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Part I: Solid State Studies of Larger Calixarenes : Part II: Synthesis and Characterization of MetallocalixarenesSmith, Janna Marie 05 1900 (has links)
Calixarenes are a class of macrocyclic compounds that have garnered interest in large part because of their ability to form host-guest complexes with various types of molecules. For all of the studies of complex formation by calixarenes, most of the work to date has concentrated upon the smaller calixarenes, and little is understood about the relationship between the complexes formed when in solution and that observed in the solid state. The first part of the study, presented in Chapter 3, is of the solid-state properties of two of the larger calixarenes, and in comparison to other reported structures reveals patterns to the observed conformations both in the solid state and in solution. The formation of metal complexes has also been investigated and has focused extensively upon the metals as guests. Thus, the ability of the calixarenes to act as ligands in inorganic complexes has been virtually untapped, despite the polyoxo binding site they can easily provide, and very few metallocalixarenes have been reported. The second part of this study goes beyond the simple solid-state properties of such compounds, and involves the synthesis of several metallocalixarenes as part of a project directed at the functionalization of calixarenes with the components of a class of catalysts known to polymerize various olefins. These catalysts, commonly referred to as Ziegler-Natta catalysts, are introduced in Chapter 4. The new compounds presented here--three new aluminocalixarenes in Chapter 5 and a new titanocalixarene in Chapter 6--were synthesized so as to contain some of the same components observed in several of the other catalysts. These new compounds have been characterized crystallographically as well as through proton and multinuclear NMR, and observed conformational patterns are discussed.
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The effect of microwave heating on manganese promoted iron based Fischer-Tropsch catalystsMohiuddin, Ebrahim 18 January 2012 (has links)
MSc., Faculty of Science, University of the Witwatersrand, 2011 / A study was performed in order to investigate the effect of preparation method and the
effect of microwave heating on a manganese promoted iron based Fischer-Tropsch
catalyst. The effects of preparation method and microwave heating on the structure and
morphology of the catalyst, its surface area and reduction behavior were investigated
using various techniques such as Transmission electron microscopy (TEM), Powder x-ray
diffraction (PXRD), surface area measurements (BET) and temperature programmed
reduction (TPR). The FTS performance of the catalysts were also studied using a fixed
bed reactor with Fischer-Tropsch Synthesis conditions (270 C, flow rate of 30 ml/min,
H2/CO ratio = 2, pressure of 10 bar). Characterization of the catalysts calcined at 350 C
revealed that manganese enriched the surface of impregnated Mn/Fe catalysts and
suppressed the reduction of the iron catalyst. However, the Mn acted as a structural
promoter in the co-precipitated catalysts and also promoted the reduction of Fe2O3 as the
manganese content increased. The co-precipitated catalyst calcined at 650 C suppressed
the reduction of iron. The impregnated catalysts showed similar conversion (~ 70%) for
catalysts with Mn loadings 5%, 10% and 20%. This suggests Mn promotes the activity of
the iron catalyst since less iron is present in the catalyst as the manganese loading is
increased. The co-precipitated catalysts showed a 10 wt% Mn loading to be the optimum
amount for increased activity and selectivity to C2 – C4 hydrocarbons, lower molecular
weight olefins and a lower selectivity to heavier molecular weight hydrocarbons relative
to Mn loadings of 5, 20 and 50 wt%. Mn loadings in excess of 10 wt% showed a slight
increase in selectivity to heavier weight hydrocarbons. The impregnated catalysts showed
very little difference in activity and selectivity but the co-precipitated catalyst showed a
decrease in activity after the catalyst was microwave heated. A slight increase in
selectivity to lower weight olefins and heavier molecular weight hydrocarbons was noted
after microwave heating. The TPSR (Temperature programmed surface reaction) results
revealed that this may be due to the stronger adsorption of CO on the surface of the
catalyst after microwave heating. A similar trend was observed for catalysts promoted
with 0.1 wt% potassium i.e. a slight increase in selectivity to heavier weight
hydrocarbons after microwave heating.
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Structure and properties of BiCuSeO-type thermoelectric materials / Structure et propriétés des matériaux thermoélectrique de type BiCuSeOLi, Jing 24 July 2015 (has links)
La conversion d’énergie par effet thermoélectrique (TE), qui peut être utilisée pour convertir de la chaleur perdue en électricité, a reçu une attention soutenue ces dernières décennies. L’efficacité d’un système TE est caractérisé par le facteur de mérite adimensionnel, ZT=(S²σ/κ)T, où S, σ, κ, et T sont respectivement le coefficient Seebeck, la conductivité électrique, la conductivité thermique et la température absolue. Récemment, les matériaux à base de chalcogénures de cuivre ont attiré un intérêt au sein de la communauté de la thermoélectricité du fait de leur conductivité thermique faible, qui conduit à des propriétés thermoélectriques prometteuses. BiCuSeO et BaCu2Se2 sont deux de ces matériaux. Ils possèdent une conductivité thermique intrinsèquement très faible et un coefficient Seebeck élevé. Mais leur conductivité électrique est faible, ce qui limite l’amélioration de leurs propriétés thermoélectriques.Dans cette thèse, la conductivité électrique de BiCuSeO est améliorée par dopage par Ba et par texturation. Se est substitué à S dans BiCuSeO pour réduire les coûts et diminuer la conductivité thermique. Un dopage par Na est effectué dans BaCu2Se2 pour augmenter sa concentration de porteurs et améliorer sa conductivité électrique. / The thermoelectric (TE) energy conversion technology, which can be used to convert wasted heat into electricity, has received much attention in the past decade. The efficiency of TE devices is characterized by the dimensionless figure of merit ZT=(S²σ/κ)T, where S, σ, κ, and T are the Seebeck coefficient, the electrical conductivity, the thermal conductivity, and the absolute temperature, respectively.Recently, copper chalcogenides based materials have attracted extensive interest in the thermoelectric community due to low thermal conductivities, which lead to the promising excellent thermoelectric properties. BiCuSeO and BaCu2Se2 are two of them. They exhibit intrinsically very low thermal conductivity and large Seebeck coefficient. But their electrical conductivity is low, limiting the enhancement of their thermoelectric properties.In this thesis, Ba doping and texture are taken out in BiCuSeO to improve its electrical conductivity. Se is substituted by S in BiCuSeO to decrease its price and decrease its thermal conductivity. Na doping is taken out in BaCu2Se2 to increase its carrier concentration and improve its electrical conductivity.
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Mechanistic studies of electrochemical double layer capacitors using solid-state NMR spectroscopyWang, Hao January 2014 (has links)
No description available.
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Thermoelectric properties of new transition metal arsenides and antimonidesSoheilnia, Navid January 2007 (has links)
The main focus of this work is on exploratory investigation of thermoelectric (TE) materials. Thermoelectric devices are solid-state devices that convert thermal energy from a temperature gradient into electrical energy (Seebeck effect), or convert electrical energy into a temperature gradient (Peltier effect). Modifying existing materials and finding new materials with proper thermoelectric properties are the two approaches considered in this research. Good thermoelectric materials are usually narrow band gap semiconductors with large Seebeck coefficient, reasonably high electrical conductivity and low thermal conductivity. Early transition metal antimonides and arsenides, with unique structural features were chosen for finding high performance TE materials.
During the investigation of group four antimonides, a series of new ternaries, ZrSiδSb2-δ, ZrGeδSb2-δ and HfGeδSb2-δ was developed. Single crystal X-ray diffraction was used for crystal structure determination, and energy depressives X-ray analysis (EDX) was used for compositional analysis. Metallic properties of these compounds were predicted by electronic structure calculations and confirmed by physical property measurements.
It was revealed that Mo3Sb7 turns semiconducting by partial Sb/Te exchange. Similarly, isostructural Re3As7 was modified to become semiconducting by partial Ge/As exchange. Crystal structures were determined by single crystal X-ray and powder X-ray diffraction utilizing Rietveld method. Electronic structures were determined by using the LMTO method and confirmed the semiconducting properties of these ternary compounds. Physical property measurements showed exceptional TE properties for these compounds. It was also confirmed by the X-ray single crystal analysis that it is possible to intercalate different cations with the proper size into the existing cubic voids of the structure. The effect of cation intercalation on physical properties of these compounds were investigated and revealed the enhancement of transport properties as a result of this intercalation.
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Discrete, one-, two-, and three-dimensional copper(I) coordination networks towards the rational design of extended solids /Lopez, Susan, January 2000 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.
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Solid state nuclear magnetic resonance techniques for determining structure in proteins and peptides /Bower, Peter Velling. January 2001 (has links)
Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 233-234).
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Solid state chemistry of the spin transition polymers [FE(Htrz)₃](CIO₄)₂ and [FE(NH₂trz)₃](CIO₄)₂ /Smit, Eugene. January 2000 (has links)
Thesis (M.Sc. (Chemistry))--University of Pretoria, 2000. / Summaries in Afrikaans and English. Also available online.
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Discrete, one-, two-, and three-dimensional copper(I) coordination networks : towards the rational design of extended solids /Lopez, Susan, January 2000 (has links)
Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.
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Multiple-pulse techniques for solid-state nuclear magnetic resonance spectroscopy of materials / Anthony D. MontinaMontina, Anthony D, University of Lethbridge. Faculty of Arts and Science January 2010 (has links)
Solid state NMR has the ability to obtain detailed structural information at the
molecular level in materials. This has led to the development of a large number of high
resolution techniques, some of which utilize multiple pulse methods. The behaviour of
these multiple pulse techniques has, to date, been explained using either relaxation or
spin dynamics. Ultimately, an explanation based on a combination of both dynamics is
required in order to properly understand the underlying mechanism of these techniques.
This work presents an explanation of the experimental behaviour observed for three
multiple pulse domain selection techniques: the DIVAM, Direct DIVAM, and Refocused
DIVAM sequences. This is based on a combination of spin and relaxation dynamics and
is accomplished using both analytical expressions and simulations obtained using a
general simulation program for solid-state NMR spectroscopy (SIMPSON). / xviii, 179 leaves ; 29 cm
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