Preparation and characterization of a novel solid solution of aluminum in tungsten carbide by mechanically activated high-temperature reaction

In this work, a novel substitutional solid solution (W0.8Al0.2)C was synthesized by mechanically activated high-temperature reaction. X-ray diffraction was used for phase identification during the whole reaction process. Environment scanning electronic microscopy-field emission gun and energy dispersive x-ray were used to investigate the microstructure and the quantitative material composition of the specimen. (W(0.8)A(10.2))C was found to crystallize in the WC-type, and the cell parameters were a = 2.907(1) angstrom and c = 2.837(1) angstrom. The hardness of (W0.8Al0.2)C was tested to be 19.3 +/- 1 GPa, and the density was 13.19 +/- 0.05 g cm(-3).

A dinuclear aluminum 8-hydroxyquinoline complex with high electron mobility for organic light-emitting diodes

A dinuclear aluminum 8-hydroxyquinoline complex (DAlq(3)) with improved electron mobility was designed for organic light-emitting diodes. The electron mobility in DAlq(3) was determined via transient electroluminescence (EL) from bilayer devices with structure of indium tin oxide (ITO)/N,N-'-di(naphthalene-1-yl)-N,N-'-diphenyl-benzidine (NPB)/DAlq(3)/Mg:Ag. It was found that the electron mobility in DAlq(3) is between 3.7-8.4x10(-6) cm(2)/Vs at electric fields ranging between 1.2x10(6) and 4.0x10(6) V/cm, which is a factor of two higher than that in Alq(3). The DAlq(3) also shows a higher EL efficiency of 2.2 cd/A (1.2 Lm/W), as compared to Alq(3) with an EL efficiency of 2.0 cd/A (1.0 Lm/W), which is attributed to more balanced electron and hole recombination due to the improved electron mobility of DAlq(3).

Novel bis(8-hydroxyquinoline)phenolato-aluminum complexes for organic light-emitting diodes

A novel series of emitting aluminum complexes containing two 8-hydroxyquinoline ligands (q) and a phenolato ligand (p) were synthesized and characterized. Double layer organic light-emitting diodes (OLEDs) were fabricated using these complexes as luminescent layers, and strong electroluminescence (EL) was observed. It was found that their emitting wavelengths were mainly determined by the first ligands (q). Cyclic voltammograms revealed a partially irreversible n-doping process and indicated that these complexes show excellent electron-transporting ability.

Synthesis-dependent luminescence properties of Y3Al5O12 : Re3+ (Re=Ce, Sm, Tb) phosphors

By using metal nitrates and oxides as the starting materials, Y2Al5O12 (YAG) and YAG:Re3+ (Re = Ce, Sm, Th) powder phosphors were prepared by solid-state (SS), coprecipitation (CP) and citrate gel (CG) methods. The resulting YAG and YAG-based phosphors were characterized by XRD, FT-IR, SEM and photoluminescent excitation and emission spectra. The purified crystalline phases of YAG were obtained at 800 degreesC (CG) and 900 degreesC (CP, SS). At an identical annealing temperature and doping concentration, the doped rare-earth ions showed the stronger emission intensity in the CP- and SS-derived phosphors than the CG-derived YAG phosphors. The poor emission intensity for the CG-derived phosphors is mainly caused by the contamination of carbon impurities from citric acid in the starting materials.

A highly reduced polyoxoanion with phosphorus-centered alternate layers of Mo/V oxides, [(PMo2Mo6V4O40)-Mo-V-V-VI-O-IV((VO)-O-IV)(2)](9-)

An unusual polyoxometalate [H2N(C2H4)(2)NH2](4)(H3O)[(PMO2Mo6V4O40)-Mo-V-V-VI-O-IV((VO)-O-IV)(2)].H2O is hydrothermally synthesized and characterized by IR, UV-VIS, elemental analyses, X-ray photoelectron spectrum, ESR, TG and Single crystal X-ray diffraction. The title compound crystallizes in the orthorhombic space group Pbca with a = 15-227(5), b = 19.491(4), c = 18.737(3) Angstrom, V = 5123(2) Angstrom(3), Z = 4, and R-1 (wR(2)) = 0.0726(0.1416). The compound contains an unusual highly reduced pseudo-Keggin type polyoxoanion and exhibits an interesting phosphorus-centered alternate arrangement of layers of molybdenum and vanadium oxides.

Preparation and properties of polyimide films codoped with barium and titanium oxides

Polyimide hybrid films containing bimetalic compounds were obtained by codoping poly(amic acid) with a barium and titanium precursor prepared from BaCO3, Ti(OBu)(4), and lactic acid followed by casting and thermal curing. FTIR, WAXD, and XPS measurements showed that barium and titanium precursor could be transformed to BaTiO3 at a temperature above 650 degreesC, while the mixed oxides were only found in hybrid films. The measurements of TEM and AFM indicated a homogeneous distribution of inorganic phase with particle sizes less than 50 nm. The hybrid films exhibited fairly high thermal stability, good optical transparency, and promising mechanical properties. The incorporation of 10 wt % barium and titanium oxide lowered surface and volume electrical resistivity by 2 and 5 orders, respectively, increasing dielectric constant from 3.5 to 4.2 and piezoelectric constant from 3.8 to 5.2 x 10(-12) c/N, relative to the nondoped polyimide film.

High-pressure and-temperature synthesis and characterization of mixed valence perovskite oxides LaTi1-xMgxO3

Perovskite oxides LaTi1-xMgxO3 (x = 0.25, 0.5) were synthesized using high-pressure and-temperature method. LaTi0.75Mg0.25O3 is a new compound. This new synthesis route has some advantages. XRD analysis showed that the x = 0.25 sample belongs to cubic perovskite-type structure and the a = 0.5 sample belongs to orthorhombic perovskite-type structure. EPR measurement indicated that Ti ions were in mixed valence state of +3 and +4. IR measurement indicated that the vibration frequency and width of BO6 octahedron stretching vibration absorption band decreases with the increasing of x. The valence state of Ti ions can be altered by high-pressure and-temperature. (C) 2000 Elsevier Science S.A. All rights reserved.

Simultaneous spectrophotometric determination of trace iron (III) and aluminum (III) with hybrid linear analysis

Hybrid linear analysis (HLA) was applied to resolution of overlapping spectra of Fe3+-salicylfluorone and Al3+-salicylfluorone complexes and simultaneous spectrophotometric determination of Fe3+ and Al3+. The absorbance matrix of 7 standard mixtures at 41 measuring points ranged from the wavelength of 550 nm to 630 nm was used for calibration. To avoid the effect of interaction between the two components on the determination, the column vector of K matrix obtained from the standard mixtures with least squares was used as the pure spectrum of component. The recoveries of the two elements for the analysis of the synthetic samples were 93.3% similar to 107.5% in the range of the concentration ratio of Fe3+:Al3+ = 10:1 to 1:8. Comparing with the partial least squares (PIS) model, the HLA method was simple, accuracy and precise.

Co-Cu-Al mixed oxides derived from hydrotalcite-like compound for NO reduction by CO

Various hydrotalcite based catalysts were prepared for catalytic removal of NO (NO reduction by CO). The general formula of hydrotalcite compounds (HTLc) was Co-Cu-Al-HTLc. Precalcination of these materials at 450 degrees C for NO reduction by CO, was necessary for catalytic activity. All catalysts except Co-A1 and Cu-Al have very good activity at lower temperature for NO reduction by CO. All samples were characterized by XRD and BET. The tentative reaction mechanism was also proposed.

The electrical and magnetic properties of lanthanide alkaline-earth transition-metal oxides

Five Ln(2)SrMCuO(6.5) oxides (M = Co, Ln = Y and Ho; M = Fe, Ln = Y, Ho, and Dy) were synthesized, and their crystal structures, IR spectra, and physical properties were studied. They have almost the same structure and crystallize in orthorhombic systems. Below room temperature, Y2SrFeCuO6.5, a known layered oxide, shows antiferromagnetic behavior, but the four new oxides are paramagnetic. Y2SrFeCuO6.5 fits the Curie-Weiss law in the temperature range 300-100 K, but Y2SrCoCuO6.5 shows complex magnetic behavior because of the disproportion of some Co+3 to Co+2 and Co+4 The five oxides are all p-type semiconductors in the measured temperature range and have large electrical resistivities at room temperature.

Catalytic reduction of NO, by CO on hydrotalcites-derived mixed oxides CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu)

Two series of mixed oxides, CoAlM and MgAlM (M = Cr, Mn, Fe, Co, Ni, Cu), were prepared by calcining their corresponding hydrotalcite-like compounds (HTLc). The ratio of Mg: Al: M (or Co: Al: hi) was 3:1:1. The catalytic activity of all samples for the reaction of NO + CO was investigated. The results showed that the activity of CoAlM was much higher than that of MgAlM. The structure and the property of redox were characterized by XRD and H-2-TPR. The results indicated that only MgO phase was observed after calcining MgAlM hydrotalcites, and the transition metals became more stable. The spinel-like phase appeared in all of CoAlM samples after the calcination, and the transition metals were changed to be more active, and easily reduced. The activities of three series of mixed oxides CoAlCu obtained from different preparation methods, different ratio of Co:Al: Cu and at different calcination temperatures, were studied in detail for proposing the mechanism of reaction. The ability of adsorption of NO and CO were investigated respectively for supporting the mechanism.

Preparation, charactreization, and catalytic properties of Co-M-Al (M = transition metal) mixed oxides derived from hydrotalcite-like compound

Hydrotalcite-like compounds (HTLcs) CoMAlCO3, where M stands for Cr, Mn, Ni, Cu, or Fe, were synthesized by coprecipitation. After calcination at 450 degrees C, they became mixed oxides with spinel-like structure. The mixed oxides were characterized by XRD, BET, chemical analysis and the adsorption of NO. The catalytic decomposition of NO and its reduction by CO were studied over these mixed oxides. The study showed that the catalytic activity for removal of NO, was very high. The reaction mechanism is proposed and the effects of d-electrons of the transition metals on catalytic activity are elucidated.

Valence stability and change of Eu(II)in oxides

Valence stability and change of Eu(II) in oxides have been studied by luminescence spect a. The results show that the valence stability and change of Eu(II)in oxides is closely related to the radius and electric charge of positive ions substituted by Eu(II) and crystal structure of the host such as Al2O3 which can form alpha-Al2O3 single phase and alpha-Al2O3 and gamma-Al2O3 mixed phases under different reaction temperatures. A, fairly good explanation is made by the proposed relation between energy coefficient and crystal structure for the first time to the observed experiment results. if the energy coefficients of substitution ions is more than that of Eu(II), the lattice substitution of Eu(II)for these ions is not occured generally and valence stare of Eu(II)is not stable and be easily changed into Eu(III). The lattice of gamma-Al2O3 can stablize the valence state of Eu(II)within certain coped concentration and in alpha-Al2O3 crystal lattice Eu(II)can be easily changed into Eu(III).

Catalytic reduction of NO by CO with hydrotalcite derived mixed oxides

Catalysts with spinel structure derived from Hydrotalcite-like Compounds (HTLcs) containing cobalt have been investigated in NO catalytic reduction by Co. It was found that catalysts with spinel structures derived from HTLcs had obviously higher activity than that prepared from general methods. A two-step reaction was observed during the reaction curse: NO was first reduced to N2O by Co, and with the increase of temperature, the N2O was reduced to N-2. The reactivity of the catalysts studied increased with the amount of cobalt-content in the catalyst, and decreased with the calcination temperature. The crystal defect would play an important role in the reaction.