Dissertations / Theses on the topic 'Carbothermal reduction and nitridation'
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Cho, Young Whan. "Synthesis of nitrogen ceramic powders by carbothermal reduction and nitridation." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277802.
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Terner, Mark Robert. "The production of low-cost α-sialons via carbothermal reduction-nitridation of slag-based mixtures." Monash University, School of Physics and Materials Engineering, 2003. http://arrow.monash.edu.au/hdl/1959.1/9577.
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Harrison, Robert. "Processing and characterisation of ZrCxNy ceramics as a function of stoichiometry via carbothermic reduction-nitridation." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/24810.
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Carbothermal reduction-nitridation of ZrO2 has been studied in the context of application of non-oxide zirconium ceramics as fuel components in advanced nuclear fuels. Varying processing parameters of nitridation of ZrCx (where 0.7 x 1) powders revealed the rate increased with dwell time, dwell temperature and higher carbon content of the starting ZrCx powders. A novel mechanism is reported whereby nucleation of small ( 500 nm) ZrN containing crystals occurs on the surface of the ZrCx powder particles, growing separate to the carbide particle and resulting in mixed phases. Sintering of the ZrCxNy powders by hot pressing resulted in higher densities than commercially-available ZrC powders suggesting nitrogen content improves the sinterability of ZrC containing ceramics. Thermal and electrical conductivity of the ZrCxNy ceramics were all higher than the ceramics produced from commercially-available ZrC and ZrN powders. Room temperature thermal conductivities of the ZrCxNy ceramics were found to be 35 and 43 Wm-1K-1 for the lowest and highest N-containing ZrCxNy ceramics and increased with temperature to 45 and 55Wm-1K-1 respectively at 2073 K. Electrical conductivities were in the range 250-450 x 104 -1m-1 for the ZrCxNy ceramics (at 298 K) and again increased with increasing nitrogen content. The increase in thermal conductivity of ZrCxNy with nitrogen content is due to the increase in electrical conductivity. Oxidation studies of ZrN revealed oxidation begins at around 773 K with an initial destabilisation of ZrN occurring at around 673 K. A decrease in oxidation rate was observed between lower (973-1073 K) and higher temperatures (1173-1273 K). This is attributed to dense protective oxide scales forming at higher temperature (1173-1273 K) compared to porous oxide scales forming at lower temperature ( 1073 K). However, this protective layer fails at higher temperature (1373 K), attributed to increased oxygen diffusion through the oxide layer.
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Du, Xiaoyang 1960. "Carbothermal reduction of ilmenite and fayalite." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/290600.
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In order to eliminate thermodynamic limitations during H₂ and CO reduction processes, a novel carbothermal reduction process is proposed to generate lunar oxygen for propellant and life support on the lunar surface. The kinetics and mechanism of the carbothermal reduction of synthetic ilmenite and fayalite (simulants for lunar ilmenite and fayalite) were investigated in the present study. Carbothermal reduction of ilmenite with charcoal powder was studied between 975°C and 1100°C. It was found that the reduction process is controlled by the carbon gasification reaction instead of by the rate of ilmenite reduction with carbon monoxide, which has been claimed to be the rate limiting step by several prior researchers. The activation energy obtained using a simplified carbon gasification model for this reduction is 27.2 kcal/mole. The reduction products were studied by SEM and XRD and it was found that the major products are α-Fe and TiO₂ at temperatures below 1000°C; at 1050°C, α-Fe and Ti₉O₁₇ were observed; at 1100°C, α-Fe and Ti₄O₇ were observed. Iron is completely segregated from the titanium oxides in the product. Carbothermal reduction of ilmenite with deposited carbon was investigated between 775°C and 1000°C. An extremely fast reduction rate (more than ten times faster than charcoal powder reduction) was observed. The reduction rate-limiting step is believed to be the ilmenite reduction with carbon monoxide. The activation energy calculated by a simplified model is 50 kcal/mole between 775°C and 900°C, and 17.6 kcal/mole above 900°C. It was also found that TiO₂ can be reduced to much lower oxygen content titanium oxides than during powdered charcoal reduction. The temperature and particle size effects during carbothermal reduction of synthetic fayalite were investigated. The product morphology of this reduction showed that α-Fe and α-cristobalite are the main products at temperatures above 1100°C, at lower temperatures, α-Fe, α-quartz and amorphous silica are the main products. The iron produced by reduction is segregated from the SiO₂ phases and agglomerates in large particles, which is different from the product morphology observed during hydrogen reduction of fayalite. In order to better understand the mechanism and kinetics of the carbothermal reduction process, a mathematical model was developed to simulated the CO₂/CO ratio, CO and CO₂ partial pressure distributions, conversion, etc. during the reduction process. Using the model to treat the reduction of ilmenite with charcoal powder reproduces experimental results very well.
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Dewan, Mohammad Ashikur Rahman Materials Science & Engineering Faculty of Science UNSW. "Carbothermal synthesis of titanium oxycarbide." Awarded By:University of New South Wales. Materials Science & Engineering, 2009. http://handle.unsw.edu.au/1959.4/44511.
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The aim of the project was to establish the rate and mechanisms of solid stage reduction of titania and ilmenite ores. The project examined carbothermal reduction of titania and various types of ilmenite ores in argon, helium, hydrogen, and their mixtures. Effect of CO in the gas atmosphere on reduction behavior of titania and primary ilmenite ore was also studied. Isothermal and non-isothermal reduction experiments were conducted in a fixed bed reactor in the high temperature furnace in the temperature range up to 1500oC. The off-gas composition in the reduction process was monitored by a CO/CO2/CH4 infrared analyser. The extent of reduction was calculated using data on gas composition and LECO oxygen analysis. Phase composition and morphology of reduced samples were studied using XRD, SEM and optical microscopy. The major findings of this project are as follows: The reduction of titania to titanium oxycarbide occurred in the following sequence: TiO2 → Ti5O9 → Ti4O7 → Ti3O5 → Ti2O3 → (TiO-TiC) solid solution. Carbothermal reduction of ilmenite concentrates proceeded in two main stages. In the first stage pseudorutile and ilmenite were reduced to metallic iron and titania. Second stage involved the reduction of titania to titanium oxycarbide. Rate and degree of reduction of titania and ilmenite concentrates increased with increasing temperature. Reduction rate of titania and ilmenite concentrates was faster in hydrogen than in helium and argon. The difference in the reduction behavior in helium and argon was insignificant; reduction rate of ilmenite was slightly faster in helium than in argon. High rate of reduction of titania and ilmenite in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of titania and ilmenite concentrates; hydrogen reduced pseudorutile to iron and titania. Titania was further reduced to titanium oxycarbide by carbon through methane. Increased gas flow rate slightly improved the reduction rate in hydrogen and suppressed the reduction in inert gases. Addition of CO to hydrogen and inert gases above 3 vol% suppressed the reduction process.
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Durham, Simon J. P. "Carbothermal reduction of silica to silicon nitride powder." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74221.
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The processing conditions for carbothermal reduction of silica to silicon nitride was found to be sensitive to several key processing parameters: namely the intimacy of mixing of carbon and silica, the temperature, the specific high surface area of carbon, the nitrogen gas purity and the action of the nitrogen gas passing through the reactants.Sol-gel processing was found to provide superior mixing conditions over dry mixing, which allowed for complete conversion to silicon nitride at optimum carbon:silica ratios of 7:1. The ideal reaction temperature was found to be in the range of 1500$ sp circ$C to 1550$ sp circ$C. Suppression of silicon oxynitride and silicon carbide was achieved by ensuring that: (a) the nitrogen gas was gettered of oxygen, and (b) that the gas passed through the reactants. Thermodynamic modelling of the Si-O-N-C system showed that ordinarily the equilibrium conditions for the formation of silicon nitride are very delicate. Slight deviations away from equilibrium leads to the formation of non-equilibrium species such as silicon carbide caused by the build-up of carbon monoxide. Reaction conditions such as allowing nitrogen gas to pass through the reactants beneficially moves the reaction equilibrium well away from the silicon carbide and silicon oxynitride stability regions.
The particle size of silicon nitride produced from carbon and silica precursors was of the order of 2-3 $ mu$m and could only be reduced to sub-micron range by seeding with ultra-fine silicon nitride. It was shown that the mechanism of nucleation and growth of unseeded reactants was first nucleation on the carbon by the reaction between carbon, SiO gas and nitrogen (gas-solid reaction), and then growth of the particles by the gas phase reaction (CO, SiO, N$ sb2$).
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Bejarano, Cesar. "Carbothermal reduction of sulfur dioxide using oil-sands fluid coke." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0016/MQ53340.pdf.
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Jain, Anubhav. "Synthesis and Processing of Nanocrystalline Zirconium Carbide Formed by Carbothermal Reduction." Thesis, Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4797.
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Zirconium carbide (ZrC) powders were produced by carbothermal reduction reactions using fine-scale carbon/metal oxide mixtures as the starting materials. The reactant mixtures were prepared by pyrolytic decomposition of solution-derived precursors. The latter precursors were synthesized via hydrolysis/condensation of metal-organic compounds.
The first step in the solution process involved refluxing zirconium alkoxide with 2,4 pentanedione ("acacH") in order to partially or fully convert the zirconium alkoxy groups to a chelated zirconium diketonate structure ("zirconium acac"). This was followed by the addition of water (under acidic conditions) in order to promote hydrolysis/condensation reactions. Precursors with variable carbon/metal ratios were produced by varying the concentrations of the solution reactants (i.e., the zirconium alkoxide, "acacH," water, and acid concentrations.) It was necessary to add a secondary soluble carbon source (i.e., phenolic resin or glycerol) during solution processing in order to obtain a C/Zr molar ratio close to 3 (as required for stoichiometry) in the pyrolyzed powders.
The phase development during carbothermal reduction was investigated for oxide-rich carbon-deficient and slightly carbon-rich compositions. The reaction was substantially completed after heat treatments in the range of ~1400-1500oC. The crystallite sizes were in the range of ~100-130 nm. However, some oxygen dissolved in the lattice and some free carbon was present. Heat treatment at temperatures >1600oC was required to complete the reaction.
The dry-pressed powder compacts, with varying C/Zr molar ratios, were pressureless sintered to relative densities in the range of ~98-100% at 1950oC.
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Taneka, S. "Carbothermal reduction of friable chromite in a small-scale transferred-arc furnace." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37873.
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Kononov, Ring Materials Science & Engineering Faculty of Science UNSW. "Carbothermal solid state reduction of manganese oxide and ores in different gas atmospheres." Publisher:University of New South Wales. Materials Science & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41459.
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The aim of the project was to establish rate and mechanisms of solid state reduction of manganese ores. The project studied carbothermal reduction of manganese oxide MnO, two Groote Eylandt (Australian) and Wessels (South African) manganese ores in hydrogen, helium and argon atmospheres at temperatures up to 1400C for MnO and 1200C for manganese ores. Experiments were conducted in the fixed bed reactor with on-line off-gas analysis. The major findings are as follows. ?? Rate and degree of reduction of MnO and ores increased with increasing temperature. ?? Reduction of MnO and manganese ores at temperatures up to 1200C was faster in helium than in argon, and much faster in hydrogen than in helium. The difference in MnO reduction in hydrogen and helium decreased with increasing temperature to 1400C. ?? Addition of up to 7 vol% of carbon monoxide to hydrogen had no effect on MnO reduction at 1200C. ?? In the process of carbothermal reduction of ores in hydrogen at 1200C, silica was reduced. ?? Reduction of both GE ores was slower than of Wessels ore. This was attributed to high content of iron oxide in the Wessels ore. ?? Carbon content in the graphite-ore mixture had a strong effect on phases formed in the process of reduction; thus, in the reduction of Wessels ore with 12-16 wt% C, a-Mn and Mn23C6 were formed; when carbon content was above 20 wt%, oxides were reduced to carbide (Mn,Fe)7C3. ?? Kinetic analysis showed that mass transfer of intermediate CO2 from oxide to graphite in carbothermal reduction in inert atmosphere was a contributing factor in the rate control. ?? High rate of reduction of manganese oxide in hydrogen was attributed to formation of methane which facilitated mass transfer of carbon from graphite to oxide. Hydrogen was also directly involved in reduction of manganese ore reducing iron oxides to metallic iron and higher manganese oxides to MnO. Reduction of Wessels and Groote Eyland Premium Fines ores in the solid state is feasible at temperatures up to 1200C; while temperature for solid state reduction of Groote Eyland Premium Sands is limited by 1100C.
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Mariappan, L. "In-Situ Synthesis Of A12O3_ZrO2_SiCw Ceramic Matrix Composites By Carbothermal Reduction Of Natural Silicates." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/215.
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This thesis outlines the work done on in-situ synthesis of Al2O3-ZrO2-SiCw ceramic composites and their property evaluation. The introductory chapter deals with the literature survey on ceramic matrix composites, properties desirable for structural applications and toughening mechanisms associated with these composites. The role of whisker toughening in ceramic matrix composites, the growth mechanisms involved in whisker growth and the conditions that favour or hamper the whisker growth are also discussed. The advantages and disadvantages of in-situ synthesis of composites as compared to physical mixing are also dealt with. The objective and scope of the work undertaken are outlined at the end.
The second chapter describes the experimental techniques associated with carbothermal synthesis and characterisation of reaction products as well as properties of hot pressed bulk composites. The equipments used for this work are described here.
The third chapter focuses on the results obtained by the carbothermal reduction of mixtures of kaolin, sillimanite and zircon taken in various proportions. The formation of the product phases with respect to variations in temperature, variations in composition and effect of catalyst is analysed with the help of XRD while their morphology is analysed using SEM. The conditions favouring the formation of tetragonal zirconia without the addition of stabilizers is also enumerated here.
The fourth chapter deals with the compaction of these composite powders and the evaluation of some physical, thermal and mechanical properties. Density and porosity, coefficient of thermal expansion, modulus of rupture and fracture toughness of the composite specimens are evaluated and compared with binary and ternary composites made by other methods.
Finally the thesis concludes by summarizing the work done and briefly projecting the areas for future work.
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Duddukuri, Ramesh. "SYNTHESIZING AND CHARACTERIZATION OF TITANIUM DIBORIDE FOR COMPOSITE BIPOLAR PLATES IN PEM FUEL CELL." OpenSIUC, 2012. https://opensiuc.lib.siu.edu/theses/862.
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This research deals with the synthesis and characterization of titanium diboride (TiB2) from novel carbon coated precursors. This work provides information on using different boron sources and their effect on the resulting powders of TiB2.The process has two steps in which the oxide powders were first coated with carbon by cracking of a hydrocarbon gas, propylene (C3H6) and then, mixed with boron carbide and boric acid powders in a stoichiometric ratio. These precursors were treated at temperatures in the range of 1200-1400° C for 2 h in flowing Argon atmosphere to synthesize TiB2.The process utilizes a carbothermic reduction reaction of novel carbon coated precursor that has potential of producing high-quality powders (sub-micrometer and high purity). Single phase TiB2 powders produced, were compared with commercially available titanium diboride using X-ray diffraction and Transmission electron microscopy obtained from boron carbide and boric acid containing carbon coated precursor.
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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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Sondhi, Anchal. "Investigations in the Mechanism of Carbothermal Reduction of Yttria Stabilized Zirconia for Ultra-high Temperature Ceramics Application and Its Influence on Yttria Contained in It." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc500159/.
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Zirconium carbide (ZrC) is a high modulus ceramic with an ultra-high melting temperature and, consequently, is capable of withstanding extreme environments. Carbon-carbon composites (CCCs) are important structural materials in future hypersonic aircraft; however, these materials may be susceptible to degradation when exposed to elevated temperatures during extreme velocities. At speeds of exceeding Mach 5, intense heating of leading edges of the aircraft triggers rapid oxidation of carbon in CCCs resulting in degradation of the structure and probable failure. Environmental/thermal barrier coatings (EBC/TBC) are employed to protect airfoil structures from extreme conditions. Yttria stabilized zirconia (YSZ) is a well-known EBC/TBC material currently used to protect metallic turbine blades and other aerospace structures. In this work, 3 mol% YSZ has been studied as a potential EBC/TBC on CCCs. However, YSZ is an oxygen conductor and may not sufficiently slow the oxidation of the underlying CCC. Under appropriate conditions, ZrC can form at the interface between CCC and YSZ. Because ZrC is a poor oxygen ion conductor in addition to its stability at high temperatures, it can reduce the oxygen transport to the CCC and thus increase the service lifetime of the structure. This dissertation investigates the thermodynamics and kinetics of the YSZ/ZrC/CCC system and the resulting structural changes across multiple size scales. A series of experiments were conducted to understand the mechanisms and species involved in the carbothermal reduction of ZrO2 to form ZrC. 3 mol% YSZ and graphite powders were uniaxially pressed into pellets and reacted in a graphite (C) furnace. Rietveld x-ray diffraction phase quantification determined that greater fractions of ZrC were formed when carbon was the majority mobile species. These results were validated by modeling the process thermochemically and were confirmed with additional experiments. Measurements were conducted to examine the effect of carbothermal reduction on the bond lengths in YSZ and ZrC. Subsequent extended x-ray absorption fine structure (EXAFS) measurements and calculations showed Zr-O, Zr-C and Zr-Zr bond lengths to be unchanged after carbothermal reduction. Energy dispersive spectroscopy (EDS) line scan and mapping were carried out on carbothermaly reduced 3 mol% YSZ and 10 mol% YSZ powders. Results revealed Y2O3 stabilizer forming agglomerates with a very low solubility in ZrC.
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Fiefhaus, Silas R. "The Optimization of The Synthesis and Characterization of Vapor-Liquid-Solid Grown ZnO Nanowires." UKnowledge, 2016. http://uknowledge.uky.edu/chemistry_etds/62.
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ZnO nanowires are a promising material with great semiconductor properties. ZnO nanowires were prepared by carbothermal reduction and vapor-liquid-solid growth mechanism. Altering a variety of parameters ranging from mole to mole ratio of ZnO to C all the way to gas flow rate was examined. The nanowires were then characterized and their morphology examined under a SEM to observe what effect the parameter had on the morphology of the nanowires. From the experiments and the parameters tested it was observed that in order to produce the highest quality straight nanowires one should use a mole to mole ratio of ZnO to C graphite of 1 to 3. With a dwell temperature and time of 900 °C for 3 hours. A gold seed catalyst of 4nm and a gas flow rate of 50 to 100sccm of Ar provides the straightest nanowires. Understanding the effect of each parameter on the morphology of ZnO nanowires is vital for the current research. This will only lead to further the research and provide a better understanding of the growth mechanism of these wires and how the production of specific wires with certain morphologic features and characteristics can be achieved.
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Adipuri, Andrew Materials Science & Engineering Faculty of Science UNSW. "Chlorination of Titanium Oxycarbide and Oxycarbonitride." Publisher:University of New South Wales. Materials Science & Engineering, 2009. http://handle.unsw.edu.au/1959.4/44405.
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The project undertook a systematic study of chlorination of titanium oxycarbide and oxycarbonitride with the aim to develop further understanding of kinetics and mechanisms of the chlorination reactions. The project studied titania, ilmenite ores, and synthetic rutile reduced by carbon in argon and nitrogen and chlorinated at different temperatures, gas flow rates and compositions. Chlorination of titanium suboxides, iron and impurities in ilmenite was also examined. Chlorination of titanium oxycarbide Ti(O,C) or oxycarbonitride Ti(O,C,N) can be implemented at 200 to 400 deg.C, while the commercial chlorination process in the production of titanium metal or titania pigment requires 800 to 1100 deg.C. This makes chlorination of Ti(O,C) or Ti(O,C,N) an attractive technology in processing of titanium minerals. Chlorination reaction is strongly exothermal, which increased the sample temperature up to 200 deg.C above the furnace temperature. The chlorination of Ti(O,C) or Ti(O,C,N) was ignited at 150 deg.C to 200 deg.C depending on the sample composition. Their chlorination at 235 deg.C to 400 deg.C was close to completion in less than 30 min. The chlorination rate of titanium oxycarbide or oxycarbonitride increased with increasing gas flow rate. Sample composition had a significant effect on the extent of chlorination. The optimum results were obtained for titanium oxycarbide or oxycarbonitride produced with carbon to titania molar ratio of 2.5; these samples contained no detectable excess of carbon or unreduced titanium suboxides. In chlorination of reduced ilmenite ores and synthetic rutile, Ti(O,C) or Ti(O,C,N), metallic iron and Ti2O3 were chlorinated. The rate and extent of chlorination of titanium increased with increasing carbon to TiO2 ratio. Chlorination of Ti2O3 was slow relative to Ti(O,C) or Ti(O,C,N) and iron; chlorination of impurity oxides such as MgO, SiO2 and Al2O3 was not observed. The project also examined chlorination of Ti(O,C) or Ti(O,C,N) in ilmenite ore and synthetic rutile after removal of iron, which was achieved by aerated leaching of reduced samples in heated flask containing 0.37 M of ammonium chloride solution. Iron removal from the ilmenite ore or synthetic rutile resulted in higher rate and extent of chlorination of titanium oxycarbide or oxycarbonitride.
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Fontaine, Florian. "Composites à matrice carbone-oxyde et carbone-nitrure : thermodynamique de l'élaboration et son impact sur les propriétés physico-chimiques, thermiques et mécaniques des composites." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14217/document.
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Les composites carbone/carbone présentent de propriétés thermomécaniques à hautes températures qui les rendent particulièrement adaptés à l’ablation ou à la friction. Leur sensibilité à l’oxydation dès 400°C a conduit à envisager leur dopage en éléments réfractaires inoxydables ou à température d’oxydation élevée. Le procédé sol-gel a permis d’introduire environ 1 % volumique d’oxyde ou de nitrure de titane ou d’aluminium dans leur matrice. Les nitrures sont obtenus par nitruration carbothermique des films d’oxydes. Deux types de sols ont été utilisés : des sols « standard » et des sols enrichis en saccharose. Le saccharose est ajouté pour prévenir la consommation du pyrocarbone lors de la nitruration. Il a par ailleurs une influence sur l’avancement de la nitruration. Les composites chargés sont ensuite densifiés par voie gazeuse, ce qui induit des transformations de phases prévues par la thermodynamique : les films de nitrure de titane sont partiellement carburés (formation de carbonitrure), et les films d’oxyde de titane sont réduits (formation d’oxycarbure). Les dépôts à base d’aluminium sont plus stables et ne subissent aucune transformation. La diffusivité thermique des composites réalisés est faiblement impactée par les charges introduites, alors que les résistances en traction/compression sont sensiblement augmentées. Par ailleurs, une rigidification des composites est observée. Leur cinétique d’oxydation est ralentie. Les composites enrichis en alumine et nitrure d’aluminium présentent des vitesses de perte de masse divisées par 2 par rapport à la référence C/C. Toutes ces propriétés sont liées directement ou non à la composition des sols, et plus particulièrement à sa teneur en saccharose. Il a en effet été montré que les sols qui en contiennent ont tendance à gélifier en surface du composite, ce qui gêne la diffusion des gaz précurseurs au cœur du composite lors de la densification. La porosité finale s’en trouve modifiée. Cette dernière a une influence non négligeable sur le comportement en compression, la diffusivité thermique et la cinétique d’oxydation des composites élaborésCarbon/carbon composites exhibit excellent mechanical and thermal properties at high temperature that make them espe-cially suitable for ablation or friction pieces. Their sensitivity toward oxidation above 400°C has lead to the will of doping them with refractory ceramics that are nonoxidizable or with a high oxidation temperature. The sol-gel process allowed to introduce 1 % in volume of titanium or aluminum oxide or nitride in the matrix. Nitrides are obtained by carbothermal nitridation of the oxide films. Two types of sols were used: the “standard” ones and those with extra sucrose. Sucrose is added to prevent pyrocarbon consumption during the nitridation. Furthermore, it was shown that it has an impact on the nitridation rate. Charged composites are then densified by Chemical Vapor Infiltration, which induces phases transforma-tions that were predicted by thermodynamics: titanium nitride films are partially carburized (formation of titanium carbonitride) and titanium dioxide films are reduced (formation of titanium oxycarbide). Aluminum-based films are more stable and don’t undergo any transformation. Thermal diffusivity of the as-synthesized composites is not much modified by the addition of these ceramics while the tensile and compressive strength are slightly increased. By the way, composites are hardened. Their oxidation kinetics is slowed down. Aluminum-rich composites exhibit a weight loss divided by two compared to the C/C reference. All those properties are directly, or not, linked to the composition of the sols, in particular to their sucrose content. Indeed, it was shown that sucrose-containing sols rather jellify on the surface of the composite, thus preventing the diffusion of precursor gases to the heart of the pieces. The final porosity is then modified. The porosity has an important impact on the compressive strength, thermal diffusivity and oxidation kinetics of the synthesized composites
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Carvalho, Raquel Guilherme de. "Redu??o carbot?rmica de TiO2 por descarga em c?todo oco." Universidade Federal do Rio Grande do Norte, 2011. http://repositorio.ufrn.br:8080/jspui/handle/123456789/15673.
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In this study we used the plasma as a source of energy in the process of carbothermic reduction of rutile ore (TiO2). The rutile and graphite powders were milled for 15 h and placed in a hollow cathode discharge produced by in order to obtain titanium carbonitride directly from the reaction, was verified the influence of processing parameters of plasma temperature and time in the synthesis of TiCN. The reaction was carried out at 600, 700 and 800˚C for 3 to 4 hours in an atmosphere of nitrogen and argon. During all reactions was monitored by plasma technique of optical emission spectroscopy (EEO) to check the active species present in the process of carbothermal reduction of TiO2. The powder obtained after the reactions were characterized by the techniques of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The technique of EEO were detected in all reactions the spectra CO and NO, and these gas-phase resulting from the reduction of TiO2. The results of X-ray diffraction confirmed the reduction, where for all conditions studied there was evidence of early reduction of TiO2 through the emergence of intermediate oxides. In the samples reduced at 600 and 700˚C, there was only the phase Ti6O11, those reduced to 800˚C appeared Ti5O9 phases, and Ti6O11 Ti7O13, confirming that the carbothermal reduction in plasma, a reduction of the ore rutile (TiO2) in a series of intermediate titanium oxide (TinO2n-1) where n varies between 5 and 10
Neste trabalho foi utilizado o plasma como fonte energ?tica no processo de redu??o carbot?rmica do min?rio rutilo (TiO2). Os p?s de rutilo e grafite foram mo?dos durante 15 h e introduzidos numa descarga produzida por c?todo oco a fim de obter carbonitreto de tit?nio diretamente da rea??o, sendo verificado a influ?ncia dos par?metros de processamento de plasma, temperatura e tempo na s?ntese de TiCN. As rea??o foram efetuadas a 600, 700 e 800˚C por 3 e 4 horas numa atmosfera de nitrog?nio e arg?nio. Durante todas as rea??es o plasma foi monitorado pela t?cnica de espectroscopia de emiss?o ?ptica (EEO) para verificar as esp?cies ativas presente no processo de redu??o carbot?rmica de TiO2. Os p?s obtidos ap?s as rea??es foram caracterizados pelas t?cnicas de difra??o de raios X (DRX) e microscopia eletr?nica de varredura (MEV). Pela t?cnica de EEO foram detectados em todas as rea??es os espectros CO e NO, sendo essas fases gasosas resultante da redu??o do TiO2. Os resultados de difra??o de raios X confirmou essa redu??o, onde para todas as condi??es estudadas houve evid?ncia de in?cio da redu??o do TiO2 atrav?s do aparecimento de ?xidos intermedi?rios. Nas amostras reduzidas a 600 e 700˚C observou-se apenas a fase Ti6O11, naquelas reduzidas a 800 ˚C apareceram as fases Ti5O9, Ti6O11 e Ti7O13, comprovando que com a redu??o carbot?rmica em plasma, houve redu??o do min?rio rutilo (TiO2) em uma s?rie de ?xido intermedi?rios de tit?nio (TinO2n-1) onde n varia entre 5 e 10
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Chuayboon, Srirat. "Solar fuels production from thermochemical gasification and reforming of carbonaceous feedstocks." Thesis, Perpignan, 2019. http://www.theses.fr/2019PERP0019.
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Les procédés thermochimiques solaires étudiés concernent la conversion de charges hydrocarbonées solides ou gazeuses en syngas, ainsi que la réduction d’oxydes en métaux en utilisant l’énergie solaire concentrée pour effectuer les réactions endothermiques, permettant ainsi le stockage de l’énergie solaire intermittente en carburants sans émissions de CO2. Ce travail a pour objectif l’étude expérimentale de trois procédés solaires incluant la gazéification de biomasse, le reformage de méthane en boucle chimique, et la carboréduction de ZnO et MgO. La gazéification et le reformage permettent la valorisation de biomasse bois et de méthane en syngas, tandis que la carboréduction permet de produire Zn et Mg à partir de ZnO et MgO. Ces procédés ont été étudiés dans des réacteurs solaires de 1.5 kWth, en utilisant le rayonnement concentré fourni par des systèmes à concentration du laboratoire PROMES, Odeillo, France. L’impact des paramètres opératoires de chaque procédé sur les mécanismes réactionnels, conversion, rendement, et performances énergétiques a été évalué en détail. Ces procédés ont permis d’améliorer la conversion chimique, les rendements en syngas, les efficacités énergétiques tout en permettant un stockage de l’énergie solaire en combustibles transportables, avec des performances globales supérieures aux procédés conventionnels. De plus, leur faisabilité, fiabilité et robustesse pour la conversion de méthane et biomasse en syngas et la production de Mg et Zn en fonctionnement batch ou continu sous pression réduite ou atmosphérique en conditions solaires réelles ont été démontrésThe investigated solar thermochemical processes consist of the thermochemical conversion of solid and gaseous carbonaceous feedstocks into syngas as well as metal oxides reduction into metal commodities utilizing concentrated solar energy to drive endothermic chemical reactions, thereby enabling intermittent solar energy storage into solar fuels and avoiding CO2 emissions. This work aims to experimentally investigate three key solar thermochemical conversion approaches regarding biomass gasification, chemical looping reforming of methane, and carbothermal reduction of ZnO and MgO. Solar gasification and solar chemical looping reforming allowed valorizing wood biomass and methane into syngas, while solar carbothermal reduction was applied to produce Zn and Mg from ZnO and MgO. Such solar thermochemical processes were performed in 1.5 kWth prototype solar chemical reactors, utilizing highly concentrated sunlight provided by a solar concentrator at PROMES laboratory, Odeillo, France. The impact of controlling parameters of each process on the reaction mechanism, conversion, yields, and process performance, during on-sun testing was investigated and evaluated thoroughly. Such processes were proved to significantly improve the chemical conversion, syngas yields, energy efficiency, with solar energy storage into transportable fuels, thereby outperforming the conventional processes. Moreover, their feasibility, reliability, and robustness in converting both methane and biomass feedstocks to syngas as well as producing Mg and Zn metals in batch and continuous operation under vacuum and atmospheric conditions during on-sun operation were successfully demonstrated
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Réjasse, Florian. "Etude de la réactivité des dioxydes métalliques du groupe IVb en présence de carbone par une approche (micro)-structurale : Application à la modélisation des diagrammes de phases ternaires Me-C-O (où Me = Ti, Zr, Hf)." Thesis, Limoges, 2015. http://www.theses.fr/2015LIMO0099/document.
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Durant ce travail, la réactivité des dioxydes du groupe IVb (TiO2, ZrO2, HfO2) en contact avec du carbone turbostratique a été étudiée afin de comprendre les mécanismes réactionnels de la réduction carbothermique. Cette voie de synthèse a également permis d’obtenir des phases oxycarbures sous forme pulvérulente afin d’étudier les différents domaines de stabilité des solutions solides en fonction de la température de traitement thermique. L’ajout d’oxygène à la structure cristalline des carbures modifie le comportement de ces matériaux au frittage ainsi que leurs propriétés macroscopiques. Par conséquent, la détermination des limites des différentes solutions solides requiert l’utilisation d’une méthodologie précise. En couplant les différentes techniques de caractérisation (analyse chimique élémentaire, DRX, dosage de phases, MET), les compositions des phases oxycarbures synthésisées ont ainsi pu être déterminées. Afin de compléter cette étude, la réactivité de monolithes de carbure de titane en contact avec du dioxyde de titane a été étudiée lors de traitements thermiques de recuit sous charge en atmosphère confinée. L’identification des phases en équilibre constituent des données diagrammatiques nécessaires aux première tentatives de modélisation thermodynamique des diagrammes de phases ternaires Me-C-O (ou Me = Ti, Zr, Hf) par la méthode semi-empirique CALPHADDuring this work, the reactivity of group IVb dioxides (TiO2, ZrO2, HfO2) in contact with turbostractic carbon has been investigated in order to understand the reactional mechanisms of the carbothermal reduction. This way of synthesis has also allowed us to obtain oxycarbides phases in powder form to study the different stability domains of solids solutions with respect to the temperature of heat treatment. The addition of oxygen within the crystalline structure modifies the sintering behaviour of these materials and also their macroscopic properties. Consequently, the determination of solid solution boundaries requires an accurate methodology. A broad panoply of characterization techniques are coupled (Elemental analysis, XRD, Quantification of phases, TEM) to determine the compositions of oxycarbide phases. In order to complete this study, the reactivity of titanium carbide monoliths in contact with titanium dioxide has been studied during heat treatments of annealing under pressure in confined atmosphere. The identification of phases in equilibrium constitutes diagrammatic data which are necessary for the preliminary attempts of thermodynamic modeling of ternary phases diagrams Me-C-O (where Me = Ti, Zr, Hf) using the semi-empirical CALPHAD method
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Borchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann, and Stefan Kaskel. "Preparation and application of cellular and nanoporous carbides." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-138910.
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A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this reviewDieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich
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Borchardt, Lars, Claudia Hoffmann, Martin Oschatz, Lars Mammitzsch, Uwe Petasch, Mathias Herrmann, and Stefan Kaskel. "Preparation and application of cellular and nanoporous carbides." Royal Society of Chemistry, 2012. https://tud.qucosa.de/id/qucosa%3A27792.
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A tutorial review on cellular as well as nanoporous carbides covering their structure, synthesis and potential applications. Especially new carbide materials with a hierarchical pore structure are in focus. As a central theme silicon carbide based materials are picked out, but also titanium, tungsten and boron carbides, as well as carbide-derived carbons, are part of this review.Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.
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Zeng, Wen Hong, and 曾文宏. "Synthesize aluminium nitride from carbothermal reduction & nitridation of aluminium hydroxide." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/47783247357525260525.
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Hsu, Pei-Ju, and 徐沛儒. "The carbothermal reduction and nitridation of rice husk ash with iron powder addition." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/35154394454770268886.
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碩士國立中央大學
化學工程與材料工程研究所
90
The carbothermal reduction and nitridation of rice husk ash with iron powder addition was investigated by weight change measurement. In this study, the operating variables have been discussed include: nitrogen flow rate, amount of iron powder addition in the reactant, pellet-forming pressure, sample weight, and reaction temperature. The analysis of this experiment is conducted by inductively coupled plasma-mass spectrometer (ICP-MS), element analysis (EA), BET surface area, X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental results indicated that the conversion of rice husk ash is increased with an increasing nitrogen flow rate and the effect is not appreciable when the flow rate exceeds 500ml/min. The conversion of rice husk ash is increased with an increasing amount of iron powder addition in the reactant. Increasing the pellet-forming pressure could increase the conversion, the effect is not appreciable when the pellet-forming pressure is above 9.65x105 kPa. Moreover, the reaction rate and the conversion of the rice husk ash are significantly increased with higher reaction temperature. The reaction product is fibrous shape β- SiC with iron addition. We conjectured that the formation of liquid Fe-Si alloy is an important way for β- SiC growth. In the chemical reaction controlled region, the activation energy of the reaction is 566.69 kJ /mol when iron powder addition is 1wt% .
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Wang, Yung-Mou, and 王勇謀. "The Carbothermal Reduction and Nitridation of Rice Husk Ash with Silicon Powder Addition." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/36570756694452070335.
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碩士國立中央大學
化學工程與材料工程研究所
91
Abstract The carbothermal reduction and nitridation of rice husk ash with silicon powder addition was investigated by weight change measurement. The reaction were carried out in a vertical reaction tube heated by a tubular furnace. In this study, the operating variables have been discussed included: nitrogen flow rate, amount of silicon powder addition in the reactant, grain size, sample weight and reaction temperature. The analysis of this experiment is conducted by element analysis (EA), inductively coupled plasma-mass spectrometer (ICP-MS), BET surface area, X-ray diffraction (XRD) and scanning electron microscope (SEM). The experimental results indicated that the conversion of rice husk ash is increased with an increasing nitrogen flow rate and the effect is not appreciable when the flow rate exceeds 400ml/min. The conversion of rice husk ash is increased with an increasing amount of silicon powder addition in the reactant. Reducing the grain size of rice husk would accelerate the reaction rate. Moreover, the reaction rate and the conversion of rice husk ash is significantly increased with higher reaction temperature. The reaction product is fibrous shape a-Si3N4 with silicon addition. In the chemical reaction controlled region, the activation energy of the reaction is 478.5 kJ/mol when silicon powder addition is 1wt %.
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Yu, Cheng-Kuo, and 余建國. "A Study on the Kinetics of Carbothermal Reduction & Nitridation of Titanium Dioxide." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/00891119641732068943.
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碩士國立臺灣科技大學
化學工程研究所
83
Carbothermal reduction and nitridation of titanium dioxide was investigated by X-rey diffraction and gas chromatograph. The effect of the following factors on the formation rate of TiNxCY has been studied:(1)flow rate of nitrogen(2)sample height(3)rea ction temperature(4)C/TiO2 molar ratio(5)grain size(6)initial bulk density of solid sample(7)carbon source and(8)TiO2 source. Experimental results indicated that anatase was transformated to rutile before it was reacted to produce TiN. The solid product of the reaction is the solid solution of TiN and TiC. The amount of TiN in the solution product may be increased by increasing the reaction temperature or decreasing the initial molar ratio of C/TiO2 . The gas products of the reaction are mostly CO and trace amount of CO2. The reaction rate was found to be increased by increasing the nitrogen flow rate , molar ratio of C/TiO2 or reaction temperature. The rate was also observed to be increased by decreasing the sample height , the grain size of carbon or titanium dioxide or initial bulk density Experimental results showed that a chemical reaction control region can be reached if the flow rate of nitrogen is higher than 1.5E-5 m3/s and the sample height is kept under 0.004 m . Empirical rate expressions of the yoeld of TiNxCy were also determined shown.
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Chen, Yan-Wei, and 陳彥瑋. "Process Development for Carbothermal Reduction and Nitridation Synthesis of alpha-SiAlON Phosphors by Using Solution Combustion Synthesized Precursors." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/71315113766484607359.
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碩士國立成功大學
化學工程學系碩博士班
97
A commercial and potential method to synthesis nitrides or oxynitrides currently is reducing oxides at nitrogen atmosphere. Our laboratory has already successfully product silicon nitride and aluminum nitride from silicon oxide and aluminum oxide. This study used previous technical basis that our laboratory established to synthesis an advanced oxynitride material, SiAlONs which include silicon, aluminum, oxygen and nitrogen atom in its structure. Solution combustion synthesis we used that could help nitridation reaction precursors mix very well and close to nano-scale particle size. We could obtain α-SiAlON which was mainly phase in the product after precursors underwent carbothermal reduction nitridation and doped activator made the host have luminescent property. The study mainly focused on 1. carbon ratio, 2. reaction temperature, 3. seeds effects, 4. activator concentrations, 5. the effects of morphology of the precursors. The analytic instruments included XRD, PL, SEM and the best result achieved in this study when carbon was 4 times theoretical value, reaction temperature was 1500℃, Eu2+ was doped 0.5 and seed was doped 50 mol﹪.According to the SEM, we observed particle size distribution was from submicron to micron.
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Chen, Jia-hong, and 陳嘉鴻. "Carbothermal reduction sintering of silicon carbide." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/89974486629123552901.
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碩士國立聯合大學
材料科學工程學系碩士班
96
The objective of this study is to investigate the structure and electrical resistivity of SiC ceramics that added different amount of boron carbides, sintered at air and CO/CO2 in 1350 ~ 1400℃. This research shows that optimal mixed ratio of partical size of 1 ~ 10 μm and 40 ~ 60 μm by slip-casting in plaster of Paris and comparison of properties of bulk density, microstructure and electrical resistivity of sintered body was produced by adding amount of 0%、1%、2%、5% of boron carbide and sintering at various temperature in difference atmospheres. According to experiment result, we obtained the optimal condition without plasticizer that particle size of 1 ~ 10μm, 40 ~ 60μm and water of mixed ratio 3:3:4. We obtained the result that the highest density of sintered SiC by adding 1% boron carbide using Archimedes’ principle. Comparison of the result that the bulk density of sintering in air higher than sintering at CO/CO2 atmosphere due to formation of silica by SiC of oxidation infiltrated between particles. According the analysis result by XRD, generation of β-SiC by sintering at CO/CO2 atmosphere leads to electrical resistivity of sintering body decrease. In addition, we obtained that relative content of β–SiC significantly increased with higher reaction temperature by analysis of XRD and NMR.
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LEE, JYH-JEN, and 李志仁. "Kinetics of Carbothermal Reduction of Zinc Ferrite." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/41745166098073330366.
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碩士國立臺灣科技大學
化學工程系
88
Kinetics of carbothermal reduction of zinc ferrite was studied in this study. A box furnace was used to synthesize zinc ferrite. X-ray diffractometer, wetting-chemical analysis method, surface area meter and scanning electron microscope were employed to monitor the changes of composition and physical properties during reaction. On the other hand, thermogravimetic analyzer was used to study the effects of processing parameters on the conversion rate of zinc ferrite. It was found that zinc ferrite of 96.84% pure could be synthesized under following conditions : molar ratio of ZnO/Fe2O3 of 1 ; air flown over sample through suction of hood ; temperature of 1,123 K and time of 18,000 s. Zinc ferrite was found to decompose to ZnO and Fe2O3 initially. ZnO was then rapidly reduced to zinc vapor and carbon monoxide which were escaped from solid sample. Fe2O3 was also reduced FeO. However, the rate was slower. It was transformed to Fe through FeO. Pore surface area of solid sample increased with reaction time while pore volume and pore diameter were increased and then decreased with time. They are due to the escaping of zinc vapor and the expansion of FeO. A model was proposed to explain the reaction. As to the effects of processing parameters on the rate of carbothermal reduction of zinc ferrite, following results were found : conversion rate of zinc ferrite could be increased by increasing the flow rate of agron stream or reaction temperature. The rate was also found to be increased by decreasing the height of solid sample, molar ratio of ZnFe2O4/C, the grain size of carbon agglomerate or the initial bulk density of solid sample.
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Yang, Yi-lin, and 楊憶琳. "Preparation of Bio-Carbide by Carbothermal Reduction." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/10511679917928245206.
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碩士國立聯合大學
化學工程學系碩士班
94
The research of the ceramic material mineralized from the biomaterial has become a popular trend and has been widely used in many applications. This work intends to combine bionics and materials science by carbothermal reduction to prepare bio-carbides. The discarded timber was selected as the raw material due to the rise in environmental consciousness and the consideration of the cost of R&D. The timber was carbonized at high temperature for 2 hours in the inert gas. The carbonized wood was then selected as the porous template. Porous bio-carbides with woodlike microstructures were prepared by carbothermal reduction reaction at high temperature. This kind of woodlike microstructures was fabricated either by infiltrating one of the following species, TEOS/TTIP/Si/Ti, into woodceramics under vacuum condition or in the inert gas. This research focuses on the preparations of porous bio-template, bio-SiC, bio-TiC, and porous bio-Ti3SiC2. The results provide some useful guidelines in biomimetic processes.
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Lin, Thung-Hsien, and 林宗憲. "Synthesis of Electronic Grade Silicon Carbide Powders by Carbothermal Reduction." Thesis, 2015. http://ndltd.ncl.edu.tw/cgi-bin/gs32/gsweb.cgi/login?o=dnclcdr&s=id=%22103TIT05397033%22.&searchmode=basic.
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碩士國立臺北科技大學
資源工程研究所
103
Recently, SiC has been widely used in many fields owing to its high hardness, heat resistance, corrosion resistance, oxidation resistance and high thermal conductivity. In this study, high purity SiO2 powders (> 99.99%) were used as the source of silicon and the graphite powders were employed as the reducing agent. The objective of this study is to synthesize high purity SiC powders (> 99.99%) by carbonthermal reduction under argon atmosphere. Due to the high crystallinity of graphite, the chemical bond can&;#39;t be broken easily without adding catalyst, optimizing reaction temperature and time have been conducted. All experiments were operated at 1400 ~ 1600℃ for certain hours. The purified products were characterized by XRD and SEM. The purity of SiC was acquired through ICP-AES. The results indicated that β-SiC with the purity of 99.99895％ was synthesized. A series of experimients with parameters including various molar ratio of graphite to silica, reaction temperature, reaction time and after-treatment were carried out to investigate the optimal condition for the synthesis of SiC.
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Meng-PangChang and 張孟邦. "Growth of ZnGa2O4 nanowires on a ZnO film by carbothermal reduction." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/85253309652029437334.
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碩士國立成功大學
材料科學及工程學系碩博士班
98
The growth of ZnGa2O4 nanowires (NWs) on ZnO-coated Si substrates by carbothermal reduction of Ga2O3 powder as a function of the thickness of ZnO film and the weight of Ga2O3 powder was studied. With the weight of Ga2O3 powder held at 0.3-0.4 g, abundant and pure ZnGa2O4 NWs could grow at 550-650℃ on the 0.9 μm-thick ZnO film. Thinner ZnO film, more Ga2O3 powder, and higher substrate temperature favored the growth of Ga2O3 nanobelts. The growth of ZnGa2O4 NWs followed the vapor-solid process. The photolumescence spectra of ZnGa2O4 NWs showed the emission peaks around 460-480 nm.
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Chuang, Chih-Ming, and 莊誌銘. "The effects of transition metals on carbothermal reduction synthesis ofβ-SiC." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/59958600947990128356.
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碩士大同大學
材料工程學系(所)
92
This research is divided into two parts. In the first part, I will use phenolic-resin and Ludox were as the starting materials and add transition metals and use carbothermal reduction to synthsize β-SiC powder. I will discuss the effect of the kinds and the amount of additive on reaction temperature of β-SiC and powder properties. The other part of this research is that I will use activated carbon fabric and TEOS to prepare SiC fabric by shape memory synthesis. I hope that the morphology of SiC preserved the morphology of carbon. Adding Fe, Co, Ni, Cu enhance β-SiC formation at lower temperature. Adding Fe and Cu caused product to sinter. The product remained as powder when reactants contained Co and Ni. Although reactant with Cu can form β-SiC at 1300℃, the melting point of Cu is lower than reaction temperature, which leads reactants stick together as a cake the reaction surface decreases. Consequently, the reactant can not effectively convert into β-SiC. Adding Mn into reactants can not produce β-SiC at lower temperature. The reason is similar to that of adding Cu. The existence of Mn promoted SiO(g) formation but can not enhance reactants to convert to β-SiC. The yields of adding 1wt% Fe, Co, Ni after reaction at 1400℃ are higher than that of reactants without additives after reaction at 1400℃. The yields of adding 1wt% Fe, Co are even higher than reactants without additives after reaction at 1500℃. It can be seen that adding 1wt% Fe, Co, Ni can promote β-SiC formation at low temperature. The highest yield is by adding 1wt% Fe which is 76.87%. Adding Co has the second highest yield (73.14%) and adding Ni has 30.40% of yield, but it near to reactants without additives after reaction at 1500℃ (32.07%). The product of adding 1wt% Fe was sintered so that it needed to crush and mill. The yield of samples adding 1wt% Co was near to that of sample adding 1wt% Fe. The powder contained few whisker. Its particle size is about 100~200nm. The product of samples adding 1wt% Ni contains a lot of whisker. After reaction at 1500℃ for 8hr, activated carbon fabric can convert to β-SiC fabric. The product remains the shape of carbon and is flexible. Activated carbon fabric has many micro-pore on surface after activated process. The micro-pore provides many reaction area and promote reaction.
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Chen, Chih-yung, and 陳智勇. "Kinetics of Synthesis of Silicon Carbide through Carbothermal Reduction of Silicon Oxide." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/94220456840643778964.
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碩士國立台灣工業技術學院
化學工程技術研究所
85
The kinetics of synthesis of silicon carbide through carbothermal reduction of silicon dioxide has been studied in our experiment. X-ray diffraction analysis were employed to determine the content of products. The effects of several parameters on the reaction rate were obtained. Experimental results indicated that the reaction rate could be increased by decreasing the flow rate of He, the SiO2/C ratio, the grain size of silicon oxide or carbon and the initial density of solid sample. The rate could also be increased by increasing the height of solid sample and the reaction temperature. It was also found implicitly that SiO was an intermediate product. The activation energy of the production of β-SiC was found to be 436kJ/mole. Following are the empirical rate expressions of conversions of carbon, silicon oxide and production of silicon carbide obtained by regression of the experimental data： dCc-rc = - -------- = 7.6E4 *exp(-412,132/RT) *dsio2^(-0.742)* dc^(-0.549) dt *Csio2^(0.308)* Cc^(0.316)*Csic^(-0.046)*D^(-0.218) *f^(-0.311)*h^(0.460) dCc-rsio2 = - ------ = 1.2E4 *exp(-401,513/RT) *dsio2^(-0.801)*dc^(-0.392) dt *Csio2^(0.476)*Cc^(0.283)*Csic^(-0.077)*D^(-0.241) *f^(-0.304)*h^(0.412) dCsicrsic = -------- = 2.5E4 *exp(-436,012/RT) *dsio2^(-0.474)*dc^(-0.315) dt *Csio2^(0.407)*Cc^(0.328)*Csic^(0.013)*D^(-0.234) *f^(-0.352)*h^(0.414) The applicable range of the empirical rate expressions are flow rate of He 1x10-5 - 5x10-5 m3/s, sample height 0.007 - 0.020m, reaction temperature 1,573 - 1,773K, SiO2/C molar ratio 1/5 - 1/1, grain size of silicon oxide 0.000042 - 0.000113m, grain size of carbon 0.000051 - 0.000134m and initial bulk density 339.5 - 577.2kg/m3.
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Liao, Kuo-Hong, and 廖國宏. "The Influence of silicon on the Carbothermal Reduction and Nitriding of Silica." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/03150444976075271505.
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碩士國立中央大學
化學工程研究所
88
The carbothermal reduction and nitridation of silicon dioxide with silicon powder addition was investigated by weight gain measurement. The reaction were carried out in a vertical reaction tube heated by a tubular furnace. In this study, the operating variables have been discussed included: nitrogen flow rate, amount of silicon powder added in the reactant, silicon dioxide/carbon molar ratio, sample weight, and reaction temperature. The analysis of this experiment is conducted by X-ray diffraction (XRD), scanning electron microscope (SEM), BET surface area, and inductively coupled plasma-mass spectrometer (ICP-MS). The experimental results indicated that the conversion of silicon dioxide is increased with an increasing nitrogen flow rate and the effect is not appreciable when the flow rate exceeds 500ml/min. The conversion of silicon dioxide is increased with an increasing amount of silicon powder added in the reactant. An excess of carbon powder and decrease of the sample weight are required to promote the conversion, however, the effect is not appreciable when the molar ratio is above 5 and sample weight is below 0.3g. Moreover, the reaction rate and the conversion of silicon dioxide is significantly increased with higher reaction temperature. The reaction product is fibrous shape β-SiC with silicon powder addition. We conjectured that the large formation of gaseous SiO is an important way for β-SiC growth.
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Yi-ChiHuang and 黃奕齊. "Microstructure and Mechanical Properties of SPS Sintered Nano-Si3N4 Ceramics via Carbothermal Reduction Method." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/67670024427847766667.
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Lin, Yu-Chiao, and 林郁喬. "The study of the growth of SiO2 nanowires via carbothermal reduction of CuO powders." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/53098791869146267199.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
93
The growth of SiO2 nanowires（SiONWs）via carbothermal reduction of CuO powders as functions of the growth temperature, time, Ar flow rate, the carbon concentration in the CuO/carbon powders, and the oxygen concentration in the Ar/O2 flow were studied. Significant amount of SiONWs were grown on the Si substrate without the catalyst from the CuO/carbon powders at a temperature of 1000℃-1100℃ in a flowing Ar with the flow rate of 100 sccm. Without using CuO/carbon powders SiONWs could not be readily grown. A small amount of SiC associated with SiONWs was grown from the CuO/carbon powders with a higher proportion of carbon. The minimum Ar flow rate required for the growth of SiONWs was about 10 sccm and the amount as well as the diameter of SiONWs increased with increment of the Ar flow rate, revealing that the vapor transport assisted by the Ar flow is an important mechanism for the nucleation and growth of SiONWs. The growth of SiONWs mainly originated in the cracks which were formed in the Si substrate due to the generation of SiO(g) from the reaction between CO2 and the Si substrate. The introduction of O2 into the Ar flow could generate siginficant amount of CO and thereby suppress the growth of SiONWs. The present studies reveal that the growth of SiONWs via carbothermal reduction of CuO powders mainly follows the vapor-solid（VS）mechanism.
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Hsieh, Wen-yuan, and 謝文元. "Growth of WO3 nanowires and Ge-Si1-xGexOy core-shell nanowires via carbothermal reduction." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/56987325131401913860.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
95
Effects of adding GeO2 to WO3 powders on enhancing the growth of WO3 nanowires (NWs) and Ge-Si1-xGexOy core-shell NWs ( Ge-SiGeO NWs) via the carbothermal reduction process in Ar at a flow rate of 25-400 sccm at a temperature of 900-1100°C were studied. Upon the thermal evaporation or carbothermal reduction of WO3 powders at 900°C no NWs were grown. The growth of WO3 NWs follows the vapor-solid (VS) process, where GeO2 powders act as an oxidizer. Introducing 1-5% O2 into flowing Ar enhanced the growth of GeO2 NWs and WO3-GeO2 core-shell NWs at 900°C. More O2 suppressed the growth of NWs because of the exhaustion of much graphite powders. At 1050-1100°C the growth of Ge-SiGeO NWs following the VS process were observed. In addition, the growth mechanisms of WO3, GeO2, and Ge-SiGeO NWs are discussed, respectively.
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Heidlage, Michael Gregory. "Sustainable ammonia synthesis via thermochemical reaction cycle." Diss., 2018. http://hdl.handle.net/2097/38948.
Full textAbstract:
Doctor of PhilosophyDepartment of Chemical Engineering
Peter H. Pfromm
Since its inception, the Haber-Bosch (HB) process for ammonia (NH3) synthesis has allowed for a significant increase in global food production as well as a simultaneous decrease in global hunger and malnutrition. The HB process is estimated to be responsible for the subsistence of 40% of the world population as approximately 85% of the over 182 metric tons of NH3 produced in 2017 was used as fertilizer for crop production. The natural gas consumed (mostly to generate H2) represents approximately 2% of the global energy budget, while the CO2 produced is about 2.5% of all global fossil CO2 emissions. Approximately 40% of food consumed is essentially natural gas transformed by the HB process into agricultural products. However global food production will need to double due to expected increase in world population to 9.6 billion by 2050 and rising demand for protein among developing nations. A novel thermochemical reaction cycle for sustainable NH3 synthesis at atmospheric pressure is explored herein. Both thermochemical and kinetic rationales are discussed regarding choice of Mn as the cycled reactant. The energetic driving force for these reactions is conceptually derived from concentrated solar energy. Mn was reacted with N2 forming Mn-nitride, corrosion of Mn-nitride with steam at 500 °C formed MnO and NH3, and lastly MnO was reduced at 1150 °C in a 4 vol % CH4 – 96 vol % N2 stream to Mn-nitride closing the cycle. Optimum nitridation at 800 °C and 120 min produced a Mn6N2.58-rich Mn-nitride mixture containing 8.7 ± 0.9 wt. % nitrogen. NH3 yield was limited to 0.04 after 120 min during nitride corrosion but addition of a NaOH promotor improved NH3 yield to 0.54. Mn6N2.58 yield was 0.381 ± 0.083 after MnO reduction for 30 min with CO and H2 but no CO2 detected in the product. Mn-nitridation kinetics were investigated at temperatures between 600 and 900 °C for 10 and 44 μm reactant powder particle sizes. That equilibrium conversion decreased with increasing temperature was confirmed. Jander’s rate law, which assumes gaseous reactant diffusion through a solid product layer, described the experimental data reasonably well. The rate constants and initial rates were as much as an order of magnitude greater for the 10 μm Mn reactant particle size. Additionally the activation energy was found to be 44.1 kJ mol-1 less for the 10 μm reactant particle size. Reducing the particle size had a small but positive effect on Mn-nitridation kinetics. Further reducing particle size will likely have a greater impact. A review of relevant classical thermodynamics is discussed with special attention paid to open systems. Confidence issues regarding over-reliance on x-ray diffraction are considered with options suggested for mitigation. Opportunities for future work are assessed.
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Tsai, Sheng-Fong, and 蔡昇峰. "Ni-catalyzed growth of Ge and GeO2 nanostructures by the thermal evaporation and carbothermal reduction methods." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/50522118476404850748.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
96
On the thermal evaporation of Ge powders at 950˚C in Ar, the growth of Ge nanowires (GeNWs), Ge nanobelts (GeNBs), and GeO2 nanowires (GeONWs) by the Ni catalyst was studied. The Ni-catalyzed growth of GeNWs and GeNBs at 420-500˚C followed the vapor-solid-solid (VSS) process with the top-growth mode. The GeNWs and GeNBs favored the <110> and <112>, and <112>growth orientations, respectively. The surface energy plays an important role in determining the growth direction of Ge nanostructures. At higher temperatures, 600~660˚C, the first VSS growth of GeONWs was observed. This result is contrary to the previous reports that the growth of GeONWs follows the vapor-solid (VS) process regardless of the presence of metal catalysts. The growth mode of Ni-catalyzed GeNWs may be independent of the synthesis method and growth temperature. Meanwhile, the growth mechanisms of Ni-catalyzed Ge and GeO2 nanostructures are discussed. The same Ni-catalyzed growth mode of Ge and GeO2 nanostructures was also observed in the carbothermal reduction of GeO2 powders. However, the growth temperature of GeONWs raised up to 720~750˚C which are higher than that, 600~660˚C for the thermal evaporation of Ge powders.
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Kumar, Rakesh. "Development And Validation Of Two-Dimensional Mathematical Model Of Boron Carbide Manufacturing Process." Thesis, 2006. http://hdl.handle.net/2005/411.
Full textAbstract:
Boron carbide is produced in a heat resistance furnace using boric oxide and petroleum coke as the raw materials. In this process, a large current is passed through the graphite rod located at the center of the cylindrical furnace, which is surrounded by the coke and boron oxide mixture. Heat generated due to resistance heating is responsible for the reaction of boron oxide with coke which results in the formation of boron carbide. The whole process is highly energy intensive and inefficient in terms of the production of boron carbide. Only 15% charge gets converted into boron carbide. The aim of the present work is to develop a mathematical model for this batch process and validate the model with experiments and to optimize the operating parameters to increase the productivity.
To mathematically model the process and understand the influence of various operating
parameters on the productivity, existing simple one-dimensional (1-D) mathematical
model in radial direction is modified first. Two-dimensional (2-D) model can represent
the process better; therefore in second stage of the project a 2-D mathematical model is also developed. For both, 1-D and 2-D models, coupled heat and mass balance equations are solved using finite volume technique. Both the models have been tested for time step and grid size independency. The kinetics of the reaction is represented using nucleation growth mechanism. Conduction, convection and radiation terms are considered in the formulation of heat transfer equation. Fraction of boron carbide formed and temperature profiles in the radial direction are obtained computationally.
Experiments were conducted on a previously developed experimental setup consisting of
heat resistance furnace, a power supply unit and electrode cooling device. The heating
furnace is made of stainless steel body with high temperature ceramic wool insulation. In
order to validate the mathematical model, experiments are performed in various
conditions. Temperatures are measured at various locations in the furnace and samples
are collected from the various locations (both in radial and angular directions) in the furnace for chemical analysis. Also, many experimental data are used from the previous work to validate the computed results. For temperatures measurement, pyrometer, C, B and K type thermocouple were used.
It is observed that results obtained from both the models (1-D and 2-D) are in reasonable agreement with the experimental results. Once the models are validated with the experiments, sensitivity analysis of various parameters such as power supply, initial percentage of B4C in the charge, composition of the charge, and various modes of power supply, on the process is performed. It is found that linear power supply mode, presence of B4C in the initial mixture and increase in power supply give better productivity (fraction reacted). In order to have more confidence in the developed models, the parameters of one the computed results in the sensitivity analysis parameters are chosen (in present case, linear power supply is chosen) to perform the experiment. Results obtained from the experiment performed under the same simulated conditions as computed results are found in excellent match with each other.
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Chang, Shin-Yun, and 張詩芸. "Investigation of nanosize chromium carbide prepared by MOCVD in Fluidized Bed-carbothermal reduction process and phase evolution mechanisms." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/50587695729078655602.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
96
Nanochromium carbide were prepared by metal-organic chemical vapor deposition (MOCVD) method in a fluidized bed and carburized in the mixtures of CH4/H2 atmosphere in temperature ranged from 700-850 oC. Under these conditions, the carburization process involved carbon deposition on the outer surface of the powder, diffusion of carbon into nanopowder as well as carbide formation, Cr2O3, metastable Cr3C2-x and stable Cr3C2. The relation among the products, reduction temperature and time was summarized from the XRD. TEM is employed to investigate the detailed structure of the carbon diffusion layer. Use the STEM line scan mode to find out the compositional gradient within the interlayer: Cr3C2-x 、 Cr3C2 and pure C amorphous. The experimental results indicated that, carbonthermal reduction process of Cr2O3 consists of two steps, the rate-controlling step is CO /CO2 gas diffusion through the layer of reduction products. With the longer duration time, the stoichiometry of the mixture Cr3C2-x is the first carbide form, then to form stable Cr3C2.。 The hot-pressed Cr3C2/Al2O3 nanocomposites have better mechanical performances such as bending strength, and hardness than the monolithic Al2O3. The nano-sized Cr3C2 particles were mainly located within the Al2O3 grains as well as on the Al2O3 grain boundaries.
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Bi-JrLi and 李筆智. "Study of Structural and Photoluminescent Properties of Ca3(Sc,Zn)2Si3O12: Ce3+ Green Phosphors by Carbothermal Reduction Method." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/41931299914920815128.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
101
In this study, we used the carbothermal reduction(CTR) method to produce Ca3Sc2Si3O12:Ce3+ (CSS:Ce). The CSS:Ce by CTR method was compared with that fired in air to analyze whether the optical performance could be improved or not. And then we used CTR method and added Zn2+ ions into CSS:Ce to substitute for Sc3+. We could get the Ca2.955Sc2-(2/3)xZnxSi3O12:Ce3+ (x=0~0.5) (CSZS:Ce) green phosphors. Finally, compared with Ca2.955Sc2-yAlySi3O12:Ce3+ (y=0~0.4) (CSAS:Ce), which were other CSS:Ce researches in our lab, we could analyze the relationship between the ion doping and thermal stability of optical properties. The results show the three highlights. Firstly, the luminescent intensity of CSS:Ce by CTR method was better than that fired in air. This was attributed that more Ce3+ ions were doped into the structure, which was proved by X-ray absorption spectrum and Raman scattering spectrum. Secondly, by CTR method, Zn2+ doping could effectively improve the optical performance and thermal stability. The chemical formula were Ca2.955Sc2-(2/3)xZnxSi3O12:Ce3+ (x=0~0.5). When Zn2+ doping content (x) was 0.3, the optical performance was the best. From XRD patterns, Raman scattering spectra, and FTIR spectra, it was observed that residual Sc2O3 content decreased. However, when x (Zn2+ doping content) was more than 0.2, the new impurity phase, Ca3Si3O9 (Pseudowollastonite, psW), was produced. Impurity phase could weaken the optical performance. Additionally, SEM showed Zn2+ doping brought about liquid phase sintering. Liquid phase sintering could cause samples to diffuse more uniformly in firing process and effectively improve optical performace. Thirdly, compared with Ca2.955Sc2-yAlySi3O12:Ce3+ (CSAS:Ce), which are other CSS:Ce researches in our lab, Zn2+ doping could enhance the thermal stability but Al3+ doping could not. This was attributed that Al3+ doping would decrease the activation energy of thermal quenching behavior and increase the energy of effective phonons. Therefore, the thermal stability of CSZS:Ce were better than CSAS:Ce. The above-mentioned results shows the CSZS:Ce phosphors are very excellent material as color conversion material for high power LED
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Ko, Chih-Yuan, and 柯志遠. "Growth of Si1-xGexOy nanowires, and Ge/Si1-xGexOy, and GeO2/Si1-xGexOy core-shell nanowires via carbothermal reduction." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/21820389750400048760.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系碩博士班
94
The effects of a grown SiO2 layer on the Si substrate and the CuO additive in GeO2 powders on the enhanced growth of Ge-Si1-xGexOy and GeO2-Si1-xGexOy core-shell nanowires via carbothermal reduction at 1050-1100℃ in flowing Ar were studied. Without adding CuO into GeO2 powders only Ge-Si1-xGexOy nanowires were grown on the SiO2/Si substrate, while no nanowires could be grown on the Si substrate. Adding CuO into GeO2 powders enhanced the growth of GeO2-Si1-xGexOy and Ge-Si1-xGexOy nanowires on the Si substrate as well as that of GeO2-Si1-xGexOy nanowires on the SiO2/Si substrate. The growth of nanowires follows the vapor-solid process. The present studies reveal that the oxidation of the Si substrate plays an important role in enhancing the growth of Ge-Si1-xGexOy and GeO2-Si1-xGexOy nanowires via carbothermal reduction of GeO2 powders. The mechanisms for precipitation of Ge and GeO2 cores in the Si1-xGexOy nanowires on Si and SiO2 substrates are discussed, respectively. Upon carbothermal reduction of GeO2/CuO powders at 1100℃, not only the Ge-Si1-xGexOy and GeO2-Si1-xGexOy nanowires but also the cord-like nanowires, tubes, and chain-like wires with the chemical compositions of Si, Ge, and O were grown on the Si substrate. The tubes and chain-like wires are also composed of many Si1-xGexOy nanowires. The growth of cord-like nanowires, tubes, and chain-like wires is govern by the CuSiGe- and SiGe-catalyzed vapor-liquid-solid mechanisms, where Ge, Si, and Cu are fed from the vapor phase. For the tubes and chain-like wires the nucleation and growth of Si1-xGexOy nanowires occur on the lower surface of the droplet except the central region. As growth continues the nanowires exert a force to lift the droplet upward, forming a tubular structure. The diameters of the chain-like wires are periodically modulated. Their growth may be explained in terms of the periodic instability using the feedback mechanism. As the chain-like wire grows up, it can eventually grow into a microtube without periodic instability. The suppression of the periodic instability for the wires with larger diameter may be attributed to the decrease of the vapor supersaturation at the vapor-liquid interface due to the Gibbs-Thomson effect. In the present study, the tube can be specified as the chain-like wire with a very large wavelength.
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Hwang, Yih-Chyang, and 黃意強. "The Investigation of End-of-Range Defect Reduction in Shallow Junctions Using Plasma Nitridation and Carbon Implantation." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/36325652545423249225.
Full textAbstract:
碩士國立交通大學
材料科學與工程研究所
84
The end-of-range (EOR) defects were obserced in germanium implantated Si single crystal wafer after thermal annealing. Most of the EOR defects were found to be dislocation loops of interstitial type confined to amorphous-crystalline interface. In this work, we studied the effect of plasma surface nitridation to reduce the EOR defects. Experimental resultsindicated that the Si nitride layer was able to serve as a vacancy source which, in turn, effectively reduced the size and number of the EOR dislocation loops. Another part of this work is to study the effect of carbon implantation to reduce the transient diffusion (TED) of implanted boron. It was foundthat the carbon implantation could effectively remove the EOR defects. However, hair-pin dislocations were also observed after annealing. Thehair-pin dislocations were most likely formed when the projected range (Rp) of carbon implantation was located in the vicinity of the amorphous/crystalline (a/c) interface created by Ge implantation.