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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.
41

Polyhedral Boranes and Carboranes as Versatile Species Employed in the Pursuit of Imaging Methods and of Nanostructured Materials

Michel, Sheila 19 September 2012 (has links)
Polyhedral boranes and carboranes have acquired their popularity for constructing meso and nano-size structures for an array of applications from pharmaceuticals to material science. These three-dimensional boranes range from 4 to 22 boron atom per molecules with delocalized bonding analogous to aromatic compounds. The unique vibrational spectroscopy of the BH function allows for possible application of these species to bioimaging. Silver nanoparticles functionalized with ortho-carboranes have been reported for bioimaging using Surface-enhanced Raman scattering (SERS). The silver nanoparticles were functionalized with antibodies specific to cancer cell receptors. Bonding thiol-substituted carboranes to these particles allowed for observation of enhanced Raman signals as the imaging mode. Here, attempts to synthesize second generation carborane molecules with additional Raman-active group such as nitrile were conducted. Hybrid diblock copolymers have the ability to self-assemble in different morphological patterns depending on the type and ratio of monomers and the compatibilities in various solvents. Linear hybrid diblock copolymers were synthesized by ring-opening metathesis polymerization (ROMP) reactions with norbornenyl-based decaborane and various amounts of norbornene and norbornenyl-ester derivative monomers. Their self-assembly behaviour in various solvents were characterized by NMR, TGA, DSC, and SEM. P(norbornene)60-b-p(norbornenyl-decaborane)40 polymers showed lamellar morphology patterns when slowly evaporated from chloroform. Based on results and the SEM images, a few of these diblock copolymers were used as ceramic precursors and pyrolyzed to elevated temperatures forming boron nitride and boron carbonitride nano-ordered ceramics
42

Development of a method to fix a Boron-based preservative into timber

Govender, Kesunathan January 2003 (has links)
Submitted in partial fulfillment of the requirements for the degree of Master of Technology: Chemistry, Durban Institute of Technology, Durban, 2003. / Boron, in spite of its exceptional properties as a timber preservative, is not widely used for this purpose. The three key agents that contribute to the destruction of timber are insects, fungi and ultraviolet radiation. Boron is a good fungicide and insecticide and the acrylic/styrene polymer blend resists ultraviolet attack. Treating timber with boron compounds is very easy and, in most instances, does not require sophisticated equipment. The movement of boron into timber is diffusion driven and requires moisture of between 30-50% in the timber. Unfortunately, this superb mobility of boron results in one major disadvantage, namely, the leaching of boron when moisture enters timber. Various methods have been used to impede the movement of boron out of timber (wax coating, paints, varnishes and water-based polymer coatings. None of them have been completely successful. For instance, varnishes, used to prevent boron from leaching out of timber are unsuitable because they also prevent moisture leaving the timber. This results in blistering of the coatings used to contain the boron. In this project, an all-in-one system was developed by systematically varying the nature of the boron compound and the polymer. The successful formulation, which contained disodium octaborate tetrahydrate, as the source of boron and a styrene acrylic polymer blend, has been found to: Allow the uninhibited diffusion of boron into timber. Form a clear continuous polymer film on curing on the surface of the timber. o Display good resistance to ultraviolet attack on the polymer and the timber substrate The product developed has been formulated with the following concentrations: 60 grams per litre of boric acid equivalent 150 grams per litre of boric acid equivalent 200 grams per litre of boric acid equivalent The efficiency of the acrylic/styrene polymer barrier was shown by performing qualitative tests for the presence of boron on the surface of the timber treated with the all-in-one formulation. Furthermore, leaching tests were performed by submerging the treated timber in water and thereafter, analyzing the water for leached boron at regular intervals. The results of these tests showed that the new formulation (60 gIL, 150 gIL and 200 gIL) is suitable for treatment of timber that is destined for above - ground applications. The preservative containing a concentration equivalent to 60 gIL of boric acid was sufficient for remedial treatment. The preservative containing an equivalent of 150 gIL and 200 g/L of boric acid was ideal for treating freshly felled timber. The patent application for this preservative has been accepted. / M
43

A Boron Alkylidene-Alkene Cycloaddition Reaction: Application to the Synthesis of Aphanamal

Deaton, Timothy Maxwell January 2017 (has links)
Thesis advisor: James P. Morken / Described herein is the exploration of a novel methodology whereby boronate-ester bearing cyclopentanes are produced by reaction between an unactivated olefin and what is described as a boron alkylidene. The mechanism is evaluated and concluded to proceed through a boracyclic intermediate that is achieved by a closed-shell, carbanion addition to the olefin. This mechanistic conclusion is arrived upon by considering two likely alternative routes (an open-shell, radical cyclization and a [2+2] concerted process) and providing evidence to refute them. A reaction scope is established as well as the utility of the methodology through the racemic synthesis of a natural sesquiterpene: aphanamal. Finally, the future of the reaction development will be considered by providing a single example of a 6-endo cyclization. / Thesis (MS) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
44

New Concepts, Catalysts, and Methods for Enantioselective Synthesis of C-B and C-C Bonds

Radomkit, Suttipol January 2016 (has links)
Thesis advisor: Amir H. Hoveyda / Chapter 1. Part A: N-Heterocyclic Carbenes Catalyzed Enantioselective Boryl Conjugate Additions to α,β-Unsaturated Ketones, Esters, Weinreb Amides and Aldehydes. The first broadly applicable enantioselective boryl conjugate addition reactions to a variety of α,β-unsaturated carbonyls are reported. Transformations are promoted by 5.0 mol % of a chiral Lewis basic N-heterocyclic carbene. The distinctive feature of the reactions in chemoselectivity of the method compared to the Cu-catalyzed variants has been illustrated. Part B: Enantioselective Synthesis of Boron-Substituted Quaternary Carbon Stereogenic Centers through N-Heterocyclic Carbenes Catalyzed Boryl Conjugate Additions to Cyclic and Acyclic Enones The first examples of Lewis base catalyzed enantioselective boryl conjugate additions that afford products containing boron-substituted quaternary carbon stereogenic centers are presented. The carbon–boron bond forming reactions are promoted by 1.0–5.0 mol % of a chiral N–hererocyclic carbene. Cyclic or linear α,β–unsaturated ketones can be used as suitable substrates and the desired products are obtained in 63–95% yield and 91:9 to >99:1 enantiomeric ratio. The utility of the Lewis base-catalyzed approach is demonstrated in the context of an enantioselective formal synthesis of antifungal natural product crassinervic acid. Chapter 2. Enantioselectivity Fluctuations in Phosphine–Cu-Catalyzed Enantioselective Boron-Allyl Addition to Aryl-Substituted Olefins. Catalytic enantioselective multicomponent processes involving B2(pin)2, aryl or heteroaryl monosubstituted olefins, and allylic phosphates or carbonates are disclosed. Transformations promoted by a chiral Cu–phosphine complex afford products that contain a primary C–B(pin) bond and an allyl-substituted tertiary carbon stereogenic center in up to 84% yield and 98:2 enantiomeric ratio. The utility of the approach is showcased in the enantioselective formal synthesis of biologically active heliespirones A and C. Based on mechanistic and computational studies, we show that enantioselectivities variations can depend on electronic and/or steric factors of the alkene substrate and the allyl electrophile as well as their concentration. In most cases, selectivity loss can be minimized and that the resulting insights are also applicable to reactions involving Cu–H species. Chapter 3. Synthesis of Vicinal Diboronate Compounds through Practical Phosphine–Copper Catalyzed Three-Component Processes. The phosphine–Cu-catalyzed multicomponent processes have been developed for a practical and direct synthesis of vicinal diboronate compounds. Reactions of alkenyl–boronates, allylic phosphates, and diboron reagents are promoted by 2.5–10 mol % of a Cy3P–Cu complex affording a wide range of desirable vicinal diboronate products. The ability for easy access to either regioisomers of the products with a C–B(pin) and an adjacent C–B(dan) bond that can be site-selectively functionalized is a noteworthy feature of the method. / Thesis (PhD) — Boston College, 2016. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.
45

Novel artificial photosynthetic models based on boron dipyrromethenes.

January 2009 (has links)
Huang, Yingsi. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2009. / Includes bibliographical references (leaves 105-106). / Abstracts in English and Chinese. / Abstract --- p.i / Abstract (in Chinese) --- p.iii / Acknowledgment --- p.v / Table of Contents --- p.vii / List of Figures --- p.x / List of Schemes --- p.xv / List of Tables --- p.xv / Abbreviations --- p.xvi / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Natural Photosynthesis --- p.1 / Chapter 1.1.1 --- Process of Natural Photosynthesis --- p.1 / Chapter 1.1.2 --- Chromophores of Natural Photosynthesis --- p.2 / Chapter 1.1.3 --- Mechanism of Natural Photosynthesis --- p.3 / Chapter 1.2 --- Development of Artificial Photosynthetic Models --- p.4 / Chapter 1.2.1 --- Models Based on Porphyrins and Fullerene Derivatives --- p.6 / Chapter 1.2.2 --- Models Based on Boron Dipyrromethenes (BDPs) --- p.12 / Chapter 1.2.3 --- Applications of Artificial Photosynthetic Models --- p.14 / Chapter 1.3 --- Boron Dipyrromethenes (BDPs) --- p.15 / Chapter 1.3.1 --- General --- p.15 / Chapter 1.3.2 --- Energy Transfer Systems Based on BDPs --- p.16 / Chapter 1.3.2.1 --- BDPs as Energy Donors --- p.16 / Chapter 1.3.2.2 --- BDPs as Energy Acceptors --- p.22 / Chapter 1.3.2.3 --- BDPs as both Energy Donors and Acceptors --- p.26 / Chapter 1.4 --- References --- p.30 / Chapter Chapter 2 --- "Synthesis, Characterization, and Photophysical Properties of the Triad BDP-SiPc-MSBDP as an Artificial Photosynthetic Model" --- p.35 / Chapter 2.1 --- Introduction --- p.35 / Chapter 2.2 --- Results and Discussion --- p.38 / Chapter 2.2.1 --- Preparation and Characterization --- p.38 / Chapter 2.2.2 --- Electronic Absorption and Photophysical Properties --- p.45 / Chapter 2.2.3. --- Electrochemical Properties --- p.50 / Chapter 2.3 --- Conclusion --- p.52 / Chapter 2.4 --- Experimental Section --- p.52 / Chapter 2.4.1 --- General --- p.52 / Chapter 2.4.2 --- Photophysical Studies --- p.53 / Chapter 2.4.3 --- Electrochemical Studies --- p.54 / Chapter 2.4.4 --- Synthesis --- p.54 / Chapter 2.5 --- References --- p.58 / Chapter Chapter 3 --- "Synthesis, Characterization, and Photophysical Properties of the Pentad SiPc(MSBDP-BDP)2" --- p.60 / Chapter 3.1 --- Introduction --- p.60 / Chapter 3.2 --- Results and Discussion --- p.61 / Chapter 3.2.1 --- Preparation and Characterization --- p.61 / Chapter 3.2.2 --- Ground-State Electronic Properties and Energy Transfer Processes of BDP-MSBDP 3.3 --- p.66 / Chapter 3.2.3 --- Photophysical Properties of the Pentad SiPc(MSBDP-BDP)2 (3.1) --- p.68 / Chapter 3.2.4 --- Electrochemical Properties of the Pentad SiPc(MSBDP-BDP)2 (3.1) --- p.73 / Chapter 3.3 --- Conclusion --- p.75 / Chapter 3.4 --- Experimental Section --- p.75 / Chapter 3.4.1 --- General --- p.75 / Chapter 3.4.2 --- Synthesis --- p.75 / Chapter 3.5 --- References --- p.80 / Chapter Chapter 4 --- Novel Artificial Photosynthetic Models Constructed by Supramolecular Methodology --- p.81 / Chapter 4.1 --- Introduction --- p.81 / Chapter 4.2 --- Results and Discussion --- p.83 / Chapter 4.2.1 --- Preparation and Characterization --- p.83 / Chapter 4.2.2 --- Ground-state Electronic Properties and Energy Transfer Process of Compound 4.6 --- p.86 / Chapter 4.2.3 --- Formation and Properties of Assembly 4.1 (ZnTPP.4.6) --- p.89 / Chapter 4.2.4 --- Formation and Properties of Assembly 4.2 [Ru(CO)TPP.4.6] --- p.95 / Chapter 4.2.5 --- Comparison of the Assemblies 4.1 and 4.2 --- p.100 / Chapter 4.3 --- Conclusion --- p.101 / Chapter 4.4 --- Experimental Section --- p.101 / Chapter 4.4.1 --- General --- p.101 / Chapter 4.4.2 --- Synthesis --- p.102 / Chapter 4.5 --- References --- p.105
46

Chemical analysis for boron in nuclear reactor coolant water /

McDaniel, Dawn Marie. January 1983 (has links)
Thesis (M.S.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 125-127). Also available on the World Wide Web.
47

Boron carbide devices for neutron detection applications

Day, Ellen E. January 1900 (has links)
Thesis (Ph.D.)--University of Nebraska-Lincoln, 2006. / Title from title screen (site viewed on Mar. 13, 2007). PDF text: xiii, 159 p. : ill. (some col.) UMI publication number: AAT 3223008. Includes bibliographical references. Also available in microfilm, microfiche and paper format.
48

Polyhedral Boranes and Carboranes as Versatile Species Employed in the Pursuit of Imaging Methods and of Nanostructured Materials

Michel, Sheila 19 September 2012 (has links)
Polyhedral boranes and carboranes have acquired their popularity for constructing meso and nano-size structures for an array of applications from pharmaceuticals to material science. These three-dimensional boranes range from 4 to 22 boron atom per molecules with delocalized bonding analogous to aromatic compounds. The unique vibrational spectroscopy of the BH function allows for possible application of these species to bioimaging. Silver nanoparticles functionalized with ortho-carboranes have been reported for bioimaging using Surface-enhanced Raman scattering (SERS). The silver nanoparticles were functionalized with antibodies specific to cancer cell receptors. Bonding thiol-substituted carboranes to these particles allowed for observation of enhanced Raman signals as the imaging mode. Here, attempts to synthesize second generation carborane molecules with additional Raman-active group such as nitrile were conducted. Hybrid diblock copolymers have the ability to self-assemble in different morphological patterns depending on the type and ratio of monomers and the compatibilities in various solvents. Linear hybrid diblock copolymers were synthesized by ring-opening metathesis polymerization (ROMP) reactions with norbornenyl-based decaborane and various amounts of norbornene and norbornenyl-ester derivative monomers. Their self-assembly behaviour in various solvents were characterized by NMR, TGA, DSC, and SEM. P(norbornene)60-b-p(norbornenyl-decaborane)40 polymers showed lamellar morphology patterns when slowly evaporated from chloroform. Based on results and the SEM images, a few of these diblock copolymers were used as ceramic precursors and pyrolyzed to elevated temperatures forming boron nitride and boron carbonitride nano-ordered ceramics
49

Processing of Boron Carbide

Cho, Namtae 07 July 2006 (has links)
The processing of boron carbide powder including sintering optimization, green body optimization and sintering behavior of nano-sized boron carbide was investigated for the development of complex shaped body armor. Pressureless sintered B4C relative densities as high as 96.7% were obtained by optimizing the soak temperature, and holding at that temperature for the minimum time required to reach terminal density. Although the relative densities of pressureless sintered specimens were lower than that of commercially produced hot-pressed B4C, their (Vickers) hardness values were comparable. For 4.45cm diameter and 1.35cm height disk shaped specimens, pressureless sintered to at least 93.0% relative density, post-hot isostatic pressing resulted in vast increases in relative densities (e.g. 100.0%) and hardness values significantly greater than that of commercially produced hot-pressed B4C. The densification behavior of 20-40nm graphite-coated B4C nano-particles was studied using dilatometry, x-ray diffraction and electron microscopy. The higher than expected sintering onset from a nano-scale powder (15008C) was caused by remnant B2O3 not removed by methanol washing, keeping particles separated until volatilization and the carbon coatings, which imposed particle to particle contact of a substance more refractory than B4C. Solid state sintering (1500-18508C) was followed by an arrest in contraction attributed to formation of eutectic liquid droplets of size more than 10X the original nano-particles. These droplets, induced to form well below known B4C-graphite eutectic temperatures by the high surface energy of nano-particles, are interpreted to have quickly solidified to form a vast number of voids in particle packing, which in turn, impeded continued solid state sintering. Starting at 22008C, a permanent liquid phase formed which facilitated a rapid measured contraction by liquid phase sintering and/or compact slumping.
50

Synthesis of Boron-Containing Carbon Nanotubes Catalyzed by Cu/£^- Al2O3

Yang, Dong-Rong 20 August 2012 (has links)
none

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