Photoluminescence Spectra and Crystallization of θ-Al2O3 and α-Al2O3 from AlOOH-Fe(NO3)3 Gels

Diphasic boehmite derived unseeded and seeded (by either -Al₂O₃, -Fe₂O₃, or Fe(NO₃)₃) alumina gel planar monoliths were examined by DTA, XRD and photoluminescence spectroscopy. Luminescence spectra enable sensitive monitoring of the - and -Al₂O₃ crystallization in heat-treated gels due to Cr³⁺ impurity traces. Fe(NO₃)₃ unlike other seeds effectively influences crystallization of both - and -Al₂O₃. The present results are interpreted as prevailing solution or Fe³⁺ ion effect on the crystallization process.     

Synthesis of α-amino nitriles through Strecker reaction of aldimines and ketoimines by using nanocrystalline magnesium oxide

Strecker reactions of various aldimines as well as ketoimines with TMSCN proceeded smoothly under mild conditions to give the corresponding α-amino nitriles and α,α-disubstituted α-amino nitriles, respectively, in good to excellent yields in the presence of nanocrystalline magnesium oxide. The reaction proceeds through hypervalent silicate species by coordination to O²⁻/O⁻ (Lewis basic site) of nanocrystalline magnesium oxide, proved by ²⁹Si NMR.     

Synthesis and electrochemical characterization of LiMn2−xAlxO4 powders prepared by mechanical alloying and rotary heating

LiMn_2−xAl_xO₄ (0.0⩽x⩽0.10) intercalation powders have been synthesized by mechanical alloying followed by rotary heating. The precursor of LiMn_2−xAl_xO₄ has been prepared using LiOH · H₂O, MnO₂, and Al₂O₃ by mechanical alloying, which ensured a high level of homogeneity in the chemical composition of the precursor and resulted in a reduction in the synthesis temperature and heating time. Highly crystallized LiMn_2−xAl_xO₄ powders were obtained by subsequent rotary heating of the precursor at 600 °C for 3 h. Rotary heating enhanced the experimental control in particle size distribution of the final products. The synthesized LiMn_2−xAl_xO₄ powder has a narrow particle size distribution, high discharge capacities and good cycleability. Compared with the conventional solid-state reaction process, the present method of mechanical alloying combined with rotary heating should be a suitable technique of decreasing synthesis temperature and shortening heating time, and enhancing the uniformity of particle size of the product.     

Synthesis and characterization of ultrafine γ-Al2O3:Cr nanoparticles and their performance in antibacterial activity

Journal of Sol-Gel Science and Technology - Preventing the growth of potentially deadly bacteria by newly synthesized nanoparticles (NPs) is of great importance in the development of future drugs....     

Synthesis and photocatalytic properties of α-Fe2O3 nanoellipsoids

A simple and a novel chemical approach was used for the growth of α-Fe₂O₃ nanostructures. Field emission scanning electron microscopy analysis revealed the monodisperse nanoellipsoid morphology of α-Fe₂O₃ nanostructures. The sizes of the short axis and the long axis of these ellipsoids were in the ranges of 50–60 nm and 40–50 nm, respectively. XRD analysis revealed that the product exhibited α-Fe₂O₃ phase. Comprehensive TEM and HRTEM analysis revealed that α-Fe₂O₃ nanoellipsoids are single crystal in nature. The methylene blue decomposition kinetics was studied for different irradiation time. The methylene blue was totally decomposed by increasing the irradiation time up to 220 min.     

Characterization of synthetic hematite (α-Fe2O3) nanoparticles using a multi-technique approach

The aim of this work was to investigate the surface structure of aqueous hematite dispersions characterized by a large variability of morphology and particle size combining structural investigations obtained from Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) techniques with in vitro particle size distributions and zeta potential measurements from Dynamic Light Scattering (DLS) technique, and we achieved a self-consistent and detailed characterization of hematite particles whose sizes and morphologies could be correlated to the synthesis conditions (type of added anion, Al substitution and pH). Surface AFM characterization provided an accurate analysis of particle microstructure and also indicated that the growth of microcrystals followed different surface roughness. DLS, AFM, and TEM techniques furnished complementary information on the average particle dimensions, whose variation could be attributed to the morphological difference of hematites, ranging from platy to regular or irregular hexagonal or ellipsoidal shape. Finally, a correlation between the average particle dimensions and the measured zeta potential was also been found in aqueous dilute suspensions characterized by neither pH nor-ionic-strength-control, for which a drop of zeta potential from positive to negative values was detected for hematite particle dimensions larger than a threshold size of ~150 nm.     

Preparation and Characterization of Fe/Al2O3 Nanocomposites

IntroductionAl2O3ceramic objects have a wide scope of appli-cations because of their high hardness, high intensity,low density, and superior chemical stability, whereasmetals are widely used for their excellent propertiessuch as good ductibility, electric…     

Preparation and Characterization of High-quality α-Al2O3/Al4.59Si1.41O9.7/Al2TiO5 Multiphase Material

The α-Al2O3/Al4.59Si1.41O9.7/Al2TiO5 multiphase material with high performance was prepared by reaction sintering. The influence of different formulas on the structures and properties of multiphase material was investigated to determine the optimal formula. Crystalline structure and cell parameters of sintered samples were characterized by XRD. Microstructure of all samples was observed by SEM. The properties of sintered samples were investigated. The results show that corundum phase (α-Al2O3 ), mullite solid solution phase (Al4.59Si1.41O9.7 ) and aluminium titanate phase (Al2TiO5 ) were formed in the sintered samples. Different formulas would not change the symmetry of each crystalline phase, but caused slight change in their cell parameters. The optimal formula was determined to be coarse corundum of 36%, fine corundum of 21%, total amount of three kinds of clay of 33%, and TiO2 of 12%, which possessed a comparatively ideal microstructure and optimal properties.     

Simultaneous synthesis and consolidation of nanocrystalline 3Co–Al2O3 composite by pulsed-current-activated heating,and the mechanical properties of the material

Nanopowders of CoO and Al were fabricated by high-energy ball milling. Highly dense nanostructured 3Co–AlO₃ composite was then synthesized and consolidated, within 2 min, from mechanically activated powder (3CoO and Al) under 80 MPa pressure, by a pulsed-current-activated sintering method. The advantage of this process is that it enables very rapid densification to near theoretical density and prevents grain growth in nanostructured materials. The grain sizes of Co and Al₂O₃ in the composite were calculated. The average hardness and fracture toughness of nanostructured 3Co–AlO₃ composite were also investigated.     

Synthesis and electrochemical properties of regular hexahedron α-Fe2O3

Synthesis of α-Fe₂O₃ compound with regular hexahedron shape is firstly reported. X-ray diffraction and scan electron microscope are used to characterize the structure and morphology of the prepared sample, respectively. The average edge length of hexahedron is about 0.9 μm. A reaction mechanism has been proposed. The pH value is a crucial factor for the formation and shape of α-Fe₂O₃. Moreover, electrochemical impedance spectroscopy and charge-discharge test of α-Fe₂O₃ as anode material in lithium ion batteries are evaluated. The data indicate that the synthesized regular hexahedron α-Fe₂O₃ can show better electrochemical properties than that of the commercial.     

Synthesis and characterization of α,ω-dichloro-polymethylphenylsilane

The synthesis of a functional polysilane, α,ω-dichloro-polymethylphenylsilane (α,ω-dichloro-PMPS), based on the Wurtz-type reductive coupling, has been considered. A study of some reaction parameters shows that both yield and molecular weight distribution of α,ω-dichloro-PMPS can be greatly influenced by the work-up conditions, reaction time, monomer concentration and temperature during the initiation of the polymerization. By varying the synthesis conditions, different ratios of high and low molecular weight fractions were obtained. Samples of different molecular weight were isolated by fractional precipitation of the crude polymers. The chlorine-end functionalization was confirmed by ²⁹Si NMR spectroscopy and the concentration of end-groups was quantitatively determined by elemental analysis of chlorine.     

Synthesis of α-CN and α-CF3 N-heterocycles through tandem nucleophilic additions

Using a readily available secondary aminoalkyne as starting material, a powerful strategy was discovered to prepare precursors of biologically important unnatural cyclic aminoacids and fluorinated N-heterocycles with important ring sizes (e.g., 5-7) in a one-pot reaction using two nucleophilic additions in a tandem fashion.     

Uranyl orthovanadate of composition (UO2)3(VO4)2 · 4H2O: Synthesis and characterization

Uranyl orthovanadate of composition (UO₂)₃(VO₄)₂ · 4H₂O was prepared by heating uranovanadic acid HVUO₆ · 2H₂O under hydrothermal conditions at 200°C. X-ray fluorescence analysis, high-temperature X-ray diffraction, scanning calorimetry, and IR spectroscopy served to study dehydration and to determine the structure, X-ray diffraction, and spectroscopic characteristics of dehydration products.     

Size-dependence of the heat capacity and thermodynamic properties of hematite (α-Fe2O3)

The heat capacity of a 13 nm hematite (α-Fe₂O₃) sample was measured from T = (1.5 to 350) K using a combination of semi-adiabatic and adiabatic calorimetry. The heat capacity was higher than that of the bulk which can be attributed to the presence of water on the surface of the nanoparticles. No anomaly was observed in the heat capacity due to the Morin transition and theoretical fits of the heat capacity below T = 15 K show a small T³ dependence (due to lattice contributions) with no T^3/2 dependence. This suggests that there are no magnetic spin-wave contributions to the heat capacity of 13 nm hematite. The use of a large linear term to fit the heat capacity below T = 15 K is most likely due to superparamagnetic contributions. A small anomaly within the temperature range (4 to 8) K was attributed to the presence of uncompensated surface spins.     

Conductivity of Al2(WO4)3–WO3 and Al2(WO4)3–Al2O3 Composites

Russian Journal of Electrochemistry - Composites of (1 – x)Al2(WO4)3–xWO3 and (1 – x)Al2(WO4)3–xAl2O3 are synthesized and their conductivity is studied as dependent on the...     

Properties and consolidation of nanocrystalline 3Cu–Al2O3 composite by rapid sintering

Nanopowders of Cu and Al₂O₃ were synthesized from 3CuO and 2Al powders by high-energy ball milling. Nanocrystalline Al₂O₃ reinforced composite was consolidated by pulsed-current activated sintering method within 2 min from mechanically synthesized powders of Al₂O₃ and Cu. The relative density of the composite was 96%. The average hardness and fracture toughness values obtained were 540 kg/mm² and 6.3 MPa m^1/2, respectively.