Search results for "CONI"
showing 10 items of 984 documents
Micromechanical approach of the high temperature oxidation of zirconium: study of the Zr/ZrO2 interfacial epitaxy with Bollmann's method
1997
The method of Bollmann has been used to determine the role of epitaxy in the formation of the mechanical stress field near the metal/oxide interface during the high temperature oxidation of zirconium. The strains due to epitaxy combine with those due to both oxygen diffusion in metal and thermal expansion of the metal/oxide composite in a model based on a micromechanical formalism. The calculated values are compared to experimental results and the applicability of Bollmann's method to this problem is discussed.
Study on the initial stages of water corrosion of fluorozirconate glasses
2004
Abstract The surface corrosion process associated with the hydrolysis of fluorozirconate glass, ZBLAN (53ZrF 4 , 20BaF 2 , 20NaF, 4LaF 2 , 3AlF 3 ) was investigated using X-ray photoelectron spectroscopy (XPS), grazing-incidence small angle X-ray scattering (GISAXS), X-ray reflectivity (XRR) and scanning electron microscopy (SEM). After a short exposure period (25 min) of the glass surface to deionized water the XPS data indicate an increase of the oxygen content accompanied by a decrease of fluorine concentration. The analysis of the chemical bonding structure identified the predominant surface reaction products as zirconium hydroxyfluoride and oxyfluoride species. The second most abundant…
ChemInform Abstract: Enantioselective Synthesis of Substituted Indoles Through Zirconium(IV)-Catalyzed Friedel-Crafts Alkylation.
2013
The method allows the introduction of a C-3 side chain bearing a tertiary stereogenic center.
Complexes of titanium and zirconium containing a tridentate linked amido–cyclopentadienyl ligand with a soft donor group: synthesis, structure, and e…
1999
Abstract Group 4 metal complexes M(η5:η1-C5R4SiMe2NCH2CH2SMe)Cl2 (R=H, M=Ti; R=Me, M=Ti, Zr) containing the thioether-functionalized linked amido–cyclopentadienyl ligand were synthesized and characterized by 1H- and 13C-NMR spectroscopy, mass spectrometry, and elemental analysis. The crystal structures of the complexes Ti(η5:η1-C5H4SiMe2NCH2CH2SMe)Cl2 and Zr(η5:η1:η1-C5Me4SiMe2NCH2CH2SMe)Cl2 were determined by single-crystal X-ray diffraction studies. The titanium complex is a conventional three-legged piano-stool molecule without an intramolecular interaction between the sulfur donor group and the titanium center, whereas the zirconium complex adopts a trigonal bipyramidal structure, with …
A doubly bridged isodicyclopentadienyl zirconium complex: bis{N-(3,5-dimethylphenyl)-N-[(η5-isodicyclopentadien-2-yl)dimethylsilyl]amido-κN}zirconium…
2002
Transmetallation of the dilithium salt of (3,5-dimethyphenylamino)(isodicyclopentadienyl)dimethylsilane by treatment with zirconium tetrachloride in a 2:1 ratio leads to the substitution of all four chloride ligands. With the applied stoichiometry, the title complex, [Zr(C(20)H(25)NSi)(2)].C(4)H(10)O, was obtained and crystallized from diethyl ether. X-ray diffraction characterization showed that both isodicyclopentadienyl ligands (alternatively called 4,5,6,7-tetrahydro-4,7-methano-1H-indene) are complexed to the metal on their exo face in a completely stereoselective manner and that they are eta(5)-bonded to the Zr atom.
Ethylene polymerization with FI complexes having novel phenoxy-imine ligands: Effect of metal type and complex immobilization
2011
A series of bis(phenoxy-imine) vanadium and zirconium complexes with different types of R3 substituents at the nitrogen atom, where R3 = phenyl, naphthyl, or anthryl, was synthesized and investigated in ethylene polymerization. Moreover, the catalytic performance was verified for three supported catalysts, which had been obtained by immobilization of bis[N-(salicylidene)-1-naphthylaminato]M(IV) dichloride complexes (M = V, Zr, or Ti) on the magnesium carrier MgCl2(THF)2/Et2AlCl. Catalytic performance of both supported and homogeneous catalysts was verified in conjunction with methylaluminoxane (MAO) or with alkylaluminium compounds (EtnAlCl3−n, n = 1–3). The activity of FI vanadium and zirc…
Electrochemistry of vanadium-doped ZrSiO4Site-selective electrocatalytic effect on nitrite oxidation
2004
The electrochemistry of vanadium-doped zircon (VxZrSiO4, 0 < x < 0.10) has been studied using abrasive-conditioned paraffin-impregnated graphite electrodes. It is compared with that of ZrSiO4, ZrO2, and vanadium-doped tetragonal and monoclinic zirconias. In contact with acetic/acetate and HCl + NaCl electrolytes, zirconium materials are reduced to Zr(III) at potentials near to −0.5 versus AgCl/Ag and to Zr metal at potentials more negative than −1.2 V, via proton-assisted reductive processes, influenced by the complexing action of chloride ions. Vanadium-centred oxidation processes appear at potentials from +0.2 to +0.7 V enabling for a distinction between different coordinative arrangement…
Determination of hydrogen peroxide using glassy carbon and graphite/polyester composite electrodes modified by vanadium-doped zirconias
2002
Abstract Synthetic monoclinic and tetragonal vanadium-doped zirconias (VZrO2) with vanadium loading ranging from 0.5 to 15 mol% are used to modify glassy carbon and graphite/polyester composite electrodes able to detect oxygen and hydrogen peroxide in neutral aqueous media. Electrodes modified by monoclinic VZrO2 decrease the overpotential for the reduction of oxygen and hydrogen peroxide in neutral and alkaline media and enhance their reduction currents with respect to unmodified carbon electrodes. This is associated to seven-coordinated vanadium centers isomorphously substituting zirconium ones in the ZrO2 lattice. The catalytic effect shows site-selectivity, since it is almost entirely a…
Zirconium, hafnium and yttrium complexes containing two linked amido— tetramethylcyclopentadienyl ligands: Synthesis, reactivity and molecular struct…
1998
Abstract Zirconium and hafnium complexes M(η5: η1−C5Me4SiMe2NR′)xCl(4−2x) (M = Zr, Hf; x = 1, 2; R′ = iPr, tBu) containing one or two linked amido-tetramethylcyclopentadienyl ligands C5Me4SiMe2NR′ have been synthesized by the reaction of the dilithium derivative Li2(C5Me4SiMe2NR′) with MCl4(THF)2. The crystal structure of the hafnium complex Hf(η5: η1−C5Me4SiMe2NiPr)2 has been determined by a single-crystal X-ray diffraction study and shows a C2-symmetric helical metallocene, in which the amido ligands are bonded as π-donor ligands with Hf—N bond lengths of 2.115(2) A. The isoelectronic heterobimetallic yttrium complex Li[Y(η5: η1−C5Me4SiMe2NCH2CH2OMe)2] reacts with phenylacetylene to give …
Separation of 90Nb from zirconium target for application in immuno-PET
2014
Abstract Fast progressing immuno-PET asks to explore new radionuclides. One of the promising candidates is 90Nb. It has a half-life of 14.6 h that allows visualizing and quantifying biological processes with medium and slow kinetics, such as tumor accumulation of antibodies and antibodies fragments or drug delivery systems and nanoparticles. 90Nb exhibits a positron branching of 53% and an average kinetic energy of emitted positrons of E mean =0.35 MeV. Currently, radionuclide production routes and Nb V labeling techniques are explored to turn this radionuclide into a useful imaging probe. However, efficient separation of 90Nb from irradiated targets remains in challenge. Ion exchange based…