of Al_6Si_2O_(13) and formation of SiC.The average particle size of β-SiC andα-Al_2O_3 is about 1 μm and that of Al_6Si_2O_(13) is 5-10μm.The formation process of SiC-Al_2O_3-Al_6Si_2O_(13)powder includes the decomposition of mullite in fly ash and formation of SiC.     

Effect of Polyethylene Glycol (PEG) Powder on Compressibility and Microstructural Properties of Sintered α-Alumina

This study examines the effect of various contents of polyethylene glycol (PEG) powders on density, compressibility, and microstructural properties of sintered α-alumina samples. Moreover, the effect of compaction pressure on the green density of the compacts is studied by applying different pressures ranging from 400 to 550 MPa. Samples were prepared by mechanical blending of alumina and various amounts of PEG powders in a Turbula mixer. The binder contents vary from 1 wt.% to 4 wt.%. The as-prepared mixture was compacted in a universal machine at room temperature under the pressure of 6 MPa to produce disk-shaped samples in a pre-compaction step. Experimental results revealed that adding various amounts of PEG powders has a detrimental effect on the green density of alumina pellets and decreases the green density from 1.95 to 1.87 g/cm³. The results also show that sintered density of samples increased by increasing the compaction pressure to pressures higher than 400 MPa. It is observed that a sudden increase in green density has been observed between 450 and 550 MPa.     

Preparation and Properties of ε-Fe3N-Based Magnetic Fluid

In this work, ε-Fe₃N nanoparticles and ε-Fe₃N-based magnetic fluid were synthesized by chemical reaction of iron carbonyl and ammonia gas. The size of ε-Fe₃N nanoparticles was tested by TEM and XRD. Stable ε-Fe₃N-based magnetic fluid was prepared by controlling the proper ratio of carrier liquid and surfactant. The saturation magnetization of stable ε-Fe₃N-based magnetic fluid was calculated according to the volume fraction of the particles in the fluid. The result shows that both the calculated and measured magnetizations increase by increasing the particle concentration. With the increasing concentration of the ε-Fe₃N particles, the measured value of the magnetic fluid magnetization gradually departs from the calculated magnetization, which was caused by agglomeration affects due to large volume fraction and large particle size.     

Preparation and Luminescence Properties of Ba_（2-x）B_2O_5：xSm~（3＋） Red-Emitting Phosphor

采用高温固相法合成了Ba2–xB2O5：xSm3＋红色荧光粉。研究了Sm3＋掺杂量对样品发光性质的影响。结果表明,合成物质为纯相Ba2B2O5晶体结构。主激发峰为342nm（6H5/2→4H9/2）、359nm（6H5/2→4D3/2）、372nm（6H5/2→6P7/2）、400nm（6H5/2→4F7/2）、436nm（6H5/2→4G9/2）、450～510nm（6H5/2→4I13/2,4I9/2,4I11/2,4G7/2）。主发射为550～575nm（4G5/2→6H5/2）、580～620nm（4G5/2→6H7/2）及630～660nm（4G5/2→6H9/2）,其中以400nm激发的峰值最大。随着Sm3＋掺量x的增大,发光强度先增大后减小,在x=0.06时达到最大值。分析表明其浓度猝灭的机理是电偶极–电四极相互作用。     

Selective Production of H2 from Ethanol at Low Temperatures over Rh/ZrO2–CeO2 Catalysts

A series of Rh catalysts on various supports (Al₂O₃, MgAl₂O₄, ZrO₂, and ZrO₂–CeO₂) have been applied to H₂ production from the ethanol steam reforming reaction. In terms of ethanol conversion at low temperatures (below 450 °C) with 1wt% Rh catalysts, the activity decreases in the order: Rh/ZrO₂–CeO₂ > Rh/Al₂O₃ > Rh/MgAl₂O₄ > Rh/ZrO₂. Support plays a very important role on product selectivity at low temperatures (below 450 °C). Acidic or basic supports favor ethanol dehydration, while ethanol dehydrogenation is favored over neutral supports at low temperatures. The Rh/ZrO₂–CeO₂ catalyst exhibits the highest CO₂ selectivity up to 550 °C, which is due to the highest water gas shift (WGS) activity at low temperatures. Among the catalysts evaluated in this study, the 2wt% Rh/ZrO₂–CeO₂ catalyst exhibited the highest H₂ yield at 450 °C, which is possibly due to the high oxygen storage capacity of ZrO₂–CeO₂ resulting in efficient transfer of mobile oxygen species from the H₂O molecule to the reaction intermediate.     

Influence of Synthesized Super Al2O3 Powder on the Properties of Alumina Castable

The in fluence of three different Al2O3 powder on self-flowing alumina castable was studied.Maximum compaction of sample was computed by Andresen Equation.The result showed that the Al2O3 powder.which has much smaller particle size,could improve the microstructure and the mechanical properties of castable under room temperature and high temperature.With the same powder size,the room tem perature strength of the castable added with Al2O3 powder properties of which were altered by adding mineralizing agent,was higher than that of the castable added with common Al2O3 powder ,but the flowability of these three different castable was almost the same.     

Preparation,Characterization, and Properties of Novel Polyimide–SiO2 Hybrid Composites Based on Bipyridine for Low Dielectric Applications

Novel low dielectric polyimide–SiO₂ hybrid materials containing bipyridine were prepared with three-step sol–gel process from poly(amic acid)s. (3-Aminopropyl)triethoxysilane as coupling agent was used to increase the intrachain chemical bonding between the polyimide and SiO₂ groups. The thermal, dielectric, and physical properties of the hybrid materials were investigated and correlated with the porous structure. The glass transition temperatures of all the hybrids were found to be higher than polyimides. The effect of SiO₂ groups on the porous structure and dielectric properties was investigated. The dielectric constant of the hybrid materials was observed a decrease from 3.30 to 2.15 with increased SiO₂ amount.     

Preparation and Properties of Water-Soluble PAA–PAS/SiO2 Hybrid Materials

Copolymers with different weight ratios of AA/PAS (acrylic acid/poly(DL-aspartic acid)) were synthesized and blended with sol-gel precursors to prepare water-soluble PAA–PAS/SiO₂ inorganic/organic hybrid materials. The PAS polymer or its copolymer in PAA–PAS/SiO₂ formed hydrogen bonds with SiO₂ and the amorphous structure of the hybrid material varied with the weight ratio of PAA. The hybrid materials exhibited enhanced thermal resistance over the copolymer alone. All hybrid materials were water-soluble and relatively insoluble in organic solvents.     

Effect of Industrial Alumina Powder Particle Size on Preparation of Active α-Al2O3 Micropowder

To study the effect of the particle size of industrial alumina powder on the properties of active alumina micropowder(α-Al2O3 micropowder),the fine powders with...     

Kinetics on Hydrogenation of Cyclopentadiene over Pd/γ-Al_2O_3 Catalyst

The macrokinetics of hydrogenation of cyclopentadiene was investigated over Pd/γ-Al_2O_3 catalyst. Experimental results showed that the relationship between the constituents and reaction time was in agreement with the characteristic of consecutive irreversible first-order reaction.Analysis on the reaction mechanism of selective hydrogenation of cyclopentadiene indicated that it is reasonable to express the hydrogenation rate of cyclopentadiene in the power law form.Parameters of the kinetic model were obtained by the Gauss-Newton method based on the experimental data.From the statistic test and residual error distribution the kinetic model was proved to be adequate.     

Preparation, Characterization, and Photoelectric Properties of Langmuir–Blodgett Films of Some Europium-Substituted Polyoxometalates and 2-Aminofluorene with Tunable Emission Color

A new series of organic/inorganic composite Langmuir–Blodgett (LB) films consisting of 2-aminofluorene (Fl–NH₂) as the π-conjugated organic molecule, an europium-substituted polyoxometalate (POM, POM = Na₉EuW₁₀O₃₆, K₁₃[Eu(SiW₁₁O₃₉)₂] and K₅[Eu(SiW₁₁O₃₉)(H₂O)₂], which are denoted by EuW₁₀, EuW₂₂ and EuW₁₁, respectively) as the inorganic component, were prepared. Structural and photophysical characterization of these LB films were achieved by π–A isotherms, UV–Vis absorption and photoluminescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, and surface photovoltage spectroscopy. Our experimental results indicate that stable Langmuir and LB films are formed in pure water and POM sub-phases. Luminescence spectra of the prepared hybrid LB films show that tunable emission color can be obtained due to the dual-emissive nature of the mixed Fl–NH₂/POM blends. These 2-aminofluorene-based LB films displayed interesting electrical conductivity behavior. Among them, Fl–NH₂/EuW₁₁ 3-layer films showed a good electrical response with the a tunneling current up to ± 100 nA when the voltage was monitored at ?0.8 to 1.5 V. These LB composites show good photovoltage responses and a photovoltage of 2.7 μV can be obtained for the Fl–NH₂/EuW₂₂ system when it is excited by light.     

Synthesis and Characterization of Mn–Ce–VOx/TiO2 Nanocomposite for SCR of NOx at Low Temperatures: Role of Mn,Ce and V Oxide

Topics in Catalysis - Mn–Ce–VOx/TiO2 (MnCeVTi), Mn–CeOx/TiO2 (MnCeTi) and Mn–VOx/TiO2 (MnVTi) nanocomposites as SCR DeNOx catalysts were synthesized by a modified...     

Preparation of Ru(η3-2-alkenylallyl)(CO)Cl(PPh3)2 complexes via carbometallation of allenes with alkenyl ruthenium complexes

Alkenyl ruthenium complex, Ru(CHCHR)(Cl)(CO)(PPh₃)₂ 1, reacted with allenes 2 to give η³-allyl ruthenium complexes, Ru(η³-2-alkenylallyl)(Cl)(CO)(PPh₃)₂ 3, in good yields. The reaction depends on the structure of the alkenyl group. When R was phenyl or methoxycarbonyl group, the carbometallated complex 3 was yielded as a sole product. However, when R was butyl or trimethylsilyl group, besides the carbometallation product as main product, was obtained a small amount of 2-unsubstituted η³-allyl ruthenium complex which was formed via β-elimination of the alkenyl complex followed by the reaction with allene. Structure of 3 was determined by the X-ray crystal structure analysis.     

Mechanical Properties of Ceramics Prepared from a Nanocrystalline ZrO2 – 3 mol.% Y2O3 Powder

Ceramics of ZrO₂ – 3 mol.% Y₂O₃ composition prepared from commercial raw materials by cold isostatic pressing technique at sintering temperatures from 1100 to 1500°C are studied. Best mechanical properties were found in material sintered at 1350°C: density, 5.95 g/cm³; bending strength, 1200 MPa, and crack resistance, about 18 MPa m^1/2. The mechanical properties of ceramic materials sintered at 1300 and 1500°C are inferior by roughly a factor of 1.5, despite virtually the same density and grain size. This difference is explained as due to the different properties of the intergranular material in ceramics sintered at different temperatures.     

Preparation,Properties and Growth Mechanism of Low-Cost Porous Si3N4 Ceramics with High Levels of β-Si3N4 Powders

Silicon - Nowadays, porous Si3N4 ceramics are fabricated by high purity α-Si3N4 powders, resulting in a higher cost of production. To reduce cost and save energy, in this research, high levels...     

Rheo-Engineering Properties of Mixed SiO2/Al2O3 Suspensions and Related Materials. III. The Fused Quartz – Fused Corundum System

A corundum suspension at pH = 7 with a 58% volume concentration of the solid phase and a molding porosity of 20% is prepared. The properties of fused quartz + fused corundum mixed suspensions are studied. Based on a mixed binder of composition 50% SiO₂ + 50% Al₂O₃ and a fused quartz filler, a castable is prepared which, heat treated at 1150°C, exhibited the following properties: open porosity — 13%, compressive — 80 MPa, temperature for strain onset under loading — 1250°C, thermal stability — 10 heat-cool cycles (1000°C – water). The new castable exhibits a higher slag resistance against the conventional quartz-based castable.