Garratt–Braverman cyclization on basic alumina: a green protocol with improved selectivity

A green protocol (compared to the existing methodology) for carrying out Garratt–Braverman cyclization has been developed. The method involves stirring a pre-absorbed bispropargyl sulfone/ether/sulfonamide over basic alumina. The reaction with sulfones was over within 10–15 min at room temperature whereas for the ether/sulfonamide the reaction took 6–8 h at 130 °C. The products, aryl naphthalene derivatives, are obtained by simple filtration through Celite, in excellent yields.     

Column preconcentration and electrothermal atomic absorption spectrometric determination of rhodium in some food and standard samples

In the present work, an electrothermal atomic absorption spectrometric method has been developed for the determination of ultra‐trace amounts of rhodium after adsorption of its 2‐(5‐bromo‐2‐pyridylazo)‐5‐diethylaminophenol/tetraphenylborate ion associated complex at the surface of alumina. Several factors affecting the extraction efficiency such as the pH, type of eluent, sample and eluent flow rates, sorption capacity of alumina and sample volume were investigated and optimized. The relative standard deviation for eight measurements of 0.1 ng/mL of rhodium was ±6.3%. In this method, the detection limit was 0.003 ng/mL in the original solution. The sorption capacity of alumina and the linear range for Rh(III) were evaluated as 0.8 mg/g and 0.015–0.45 ng/mL in the original solution, respectively. The proposed method was successfully applied for the extraction and determination of rhodium content in some food and standard samples with high recovery values.     

Charge Density Overcomes Steric Hindrance of Ferrocene Surfactant in Switchable Oil-in-Dispersion Emulsions

A ferrocene surfactant can be switched between single and double head form (FcN⁺C₁₂/Fc⁺N⁺C₁₂) triggered by redox reaction. FcN⁺C₁₂ can neither stabilize an O/W emulsion alone nor an oil-in-dispersion emulsion in combination with alumina nanoparticles due to the steric hindrance of the ferrocene group. However, such steric hindrance can be overcome by increasing the charge density in Fc⁺N⁺C₁₂, so that oil-in-dispersion emulsions can be co-stabilized by Fc⁺N⁺C₁₂ and alumina nanoparticles at very low concentrations (1×10⁻⁷ M (≈50 ppb) and 0.001 wt %, respectively). Not only can reversible formation/destabilization of oil-in-dispersion emulsions be achieved by redox reaction, but also reversible transformation between oil-in-dispersion emulsions and Pickering emulsions can be obtained through reversing the charge of alumina particles by adjusting the pH. The results provide a new protocol for the design of surfactants for stabilization of smart oil-in-dispersion emulsions.     

V2O5/MO-Al2O3（M = Mg，Ca，Sr，Ba）催化剂用于正丁烷催化氧化脱氢反应

采用浸渍法制备了不同V2O5担载量的V2O5/MO-Al2O3(M = Mg, Ca, Sr, Ba)催化剂,钒物种的前驱体为偏钒酸铵.对制备的催化剂进行了一系列表征,并对催化剂上正丁烷选择性氧化脱氢制取丁烯进行了反应研究.表征结果(包括比表面积、X射线衍射、傅里叶红外光谱、氢气程序升温还原和拉曼光谱)显示,不同碱土金属元素掺杂的催化剂显示不同的钒价态信息和催化性能.其中掺杂Ca, Sr, Ba的催化剂,正钒酸盐相很难被还原,因此催化剂的氧化还原循环难以建立,导致以上三种催化剂在正丁烷氧化脱氢反应中活性较低.然而, Mg掺杂的催化剂却显示出较高的催化活性和选择性.实验结果表明：在Mg掺杂的载体上担载5% V2O5的催化剂上600°C时可获得高达30.3%的正丁烷转化率和64.3%的烯烃总选择性.这与V2O5担载量为5%时,在获得高度分散的钒氧化合物物种时可使MgO晶相稳定存在密切相关.     

One-Pot Synthesis of 3,4-Dihydropyrimidin-2(1H)-ones and Their Sulfur Derivatives with H2SO4 Supported on Silica Gel or Alumina

The one-pot condensation of aromatic aldehydes, β-dicarbonyl compounds, and urea or thiourea in the presence of H₂SO₄ supported on silica gel or alumina (80% m/m) in refluxing n-hexane produces 3,4-dihydropyrimidin-2(1H)-ones and their sulfur derivatives in high to excellent yields.     

Structure and optical features of silicon carbide nanocrystals confined in alumina matrices

Thin films based on silicon carbide and alumina were synthesized by means of rf-sputtering using a co-deposition process. Several nanostructures were created which consist of thin films (∼200 nm thick) with homogeneous distribution of SiC nanocrystals (∼5 nm mean diameter) in the host alumina matrices. Characterization methods including X-ray photoelectrons spectroscopy (XPS), UV-vis absorption and photoluminescence (PL) were used to identify the involved structures, compositions and optical features of these nanostructures. Thus, XPS investigations were relevant to point out the involved chemical bonding in the core SiC nanocrystals and in the host alumina environments. Additionally, mixed bonding such as Si-O-C was also shown and seems to correlate with the SiC-alumina interfaces. Optical properties of the nanostructures films such as UV-vis absorption and photoluminescence (PL) were measured in representative samples and compared to simulated PL responses obtained by a theoretical model.     

Laser carbonitriding of alumina surface

Laser carbonitriding of alumina surfaces is examined. Temperature and stress fields developed during the laser heating of the substrate surface are predicted using the finite element method in line with the experimental conditions. The formation of Al(C, N) and AlN compounds in the surface region of irradiated workpiece is examined using X-ray Photoelectron Spectroscopy (XPS) and X-ray Diffraction (XRD). The microstructural and morphological changes in the laser irradiated region are examined using Scanning Electron Microscope (SEM). The microhardness of the resulting surface is measured and compared with the base material hardness. It is found that high temperature gradient is developed in the irradiated region, which in turn, results in high residual stress levels in this region. XPS and XRD data reveal the presence of Al (C, N) and AlN compounds in the surface region. The microhardness in the surface region of the laser treated workpiece increases significantly.     

Superhydrophobic alumina surface based on stearic acid modification

A novel superhydrophobic alumina surface is fabricated by grafting stearic acid layer onto the porous and roughened aluminum film. The chemical and phase structure, morphology, and the chemical state of the atoms at the superhydrophobic surface were investigated by techniques as FTIR, XRD, FE-SEM, and XPS, respectively. Results show that a super water-repellent surface with a contact angle of 154.2° is generated. The superhydrophobic alumina surface takes on an uneven flowerlike structure with many nanometer-scale hollows distribute in the nipple-shaped protrusions, and which is composed of boehmite crystal and γ-Al₂O₃. Furthermore, the roughened and porous alumina surface is coated with a layer of hydrophobic alkyl chains which come from stearic acid molecules. Therefore, both the roughened structure and the hydrophobic layer endue the alumina surface with the superhydrophobic behavior.     

Atmospheric reactive plasma sprayed Fe-Al2O3-FeAl2O4 composite coating and its property evaluation

In the present study, Fe-Al₂O₃-FeAl₂O₄ composite coatings were successfully deposited by reactive plasma sprayed Al/Fe₂O₃ agglomerated powder. Phase composition and microstructure of the coatings were determined by XRD and SEM. The results indicated that the composite coatings were principally composed of three different phases, i.e. FeAl₂O₄ phase as main framework, dispersed ball-like Fe-rich phase, and small splats of Al₂O₃ phase, and it was thought that the in situ synthesized metal phase was helpful to toughen the coating matrix. According to the results of the indentation and frictional wear tests, the composite coating exhibited excellent toughness and anti-friction properties in comparison with conventional Al₂O₃ monophase coating, though its microhardness value was a little lower than that of Al₂O₃ coating. The formation mechanism and the toughening mechanism of the composite coating were clarified in detail.     

Tunnel magnetoresistance in alumina, magnesia and composite tunnel barrier magnetic tunnel junctions

Using magnetron sputtering, we have prepared Co-Fe-B/tunnel barrier/Co-Fe-B magnetic tunnel junctions with tunnel barriers consisting of alumina, magnesia, and magnesia-alumina bilayer systems. The highest tunnel magnetoresistance ratios we found were 73% for alumina and 323% for magnesia-based tunnel junctions. Additionally, tunnel junctions with a unified layer stack were prepared for the three different barriers. In these systems, the tunnel magnetoresistance ratios at optimum annealing temperatures were found to be 65% for alumina, 173% for magnesia, and 78% for the composite tunnel barriers. The similar tunnel magnetoresistance ratios of the tunnel junctions containing alumina provide evidence that coherent tunneling is suppressed by the alumina layer in the composite tunnel barrier.