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1
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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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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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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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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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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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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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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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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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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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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Igiehon, Uwagboe Osamede. "Carbothermic reduction of complex sulphides." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46358.
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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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Previous issue date: 2011-11-23Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico
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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Frank, Robert A. "Physical chemistry of carbothermic reduction of alumina." Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/15150.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE
Vita.
Bibliography: leaves 177-180.
by Robert A. Frank.
M.S.
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VEIGA, SONIA M. B. da. "Obtencao e caracterizacao do composito Alsub2Osub3-SiC-ZrOsub2." reponame:Repositório Institucional do IPEN, 1996. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10469.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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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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Lundgren, Emil. "Preparation of uranium carbide through carbothermic reduction of uranium dioxide." Thesis, KTH, Fysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-149675.
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The project started with a preparatory literature study and thermodynamic consid- erations. The main purpose was to synthesise uranium carbide through carbothermic reduction. The synthesis method was developed through a serie of experiments. Ele- mental analysis for carbon, oxygen and nitrogen was performed on the product and modifcations were made to the method based on the results in the analysis. In addition, XRD was performed to complement the elemental analysis and obtain in- formation about the structure and phases present in the product. The purest product contained 1.9 wt. % oxygen, 1.3 wt. % nitrogen and 5.2 wt. % carbon. The stoi- chiometric composition of the product was UC1.1 O0.3 N0.2. The conclusion is that in order to obtain a pure carbide it is important to ensure good mixing of reactants and minimise potential contamination.
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BENIQUE, FERRY SABEL BELISARIO. "CONTRIBUTION AT CARBOTHERMIC SELF-REDUCTION OF AGGLOMERATES OF MANGANESE OXIDES." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2007. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=11024@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICONeste trabalho, foram feitas experiências de redução em temperaturas na faixa de 900°C a 1300°C, usando briquetes auto-redutores contendo óxidos de manganês e carvão vegetal, visando investigar o processo de redução de MnO2 para MnO. É apresentado um panorama geral do manganês, indicando os principais produtos, entre eles, o MnO para uso agropecuário e a liga FeMn, insumo siderúrgico e evidenciando os aspectos termodinâmicos e cinéticos no processamento para a obtenção destes produtos. Cabe assinalar que o MnO é um produto intermediário no processo de fabricação da liga ferro-manganês. Mostram-se também detalhes do procedimento experimental, caracterização dos materiais utilizados e as discussões sobre os resultados obtidos. Na determinação das conversões de MnO foi utilizado o método de análise química de titulação por complexometría com EDTA. A partir dos resultados experimentais foi proposto um modelo para determinação dos parâmetros cinéticos. Pelos resultados da redução de Mn+4 para Mn+2, foi possível distinguir dois estágios nas temperaturas ensaiadas. O primeiro estágio foi marcado por altas velocidades de reação, a até aproximadamente 10 minutos de experimentação, alcançando conversões elevadas de MnO; como foi o caso dos ensaios nas temperaturas de 1000°C e 1200°C, que já indicavam em 10 minutos valores de conversões iguais a 0.94. Já para o segundo estágio, após os 10 minutos iniciais de experimentação, as velocidades e os valores da conversão apresentaram uma queda, sugerindo que o produto do primeiro estágio, o MnO, poderia estar começando a se transformar em outra substancia ( provavelmente o Mn3C ). Por não ser objetivo desta dissertação determinar a natureza da citada transformação, apenas a evidência de sua ocorrência foi aqui explicitada, ficando os estudos mais detalhados para outro trabalho. O modelo cinético concluiu que o processo se passava essencialmente em duas etapas : uma para tempos curtos e outra para tempos longos, sendo o tempo de experimentação em torno de 10 minutos a fronteira destas etapas . O valor da energia de ativação para a etapa em tempos menores, ou seja, inferiores a 10 minutos, foi, nas temperaturas estudadas, 1000, 1100, 1150 e 1200°C, de 11,50 KJ/mol e o fator de freqüência pré-exponencial 0,057 mHz, sugerindo um controle difusional.. Já para os tempos maiores que 10 minutos, os experimentos nas temperaturas de 900, 1000, 1100, 1150, 1200 e 1300°C, muito embora não se tenha pesquisado a natureza do novo composto ( possivelmente o carboneto de manganês ), forneceu para a energia de ativação o valor de 46,10 KJ/mol e para o fator de freqüência pré-exponencial 48,045 Hz, sugerindo, em conseqüência, um mecanismo predominantemente misto, ou seja, equilibradamente difusional e químico.
In this work, aiming at the investigation on the reduction process of manganese dioxide to manganese oxide, experiments were made using selfreducing briquettes containing manganese oxides and charcoal, at temperatures ranging from 900 to 1300oC. A general overview of the manganese is presented, indicating its principal products such as, the farming usage of MnO and the steelmaking application of the FeMn alloys, also emphasizing the thermodynamical and kinectical aspects of their productions. It is worthwhile to emphasize that MnO is an intermediary product in the production of the FeMn alloy. Experimental details concerning materials characterization and discussion on the obtained results, are also presented. In the determination of the MnO conversion the complexometric titration with EDTA chemical procedure was applied. From these determinations a model was proposed for the calculation of the kinectic parameters. The experimental results of reduction, from Mn+4 towards Mn+2 , it was possible to identify two stages for the reactions in the temperature range from 900 to 1300 C. An onset stage was marked by high reaction rates, lasting for the first 10 minutes, achieving high MnO conversions. In the experiments carried out in the range of 1000 to 1200oC, for instance, a 0,94 conversion was attained within just 10 minutes. As for the second stage, beginning after 10 minutes, the conversion showed a decrease, suggesting that the product of the first stage, the MnO, could be suffering a transformation, generating an other substance - probably Mn3C. Being this a new process, out of the scope of this work, its elucidation is left here as a suggestion for later works. Wrapping up the kinetic model, a time frontier between the two processes, around 10 minutes, was considered . Below this limit, i.e., in the temperatures - 1000, 1100, 1150 and 1200oC -, the process exhibited an apparent activation energy of 11.50 kJ x mol -1 and a pre-exponential frequency factor of 57 µHz, inferring a diffusion control. As for times beyond 10 minutes, in experiments at 900, 1000, 1100, 1150, 1200 e 1300°C, though the nature of a new compound was not probed - possibly a manganese carbide - it was possible to measure a new apparent activation energy, 46.10 kJ x mol -1 , with a pre- exponential frequency factor of 48 Hz, values coherent with a mixed control, i.e., between the diffusional and the chemical mechanisms.
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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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Hu, Xianfeng. "Studies on Carbothermic Reduction of Chromite in the Presence of FeOx." Doctoral thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60100.
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Direct chromium alloying by chromite ore is a promising technology for producing Crcontainingsteels, as the ferrochrome production process and the chromium alloying processare integrated into a single step, which has the potential of saving energy and raw materials.In this work Thermogravimetric Analysis experiments and induction furnace experiments (upto 80-kg scale) have been carried out to investigate the carbothermic reduction process ofchromite in the presence of FeOx (iron, mill scale or magnetite). The aims are to investigatethe effect of FeOx on the carbothermic reduction of chromite and to explore the potential ofdirectly alloying steel with chromium by the designed alloying precursor ‘chromite ore +FeOx + carbonaceous material’.The results from the Thermogravimetric Analysis experiments show that FeOx can enhancethe carbothermic reduction of chromite and the enhancing effect increases when increasedamounts of FeOx are added to the chromite. The enhancing effect is attributed to the presenceof added metallic iron or the metallic iron reduced from mill scale or magnetite, which candecrease the activity of chromium by having chromium dissolve in the iron in situ. The resultsfrom the induction furnace experiments show that the steel can be directly alloyed withchromium by using the designed alloying precursor ‘chromite ore + mill scale + petroleumcoke’ and the chromium yield from chromite ore increases when increased amounts of millscale are added to the alloying precursor.The designed alloying precursor, on one hand, can be potentially used to directly alloy steelwith chromium in the Electric Arc Furnace steelmaking process and, on the other hand, can bepotentially used to produce Cr pre-alloyed iron powder or Cr pre-alloyed Direct Reduced Ironby the solid-state reduction process. The proposed applications have the potential to improvethe raw materials efficiency and energy efficiency.
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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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Yoon, Su-Jong. "Synthesis and characterization of ceramics in the Ti-B-N-C system." Thesis, Brunel University, 1994. http://bura.brunel.ac.uk/handle/2438/5352.
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Titanium and boron nitride and carbide, titanium diboride were synthesized by carbothermic reduction as single phase as well as mixtures intended to form composite materials. The aim of the project is to study the physical chemistry of carbothermic reduction for the production of pure nonoxide ceramic powders and also for the in-situ formation of ceramic/ceramic partially-densified composites. The thermodynamic and kinetic factors that govern the phase constituents are discussed and the effect of processing parameters on the morphology and extent of reduction are also established. The first part of the present investigation is aimed at the production of titanium nitride, carbonitride and carbide powders and the in-situ formation of TiN/TiC partially-densified composites by the carbothermic reduction of titania in suitable nitriding atmospheres. The investigation includes the aspects of the thermodynamics and kinetics of the nitriding reaction and points out the reaction mechanism by identifying the phase formed after the nitridation process. The microstructures produced after the reduction-nitridation process have been correlated with the thermodynamic and kinetic parameters. The synthesized titanium nitride powder was identified as the carbonitride phase, Ti(CxN1_x), having a range of composition. The rate of reduction of TbO2 was found to be determined by the rate of oxygen diffusion in the sub-oxide lattice and the derived value of activation energy in the temperature range 1473K to 1773K from the Arrhenius plot is 120 kJ-mole-1 of T102. TI305 was found as a high temperature precursor phase for the formation of titanium nitride. The use of iron chloride as catalyst and activated charcoal in the mixtures of oxide increased the yield of titanium nitride phase by enhancing the rate of reduction of titanium oxides. The morphology of titanium carbonitride particles was dependent upon the reactivity of carbon and the temperature. The calculated equilibrium phase fields were found to be in agreement with the experimental data and provide a means to select the variables for the reduction condition for designing a required ceramic microstructure. The microstructure of boron nitrides is closely related to the structural chemistry of carbon and nitriding agent. The main aim of the second part of the project was to synthesize boron nitride and carbide powders and whiskers by carbothermic reduction of boric anhydride (6203) in nitrogen atmosphere and also to understand a relation between the processing parameters and the phases produced. The effect of processing conditions such as the gas composition, reactivity of carbon, reaction temperature and time as well as the composition of starting materials on the synthesis of boron nitride and carbide phases were studied. The reactivity of carbon, B/C ratio and gas composition were the most important variables that determined the formation, structure and morphology of the nitride. During the nitridation process, boron carbide phase also formed and played a significant role. The investigation also reports the evidence for the formation of metastable forms of BN i. e wurtzite and cubic BN. We also report the results of the solubility of nitrogen in C-saturated B4C structure. The third part of the present work is aimed at the production of TiB2 powders. Aspects of the formation of two or three ceramic phase mixtures were also examined together with the relative stability of the single phase mixed diborides with respect to pure diboride phase. The central aim of this part is to establish the mechanism of the synthesis reaction leading to the formation of uniform size of titanium diboride crystals. Titanium boride (TiB2) powder was produced in the powder form by the reduction of ingredient oxides with carbon via a gas-solid phase reaction. For the production of the composite microstructure, the nitrogen partial pressure was found to be the most critical factor. In the composite microstructure, the titanium nitride particles have a submicrometer size whereas the boride particle size is only a few micrometers with predominantly hexagonal morphology. Some calculated equilibrium phase fields have been experimentally verified. The empirical verification is a useful tool to establish the correctness of the calculated phase diagram. The theoretical approach therefore enables to identify the condition for the formation of phase mixtures. The constituent phases depend on the reduction conditions. For example, nitrides in equilibrium with Ti62 can only form above a critical nitrogen partial pressure whereas TiC or B4C form in the inert atmospheres. This result is applicable to all other ceramics. The investigation also shows the viability of production of the composite powder mixture via the oxide co-reduction technique. The synthesis of TIB2/TiN, TiB2ýC, TB2/TN/BN and mixed diboride composites is possible by employing the reduction route.
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Kahramansoy, Eylem. "Production Of Hexagonal Boron Nitride By Carbothermic Reduction Of Colemanite-boric Oxide Mixtures." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613595/index.pdf.
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Carbothermic production of hexagonal BN by using boric acid and ground colemanite mined from BigadiçRegion in Turkey was investigated by subjecting pellets prepared from B2O3, activated carbon and colemanite mixtures to nitrogen gas at 1500°
C. Similar to CaCO3 addition, colemanite addition to the B2O3-C mixtures resulted in higher amounts of h-BN in the final products. As a result of the experiments conducted with colemanite and CaCO3 additions providing the same quantity of CaO to the initial mixtures, similar amounts of hexagonal BN in the reaction products were observed. As a result of the experiments conducted with different compositions of colemanite- B2O3- C mixtures, 5 wt % colemanite addition was determined to be the optimum composition giving the highest amount of hexagonal BN in the reaction products. Increasing duration of the experiments increased the amount and particle size of h-BN formed in the products. Optimum amount of colemanite addition resulted in higher amounts and coarser particles of h-BN in the products than the optimum amounts of CaCO3 addition.
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Agarwal, Ashish 1975. "Mechanism of silicon transfer in tuyere injected reactors by carbothermic reduction of silica." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/39631.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Vita.
Includes bibliographical references (leaf 63).
The melting zone in a cupola has temperatures greater than 1773 K and a reducing atmosphere. This condition is suitable for the carbothermic reduction of silica. The key to the applicability of carbothermic reduction of silica for Ferro-alloy production is rapid in-situ production of SiC and its subsequent dissolution in the hot metal. The main objective of this investigation was to study the kinetics of the carbothermic reduction process and determine the optimum parameters for rapid and complete in-situ conversion of silica to SiC. At temperatures above 1773 K the key reactions in the carbothermic reduction process are (1) SiO2(s) + CO(g) = SiO(g) + C0 2(g), (2) SiO(g) + 2C(s) = SiC(s) + CO(g), (3) C(s) + C0 2(g) = 2CO(g). To meet the objective of this study, conditions must be such that the surface reactions occurring at the carbon and silica surfaces are rate limiting and the entire silica is converted to SiC. Pellet composition and structure in terms of carbon to silica ratio, their particle sizes and compaction pressure that ensure surface reaction is rate controlling, were determined. The gassolid reaction kinetics was mathematically modeled in terms of the process parameters. It was observed that the reaction kinetics improved by reducing both carbon and silica particle sizes. However, below a certain critical particle size there was no significant improvement in the reaction kinetics. For complete conversion of SiO2 to SiC, excess carbon and critical porosity are necessary to ensure that the entire SiO(g) generated by reaction (1) is consumed via reaction (2) within the pellet.
by Ashish Agarwal.
S.M.
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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.
Full textAbstract:
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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Chin, Earle J. "Carbothermic reduction of pyrochlore and niobium pentoxide in a transferred arc plasma : a thesis." Thesis, McGill University, 1989. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75989.
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The carbothermic reduction of pyrochlore and niobium pentoxide was studied, with and without the addition of iron as a solvent, in an argon transferred-arc plasma with a single stationary pellet reactor system. A conversion-time model, based on experimental and theoretical studies, was proposed to describe the carbothermic reduction reaction systems. The experimental results confirmed the applicability of the model.The carbothermic reduction of pyrochlore and niobium pentoxide were studied in the temperature range 1530-2440 and 1625-2855 K, respectively. The rate was independent of particle size but was influenced by the separation between the oxide and carbon particles. The rate was lower than the model predictions above a certain conversion, the level of which increased with temperature and carbon concentration.
The carbothermic reduction of pyrochlore and niobium pentoxide with iron addition were studied in the temperature range 1430-2125 and 1575-2440 K, respectively. The rates were independent of particle size but was enhanced by the presence of iron. Deviation from the model was observed to be less at high conversion levels.
Preliminary investigation of the conversion rate for the carbothermic reduction of a pyrochlore and ferric oxide mixture was done to simulate the type of reactants that would be used in a commercial process. The rate was improved by the addition of iron oxide.
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Frank, Robert A. (Robert Antony). "Physical chemistry of the carbothermic reduction of alumina in the presence of a metallic solvent." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/14216.
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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1989.Vita.
Includes bibliographical references (leaves 354-372).
by Robert A. Frank.
Sc.D.
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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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Junior, Ivan Parreiras de Carvalho. "Estudo da utilização de energia de microondas na redução de minério de ferro por carbono na forma de pelotas auto-redutoras." Universidade de São Paulo, 2001. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-18122001-143418/.
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A redução carbotérmica do minério de ferro é a mais importante reação na fabricação do ferro, e tem sido obtida principalmente em Alto-Forno. Nos últimos anos, muitos processos novos foram propostos como alternativas e vários tipos de reatores foram testados. O processo mais promissor foi aquele em que a mistura minério de ferro e material carbonáceo eram aquecidos a altas temperaturas, promovendo a reação com formação do ferro metálico. Tornou-se claro que um dos principais obstáculos para a rápida reação é a transferência de calor da região externa para o centro da mistura. Por outro lado, muitos estudos têm mostrado que o aquecimento por microondas é muito efetivo em processos industriais, como secagem e sinterização de cerâmicos. No aquecimento por microondas, o material é aquecido a partir de seu interior, logo evita a obrigação de um aquecimento de fora para dentro do material. Neste trabalho, o aquecimento por microondas foi aplicado para a redução carbotérmica da hematita. Os resultados obtidos mostraram que é possível aquecer a mistura minério de ferro - carbono acima da temperatura de reação e que a taxa de reação é comparável à obtida por aquecimento convencional utilizando-se a mesma mistura.The carbothermic reduction of iron ores is the most important reaction in ironmaking, and has been performed mainly in the Blast Furnace. In the last years, several new processes have been proposed as alternatives, and many types of reactors have been tested. The most promising processes are those in which a mixture of iron ore and carbonaceous material is heated at high temperatures, promoting the reaction with formation of metallic iron. It became clear that one of the main obstacles to a fast reaction is heat transfer from the surroundings to the core of the mixture. On the other hand, several studies have shown that microwave heating is very effective in some industrial processes, like drying and sintering of ceramics. In the microwave heating, the material is heated from the inside, thus avoiding the constraints of heat transfer from the surroundings to the inner part of the material. In this work, microwave heating has been applied to the carbothermic reduction of hematite. The obtained results have show that it is possible to heat iron-carbon mixture above the reduction temperature, and the reaction rates have been compared to those obtained employing conventional heating with the same mixtures .
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CASTRO, ANGELA R. M. de. "Estudo e otimizacao do processo de obtencao de carbeto de boro por reducao carbotermca." reponame:Repositório Institucional do IPEN, 1989. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10216.
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Made available in DSpace on 2014-10-09T12:36:06Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T13:59:50Z (GMT). No. of bitstreams: 1 10924.pdf: 1837925 bytes, checksum: 94c2a732e0e9681748e33e1a4a0a7319 (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Castro, Edmilson Renato de. "Contribuição ao desenvolvimento da redução carbotérmica de óxidos metálicos empregando energia de microondas." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-18112009-083224/.
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O presente trabalho apresenta um equipamento para o processamento de reduções carbotérmicas sob campo de micro-ondas, permitindo pleno controle da potência fornecida e da medida da energia de micro-ondas efetivamente aplicada à carga em processo de redução podendo assim realizar balanços de energia e determinação de taxa de reação com altos níveis de confiança. O equipamento permite, sobretudo, a medida simultânea de temperatura e de massa do material sob redução, e a fácil reprodutibilidade das condições de ensaio. O protótipo opera com um gerador de micro-ondas de 2.45 GHz e potência variável até 3000 W. A amostra é mantida sob atmosfera de argônio. Nos testes operacionais do protótipo procedeu-se à redução carbotérmica de minério de ferro de Carajás, utilizando coque de petróleo como redutor através de pelotas esféricas com massa de 3,5 g e diâmetro de 15 mm. Obtiveram-se curvas cinéticas de redução de minério de ferro e de consumo de energia durante o processo. Os dados colhidos com este protótipo permitiram realizar uma análise da energia de micro-ondas efetivamente consumida na redução do minério.This work presents of a device for microwave enhanced carbothermic reductions which permits the full control of microwave power irradiated, the measurement of effectively applied microwave power to the charge in process thus performing a high confidence determination of rate of reaction and energy balance. In particular, the simultaneous records of its temperature and mass loss, and good reproducibility of operation parameters, are obtainable. This prototype works with a 2.45 GHz microwave generator with variable power up to 3000 W. Samples are processes under argon gas atmosphere. Operational tests for Carajás iron ore reduction with petroleum coke were performed using spherical pellets with weight of 3,5 g and diameter of 15 mm. Kinetic curves of iron ore reduction and effective consumption of microwave power curves were determined. These results made possible to perform an analysis of actual energy consumption for enhanced microwave iron ore carbothermic reduction.
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Mourão, Marcelo Breda. "Análise do processo de redução de minério de ferro por carbono na forma de pelotas auto-redutoras." Universidade de São Paulo, 1988. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-25072017-152106/.
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Através de revisão bibliográfica e estudo experimental, o presente trabalho apresenta uma análise da influência de diversos parâmetros sobre a velocidade da reação entre minério de ferro e carbono, aglomerados na forma de pelotas auto-redutoras. Os parâmetros estudados foram: temperatura, tipo e quantidade de redutor, uso de adições, composição e vazão dos gases no recipiente de reação, tamanho da pelota. A técnica experimental consistiu em medi-se a velocidade de reação por análise termogravimétrica, complementada por análise do gás de saída e difração de Raios-X em pelotas parcialmente reduzidas. Verificou-se que o mecanismo controlador da velocidade de reação é determinado por um conjunto de parâmetros inter-relacionados, e que pode mudar o progresso de reação. A etapa química da reação é controlada pela gaseificação do carbono por CO2. Transporte de calor e difusão gasosa através dos poros da pelota exercem forte influência sobre a velocidade; os fatores que favorecem a influência de transporte de calor são: aumento de temperatura; aumento da reatividade do redutor; uso de catalisador; diminuição do diâmetro da pelota; início de reação; redução sob atmosfera CO/CO2 de composição próxima ao equilíbrio wustitaferro. A influência de difusão gasosa se faz sentir quando a reação é efetuada sob atmosfera de gás inerte, que penetra nos poros da pelota, diluindo a atmosfera CO/CO2 reinante no interior da mistura de partículas. Nessas condições, esta influência é maior quanto menor for a temperatura de reação, quanto menos reativo for o redutor, quanto menor for a pelota, e nos estágios finais de reação. Verificou-se ainda que parâmetros relacionados à composição das pelotas, bem como a temperatura do processo, tem grande influência sobre o comportamento dimensional dos aglomerados.Assim, pelotas com ganga básica (com carvão vegetal e adições básicas) tendem a inchar catastroficamente, ao passo que pelotas com ganga ácida (com coque ou carvão mineral como redutores) não apresentam este fenômeno. Microscopia eletrônica de varredura indicou a presença de ferro filamentar em pelotas que apresentaram inchamento catastrófico. Analisou-se ainda como a presença de matéria volátil no redutor afeta a cinética de reação e o comportamento dimensional das pelotas, e também sob que condições o ferro formado na redução catalisa a reação.The factors that affect the rate of reaction between iron oxides and carbon were analysed by means of literature review and experimental investigation. The iron ore and the carbon were agglomerated in the form of self-reducing pellets. The investigated variables were: temperature, type and amount of redactor, presence of additives, gas composition and flow in the reactor vessel, and pellet\'s size. The experimental technique employed was thermogravimetric analysis, complemented by gas analysis and X-ray diffraction. It was shown that the rate control may change in the course of the reaction, and it depends on a number of interrelated varibles. The slowest reaction of the chemical step is the carbon gaseification by CO2. Heat transfer and gaseous diffusion through pellets pores play an important role in the rate; the factors that favours the heat transfer influence are: temperature increase, reducto\'s reactivity increase, the use of catalyst, pellet\'s size decrease, start up the reaction; reduction under CO/CO2 atmosphere near wustite-iron equilibrium. When the reaction is performed under inert gas atmosphere, gaseous diffusion through pellet\'s pores can dilute the CO/CO2 atmosphere prevailing in the pallet\'s core. Under these conditions, this effect is more pronounced for lower temperature, lower carbon reactivity, smaller pellets and at the end of the reaction. It was also found that variables related to pellet composition as well as process temperature greatly affect the pellet\'s dimensional behavior. In fact, pellets containing basic guangue (e.g.wood charcoal and/or basic additives) show catastrophic swelling; in contrast, pellets containing acid gangue (e.g. coke or coal) have good dimensional stability. Iron whiskers were observed with scanning electron microscope on pellets that swell catastrophically. The influence of reductor\'s volatile matter upon kinetics and dimensional behavior of pellets was also analysed as well as the catalysis of the reaction by the iron formed in the course of the reduction.
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ROCHA, JOSE C. da. "Estudo da influencia das caracteristicas do po de nitreto de silicio sobre a sinterabilidade e propriedades mecanicas do sinterizado." reponame:Repositório Institucional do IPEN, 1995. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10439.
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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Zambrano, Adolfo Pillihuaman. "Estudo da redução de pelotas auto-redutoras de cromita." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-04092006-165035/.
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Neste trabalho estuda-se o comportamento de redução para a obtenção da liga FeCrAC a partir da pelota auto-redutora feita de minério de cromita, coque de petróleo, ferro-silicio, cal hidratada, sílica e cimento portland ARI. As principais variáveis consideradas são: teor de redutor na composição da pelota, quantidade do redutor, temperatura e tempo. Inicialmente os materiais (cromita, ferro-silício, coque de petróleo, cal hidratada, sílica e cimento Portland ARI), foram caracterizados por: análise química e análise granulométrica. Após a caracterização os materiais (cromita, ferro-silício, coque de petróleo e cimento Portland ARI) foram aglomerados na forma de pelotas juntamente com cal hidratada e sílica para ajuste da basicidade quaternária da escória. A redução das pelotas foi feita num forno de indução que pode atingir temperaturas de até 1973K (1700oC). Todos os experimentos de redução foram realizados no aparato experimental utilizando-se cadinhos de grafite nas temperaturas de 1773K (1500oC), 1823K (1550oC) e 1873K (1600oC). Após os ensaios de redução os produtos obtidos (escória e metal) foram analisados por microscopia ótica, por microscopia eletrônica de varredura (MEV) e análise por EDS. O efeito do aumento da temperatura na redução da cromita é significativo. Houve aumento na velocidade de redução de 4 a 6 vezes com o aumento de 1773K (1500oC) para 1873K (1600oC). Os resultados indicam um efeito marcante de pequenas adições de Fe-Si na velocidade de redução da cromita. Na temperatura de 1773K (1500oC) as adições até ~2% de Fe-Si são benéficas e para adições maiores praticamente não há vantagens técnicas e econômicas. Os tempos necessários para atingir a fração unitária de redução foram 12, 7,5 e 5 minutos para adições de Fe-Si de 0, ~1%, e ~2%, respectivamente; a temperatura de 1823K (1550oC). À temperatura de 1873K (1600oC) as adições de Fe-Si na pelota apresentam também efeitos significativos na velocidade de redução, porém adições de ~1%, e ~2% mostraram os mesmos resultados, indicando que o teor ótimo de adição de Fe- Si na pelota deve estar em torno de 1%. Verificou-se que a utilização de pelotas auto-redutoras contendo 26% em excesso, sobre o estequiométrico, de coque de petróleo aumentou o rendimento de recuperação de Cr de 96% para 98%. O rendimento e a eficiência do processo de auto-redução supera aos processos convencionais de produção de FeCrAC, obtendo-se altas recuperações de cromo na faixa de 96% até 98% para Cr.The reduction behaviors, at high temperature, of the self-reducing pellets of chromites for production of high carbon ferro-chromium are studied in this work. The influences of the temperature, of the excess of reductant and the small addition of the Fe-Si were analyzed. The materials used (chromites, petroleum coke, Portland cement, hydrated lime and silica) were characterized chemically and by size distribution. The composite pellets (self-reducing) were produced aiming a quaternary basicity of 0.91. The reductant was calculated considering a stoichiometry of reduction and dissolution of 4wt%C in the final metallic phase. The reduction experiments were made in a special system, in argon atmosphere, heated by induction and at temperatures of 1773, 1823 and 1873K. The dried pellets were placed into a pre-heated graphite crucible and left there along up to no gas evolution was observed. The results of the reacted fraction with time were plotted and the obtained product (metallic and slag phases) after experiments were analyzed by optical and by electron micrograph. The chemical estimations were made by micro-analysis (EDS) The effect of increasing the temperature of reduction was sensitive, such that, the reduction rate increased 4 to 6 times with increase of temperature from 1773 to 1873. The small additions, up to 2% of Fe-Si, for substituting the equivalent fixed carbon of the petroleum coke showed to improve substantially the reduction rate, almost doubling it in comparison with pellets without any addition. The use of excess of 26%, over the stoichiometry, of the petroleum coke decreased around 50% of the chromium content in the slag, with relation to pellet without excess. The chromium recovery yield reached 98%. This result coupled with very high reduction rate of self-reducing pellets show the potential for self-reducing processes for ferro-chromium production.
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Castro, Edmilson Renato de. "Contribuição ao estudo da redução carbotérmica de minério de ferro empregando energia de micro-ondas." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-18012017-145505/.
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Com a proposta de selecionar a melhor conformação de um forno para redução carbotérmica com micro-ondas, dois tipos de cavidades com formatos paralepipédico e hexagonal foram projetadas e construídas. Os dois com uma característica em comum, o pleno controle da potência fornecida e da medida da energia de micro-ondas efetivamente aplicada à carga em processo de redução podendo assim realizar balanços de energia e determinação de taxa de reação com altos níveis de confiança. Eles permitem, sobretudo, a medida simultânea de temperatura e de massa do material sob redução, e a fácil reprodutibilidade das condições de ensaio. Os fornos paralepipédico e hexagonal operam com geradores de micro-ondas de 2,45 GHz e potência ajustável até 6 kW. Durante os ensaios as amostras foram mantidas sob atmosfera de argônio. Nos testes operacionais dos fornos procedeu-se à redução carbotérmica de minério de ferro de Carajás, utilizando carvão mineral Chipanga como redutor através de pelotas auto redutoras. Obtiveram-se curvas cinéticas de redução de minério de ferro, temperatura e de consumo de energia durante o processo. Os dados colhidos com estes fornos permitiram realizar análises estatísticas da eficiência de cada tipo de forno através da taxa de reação obtida além da energia de micro-ondas efetivamente consumida na redução do minério. Ainda, foi construído um forno cilíndrico, portanto extrapolando o formato hexagonal, com potência de 15 kW, com o objetivo de averiguar como o conjunto pelotas/cavidade se comporta em condições mais drásticas.This work deals with two different types of microwave cavities to be used in carbothermic reduction that were designed and built in order to select a better furnace conformation. Parallepipedic and hexagonal shapes were used for this purpose. Both of them share some common characteristics: full control of the power supplied to the furnace, and measurement of the effective microwave power applied to the load under reduction process. These characteristics help to achieve energy balance and reaction rate with high confidence levels. Simultaneous measurements of mass and temperature versus time are also easily done and helps reproduction of each test condition. The parallelepiped and hexagonal ovens are excited by 2.45 GHz microwave generators with adjustable power up to 6 kW. Argon gas atmosphere was used when processing the samples. Operational tests of the carbothermic reduction of iron ore from Carajás were done by the use of self-reducing pellets of Chipanga coal. Temperature and other data collected during the processes allowed calculation of their kinetic curves and energy consumption. The efficiency of each kind of furnace was obtained from statistical analysis of the data using reaction rate as well as the microwave energy consumption. Finally, going further from the hexagonal shape, a cylindrical furnace was built in order to verify the behavior of the pellets/cavity groups in heavier conditions with applied power up to 15 kW.
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Nogueira, Alberto Eloy Anduze. "Estudo da redução carbotérmica de minérios de ferro na forma de pelotas ou misturas autorredutoras em forno rotativo." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/3/3133/tde-06122010-135201/.
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A finalidade deste trabalho é estudar a redução carbotérmica de minério hematítico com misturas e pelotas autorredutoras em um forno rotativo experimental. Trabalhou-se com duas temperaturas, a 1673 e 1773 K (1400 a 1500 °C), em fluxo de argônio de 1Nl/min, em um forno rotativo experimental aquecido por resistências, com uma rotação fixa de 5 rpm. Foram realizadas diversas experiências, alterando variáveis como a temperatura, composição e quantidade da escória, tipo de redutor, e tipo de conformação. Foi estudado o tempo de residência das pelotas e misturas autorredutoras dentro do forno e sua interrelação com a inclinação do mesmo. Mediu-se a resistência a compressão de diferentes composições de pelotas. Foi analisada a fração de redução atingida nas experiências com ajuda de um método indireto proposto neste trabalho, atingindo-se frações de redução acima de 98%. Especial atenção foi dada para os casos limites estudados, o primeiro com uma mistura autorredutora de 81% de minério hematítico de baixo teor, 19% de coque de petróleo,+10% cimento ARI, processada a 1773 K (1500 °C) com 33% de escória final, a qual, apesar da grande quantidade de escória, atingiu uma fração de redução de 98,7%; e o segundo, para uma mistura autorredutora de 43,5% de minério hematítico de baixo teor, 56,5% de pó de serragem, processada a 1773 K (1500 °C), a qual atingiu uma fração de redução de 99,2%, provando, com as ressalvas cabíveis, a factibilidade de reduzir diretamente com pó de serragem. Com base nas observações experimentais sugeriram-se modelos do processo de redução-fusão tanto das misturas como das pelotas autorredutoras no forno rotativo. Analisaram-se a composição da escória e a composição da fase metálica obtida. Para comparar o grau de coalescimento entre as amostras, foram levantadas as análises granulométricas de cada uma delas, comparando-se as porcentagens em massa dos nódulos de ferro-carbono com diâmetro superior a 7,93 mm. Atenção especial foi dada ao método de desagregação do produto; pela ausência de normas técnicas especificas para processos autorredutores, foi empregada uma adaptação do método de desagregação por tambor (ASTM E279-95), e validada por moagem manual. Estudou-se o efeito das variáveis: temperatura de processamento, temperatura liquidus da escória, da quantidade de escória de alta temperatura liquidus, da quantidade de voláteis do redutor, da quantidade do redutor, e da ausência de conformação. Entre os resultados destas experiências tem-se que a maior temperatura de processamento leva a maior grau de coalescimento. Na medida em que a escória do sistema não se liquefaz, o processo de coalescimento é prejudicado. Na medida em que a quantidade de escória com alta temperatura liquidus aumenta, o grau de coalescimento decresce. Ao se aumentar a quantidade do redutor acima do necessário para a correta redução, carburação e colaescimento, prejudica-se o processo de formação dos nódulos de ferro-carbono. Ao se comparar o grau de coalescimento obtido entre as misturas e as pelotas autorredutoras, temse que o desempenho das misturas autorredutoras é superior. Para aclarar o efeito da temperatura liquidus da escória no processo de carburação e coalescimento, foram realizadas experiências paralelas para estudar como a temperatura liquidus da escória e a ausência do FeO afetava o coalescimento. Ao estudar o transporte de carbono pelas escórias sem e com a presença de um óxido redutível, tem-se que o transporte do óxido de ferro na escória sem agitação é um fenômeno difusivo.The purpose of this work is to study the carbothermal reduction of hematite ore as self-reducing mixtures or pellets in an experimental rotary kiln. Two different temperatures were employed, 1673 and 1773 K (1400-1500 ° C) in an experimental rotary kiln heated by resistors, with a fixed rotation of 5 rpm and under an argon flow of 1Nl/min. Several experiments were performed by changing variables such as temperature, composition and quantity of slag, type of carbonaceous material, and type of conformation. The residence time inside the furnace and its interrelation with the slope of the kiln containing self-reducing pellets or mixtures was studied. It was measured the compressive strength of pellets of different compositions. It has been analyzed the fractional reduction achieved in the experiments with the help of an indirect method proposed in this work, reaching fractional reduction above 98%. Special attention was given to some cases, the first one with a self-reducing mixture of 81% low grade ore, 19% petroleum coke, ARI +10%, processed to 1773 K (1500 ° C) with 33% final slag, which despite the large amount of slag reached a fractional reduction of 98.7%, and the second for a self-reducing mixture of 43.5% low-grade ore, 56.5% of sawdust processed to 1773 K (1500 ° C) which reached a fractional reduction of 99.2%, proving, with reasonable exceptions, the feasibility of reducing directly with sawdust. Based on experimental observations, process models of both the reduction-melting of self-reducing mixtures and pellets in the rotary kiln were proposed. The composition of slag and composition of the metallic phase obtained were analyzed. To compare the degree of coalescence between the samples, particle size analysis of each one was performed, comparing the percentages by weight of iron-carbon nuggets with a diameter greater than 7.93 mm. Regarding the method of disintegration of the product, due to the lack of technical standards for specific self-reducing processes, the drum method (ASTM E279-95) was adapted and validated by manual grinding. It was studied the effect of the following parameters: processing temperature, slag liquidus temperature, the amount of high liquidus temperature slag, amount of volatile matter of the reducing agent, the amount of reducing agent, and the absence of conformation. These experiments have shown that the higher the processing temperature, the greater the degree of coalescence, and also that as long as the slag does not melt, the coalescence process is impaired. As the amount of slag with high liquidus temperature increases, the degree of coalescence decreases. Increasing the amount of carbonaceous material above to that necessary to reduction and carburization undermines the process of formation of iron-carbon nuggets. When comparing the degree of coalescence obtained between the self-reducing mixtures and pellets, it has been shown that the performance of self-reducing mixtures is superior. To clarify the effect of the slag liquidus temperature in the carburization and coarsening process, experiments were conducted to study how the liquidus temperature of the slag and the absence of FeO affected the coarsening. By studying the transport of carbon in slags with and without the presence of a reducible oxide, it has been shown that the transport of iron oxide in the slag without agitation is a diffusive phenomenon.
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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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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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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.
Full textAbstract:
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.
49
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.
Full textAbstract:
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.
50
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.
Full textAbstract:
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% .