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1
Bellina, Paul J. "High-temperature oxidation of bulk RuAl alloy." Stuttgart Max-Planck-Inst. für Metallforschung, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?idn=980343135.
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Kim, Bae-Kyun. "High temperature oxidation of low carbon steel." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19519.
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The quality of steel may be seriously affected by the surface defects that appear on slab surfaces after hot rolling. These defects are related to iron oxidation and, in order to reduce the occurrence of these defects, it is necessary to better understand the formation of iron oxides during high temperature oxidation and the oxide descaling mechanisms. However, systematic research tools and experimental strategies for addressing these issues have not yet been developed. In addition, the mechanisms of oxide cracking and failure have not been understood. In this thesis, research tools and strategies are proposed for studying the high temperature oxidation of low carbon steels. These tools allow the presentation of new data on the phase composition of iron oxides at elevated temperature, characteristics of iron oxide formation, oxide microstructure and texture, oxide defects, and stress distributions in different oxide layers, as well as residual stresses. The microscopic model that was proposed for description of oxide failure allows better understanding of the mechanism for surface defect formation during hot rolling. To describe the dynamics of phase composition changes in textured oxides at elevated temperature, a new phase analysis method is proposed. This x-ray diffraction phase analysis is based on the Rietveld and Dickson's methods, and is used for investigating the effect of alloying elements on the oxidation process. This method was also adopted to track in-situ phase composition changes during high temperature oxidation of commercial low carbon steels. The structure of oxides on low carbon steels, pure iron, and Si-steels was systematically examined by orientation imaging microscopy (OIM). It is demonstrated that OIM can be an invaluable tool for visualizing the oxide microstructure texture and studies of oxide defects. In order to simulate industrial hot rolling of oxidized steel sheet, high temperature oxidations tests were made in the tube furnace up to 950°C, in air. The oxidation process and microstructure development were described using OIM maps including image quality (IQ) and inverse pole figure (IPF) maps. The three different iron oxides phases could be distinguished and the characteristics of oxides with different oxidation histories were compared. Iron oxides developed during high temperature oxidation consisted of wustite (FeO), magnetite (Fe304), and hematite (Fe20s) structures with varying texture, grain shape and size. In order to understand the mechanical properties of iron oxides, residual stresses in the three iron oxides phases were assessed using a specially designed x-ray stress measurement system. The stress distributions in the oxide layers were also simulated using finite element simulation of the hot rolling process.
3
Arnold, Ramsey Paul. "Silicon carbide oxidation in high temperature steam." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/76940.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 119-123).
The commercial nuclear power industry is continually looking for ways to improve reactor productivity and efficiency and to increase reactor safety. A concern that is closely regulated by the Nuclear Regulatory Commission is the exothermic zircaloy-steam oxidation reaction which can potentially occur during a loss of coolant accident (LOCA), and may become autocatalytic beyond 1,200 0C, thus generating a large amount of hydrogen. The concern for the zircaloy oxidation reaction has been heightened since the March 2011 events of Fukushima, Japan. One solution offering promising results is the use of silicon carbide (SiC) cladding in nuclear reactor fuel rod designs. SiC, a robust ceramic which reacts very slowly with water or steam, has many features that meet or exceed that of zircaloy including the ability to withstand higher temperatures due to a higher melting point and the ability to absorb fewer neutrons than zircaloy which would allow for increased safety margins and fuel burnup. An experimental investigation of the oxidation performance of a-SiC during a postulated LOCA event was performed. The test facility was designed and fabricated to test the oxidation rates of zircaloy and SiC in a high temperature, high-purity, flowing steam environment. Studies of zircaloy-4 oxidation were conducted to validate the test facility for this purpose. Thirty six zircaloy-4 tests lasting up to 30 minutes, at temperatures ranging from 800°C to 1,200°C, were completed and compared to existing models and literature data. Additionally, six longer duration a-SiC tests lasting from 8 hours to 48 hours, at temperatures of 1,140°C and 1,200°C, were completed. These tests clearly show that, from an oxidation perspective, SiC significantly outperforms zircaloy in high-flowing, superheated steam. For zircaloy, results from the most intense temperature/duration testing combination of 1,200°C for 30 minutes show 15.6 percent weight gain. For the most intense SiC tests at 1,200°C for eight hours, a weight loss of two orders of magnitude less occurred, a 0.077 percent weight loss. The four 24 hour and 48 hour SiC tests at 1,140°C also correlate well with the expected paralinear oxidation trend and further confirm that SiC is more resistant to oxidation in high temperature steam than zircaloy.
by Ramsey Paul Arnold.
S.M.
4
Holcomb, Gordon Randolph. "The high temperature oxidation of hafnium-carbide /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487596807821735.
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Marsh, M. G. "The effect of a temperature gradient on high temperature fretting wear." Thesis, University of Nottingham, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267625.
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Okano, Terumi. "High temperature mercury oxidation kinetics via bromine mechanisms." Worcester, Mass. : Worcester Polytechnic Institute, 2009. http://www.wpi.edu/Pubs/ETD/Available/etd-012509-223212/.
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Arnold, K. "High temperature oxidation behaviour of nickel-base superalloys." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3005778/.
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The Ni-base superalloys are a popular range of materials for study following consolidation by additive manufacturing (AM) techniques, such as selective laser melting (SLM). However, very little work has been done to assess the high temperature oxidation behaviour of Ni-base superalloys fabricated by SLM, despite the fact that this class of alloy is designed primarily for operation at temperatures >650°C. In the present work, the isothermal oxidation behaviour of the Ni-base superalloys Alloy 718 and Alloy 625 was studied following consolidation by SLM. A third Ni-base superalloy, Haynes 230, which is doped with a small amount of the reactive element La, was also studied following SLM-consolidation. The same three alloys were studied in wrought form for comparison purposes. Also studied following consolidation by SLM were oxide dispersion strengthened (ODS) derivatives of Alloy 625 and Haynes 230, which contained a 0.5 Wt. % addition of Y2O3, added by mechanical alloying (MA), and developed during the project for which the present work was conducted. Comparators for the ODS variants of Alloy 625 and Haynes 230 were fabricated by spark plasma sintering (SPS). All of the alloys were oxidised in laboratory air at 900°C and the oxidation kinetics determined using thermogravimetric analysis (TGA), or from scale thickness measurements. The work has shown that SLM-consolidated Alloy 718 oxidised slightly faster than wrought Alloy 718. SLM-consolidated Haynes 230 oxidised ~3x faster than wrought Haynes 230 alloy, but SLM-consolidated Alloy 625 oxidised ~2x slower than wrought Alloy 625. The ODS variant of Alloy 625, in SLM-consolidated and SPS-consolidated forms, oxidised ~10x more slowly than wrought Alloy 625. The SLM-consolidated ODS variant of Haynes 230 oxidised at approximately the same rate as wrought Haynes 230, but in SPS-consolidated form the ODS variant of Haynes 230 oxidised ~10x faster than wrought Haynes 230. The improvement in the oxidation resistance of the ODS variant of Alloy 625 is attributed to the well-known reactive element effect, which occurs when alloys are appropriately doped with reactive elements. The reduction in the oxidation resistance of the SPS-consolidated ODS variant of Haynes 230 is attributed to overdoping of the alloy with reactive elements, which is known to decrease the oxidation resistance of nickel-base alloys. It is proposed that SLM-consolidation improves the oxidation resistance of the ODS variant of Haynes 230 by ‘slagging off’ reactive elements from the alloy during consolidation, but for the same reason, the oxidation resistance of Haynes 230 is reduced by SLM-consolidation.
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Ooi, Thian Ngan. "High temperature oxidation of platinum aluminide coated CMSX-4." Thesis, Imperial College London, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444569.
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Daloz, William. "Developing a high temperature, oxidation resistant molybdenum-silica composite." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54375.
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A new powder processing approach to produce oxidation resistant molybdenum alloys for high temperature use has been developed. Oxidation protection is provided by fine dispersion of silica glass particles within a molybdenum matrix. As the molybdenum oxidizes, the glass is exposed and melts to form a self-healing protective oxide coating. Additionally, homogeneously dispersed Mo5SiB2 and/or Mo2B provide boria upon oxidation which reduces glass viscosity and allows flowing glass to coat the surface while remaining solid internally. This is similar to the oxidation protection used in Mo-3Si-1B (wt%) systems; however embedding the glass directly into the Mo matrix and eliminating the Mo3Si (A15) phase provides the same volume of glass at lower volume fractions of brittle phases and also without embrittling Si impurities in solution in Mo. Additionally the glass composition can be tailored for different applications and different temperatures beyond that achievable in Mo-Si-B based systems. A variety of microstructures, compositions and additional components for improved oxidation protection are also explored, and mechanisms of the oxidation protection are discussed.
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Miller-Oana, Melia. "Oxidation Behavior of Carbon and Ultra-High Temperature Ceramics." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/605121.
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Hypersonic vehicles require material systems that can withstand the extreme environment they experience during flight. Carbon-based materials and ultra-high temperature ceramics are candidates for materials systems that will protect hypersonic vehicles. In order to study the material response, an oxyacetylene torch facility and thermal gravimetric analysis are used to investigate the gas-solid interactions under conditions that simulate aspects of flight. The oxyacetylene torch facility is characterized as a function of position from the tip for heat flux and oxygen content. By understanding the local heat flux and oxygen conditions, experiments are designed so that graphite ablation rates can be measured as a function of heat flux and partial pressure of oxygen. Further investigation shows that composition of the material influences the temperature response where ultra-high temperature ceramics exhibit the lowest surface temperatures. Using thermal gravimetric analysis, the isothermal oxidation behavior of ultra-high temperature ceramics from 1000-1600°C is investigated using a Dynamic Non- Equilibrium method in order to understand the reaction kinetics of ZrB₂-SiC where parabolic rate constants are determined. Isothermal oxidation behavior is compared to non-isothermal mass gain and oxide scale formation where specimens oxidized isothermally gain 3 times more mass and have oxide scales 4 times as thick. Finally, the effect of SiC content in ZrB₂ on temperature during oxyacetylene torch testing is determined. Increasing the amount of SiC results in lower front face temperatures because more heat is absorbed due to the endothermic reactions of evaporation of SiO₂.
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Devkate, Pushkar. "High temperature oxidation of HSLA steel under vapor conditions." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-80125.
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Hallum, Gary W. "High temperature effects of oxidation on MgO-SiC composites /." The Ohio State University, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487678444258932.
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Moricca, Maria del Pilar. "High temperature oxidation characteristics of Nb-10W-XCr alloys." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Ekström, Madeleine. "Oxidation and corrosion fatigue aspects of cast exhaust manifolds." Doctoral thesis, KTH, Mekanisk metallografi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-166274.
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Emission regulations for heavy-duty diesel engines are becoming increasingly restrictive to limit the environmental impacts of exhaust gases and particles. Increasing the specific power output of diesel engines would improve fuel efficiency and greatly reduce emissions, but these changes could lead to increased exhaust gas temperature, increasing demands on the exhaust manifold material. This is currently the ferritic ductile cast iron alloy SiMo51, containing about 4 wt% Si and ~1 wt% Mo, which operates close to its fatigue and oxidation resistance limits at peak temperature (750C). To ensure high durability at higher temperatures, three different approaches to improving the life of exhaust manifolds were developed in this thesis. The first approach was to modify SiMo51 by adding different combinations of Cr and Ni to improve its high-temperature strength and oxidation resistance, or by applying a thermal barrier coating (TBC) to reduce the material temperature and thereby improve fatigue life. In the second approach, new materials for engine components, e.g. austenitic ductile iron and cast stainless steel, were investigated for their high-temperature fatigue and oxidation properties. In order to identify the most suitable alloys for this application, in the third the environmental effects of the corrosive diesel exhaust gas on the fatigue life of SiMo51 were investigated. The high-temperature oxidation resistance of SiMo51 at 700 and 800C in air was found to be improved by adding Cr, whereas Ni showed adverse effects. The effects of solid-solution hardening from Ni and precipitation hardening from Cr were low at 700C, with improvements only at lower temperatures. Applying a TBC system, providing thermal protection from a ceramic topcoat and oxidation protection from a metallic bond coat, resulted in only small reductions in material temperature, but according to finite element calculations still effectively improved the fatigue life of a turbo manifold. Possible alternative materials to SiMo51 identified were austenitic cast ductile iron Ni-resistant D5S and austenitic cast stainless steel HK30, which provided high durability of exhaust manifolds up to 800 and 900C, respectively. Corrosion fatigue testing of SiMo51 at 700C in diesel exhaust gas demonstrated that the corrosive gas reduced fatigue life by 30-50% compared with air and by 60-75% compared with an inert environment. The reduced fatigue life was associated with a mechanism whereby the crack tip oxidized, followed by crack growth. Thus another potential benefit of TBC systems is that the bond coat may reduce oxidation interactions and further improve fatigue life. These results can be used for selecting materials for exhaust applications. They also reveal many new research questions for future studies. Combining the different approaches of alloy modification, new material testing and improving the performance using coatings widened the scope of how component life in exhaust manifolds can be improved. Moreover, the findings on environmental interactions on SiMo51 fatigue provide a completely new understanding of these processes in ductile irons, important knowledge when designing components exposed to corrosive environments. The novel facility developed for high-temperature corrosion fatigue testing can be useful to other researchers working in this field.QC 20150507
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Andrews, Paul. "The high temperature oxidation of a silicon nitride based material." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235596.
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Lamkin, Michael Alan. "The high-temperature oxidation and corrosion of a silicon nitride." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.277876.
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Rizzi, M. "HIGH TEMPERATURE OXIDATION PHENOMENA'S STUDY OF HIGH ALLOYED MATERIALS FOR POWER GENERATION PLANTS." Doctoral thesis, Università degli Studi di Milano, 2012. http://hdl.handle.net/2434/168364.
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The aim of the doctorate project is the study of the corrosion and oxidation behavior of some commercial and more recent SS and Ni based alloys for high temperature applications in order to verify their possible use either at operative conditions higher than conventional (temperature up to 900°C) or in different environment (oxygen, air, carburizing atmospheres).
During the first year, the following aspects were investigated:
- Microstructural characterization of solution annealed AISI 310N, 347HFG and 304 HCu (the latter supplied also in the shoot peened condition) was carried out. An homogeneous austenitic fine grain structure accompanied with Nb segregation was observed for 347HFG and 304HCu. In the case of 310N the grains were coarser and the presence of Si segregation were randomly detected beside Nb.
- Microhardness profiles (HV50) were conducted to evaluate the penetration effects of shoot peening treatment at depths as high as 150-200 m.
- Discontinuous oxidation testing were performed at temperatures in the range of 700-900°C under 15 Nm3/h flowing moist air atmosphere for 7 days. The preliminary results seem to confirm an oxidation susceptibility in the following order: 310N<347HFG<304HCu.
During the second year, the following activities have been carried out:
- Oxidation kinetic study (thermogravimetric tests) of as received AISI 310N, 347HFG, 304HCu and Alloy 617 in oxygen atmosphere at 900°C; 310N, 347HFG and Alloy 617 show a protective oxidation kinetic, while 304HCu suffers from spalling.
- Investigation of grown oxide layer nature of all SS by microscopic techniques revealed an average oxide thickness in the range of 5 – 15 m for 347HFG; about 5 m until spallation for 304HCu and less than 5 m for 310N. In the case of 347HFG a three layer oxide was clearly detected consisting of a first layer of Cr oxides followed by a mixed Fe and Cr oxide and finally an external layer of FeOx. For 310N only a Cr oxide layer was detectable; for 304HCu the layer being essentially Fe-Cr oxides. Result confirmed also by GDOES.
- Study of the electrochemical behaviour of as received and oxidized SS specimens by means of polarization curves. All “as received” specimens exhibit a similar passive behaviour in terms of both potentials and current densities, apart the point corresponding at the critical passive current (icr). For oxidized specimens a statistical approach should be followed.
During the third year, in addition to the accomplishment of the previous topics, new electrochemical approaches were tested during a period spent by the candidate following Dr. Digby Macdonald's research labs at The Pennsylvania State University. Activities were focused on the passivity study of 347HFG stainless steel. Starting from the results of the potentiodynamic studies, an electrochemical impedance spectroscopy procedure was setted up; results were optimized by applying the “point defect model” developed by the same Dr. Macdonald revealing kinetic parameters of the passive layer and is semiconductive nature that is essentially n-type for all anodic potential values except near the breakdown in which assume a p-type character.
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Knafelc, Joseph. "High temperature oxidation experiments of olivine with implications for mantle magnetism." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1893.
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Mantle xenoliths have been used to interpret the magnetic characteristics of the lithospheric mantle because their rapid rate of ascent to the surface does not allow enough time for alteration. Studies of mantle xenoliths have suggested that magnetite in the mantle contributes to long wave length magnetic anomalies over areas of suppressed geothermal gradients (cratons, forearcs). Magnetite will only form in oxidizing conditions. This leads to a debate if mantle xenoliths become altered through oxidation to form magnetite in the mantle before ascent, during ascent (decompression), or after ascent at the surface. Natural and experimental occurrences of magnetite forming as inclusions or dislocations in fosterite from Fe-impurities suggest that oxidation of olivine is a mechanism for magnetite formation in the mantle. To test this, high olivine samples were placed into a furnace at 600C and 900C in free air at 1bar of pressure, removing samples at different time increments ranging from 0.2 to 625 hours. These temperatures were used because they represent mantle like temperatures in oxidizing conditions. After oxidation, samples from the 900C experiment show evidence for magnetite/hematite formation after only 0.2 hours and the amount of Fe-oxide formation increases with time. Samples from the 600C experiment show significant alteration and Fe-oxide formation after 125 hours. These results suggest that it is possible for magnetite to form from the Fe in the fayalite component of fosterite in the mantle from oxidizing event such as metasomatism.
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Chess, P. M. "A study of the high temperature oxidation behaviour of aluminised steel." Thesis, Bucks New University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.373579.
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Gould, Peter John. "The high temperature oxidation of chromium and chromium implanted with cerium." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46790.
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Mohammad, F. Z. "Novel oxidation protection system for carbon-carbon composites at high temperature." Thesis, Cranfield University, 2005. http://dspace.lib.cranfield.ac.uk/handle/1826/11433.
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Carbon-carbon composite materials have been identified as one of the most
potential materials for light weight and high temperature applications. Mechanical
properties of carbon-carbon composites do not degrade even at temperature as high as
2000°C. However the main problem in their use in high temperature oxidizing
environment is their tendency to oxidize at temperatures of 400°C and above. Therefore
some oxidation protection mechanism is mandatory to make these materials available for
high temperature applications.
It is the purpose of the current research to develop a viable high temperature
oxidation protection system for carbon-carbon composites. It has been shown that such a
coating system must have at least two layers; a gradient porous SiC layer aimed to
redistribute the stress produced due to CTE (coefficient of thermal expansion) mismatch
and a dense top layer of a suitable material meant to protect carbon-carbon composite
substrate from oxidation. Materials for the top layer experimented during the current
research were SiC, ShN4 and HfC. Pack cementation technique was used to develop the
gradient SiC layer while top dense layers were deposited by using the reactive sputtering
technique. To improve the oxidation protection and crack resistance of the top dense
coating multilayering approach was adopted.
During the current research basically four different coating systems were
produced, characterized and then tested at high temperature for their oxidation
performance. These coating systems were, gradient SiC layer plus dense sputtered SiC
layer, gradient SiC layer plus dense sputtered ShN 4 layer, gradient SiC layer plus dense
sputtered SiC/ShN 4 layers, gradient SiC layer plus dense sputtered SiClHfC layers.
Oxidation testing of these coatings in atmosphere showed that these coatings are
thermodynamically stable at all test temperatures studied (1300-1575°C), except coatings
with a ShN 4 layer. ShN4 becomes thermodynamically unstable at 1575°C. These coatings
remained mechanically stable (no spallation) except the coatings with HfC layers.
Coatings with HfC layers spalled off at all temperatures. Investigation into the causes of
spallation indicated that the thickness (20-25 flm) of the converted SiC gradient layer was
insufficient, plus the processing conditions during the deposition of HfC were the main
causes for their failure.
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Kakarlapudi, Purushotham Raju. "High temperature oxidation response of Nb-20W-10Cr alloy in air." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2008. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Ventura, Julieta Angelica. "High temperature oxidation behavior of Nb-20Mo-15Si-5B-20Cr alloy." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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JACOB, YVAN PIERRE. "A pre-normative research on the isothermal and cyclic oxidation high temperature oxidation behaviour of chromium." Clermont-Ferrand 2, 2001. http://www.theses.fr/2001CLF22279.
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De nombreux parametres experimentaux intervenant lors de l'oxydation du chrome a haute temperature ont ete etudies afin de comprendre leurs effets sur la croissance et l'integrite de la couche de chromine qui se forme lors de cette oxydation. Hormis les techniques classiques utilisees pour l'etude de l'oxydation a haute temperature, nous nous sommes servis de la methode d'activation nucleaires des couches minces (tla) permettant de quantifier les pertes eventuelles d'oxyde par ecaillage lors d'oxydations isothermes ou cycliques. Le but de ce travail, par l'etude systematique de differents parametres, est de servir de reference et de permettre une comparaison et une traduction correcte des resultats provenant de differentes etudes. Nous avons montre que l'oxydation isotherme du chrome suit un regime parabolique avec une fracturation periodique de la chromine due a une nitruration du metal (diffusion d'azote dans le metal). En cyclage, a 1000\c, nous avons detecte un decollement de l'oxyde principalement dans les angles des echantillons. Nous avons egalement mis en evidence le role benefique du si et negatif du c (present sous forme d'impuretes) sur l'oxydation. En atmosphere humide, l'oxygene de la vapeur d'eau participe a la formation de la chromine. Enfin, nous avons observe que la diffusion aux joints de grains de l'oxyde augmente en presence d'azote et/ou de vapeur d'eau. Plus la frequence de cyclage est faible et plus nous avons un ecaillage important de l'oxyde du a une accumulation des contraintes de croissance. Les echantillons de petites dimensions montrent des decollements proportionnellement plus important lors d'oxydations cycliques a 1000\c. Nous avons egalement montre que la preparation de la surface n'a pas d'effet sur le mecanisme et la vitesse d'oxydation. Enfin l'yttrium implante a un effet benefique uniquement a 800 et 900\c en limitant la prise de masse, la diffusion d'azote et la fracturation de la couche.
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Walker, Luke Sky. "Processing of Ultra High Temperature Ceramics." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228496.
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For hypersonic flight to enable rapid global transport and allow routine space access thermal protection systems must be developed that can survive the extreme aerothermal heating and oxidation for extended periods of time. Ultra high temperature ceramics (UHTCs) are the only potential materials capable of surviving the extreme hypersonic environment however extensive research in processing science and their oxidation properties are required before engineering systems can be developed for flight vehicles. Investigating the role of oxides during processing of ultra high temperature ceramics shows they play a critical role in both synthesis of ceramic powders and during densification. During spark plasma sintering of UHTCs the oxides can result in the formation of vapor filled pores that limit densification. A low temperature heat treatment can remove the oxides responsible for forming the vapor pores and also results in a significant improvement of the densification through a particle surface physical modification. The surface modification breaks up the native continuous surface oxide increasing the surface energy of the powder and removing the oxide as a barrier to diffusion that must be overcome before densification can begin. During synthesis of UHTCs from sol-gel the B₂O₃ phase acts as the main structure of the gel limiting the transition metal oxide network. While heat treating to form diborides the transition metal oxide undergoes preferential reduction forming carbides that reduce B₂O₃ while at high temperature encourage particle growth and localized extreme coarsening. To form phase pure borides B₂O₃ is required in excessive quantities to limit residual carbides, however carbide reduction and grain growth are connected. When the UHTC systems of ZrB₂-SiC are exposed to oxidation, either as dense ceramics or coatings on Carbon-Carbon composites, at high temperatures they undergo a complex oxidation mechanism with simultaneous material transport, precipitation and evaporation of oxide species that forms a glass ceramic protective oxygen barrier on the surface. The composite effect observed between the oxides of ZrB₂-SiC enables them to survive extreme oxidizing environments where traditional SiC oxidation barrier coatings fail.
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Harrington, M. T. "Oxide growth on ferritic stainless steels exposed to high temperature steam." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233277.
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Sukdeo, Preeyanand. "CFD simulation of nuclear graphite oxidation / P. Sukdeo." Thesis, North-West University, 2010. http://hdl.handle.net/10394/4231.
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This study investigates the development of a strategy to simulate nuclear graphite oxidation with
Computational Fluid Dynamics (CFD) to determine an estimate of graphite lost.
The task was achieved by comparing the results of the CFD approach with a number of different
experiments. For molecular diffusion, simulated results were compared to analytical solutions.
Mass flow rates under conditions of natural convection were sourced from the 2002 NACOK
experiment. Experimental data from the KAIST facility were sourced for the basic oxidation of
graphite in a controlled environment. Tests included the reactions of carbon with oxygen and
with carbon dioxide.
Finally, the tests at NACOK from 2004 and 2005 were chosen for comparison for the simulation
of oxidation. The 2005 test considered two reacting pebble bed regions at different
temperatures. The 2004 test included multiple detailed structural graphite.
Comparison of results indicated that the phenomenon of diffusion can be correctly simulated.
The general trends of the mass flow rates under conditions of natural convection were obtained.
Surface reaction rates were defined with user functions in Fluent. Good comparisons of the
simulated and the KAIST experimental results were obtained.
For the 2005 NACOK comparison, the pebble bed regions were simulated with a porous
medium approach. Results showed that correct trends and areas of oxidation were estimated.
The 2004 tests were with a combination of a porous medium and surface reaction approaches.
More detailed oxidation experimental data would possibly improve the accuracy of the results.
This research has shown that the CFD approach developed in the present study can identify
areas of maximum oxidation although the accuracy needs to be improved. Both the porous and
detailed surface reaction approaches produced consistent results. The limitations of the
approach were discussed. These included transient phenomena which were estimated with
steady state simulations, and the effects of change in geometry were not considered.Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2010.
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Duncan, Julia Carmel. "The effect of nitrogen, niobium and temperature of the high temperature oxidation of titanium aluminide alloys." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/49663.
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Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Includes bibliographical references (leaves 237-247).
This is especially attractive for reducing the engine weight and increasing the thrust/weight ratio. Increasing the operating temperature and thereby the engine efficiency has approached the maximum possible operating temperature for currently used materials. A model set of three intermetallics -- unalloyed [gamma]-TiAl, unalloyed [alpha]-Ti 3Al and a nearly stoichiometric Ti2NbAl (an orthorhombic intermetallic structure) -- was chosen and investigated under a variety of experimental conditions. Gas mixtures of varying oxygen concentrations in both argon and nitrogen allowed the effect of oxygen concentration on oxidation kinetics to be investigated. The Ti 2NbAl-alloy was specifically chosen to examine the effect of Nb in a intermetallic compound (with Nb substituting for one Ti in the Ti 3Al intermetallic structure). This is in contrast to Nb as a simple alloy addition to y-TiAl or c 2-Ti 3Al. Exposures at temperatures of 700°C and 800°C for 20 and 100 hours were studied (compared to temperatures of 900°C or higher used by other investigators), since these temperatures promoted a more protective scale. Additionally, the scale composition is sensitive to temperature and restricts the conventional practice of corrosion study acceleration by raising the experimental temperature. The resulting corrosion scales were analyzed using electron microscopy (scanning and transmission), x-ray diffraction and thermogravimetric analysis. The effect of nitrogen in the gaseous environment was explored. The impact of Nb on the oxidation of the intermetallics was found to be more protective than what might be expected from examining the thermodynamics and kinetics of the Ti-Al-Nb-O-N system. At times an alternating layered scale structure resulted and the effect of N, Nb and the lower temperatures used in this study is summarized. The oxidation rate of the Ti 2NbAl-alloy fell between the rates for y-TiAl and c 2-Ti 3Al, with the scale on y-TiAl growing at the slowest rate of the three compositions. However, the superior mechanical properties of Ti2 NbAl-alloy combined with the acceptable corrosion resistance promote its consideration for replacing those portions of the engine operating at intermediate temperatures that would result in significant weight and cost savings.
by Julia Carmel Duncan.
Sc.D.
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Segura-Cedillo, Ismael. "Fused metallic slurry coatings for improving the oxidation resistance of wrought alloys." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/fused-metallic-slurry-coatings-for-improving-the-oxidation-resistance-of-wrought-alloys(afb1e478-980c-422c-b6da-25e15c03e6b2).html.
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The aim of this project was to investigate the potential of fused-slurry coatings for improving the oxidation resistance of wrought alloys. Slurry-aluminised coatings were deposited on Alloy 800H (Fe-33Ni-20Cr), Alloy HCM12A (Fe-12Cr-2W), Alloy 214 (Ni-16Cr-4Al-3Fe), Fe-27Cr-4Al and Fe-14Cr-4Al alloys. The slurry contained a cellulose-based binder in an aqueous carrier and spherical aluminium powder, with a particle size below 20 microns. The slurries were applied with a paint-brush, dried in air and heat treated in either hydrogen or argon at temperatures between 700 and 1150C. The slurries were characterised by thermogravimetry, differential scanning calorimetry and viscometry. The coatings were characterised by optical microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, X-ray diffraction and Vickers hardness measurements. The oxidation resistance of selected slurry-coated specimens was assessed in air at 1000 and 1100C in tests lasting up to 1000 hours.Slurry-aluminising was found to be a simple, effective way of forming protective coatings that were similar in composition and microstructure to chemical vapour deposits. However, it was difficult to control the amount of slurry applied to the substrate and produce coatings of uniform thickness.The coatings on Alloy HCM12A and the Fe-Cr-Al alloys contained cracks in the brittle FeAl phase due to tensile stresses arising from differences in the thermal expansion coefficients of the substrates and the coatings. Rapid interdiffusion between the coatings and the ferritic substrates resulted in the appearance of Kirkendall voids.Coatings on Alloy 214 required a two-stage heat treatment to convert the brittle δ-Ni2Al3 to β-NiAl. Cracking along the coating/substrate interface was prevented by limiting the coating thickness to a maximum of 250 microns. During oxidation at 1100C, the β-NiAl was converted to γ'-Ni3Al. After 1000 h, the centre of the coating consisted chiefly of γ'-Ni3Al and bands of austenite (γ-Ni) were present at the inner and outer edges of the coating. The aluminium content at the coated surface was higher than the original aluminium content of the alloy, the protective alumina scale was improved and the oxidation life of the substrate was extended. An additional life of 1250 h at 1100C is estimated from a slurry coating before the aluminium content returns to that of the original alloy (4%), providing a potential improvement in oxidation resistance.Microstructural changes such as grain growth, sensitisation and formation of aluminium nitride particles near the coating/substrate interface, were detected in the alloy substrates after forming the slurry coatings. However, these microstructural changes did not detract from the good performance of the coatings during oxidation tests at 1100C.The work in this study has demonstrated a low-cost method of coating high-temperature alloys providing coatings with microstructures, densities and modes of degradation similar to those obtained by other coating methods. The coatings are potentially applicable to a wide range of high-temperature substrates.
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Lukaszewicz, Mikolaj. "Steam oxidation of advanced high temperature resistant alloys for ultra-supercritical applications." Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/7917.
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Steam oxidation of heat exchanger tubing is of growing interest as increasing the efficiencies of conventional pulverised fuel fired power plants requires higher steam temperatures and pressures. These new, more severe steam conditions result in faster steam oxidation reactions, which can significantly reduce the lifetime of boiler components. This thesis reports results from an investigation of the steam oxidation of the high temperature resistant alloys. It covers an analysis of the impact of temperature, steam flow rate, specimen shape and specimen surface finish on oxidation of resistant materials. Additionally, the mechanism of steam oxidation was invastigated with the oxygen 18 water. The results show that an increased steam flow rate not only causes faster oxidation rates but also a change in oxide scale morphology. In case of T23, it triggers formation of micro-layered inner oxide, whereas for T92 it promotes the formation of an outer haematite layer. For austenitic steels, the faster steam flow increases the formation of initially protective oxide scales, but also accelerates the growth of oxide nodules with prolonged exposure times. The analysis of the different surface finishes show that clearly the change of the surface finish from ground to polish and pickled (as received) accelerates the oxidation process for austenitic steels, the ground specimens show the slowest oxidation, whereas the pickled specimens oxidise much faster and form thicker scales. Finally, the study of oxidation mechanism show that steam oxidation is not only controlled by the inner diffusion of the oxygen ions but the diffusion of the hydroxides have a significant impact on oxides formation. The results of the study suggest that the hydroxide ions influence formation of the inner oxides.
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Cisloiu, Cezar. "High temperature stress accerated grain boundary oxidation mechanism on INCONEL 783 superalloy." Morgantown, W. Va. : [West Virginia University Libraries], 2001. http://etd.wvu.edu/templates/showETD.cfm?recnum=1907.
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Thesis (M.S.)--West Virginia University, 2001.Title from document title page. Document formatted into pages; contains vii, 64 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 62-64).
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THANNEERU, RANJITH. "VACANCY ENGINEERED DOPED AND UNDOPED NANOCRYSTALLINE RARE EARTH OXIDE PARTICLES FOR HIGH TEMPERATURE OXIDATION RESISTANT COATING." Master's thesis, University of Central Florida, 2007. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/3986.
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Rare earth oxides with trivalent lattice dopants have been of great interest to researchers in the recent years due to its potential applications in catalysis and high temperature protective coatings. The ability to store oxygen in rare earths is the basis for catalysis because of the ability to change valence states which causes the presence of intrinsic oxygen vacancies in the crystal lattice. Although, several doped-rare earth oxide systems in micron scale have been investigated, the doping effect in cerium oxide nanoparticles with well characterized particle size has not been studied. The doping of ceria at that small size can be very beneficial to further improve its catalytic properties and alter the high temperature phases in alloy systems. Cost effective room temperature chemical methods are used in the current work to synthesize uniformly distributed undoped and doped (dopants: La, Nd, Sm, Gd, Y and Yb) rare earth oxide nanoparticles. In the present study, the variation of the properties in nanocrystalline ceria (NC) synthesized by microemulsion method is studied as a function of dopant size and its concentration. To further understand, the role of dopant (cation) size on the oxygen vacancy concentration, doped nanocrystalline oxide powders were analyzed by Raman Spectroscopy, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). XRD studies showed that lattice parameter change in nanocrystalline oxide by doping trivalent rare earth elements is largely depending on size of trivalent ions. It showed that by doping larger cations (Gd3+ and Y3+) compare to Ce3+ causes lattice expansion where as smaller cations (Yb3+) leads to lattice contraction. It also showed that the lattice expansion or contraction is directly proportional to dopant concentration. The results of Raman Spectroscopy showed that the correlation length decreases resulting in increase in oxygen vacancies for larger trivalent dopants (Sm3+, Gd3+ and Y3+). However, the correlation length increases resulting in decrease in oxygen vacancies for smaller trivalent dopants (Yb3+) compare to nanocrystalline ceria. These nanostructured oxides are further applied to develop high temperature oxidation resistance coatings for austenitic steels. The present study investigates the role of oxygen vacancies in the performance of high temperature oxidation resistance as a function of various trivalent dopants and dopant concentration. NC and La3+ doped nanocrystalline ceria (LDN) particles were coated on AISI 304 stainless steels (SS) and exposed to 1243K in dry air for longer duration and subjected to cycling. The results are further compared with that of micro-ceria (MC) coatings. The coated samples showed 90% improvement in oxidation resistance compared to uncoated and MC coated steels as seen from the SEM cross-sectional studies. XRD analysis showed the presence of chromia in both NC and 20 LDN samples which is absent in uncoated steels. From SIMS depth profiles, Fe, Ni depletion zones are observed in presence of LDN coated sample indicating diffusion through the oxide layer. The role of oxygen vacancies in the nanoceria coatings on the early formation of protective chromia layer is discussed and compared to its micron counterpart. This study helps in understanding the role of oxygen vacancies to protect austenitic stainless steel at high temperature and confirms the oxygen inward diffusion rather cation outward diffusion in rare earth oxide coatings. It also gives an idea to identify the type of dopant and its concentration in nanocrystalline cerium oxide which supplies the critical oxygen partial pressure required at high temperature to form primarily impervious chromia layer.M.S.M.S.E.
Department of Mechanical, Materials and Aerospace Engineering;
Engineering and Computer Science
Materials Science & Engr MSMSE
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Papazoglou, Efstratios. "On porcelain bonding, oxidation, mechanical properties and high-temperature distortion of high-palladium dental casting alloys." The Ohio State University, 1999. http://catalog.hathitrust.org/api/volumes/oclc/47770015.html.
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Thesis (Ph. D.)--Ohio State University, 1999.Advisor: William A. Brantley, Oral Biology Program. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.
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Khetan, Vishal. "High temperature oxidation and wear properties of magnetron sputtered AlTiTaN based hard coatings." Doctoral thesis, Universite Libre de Bruxelles, 2016. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/225493.
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Hard nanostructured TiAlN coatings have gained high importance in the field of protective tribological coatings. Nevertheless, their use regarding high temperature (>800°C) applications such as dry high speed machining still remains a challenge. Addition of elements such as Ta or Y has shown a beneficial impact on these properties. But for a better performance of these coatings, an in-depth understanding of their oxidation and wear mechanisms over a wider range of temperatures is needed which is currently unavailable in the literature. This work investigated the wear and oxidation properties of AlTiTaN hard coatings deposited by reactive magnetron sputtering at a substrate temperature of 250°C. Depending on process conditions, coatings with a preferential crystallographic orientation of cubic {111} or {200} with a columnar microstructure were observed. The oxidation and wear mechanisms for these coatings were investigated between 700°C and 950°C in air for various test durations. Further, the influence of Y doping in AlTiTaN coating was also studied.By combining Dynamic-Secondary Ion Mass Spectrometry ,X-ray diffraction (XRD) and Transmission Electron Microscopy measurements, it was demonstrated that a single amorphous oxide layer comprising of Ti, Al and Ta oxides formed at 700°C became a bilayer composed of a crystalline Al rich layer (protective Al2O3) and a Ti/Ta rich oxide layer at 900°C. The oxidation mechanism was governed primarily by inward diffusion of O at 700°C while from 800°C onwards outward diffusion of Al and inward diffusion of O controlled the reaction rate. A correlation between the oxidation kinetics and wear mechanism of AlTiTaN coatings, investigated at 700°, 800° and 900°C, was established.Doctorat en Sciences de l'ingénieur et technologie
info:eu-repo/semantics/nonPublished
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Bashir, Khalid Mohammed. "The development of phenolic resin-based carbons with improved high temperature oxidation resistance." Thesis, University of Bath, 1988. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760583.
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Morton, Thomas Joseph. "Development of high temperature/oxidation-resistant PVD coatings for cutting tools using HIPIMS." Thesis, Sheffield Hallam University, 2017. http://shura.shu.ac.uk/16598/.
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A series of high temperature and oxidation resistant, nanoscale, multilayer PVD, hard coatings have been developed through combine DC Unbalanced Magnetron (UBM) and High Power Impulse Magnetron Sputtering (HIPIMS) deposition technologies. The properties of the coatings lend themselves to the application of protecting cutting tools exposed to harsh environment such as the dry, high-speed machining of abrasive materials. This thesis discusses the literature supporting the project and pays tribute to the development of coatings that formed the foundation for the CrAlYBCN/AlSiCN coating series. Plasma diagnostics optimised the process conditions for deposition; a highly ionised metal rich plasma was generated to investigate the effect of process conditions during the pretreatment step. It was found that metal ion implantation into the substrate was successful and that ramping the cathode charge had little effect of the sputter rate of the substrate. Ion etching removed loosely bound surface grain to improve adhesion. A series of coatings were developed that were deposited at different levels of target poisoning, in an attempt to improve coating properties by process control and stoichiometry. Superhard coatings able to withstand temperatures of over 800 °C were produced. The coatings were subjected to a series of mechanical and thermal testing using pin on disk, microhardness, scratch test, Rockwell indentation, isothermal heat treatment and thermogravimetric analysis. Mechanisms of wear and oxidation process have been proposed based on the evidence given. Through coating development two coatings were indicated as having the desired chemical, thermal and mechanical properties suitable for cutting tests. The coating that was deposited at higher bias improved the tool lifetime by 5 times.
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Agrizzi, Ronqueti Larissa. "Study of grain boundary oxidation of high alloyed carbon steels at coiling temperature." Thesis, Compiègne, 2018. https://bibliotheque.utc.fr/Default/doc/SYRACUSE/2018COMP2405.
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Les aciers à haute résistance (AHSS) ont été largement utilisés dans le cadre d’applications automobiles visant à améliorer la sécurité et l’allègement des structures. Afin d'atteindre les objectifs en termes de propriétés mécaniques, ces nouveaux aciers sont composés de teneurs en éléments d’alliages beaucoup plus élevés (par exemple silicium et manganèse) que les aciers usuels. En conséquence, l'AHSS est susceptible de subir une oxydation interne sélective lors du refroidissement des bobines d’acier. L'oxydation sélective interne, en particulier l'oxydation aux joints de grains (GBO), est actuellement l'un des principaux obstacles à la production de ces aciers. Elle réduit le nombre de cycles avant la rupture de fatigue et rend ainsi difficile l’obtention des spécifications du client. Par conséquent, ce travail de thèse était axé sur l'effet de plusieurs paramètres sur le comportement à l’oxydation interne sélective. Parmi eux, l'impact de la décarburation, l'influence de la température de bobinage et de la couche de calamine, l'effet de différentes teneurs en silicium et / ou en manganèse et leur comportement en diffusion. De plus, l'impact de la désorientation des joints de grains sur l'oxydation interne a également été étudié. Des alliages modèles à base de fer binaires / ternaires ainsi que des aciers industriels ont été étudiés via un large ensemble de techniques expérimentales. Ces analyses ont mis en évidence une décarburation stable pour tous les échantillons étudiés qui n'a pas d'impact sur l'oxydation interne sélective pour une longue exposition aux conditions isothermes. Les profondeurs d’oxydation aux joints de grain ont été examinées selon les différentes configurations de tests et se sont révélées sensibles aux teneurs en silicium ou en manganèse. Pour certaines d'entre elles, différents comportements de diffusion du silicium ont été identifiés vis-à-vis de l'oxydation des joints de grains, en fonction des températures. Considérant quelques hypothèses restrictives, l'application de la théorie de l'oxydation interne sélective de Wagner a permis de déterminer le coefficient de diffusion de l'oxygène aux joints de grain. Pour surmonter certaines limites du modèle de Wagner, un modèle d'oxydation sélective a été appliqué pour comprendre l'effet de différents paramètres sur la pénétration de l'oxygène à l'intérieur du métal et principalement sur la profondeur des joints de grain affectée par l'oxydation sélective. Les connaissances acquises à partir de ce travail de thèse aideront à comprendre et à limiter l'oxydation sélective interne (principalement l’oxydation aux joints de grain) dans les aciers avec des compositions complexes en éléments d’alliage. En outre, les résultats peuvent être utilisés pour évaluer les paramètres d’un modèle d'oxydation sélectiveAdvanced high-strength steels (AHSS) have been widely used in automotive industry to improve safety and fuel economy. In order to reach the mechanical properties targets, these new steels are composed by much higher alloy contents (e.g. silicon and manganese) than usual steels. As consequence, the AHSS may suffer of selective internal oxidation during the cooling of hot coil. The selective internal oxidation, especially the grain boundary oxidation (GBO), is currently one of the main obstacles to the production of these steels. It reduces the number of cycles before fatigue failure and thus, makes it difficult to reach the specifications of the customer. Therefore, this PhD work was focused on the effect of several parameters on selective internal oxidation behavior. Among them, the impact of decarburization, the influence of coiling temperature and the mill scale, the effect of different silicon and/or manganese contents and their diffusion behavior. Moreover, the impact of grain boundary misorientation on grain boundary oxidation was also investigated. Either binary/ternary iron-based model alloys as well as industrial steels were investigated by a large set of experimental techniques. This analysis showed a stable decarburization for all investigated samples that does not impact the selective internal oxidation for long exposure time in isothermal conditions. The GBO depths were examined according to the different test configurations and were found dependent for some cases on silicon or manganese content. For some of them, different silicon diffusion behaviors were identified with regards to grain boundary oxidation depending on temperatures. Considering some restrictive hypotheses, the application of Wagner’s theory of selective internal oxidation allowed determining the grain boundary diffusion coefficient of oxygen. To overcome some limitations of Wagner’s model, a model of selective oxidation has been applied to understand the effect of different parameters on the penetration of oxygen inside the metal and principally on the grain boundary depth affected by selective oxidation. The knowledge acquired from this PhD work will help to understand and limit the selective internal oxidation (mainly GBO) in new steels with complex alloy compositions. Furthermore, the results may be used to assess a model of selective oxidation
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Nguyen, QuynhGiao N. "High Temperature Volatility and Oxidation Measurements of Titanium and Silicon Containing Ceramic Materials." Abstract only. Full text release has been delayed at the author's request until December 31, 2010, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1239291812.
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Thesis (Ph.D.)--Cleveland State University, 2008Abstract. Includes bibliographical references (p. 110-111). Electronic full text release has been delayed at the author's request until December 31, 2010.
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Jones, David C. "NANOMECHANICAL CHARACTERIZATIONS OF HIGH TEMPERATURE POLYMER MATRIX COMPOSITE RESIN: PMR-15 POLYIMIDE." Lexington, Ky. : [University of Kentucky Libraries], 2009. http://hdl.handle.net/10225/1040.
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Thesis (M.S.)--University of Kentucky, 2009.Title from document title page (viewed on August 6, 2009). Document formatted into pages; contains: ix, 65 p. : ill. (some col.). Includes abstract and vita. Includes bibliographical references (p. 59-62).
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Evin, Harold. "Low Cr alloys with an improved high temperature corrosion resistance." Thesis, Dijon, 2010. http://www.theses.fr/2010DIJOS082/document.
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Les aciers ferritiques à faible teneur en chrome tel que le T/P91 sont largement utilisés dans les centrales de productions d’électricité pour leurs bonnes propriétés mécaniques et leur faible coefficient d’expansion thermique. Cependant, la demande croissante en énergie alliée à la nécessité de réduire les émissions de gaz à effet de serre, conduisent à envisager l’augmentation des conditions d’utilisation (température et pression) de ces matériaux. Des études ont montré qu’en modifiant la température de fonctionnement et la pression de vapeur d’eau de 538°C/18.5 MPa à 650°C/30 MPa, le rendement des centrales thermiques progressait d’environ 8%. Se pose alors la question de la tenue à la corrosion à haute température des aciers à 9% de chrome. Au cours de ces travaux, le comportement d’un acier ferritique/ martensitique à 9% de chrome a été étudié à 650°C sous air sec et sous vapeur d’eau de matière isotherme et en conditions de cyclage thermique. La prise de masse des échantillons renseigne sur la cinétique de la réaction d’oxydation et l’adhérence des couches d’oxydes formées. Les produits de corrosion ont été caractérisés par plusieurs techniques d’analyses dans l’optique de clairement identifiés les oxydes en présences et leurs mécanismes de formation. Des oxydes mixtes de fer et de chrome (Cr,Fe)2O3 sont dans un premier temps formés et assurent s’avèrent être temporairement protecteur. Pour des longs temps d’oxydation ou des températures supérieures à 650°C, la magnétite Fe3O4 et l’hématite Fe2O3 sont les principaux oxydes formés, montrant ainsi l’inadéquation des nuances à faible teneur en chrome pour une utilisation dans des conditions aussi drastiques. Dans l’optique d’augmenter la résistance à la corrosion à haute température de cet alliage, diverses solutions ont été envisagées tel que l’aluminisation par cémentation en caisse, les revêtements d’oxydes de terre rare par MOCVD, ou encore l’ajout d’éléments d’addition. Ces solutions ont été également testées à 650°C sous air sec et sous vapeur d’eauThe improvement of high temperature oxidation resistance of low chromium content steels, such as T/P91, is of great interest in regards with their application in thermal power generating plants. Indeed, they possess good creep properties, and low thermal expansion coefficient. Important needs in energy together with environmental issues place power generation plants under constraints which lead to develop high efficiency systems. A usual way to increase the efficiency consists in increasing temperature and pressure parameters of the power generating plant. Studies has shown that the total efficiency of a plant increases by nearly 8 % when changing the steam parameters from 538°C/18.5 MPa to 650°C/30 MPa. Then, the problem of corrosion resistance of 9% chromium steel in those conditions is asked. In this work, the behavior of a ferritic / martensitic 9% chromium steel has been studied at 650°C in dry air and in water vapor containing environment in both isothermal and thermal cyclic conditions. The weight gain of samples provides information on the kinetics of the oxidation reaction and the adhesion of formed oxide scale. Corrosion products were characterized by several analytical techniques in order to identify oxides with accuracy and to understand their formation mechanisms. Mixed iron and chromium oxides (Cr, Fe) 2O3 are initially formed and provide temporary protection to the substrate. For long time exposure or temperatures above 650°C, magnetite, Fe3O4 and hematite Fe2O3 are the main oxides formed, highlighting the fact that low chromium steel are inappropriate for applications in such drastic conditions. In order to increase the high temperature corrosion resistance of this alloy, various solutions have been proposed as aluminizing by pack cementation, reactive element oxides coatings of by MOCVD, or addition of alloying elements in the steel composition. These solutions were then tested at 650 ° C in dry air and in water vapor environments
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Persson, Petter. "Maximum element temperature for Kanthal Super 1800S in flowing nitrogen atmosphere with low content of oxygen." Thesis, Uppsala University, Materials Science, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-121411.
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Abstract
The behavior for MoSi2 based high temperature heating elements for resistive heating has been examined in elevated temperature and low oxygen content environment. MoSi2 spontaneously forms a protective SiO2 scale at high temperature if the amount of oxygen in the ambient atmosphere is sufficient according to the following reaction:
5MoSi2 + 7O2(g) 7SiO2 + Mo5Si3
If the oxygen content at a specific temperature is too low, SiO(g) is more stable than SiO2 and the following reaction will occur instead:
2SiO2 2SiO(g) + O2(g)
Then surface will be Si-deplated and finally, the base material will be exposed. Si and Mo will oxidize and degas from the surface as SiO and MoO3 with severe diameter reduction of the heating element as a result. It is therefore of high interest to find the relationship between the maximum element temperature and the oxygen content in the ambient atmosphere to be able to fully exploit the potential of the heating elements and also to aid and help diagnose customer complaints.
After 14 full scale tests in a custom made atmospheric furnace, the following equation could be calculated:
p(O2) = 1.748·100.01677·T·log(e)-10
The equation gives the minimum oxygen content at a specified temperature. The equation is based on 100 hours tests at atmospheric pressure, gas flow rate of 4 liter per minute, varying temperature and varying oxygen content. Nitrogen has been used as carrier gas for the oxygen.
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Xu, Mengyao. "Oxidation Behavior of Nb-Si-Ti-Cr-Al-X Based Multi-Component Alloys." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155821250.
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Thorning, Casper. "Grain boundary ridge formation during initial high temperature oxidation of Mn/Al TRIP steel /." Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4081.
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Rannou, Benoît. "Slurry coatings from aluminium microparticles on Ni-based superalloys for high temperature oxidation protection." Phd thesis, Université de La Rochelle, 2012. http://tel.archives-ouvertes.fr/tel-00839790.
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Because of their good mechanical resistance at high temperature, Ni-based superalloys are used for aero-engine and land-based turbines but undergo "dry" oxidation between 900 and 1500°C. These materials are thus coated with nickel-aluminide coatings (BC). An additional thermal barrier coating (TBC) is generally applied in the hottest sections of the turbines (T>1050°C) to lower the impact of the temperature on the substrate. In the framework of the European research programme "PARTICOAT", this PhD work was focused on the growth mechanisms of a full protective coating system (BC+TBC) in a single step process, using a water-based slurry containing a dispersion of Al micro-particles to satisfy the European environmental directives. The rheological and physico-chemical characterizations showed the slurry stability up to seven days. After depositing the latter by air spraying, a tailored thermal treatment resulted in a nickel-aluminide coating (β-NiAl) similar to the conventional industrial ones but through an intermediate Al liquid phase stage. Simultaneously, the oxidation of the Al micro-particles brought aboutthe formation of a top alumina "foam" (PARTICOAT concept). After a validation step of the mechanisms involved in pure Ni substrate, the extrapolation of the process to several Ni-based superalloys (René N5 (SX), CM-247 (DS), PWA- 1483 (SX) and IN-738LC (EQ)) revealed different coating compositions and microstructures. A particular attention was therefore paid onto the effect of alloying elements (Cr, Ta, Ti) as well as their segregation in the coating. The high temperature behaviour of the coated samples has been studied through isothermal oxidation (1000h in air between 900 and 1100°C) and showed that the oxidation and interdiffusion phenomena ruled the degradation mechanisms. Besides, the electrodeposition of ceria before the application of the PARTICOAT coating allowed to strongly limit interdiffusion phenomena and stabilized the nickel aluminide coating.
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Morra, Martin M. (Martin Mathew). "Stress accelerated grain boundary oxidation of incoloy alloy 908 in high temperature oxygenous atmospheres." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11513.
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Mogire, Evans O. "Microstructural characterisation of high temperature oxidation of boiler materials for coal fuelled power plants." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13189.
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Due to the projected increase in global electricity demand, it is estimated that nearly 1400GW of new coal fired power plants will be built providing about 38% of global electricity demand in 2030. This growth will have a negative impact on the environment through the emission of CO2, a greenhouse gas detrimental to the climate, unless stringent emission targets for the coal fired power plants are put in place. This has resulted in placing more emphasis on the need for adopting the best available technologies for ‘new built' plants or through retrofit of existing plants or the construction of high efficiency power plants with CO2 capture and storage technologies. The high efficiency power plants are mainly achieved by operating the boilers at higher temperatures of up to 700°C compared to the conventional power plants operating at ~ 565°C. This expected temperature increase will have an effect on the material degradation mechanisms of both the existing and proposed new alloy materials for the critical components of the boilers, that is, headers, superheaters, reheaters and wall membranes. This thesis explores the material degradation mechanisms associated with the high temperature oxidation and/or corrosion of the alloy materials found in these components.
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Qian, Lingyi. "Fabrication, characterisation and oxidation behaviour of Pt-based bond coats for high temperature applications." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/39531/.
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Over the years, platinum modified aluminide (PtAl) bond coats have been used in high temperature protection systems for commercial aircraft engines to protect turbine blades from high temperature oxidation and corrosion. In the process of operation, the oxidation and rumpling behaviours of the bond coats are the key factors in determining the lifetime of the thermal barrier coating. The latest development in aircraft engines has given rise to the need for bond coats with better oxidation and rumpling resistance at high temperature. This investigation aims to improve the oxidation and rumpling resistances of general PtAl bond coats by introducing ZrO2 nanoparticles, Ir and Pd additions: ZrO2 nanoparticles were incorporated into PtAl bond coats by co electrodeposition in an attempt to enhance their performance by exploiting the effect of reactive element (Hf, Zr, etc.) oxides. PtAl coatings with and without ZrO2 nanoparticles were deposited onto three commercially available Ni-based superalloys, namely, Mar-M-247, Mar-M-246 and Inconel 718. Thermal cycling oxidation tests were performed to evaluate the influence of ZrO2 addition and substrate composition. The addition of ZrO2 particles to PtAl coatings on Mar M 246 and Inconel 718 appeared to accelerate the growth of thermally grown oxide and reduced the rumpling of thermally grown oxide. However, when depositing PtAl coatings with ZrO2 nanoparticles on Mar-M-247, there was no changes, as mentioned above, in thermally grown oxide. Through the analysis of the coatings on different substrates, the interactions among Hf, Al and ZrO2 have been revealed and clarified, which offers a better understanding of the reactions of ZrO2 and the influence of substrate composition on bond coats. Ir and Pd coatings were deposited by means of electroplating and electroless plating respectively to explore the effects of other platinum group metals. Ir-modified PtAl coatings were investigated on Mar-M-246 with different vacuum annealing durations before the cyclic thermal test, which presented a significant reduction in growth rate of TGO and inward diffusion of Al in the oxidation test. Instead of oxygen diffusion barrier, Ir exhibited a diffusion barrier to Al possibly by forming a high temperature solid solution with Al, which has a higher melting point than general β-NiAl phase. As a result, it restrained the inward diffusion of Al and slowed down the outward diffusion of Al, thus improving the oxidation resistance. In addition, Ir concentration produced an effect on the diffusion barrier of Ir. When it is reduced lower than 15 wt.%, the barrier effect of Ir begins to degrade, which provides a better comprehension of the diffusion barrier effect of Ir. However, Pd-modified PtAl coating did not strengthen oxidation resistance, which may be caused by the phosphorus precipitates generated from the electroless plating process. ZrO2 and Pd-modified PtAl bond coats were further investigated with 8 wt.% yttria stabilised zirconia top coat. Comparison between conventional PtAl and high velocity oxygen fuel sprayed NiCoCrAlY bond coats was made as well. Isothermal and cyclic thermal oxidation tests were carried out to evaluate the prepared bond coats. ZrO2 modified PtAl coating showed the best oxidation and rumpling resistance in cyclic thermal oxidation, while Pd-modified PtAl coating was worse than conventional PtAl coating and better than the NiCoCrAlY coating. It has been observed that ZrO2- and Pd-modified PtAl bond coats are affected by different methods of oxidation test. Isothermal oxidation has a greater impact on ZrO2- and Pd-modified PtAl bond coats. The difference is considered to be a consequence of long term annealing in isothermal oxidation, which leads to a fast grain boundary diffusion of Al.
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Lee, Kok Loong. "Deformation behaviour of Cu-Cr in-situ composite." Thesis, University of Leicester, 2004. http://hdl.handle.net/2381/11077.
Full textAbstract:
With the increasing requirements for higher strength materials with high electrical conductivity, a lot of interest has been paid to develop Cu-based composites in the last 25 years. These composites have superior tensile strength, combined with good electrical conductivity, to that exhibited by pure Cu and conventional Cu alloys. To date, much of the research carried out on this composite has focused on the mechanical and electrical properties of the as processed material. However, there is a basic lack of understanding of the way in which the properties may change or degrade during service. Without this knowledge, these composites cannot be fully and safely exploited. Thus the objective of this study was to investigate the thermo-mechanical behaviour of a Cu-Cr composite, and the nature and extent of any damage mechanisms occurring within the composite over a wide range of experimental conditions. Neutron diffraction was used to investigate the deformation behaviour of the individual phases in the composite and their interaction through elastic and plastic loading at room temperature. For the composite, a fairly good agreement was observed in the phase strains predicted by the Eshelby theory and measured by neutron diffraction. In-situ tensile tests in the SEM were also performed to study the damage mechanism of the composite. Tensile and creep tests were carried out in air and in vacuum over a wide range of temperatures. To provide data for comparison with the composite material, pure Cu specimens were tested whenever possible. Creep resistance increases significantly with the introduction of Cr fibres into Cu. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. Damage characteristics and distributions were found to be similar during tensile and creep testing.
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MASSA, ANDREA. "Development of manganese oxide films for the electro-oxidation of phenol at high temperature and pressure." Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2675216.
Full textAbstract:
This thesis is divided into three main parts.
In the first part, the concept of a MJ-PEM reactor will be introduced, and its design and calculations will be explained. A MJ-PEM reactor is the result of the coupling of a Multi-Junction Solar Cell (MJSC) and a Polymer Electrolyte Membrane (PEM) electrolyzer, able to work at high temperatures and pressures (up to 150°C and 30 bar). Two scenarios for the application of this system were investigated: in the first one, the anodic chamber is used for the oxidation of recalcitrant organics contained in wastewater, while the cathodic compartment is used for the evolution of H2, for storage or direct use on site; in the second one, the H2 produced at the cathode is sent to an anaerobic digestion process, to boost the biomethanation step, whereas at the anode O2 is evolved and it is exploited for the digestate stabilization and disinfection. Both the scenarios proved to be feasible and effective, due to a high degree of integration between stoichiometric and thermal requirements of different systems, allowing to carry out both waste or wastewater treatment on one side, and hydrogen or natural gas production on the other side. The second part of this work concerns the synthesis and the characterization of electrodes based on manganese oxides, for the electro-oxidation of recalcitrant organics. Phenol was chosen as target molecule, due to its high refractoriness and stability, and its wide presence in industrial plants. Manganese oxides are extensively used in electrochemistry, and they were chosen because of their low cost, high abundance, and low toxicity. Different types of manganese oxides (MnOx) were synthesized by electrodeposition on two substrates, namely metallic titanium and titania nanotubes (TiO2-NTs). X-Ray Diffraction (XRD) and X-Ray Photoelectron Spectroscopy (XPS) were used to analyze the oxidation states of manganese, whereas Field Emission Scanning Electronic Microscopy (FESEM) was employed to investigate the morphology of the samples and the penetration of manganese oxides inside the NTs. The electrochemical properties of the electrodes have been investigated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV), showing that both calcination and electrodeposition over TiO2-NTs gave more stable electrodes, exhibiting a marked increase in the current density. The activity of the proposed nanostructured samples towards phenol degradation has been investigated. Tetravalent manganese (α-MnO2) resulted to be the most active phase, with a phenol conversion of 42.7%. Trivalent manganese (α-Mn2O3), instead, reported the highest stability, with an average working potential of 2.9 V vs. RHE, and the highest tendency for oxygen evolution reaction, reaching 0.4 mA/cm2 at 2.5 V vs. RHE. TiO2-NTs interlayer contributed in all cases to the decrease in the final potential reached after the reaction time of about 1 – 1.5 V, due to the improved contact with the catalyst film and the prevention of passivation of the titanium substrate. In the third part, the most performing electrodes were selected from the ones synthesized in the second part. They were tested in High Temperature, High Pressure (HTHP) reactor, designed in Politecnico di Torino for kinetic studies on electro-degradation of refractory organics in wastewaters, under Catalytic Wet Air Oxidation (CWAO) conditions, i.e. 150°C and 30 bar. The most stable (α-Mn2O3) and the most active (α-MnO2) manganese oxides were compared, both at ambient and CWAO operative conditions, with some of the most effective electrodes used in this field: Sb-doped SnO2 and RuO2. Results showed that manganese oxides, especially α-Mn2O3, is more than tripled at 150°C and 30 bar, reaching values of phenol oxidation close to the ones of Sb-SnO2 and RuO2. This phenomenon can be attributed to the higher tendency of manganese in its Mn3+ form to oxidize water to O2, that is wasted at ambient conditions, while is better employed at high temperatures (high kinetics, low overpotentials) and high pressures (improved O2 solubility).
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Cory, N. J. "The hydrogen emission and kinetics of the high temperature oxidation of ferritic steels by super-heated steam." Thesis, University of Reading, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381910.
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