Microwave hybrid sintering of Al2O3 and Al2O3–ZrO2 composites,and effects of ZrO2 crystal structure on mechanical properties,thermal properties,and sintering kinetics

Structural ceramics such as Al₂O₃ and Al₂O₃–ZrO₂ composites are widely used in harsh environment applications. The conventional sintering process for fabrication of these ceramics is time-consuming method that requires large amount of energy. Microwave sintering is a novel way to resolve this problem. However, to date, very limited research has been carried out to study the effects of different ZrO₂ crystal structures on Al₂O₃–ZrO₂ composites, especially on the sintering kinetics, when fabricated by microwave sintering.The microwave hybrid sintering of Al₂O₃ and Al₂O₃–ZrO₂ composites was performed in this study. Tetragonal zirconia and cubic zirconia were used as two different reinforcements for an α–alumina matrix, and the mechanical and thermal properties were studied. It was found that Al₂O₃ experienced a remarkable increase in fracture toughness of up to 42% when t-ZrO₂ was added. Al₂O₃–c-ZrO₂ also showed increased fracture toughness. The sintering kinetics were also thoroughly investigated, and the average activation energy values for the intermediate stage of sintering were estimated to be 246 ± 11 kJ/mol for pure Al₂O₃, 319 ± 71 kJ/mol for Al₂O₃–c-ZrO₂, and 342 ± 77 kJ/mol for Al₂O₃–t-ZrO₂. These values indicated that the activation energy was increased by the addition of either type of ZrO₂, with the highest value shown by Al₂O₃–t-ZrO₂.     

Ruthenium catalyzed copolymerization of 2-acetylphenanthrene and α,ω-dienes

Summary Copolymers with 2-aceto-1,3-phenanthrenylene units in the chain have been directly prepared by Ru catalyzed step-growth copolymerization of 2-acetyl phenanthrene and ,-dienes such as 1,3-divinyltetramethyldisiloxane. Copolymers which incorporate 2-aceto-1,3-phenanthrenylene units possess higher T_gS and increased thermal stability compared to analogous copolymers which have 2-aceto-5-phenyl-1,3-phenylene(biphenyl) or 2-aceto-1,3-phenylene units. Fluorescence spectra of these copolymers have been obtained.     

Synthesis and reactivity of an 2-azabutadiene-based π-conjugated dithioether: Formation of a N,S-ligated molybdenum chelate complex and C,N,S-pincer complexes of palladium and platinum

Nucleophilic attack of sodium isopropylthiolate on 4,4-dichloro-1,1-diphenyl-2-azabuta-1,3-diene [Cl₂CC(H)–NCPh₂}] (1) affords the 2-azabutadiene derivative [(i-PrS)₂CC(H)–NCPh₂] (2). Upon irradiation of Mo(CO)₆ in THF in the presence of 2, the chelate complex cis-[(OC)₄Mo{(i-PrS)₂CC(H)–NCPh₂}] (3) is obtained. Coordination on Mo occurs through the imine nitrogen and a thioether group. Polydentate dithioether 2 acts as N,C,S-pincer ligand after orthometallation reaction with Pd(II) or Pt(II). The molecular structures of 2 and (C,N,S)-[(i-PrS)₂CC(H)–NC(Ph)C₆H₄)PtCl] (4b) have been determined by X-ray diffraction studies.     

Excess Molar Volumes and Viscosities of Binary Mixtures of p-Xylene with Cyclohexane, n-Heptane, n-Octane, Sulfolane, N-Methyl-2-pyrrolidone and Acetic Acid at 303.15 K and 323.15 K and Atmospheric Pressure

Experimental data on density and viscosity at 303.15 K and 323.15 K are presented for the binary mixtures of p-xylene with cyclohexane, n-heptane, n-octane, sulfolane, N-methyl-S-pyrrolidone and acetic acid. From these data, the excess molar volume and deviations in viscosity have been calculated. The computed quantities have been fitted to the Redlich-Kister Equation to derive coefficients and estimate the standard error values. Results are discussed in terms of intermolecular interactions.     

Chemisorption of halogen on carbon—II Thermal reversibility of Cl2, HCl and H2 chemisorption

There are surface double bonds on carbons which differ from the graphitic surface π-bonds in their chemical reactivity. They may be created by degassing prechlorinated or prehydrogenated carbon samples, besides their natural occurrence in nontreated carbons.Cl₂, H₂ and HCl may be added to these double bonds and partially degassed by thermal cycling in presence of the gases. This indicates that at least part of these olefinic bonds are thermally labile and are, therefore, important for catalysis and surface chemical modifications of carbons. The surface concentration of the labile bonds is low, amounting to a few hundredths of meq/100m² of carbon surface area. Discrimination between physisorption and chemisorption of H₂ on carbon can be made by analysis of the dependence of adsorption on temperature. With Cl₂, considerable overlap between the two processes takes place.     

Fabrication,Mechanical Properties and Microstructure of CaO Stabilized ZrO2 Refratory

The fabrication processing of CaO stabilized ZrO2 refractory was investigated by studying the effects of processing parameters such as forming pressure and sintering temperature on the properties of the obained samples,It was found that the bulk density of CaO-ZrO2 refractory could attain 4.78g/cm^3,equivalent to about 85% of theoretical density,when sintering process was carried out at 1780℃ two hours.The flexural strength at room and elevated temperatures(1200℃) was measured,and could reach 53 MPa and 39 MPa respetively,exhibiting a good strength retention to high temerature.The,SEM microguraphs on the fracture surface suggested that the materials fractured along the grain boundaries as wel as through the grais.For comparsion,the relevant data of one Vesuvius CaO-ZrO2 product(Vesuvius Corporation,U.S.A) were also presented.     

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.     

Measurement and correlation of solid–liquid phase equilibria for binary and ternary systems consisting of N-vinylpyrrolidone, 2-pyrrolidone and water

The solid–liquid equilibria(SLE)for binary and ternary systems consisting of N-Vinylpyrrolidone(NVP),2-Pyrrolidone(2-P)and water are measured.The phase diagrams of NVP(1)+2-P(2),NVP(1)+water(2),NVP(1)+2-P(2)+1 wt%water(3)and NVP(1)+2-P(2)+2 wt%water(3)are identified as simple eutectic type with the eutectic points at 263.75 K(x_(1E)=0.5427),251.65 K(x_(1E)=0.3722),260.25 K(x_(1E)=0.5031)and256.55 K(x_(1E)=0.4684),respectively.The phase diagram of 2-P(1)+water(2)has two eutectic points(x_(1E)=0.1236,T_E=259.15 K and x_(1E)=0.7831,T_E=286.15 K)and one congruent melting point(x_(1C)=0.4997,T_C=303.55 K)because of the generation of a congruently melting addition compound:2-P·H_2O.The ideal solubility and the UNIFAC models were applied to predict the SLE,while the Wilson and NRTL models were employed in correlating the experimental data.The best correlation of the SLE data has been obtained by the Wilson model for the binary system of NVP+2-P.The UNIFAC model gives more satisfactory predictions than the ideal solubility model.     

Flammability of Vapor–Gas Mixtures C2F4, SO3, and C2F4OSO2

Flammability limits and conditions of flegmatization of vapor–gas mixtures by helium and perfluoropropane are determined. For most mixtures, the maximum pressure of explosion and the maximum growth rate of pressure in explosion are determined. Addition of sulfuric anhydride to tetrafluoroethylene significantly decreases the minimum energy of flammability as compared to pure tetrafluoroethylene but weakly affects the maximum pressure of explosion and pressure growth rate in explosion. It is found that pure vapors of tetrafluoroethanesultone present an explosive hazard, but its mixtures with sulfuric anhydride are most dangerous.     

Mössbauer spectroscopy,XRPD, and SEM study of iron-containing Na2O-B2O3-SiO2 glasses

Glasses in the Na₂O-B₂O₃-SiO₂-Fe₂O₃ system are suitable for producing magnetic porous glasses—host matrices for multiferroic composite materials for spintronics applications. Successful synthesis of such materials is dependent on the knowledge of crystallization and immiscibility areas in this system. Here, we report new findings for such glasses with a constant SiO₂ concentration of 70 mol %, containing 7-12 mol % Fe₂O₃, whose compositions lie in the low (2 mol % Na₂O) and higher (8-12 mol % Na₂O) alkali regions, heat-treated at 550°C. Glasses were studied using analytical chemistry methods and investigated by means of Mössbauer spectroscopy, XRPD and SEM. We outlined the immiscibility area boundary in the chosen silica cross-section for 550°C, indicating the region of interconnected morphology and the crystallization fields of magnetite and FeSiO₃, and correlated them with data on the valence and coordination state of iron in glasses. We find that both Fe³⁺ and Fe²⁺ ions in the low-alkali region are octahedrally coordinated, in higher alkali area Fe³⁺ and Fe²⁺ are tetrahedrally and octahedrally coordinated, respectively. A significant amount of Fe²⁺ in the low-alkali region can be the cause of the FeSiO₃ formation. The usual crystalline phase in non-X-Ray amorphous glasses is magnetite, precipitating at the annealing stage.     

Comparison of Mg–Al layered double hydroxides intercalated with OH− and CO32− for the removal of HCl,SO2, and NO2

Journal of Porous Materials - Two different Mg–Al layered double hydroxides (LDHs), OH?Mg–Al LDH and CO3?Mg–Al LDH, are prepared and utilized for the efficient removal...     

Growth,doping and characterization of epitaxial thin films and patterned structures of AlN,GaN, and AlxGa1−xN

Advancements in the doping of GaN and Al_xGa_1−xN thin films, and the growth of GaN and Al_xGa_1−xN structures on patterned heterostructure substrates via metalorganic vapor phase epitaxy are reported. The acceptor-type behavior of Mg-doped GaN films grown in N₂ diluents is presented. Net ionized impurity concentrations up to 8×10¹⁸ cm⁻³ and Hall mobilities up to ≈14 cm² V⁻¹ s⁻¹ were measured for Mg-doped films grown in N₂ in the as-grown condition. Donor and acceptor doping of Al_xGa_1−xN alloys was performed. Acceptor doping of Al_xGa_1−xN for x≤0.13 and donor doping for x≤0.58 were achieved for films deposited at 1100 °C. Lateral epitaxial overgrowth of GaN and Al_xGa_1−xN layers was investigated. The growth and coalescence of GaN and Al_xGa_1−xN stripes patterned in SiO₂ and/or SiN_x masks deposited on GaN, including aligned second lateral epitaxial overgrowth on initial laterally overgrown GaN layers, are discussed.     

Experimental Measurement and Correlation of the Solubility of Methyl-acetyl-naphthalene in n-Heptane,n-Octane,and n-Dodecane

1 INTRODUCTION 2-Methyl-6-acetylnaphthalene (2,6-MAN) is a type of white or pale yellow, powdery crystal, with a melting point of 332.15K. It is an important interme- diate[1] used for producing 2,6-naphthalene dicarbox- ylic acid (2,6-NDA), which has very extensive appli- cations in not only the light, electronic, and defense industries, but in many other areas. In particular, 2,6-NDA is an important monomer of liquid crystal polyester material (LCP) and polyethylene naphtha- lene-2…     

Synthesis, Characterization, Conductivity, Band Gap, and Thermal Analysis of Poly-[(2-mercaptophenyl)iminomethyl]-2-naphthol and Its Polymer–Metal Complexes

Oxidative polycondensation reaction conditions of [(2-mercaptophenyl)iminomethyl]-2-naphthol (2-MPIM-2N) were studied using oxidants such as air and NaOCl in an aqueous alkaline medium between 40 °C and 90 °C. The structure of poly-[(2-mercaptophenyl)iminomethyl]-2-naphthol (P-2-MPIM-2N) was characterized by ¹H- ¹³C NMR, FT-IR, and UV–Vis spectroscopy, size exclusion chromatography (SEC), and elemental analysis. At optimum reaction conditions, the yield of P-2-MPIM-2N was found to be 78 and 82% for air and NaOCl oxidants, respectively. From SEC measurements, the number-average molecular weight (M _n ), weight-average molecular weight (M _w ) and polydispersity index (PDI) of P-2-MPIM-2N are 2900, 3500 g mol⁻¹ and 1.207; 2200, 2500 g mol⁻¹ and 1.136, for air and NaOCl oxidants, respectively. Polymer–metal complexes were synthesized by the reaction of P-2-MPIM-2N with Co²⁺, Cu²⁺, Zn²⁺, Pb²⁺ and Cd²⁺ ions. The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and electrochemical band gaps (E^￠_g E^{\prime}_{g} ) of 2-MPIM-2N and P-2-MPIM-2N were −5.97, −2.66 and 3.31 eV and −5.82, −2.68 and 3.14 eV, respectively. The conductivity of polymer and polymer–metal complexes were determined in the solid state. Conductivity measurements of doped and undoped Schiff base polymer and polymer–metal complexes were carried out at room temperature and atmospheric pressure by the four-point probe technique using an electrometer. The conductivities of the polymer and polymer–metal complexes increased when iodine was used as doping agent.     

Structural,textural, surface chemistry and sensing properties of mesoporous Pr,Zn modified SnO2–TiO2 powder composites

Mesoporous Zn and Pr modified SnO₂-TiO₂ mixed powders (Sn:Ti:Zn:Pr contents 60:20:15:5) have been prepared by a modified sol–gel method involving Tripropylamine (TPA) as chelating agent, TritonX100 as template and Polyvinylpyrrolidone as dispersant and stabilizer, respectively. The obtained gels have been dried at different temperatures and calcined in air at 600 and 800 °C, respectively. Phase identification of the synthesized samples and their evolution with the calcination temperature has been performed by X-ray diffraction. N₂ adsorption/desorption isotherms were found to be characteristic for mesoporous materials, showing relatively low values for the specific surface area (15–32 m² g⁻¹) and nanometric sized pores. In case of the sample calcined at 800 °C, a bimodal pore size distribution can be observed, with maxima at 20 and 60 nm. SEM results demonstrate a porous nanocrystalline morphology stable up to 800 °C. The surface chemistry investigated by XPS reveals the presence of the elements on the surface as well as the oxidation states for the detected elements. At 800 °C a diffusion process of Sn from surface to the subsurface/bulk region accompanied by a segregation of Ti and Zn to the surface is noticed, while Pr content is unchanged. The sensing properties of the prepared powders for CO detection have been tested in the range of 250–2000 ppm and working temperatures of 227–477 °C.     

TG and DTA investigation of ZrO2–SO 4 2– catalysts exposed to hexane, methylcyclopentane and cyclohexane

ZrO₂– catalysts with different sulfur contents were analysed with thermal methods coupled with mass spectrometry after exposure to mixtures of hexane, methylcyclopentane, and cyclohexane in argon. The reaction of the hydrocarbons led to carbonaceous deposits, but an important part of hydrocarbon remained chemisorbed as well. Heating these samples in He atmosphere provoked the decomposition of these deposits with evolution of CO₂ and CO, and also of SO₂ and SO. At the same time, COS was evidenced in the reaction products. The release of these molecules occurred below the activation temperature of the catalysts. The behavior of the catalysts depended both on reactant molecule and sulfur content. The analyses clearly evidenced the oxidation ability of ZrO₂–SO catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Char gasification in steam at 1123 K catalyzed by K,Na, Ca and Fe—effect of H2, H2S and COS

Gasification of unloaded and loaded Saran char was followed at 1123 K and 0.1 MPa total pressure in a N₂ or H₂ atmosphere to which ~ 3 kPa H₂O and, in some cases, ~ 500 ppm H₂S or COS were added. Potassium, Na and Ca are excellent catalysts for the gasification of Saran char by steam. Hydrogen inhibits catalysis by K, Na and Ca but promotes catalysis by Fe. The extent of the effect of H₂S (or COS) on inhibiting char gasification by steam depends upon whether it is added to wet N₂ or wet H₂. The inhibitory effect is much more marked in wet H₂ in all cases. Likewise, the time required to recover catalyst activity, following exposure to H₂S or COS, is much greater in the presence of wet H₂ than in the presence of wet N₂.     

Synthesis, Electrical Measurement, and Field Emission Properties of α-Fe2O3 Nanowires

α-Fe₂O₃ nanowires (NWs) were formed by the thermal oxidation of an iron film in air at 350 °C for 10 h. The rhombohedral structure of the α-Fe₂O₃ NWs was grown vertically on the substrate with diameters of 8–25 nm and lengths of several hundred nm. It was found that the population density of the NWs per unit area (D _NWs) can be varied by the film thickness. The thicker the iron film, the more NWs were grown. The growth mechanism of the NWs is suggested to be a combination effect of the thermal oxidation rate, defects on the film, and selective directional growth. The electrical resistivity of a single NW with a length of 800 nm and a diameter of 15 nm was measured to be 4.42 × 10³ Ωcm using conductive atomic force microscopy. The field emission characteristics of the NWs were studied using a two-parallel-plate system. A low turn–on field of 3.3 V/μm and a large current density of 10⁻³ A/cm² (under an applied field of about 7 V/μm) can be obtained using optimal factors of D _NWs in the cathode.     

Influence of the Steric Hindrance,Ligand Hydrophobicity,and DN of solvents on Structure and Extraction of Cu(II) Complexes of 1‐Alkyl‐2‐Ethylimidazoles

Abstract

Formation of Cu(II) complexes of 1‐alkyl‐2‐ethylimidazoles (where alkyl=propyl, butyl, pentyl, hexyl, and octyl) has been studied by using the liquid‐liquid partition method, at 25°C and a fixed ionic strength of the aqueous phase (I=0.5; (HL)NO₃, KNO₃). The complexes were extracted with 2‐pentanone, 2‐butanol, isoamyl alcohol, 2‐ethyl‐1‐hexanol, dichloromethane, trichloromethane, and toluene. The length of the 1‐alkyl group and the nature of solvent have been shown to influence the extraction process. Extraction curves (log D_M vs. pH) are displaced towards lower pH's with increasing chain length of the 1‐alkyl substituent and donor number of the solvents. Stability constants of the complexes in aqueous solution were determined as well as their partition ratios between the aqueous and organic phase. The stability of the Cu(II) complexes increased with increasing 1‐alkyl chain length. The stability constants are comparable with β_n ones for the Cu(II) complexes of 1‐alkyl‐2‐methylimidazoles, but smaller than those of the Cu(II)–1‐alkylimidazole counterparts. The P_c‐partition ratios of the 1‐alkyl‐2‐ethylimidazole complexes with Cu(II) are high, and increased with increasing 1‐alkyl chain length and the donor number of the solvents. Both the strong steric effect of the ethyl substituent at position 2 and the bulkiness of the 1‐alkyl‐2‐ethylimidazole molecules as well as the strong electron‐donating properties of the solvent molecules have an effect on the change of the coordination number of Cu(II) from 6 to 4. The 4‐coordinate Cu(II) complexes (distorted tetrahedron) are more readily extractable by organic solvent than are the 6‐coordinate ones and for this reason their partition constants, P_c, are high. This finding offers the possibility of extraction of the Cu(II) ions from a mixture cations.