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Temperature and concentration dependence of hydrogen diffusion in vanadium measured by optical transmissionBook, Stefan January 2014 (has links)
Hydrogen diffusion is investigated in a 50 nm film of vanadium and a vanadium superlattice. Diffusion constants for three different temperature and pressure pairs are determined for the 50 nm film. The diffusion constants for the temperature and pressure pairs are determined to be 4.5 $\pm$ 0.1 $\cdot 10^{-5} \text{ cm}^{-2}$ at 463 K and 0.05 H/V, 5.6 $\pm$ 0.1 $\cdot 10^{-5} \text{ cm}^{-2}$ at 463 K and 0.12 H/V and 8.0 $\pm$ 0.2 $\cdot 10^{-5} \text{ cm}^{-2}$ at 493 K and 0.05 H/V. The temperature and concentration dependence of the diffusion constants are determined. A concentration dependence of the diffusion constant is found with a higher rate of diffusion for a higher hydrogen concentration. The activation energy of chemical diffusion is determined to be 0.38 $\pm$ 0.03 eV.
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Oxidovanadium complexes with N-donor heterocyclic chelates.Hlela, Thulani Innocent. 12 February 2014 (has links)
The growing significance of vanadium in medicinal inorganic chemistry is due to the diverse
biological activities of its metal complexes, as elaborated in Chapter 1. These biological
activities stem from the fact that vanadium is an essential trace element as well as its ability to
form active pro-drugs under physiological conditions. To improve the bio-availability of these
potential metallopharmaceuticals, the use of biologically relevant ligand systems such as
heterocyclic ligands were considered. These chelators should provide the stability and the ability
to promote absorption through cell-membranes. The techniques as described in Chapter 2 were
employed to analyze and characterize the formulated heterocyclic ligands and their metal
complexes. The attained research findings are mainly divided into two studies which involve the
explorative coordination chemistry of two classes of ligands: 2-pyridylbenzimidazole (see
Chapter 3) and 2-phenylsubstituted heterocyclics (see Chapter 4). An additional brief study is
described in Chapter 5 which discusses the attempted coordination of a uracil Schiff base ligand.
In Chapter 3, the coordination behaviour of Hpybz (2-pyridylbenzimidazole) towards vanadium
in various oxidation states (i.e. +III/IV/V) was explored. The six-coordinate complex cis-
[VVO2(Hpybz)(pybz)] (1) was isolated as the CH3OH.(H2O)2 hydrate from the reaction of
NH4VO3 and Hpybz in aqueous methanol. The crystal structure shows that the vanadium is
bonded to two cis-oxido ligands, and to the two bidentate ligands pybz and Hpybz. This
combination of ligands confers six-coordination on the metal centre, which is a rare coordination
number for a mononuclear dioxido complex of vanadium(V). From the reaction between Hpybz
and VCl3 the cationic complex salt cis-[VIII(OH)2(Hpybz)2]Cl (2) was formed. The ligands in cis-
[VIII(OH)2(Hpybz)2]Cl exhibits the same coordination behaviour as in 1, but instead of the
dioxido moiety present in 1, two hydroxyl co-ligands are coordinated to the metal centre, with
both chelator ligands neutral. Conductivity measurements in DMF affirmed that the compound is
a 1:1 electrolyte. A novel binuclear mixed-valence oxidovanadium compound, (μ-
O)[VVO(pybz)2.VIVO(Hpybz)(acac)] (3), was obtained from the reaction of Hpybz with
VO(acac)2. ESR analysis illustrates paramagnetic behaviour typical of a type I dimer. The metal
compound, VO(Hpbyz)2SO4 (4).H2O was isolated in a good yield from the reaction of two
equivalents of Hpybz with vanadyl sulfate.
Chapter 4 reports the isolation of oxidovanadium compounds with 2-phenylsubstituted
benz(imidazole/othiazole/oxazole) chelators. The 2:1 molar reaction between NH4VO3 and 2-
hydroxyphenylbenzothiazole (Hobs) led to the formation of a polynuclear vanadium(IV)
complex, [VO(obs)2]n (1). The atmospheric oxygen-induced oxidation reaction of VCl3 and 2-
hydroxyphenyl-1H-benzoxazole (Hobo) afforded a similar oxidovanadium compound,
[VO(obo)2]n (2). A characteristic eight-line isotropic signal was observed in the ESR spectrum of
2 in DMF while, due to the poor solubility of 1, a singlet was attained upon analysis of the single
crystals. A diamagnetic dioxidovanadium(V) complex, cis-[VO2(obz)py] (3) (Hobz = 2-
hydroxyphenyl-1H-benzimidazole) was isolated from the reaction of NH4VO3 and Hobz in a
methanolic solution. A broad singlet is found in the 51V NMR spectrum at -520.7 ppm for the
d0-vanadium centre. The intra-ligand (π-π*) relaxations [466 nm for 1, 376 nm for 2 and 469 nm
for 3] could be observed in the emission spectra which were obtained in anhydrous DMF. In an
effort to synthesize a coordination compound of vanadium, the reaction of a heterocyclic ligand,
2-mercaptophenyl-1H-benzimidazole (Hsbz) with vanadyl sulfate resulted in an unexpected
reaction product, [C26H20N4S2].[SO4].4H2O (4).
In Chapter 5, the metal-induced cyclization of 5-amino-6-[(Z)-(2-hydroxybenzylidene)amino]-
1,3-dimethylpyrimidine-2,4-(1H, 3H)-dione (H3duo) by NH4VO3 resulted in the formation of a
cyclized benzimidazole derivative, 8-(2-hydroxyphenyl)-1,3-dimethyl-1H-purine-2,6-(3H, 7H)-
dione (1). The IR spectra of H3duo and its cyclized form are nearly identical where only minor
shifts in the significant bands are observed. The molecular transformation was more evident
when comparing the 1H NMR spectra of H3duo and 1. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2013.
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Solubility and diffusion of vanadium compounds and asphaltene aggregatesDechaine, Greg Paul 06 1900 (has links)
Most crude oils contain traces of vanadyl porphyrins within their asphaltene fraction. Although these metals are only present in trace quantities, they have a significant detrimental impact on crude oil processing units; therefore, their selective removal is highly desirable. The current work studied the interaction of these vanadyl porphyrins with asphaltenes using two approaches: 1) equilibrium solubility measurements of model porphyrins and 2) membrane diffusion measurements in dilute solution. Solubility measurements with model porphyrins showed that simple model porphyrins fit the operational definition for asphaltenes, exhibiting negligible solubility in n-heptane and orders of magnitude higher solubility in toluene. Measurement of the melting point properties enabled modeling of their solubility behaviour and showed that simple models incorporating solubility parameters (Regular solution and Flory-Huggins) were not capable of describing the observed behaviour. Diffusion measurements were done using model vanadyl porphyrins, asphaltenes, and petroporphyrins in toluene using a stirred diffusion cell equipped with ultrafiltration membranes (Ultracel YM and Anopore). The pore sizes were varied between 3-20 nm to retain aggregates while allowing free molecules to diffuse. The permeate was continuously monitored using in situ UV/Visible spectroscopy. These experiments determined that the size of the asphaltene aggregates at 1 g/L in toluene at 25C were in the range of 5-9 nm. An increase in temperature results in an increase in asphaltene mobility but does not reduce the size of the asphaltene structures below 5 nm. Likewise, a decrease in concentration to 0.1 g/L did not result in a decrease in size. It was also observed that the exclusion of a large portion of the total asphaltenes by pores < 5 nm eliminates the absorbance of visible light (>600 nm) indicating the presence of Rayleigh scattering for the aggregated species in solution. The petroporphyrins are larger than the model vanadyl porphyrins as indicated by pore hindrance effects within smaller pores. An increase in temperature results in an increase in petroporphyrin mobility, although decreasing the asphaltene concentration does not. The mobility of the vanadyl petroporphyrins is affected by the origin of the sample (Safaniya, Venezuela, Athabasca) and is therefore not universal. / Chemical Engineering
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Selective oxidation of propylene to acrolein over vanadium and niobium doped bismuth molybdatesLi, Xin. January 2009 (has links)
Thesis (M.Ch.E.)--University of Delaware, 2008. / Principal faculty advisors: Mark A. Barteau and Douglas J. Buttrey, Dept. of Chemical Engineering. Includes bibliographical references.
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Metal-semiconductor transitions in nanoscale vanadium dioxide thin films, subwavelength holes, and nanoparticles /Donev, Eugenii U. January 2008 (has links)
Thesis (Ph. D. in Physics)--Vanderbilt University, Dec. 2008. / Title from title screen. Includes bibliographical references.
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A continuum surface layer effect in polycrystalline aggregates /Laurent, Michel P., January 1994 (has links)
Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 250-253). Also available via the Internet.
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51V-MAS-NMR-Untersuchungen an Modellkomplexen für vanadiumhaltige HaloperoxidasenSchweitzer, Annika January 2009 (has links)
Zugl.: Jena, Univ., Diss., 2009
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Theory and modeling of microstructural evolution in polycrystalline materials solute segregation, grain growth and phase transformation /Ma, Ning, January 2005 (has links)
Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xvii, 181 p.; also includes graphics (some col.). Includes bibliographical references (p. 168-181). Available online via OhioLINK's ETD Center
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Effects of molybdenum, vanadium, tungsten and cobalt on growth of rhizobia and their hostsJha, Kali Kant, January 1963 (has links)
Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 143-153).
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Development of a control strategy for the open slag bath furnaces at Highveld Steel and Vanadium Corporation Ltd.Steinberg, W. S. January 2009 (has links)
Thesis (M.Eng.(Metallurgical Engineering))--University of Pretoria, 2008. / Abstract in English. Includes bibliographical references.
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