Tesis sobre el tema "Boron"
Siga este enlace para ver otros tipos de publicaciones sobre el tema: Boron.
Crea una cita precisa en los estilos APA, MLA, Chicago, Harvard y otros
Consulte los 50 mejores tesis para su investigación sobre el tema "Boron".
Junto a cada fuente en la lista de referencias hay un botón "Agregar a la bibliografía". Pulsa este botón, y generaremos automáticamente la referencia bibliográfica para la obra elegida en el estilo de cita que necesites: APA, MLA, Harvard, Vancouver, Chicago, etc.
También puede descargar el texto completo de la publicación académica en formato pdf y leer en línea su resumen siempre que esté disponible en los metadatos.
Explore tesis sobre una amplia variedad de disciplinas y organice su bibliografía correctamente.
1
Brain, Paul Terence. "Studies of some compounds containing boron-boron bonds". Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291091.
Texto completo
2
Zhu, Xiaojing. "Processability of Nickel-Boron Nanolayer Coated Boron Carbide". Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/28633.
Texto completoResumen
This dissertation work focuses on the processability improvement of B4C, especially the compaction and sintering improvement of B4C by applying a Ni-B nanolayer coating on individual B4C particles.
A modified electroless coating procedure was proposed and employed to coat nanometer Ni-B layer onto micron-sized B4C particles. The thickness was able to be tuned and controlled below 100 nm. Key parameters, including the amount of nickel source, the amount of the surface activation agent (PdCl2), the amount of the complexing agent (C2H8N2), and the addition rate of the reducing agent (NaBH4) were studied. When the targeted thickness was 5 nm, a continuous and uniform nanolayer coating was obtained with the optimal condition of individual parameter combined.
Reduction of the as-coated B4C powder in a H2-Ar atmosphere was studied between 400-900ºC to reduce the surface oxidesâ Ni2O3 and B2O3. Reduction at 800ºC in hydrogen atmosphere was found to be the most effective condition to remove oxygen in the coating layer, with Ni2B as the reduction product.
Compaction of the as-received, separated and uncoated, and separated with Ni-B coating B4C powders using uniaxial die compaction and combustion driven compaction (CDC) techniques was studied. CDC technique showed the advantage over the traditional uniaxial die compaction by yielding much higher green density and green strength (73% vs. 53.8% green density for the Ni-B coated B4C). Among compacts obtained from the same technique, Ni-B coated B4C compact yielded the densest packing with crack-free compact surface and the highest strength, demonstrating more bonding between B4C particles provided by Ni-B surface coating.
Sintering of the Ni-B coated B4C in an Ar atmosphere between 1150 - 1600ºC with soaking time of 2 hrs and 10 hrs was studied. Liquid phase was found to form during the sintering process. Density measurement showed that the liquid phase Ni-B formed greatly facilitated B4C densification. Considerable density increase and inter-granular connection was achieved when sintered at 1600ºC for 10 hrs. The density enhancement by Ni-B coating was supported by transmission electron microscopy-energy dispersive spectroscopy (TEM-EDS) examination which showed that there was B4C species diffusion into liquid Ni-B phase. This liquid phase enhanced the diffusion of B4C species and formed strong bonding between B4C grains by dissolving small B4C particles and sharp edge and corners of B4C particles. Strength test demonstrated that the Ni-B coating dramatically improved the strength of B4C compacts by yielding a much higher strength of the Ni-B coated samples than the uncoated samples (13.97 vs. 1.79 MPa for the uinaxial die compacted samples, 27.03 vs. 2.21 MPa for the CDC samples). Electrical conductivity Ni-B coated B4C samples was also shown to be improved with the electrical resistivity being reduced from infinite for pure B4C samples to 1.8à 10-3 Ω⠢m for the Ni-B coated samples.
This research work has shown that with the Ni-B coating, B4C densification can start at a temperature as low as 1600ºC via a liquid phase sintering process.Ph. D.
3
DeGraffenreid, Allison Lynne. "Studies on boron - nitrogen and boron - gadolinium compounds". The Ohio State University, 1995. http://rave.ohiolink.edu/etdc/view?acc_num=osu1294835746.
Texto completo
4
Slade, Alexander Mason Electrical Engineering UNSW. "Boron tribromide sourced boron diffusions for silicon solar cells". Awarded by:University of New South Wales. Electrical Engineering, 2005. http://handle.unsw.edu.au/1959.4/21850.
Texto completoResumen
This thesis undertakes the development, characterization and optimization of boron diffusion for silicon solar cells. Heavy diffusions (sheet resistance < 40 Ohm/square) to form a back surface field, and light diffusions (sheet resistance > 100 Ohm/square) to form oxide-passivated emitters were developed. Test structures and solar cells were fabricated to assess uniformity, lifetime and recombination effects due to the light and heavy boron diffusions. It was found that the growth of a thin ~200 ??, thermal oxide, during stabilization ??? immediately prior to the boron diffusion - was required to maintain high lifetime and reduce surface recombination (reducing the emitter saturation current density) for all boron diffusions. The heavy boron diffusion process was incorporated into the single side buried contact solar cell processing sequence. The solar cells fabricated had both boron diffused and Al/Si alloyed P+ regions for comparison. This research conclusively showed that boron diffused solar cells had significantly higher open circuit voltage compared to Al/Si alloyed devices. Fabrication of n-type solar cells, and their subsequent characterization by overlayed secondary electron image and the electron beam induced current map showed that the Al/Si alloy varied in depth from 5 to 25 micrometers deep. Methodology and characterization for light, oxide-passivated boron diffusions are also presented. This study yielded boron diffused emitters (sheet resistance > 100 Ohm/square) with low emitter saturation current. It was observed that this was possible only when the thermal oxidation after the boron diffusion was minimal, less than 1,000 ??. This was due to the segregation effect of boron with oxide, decreasing the surface concentration that in turn decreased the electric field repulsion of electrons from the surface. Device modelling of n-type solar cells is presented where the parameters of the modelling include the results of the light, oxide-passivated boron diffusions. This modelling shows n-type-base material with light oxide-passivated boron diffusion has higher potential conversion efficiency than forming a solar cell from phosphorous diffused p-type material.
5
Yamamoto, Akihiko. "Boron-based organic reactions using boron cyanides and chlorides". 京都大学 (Kyoto University), 2006. http://hdl.handle.net/2433/143990.
Texto completoResumen
Kyoto University (京都大学)0048
新制・課程博士
博士(工学)
甲第12293号
工博第2622号
新制||工||1370(附属図書館)
24129
UT51-2006-N978
京都大学大学院工学研究科合成・生物化学専攻
(主査)教授 杉野目 道紀, 教授 檜山 爲次郎, 教授 村上 正浩
学位規則第4条第1項該当
6
Spivack, Arthur J. "Boron isotope geochemistry". Thesis, Massachusetts Institute of Technology, 1986. http://hdl.handle.net/1721.1/15187.
Texto completoResumen
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and Woods Hole Oceanographic Institution, 1986.MICROFICHE COPY AVAILABLE IN ARCHIVES AND LINDGREN
Vita.
Includes bibliographies.
by Arthur J. Spivack.
Ph.D.
7
Castro, Susana Patricia. "CHARACTERIZATION OF THE BORON DOPING PROCESSUSING BORON NITRIDE SOLID SOURCE DIFFUSION". NCSU, 1999. http://www.lib.ncsu.edu/theses/available/etd-19990523-142337.
Texto completoResumen
CASTRO, SUSANA PATRICIA. Characterization of the Boron Doping Process UsingBoron Nitride Solid Source DiffusionThe purpose of this research has been to develop an optimum process for the borondoping of implants and polysilicon gates of metal-oxide-semiconductor (MOS) devices.An experimental design was constructed to determine the effects of diffusiontemperature, time, and ambient on characteristics of the doping process. A temperaturerange of 800 to 1000 degrees Celsius was studied with a diffusion time between 10 and60 minutes. Two diffusion ambients were used for doping processes, a pure nitrogenambient and a nitrogen-oxygen gaseous mixture. Device wafers were fabricated, and thetesting of MOS capacitors and van der Pauw test structures was performed to determinethe effect of diffusion conditions on flatband voltage and poly gate doping. Materialscharacterization techniques were used on monitor wafers for each diffusion process todetermine the wafer structure formed for each process and evaluate the effectiveness ofthe deglaze etch. The processes that resulted in the best device characteristics withoutsuffering from significant poly depletion effects and flatband voltage shifts were wafersdoped at 800 degrees Celsius in a pure nitrogen atmosphere for 20 minutes and 45minutes. The presence of oxygen in the atmosphere caused the depletion of boron fromthe Si wafer surface. The formation of the Si-B phase only occurred on devices processedat 1000 degrees Celsius. The deglaze process used in this experiment did not fullyremove this layer, and thus all devices doped at this temperature were seriously degraded.
8
Leenhouts, James Merrell 1968. "Behavior of boron and boron isotopes during uptake by Atriplex canescens". Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284177.
Texto completoResumen
This research was conducted to determine the potential for using plants to obtain samples of boron isotopes from groundwater, sod moisture and fracture water. In essence, this work sought to ascertain whether plants can function as in-situ samplers for boron as an environmental isotope. At present, very little is known about the behavior of boron isotopes in plants so this study was designed to reveal any isotopic fractionation that might occur during plant uptake by a specific species under carefully controlled conditions. The relationship between the boron isotope ratios sequestered in the leaves of the species Atriplex canescens and the growth conditions of the plant were investigated using a semi-hydroponic greenhouse experiment. Nutrient boron concentration and solution pH were selected as experimental variables as these parameters span large ranges in nature. In addition, the mechanism through which plants take up anionic nutrients suggests that boron isotope fractionation could occur. The experimental setup was a randomized factorial block design and the plants were provided six different nutrient solutions with pH values ranging from 7.5 to 9.5 and boron concentrations varying from 0.1 mg/L to 10.0 mg/L. Boron concentration in the plant's leaf and stem samples followed expected patterns, with the highest boron amount in the leaves of the plants fed nutrient solution with 10.0 mg/L B. The stern samples of plants fed 0.1 mg/L B contained the least boron. The ratio of boron in plants fed 10.0 mg/L vs. 0.1 mg/L B was far less than the 100:1 ratio of boron in the nutrients, which implies that a component of uptake is actively controlled by the plant. Negative thermal ionization mass spectrometry was employed to analyze the minute amounts of boron extracted from digests of the plant tissues. Statistical tests were utilized to determine that, contrary to the hypothesis, no significant isotopic fractionation occurred during uptake at any treatment pH level. The results of this research indicate that the species Atriplex canescens can provide samples of boron isotopes which closely represent the isotopic signature of the plant's water source.
9
Noguchi, Hiroyoshi. "Boron-based organic synthesis through reactivity control by substituents on boron". 京都大学 (Kyoto University), 2008. http://hdl.handle.net/2433/136275.
Texto completo
10
Chung, Yoonsun. "Radiobiological evaluation of new boron delivery agents for boron neutron capture therapy". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/44784.
Texto completoResumen
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.Includes bibliographical references (p. 123-132).
This thesis evaluates the radiobiological effectiveness of three new boron compounds namely a boronated porphyrin (BOPP) and two liposome formulations for neutron capture therapy (BNCT). The methodology utilizes in vitro and in vivo comparisons that characterize compounds relative to boric acid and boronophenylalanine (BPA). In vitro evaluations utilized a colorimetric assay and 96-well plates to minimize the quantities of compound required for testing. The assay was optimized for the murine SCCVII, squamous cell carcinoma to determine the chemical toxicity and relative cellular uptake of a compound. BOPP was toxic at low concentrations and comparisons between the different compounds for thermal neutron irradiations were performed with approximately 5 [mu]g 10B/ml in the culture medium to allow radiation induced effects to govern the observed response. Using less than 300 [mu]g of compound and 250 kVp X-rays as control irradiations, a compound biological effectiveness (CBE) of 3.3 ± 0.7 was determined for BOPP that is comparable to the result for boric acid (3.5 ± 0.5) indicating a non-selective intracellular accumulation of 10B. BPA has a significantly higher CBE of 6.1 + 0.7. Boronated liposomes (MAC-16 and MAC+TAC) were evaluated with the EMT-6 murine mammary carcinoma. Biodistribution studies showed high 10B uptake in tumor (20-40 [mu]g 10B/g) 30 hours after a single i.v. injection (dose 6-20 [mu]g 10B per gram of body weight). Tumor control experiments were performed using thermal neutrons to study the efficacy of the boron delivered by liposomes and BPA. The MAC-16 produced a 16 % tumor control and BPA (dose 43 [mu]g 10B/gbw) 63 % for tumor boron concentrations of approximately 20 [mu]g 10B/g and the same neutron fluence.
(cont.) Liposome doses were limited by injection volume and so two injections were tried 2-hours apart that doubled the boron concentration in tumor compared to a single administration. This improved the therapeutic response to 67 % with less apparent skin damage than with BPA. Microscopic studies using fluorescent labeled liposomes revealed 10B was nonuniformly distributed and concentrated at the edge of the tumor. Based on these studies in the tumor cell lines chosen neither of the compounds appear superior to BPA.
by Yoonsun Chung.
Ph.D.
11
Castro, Susana Patricia. "Characterization of the boron doping process using boron nitride solid source diffusion". Raleigh, NC : North Carolina State University, 1999. http://www.lib.ncsu.edu/etd/public/etd-2923142349901421/etd.pdf.
Texto completo
12
Cui, Jian. "Synthesis and characterization of new boron-nitrogen and boron-nitrogen-phosphorus systems". [Fort Worth, Tex.] : Texas Christian University, 2009. http://etd.tcu.edu/etdfiles/available/etd-03162010-123538/unrestricted/Cui.pdf.
Texto completo
13
Ceberg, Crister. "Pharmacokinetics and biodistribution of boron compounds foundations for boron neutron capture theory /". Lund : Dept. of Radiation Physics, Lund University, 1994. http://books.google.com/books?id=wnhrAAAAMAAJ.
Texto completo
14
Asad, Adil. "External and internal boron requirements of plants using boron buffered solution culture". Thesis, Asad, Adil (1998) External and internal boron requirements of plants using boron buffered solution culture. PhD thesis, Murdoch University, 1998. https://researchrepository.murdoch.edu.au/id/eprint/52442/.
Texto completoResumen
In soils and in conventional nutrient solutions, establishing the internal and external boron (B) requirements of plants is often confounded because the external B concentration changes during plant growth. On the other hand, the major problem of working with low B concentrations in conventional nutrient solutions is that these concentrations are quickly depleted as B is taken up by the plant roots. Hence in most conventional solution cultures, the initial B concentration is often very high to ensure adequate supply of B throughout an experiment. This research was carried out to develop a solution culture system in which the free B concentration would be buffered at constant concentrations, ranging from low to high. This developed B-buffered solution culture system was then tested as a means of determining the internal and external B requirements of different plant species. Further experiments were conducted to study the external and internal B requirements of plants at different growth stages, and to study distribution of B in different plant parts by using the above B-buffered solution culture system.
The B specific resin, Amberlite IRA 743, which complexes H3BO3 on its Nmethyl glucamine functional groups, was chosen for this study because the B saturated resin maintained a realistic equilibrium B concentration in solution and there was no evidence that the resin had significant effects on plant growth other than in releasing and equilibrating B in the nutrient solution. The resin released nitrogen (N) into solution but, provided an adequate solution N supply was maintained, there were no indirect effects of the resin on plant growth apart from its control of B solution concentration.
The B sorption capacity of the resin varied from 2.2 to 5.0 mg B/g resin. Boron saturated resin maintained an equilibrium solution B concentration of 46 μM when added at the rate of 2 g of resin to 1L of B-free triple deionised water. Plants grown in complete nutrient solution with B-saturated resin added at 1 g per litre of nutrient solution grew as well as plants grown in conventional nutrient solution containing 9.2 μM B and their shoots contained adequate B concentrations for growth.
Glasshouse experiments were undertaken to establish buffered B concentrations ranging from deficient to adequate in nutrient solutions. Supplying different amounts of B saturated resin, Amberlite IRA 743, per unit solution volume; and loading the resin with B at 1 to 100 % of full saturation resulted in solution B concentrations (μM) ranging from 0.17 to 2.9 and from 0.05 to 27.0, respectively. The latter method was more effective in producing a wide range of B supply, from deficiency to adequacy. By this method critical external and internal B concentrations at vegetative growth of canola were 0.6 fjM B and 6-8 mg B kg dry weight, respectively. At solution B concentrations from 0.04 to 0.3 μm, canola (Brassica napus L.) plants remained alive but both shoot and root growth were stunted with classical B deficiency symptoms. Increasing solution B concentrations progressively increased B concentrations in shoots and roots. In roots, B concentrations were less than one-third of those in lower shoots and less than those in upper shoots, except in B-deficient plants. At 0.04 μM B, plants absorbed no B from solution. Increasing solution B concentrations from 0.1 to 26.5 μM increased relative B uptake rates from 0.005 to 0.1 μ mole g root fresh weight day . Maximum root efficiency, defined as relative uptake rate divided by the solution B concentration, was achieved at 0.04 to 0.3 μM B in solution. With increasing solution B concentrations, relative uptake rates of calcium decreased from 248 to 10 μ mole g-1 root fresh weight day-1. The results suggest that B specifically inhibited calcium absorption or accelerated calcium efflux.
Canola was grown to flowering in a subsequent experiment to study the effect of external B concentration, established with B-loaded resin, on the distribution of B in plants and to investigate the external B concentrations for near maximum vegetative and reproductive growth. Mean B concentrations in B-buffered nutrient solutions ranging from 0.36 to 46.6 μM were achieved by loading B-specific resin at 4 to 100 % of full saturation. At low levels of B, the resin maintained constant B in nutrient solutions from Day 0 to 55.
When relative growth rates for the periods 0-10, 10-22 and 22-55 DAT were related to mean external B concentration, the critical external B concentration for the growth period of 0-55 DAT remained unchanged with time and plant growth stage. Boron concentrations in shoots and roots increased strongly with increasing solution B concentrations up to 1-2 μM B and then more weakly with increases in solution B above 2 μM B. At deficient to marginal external B concentrations, stems had higher B concentrations than leaf blades on Days 10 and 22 but not at Day 55. Although the plants at low external B (< 0.45 μM) concentrations had some vegetative growth they did not produce reproductive parts compared to the plants with adequate B. At the flowering stage, maximum B concentration was found in florets and growth of these plant parts was more sensitively depressed by low B than vegetative plant parts. At 0.86 μM B in nutrient solutions, plants achieved maximum vegetative dry matter and flowered normally. Plants supplied with < 0.45 μM B produced no flowers or flowers were abnormal with aborted stamens and pistils. At 0.35 μMB, plants, whilst stunted, continued to produce vegetative dry matter though reproductive growth was completely suppressed. At flowering higher B concentrations occurred in the flowers (50.3 mg/kg dry weight) than in leaf (19.9 mg/kg dry weight), stem (19.0 mg/kg dry weight) or root (14.7 mg/kg dry weight). This study suggested that external B requirements for canola at the reproductive stage is 0.86 μM for maximum or near to maximum growth.
External and internal B requirements of three plant species were studied using the B-buffered solution culture technique. In a glasshouse solution culture experiment, B concentrations were buffered with B saturated resin (Amberlite IRA 743); and loading the resin with B at 1 to 100 % of full saturation. Average B concentrations (μM) in nutrient solutions ranged from 0.04-28.3. The external and internal B requirements of a monocot (wheat, Triticum aestivum), a herbaceous dicot (sunflower) and a woody dicot (marri Corymbia calophylla) were examined using the buffered culture system.
Plants were harvested after 10 and 20 days (wheat and sunflower) or 20 and 40 days (marri). At low external B (< 0.13 μM), growth of marri and sunflower was severely depressed, whereas the growth of wheat plants was only weakly depressed at 0.04 pM B in solutions. Where maximum dry weight of shoots was obtained, B concentrations (mg/kg) in leaf blades at the first harvest were 17.9, 19.7 and 1.2, for marri, sunflower and wheat, respectively. Results of this experiment suggested that the two dicotyledons marri and sunflower have higher external and internal B requirements than wheat. Increasing solution B from 0.05 to 28.5 μM increased relative B uptake rates from 0.43-1.02, 0.64-0.94 and 0.02-0.07 μ mole g-1 root dry weight day -1 in the case of marri, sunflower and wheat, respectively. Thus, the higher internal and external B requirements of sunflower and marri compared to wheat were supported by higher rates of B absorption.
In conclusion, the B-buffered solution culture system developed in this study has considerable potential for B nutrition studies of plants. This system is robust and easy to establish. Whilst B-specific resin supplied B to canola till flowering stage at higher B loadings (> 16% of full B saturation of resin) it did not maintain constant B concentrations for more than 22 days growth. The length of time for which effective buffering of solution B was achieved appeared to vary with rate of biomass accumulation which, in turn, was a function of time of year and plant species. It is suggested that buffered B concentrations in nutrient solutions may be achieved for experiments of long duration either by increasing the amounts of resin per unit nutrient solution or replacing the B-specific resin after every 8-10 days.
15
Cho, Namtae. "Processing of Boron Carbide". Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/11567.
Texto completoResumen
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.
16
Ozkol, Engin. "Production Of Boron Nitride". Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12609646/index.pdf.
Texto completoResumen
Boron nitride is found mainly in two crystal structuresin hexagonal structure (h-BN) which is very much like graphite and in cubic structure (c-BN) with properties very close to those of diamond. h-BN is a natural lubricant due to its layered structure. It is generally used in sliding parts of the moving elements such as rotating element beds in turbine shafts. Since c-BN is the hardest known material after diamond it is used in making hard metal covers. In addition to its possible microelectronics applications (can be used to make p-n junction), its resistance to high temperatures and its high forbidden energy gap are its superiorities over diamond. Recent studies have shown that c-BN can be produced by Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD) in plasma. But these studies have failed to determine how all of the production parameters (boron and nitrogen sources, composition of the gas used, substrate, RF power, bias voltage, substrate temperature) affect the c-BN content, mechanical stress and the deposition rate of the product with a systematic approach. The systematic study was realized in the range of available experimental ability of the present PVD and CVD equipment and accessories. The BN films were produced in the plasma equipment for CVD using RF and MW and magnetron sputtering and were studied with the measurement and testing facilities. It is believed that with this approach it will be possible to collect enough experimental data to optimize production conditions of BN with desired mechanical and optoelectronic properties. h-BN films were successfully deposited in both systems. It was possible to deposit c-BN films with the MW power, however they were weak in cubic content. Deposition at low pressures eliminated the hydrogen contamination of the films. High substrate temperatures led to more chemically and mechanically stable films.
17
Smil, David V. "Boron tethered radical cyclizations". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0006/MQ40735.pdf.
Texto completo
18
Lee, Hyukjae. "Sintering of boron carbide". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19631.
Texto completo
19
Keep, Ann Kathleen. "Ruthenium boron cluster chemistry". Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/272941.
Texto completo
20
Böhlke, Steffen. "Untersuchungen zur Borflüchtigkeit bei der Einspeisung von Bor in SWR-Brennelemente bei transienten Kernzuständen". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-37939.
Texto completoResumen
In Siedewasserreaktoren ist ein Boreinspeisesystem diversitär wirkend zur Reaktorschnellabschaltung installiert. Dieses System garantiert, dass der Reaktor beim Versagen des Schnellabschaltesystems in einen unterkritischen Zustand überführt werden kann. Der aufgrund der Nachzerfallsleistung entweichende Dampf trägt jedoch ständig einen Teil des eingespeisten Bors in Form von Borsäure mit sich. Da dieser Prozess bisher nicht quantifiziert wurde, ist somit das Eintreten einer Rekrititkalität während der Transiente ohne weitere Untersuchungen nicht auszuschließen. In der vorliegenden Arbeit erfolgt die Erstellung einer fundierten Datenbasis zur Quantifizierung des Borverlusts an verschiedenen Betriebspunkten. Dazu stehen nach vorheriger Konstruktion und Inbetriebnahme zwei Versuchsanlagen zur Verfügung, ein Versuchsautoklav und der Siedewasserreaktor-Simulator BORAN. Das in diesen Versuchsanlagen enthaltene und als Kühlmedium genutzte entionisierte Wasser wird wie bei einem Siedewasserreaktor mit einer hochkonzentrierten Lösung der Borverbindung Dinatrium-Pentaborat-Dekahydrat versetzt. Für weiterführende Untersuchungen findet auch Borsäure Verwendung. Die Bestimmung des Borgehalts der Kondensate des entwichenen Dampfes erfolgt mit Massenspektrometrie mit induktiv gekoppeltem Plasma (ICP-MS). Die durch Variation von Borkonzentration, Temperatur, pH-Wert und Volumendampfgehalt erzeugten Messdaten fließen in einem Flüchtigkeitsmodell in Form einer empirischen Gleichung zusammen, welches in den Thermohydraulikcode ATHLET implementiert wird. Experimente am SWR-Simulator BORAN und entsprechende Rechnungen mit dem modifizierten Code ATHLET von Langzeit-Deborierungstransienten bei unterschiedlichen Randbedingungen bestätigen das Flüchtigkeitsmodell. Gleichzeitig erfolgt mittels dieser Experimente die Validierung des Modells im ATHLET mit hinreichender Genauigkeit. Mit den Ergebnissen aus Rechnungen und Experimenten wird das Boreinspeisesystem in seiner aktuellen Konfiguration bewertet und mit zukünftigen Konzepten verglichen. Schlussendlich erfolgt der Nachweis, dass die Funktionalität des Boreinspeisesystem aus dem Blickwinkel der durchgeführten Analysen, trotz der nachgewiesenen Borflüchtigkeit, die Forderungen der KTA 3103 erfüllt und aufgrund der nachgewiesenen Borflüchtigkeit binnen der ersten beiden Stunden der Transiente keine Rekritikalität verursacht wirdIn boiling water reactors a boron injection system as an alternative system is installed to guarantee that the reactor shut down in case of a total or partial ATWS accident. Because of the heat generated by the fission products after shutting down a part of the injected boron is evaporated as boron acid. This process is not characterized quantitatively yet. This is the reason that the incidence of recriticality during a transient cannot be excluded without further research. In the following studies a funded database quantifying the loss of boron is established. The volatility of the boron solution was measured by experiments in a small autoclave and in a boiling water reactor simulator called BORAN after construction. The deionised water used as coolant in the facilities will be enriched with boron by a high concentrated solution of Disodium-Pentaborate-Decahydrate. The measurement of the boron concentration in the condensates of the exhausted vapour is carried out by inductively-coupled-plasma mass-spectrometry (ICP-MS). For additional analysis boron acid is also used. The boron concentration in the vapour mainly depends on the temperature and void fraction of the two-phase-flow. This volatility model in form of an empiric equation is implemented in the thermo hydraulic ATHLET-code. Furthermore the reason of the volatility of the analysed solutions will be discussed within a chemical and physical background. Experiments at the BORAN facility and corresponding calculation with the modified ATHLET-code of long time deboration transients with different boundary conditions prove the volatility model. Thereby the code will be validated with sufficient accuracy. The modified code with an adapted Input-Dataset provides the possibility to calculate transients with the loss of boron. With the consideration of the volatility the demand of the KTA-rule 3103 on the Boron injection system is also grantable
21
Nguyen, Thi Thu Hien. "Study of new exchangers for boron removal from water containing high concentration of boron". Thesis, Toulouse, INPT, 2017. http://www.theses.fr/2017INPT0138/document.
Texto completoResumen
Le bore est nécessaire pour le développement des plantes supérieures (structuration de la paroi végétale). Il pose cependant des problèmes (défoliation, pourriture et chute des fruits mûrs). Pour l’homme, sa toxicité se traduit par des nausées, des diarrhées, des troubles du développement intellectuel, neurologique et physique. La pénurie en eau douce conduit à dessaler l’eau de mer pour augmenter la quantité en eau destinée à la consommation humaine, l’industrie et l’agriculture. Lors de ce procédé, il faut éliminer les ions majeurs mais aussi le bore présent à des concentrations élevées (> 4,5 mg L–1, environ 0,45 mM). Son usage dans l’industrie et son rejet dans l’environnement conduisent à la pollution des eaux souterraines et de surface. Son élimination est donc indispensable, sachant que l’Organisation Mondiale de la Santé recommande une valeur guide de 0,5 mg L–1 dans l’eau potable et une valeur maximale de 0,3 mg L–1 dans l’eau utilisée pour l’irrigation. Cette thèse porte sur l’étude cinétique et thermodynamique des échanges du bore à la surface de différents matériaux en fonction de paramètres physico-chimiques (pH, concentration initiale …) à l’aide d’essais en réacteurs fermés et en colonnes. Deux types de résines commerciales ont été choisies : (i) les résines échangeuses d’anions Ambersep 900-OH et Amberlite IRA 402 Cl avec des fonctions ammonium, (ii) les résines spécifiques Amberlite IRA 743 et Diaion CRB 03 ayant des fonctions méthylglucamine. Les premières essais en réacteurs fermés montrent que les échanges liquide-solide sont rapides avec une élimination du bore > 96 % pour t < 30 min pour Amberlite IRA 743, Diaion CRB 03 et Ambersep 900-OH. Pour t > 2 h, un équilibre est observé pour toutes les résines. Le modèle du pseudosecond ordre permet de décrire la cinétique de sorption pour les 4 résines. A l’équilibre, l’adsorption est maximum d’une part dans une gamme de pH compris entre 6 et 12 pour les 2 résines sélectives Amb IRA 743 et CRB 03, et d’autre part pour un pH de 8 pour la résine Ambersep 900-OH et un pH 10 pour la résine Amberlite IRA 402 Cl. A pH 8 et pour les concentrations en bore < 20 mM, la sorption du bore est représentée par le modèle de type Langmuir pour Amberlite IRA 743, Ambersep 900-OH et Diaion CRB 03. Par contre, la rétention du bore sur Amberlite IRA 402 Cl suit une isotherme de type linéaire. A pH 8 et pour des concentrations en bore < 20 mM, les capacités de sorption sont : 1, 0,7, 0,3 et 0,05 mmol g–1 pour Diaion CRB 03, Amberlite IRA 743, Ambersep 900-OH et Amberlite IRA 402 Cl, respectivement. Les résines Ambersep 900-OH, échangeuse d’anions, et Amberlite IRA 743, sélective, ont été utilisées pour les essais en colonnes en fonction de la concentration en bore et du temps de séjour. Pour la résine spécifique, le temps de séjour dans la colonne affecte fortement le comportement du bore : lorsqu’il diminue, son élution est rapide suivie d’une longue traînée ; lorsqu’il augmente, la courbe de percée correspond à un système à l’équilibre. Pour un temps de séjour élevé, les résultats confirment la non-linéarité observée lors des essais en réacteurs fermés. Pour la résine échangeuse d’anions, la non-linéarité est aussi confirmée. Ces essais permettent de différencier le comportement du bore lors de sa désorption. La régénération est obtenue après des traitements acides et basiques pour la résine spécifique alors qu’un traitement alcalin est suffisant pour la résine anionique. Une étude plus détaillée des mécanismes est en cours et permettra de les intégrer dans un même modèle. La fixation du bore sur des pectines et sa rétention par des membranes d’ultrafiltration (membranes de seuil de coupure différent) a aussi été étudiée. Les pectines ont été caractérisées (composition en sucre et en bore présent initialement) et la viscosité des solutions pectiques mesurée. Des essais de filtration ont permis de déterminer l’efficacité de production et de rétention du bore sur ces matériauxBoron is an element, which is necessary as essential nutrient for living organisms, especially for plants where it is involved in cell wall composition. But boron excess can cause some problems on the development of plants (defoliation, decay and fall unripe fruits), of humans and animals such as nausea, diarrhoea, dermatitis, lethargy. Boron toxicity also changes blood composition, caused disorder in neurological, physical, intellectual development. Nowadays, due to the shortage of fresh water sources, seawater desalination has been becoming an alternative fresh water supply. However, the presence of boron in seawater is quite high (4.5 mg L–1, around 4.5 mM). Moreover, the increasing use of boron in industries and its discharge to the environment has led to the contamination of surface and ground waters. As the result, boron removal, in production of drinking water becomes very important. Therefore, the World health organization has recommended a guideline of 0.5 mg L–1 B in drinking water and a maximum limit of 0.3 mg L–1 B in fresh water used for irrigation. The objective of this thesis is to study the mechanisms of boron surface exchange on different materials versus time and at equilibrium depending on some physicochemical parameters such as pH, initial boron concentration, reaction time in order to find a new exchanger for boron removal. Boron removal was carried out by ion exchange process using 2 types of resins: Amberlite IRA 743, Diaion CRB 03 as boron selective resins with methylglucamine functions, and Ambersep 900-OH and Amberlite IRA 402 Cl as anionic exchange resins with ammonium functions. From batch studies, fast exchange between resin surface and liquid phase was observed with boron removal up to at least 96 % within 30 min for Amberlite IRA 743, Diaion CRB 03 and Ambersep 900- OH. The reaction between resin surface and boron solution reached equilibrium after 2 h for all the resins. The pseudo-second order kinetic model was used to well describe the sorption kinetic process of the resins. At equilibrium, the experimental results showed that the maximum adsorption was observed to be achieved at pH 8 for Ambersep 900- OH, pH 10 for Amberlite IRA 402 Cl and independent on pH range from 6 to 12 for the 2 boron selective resins Amberlite IRA 743 and Diaion CRB 03. At pH 8 and for boron concentrations < 20 mM, the Langmuir-type relationship was used to fit the experimental data for Amberlite IRA 743, Ambersep 900- OH and resin Diaion CRB 03. In the range of studied boron concentration, the boron sorption onto Amberlite IRA 402 Cl followed linear-type behaviour. At pH 8 and for boron concentrations < 20 mM, the sorption capacities are: 1, 0,7, 0,3 et 0,05 mmol g–1 for Diaion CRB 03, Amberlite IRA 743, Ambersep 900- OH and Amberlite IRA 402 Cl, respectively. Column experiments were performed with the anionic resin Ambersep 900-OH and the selective one Amberlite IRA 743 by studying both the influence of boron concentration and the residence time. For the selective resin, if the residence time decreases, the boron breakthrough is fast followed by a long tail. For larger residence time, local equilibrium seems to be assumed. Results are thus consistent with batch experimental data. For the anionic resin, the nonlinear behaviour is also confirmed. Moreover, column experiments showed a strong difference during desorption. To regenerate resins, acid and basic treatments are necessary for the selective resin although a basic solution is enough for the anionic resin. A more detailed study of mechanisms is in progress in order to build a exchange model for predicting boron fate. Finally, characterization of pectins was also performed. Its composition (sugar and boron content) and the viscosity of pectin solutions were quantified. Filtration experiments allowed testing the efficiency of such material to remove boron too
22
Bin, Darwish Nawaf Naif. "Boron removal from saline water". Thesis, Swansea University, 2014. https://cronfa.swan.ac.uk/Record/cronfa42237.
Texto completoResumen
Although boron is an essential micronutrient for some plants, animals and humans, the range between deficiency and excess is narrow. The effects of excess boron on plants includes the reduction of root cell division, retarded shoot and root growth, inhibition of photosynthesis, deposition of lignin and suberin and decrease in leaf chlorophyll. A report by the World Health Organization (WHO) suggests a safe maximum level of boron daily intake of 13 mg/d an excessive level of boron can be toxic to and can causes serious diseases. There are several methods applied for boron removal from aqueous solutions and seawater. Among these methods, ion exchange, which is the most extensively method. Ion-exchange and adsorption are widely used techniques to remove metals and other solutes from aqueous solutions. This includes the removal of boron from reverse osmosis (RO) permeate in the process of seawater desalination. The use of boron-selective ion exchange resins based on macroporous polystyrene matrices with the active group N-methyl-D-glucamine (NMG) seems to still have the highest importance for the elimination of boron. Kinetics of adsorption or IEX is in many cases strongly influenced by diffusion resistance in particles of adsorbent. This resistance can be decreased by using smaller particles. Sorbents can be used as very fine particles which results in increase of the surface area and the process rate, considerably. Hybrid adsorption membrane filtration has gained the interest lately as it can be used for the removal of very small quantities of harmful substances from water. This thesis deals used hybrid system on both lab and pilot scale where a pilot plant was designed for the removal of boron. Boron separation combines two phenomena: i) sorption with fine sorbent particles and ii) membrane separation of B-loaded macromolecules/particles. The hybrid system includes two separation loops. Loop 1: Binding of boron (B) on Amberlite IRA743 resin (S), which is subsequently followed by separation of this (BS) complex from the water by means of semi-permeable microfiltration membrane. Here, pure water (W) is the main product whereas the complex (BS) passes to the second stage of separation. The effects of different parameters on boron removal using Amberlite IRA743 resin were investigated in this thesis. These parameters are, resin particle size, solution pH, temperature, contact time, initial boron concentration, resin concentration and the existence of different salts and ions like NaCl, Na2SO4 and MgCl2. The removal increased with increasing pH, temperature, contact time and resin dosage while it decreased with increasing initial boron concentration and resin particle size. For the microfiltration stage, three Polyvinylidene fluoride (PVDF) with different pore size have been used in this thesis. The effects of operational parameters like membrane pore size, transmembrane pressure, resin concentration and pH on permeate flux for hybrid adsorption-microfiltration were studied. The permeate flux increased with increasing the transmembrane pressure and pH but it decreased with increasing the resin concentration. The regeneration of loaded resin with boron was investigated. Hydrochloric acid (HCl) and sulfuric acid (H2SO4) at different concentrations have been used for the elution of boron from the saturated resin and then washing with sodium hydroxide (NaOH). There was an improvement in the boron removal after cycles of regeneration. The integrated adsorption-microfiltration was applied for boron removal from water and encouraging results were achieved.
23
Music, Denis. "Boron suboxide based thin films /". Linköping : Univ, 2003. http://www.bibl.liu.se/liupubl/disp/disp2003/tek835s.pdf.
Texto completo
24
Alharbi, Abdulaziz. "Deformation of hexagonal boron nitride". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/deformation-of-hexagonal-boron-nitride(6c6013c4-8c17-4dec-b250-ed3f0baea7ed).html.
Texto completoResumen
Boron nitride (BN) materials have unique properties, which has led to interest in them in the last few years. The deformation of boron nitride materials including hexagonal boron nitride, boron nitride nanosheets (BNNSs) and boron nitride nanotubes have been studied by Raman spectroscopy. Both mechanical and liquid exfoliations were employed to obtain boron nitride nanostructures. Boron nitride glass composites were synthesised and prepared in thin films to be deformed by bending test in-situ Raman spectroscopy. Hexagonal boron nitride in the form of an individual flake and as flakes dispersed in glass matrices has been deformed and Raman measurement shows its response to strain. The shift rates were, -4.2 cm-1/%, -6.5 cm-1/% for exfoliated h-BN flake with thick and thin regions and -7.0 cm-1/%, -2.8 cm-1/% for the h-BN flakes in the h-BN/ glass (I) and glass (II) composites. Boron nitride nanosheets (BNNSs) shows a G band Raman peak at 1367.5 cm-1, and the deformation process of BNNSs/ glass composites gives a shift rate of -7.65 cm-1/% for G band. Boron nitride nanotubes (BNNTs) have a Raman peak with position at 1368 cm-1, and their deformation individually and in composites gives Raman band shift rates of -25.7 cm-1/% and -23.6 cm-1/%. Glass matrices shows compressive stresses on boron nitride fillers and this was found as an upshift in the frequencies of G band peak of boron nitride materials. Grüneisen parameters of boron nitride (BN) were used to calculate the residual strains in glass matrices of BNNSs nanocomposites as well as to estimate the band shift rates which found to be in agreement with the experimental shift rate of bulk BN and BNNTs.
25
Taher, Mamoun. "Novel boron compounds in lubrication". Licentiate thesis, Luleå tekniska universitet, Industriell miljö- och processteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-25920.
Texto completoResumen
Lubricants are used to control friction and reduce wear by preventing direct contact between surfaces in a relative motion. Most of the modern lubricants and lubricant additives have been designed and optimized for ferrous materials. A growing trend towards wider use of lightweight and wear resistant non-ferrous materials calls for new efficient and environmentally friendly Lubricants. Boron compounds are attractive alternatives for the commercially available lubricants and lubricant additives. Some boron compounds have already been proven as efficient friction modifiers, antioxidants, corrosion inhibitors and antiwear additives in lubricants.In this work we focus on design, synthesis, physicochemical characterization and tribological studies of novel boron compounds. Boron based ionic liquids (ILs) and dithiocarbamates (B-DTCs) were designed, synthesized and tribologically characterized. The work was carried out in the following steps: (i) design and synthesis of novel boron compounds; (ii) physicochemical characterization of the synthesized compounds by FTIR, liquid-state (1H, 13C, and 11B) and solid-state (13C and 11B) nuclear magnetic resonance (NMR) spectroscopy, elemental analysis, thermal analysis (TG, DTA, DSC and QMS), powder XRD, density and viscosity measurements; (iii) tribological characterization using four-ball and pin-on-disc tribometers and (iv) surface analysis using Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy (SEM/EDS), optical interferometer and stylus profilometer. Some of these new boron-based compounds revealed significantly better antiwear and friction reducing performance on steel-steel contacts compared with fully formulated engine oils. (i) Nine novel ILs of pryrrolidinium bis(salicylato)borate were synthesized and physicochemically characterized. They are solid at room temperature and some of them behave as plastic crystals. Some of these ILs were tested as lubricants at 100 ºC, i.e. above their melting points. These ILs have shown significantly better antiwear and friction reducing performance in lubrication of steel-steel contacts compared to fully formulated synthetic engine oil 5W40.(ii) Nine novel room temperature ionic liquids (RTILs) of pyrrolidinium bis(mandelato)borate were synthesized and physicochemically characterized. These ILs were tribologically tested as 3 wt % additives in polyethylene glycol (PEG) and they have shown considerably better antiwear and friction reducing properties in boundary lubrication of steel-steel contacts at room temperature compared with neat PEG and engine oil 5W40.(iii) Boron based compounds containing alkylborate and dithiocarbamate groups with alkyl substitutes in one molecule were synthesized and physicochemically characterized. The influence of alkyl chain length (butyl and/or octyl substitutes at DTC and borate groups) and heterocyclicity in boron based dithiocarbamate compounds (B-DTCs) on their tribophysical properties as additives in a mineral oil was studied for steel-steel lubricated contacts.Godkänd; 2012; 20121123 (mamtah); LICENTIATSEMINARIUM Ämne: Gränsytors kemi/Chemistry of Interfaces Examinator: Professor Oleg N. Antzutkin, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet Diskutant: Professor Mark Rutland, Chalmers tekniska högskola, Göteborg Tid: Onsdag den 19 december 2012 kl 10.15 Plats: C305, Luleå tekniska universitet
26
Cherednichenko, Kirill. "Boron chalcogenides under extreme conditions". Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066602/document.
Texto completoResumen
Cette thèse porte sur l'étude des chalcogénures de bore sous conditions extrêmes. Après un bref examen de la littérature (Chapitre I) sur le bore et ses composés sous haute pression (HP), la partie expérimentale (Chapitre II) donne une description des appareils HP utilisés dans ce travail de thèse. Les techniques d'analyses employées sont décrites ainsi que les grands principes des calculs théoriques ab initio utilisés. La partie suivante est consacrée à β-B2O3 et r-BS. Le chapitre III présente les résultats de diffraction X in situ à HP et les mesures de phonons (Raman et IR) de β-B2O3 à température ambiante. Les données expérimentales ont été examinées et complétées par des calculs ab initio. Avec le jeu de données obtenues, les descriptions complètes des modifications sous pression de la structure de β-B2O3 et du comportement des phonons en compression à température ambiante ont été faites. Le chapitre IV présente les résultats de diffraction X in situ à HP et de spectroscopie vibrationnelle sur r-BS à température ambiante. En combinaison avec les calculs théoriques, la structure et la nature des phonons de r-BS sur une large plage de pression à température ambiante sont décrites. En outre, la formation d'une nouvelle phase HP métastable de BS est présentée et sa structure probable ainsi que son équation d’état sont discutés. Le chapitre V concerne la première étude in situ de diffraction X sous HP-HT du système B-Se. Selon les résultats de diffraction X et des mesures Raman effectuées sur les échantillons récupérés, un nouveau composé a été synthétisé. Ce composé est métastable à l’ambiante. Sa composition chimique et sa structure probable sont discutéesThis thesis deals with the study of the boron chalcogenides under extreme conditions. After a short review of boron and boron compounds under extreme conditions (Chapter I), the experimental part (Chapter II) provides a brief description of the high-pressure devices used in this PhD work. The employed analytical techniques are described as well as the main principles of the performed ab initio theoretical calculations. The following part is devoted to our experimental and theoretical studies of β-B2O3 and r-BS. Chapter III presents the results of in situ high pressure XRD and phonon measurements (Raman and IR) of β-B2O3 at room temperature. The experimental data were considered and completed with results of ab initio calculations. Based on the total obtained dataset the complete description of β-B2O3 structure change and phonon behavior under compression at room temperature are detailled. Chapter IV contains the results of in situ high pressure XRD and vibrational spectroscopy studies on r-BS at room temperature. In combination with results of theoretical calculations the structure and phonon nature of r-BS in a wide pressure range at ambient temperature are described. Also, the formation of a new metastable high-pressure phase of BS is described and its probable structure and EoS are discussed. The last part (Chapter V) concerns the primary in situ XRD HP-HT studies in B-Se system. Based on the results of XRD and Raman measurements of the recovered samples, a new compound was synthesized. This compound was found to be metastable at ambient conditions. Its probable chemical composition and structure are discussed
27
Cherednichenko, Kirill. "Boron chalcogenides under extreme conditions". Electronic Thesis or Diss., Paris 6, 2015. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2015PA066602.pdf.
Texto completoResumen
Cette thèse porte sur l'étude des chalcogénures de bore sous conditions extrêmes. Après un bref examen de la littérature (Chapitre I) sur le bore et ses composés sous haute pression (HP), la partie expérimentale (Chapitre II) donne une description des appareils HP utilisés dans ce travail de thèse. Les techniques d'analyses employées sont décrites ainsi que les grands principes des calculs théoriques ab initio utilisés. La partie suivante est consacrée à β-B2O3 et r-BS. Le chapitre III présente les résultats de diffraction X in situ à HP et les mesures de phonons (Raman et IR) de β-B2O3 à température ambiante. Les données expérimentales ont été examinées et complétées par des calculs ab initio. Avec le jeu de données obtenues, les descriptions complètes des modifications sous pression de la structure de β-B2O3 et du comportement des phonons en compression à température ambiante ont été faites. Le chapitre IV présente les résultats de diffraction X in situ à HP et de spectroscopie vibrationnelle sur r-BS à température ambiante. En combinaison avec les calculs théoriques, la structure et la nature des phonons de r-BS sur une large plage de pression à température ambiante sont décrites. En outre, la formation d'une nouvelle phase HP métastable de BS est présentée et sa structure probable ainsi que son équation d’état sont discutés. Le chapitre V concerne la première étude in situ de diffraction X sous HP-HT du système B-Se. Selon les résultats de diffraction X et des mesures Raman effectuées sur les échantillons récupérés, un nouveau composé a été synthétisé. Ce composé est métastable à l’ambiante. Sa composition chimique et sa structure probable sont discutéesThis thesis deals with the study of the boron chalcogenides under extreme conditions. After a short review of boron and boron compounds under extreme conditions (Chapter I), the experimental part (Chapter II) provides a brief description of the high-pressure devices used in this PhD work. The employed analytical techniques are described as well as the main principles of the performed ab initio theoretical calculations. The following part is devoted to our experimental and theoretical studies of β-B2O3 and r-BS. Chapter III presents the results of in situ high pressure XRD and phonon measurements (Raman and IR) of β-B2O3 at room temperature. The experimental data were considered and completed with results of ab initio calculations. Based on the total obtained dataset the complete description of β-B2O3 structure change and phonon behavior under compression at room temperature are detailled. Chapter IV contains the results of in situ high pressure XRD and vibrational spectroscopy studies on r-BS at room temperature. In combination with results of theoretical calculations the structure and phonon nature of r-BS in a wide pressure range at ambient temperature are described. Also, the formation of a new metastable high-pressure phase of BS is described and its probable structure and EoS are discussed. The last part (Chapter V) concerns the primary in situ XRD HP-HT studies in B-Se system. Based on the results of XRD and Raman measurements of the recovered samples, a new compound was synthesized. This compound was found to be metastable at ambient conditions. Its probable chemical composition and structure are discussed
28
Rockett, Chris H. "Flexural Testing of Molybdenum-Silicon-Boron Alloys Reacted from Molybdenum, Silicon Nitride, and Boron Nitride". Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16293.
Texto completoResumen
MoSiB alloys show promise as the next-generation turbine blade material due to their high-temperature strength and oxidation resistance afforded by a protective borosilicate surface layer. Powder processing and reactive synthesis of these alloys has proven to be a viable method and offers several advantages over conventional melt processing routes. Microstructures obtained have well-dispersed intermetallics in a continuous matrix of molybdenum solid-solution (Mo-ss). However, bend testing of pure Mo and Mo-ss samples has shown that, while the powder processing route can produce ductile Mo metal, the hardening effect of Si and B in solid-solution renders the matrix brittle. Testing at elevated temperatures (200°C) was performed in order to determine the ductile-to-brittle transition temperature of the metal as an indication of ductility. Methods of ductilizing the Mo-ss matrix such as annealing and alloying additions have been investigated.
29
Pilli, Aparna. "Atomic Layer Deposition of Boron Oxide and Boron Nitride for Ultrashallow Doping and Capping Applications". Thesis, University of North Texas, 2020. https://digital.library.unt.edu/ark:/67531/metadc1752373/.
Texto completoResumen
The deposition of boron oxide (B₂O₃) films on silicon substrates is of significant interest in microelectronics for ultrashallow doping applications. However, thickness control and conformality of such films has been an issue in high aspect ratio 3D structures which have long replaced traditional planar transistor architectures. B₂O₃ films are also unstable in atmosphere, requiring a suitable capping barrier for passivation. The growth of continuous, stoichiometric B₂O₃ and boron nitride (BN) films has been demonstrated in this dissertation using Atomic Layer Deposition (ALD) and enhanced ALD methods for doping and capping applications.
Low temperature ALD of B₂O₃ was achieved using BCl₃/H₂O precursors at 300 K. In situ x-ray photoelectron spectroscopy (XPS) was used to assess the purity and stoichiometry of deposited films with a high reported growth rate of ~2.5 Å/cycle. Free-radical assisted ALD of B₂O₃ was also demonstrated using non-corrosive trimethyl borate (TMB) precursor, in conjunction with mixed O₂/O-radical effluent, at 300 K. The influence of O₂/O flux on TMB-saturated Si surface was investigated using in situ XPS, residual gas analysis mass spectrometer (RGA-MS) and ab initio molecular dynamics simulations (AIMD). Both low and high flux regimes were studied in order to understand the trade-off between ligand removal and B₂O₃ growth rate. Optimization of precursor flux was discovered to be imperative in plasma and radical-assisted ALD processes.
BN was investigated as a novel capping barrier for B₂O₃ and B-Si-oxide films. A BN capping layer, deposited using BCl₃/NH₃ ALD at 600 K, demonstrated excellent stoichiometry and consistent growth rate (1.4 Å/cycle) on both films. Approximately 13 Å of BN was sufficient to protect ~13 Å of B₂O₃ and ~5 Å of B-Si-oxide from atmospheric moisture and prevent volatile boric acid formation. BN/B₂O₃/Si heterostructures are also stable at high temperatures (>1000 K) commonly used for dopant drive-in and activation. BN shows great promise in preventing upward boron diffusion which causes a loss in the dopant dose concentration in Si.
The capping effects of BN were extended to electrochemical battery applications. ALD of BN was achieved on solid Li-garnet electrolytes using halide-free tris(dimethylamino)borane precursor, in conjunction with NH₃ at 723 K. Approximately 3 nm of BN cap successfully inhibited Li₂CO₃ formation, which is detrimental to Li-based electrolytes. BN capped Li-garnets demonstrated ambient stability for at least 2 months of storage in air as determined by XPS. BN also played a crucial role in stabilizing Li anode/electrolyte interface, which drastically reduced interfacial resistance to 18 Ω.cm², improved critical current density and demonstrated excellent capacitance retention of 98% over 100 cycles. This work established that ALD is key to achieving conformal growth of BN as a requirement for Li dendrite suppression, which in turn influences battery life and performance.
30
Stangoulis, James Constantine Roy. "Genotypic variation in oilseed rape to low boron nutrition and the mechanism of boron efficiency". Title page, contents and summary only, 1998. http://web4.library.adelaide.edu.au/theses/09PH/09phs7856.pdf.
Texto completoResumen
Bibliography: leaves 132-159. Boron efficiency in oilseed rape (Brassica napua L. and B. juncea L.) was investigated in a wide range of genotypes. Using a solution culture screening of 10 day old seedlings, root length best described shoot growth response, and was used to characterise a total of 65 genotypes. Varieties and breeders lines tolerant of B-deficient growing conditions were identified, and the screening process validated through field trials. B responses in plants sampled at the 'green bud' stage indicated that vegetative growth is important in B efficiency. Studies were conducted to investigate the mechanism of B efficiency in oilseed rape. Results suggest no association between B efficiency and the capacity to acidify the root rhizosphere, or an increased translocation of B from root to shoot. Boron retranslocation was also studied as a mechanism of B efficiency.
31
Oz, Tufan M. "Microarray Based Expression Profiling Of Barley Under Boron Stress And Cloning Of 3h Boron Tolerance Gene". Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614203/index.pdf.
Texto completoResumen
Both deficiency and toxicity of the essential micronutrient boron (B) lead to reduced crop yield in agriculture. However, our understanding of the molecular responses of plants under B stresses to tackle the yield loss is limited. Therefore, in the present study, transcriptional alterations in sensitive and tolerant barley cultivars under B deficiency and toxicity were investigated in order to reveal the molecular responses. Transcriptomes were monitored at seedling stage by global expression profiling using oligonucleotide microarrays.
In the context of the study, we have determined that response to B toxicity in barley involved jasmonic acid and various components of biotic stress responses. Examination of expression profiles indicated that B toxicity and deficiency resulted in significant global changes in the transcriptomes of leaf and root tissues, respectively. Inter-varietal comparison of sensitive and tolerant genotypes of barley revealed that a combinatorial effect of transcription factors on regulation could alter the gene expression patterns in tolerant cultivar and provide B toxicity tolerance. Furthermore, mechanisms of vacuolar sorting or efflux by transporters and aquaporins might be contributing to the tolerance to B stresses in barley according to the results of this study.
Additionally, we have identified and cloned the HvBor1a gene encoding a putative B transporter in barley using candidate gene approach and functionally characterized its roles in the tolerance to B stresses. The full length coding sequence and also the non-coding regions of the gene were identified. It was demonstrated that the protein product of HvBor1a was localized to the plasma membrane and it displayed B transporter activity. High transcript abundances in leaf tissues of barley suggested a role for HvBor1a in re-distribution of B within the plant tissues. Interestingly, examination of last intron of HvBor1a has led to the identification of an alternatively spliced variant in certain cultivars of barley. Furthermore, interval mapping and positional cloning was performed to locate the HvBor1a on 3H B tolerance QTL and a novel CAPS marker was developed to narrow the genetic distances at the locus.
As a conclusion, this work presents, for the first time, the transcriptome profiling of a member of Triticeae under B toxicity and deficiency. The data generated should enlighten succeeding studies to unravel molecular mechanisms and signaling networks of tolerance to B stresses especially in crops like barley and wheat. The results of the study will provide novel tools and genes for conventional and biotechnological approaches for the reduction of yield loss due to B toxicity or deficiency.
32
Noyan, Selin. "Production Of Boron Nitride Nanotubes From The Reaction Of Nh3 With Boron And Iron Powder Mixture". Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615045/index.pdf.
Texto completoResumen
Boron nitride nanotubes (BNNTs), which are structurally similar to carbon nanotubes (CNTs), were synthesized in 1995 for the first time. They are made up by folding atom sheets which consist of boron and nitrogen atoms into cylindrical form. After their discovery, BNNTs have been attracting great attention due to their extraordinary mechanical, thermal, electrical, and optical properties.
In this study, BNNTs were synthesized from the reaction of ammonia gas with the boron and iron powder mixture in a tubular reactor which was connected to a mass spectrometer for on-line chemical analysis of the reactor effluent stream. The synthesized materials were purified with acid treatment. Chemical analysis results showed that nitrogen and hydrogen gases were present in addition to ammonia gas. XRD results revealed that the solid phases in the synthesized material were hexagonal boron nitride, rhombohedral boron nitride, iron, and boron-iron compounds (FeB49 and Fe3B). Reactions taking place in BNNT synthesis were proposed as the decomposition of ammonia gas which was the only gas phase reaction, the formation of boron-iron compounds from the reaction of boron with iron, and boron nitride formation from the reaction of nitrogen with boron-iron compounds.
Agglomerated, hollow, multi-walled nanotubes were synthesized with an outer diameter range of 10-550 nm. Both open and close-ended nanotubes were observed. The interlayer distance between BN sheets was measured about 0.33 nm and this distance indicated the d002 plane of hexagonal boron nitride. BNNTs exhibited Type II isotherms with a Type B hysteresis. A decrease in the surface area of the synthesized BNNTs was observed with an increase in temperature. The highest surface area was 147.6 m2/g. Average pore diameter of BNNTs synthesized at different temperatures was around 38 Å. Deposition rate of boron nitride increased with an increase in temperature. After a certain temperature, deposition rate decreased with temperature due to the sintering effect. The highest deposition rate was observed when BNNTs were synthesized with the B/Fe weight ratio of 15/1 at 1300 °
C.
33
Yoshii, Ryosuke. "Synthesis of Highly-Functional Polymers Using Characteristics of Four-Coordinated Boron-Complexes with Boron-Nitrogen Bonds". 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188610.
Texto completo
34
Binello, Emanuela. "In vitro analysis of boron-10 uptake and neutron beam design for boron neutron capture synovectomy". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38394.
Texto completo
35
Bagheri, Kazemabad Abdolreza. "Boron tolerance in grain legumes with particular reference to the genetics of boron tolerance in peas". Title page, summary and contents only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phb144.pdf.
Texto completo
36
Gao, Wei. "Crystal growth of alpha-rhombohedral boron". Thesis, Manhattan, Kan. : Kansas State University, 2010. http://hdl.handle.net/2097/4171.
Texto completo
37
Shupe, John. "Densification of nano-sized boron carbide". Thesis, Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/33818.
Texto completoResumen
Boron carbide nano-powders, singly-doped over a range of compositions, were
pressurelessly-sintered at identical temperature and atmospheric conditions in a dif-
ferential dilatometer to investigate sintering behavior. Samples that achieved relative
densities greater than 93% of theoretical density were post-HIPed. Post-HIPing re-
sulted in an increase in relative density as well as an increase in Vicker's hardness. To
optimize the sintering behavior, nano-powders with multiple dopants were prepared
based on the results of single dopant experiments. These powders were studied using
the same heating schedule as the single dopant samples. The powder with optimized
composition was selected, and 44.45 mm diameter disks were pressed to determine
the effects of sample size.
Powder composition #166 with Al, Ti, W and Mg additions was processed using
di¢çerent methods in order to create defect-free green bodies after uniaxial press-
ing. The 44.45 mm diameter compacts were heat-treated to remove organics and
B₂O₃coatings on particles and then encapsulated in an evacuated fused silica am-
pule. Encapsulated samples were HIPed at temperatures below the coarsening region
observed in the dilatometric traces of multiply-doped nano-powders. The E-HIPed
sample showed a relative density of 96% with a limited extent of nano-sized grain
microstructure.
38
Camurlu, Hasan Erdem. "Carbothermic Production Of Hexagonal Boron Nitride". Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607808/index.pdf.
Texto completoResumen
Formation of hexagonal boron nitride (h-BN) by carbothermic reduction of B2O3 under nitrogen atmosphere at 1500oC was investigated. Reaction products were subjected to powder X-ray diffraction analysis, chemical analysis and were examined by SEM. B4C was found to exist in the reaction products of the experiments in which h-BN formation was not complete. One of the aims of this study was to investigate the role of B4C in the carbothermic production of h-BN. For this purpose, conversion reaction of B4C into h-BN was studied. B4C used in these experiments was produced in the same conditions that h-BN was formed, but under argon atmosphere. It was found that formation of h-BN from B4C&ndashB2O3 mixtures was slower than activated C&ndash
B2O3 mixtures. It was concluded that B4C is not a necessary intermediate product in the carbothermic production of h-BN. Some additives are known to catalytically affect the h-BN formation. The second aim of this study was to examine the catalytic effect of some alkaline earth metal oxides and carbonates, some transition metal oxides and cupric nitrate. It was found that addition of 10wt% CaCO3 into the B2O3+C mixture was optimum for increasing the rate and yield of h-BN formation and decreasing the B4C amount in the products and that the reaction was complete in 2 hours. CaCO3 was observed to be effective in increasing the rate and grain size of the formed h-BN. Addition of cupric nitrate together with CaCO3 provided a further increase in the size of the h-BN grains.
39
Karaman, Mustafa. "Chemical Vapor Deposition Of Boron Carbide". Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608778/index.pdf.
Texto completoResumen
Boron carbide was produced on tungsten substrate in a dual impinging-jet CVD reactor from a gas mixture of BCl3, CH4, and H2. The experimental setup was designed to minimise the effect of mass transfer on reaction kinetics, which, together with the on-line analysis of the reactor effluent by FTIR,
allowed a detailed kinetic investigation possible.
The phase and morphology studies of the products were made by XPS, XRD,micro hardness and SEM methods. XPS analysis showed the existence of chemical states attributed to the boron carbide phase, together with the existence of oxy-boron carbide species. SEM pictures revealed the formation
of 5-fold icosahedral boron carbide crystals up to 30 micron sizes for the samples produced at 1300oC. Microhardness tests showed change of boron carbide hardness with the temperature of tungsten substrate. The hardness
values (Vickers Hardness) observed were between 3850 kg/mm2 and 4750 kg/mm2 corresponding to substrate temperatures of 1100 and 1300 C, respectively.
The FTIR analysis of the reaction products proved the formation of reaction intermediate BHCl2, which is proposed to occur mainly in the gaseous boundary layer next to the substrate surface. The experimental parameters are
the temperature of the substrate, and the molar fractions of methane and borontrichloride at the reactor inlet. The effects of those parameters on the reaction rates, conversions and selectivities were analysed and such analyses were used in mechanism determination studies. An Arrhenius type of a rate
expression was obtained for rate of formation of boron carbide with an energy of activation 56.1 kjoule/mol and the exponents of methane and boron trichloride in the reaction rate expression were 0.64 and 0.34, respectively, implying complexity of reaction. In all of the experiments conducted, the rate of formation of boron carbide was less than that of dichloroborane.
Among a large number of reaction mechanisms proposed only the ones considering the molecular adsorption of boron trichloride on the substrate surface and formation of dichloroborane in the gaseous phase gave reasonable
fits to the experimental data. Multiple non-linear regression analysis was carried out to predict the deposition rate of boron carbide as well as formation rate of dichloroborane simultaneously.
40
Hao, Wenjun. "Atomic layer deposition of boron nitride". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1311/document.
Texto completoResumen
Cette thèse conclut 3 années d'études doctorales sur le "dépôt de couches atomiques (ALD) de nitrure de bore (BN)". Le but de ce travail a été d'adapter la voie des céramiques dérivées de polymères (PDC) à la technique ALD pour la croissance de films minces de h-BN et l'élaboration de nanostructures fonctionnelles. Tout d'abord, un nouveau procédé d'ALD sans ammoniac en deux étapes, comprenant une croissance par ALD à basse température (80 °C) de polyborazine (PBN) à partir de 2,4,6-trichloroborazine et d'hexaméthyldisilazane suivi un traitement thermique à haute température sous atmosphère contrôlée a été développé. Ainsi, des films minces uniformes et homogènes de BN ont pu être déposés sur divers substrats. Le caractère autolimité des réactions mises en jeu ainsi que l'homogénéité des films sur des supports très structurés ont été vérifiés. De ce fait des nanostructures fonctionnelles BN ont été réalisées à partir de substrats ou de templates de dimensionnalité variée. Leurs applications en tant que revêtements protecteurs et comme filtres et éponges absorbantes pour purifier les eaux polluées par des hydrocarbures ont en particulier été étudiées. Enfin, un deuxième procédé ALD basse température (85-150°C) utilisant le tri(isopropylamino)borane et la méthylamine comme précurseurs a été préalablement étudié afin de confirmer l'adaptabilité de la voie PDC et la technique ALD. Des films minces de BN ont été obtenus sur des substrats plans et il a été prouvé que les vapeurs de tri(isopropylamino)borane peuvent infiltrer des fibres de polyacrylonitrile électrofilées.Ce travail a été entièrement réalisé à l'Université de Lyon et a reçu le soutien financier du China Scholarship Council (CSC) pour la bourse de doctorat ainsi que de l'Agence Nationale de la Recherche (projet n° ANR-16-CE08-0021-01)This thesis achieves 3 years of PhD studies on “Atomic layer deposition (ALD) of boron nitride (BN)”. The aim of this PhD work is to adapt the polymer derived ceramics (PDCs) route to the ALD technique for h-BN thin film growth and elaboration of functional nanostructures. A novel two-step ammonia-free ALD process, which includes ALD deposition of polyborazine at low temperature (80 °C) from 2,4,6-trichloroborazine and hexamethyldisilazane followed by post heat treatment under controlled atmosphere, has been established. Conformal and homogeneous BN thin films have been deposited onto various substrates. The self-limitation of the reactions on flat substrates and the conformality of the films on structured substrates have been verified. Functional BN nanostructures have thus been fabricated using substrates or templates with different dimensionalities. In particular, their applications as protective coatings as well as filter and absorber to purify polluted water from organic/oil hav e been investigated. Finally, a second low temperature (85-150 °C) ALD process using tri(isopropylamine)borane and methylamine as precursors has preliminary been studied in order to confirm the adaptability of PDCs route to ALD technique. BN thin films have been grown onto flat substrate and it has been proven that tri(isopropylamino)borane vapor can infiltrate into electrospun polyacrylonitrile fibers.This work was carried out at University of Lyon and financially supported by the National Research Agency (project n° ANR-16-CE08-0021-01)
41
Williams, Lynda B. "Boron isotope geochemistry during burial diagenesis". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0022/NQ49549.pdf.
Texto completo
42
Wade, Bruce Edward. "Boron nitride fibers from polymer precursors". Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/10035.
Texto completo
43
Kelland, Malcolm. "Organo-transition metal boron hydride chemistry". Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258164.
Texto completo
44
Vianez, Basilio Frasco. "Aspects of boron diffusion through hardwoods". Thesis, Bangor University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.358298.
Texto completo
45
Donnelly, David J. "The determination of boron in steels". Thesis, University of Wolverhampton, 1987. http://hdl.handle.net/2436/111547.
Texto completo
46
Adey, James. "Boron related point defects in silicon". Thesis, University of Exeter, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407270.
Texto completo
47
Patel, Hemant. "Boron-10 uptake in experimental gliomas". Thesis, University of Southampton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266375.
Texto completo
48
Man, H. C. "Laser glazing of iron boron alloys". Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37771.
Texto completo
49
Sabatini, Marco. "Synthesis of amides using boron catalysts". Thesis, University College London (University of London), 2018. http://discovery.ucl.ac.uk/10045230/.
Texto completoResumen
The thesis describes the research conducted towards the development of more sustainable methods for amide bond formation. The first chapter describes the importance of amide bond formation and the methods currently used for this type of transformation. Crucially, current methodologies defy in many aspects the 12 principles of green chemistry and are thus not sustainable. The subsequent chapters describe the work conducted directed at addressing problems with the current state of the art of amide bond formation. The development of a novel catalytic method for direct amidation of carboxylic acids with amines using borate esters is described. The applicability of this method for the synthesis a wide selection of amides and pharmaceutically relevant compounds is discussed and the extension of this methodology with unprotected amino demonstrated. Studies were also conducted towards understanding the mechanism of boron catalysed systems for amidation. A mechanistic hypothesis for borate systems based on kinetic studies, NMR studies and isolated reaction intermediates was elaborated. Conclusions and future outlooks based on these findings are presented.
50
Howard, William Bruce. "Accelerator-based boron neutron capture therapy". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/44479.
Texto completo