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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

The effect of very high temperature deformation on the hot ductility of a V-microalloyed steel /

Rezaeian, Ahmad. January 2008 (has links)
No description available.
62

A study into vanadium speciation : Methodology, characterisation, and identification

Patel, B. January 1989 (has links)
No description available.
63

Stability of thin film insertion electrodes

Gavanier, Beatrice January 2000 (has links)
No description available.
64

N-butane activation over ruthenium and iron promoted VPO catalysts.

January 2009 (has links)
The Fe- and Ru-promoted vanadium phosphorus oxide (VPO) catalysts were synthesized via the organic route in iso-butanol to form the VPO precursor, VOHPO4·0.5H2O. The resulting precursor was then activated in a stream of nitrogen to form an amorphous (VO)2P2O7, which crystallized after conditioning in the reactor in the presence of n-butane. The promoted catalysts were synthesized at 0.1%, 0.3% and 1% loading, pelletized and sieved to give a 300-600 μm pellet size. The catalysts were tested in a fixed-bed continuous flow micro-reactor and the products were analyzed by GC’s equipped with a flame ionization detector (FID) to monitor maleic anhydride and n-butane and a thermal conductivity detector (TCD) to monitor the carbon oxides. A range of characterization techniques were employed to determine the influence of the promoting elements on a VPO catalyst and to associate the composition of the catalysts obtained from such techniques with their performance. The characterization techniques used include X-ray diffraction (XRD), BET-surface area, ICP-OES, EDS, 31PNMR, TPR, redox titrations, ATR and SEM to determine the phase composition of the catalysts, the surface area of the promoted catalysts relative to the un-promoted VPO, elemental mole ratios, the reducibility of the catalysts, average vanadium oxidation state, determination of the anions present in the surface of the catalysts and the variations in the morphology of the catalysts, respectively. Optimization of the system involved variation of the GHSV, the reactor temperature and the promoter loading. (Activation of a 0.75% n-butane in air mixture was performed at an optimum temperature of 400oC while varying the gas hourly space velocity to establish a range of feed conversions and subsequently determine the activity of each catalyst with respect to n-butane conversion). The promoted catalysts modified the morphology of the catalysts as evidenced by the scanning electron microscopy and the X-ray diffraction patterns. Furthermore an improved conversion was obtained with these catalysts. However, only the 0.1% iron-promoted catalyst improved maleic anhydride yield leading to ca. 10% maleic anhydride yield increment. Yields of 46% and 55% were obtained at GHSVs of 2573 and 1450 per hour respectively and a temperature of 400oC. Electronic and structural modifications were encountered leading to an improved catalytic performance. The performance of this catalyst is associated with a vanadyl pyrophosphate phase (XRD), and a limited and controlled amount of V5+ species as illustrated in the TPR, and solid state 31P NMR data. Moreover, this modification can be considered both structural and electronic in nature as observed in the SEM images and FTIR spectra of this catalyst. Furthermore, this improved performance is possible at higher conversions 80 to 90% conversion. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2009.
65

Optical properties of vanadium oxide nanostructures synthesized by laser pyrolysis

Shikwambana, Lerato David 28 February 2012 (has links)
M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / In this work, the primary investigation has been on the development of the laser pyrolysis setup and its optimization for the synthesis of nano-size VO2-x films. More specifically the focus was on making VO2-x depositions using various laser pyrolysis parameters and establish in this way (1) an optimum laser wavelength threshold for the photon induced dissociation of the molecular precursors while the thermal contribution was kept minimal by using low power density (laser energy of 30 W) and (2) the lower threshold for pure thermal contributions by working with wavelengths far from resonance in order to minimize pure photon induced contributions. The interest in synthesizing nano-size VO2-x materials stems from the low metal-insulator transition temperature at near room temperature with opto-electronic and thermo-electronic properties that can be used in specialised applications. A large number of samples were synthesized under various conditions and annealed under argon atmosphere for 17 hours. XRD analysis identified the VO2 (B) and/or β-V2O5 vanadium oxide phases characteristic for certain samples grown under optimum conditions. Raman spectroscopy also confirmed these vanadium oxide phases with bands observed at 175, 228, 261, 303, 422 and 532 cm-1. SEM analysis revealed a plethora of different nanostructures of various size and shapes. The particles have a range of sizes between 55 nm to 185 nm in diameter. The particles showed morphologies which included nano-rods, nanospheres and nano-slabs. An interesting phenomenon was observed on the samples synthesized with high power density, which was observed and reported by Donev iii et al. EDS analysis on the particles was also used to probe the elemental composition of the sample. Optical studies were performed on the samples which showed transitions in the visible and infrared region in accordance with the ones observed in the international literature using different nano-synthesis methods.
66

Vanadium-51 solid-state magic angle spinning NMR spectroscopy of vanadium haloperixodases and oxovanadium (V) haloperoxidase mimics

Pooransingh-Margolis, Neela. January 2006 (has links)
Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: Tatyana Polenova, Dept. of Chemistry & Biochemistry. Includes bibliographical references.
67

Magnetic Studies On Nano-scale Radical-containing Vanadium Oxide

Huang, Yi-Fen 24 June 2006 (has links)
Recently, controlling the shape of nanoparticles during their fabrication has become a new and interesting research area. In fact, the nanoparticle has been proven that its physical properties are strikingly related to the shape of itself. After finding the carbon nanotubes in 1911, more and more nanostructure materials have been synthesized. The radical nano-scale vanadium oxide VO2.24(C12H14N2)0.061 is synthesized by hydrothermal method. VO2.24(C12H14N2)0.061 has various physical properties, and we would focus on it¡¦s magnetic properties in the thesis, including magnetic susceptibility and magnetization. The magnetic susceptibility measurements show that the antiferromagnetic transition occurs at T = 20K ~ 25K, and it has been found the specific transition at T = 265K ~ 275K in some samples. Based on the magnetization data, these materials are ferromagnetic, and the hysteresis loops exhibit unusual steps. Whenever these materials process thermal treatments or not, the steps still exist. In addition, we will analyze the impact of the production date, thermal treatment, and preserved environment to discover more colorful properties of these materials.
68

Etude de l'environnement du vanadium dans les fractions lourdes du pétrole

Berthe, Christine. January 2008 (has links) (PDF)
Reproductin de : Thèse de doctorat : Chimie moléculaire : Metz : 1983. / Titre provenant de l'écran-titre. Notes bibliographiques. Index.
69

The role of vanadium as a chemical defense of the solitary tunicate, Phallusia nigra /

Odate, Shobu. January 2003 (has links)
Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : [35]-[43]).
70

INVESTIGATION OF LOW-LYING EXCITED-STATES IN SOME VANADIUM ISOTOPES

Rickel, Dwight Gene, 1942- January 1973 (has links)
No description available.

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