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Awenat, Karim. "Development of a method for the functionalisation of polymer substrates." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365836.
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Jančík, Vojtěch. "Synthesis, structural studies and reactivity of monomeric organo aluminum and gallium amides, hydrogensulfides and hydroxides using N-heterocyclic carbene precursor for heterobimetallic systems /." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=974004693.
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Singh, Sanjay. "Monomeric organo-aluminum and gallium monohydroxides as precursor for homo- and heterobimetallic oxides synthetic, reactivity and structural investigations including gold(I) N-heterocyclic carbene complexes /." [S.l.] : [s.n.], 2006. http://webdoc.sub.gwdg.de/diss/2006/singh.
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Penugonda, Madhusudhan R. "Alumina - silicon carbide composites from kaolinite-carbon precursors by hot-pressing." Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/28509.
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The system kaolinite - carbon black consisting of cheap precursors has been investigated, in terms of its potential to form A1₂ O₃ - SiC composites. The carbothermal reduction process of mullite and silica was studied, in detail, in the range 1275° to 1810° C and over different periods, both under sintering as well as hot-pressing conditions. It was established that the reduction of mullite and silica starts around 1450° C, where the rate of reaction is very slow. Until about 1800° C during the reduction of mullite, SiO₂ gets preferentially reduced, thus forming a composite ceramic consisting of SiC and A1₂ O₃ phases.
The kinetics of the formation of SiC + A1₂ O₃ were followed in the range 1590° - 1660° C and it was noted that under hot-pressing conditions they follow a contracting cylinder model. The rate of reaction increased with the increase in temperature and followed a parabolic path with time because of the geometry of the hot-pressed specimens at each temperature. This indicated that the gas diffusion in and out of the system along the edges of the cylindrical specimens is the rate controlling step. The activation energy of the reduction process was calculated to be 922 KJ/mole. The application of pressure prior to the carbothermal reduction process seemed to be not favourable for the formation of SiC and A1₂ O₃, however, when applied after the beginning of soaking period, this greatly improved the densities and formation of SiC and A1₂ O₃.
The microstructure of the samples was analysed using SEM and TEM. It was found that the grain size of the composite ceramic was of the order of 0.2μm. SiC was present mainly in the form of fine platelets.
Finally, the isothermal compaction behaviour of the system was studied under a constant pressure in the temperature range 1200° C - 1800° C, during which the formation and carbothermal reduction of mullite and silica took place. A mathematical model based on the least squares fitting was used to fit the compaction curves. Due to the complex nature of the compaction data an empirical approach was used to interpret the data and a viscoelastic model was developed. It was found that the interactive-double-Kelvin unit having two elastic and two viscous components explained the type of compaction behaviour observed in the kaolinite + C system. One of the viscous components (η₁) and one of the elastic components (M₁) were found to be temperature sensitive.
It is concluded that starting from the cheap precursors (kaolinite and carbon black) a particulate composite of A1₂ O₃,-SiC can be produced by hot-pressing technique. SiC-whisker formation is not encountered in this system. The very fine grain size of the paniculate composite, resulting in a small flaw size, should provide the composite ceramic with good mechanical properties.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Cassara, Christopher M. "Synthesis an photochemistry of new carbene precursors." Connect to this title online, 2005. http://hdl.handle.net/1811/337.
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Thesis (Honors)--Ohio State University, 2005.Title from first page of PDF file. Document formattted into pages: contains x, 54 p.; also includes graphics. Includes bibliographical references (p. 54). Available online via Ohio State University's Knowledge Bank.
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Tabassum, Sobia. "New Chiral Carbene Precursors for Catalysis and Chiral Recognition." Clausthal-Zellerfeld Universitätsbibliothek Clausthal, 2010. http://d-nb.info/1001909348/34.
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Acauan, Luiz Henrique. "Síntese e avaliação de florestas de nanotubo de carbono utilizando hexano como precursor." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2010. http://hdl.handle.net/10183/34683.
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Esta dissertação de mestrado investigou a técnica de síntese de “florestas” de nanotubos de carbono (NTC) produzidos por deposição química de vapor catalisada sobre substratos planos (wafers) de silício monocristalino utilizando filmes finos de ferro como catalisador e hexano como precursor de carbono. Os parâmetros de síntese analisados foram: temperatura, espessura de filme catalisador e quantidade de hexano. A caracterização dos nanotubos foi feita por Espectroscopia Raman, Microscopia Eletrônica de Varredura e Transmissão. As florestas apresentaram uma grande dependência das nanopartículas formadas durante o aquecimento das amostras. Estas por sua vez dependem diretamente da temperatura e espessura do filme catalisador. A melhor dispersão de nanopartículas foi alcançada com a maior espessura analisada (3,7nm) e temperatura intermediaria (800ºC) A temperatura também controla a qualidade dos NTC’s formados e influencia na taxa de precursor convertido em carbono. O aumento desta produz NTC’s de menor diâmetro, mas maior quantidade de carbono amorfo. Já a quantidade de hexano depende apenas do carbono absorvido pelas florestas, sendo o ponto ótimo igual ao mínimo necessário pra formação destas. O uso de hexano possibilitou a produção de florestas formadas por nanotubos de parede múltipla (MWNTs) com um bom alinhamento e de qualidade superior quando comparados à MWNTs comerciais. NTC’s com parede simples também puderam ser produzidos, mas não sob a forma de florestas, pois na temperatura necessária para produzir-los há um grande acumulo de carbono amorfo.This study has investigated the method for “forest-like” carbon nanotube (CNT) production synthesized by catalytical chemical vapour deposition over flat substrates as silicon wafers, with a thin layer of iron as catalyst and hexane as carbon source. The following parameters were evaluated: temperature, the thickness of the catalyst layer and quantity of carbon source (hexane) The carbon nanotube characterization was performed by Raman spectroscopy, Scanning and Transmission Electron Microscopy The CNT forests shown a big correlation with the nanoparticles formed at the heating stage. Their syntheses depend on the temperature and catalyst thickness as well. The best nanoparticles dispersion was reach with the thickest iron layer used (3,7nm) at intermediary temperatures (800ºC). The temperature also controls the quality of the synthesized CNT and plays an important roll in precursor conversion into carbon. As we increase the temperature, the CNT’s diameter gets thinner but the amount of amorphous carbon goes up. In the other hand, the concentration of hexane only affects the forest carbon consumption, with an optimal value equal to minimum quantity necessary for its formation. The hexane was able to synthesizes a forest-like multiwalls CNT’s (MWNT’s) with a good alignment and higher quality when compared with the commercial ones. Singlewalls CNT’s were also produced but they have no forest-like shape, once that at the higher temperatures required to produce them, a huge amount of amorphous carbon also appears.
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Föllmer, Marie. "Lignin fibres prepared by coagulation : a promising precursor for carbon fibres." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0238/document.
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Les fibres de carbone sont actuellement utilisées dans les matériaux composites pour les secteurs de l'aérospatiale, l’aéronautique et les sports de compétition. Leur application sur les marchés de grande consommation est toutefois entravée par le coût élevé des matières premières et le procédé de carbonisation, notamment l’étape de stabilisation. Par conséquent,les matériaux précurseurs alternatifs et peu coûteux sont très demandés. La lignine, une ressource naturelle très abondante contenant de grandes quantités de carbone, est considérée comme un bon candidat. Jusqu'à présent, les fibres de lignine ont été principalement préparées par filage en voie fondue et en mélange avec des polymères thermoplastiques pour améliorer leur aptitude au filage et leurs propriétés mécaniques, mais en réduisant fortement leurs rendements de carbonisation et en augmentant leur prix. Nous proposons dans cette thèse des fibres précurseur à base de lignine obtenues par un procédé de filage en continu par coagulation. En combinaison avec de petites proportions d'alcool polyvinylique, on obtient des fibres composites hautement flexibles et infusibles, contenant jusqu'à 70-90 % de lignine industrielle. Notre développement nous permet de fabriquer des fibres de carbone avec des rendements de l’ordre de 30 % qui présentent des propriétés prometteuses. Jusqu'à présent, les fibres de carbone à base de lignine mentionnées dans la littérature n'atteignent pas les propriétés mécaniques requises pour des applications à hautes performances en raison de leur structure de carbone amorphe. Cependant, en incorporant des cristaux liquides de feuillets d'oxyde de graphène ou des nanocristaux de cellulose dans nos fibres précurseurs de lignine, nous pouvons améliorer l'orientation des plans de carbone obtenus après la carbonisation. Nos systèmes de fibres à base de lignine avec une structuration améliorée représentent donc une étape importante vers la mise en oeuvre industrielle de la lignine en tant que matériau précurseur «vert» pour les fibres de carbone à faible coût et à haute résistanceCarbon fibres are currently used in composite materials for the aerospace, transportation and energy sectors. Their application in mass markets however is hindered by the high cost of the fibre raw materials. Therefore, alternative and inexpensive precursor materials are in high demand. Especially lignin, a widely abundant natural resource containing high quantities of carbon, is considered as an important candidate. So far, lignin fibres have mostly been prepared by melt-spinning and by blending with thermoplastic polymers to enhance their spinnability and mechanical properties, but strongly lowering their carbonization yields and raising their price. We propose lignin-based precursor fibres obtained through a continuous wet-spinning process. In combination with only small ratios of polyvinyl alcohol, highly flexible and infusible composite fibres, containing up to 70-90 % of industrial lignin, can be obtained.Our development enables us to manufacture carbon fibres in high yields which exhibit promising properties. Until now, lignin-based carbon fibres reported in literature do not reach the mechanical properties required for high-performance applications due to their amorphous carbon structure. However, by incorporation of liquid crystalline graphene oxide flakes or cellulose nanocrystals into our lignin precursor fibres, we are able to improve the orientation of the carbon planes obtained after carbonization. Our lignin-based fibre systems with enhanced structuration thus represent an important step towards the industrial implementation of lignin as “green” precursor material for low-cost and high-strength carbon fibres
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Matzinos, Panagiotis D. "Coal-tar pitch as the matrix carbon precursor in carbon-carbon composites." Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/28083.
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Coal-tar pitch is a promising carbon matrix precursor for carbon-carbon composites. It has a suitable viscosity, high carbon yield, and it forms graphitic structures. In addition, pitch is a relatively cheap raw material. This thesis is a study on the use of coal-tar pitch as carbon matrix precursor in carbon–carbon composites.
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Geraghty, Paul Bythell. "Studies towards the synthesis of fused N-Heterocyclic carbene precursors." Thesis, University of Canterbury. Chemistry, 2013. http://hdl.handle.net/10092/8197.
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This thesis describes the preparation of a various NHC ligands with five and six-membered rings, different fused aromatic cores and the subsequent synthetic development of their complexation of with Ag, Ru and Pd. The investigation and preparation of these compunds was with the intention of exploring their chemical and physical properties. The synthesis of the NHC ligands proved to be difficult, but analysis and characterisation of the side products from the reactions helped to establish successful synthetic methodologies. In both the five and six-membered research conducted a common attribute was established of a pyrid-2-yl substituent at the 1 position or both the 1 and 3 positions, thus providing new NHC ligands to investigate.
The organic syntheis of the research focused on two NHC ligand functionalites, five and six membered rings. The six memerbered rings focused on 1H-perimidine as the core unit and the design of both bidentate and tridentate NHC ligands to mimic the structural binding relationship of 2,2’- bipyridine (bpy) and 2,2’:6’2”-terpyridine (tpy) with various metal salts. The synthesis of the bpy analogues was achieved in good overall yields with minimal synthetic challenges. However, the tpy analogue was unable to be realised due to time constraints and problems associated with its synthesis. The five membered NHC ligands synthesised were to investigate the physical effects of systematically increasing the size of its aromatic core. The main focus of the research was on the phenanthrene imidazole NHC ligands. This was investigated due to the minimal research that has been conducted on this core unit and NHC-complexes. Synthesis of the two-bidentate NHC ligands with an imidazole head group and fused phenanthrene backbone were completed, but this was with a picolyl substituent at the 1 position rather than the pyrid-2-yl substituent. This failure to isolate this product was attributed to steric influences. Pyrene-fused-imidazole NHC ligands were also investigated and pyrene offers a NHC core that hasn’t been investigated previously. However, synthesis and isolation of the NHC ligands proved to be difficult and was associated with the poor solubility of the NHC ligands.
The organometallic NHC synthesis was studied extensively with the main focus on establishing appropriate conditions to give a NHC complex. The main metal investigated was ruthenium as subsequent NHC complexes were expected to have potentially interesting properties such as luminescence. The synthesis of a perimidine and phenanthrene NHC ruthenium complexes have not been isolated before, thus giving new NHC complexes. Many different synthetic routes were attempted to synthesise a perimidine NHC ruthenium complex. However, this proved difficult due to associated higher reactivity of the carbene carbon of perimidine with a new side product as a result of this research. The phenanthrene NHC complex synthesis suffered due to time constraints but potential methodology for their synthesis is stated.
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Richards, Stephen Paul. "Imidazolium salts as convenient precursors to novel metal-carbene complexes." Thesis, University of Bath, 2004. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413916.
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Wright, Brian D. "Synthesis, Characterization, and Biological Activity of Silver Carbene Complexes and Their Precursors." University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353423024.
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Bengtsson, Andreas. "Carbon fibres from lignin-cellulose precursors." Licentiate thesis, KTH, Träkemi och massateknologi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-244756.
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It is in the nature of the human species to find solutions of complex technical problems and always strive for improvements. The development of new materials is not an exception. One of the many man-made materials is carbon fibre (CF). Its excellent mechanical properties and low density have made it attractive as the reinforcing agent in lightweight composites. However, the high price of CF originating from expensive production is currently limiting CF from wider utilisation, e.g. in the automotive sector. The dominating raw material used in CF production is petroleum-based polyacrylonitrile (PAN). The usage of fossil-based precursors and the high price of CF explain the strong driving force of finding cheaper and renewable alternatives. Lignin and cellulose are renewable macromolecules available in high quantities. The high carbon content of lignin is an excellent property, while its structural heterogeneity yields in CF with poor mechanical properties. In contrast, cellulose has a beneficial molecular orientation, while its low carbon content gives a low processing yield and thus elevates processing costs. This work shows that several challenges associated with CF processing of each macromolecule can be mastered by co-processing. Dry-jet wet spun precursor fibres (PFs) made of blends of softwood kraft lignin and kraft pulps were converted into CF. The corresponding CFs demonstrated significant improvement in processing yield with negligible loss in mechanical properties relative to cellulose-derived CFs. Unfractionated softwood kraft lignin and paper grade kraft pulp performed as good as more expensive retentate lignins and dissolving grade kraft pulp, which is beneficial from an economic point of view. The stabilisation stage is considered the most time-consuming step in CF manufacturing. Here it was shown that the PFs could be oxidatively stabilised in less than 2 h or instantly carbonised without any fibre fusion, suggesting a time-efficient processing route. It was demonstrated that PF impregnation with ammonium dihydrogen phosphate significantly improves the yield but at the expense of mechanical properties. A reduction in fibre diameter was beneficial for the mechanical properties of the CFs made from unfractionated softwood kraft lignin and paper grade kraft pulp. Short oxidative stabilisation (<2 h) of thin PFs ultimately provided CFs with tensile modulus and strength of 76 GPa and 1070 MPa, respectively. Considering the high yield (39 wt%), short stabilisation time and promising mechanical properties, the concept of preparing CF from lignin:cellulose blends is a very promising route.Det ligger i människans natur att hitta lösningar på komplexa tekniska problem, samt att alltid sträva efter förbättringar. Utvecklingen av nya material är inget undantag. Ett av flera material utvecklade av människan är kolfiber. Dess utmärkta mekaniska egenskaper samt låga densitet har gjort det attraktivt som förstärkningsmaterial i lättviktskompositer. Det höga priset på kolfiber, vilket härstammar ur en kostsam framställningsprocess, har förhindrat en mer utbredd användning i exempelvis bilindustrin. Det dominerande råmaterialet för kolfiberframställning är petroleumbaserad polyacrylonitril (PAN). Användandet av fossila råvaror och det höga priset på kolfiber förklarar den starka drivkraften att hitta billigare och förnyelsebara alternativ. Lignin och cellulosa är förnyelsebara makromolekyler som finns tillgängliga i stora kvantiteter. Det höga kolinnehållet i lignin gör det mycket attraktivt som råvara för kolfiberframställning, men dess heterogena struktur ger en kolfiber med otillräckliga mekaniska egenskaper. Däremot har cellulosa en molekylär orientering som är önskvärd vid framställning av kolfiber, men dess låga kolinehåll ger ett lågt processutbyte som i sin tur bidrar till höga produktionskostnader. Det här arbetet visar att många av de problem som uppstår med kolfiber från respektive råvara kan kringgås genom att utgå från blandningar av desamma. Prekursorfibrer från blandningar av kraftlignin och kraftmassa från barrved tillverkade med luftgapsspinning konverterades till kolfiber. Utbytet för kolfibrerna som framställdes var mycket högre än vid framställning från endast cellulosa. Ofraktionerat barrvedslignin och kraftmassa av papperskvalitet presterade lika bra som de dyrare retentatligninen och dissolvingmassan, vilket är fördelaktigt ur ett ekonomiskt perspektiv. Stabilisering är det mest tidskrävande processteget i kolfibertillverkning. I det här arbetet visades det att prekursorfibrerna kunde stabiliseras på kortare än två timmar, eller direktkarboniseras utan någon sammansmältning av fibrerna. Detta indikerar att en tidseffektiv produktion kan vara möjligt. Impregnering av prekursorfibrerna med ammoniumdivätefosfat ökade utbytet avsevärt, men med lägre mekaniska egenskaper som bieffekt. Kolfibrernas mekaniska egenskaper ökade vid en diameterreduktion. En kort oxidativ stabilisering under två timmar i kombination med tunna prekursorfibrer gav kolfiber med en elasticitetsmodul på 76 GPa och dragstyrka på 1070 MPa. Att göra kolfiber från blandningar av lignin och cellulosa är ett lovande koncept om det höga utbytet (39%), den korta stabiliseringstiden samt de lovande mekaniska egenskaperna tas i beaktande.
QC 20190226
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Mendes, Alyne Cristina Lamy. "Síntese de xerogéis de carbono utilizando divinilbenzeno como precursor." Instituto Tecnológico de Aeronáutica, 2015. http://www.bd.bibl.ita.br/tde_busca/arquivo.php?codArquivo=3247.
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Xerogéis de carbono são materiais obtidos normalmente pelo método sol-gel, metodologia que permite a obtenção de características específicas, como elevada área superficial, a partir da modificação dos parâmetros de síntese. O objetivo desse trabalho foi produzir um material de carbono poroso a partir do divinilbenzeno para aplicação como protetor térmico para reentrada atmosférica de espaçonaves e satélites. Para obtenção do maior volume de poros nos materiais finais, utilizou-se um planejamento fatorial em duas rotas sintéticas, analisando os seguintes parâmetros: porcentagem de DVB, temperatura e tempo de envelhecimento. O planejamento de composto central utilizado permitiu avaliar a influência dos parâmetros de síntese e suas interações no volume de poros dos xerogéis orgânicos. Determinou-se, assim, que os melhores materiais foram obtidos com 6% do precursor DVB, 10 dias de envelhecimento e 45oC para a síntese DVB-SnCl4 e 55oC para a DVB-Per. As caracterizações permitiram avaliar as modificações químicas, físicas e estruturais que ocorrem após os processos de secagem do gel, e carbonização dos xerogéis orgânicos. Com a espectroscopia no IR foi verificada a eliminação do solvente após a secagem e indicou a quebra das ligações entre carbono e hidrogênio. A espectroscopia Raman confirmou a existência dessas duplas ligações pela presença das bandas D e G nas amostras de xerogéis de carbono. Esses mesmos resultados de Raman, em conjunto com os dados de Difração, permitem afirmar que existe certo grau de ordenação do carbono, após o processo de carbonização, na síntese DVB-SnCl4, enquanto para a síntese DVB-Per o material apresentou apenas carbonos amorfos. As análises térmicas indicaram que os xerogéis de carbono são termicamente estáveis, já que não apresentaram alteração nas massas e nos fluxos de calor com a variação de temperatura. As micrografias obtidas permitiram visualizar a presença de cadeias reticuladas e poros para o xerogel orgânico da síntese DVB-SnCl4, enquanto para o da síntese DVB-Per verificou-se apenas rugosidade. Já nas micrografias dos xerogéis de carbono de ambas as sínteses, foi possível ver um grande volume de poros. As voltametrias indicam uma área superficial superior para a rota de síntese DVB-SnCl4, uma vez que seu coeficiente angular foi superior ao apresentado na síntese DVB-Per. Com todos os resultados obtidos, o material se mostra promissor para aplicação como protetor térmico.
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Guest, Andrew John. "Precursors for doped boron carbide thin films." Thesis, University of Salford, 2010. http://usir.salford.ac.uk/26700/.
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This Thesis is concerned with the development of high yield synthetic strategies to phosphaboranes and phosphacarboranes. These compounds have attracted attention due to their potential as single-source precursors for the deposition of thin films of doped boron carbide via plasma enhanced chemical vapour deposition. It has shown that suitable doping of the boron carbide can lead to wide band gap semiconductors and incorporation of phosphorus into the cage structure of the solid-state material is one way of achieving this aim. Chapter one discusses the chemical vapour deposition of boron carbide and goes on to describe its uses as neutron detectors and semiconductors. Chapter two presents the existing methods used for the synthesis of aminophosphines and highlights the importance of two such species, PH(NBus2)2 and PCl2N(CJln)2 . The remaining chapters cover the experimental work used for the preparation of phosphaboranes and phosphacarboranes that contain the phosphorus atom as a vertex. Chapter three focuses on the reaction of bis(dialkylamino)phosphines with decaborane and describes the synthesis of the nido-[l-nido-?^\o\\\2\ anion in high yield. In Chapter four, the use of the nido-[l-PB}oH\2\ anion to prepare a range of cluster complexes via reaction with a variety of electrophiles is discussed. Chapter five focuses on the reaction of bis(dialkylamino)phosphines with nido-5,6- dicarbadecaborane(12) and describes the synthesis of novel compounds of the formulae 6,9-R2NHP-5,6-C2 Bs Hn, (R = Pr', Bu1 ). This is considered as an intermediate product which subsequently gives a mixture of the nit/<>-7,8,\ 1- PC2B8Hn, mWo-[7,8,9-PC;>BxHio]~ and /m/o-[7,8,l 1-PC:B8 H IO ] species whose ratio is dependant on the R group. Each chapter contains a brief introduction, discusses the results obtained including multinuclear NMR spectroscopy and crystal structure data and concludes with an experimental section.
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Plaza, Recobert Minerva. "Carbón activado: evaluación de nuevos precursores y del proceso de activación con dióxido de carbono." Doctoral thesis, Universidad de Alicante, 2015. http://hdl.handle.net/10045/47053.
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Los resultados obtenidos han mostrado como el CO2 es un agente activante apropiado y muy versátil para la generación de una amplia variedad de carbones activados. De este modo, con una adecuada selección de la materia prima y el tratamiento de la misma, se puede controlar el desarrollo del tamaño de porosidad deseado durante el proceso de activación con CO2: carbones microporosos, carbones mesoporosos y carbones con meso y macroporosidad. La evaluación de dos nuevos precursores lignocelulósicos, ha resultado muy satisfactoria. Así, tanto con la cascarilla del cacao como con el hueso de níspero es posible obtener mediante activación con CO2 carbones activados con elevadas superficies y volúmenes de porosidad específicos. En el caso de la cascarilla del cacao, este precursor ha resultado ser muy interesante para la preparación de monolitos de carbón activados esencialmente microporosos con apropiadas prestaciones mecánicas sin necesidad de agente aglomerante. La materia mineral inherente de la cascarilla del cacao resulta apropiada para el desarrollo de mesoporosidad. Respecto al hueso de níspero, este precursor ha resultado muy interesante dado que permite obtener carbones superactivados tras su activación con CO2.
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Boschetti, Riccardo. "Synthesis of novel N-heterocyclic carbene precursors for new chiral complexes." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16665/.
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Lo scopo del seguente lavoro di tesi è la sintesi e lo studio di nuovi leganti chirali N-eterociclici ad anello espanso derivanti dal diacido canforico. Lo sviluppo di nuovi leganti chirali nasce dalla possibilità di utilizzo in catalisi enantioselettiva. Questa tipologia di leganti sono facilmente sintetizzati dal diacido canforico utilizzando diverse vie di sintesi. La via di sintesi utilizzata permette di ottenere facilmente una funzionalizzazione asimmetrica. Il legante è stato studiato nella sintesi di un nuovo complesso chirale di Pd(II) utilizzando diverse condizioni di reazione. Inoltre, sono state studiate numerose vie di sintesi per nuovi leganti utilizzando i precursori dei leganti e due diversi epossidi. The aim of my training period has been the synthesis of new chiral N-heterocyclic carbene precursors starting from camphoric acid. The development of new chiral ligands starts from their possible use in new catalytic systems for enantioselective transformations. These kinds of ligands are easily synthetized from camphoric acid following different strategies. The synthetic pathway used makes simple the asymmetric functionalization. The ligand was employed in the synthesis of a new complex of Pd(II) in different conditions. In addition, numerous synthetic pathways have been investigated for new ligands using their precursors and two different epoxides.
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Rossouw, Nicolaas Malan. "The production of an activated carbon from a coke precursor." Thesis, Cape Technikon, 2002. http://hdl.handle.net/20.500.11838/873.
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Thesis (MTech (Chemical Engineering))--Cape Technikon, Cape Town, 2002The activation of green '"'Smartie"" coke (a mixture of medium temperature pitch and waxy oil coke) was investigated in a laboratory scale fluidised bed (FB) and a rotary kiln as function of (1) heat treatment temperature (HIT) and (2) heat treatment time (HTt). Activation in the FB was more effective (in terms of surface area development) and the product obtained from this type of reactor had a larger percentage of mesopores than the products from the rotary kiln. It was possible to produce a product with an iodine number equal to 745 mg iodine per gram carbon. The study revealed that it is possible to tune the pore structure of "Smartie" coke derived activated carbons by changing the activation device and systematically changing the activation conditions. It was possible to obtain products ranging from a predominantly microporous structure to products with a predominantly mesoporous structure. Unfortunately, in comparison to commercially available activated carbons, the total surface areas were still too low and it will be necessary to perform further investigations focused on increasing the total surface areas. The gold adsorption tests performed on the activated carbon compared well to those of activated carbon currently in use in the gold industry.
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Taylor, Mark Parr. "TEMPERATURE AND STRAIN CONTROLLED OPTIMIZATION OF STABILIZATION OF POLYACRYLONITRILE PRECURSOR FIBERS." UKnowledge, 2012. http://uknowledge.uky.edu/me_etds/4.
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Carbon fiber is one of the leading materials for high strength and modulus, and light weight applications. Improvements in carbon fiber properties are directly dependent on all aspects of manufacture, especially the process of stabilization. Therefore, it is the goal of this thesis to study the effects of the temperature and strain profile of the stabilization process, and the resulting carbon fiber tensile properties. In addition, the precursor fibers used were spun under two different draw ratios, to study the effects of the spinning parameters. Results indicated through DMA studies that completeness of stabilization reactions can be gauged by the peak and leveling of induced stress while fibers are stabilized in isostrain conditions. Through this method, carbon fiber tensile properties were maintained from the prior methods, but saved significant time for processing. Stress vs. strain tests throughout the stabilization process created a baseline for understanding the maximum capable strain on fibers throughout the stabilization process. Lastly, this information was summarized, combined, and basic mechanical engineering principles discussed for a continuous stabilization furnace with strain control, so that further research into the stabilization process can incorporate carbon fibers made with in situ stretch control.
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Sattler, Andreas. "Investigations into s-Heptazine-Based Carbon Nitride Precursors." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-116660.
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Bortner, Michael J. "Melt Processing of Metastable Acrylic Copolymer Carbon Precursors." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/29743.
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This thesis is concerned with the development of engineering technologies that facilitate melt spinning of carbon fiber precursors in both an environmentally sound and cost effective manner. More specifically, methods were developed to avoid a degradative process in acrylonitrile copolymers (typically used in textiles and as carbon fiber precursors) that occurs as melt spinning temperatures are approached. The following set of analyses was developed to define the rheological properties required for a melt processable acrylic copolymer suitable for use as a carbon fiber precursor, and accordingly facilitated development of a processing window: measurement of steady shear viscosity as a function of both temperature and time, measurement of the magnitude of the complex viscosity (|η*|) as a function of temperature using a temperature sweep, and measurement of the angular frequency dependence of |η*|. Through a systematic screening process, the following properties were identified to afford melt spinnable acrylic precursors suitable for conversion to carbon fibers: emulsion polymerization, 85-88 mole % acrylonitrile, 11-14 mole % methyl acrylate, 1 mole % acryloyl benzophenone, intrinsic viscosity < 0.6 dL/g, steady shear viscosity ≤ 1000-2000 Pa*s at a shear rate (γ) of 0.1 s⁻¹, viscosity increases ≤ 45% over a period of 1800 seconds at 200-220°C and γ=0.1 s⁻¹. Use of the rheological analyses assisted in development of a melt spinnable carbon fiber precursor, which resulted in carbon fibers possessing a tensile strength and modulus of approximately 1.0 and 120 GPa, respectively.
A second approach was evaluated using carbon dioxide (CO₂) to plasticize AN copolymers to an extent that facilitates processing at reduced temperatures, below where thermal degradation is significant. A batch saturation method to absorb CO₂ in AN copolymers was developed. Differential scanning calorimetry and thermogravimetric analyses were used to measure the glass transition temperature (Tg) reduction and amount of absorbed CO₂ (respectively). A pressurized rheometer and measurement procedure was designed to obtain viscosity measurements of saturated AN copolymers. Up to 6.7 wt. % CO₂ was found to absorb into a 65 mole % AN copolymer with the saturation method used, resulting in a 31°C glass transition temperature (Tg) reduction, 60% viscosity reduction, and 30°C potential processing temperature reduction. It was found that CO₂ can absorb into copolymers containing up to 90 mole % AN (with the absorption methods used) with the following results (for a 90/10 mole % AN/MA copolymer): 3.0 wt. % uptake, 27°C Tg reduction, 56% viscosity reduction, and potential processing temperature reduction of 9°C. Via estimates of the required pressure, sealing fluid flow rate, and length of a pressure chamber to prevent foaming of the saturated polymer melt during extrusion, melt spinning of saturated AN copolymers appears feasible.Ph. D.
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Vélez, Diana Cristina Prochnow. "Bio-óleo de pirólise rápida como precursor de fibra de carbono." reponame:Repositório Institucional da UFPR, 2017. http://hdl.handle.net/1884/49573.
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Orientador: Dr. Washington Luiz Esteves MagalhãesDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia e Ciência dos Materiais - PIPE. Defesa: Curitiba, 24/02/2017
Inclui referências : f. 76-79
Resumo: Este trabalho apresenta uma proposta de manufatura de fibra de carbono a partir de bio-óleo de pirólise rápida. A polimerização do bio-óleo foi conduzida por meio de tratamentos térmicos a 200°C. Após a análise do ponto de amolecimento, o piche foi submetido à fiação por fusão. Tratamentos térmicos do bio-óleo com adição de lignina kraft e álcool furfurílico foram necessários para melhorar a fiabilidade e resistência durante o enrolamento dos fios. Durante os tratamentos posteriores de estabilização e carbonização, os fios com aditivos resultaram em melhores fibras de carbono que os fios tratados a partir do bio-óleo sem nenhum aditivo. As amostras de bio-óleo aditivadas foram analisadas por meio da espectroscopia do infravermelho e ressonância magnética nuclear no estado sólido após cada tratamento térmico. Foi observada a presença de grupos oxigenados e aromatização das amostras carbonizadas. As fibras de bio-óleo aditivado com lignina kraft e álcool furfurílico estabilizaram a 270°C e 2 horas, enquanto que os fios de bio-óleo não estabilizaram com um tempo de tratamento de 12 horas. Isso foi atribuído ao diâmetro destas fibras, muito elevado se comparado com fibras de poliacrilonitrila (PAN). Diâmetros elevados impedem a uniformização dos grupos oxigenados em toda a extensão das fibras. O teor de carbono foi observado através da análise elementar. O teor de carbono na amostra de bio-óleo aditivado com lignina kraft aumentou em ~ 91% na etapa da carbonização com relação ao teor de carbono inicial do tratamento térmico. Através da difração de raios-X foi observada estrutura amorfa nas amostras. Apenas o bio-óleo tratado por 3 horas apresentou um aumento característico na curva de difração de raios-X, atribuído à propriedade termoplástica e presença de compostos de baixa massa molar, os quais asseguram estrutura ordenada. Palavras-chave: Pirólise rápida. Bio-óleo. Lignina kraft. Álcool furfurílico. Tratamento térmico.
Abstract: This paper presents a purpose for the manufacture of carbon fiber from the bio-oil of the fast pyrolysis. Polymerization of the bio-oil was conducted by heat treatments at 200 ° C. After the softening point analysis, the tar was subjected to melt spinning. Bio-oil thermal treatments with addition of kraft lignin and furfuryl alcohol were necessary to improve the reliability and resistance during the winding of the wires. During subsequent stabilization and carbonization treatments, wires with additives resulted in better carbon fibers than wires treated from the bio-oil without any additives. The additive bio-oil samples were analyzed by infrared spectroscopy and solid state nuclear magnetic resonance after each heat treatment. The presence of oxygenated groups and aromatization of carbonized samples were observed. The biofuel fibers added with kraft lignin and furfuryl alcohol stabilized at 270 ° C and 2 hours, while the bio-oil wires did not stabilize with a treatment time of 12 hours. This was attributed to the diameter of these fibers, very high compared to polyacrylonitrile fibers (PAN). High diameters prevent the uniformization of the oxygen groups throughout the fibers. The carbon content was observed through elemental analysis. The carbon content in the kraft lignin-added bio-oil sample increased ~ 91% at the carbonization stage with respect to the initial carbon content of the heat treatment. Through the X-ray diffraction, amorphous structure was observed in the samples. Only the bio-oil treated for 3 hours presented a characteristic increase in the X-ray diffraction curve, attributed to the thermoplastic property and the presence of compounds of low molar mass, which ensure an ordered structure. Key-words: Fast pyrolysis. Bio-oil. Kraft lignin. Furfuryl alcohol. Heat treatment.
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Blencowe, Anton. "The development of polymerisation and surface modification techniques using diazirines as carbene precursors." Thesis, University of Reading, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.433454.
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Balachandran, Rajesh. "GAS PHASE AND SURFACE MODELING OF CHEMICAL VAPOR DEPOSITION OF PYROLYTIC CARBON ON SILICON CARBIDE FIBERS USING A PURE METHANE PRECURSOR." University of Akron / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=akron1303834116.
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Yiamsawas, Doungporn [Verfasser]. "Lignin biomaterial - from enzyme-responsive vehicles to carbon precursor / Doungporn Yiamsawas." Mainz : Universitätsbibliothek Mainz, 2016. http://d-nb.info/1103832433/34.
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Gozzi, Mauricio Fernando. "Polissilanos como precursores para carbeto de silicio." [s.n.], 1995. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249785.
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Orientador: Inez Valeria Pagotto YoshidaDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Daga, Vijay. "High temperature deformation of pan-based carbon fiber precursors." Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/11185.
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Braml, Nicole. "Investigations on precursors and polymerization processes of Carbon Nitrides." Diss., Ludwig-Maximilians-Universität München, 2015. http://nbn-resolving.de/urn:nbn:de:bvb:19-183138.
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LOUVEM, FABIANA RODRIGUES VIEIRA. "RHEOLOGICAL CHARACTERIZATION OF PETROLEUM PITCHES PRECURSORS OF CARBON FIBERS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2014. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25031@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROAs propriedades reológicas dos piches de petróleo têm grande importância no processamento e nas propriedades finais das fibras de carbono, além de auxiliar na seleção da matéria-prima. No presente trabalho, uma série de piches de petróleo com teores crescentes de anisotropia foi produzida a partir de óleo decantado proveniente do processo de craqueamento catalítico do petróleo, com o objetivo de se investigar as propriedades reológicas destes materiais, para melhor aplicá-las na produção de fibras de carbono. Um dos piches produzidos foi centrifugado em alta temperatura com o objetivo de estudar as propriedades reológicas das suas fases isotrópica e anisotrópica. Os teores e texturas das anisotropias obtidas foram analisados, respectivamente, por centrifugação em alta temperatura e por microscopia ótica com luz polarizada. Os tamanhos moleculares dos piches de petróleo foram medidos utilizando-se a técnica de Espectrometria de Massas com Ionização e Dessorção a Laser Assistida por Matriz e Análise de Íons por Tempo de Vôo (MALDI-TOF-MS). Os piches analisados apresentaram uma natureza oligomérica, e massas moleculares de até 1500 Da foram detectadas. A caracterização reológica mostrou o comportamento viscoplástico dos piches e as curvas de escoamento medidas foram ajustadas utilizando a função viscosidade de Herschel-Bulkley. As análises reológicas também mostraram o aumento da elasticidade dos piches com o progresso do tratamento térmico e o surgimento do comportamento tixotrópico. As técnicas de análise utilizadas neste trabalho se mostraram eficientes para o estudo e caracterização de piches de petróleo precursores de fibras de carbono.
Rheological properties of petroleum pitches are of major importance not only in the processing and final properties of carbon fibers, but they also helps in the selection of the raw material. In this work, a series of petroleum pitches with increasing contents of anisotropy was produced from decanted oil obtained from catalytic cracking process of petroleum, with the objective of investigate the rheological properties of these materials and its application on carbon fibers production. One of the produced pitches was centrifuged at high temperature with the objective of study the rheological properties of isotropic and anisotropic phases. The contents and textures of the obtained anisotropy were respectively analyzed by centrifugation at high temperature and by optical microscopy with polarized light. The molecular sizes of petroleum pitches were measured using the technique MALDI-TOF-MS (Matrix Assisted Laser Desorption Ionization Timeof- Flight Mass Spectrometry). The analyzed petroleum pitches exhibited an oligomeric nature and molecular masses up to 1500 Da were detected. Rheological characterization showed viscoplastic behavior of pitches and the measured flow curves were fitted using the Herschel-Bulkley viscosity function. Rheological analysis also showed the increasing of pitches elasticity with the progress of the heat treatment and the appearance of thixotropic behavior. The analytical techniques used in this work proved its efficiency on the study and characterization of petroleum pitches as carbon fibers precursors.
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Luk, Hoi Ling. "Computational and Experimental Studies of Excited States of Different Precursors of Carbenes and Nitrenes." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1342808166.
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Sparks, William Robert. "Synthesis and characterization of poly(acrylonitrile-CO-vinyl phosphonate) carbon fiber precursors." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/9164.
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Katsuda, Yuji. "Reinforcement of precursor-derived Si-(B-)C-N ceramics with carbon nanotubes." Stuttgart Max-Planck-Inst. für Metallforschung, 2005. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-25008.
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Morris, Elizabeth Ashley. "BENCH-SCALE, MULTIFILAMENT SPINNING CONDITIONS EFFECT ON THE STRUCTURE AND PROPERTIES OF POLYACRYLONITRILE PRECURSOR FIBER." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_theses/107.
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Due to its unique characteristics, carbon fiber is one of the leading materials for light weight, high strength and stiffness applications in composite materials. The development of carbon fibers approaching theoretical strengths and stiffness is a continuing process which has led to improved mechanical and physical properties over the recent years. Improvements in carbon fiber properties are directly dependent on the quality of the precursor fiber. Research and development of PAN precursor fiber requires extensive experimentation to determine how processing conditions affect the structure and properties of the precursor fibers. Therefore, it is the goal of this thesis to analyze the results of varying coagulation rates on fiber shape, density and porosity, to determine the effect of cross-sectional shape, density, and fiber diameter on the tensile strength of the fiber, and to investigate the most effective method for the reduction of fiber diameter. Results indicate a low temperature, high solvent concentration coagulating bath leads to a rounder cross section with lower void content. Reduction in fiber diameter was found to increase tensile strength while increased molecular orientation experienced during high draw down ratios led to an increase in fiber modulus.
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McMillan, Stephen Murray. "Synthesis of silicon carbide ceramics at low temperatures by an organometallic precursor rate." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240667.
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Cheng, Zhe. "Reaction Kinetics and Structural Evolution for the Formation of Nanocrystalline Silicon Carbide via Carbothermal Reduction." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5896.
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Nanocrystalline beta-silicon carbide (ß-SiC) was synthesized at relatively low temperature (<1300C) by carbothermal reduction (CTR) reaction in fine scale carbon/silica mixtures. The fine scale mixing of the reactants (i.e., carbon and silica) was achieved by solution-based processing and subsequent heat treatment.
The mechanism of the CTR reaction in the current system was investigated from different aspects. The condensates of the volatile species generated during the CTR reaction was collected and analyzed. The results supported previous investigations which suggested that the CTR reaction is a multi-step process that involves silicon monoxide (SiO) vapor as a reaction intermediate. The kinetics of the CTR reaction was investigated by isothermal weight loss study and by the study which determined the amount of SiC formed via quantitative X- ray diffraction (QXRD) analysis. The results of kinetic study were consistent with the "shrinking-core" model, in which the reaction between SiO vapor and carbon at the carbon surface to produce SiC is the rate-controlling step. In addition, several techniques, including XRD, gas adsorption analysis, laser diffraction particle size analysis, SEM, TEM, etc., had been used to study the structural evolutions of the reaction product of CTR. It was demonstrated that the evolutions of product structure characteristics such as crystallite size, specific surface area, specific pore volume, pore size distribution, particle size distribution, and powder morphology, etc. were consistent with each other and provided support to the reaction mechanism proposed.
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Consorti, Crestina Susi. "Sobre a formação de ligações carbono-carbono utilizando paladaciclos como precursores catalíticos." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2004. http://hdl.handle.net/10183/6505.
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Siciliano, Tammy J. "A Stability Comparison and Antimicrobial Evaluation of Gold N-Heterocyclic Carbenes and Their Silver Precursors." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1217264123.
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Lima, Maria Jos? Santos. "S?ntese e caracteriza??o de TaC e ?xido misto de t?ntalo e cobre nanoestruturados a partir do precursor ox?lico de t?ntalo atrav?s de rea??es g?s-s?lido e s?lido-s?lido a baixa temperatura." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/12797.
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Previous issue date: 2013-06-20Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior
The research and development of nanostructured materials have been growing significantly in the last years. These materials have properties that were significantly modified as compared to conventional materials due to the extremely small dimensions of the crystallites. The tantalum carbide (TaC) is an extremely hard material that has high hardness, high melting point, high chemical stability, good resistance to chemical attack and thermal shock and excellent resistance to oxidation and corrosion. The Compounds of Tantalum impregnated with copper also have excellent dielectric and magnetic properties. Therefore, this study aimed to obtain TaC and mixed tantalum oxide and nanostructured copper from the precursor of tris (oxalate) hydrate ammonium oxitantalato, through gas-solid reaction and solid-solid respectively at low temperature (1000 ? C) and short reaction time. The materials obtained were characterized by X-ray diffraction (XRD), Rietveld refinement, Scanning Electron Microscopy (SEM), Spectroscopy X-Ray Fluorescence (XRF), infrared spectroscopy (IR), thermogravimetric (TG), thermal analysis (DTA) and BET. Through the XRD analyses and the Reitiveld refinement of the TaC with S = 1.1584, we observed the formation of pure tantalum carbide and cubic structure with average crystallite size on the order of 12.5 nanometers. From the synthesis made of mixed oxide of tantalum and copper were formed two distinct phases: CuTa10O26 and Ta2O5, although the latter has been formed in lesser amounts
A pesquisa e o desenvolvimento de materiais nanoestruturados v?m crescendo significativamente nos ?ltimos anos. Estes materiais apresentam propriedades significativamente modificadas em compara??o ?s dos materiais convencionais, devido ?s dimens?es extremamente reduzidas dos cristalitos. O carbeto de t?ntalo (TaC) ? um material extremamente duro, apresentando elevada dureza, elevado ponto de fus?o, elevada estabilidade qu?mica, boa resist?ncia ao ataque qu?mico e choque t?rmico e excelente resist?ncia ? oxida??o e corros?o. Os compostos de T?ntalo impregnados com Cobre tamb?m possuem excelentes propriedades diel?tricas e magn?ticas. Desta forma este trabalho teve como objetivo a obten??o de TaC e do ?xido misto de t?ntalo e cobre nanoestruturado a partir do precursor tris(oxalato)oxitantalato de am?nio hidratado, atrav?s de rea??o g?s-s?lido e s?lido-s?lido, respectivamente,a baixa temperatura (1000?C) e curto tempo de rea??o. Os materiais obtidos foram caracterizados atrav?s de Difra??o de Raios-X (DRX), Refinamento Rietveld, Microscopia Eletr?nica de Varredura (MEV), Espectroscopia por Fluoresc?ncia de Raios-X (FRX), Espectroscopia de Infravermelho (IV), Termogravim?trica (TG), Analise Termodiferencial (DTA) e BET. Atrav?s das analises de DRX e do refinamento Reitiveld para o TaC com S= 1,1584 observou-se a forma??o do carbeto de t?ntalo puro com estrutura c?bica e tamanho m?dio de cristalitos na ordem de 12,5 nan?metros. Para a s?ntese realizada do ?xido misto de t?ntalo e cobre houve a forma??o de duas fases distintas: CuTa10O26 e Ta2O5, embora esta ?ltima tenha sido formada em menor quantidade
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Nallani, Chakravartula Madhavi. "Coal hydrotreatment with coal-derived solvents to produce carbon product precursors." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4237.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains viii, 134 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 119-120).
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Rubiano, Rodrigo R. (Rubiano Ray). "Low temperature deposition of metal carbide films from single source precursors." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34692.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994, and Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science & Engineering, 1994.Includes bibliographical references (leaves 71-73).
by Rodrigo R. Rubiano.
B.S.
M.S.
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Potticary, Santeri A. "Chemical and Behavioral Study of Commercial Polycarbosilanes for the Processing of SiC Fibers." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1512038635219321.
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Bhat, Gajanan S. "Stabilization of pan-based precursors for carbon fibers by Gajanan S. Bhat." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/10119.
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Hellman, Oskar. "Synthesis of framework porous sorbents using sustainable precursors." Thesis, Uppsala universitet, Nanoteknologi och funktionella material, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-445896.
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Metal organic frameworks (MOFs) is a quite recently discovered porous material group which shows potential in many different areas. One of these areas is carbon capture; the framework structure of the porous materials allows gas molecules to adsorb to the surface of the pores. MOFs are conventionally synthesised at high temperatures and with hazardous solvents. The goal of this projectwas to synthesise highly porous MOFs at room temperature with water as the main solvent, using environmentally friendly and non-hazardous precursors. As well as the room temperature synthesis, conventional synthesis methods were used with the same precursors as comparison. The materials were characterised with X-ray diffraction, thermogravimetrical methods and IR-spectroscopy. To assess the porosity of the materials, gas adsorption evaluation was performed with CO2, N2, SF6, and CH4 at 20⁰C. In the end, three novel porous magnesium-based materials and one zirconium-based material were successfully synthesised. One of the magnesium-based materials showed a moderately high CO2 adsorption (2.38mmol/g), and could be synthesised at room temperature. The zirconium-based material showed a remarkably high selectivity (17.7) for SF6 over N2 and a high surface area (550m2/g)
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Damodaran, Sundaravel. "Evolution of structure and mechanical properties during carbonization of polyacrylonitrile-based precursor fibers by Sundaravel Damodaran." Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/8505.
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TALARICO, ERICK COSTA E. SILVA. "PRODUCTION OF BORON DOPED SINGLE WALLED CARBON NANOTUBES VIA DIFFERENT PRECURSORS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=27427@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
Nanotubo de Carbono é um alótropo do Carbono cujo caráter 1D confere-lhe propriedades mecânicas, eletrônicas, térmicas, ópticas excepcionais. Por isso que cientistas têm estudado este material intensamente, tanto do ponto de vista teórico, como de um ponto de vista experimental. Um dos interesses de pesquisa experimental é se conseguir produzir de forma controlada Nanotubos de Carbono com propriedades otimizadas, para aplicações específicas. Outra linha de pesquisa experimental que existe é a de sintetizar Nanotubos de Carbono dopados, com o objetivo de se criar Nanotubos com novas propriedades físicas. A presente dissertação de Mestrado concentra-se na síntese de especificamente Nanotubos de paredes simples dopados com Boro, e tem como objetivos avaliar a viabilidade de se produzir tais Nanotubos dopados com níveis de dopagem controlados, assim como estudar as novas propriedades físicas que surgem em Nanotubos dopados. Inicialmente, neste trabalho será conduzida uma revisão da atual literatura científica sobre Nanotubos de Carbono, com foco nas diferenças físicas entre nanotubos puros e dopados. Em seguida, o aparato experimental e a metodologia utilizada serão descritos. Por fim, os resultados experimentais serão analisados objetivando-se entender a nova física por trás dos nanotubos dopados com Boro, assim como responder à questão se o método adotado conseguiu produzir Nanotubos dopados de forma controlada.
Carbon nanotube is a carbon allotrope whose unique characteristic is its 1D geometry, and that has outstanding mechanical, electronic, thermal, optical properties. Nonetheless, this material has been deeply studied from theoretical and experimental standpoints. From the experimental point of view, there is the interest to create a controlled synthesis of Carbon Nanotubes with optimized physical properties for specific purposes. Another contemporary research interest is on the synthesis of doped Carbon Nanotubes, with the objective of inducing new properties on the Nanotube. This thesis work focuses on the synthesis of, specifically, Boron doped Single Walled Carbon Nanotubes, and aims to study the feasibility of producing Carbon Nanotubes with controlled doping levels by changing the precursor substance, and to understand the new physical properties that arise from the incorporation of Boron heteroatoms on the Carbon Nanotube structure. In this thesis work, a review of the current literature about Carbon Nanotube science is conducted, with focus on the differences in properties between pristine and doped tubes. Then, the experimental setup and methodology is explained. Finally, the experimental results are analyzed in order to understand the new physics of Boron doped Single Walled Carbon Nanotubes, and answer the question of whether a controllable method has been developed to dope Carbon Nanotubes.
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Yimamu, (Imam) Maiwulidan (Mewlude). "Chemical vapour deposition of boron-carbon thin films from organoboron precursors." Licentiate thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-123909.
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Boron-carbon (BxC) thin films enriched in 10B are potential neutron converting layers for 10Bbased solid-state neutron detectors given the good neutron absorption cross-section of 10B atoms in the thin film. Chemical Vapour Deposition (CVD) of such films faces the challenge that the maximum temperature tolerated by the aluminium substrate is 660 °C and low temperature CVD routes for BxC films are thus needed. This thesis presents the use of two different organoboron precursors, triethylboron –B(C2H5)3 (TEB) and trimethylboron – B(CH3)3 (TMB) as single-source precursors for CVD of BxC thin films. The CVD behaviour of TEB in thermal CVD has been studied by both BxC thin film deposition and quantum chemical calculations of the gas phase chemistry at the corresponding CVD conditions. The calculations predict that the gas phase reactions are dominated by β-hydride eliminations of C2H4 to yield BH3. In addition, a complementary bimolecular reaction path based on H2-assisted C2H6 elimination to BH3 is also present at lower temperatures in the presence of hydrogen molecules. A temperature window of 600 – 1000 °C for deposition of X-ray amorphous BxC films with 2.5 ≤ x ≤ 4.5 is identified showing good film density (2.40 – 2.65 g/cm3) which is close to the bulk density of crystalline B4C, 2.52 g/cm3 and high hardness (29 – 39 GPa). The impurity level of H is lowered to < 1 at. % within the temperature window. Plasma chemical vapour deposition has been studied using TMB as single-source precursor in Ar plasma for investigating BxC thin film deposition at lower temperature than allowed by thermal CVD and further understanding of thin film deposition process. The effect of plasma power, total pressure, TMB and Ar gas flow on film composition and morphology are investigated. The highest B/C ratio of 1.9 is obtained at highest plasma power of 2400 W and TMB flow of 7 sccm. The H content in the films seems constant at 15±5 at. %. The B-C bond is dominant in the films with small amount of C-C and B-O bonds, which are likely due to the formation of amorphous carbon and surface oxidation, respectively. The film density is determined as 2.16±0.01 g/cm3 and the internal compressive stresses are measured to be <400 MPa.
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SimonovicÌ, Stevan. "Synthesis, reactivity and coordination chemistry of new chiral N-heterocyclic carbenes and their precursors." Thesis, University of York, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441476.
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Pezacki, John Paul. "Rate constants and mechanisms for reactions of carbenes and cations from oxadiazolines and other precursors /." *McMaster only, 1998.
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Wilkerson, Phillip D. "Synthesis of Chiral N-Heterocyclic Carbene Precursors and Key Intermediates for Catalytic Enantioselective Cyclizations of Conjugated Trienes." Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/chemistry_theses/49.
Full textAbstract:
Cocatalyzed reactions using Brønsted acids and chiral N-heterocyclic carbenes to yield highly enantioselective products have been reported recently in many journals. The development of new chiral N-heterocyclic carbenes is a competitive field among synthetic chemist. In a recent study we found that conjugated trienes could be cyclized using Brønsted acids and chiral N-heterocyclic carbenes. The synthesis of novel chiral N-heterocyclic carbene precursors, and the precursors to novel conjugated trienes are reported herein.
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Hargette, Paul Hudson. "Removal of dissolved organic carbon and organic halide precursors by enhanced coagulation." Thesis, This resource online, 1997. http://scholar.lib.vt.edu/theses/available/etd-08252008-162839/.
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