Surface studies on uranium monocarbide using XPS and SIMS

The air-exposed surfaces of sintered and are-melted UC samples were examined by XPS and SIMS. XPS results indicate that the surface is covered with a very thin layer of UO2 mixed with free carbon, which would have formed along with the oxide during the reaction between UC and oxygen or moisture. From the SIMS depth profile of oxygen, the thickness of the oxide layer is found to be approximately 10 nm. The SIMS oxygen images of the surface as a function of etching time reveal that the surface of UC consists of a top layer of adsorbed moisture/oxygen; this contamination layer is followed by a layer containing uranium oxide, uranium hydroxide and free carbon and then grain boundary oxide and finally bulk UC. The behaviour of sintered and are-melted samples is similar.

Synthesis of new transition metal nitrides, MWN2 (Mtriple bond; length as m-dashMn, Co, Ni)

We report the synthesis of ternary transition metal nitrides of the formula MWN(2) for M=Mn, Co, Ni by reaction of the corresponding MWO(4) with NH3 gas at 600-700 degrees C. MnWN2 is isostructural with the already-known FeWN2, crystallizing in a hexagonal structure (a=2.901(2), b=16.48(5) Angstrom) related to LiMoN2. CoWN2 and NiWN2 (which are isostructural amongst themselves) adopt a different hexagonal structure with a smaller c parameter. While the Mn and Fe nitrides are semiconducting, the Co and Ni nitrides are semimetallic.

Synthetic, spectroscopic and structural studies on uranium and thorium complexes of diphosphazane dioxides

Co-ordination complexes of the diphosphazane dioxides Ph(2)P(O)N(Pr-i)P(O)Ph(2) L(1). Ph(2)P(O)N(Pr-i)P(O)Ph(OC(6)H(4)Me-4) L(2) and Ph(2)P(O)N(Pr-i)P(O)(O2C12H8) L(3) with UO22+ or Th4+ ions have been synthesised and characterised by IR and NMR spectroscopy. The structures of [UO2(NO3)(2)L(1)] and [Th(NO3)(2)L(3)(1)][Th(NO3)(6)] are established by X-ray crystallography. In the former, the uranyl ion is bonded to two bidentate nitrate groups and the two phosphoryl groups of the ligand L(1); the co-ordination polyhedron around the metal is a hexagonal bipyramid. The cationic moiety in the thorium complex contains three bidentate diphosphazane dioxide ligands and two bidentate nitrate groups around the ten-co-ordinated metal.

Thermal expansion studies of substituted CTP derivatives

Several new Na, Y and Zr substituted derivatives of Ca-0.5 Ti-2(PO4)(3) (CTP) have been synthesized. These derivatives retain the hexagonal structure of the parent (CTP) compound with minor changes in lattice parameters. Linear thermal expansion coefficients (alpha) have been obtained using a high sensitivity dilatometer.

Effect of substrate on particle arrangement in arrays formed by self-assembly of polymer grafted nanoparticles

We show that the substrate affects the interparticle spacing in monolayer arrays with hexagonal order formed by self-assembly of polymer grafted nanoparticles. Remarkably, arrays with square packing were formed due to convective shearing at a liquid surface induced by miscibility of colloidal solution with the substrate.

Preparation and dielectric properties of zinc and cadmium doped barium tantalates, Ba3Zn1?xCdxTa2O9

Members of the Ba2Zn1-xCdxTa2O9 (0 less than or equal to x less than or equal to 1) series have been synthesized by solid state reactions at 1473K. Powder x-ray diffraction studies show a cubic perovskite cell with a similar to 4.1 Angstrom which increases with increase in x. Electron diffraction studies show the presence of hexagonal ordered perovskite structure in addition to the cubic structure seen by x-rays, the x = 0.5 composition showing more ordered crystallites. These samples show high dielectric constants with a maximum (epsilon(r) = 30 at 1 kHz) for the x = 0.5 member. The dielectric loss increases with increase in x at all the frequencies under study.

Neutral Nanosheets that Gel: Exfoliated Layered Double Hydroxides in Toluene

A simple strategy to exfoliate inorganic layered double hydroxide (LDH) solids to their ultimate constituent, intact single layers of nanometer thickness and micrometer size, is presented. The procedure involves intercalation of an ionic surfactant that forms a hydrophobic anchored surfactant bilayer in the galleries of the solid followed by simply stirring the intercalated solid in toluene. The method is rapid but at the same time gentle enough to produce exfoliated nanosheets of regular morphology that are electrically neutral and form stable gels at higher concentrations. In this Letter, we describe the phenomena and use molecular dynamics simulations to show that exfoliation of the LDH in toluene is a consequence of the modification of the cohesive dispersive interactions between surfactant chains anchored on opposing inorganic sheets by the toluene molecules. The toluene molecules function as a molecular glue, holding the surfactant-anchored LDH sheets together, leading to gel formation.

Ultrasonic wave characteristics of a monolayer graphene on silicon substrate

The present work deals with an ultrasonic type of wave propagation characteristics of monolayer graphene on silicon (Si) substrate. An atomistic model of a hybrid lattice involving a hexagonal lattice of graphene and surface atoms of diamond lattice of Si is developed to identify the carbon-silicon bond stiffness. Properties of this hybrid lattice model is then mapped into a nonlocal continuum framework. Equivalent force constant due to Si substrate is obtained by minimizing the total potential energy of the system. For this equilibrium configuration, the nonlocal governing equations are derived to analyze the ultrasonic wave dispersion based on spectral analysis. From the present analysis we show that the silicon substrate affects only the flexural wave mode. The frequency band gap of flexural mode is also significantly affected by this substrate. The results also show that, the silicon substrate adds cushioning effect to the graphene and it makes the graphene more stable. The analysis also show that the frequency bang gap relations of in-plane (longitudinal and lateral) and out-of-plane (flexural) wave modes depends not only on the y-direction wavenumber but also on nonlocal scaling parameter. In the nonlocal analysis, at higher values of the y-directional wavenumber, a decrease in the frequency band gap is observed for all the three fundamental wave modes in the graphene-silicon system. The atoms movement in the graphene due to the wave propagation are also captured for all the tree fundamental wave modes. The results presented in this work are qualitatively different from those obtained based on the local analysis and thus, are important for the development of graphene based nanodevices such as strain sensor, mass and pressure sensors, atomic dust detectors and enhancer of surface image resolution that make use of the ultrasonic wave dispersion properties of graphene. (C) 2011 Elsevier Ltd. All rights reserved.

Metallo-beta-lactamase and phosphotriesterase activities of some zinc(II) complexes

Metallo-beta-lactamases (m beta l) and phosphotriesterase (PTE) are zinc(II) enzymes, which hydrolyze the beta-lactam antibiotics and toxic organophosphotriesters, respectively. In the present work, we have synthesized a few asymmetric phenolate-based ligands by sequential Mannich reaction and their corresponding zinc(II) complexes. These zinc(II) complexes were studied for their m beta l and PTE activities. It is shown that the zinc(II) complexes can hydrolyze oxacillin, the beta-lactam antibiotic, at much higher rates as compared to the hydrolysis of p-nitrophenyl diphenylphosphate (PNPDPP), the phosphotriester. Among the complexes studied, the binuclear asymmetric complex 1 having a water molecule coordinated to one of the zinc(II) ions exhibits much better mbl activity than the mononuclear complexes. However, the mononuclear zinc(II) complexes having labile chloride ions exhibit significant PTE activity, which can be ascribed to the replacement of chloride ions by hydroxide ions during hydrolysis reactions. (C) 2011 Elsevier B.V. All rights reserved.

Mesoporous aluminoborates

Hexagonal, cubic and lamellar aluminoborate mesophases containing octahedral aluminium and tetrahedral boson are prepared and characterized for the first time.

On the existence of hydrotalcite-like phases in the absence of trivalent cations

alpha-Hydroxides of nickel(II) and cobalt(II) are hydrotalcite-like phases, possessing a layered double hydroxide (LDH) structure even though there are no trivalent cations in the lattice. While the LDHs acquire a positive charge on the hydroxide layers by the incorporation of trivalent cations, we suggest that the alpha-hydroxides acquire a positive charge by partial protonation of the hydroxyl ions according to the equation M(OH)(2)+xH(+) --> [M(OH)(2-x)(H2O)(x)](x+). As in the LDHs, charge balance is restored by the incorporation of anions in the interlayer region. (C) 1997 Academic Press.

Preliminary studies on the synthesis and characterisation of hydroxyapatites

Synthesis of calcium hydroxyapatite Ca-10(PO4)(6)(OH)(2) ceramic powders by a solid state reaction between commercially available tricalcium phosphate and calcium hydroxide powders has been attempted in the range 700-1000 degrees C. Reaction of tricalcium phosphate and calcium hydroxide in 3:2 molar ratio at 1000 degrees C leads to the formation of pure calcium hydroxyapatite phase. The sample has been characterised by XRD and IR spectral studies. The compacted powder is sintered to 93% of theoretical density when fired in air at 1300 degrees C for 2 hours.

Reverse flotation of silica from Kudremukh iron ore .2. Optimization of flotation process

An experimental programme based on statistical analysis was used for optimizing the reverse Rotation of silica from non-magnetic spiral preconcentrate of Kudremukh iron ore. Flotation of silica with amine and starch as the Rotation reagents was studied to estimate the optimum reagent levels at various mesh of grind. The experiments were first carried out using a two level three factor design. Analysis of the results showed that two parameters namely, the concentration level of the amine collector and the mesh of grind, were significant. Experiments based on an orthogonal design of the hexagonal type were then carried out to determine the effects of these two variables, on recovery and grade of the concentrate. Regression equations have been developed as models. Response contours have been plotted using the 'path of steepest ascent', maximum response has been optimized at 0.27 kg/ton of amine collector, 0.5 kg/ton of starch and mesh of grind of 48.7% passing 300 mesh to give a recovery of 83.43% of Fe in the concentrate containing 66.6% Fe and 2.17% SiO2.

Studies on adsorption of guar gum onto biotite mica

The interaction of guar gum with biotite mica has been investigated through adsorption, flotation and electrokinetic measurements. The adsorption densities of guar gum increase with increase of pH and the isotherms exhibit Langmuirian behaviour. Pretreatment of mica with a complexing agent such as EDTA results in a decrease in the adsorption density, highlighting the contribution of metal ions to the adsorption process. An increase in the surface face-to-edge ratio lends to an increase in the adsorption density. The flotation recoveries decrease as a function of pH, complementing the adsorption results. However, polymer depressant ability is reduced in the case of EDTA treated mica, consequent to reduction of metallic sites. Electrokinetic measurements portray conformational rearrangements of macromolecules with the loading, resulting in the shift of the shear plane, further away from the interface. Dissolution experiments indicate release of metal ions from mica, while co-precipitation tests confirm polymer-metal ion interaction in the bulk solution. The adsorption process is governed by hydrogen bonding as well as chemical interaction between guar gum and the surface metal hydroxide groups of mica. (C) 1997 Published by Elsevier Science Ltd.

Synthesis and structure of a new oxynitride Ba3W2O6N2

A new oxynitride Ba3W2O6N2 has been synthesised from the ammonolysis of Ba3W2O9. This compound crystallises in a hexagonal structure with a = 5.993(2) and c=21.40(4) Angstrom. Transmission electron microscopy (TEM) studies were carried out to elucidate the structure of this new compound. IR and Raman data are consistent with the C-3v site symmetry of the (WO3N)(3-) unit. This compound is isostructural with Ba3V2O8 reported in the literature.