Dissertations / Theses on the topic 'Silicon chromium'
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Comina, Paul John. "New methodology in organo-chromium/-silicon chemistry." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320585.
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Kovsarian, Abdolnabi. "Properties of chromium silicide on hydrogenated amorphous silicon." Thesis, University of Surrey, 1998. http://epubs.surrey.ac.uk/844566/.
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The interaction between thin films of sputter deposited chromium and hydrogenated amorphous silicon has been studied. Following deposition of the chromium films at room temperature the films were annealed over a range of times and temperatures below 350° C. It was found that an amorphous silicide was formed only a few nanometers thick with the square of thickness proportional to the annealing time. The activation energy for the process was 0.55+/-0.05 eV and the silicide growth rate prefactor ≈ 10-12 cm2/s. The formation process of the silicide was very reproducible with the value of density derived from the thickness and Cr surface density being close to the value for crystalline CrSi2 for all films formed at temperatures ≤300° C. The specific resistivity of the amorphous CrSi2 was ≈600 muO.cm and independent of annealing temperature. It was shown that the a-CrSi2 was physically and chemically stable. We have shown that a Schottky barrier is formed between a-CrSi2 and a-Si:H with a barrier height of ≈ 0.9 eV and an ideality factor ≈1.1. The current transport is controlled by diffusion or thermionic emission mechanism at low voltages but it becomes space charge limited at higher voltages. Applying a reverse or forward bias to the Cr/a-Si:H system during annealing does not change the physical and electrical properties of the interface and the behaviour is controlled only by the heat treatment history of the sample. In the Mo/a-Si:H system a very thin and stable amorphous MoSi2 layer is formed after annealing below 300° C and the formation of MoSi2 follows the diffusion law. The activation energy of silicidation is ≈ 0.4 eV and the prefactor is ≈ 10-14cm2/s. The specific resistivity of a-MoSi2 is ≈ 1000 muO.cm. In the Co/a-Si:H the composition of the resulting silicide is close to CoSi below 300° C with a resistivity of ≈ 120 muO.cm. The barrier height of the MoSi2/a-Si:H and CoSi/a-Si:H systems is ≈ 0.9 eV and confirms that the barrier height is controlled by interface states.
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Pitcher, Robert John. "Optically induced oscillations of chromium coated silicon microstructures." Thesis, University of Surrey, 1991. http://epubs.surrey.ac.uk/844610/.
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This thesis reports the effects of chromium layers on the vibrational properties of silicon microengineered structures designed as pressure sensors. Both excitation and interrogation have been achieved by optical means. Particular attention has been paid to the optically induced vibrational amplitude, Q factor and phase angle between the motion of the resonator and the incident pulsed laser light used to excite the resonator. Two silicon structures have been investigated; bridges fabricated at Birmingham University and extensively characterised by researchers at Strathclyde University, and devices fabricated at STC Technology Ltd. in Harlow. For both structures the addition of chromium layers onto the surface has had the effect of increasing the value of the amplitude divided by the Q factor. This increase occurs after a layer of chromium of about 15nm thickness has already been deposited onto the silicon. It has also been found that the value of the Q factor of the resonators has decreased with the addition of chromium layers. The phase angle of the motion has also been found to be sensitive to the thickness of the chromium layer. This angle has been observed to increase from approximately zero for bare silicon to about 40° for a few hundred Angstroms, returning towards zero phase for chromium layers of comparable thickness to the silicon thickness.
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Filonenko, Olga. "Structural Investigations of Thin Chromium Disilicide Films on Silicon." Doctoral thesis, Universitätsbibliothek Chemnitz, 2005. http://nbn-resolving.de/urn:nbn:de:swb:ch1-200500426.
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In der vorliegenden Arbeit wurden Röntgentechniken benutzt um die Struktur von dünnen (etwa 40 nm) CrSi2-Schichten, die unter UHV-Bedingungen mittels reaktive Koabscheidung und template-Verfahren auf Si(001) hergestellt wurden, zu charakterisieren. Die Ergebnisse wurden mit TEM-, SEM- und RBS-Untersuchungen korreliert und ergänzt.
Die XRD-Analysen zeigen, dass die beiden Abscheideverfahren immer zur Bildung der CrSi2-Phase führen, wobei die Kristallite mit einer bevorzugten Orientierungsbeziehung CrSi2(001)[100] || Si(001)[110] wachsen. Im ersten Teil der Arbeit wurde die Cr-Si-Koabscheidung benutzt um die Prozessparameter zu bestimmen, die zum Wachstum epitaktischer Schichten führen können. Die Strukturuntersuchungen zeigen, dass nur bei einer Substrattemperatur von 700°C nahezu geschlossene Schichten mit Kristalliten, welche lateral eine Größe bis zu 300 nm haben und neben der bevorzugten noch andere Orientierungen zum Substrat aufweisen, entstehen.
Als zweite Herstellungsmethode wurde das template-Verfahren verwendet, wo die Cr-Si-Koabscheidung auf ein vorher in-situ präpariertes ultradünnes CrSi2-template erfolgt. Die Morphologie und die Stärke der bevorzugten Orientierung der CrSi2-Schichten sind stark von der template-Dicke abhängig. Die Abscheidung auf CrSi2-templates, welche aus einer Cr-Schicht mit nominaler Dicker von 0,35 nm bis 0,52 nm entstehen, führt zum Wachstum weitgehend geschlossener, homogener und epitaktischer CrSi2-Schichten. Ein Modell, das den Einfluss der template-Dicke auf die Qualität der CrSi2-Schichten erklären kann, wird vorgeschlagen.
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Jensen, Mallory Ann. "Detecting and gettering chromium impurities in photovoltaic crystalline silicon." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/100122.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 61-67).
Photovoltaic (PV) modules provide a source of renewable electricity by harnessing solar energy. Currently, crystalline silicon dominates the PV market with an approximate market share of 90% and record solar cell efficiencies greater than 20%. However, the PV market must decrease the cost to the consumer to maintain growth and meet global electricity demands. Increasing the solar-to-electricity conversion efficiency is one of the most significant cost levers. Transition metal impurities can degrade silicon wafer-based solar cell efficiencies at concentrations as low as 1010 cm3 . By removing interstitial metals from the bulk and/or collecting interstitial metals at heterogeneous nucleation sites, phosphorous diffusion gettering renders them less detrimental in the final solar cell. While they exist for iron, kinetics process simulation tools do not yet exist for chromium, which has higher capture cross-sections for minority carriers and is therefore more detrimental in both p- and n-type materials. In this thesis, I employ synchrotron-based X-ray fluorescence microscopy to study chromium (Cr) distributions in multicrystalline silicon in as-grown material and after two phosphorous diffusion profiles. I complement quantified precipitate size and spatial distribution with interstitial Cr concentration and minority carrier lifetime measurements to provide insight into chromium gettering kinetics and offer suggestions for minimizing the device impacts of chromium. The data presented in this thesis can be used in development of kinetics process simulation tools for chromium gettering. Finally, I describe a new technique for detecting low concentrations of impurities in n- and p-type silicon. The development of high-performance silicon materials, including n-type, necessitates more sensitive impurity detection techniques, capable of measuring interstitial contaminations below 1010 cm-3. I propose the development of a free-carrier absorption-based technique that incorporates a temperature stage. By measuring injection-dependent lifetimes at a wide range of sample temperatures, the identifying parameters of lifetime-limiting defects can be deduced.
by Mallory Ann Jensen.
S.M.
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Hystad, Madeleine. "The distribution and impact of chromium impurities in compensated SoG-silicon." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemi, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-6847.
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Harte, Sean Paul. "Surface EXAFS studies of chromium and titanium upon #alpha#-quartz (0001) surfaces." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.263901.
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In this thesis two studies of reactive metal adsorption upon a low index single crystal silicon dioxide surface are presented in addition to a study of sulphur adsorption upon a low index single crystal nickel surface. Chromium growth upon the a-quartz Si02(0001) (J84xJ84) Rll 0 surface is studied at three coverages, 0.25±O.08 ML, 0.5±O.16 ML and 1.0±0.33 ML, using surface extended x-ray absorption fine structure (SEXAFS). SEXAFS measurements, from the chromium K-edge, recorded at both grazing and normal incidence show that chromium growth proceeds via the formation of mesoscopic particles with a body centred cubic (b.c.c.) like structure having an average nearest neighbour Cr-Cr distance of 2.36±O.03 A. This represents a contraction of 5.6 % from the bulk b.c.c. lattice spacing of 2.49 A. There is no evidence of a surface reaction between chromium and the surface oxygen. SEXAFS was used to study titanium reactional growth on a-quartz (0001) (J84xJ84) Rll 0 and (lx1). Three nominal coverages were studied, 0.25±O.08 ML, 0.5±O.16 ML and 1.0±O.33 ML. Both normal and grazing incidence SEXAFS data were recorded and show the formation of a spatially extensive region in which an interfacial reaction has occurred between surface oxygen and adsorbate titanium atoms. Coupled with this is the formation of subnanometre titanium clusters. The metal oxide has nearest neighbour Ti-O distances close to those of both the anatase and rutile forms of titania with the metallic titanium clusters having a Ti-Ti distance within experimental error that of bulk hexagonal close packed (h.c.p.) titanium, 2.89 A. A re-examination of the surface geometry of Ni(1l0)c(2x2)S using SEXAFS has been performed. Data out to an electron wavevector of 9 A-I are analysed with a new code to assess the influence of multiple scattering. The first shell S-Ni distance is determined to be 2.20±O.02 A with the next nearest neighbour distance being 2.29±O.02 A, giving a top-layer Ni expansion of 14±3% relative to the bulk. The influence of multiple scattering does not significantly alter these values from earlier studies.
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Harper, Mark Andrew. "Codeposition of chromium and silicon onto iron-base alloys via pack cementation /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487778663285375.
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Morgan, Andrew. "JOINING AND HERMETIC SEALING OF SILICON CARBIDE USING IRON, CHROMIUM, AND ALUMINUM ALLOYS." VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3529.
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Silicon Carbide (SiC) is increasingly gaining attention as a potential fuel cladding material, on account of its favorable thermo-mechanical and neutronic properties. The major limitations of such a cladding is currently associated with joining and hermetic sealing. The work presented here investigated the use of Al, Cr and Fe metals and a specialized alloy (FeCrAl) to achieve hermetic sealing of SiC tubes as well as a joining technology of SiC. Major part of solving this issue requires addressing joining of ceramic and metallic components, which are largely dissimilar in both thermal and mechanical properties. Preliminary experiments to bond SiC with FeCrAl resulted in adverse separation partially attributed to the differences in thermal expansion mismatch. To alleviate these problems, thin and thick coatings of the metals and alloys were applied to SiC. Qualitative microstructural characterization of the final product indicated satisfactory bonding between the materials.
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Lim, Jeongyoun. "Effects of chromium and silicon on corrosion of iron alloys in lead-bismuth eutectic." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/41288.
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Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2006.Includes bibliographical references.
The high power densities and temperatures expected for next generation nuclear applications, including power generation and transmutation systems, will require new types of heat transport systems to be economic. Present interest in heavy liquid metal coolants, especially in lead and lead-bismuth eutectic, originates from such requirements as increased heat removal capacity and enhanced safety features. However, corrosion of structural metals represents a major limiting factor in developing advanced liquid Pb-alloy coolant technology. In fact, the development of advanced structural and cladding alloys that are resistant to corrosion over a wide range of oxygen potentials in this environment would represent the enabling technology for these systems. The goal of this research was to develop a class of Fe-Cr Si alloys that are resistant to corrosion in Pb and Pb alloys at temperatures of 6000C or higher. As a necessary part of this development effort, an additional goal was to further develop the fundamental understandings of the mechanisms by which corrosion protection is achieved. A series of alloys based on the Fe-Cr-Si system were proposed as potential candidates for this application. These alloys were then produced and evaluated. The results of this evaluation verified the hypothesis that an Fe alloys with suitable levels of Cr (>12 wt%) and Si (> 2.5 wt%) will be protected by either a tenacious oxide film (over a wide range of oxygen potentials above the formation potential for Cr and Si oxides) or by a low solubility surface region (at low oxygen potentials) Experimental results obtained from model alloys after lead-bismuth eutectic exposure at 6000C demonstrated the film formation process.
(cont.) The hypothesis that Si addition would promote the formation of a diffusion barrier was confirmed by the actual reduction of oxide thickness over time. The Si effect was magnified by the addition of Cr to the system. Based on a kinetic data assessment on the experimental results of Fe-Si and Fe-Cr-Si alloys, the synergetic alloying effect of Cr and Si was revealed. An improved understanding on the kinetic process and its dependence on the alloying elements has been achieved.
by Jeongyoun Lim.
Sc.D.
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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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Müller, Tina. "Novel colour centres in diamond : silicon-vacancy and chromium centres as candidates for quantum information applications." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608164.
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Burkhard, Michael A. "Sample fabrication and experimental approach for studying interfacial sliding in thin film-substrate systems." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2006. http://library.nps.navy.mil/uhtbin/hyperion/06Sep%5FBurkhard.pdf.
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Jacuinde, Arnoldo Bedolla. "The effect of silicon and mischmetal on the structure of high-chromium cast irons for wear resistance applications." Thesis, University of Sheffield, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391044.
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Ardehali, Barani Araz. "Optimization of the critical content of tramp elements in ultra-high strength silicon chromium spring steels through thermomechanical treatment." Göttingen Cuvillier, 2007. http://d-nb.info/988382563/04.
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Ardehali, Barani Araz. "Optimization of the critical content of tramp elements in ultra-high strength silicon chromium spring steels through thermomechanical treatment /." Göttingen : Cuvillier, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=017079000&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
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Arora, William Jay. "Nanostructured Origami (TM) : folding thin films out of the plane of a silicon wafer with highly stressed chromium hinges." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33107.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 81-84).
This thesis addresses the construction of complex three-dimensional (3-D) nanostructures using only 2-D, planar nano-fabrication techniques. In the state of the art, multiple 2-D layers are fabricated in series, each directly on top of the previous. The method advocated here is Nanostructured Origami, in which multiple adjacent 2-D layers are fabricated in parallel and are then folded into the desired 3-D configuration using the appropriate folding sequence. This thesis focuses on folding actuation for this method using the residual tensile stress in vacuum-evaporated chromium to fold silicon nitride membranes. Our results conclusively demonstrate the ability to pattern these membranes with nano-scale features and then controllably fold them into a predetermined 3-D configuration. Future work will refine the fabrication procedure for large-scale manufacturing and address alignment and latching of the folded membranes.
by William Jay Arora.
M.Eng.
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OLIVEIRA, RENE R. de. "Estudo do efeito da tensão residual na microdeformação da rede cristalina e no tamanho de cristalito em aço Cr-Si-V jateado com granalhas de aço." reponame:Repositório Institucional do IPEN, 2016. http://repositorio.ipen.br:8080/xmlui/handle/123456789/27497.
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No presente trabalho foram estudados alguns efeitos causados pelo jateamento por granalhas no aço Cr-Si-V, processo que tem por objetivo aumentar a resistência à fadiga. Para este estudo a variação de parâmetros no processo são ferramentas para melhor compreender os mecanismos que influenciam esta propriedade. Os parâmetros utilizados neste trabalho foram a variação da granalha e o pré tensionamento das amostras aplicados em lâminas utilizadas em feixe de molas automobilísticas de aço de liga cromo silício vanádio (SAE 9254+V). Inicialmente foi realizada a avaliação do perfil de tensão residual, efetuada por difração de raios-x pelo método do sen2 ao longo da espessura na região onde a tensão é compressiva. Nos resultados nota-se um efeito anômalo em relação ao perfil característico da distribuição de tensão residual com a perda de compressão nas camadas iniciais em relação à superfície jateada. Com o uso da microscopia eletrônica de varredura foi observado a região afetada pelo jateamento por granalhas notando que as regiões plasticamente deformadas se encontram nas mesmas regiões onde ocorre a diminuição da tensão residual compressiva. O perfil obtido pela difração de raios-x fornece as informações necessárias com o propósito de conjugar os efeitos que a microtensão (microdeformação) influenciam na macrotensão (tensão residual). Esta relação foi comprovada pela sobreposição dos resultados encontrados na distribuição da microdeformação da rede cristalina com a tensão residual ao longo da espessura na região plasticamente deformada. Os resultados dos perfis das difrações de raios-x mostraram a existência de anisotropia de tensões entre os planos, geradas por defeitos de empilhamento e pela densidade de discordâncias. Assim sendo, para obter os valores das microtensões devem ser considerados os fatores das constantes elásticas (conforme o módulo das direções) e dos planos cristalográficos. O método aplicado foi o Williamson-Hall modificado. Além deste método outros também foram utilizados, tais como: método de Warren-Averbach e o método Single Line, este aplicando a série de Fourier, porém, ao observar os resultados, nota-se a diferença entre os valores obtidos nas deformações, tanto aos métodos quanto aos planos cristalográficos, porém a ênfase deste trabalho foi dada às características dos perfis da distribuição e não aos valores absolutos. Somando a isto, foi proporcionado o estudo da distribuição do tamanho médio de cristalito ao longo da espessura no perfil das difrações de raios-x e os resultados mostraram que esta distribuição varia de forma inversa a microdeformação. A relação entre o tamanho médio de cristalito e a variação das distâncias interplanares corresponde diretamente a alterações das densidades de discordâncias ocorridas no material que por sua vez estão ligadas às microdeformações da rede cristalina. Como complemento ao trabalho foram analisados o fator de concentração de tensão e ensaios de fadiga do material. O fator de concentração de tensão não variou conforme a utilização das granalhas S330 e S390, ambas sendo aplicadas no mesmo regime de jateamento. Os ensaios de fadiga indicaram que o pré tensionamento aumenta a vida útil nas tensões cíclicas do material estudado.
Tese (Doutorado em Tecnologia Nuclear)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Hantcherli, Muriel. "Influence d’éléments d’addition sur les transformations de la martensite revenue dans les aciers faiblement alliés." Thesis, Saint-Etienne, EMSE, 2010. http://www.theses.fr/2010EMSE0570/document.
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L’objectif de ce travail est d’optimiser la résistance au revenu d’un acier martensitique à 0,6% de carbone, faiblement allié en Cr, V, et Si/Al. Une série d’alliage modèle ternaire de haute pureté (Fe-C-X, X=Cr, V, Si, Al) a été élaborée à l’EMSE par fusion en creuset froid.. L’étude du comportement des alliages a été réalisée au moyen d’une caractérisation fine de la précipitation (Diffraction RX, MEB-FEG, MET) complétée par des mesures dilatométriques. Le comportement des alliages modèles a été comparé à celui de l’alliage industriel. Le vanadium est responsable de deux effets : (i) les carbures de vanadium bloquent la croissance des grains au cours de l’austénitisation ; (ii) le vanadium dissous permet la précipitation d’une cémentite (V,Cr,Fe)3C à l’origine d’un pic de durcissement secondaire pour un revenu vers 550°C. Le silicium a un effet particulier : il stabilise la matrice martensitique et retarde la précipitation de la cémentite vers des températures de revenu plus élevées, augmentant ainsi la résistance au revenu. Cependant, le silicium se révèle nocif pour le procédé industriel de mise en forme utilisé. Deux nouveaux alliages ont alors été élaborés pour chercher un élément de substitution à l’aluminium : un alliage ou le silicium est remplacé par l’aluminium, et un alliage ou le silicium est absent. L’aluminium reste neutre dans l’alliage mais l’étude de ces deux nuances a permis de mettre en évidence la possibilité d’utiliser une nuance ne contenant pas de silicium mais présentant une résistance au revenu comparable a celle de la nuance industrielle, du fait de la présence conjointe du chrome et du vanadiumThe purpose of this work is to optimise the strength of a tempered martensitic medium C steel, containing low-level of Cr, V and Si/Al. A series of high purity "model" ternary alloys (Fe-C–X, X=Cr, V, Si, Al) was prepared (EMSE) by the cold crucible method. The initial structures of quenched alloys were optimised through appropriate austenitizing conditions. Analysis of alloys behaviour on tempering was performed through carbide precipitation characterisation (X-ray diffraction, SEM and TEM), completed by hardness and dilatometric measurements. The behaviour of "model" alloys was compared to that of the industrial material.Vanadium addition is responsible for two effects: (i) vanadium carbides lock the grain growth during the austenitizing; (ii) dissolved vanadium promotes the precipitation of (V,Cr)3C, that is at the origin of a secondary hardening peak near 550°C. Silicon addition has an interesting effect, as it stabilises the martensitic matrix and increases the temperature of cementite precipitation. Therefore, a high value of hardness is conserved up to high tempering temperatures.Unfortunately, because of some noxious properties, the industrial process in concern excludes the presence of Si. That’s why two new model alloys have been prepared and tested, in which the silicon addition (i) was absent, or (ii) replaced by Al.Aluminium has been shown to be "neuter" vs tempering behaviour. Moreover, the interesting effect of secondary hardening (550°C) has been observed in both Si-free steels, showing that alloying with only Cr and V can be enough to get the expected behaviour of the studied steel
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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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Amor, Nait Ajjou Jamila. "Structure and reactivity of silica-supported chromium(IV) complexes." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape3/PQDD_0020/NQ48084.pdf.
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Mathieu, Catherine. "Élaboration d'un procédé industriel d'élimination de si, al et cr des bains acides de chlorure de fer et étude de l'influence du silicium sur les propriétés magnétiques des ferrites." Nancy 1, 1993. http://www.theses.fr/1993NAN10292.
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La première partie de cette thèse concerne l'élaboration d'un procédé de purification des bains chlorhydriques industriels de décapage des tôles d'acier et la mise au point d'une installation piloté en vue de la fabrication de ferrites doux. La méthode a pour but d'abaisser les teneurs en si, al et cr du bain. Elle consiste en la neutralisation de l'acidité libre des bains acides de chlorure ferreux par adjonction de fer métal, sous formes de rives d'acier résiduelles de l'industrie sidérurgique, jusqu'a un ph de 4. Cette valeur est celle d'une solution concentrée de fe(h#2o)#6#2#+, elle correspond au ph de précipitation des gels d'hydroxydes des ions plus acides que fe#2#+, soit ici les ions tri- et tétravalents que sont fe#3#+, al#3#+, cr#3#+ et si#4#+. Une opération de filtration permet ensuite l'élimination de ces espèces hydroxylées. Dans la deuxième partie, nous avons montré que l'oxydation de la fayalite silicate ferreux de formule fe#2sio#4 conduit a un fe#2o#3 ou la transition de Morin observée par spectrométrie Mössbauer est partiellement inhibée; puis nous avons démontré que le silicium s'insère dans le réseau spinelle de préférence en site tétraédrique pour former la solution solide de formule générale m#i#i#1##xfeii#2#xfeiii#2##2#xo#4 ou m#i#i est un cation métallique divalent
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Hickman, Ian. "Chromium segregation and its effect on crystallisation processes in green soda-lime-silica glass." Thesis, University of Sheffield, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505561.
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Martines, Marco Antonio Utrera [UNESP]. "Propriedades espectroscópicas de sílica contendo crômio." Universidade Estadual Paulista (UNESP), 1997. http://hdl.handle.net/11449/105812.
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martines_mau_dr_araiq.pdf: 2947884 bytes, checksum: 72629200eaa3a20a5b20f28125019cc8 (MD5)Sílica contendo crômio faz parte de uma classe importante de materiais devido às aplicações como catalisador de polimerização e de oxidação, fibras ópticas, laseres e preparação de pigmentos. Este trabalho está dividido em duas partes. A primeira refere-se ao gel úmido e seco de sílica contendo crômio. Os géis foram preparados fazendo-se a mistura das soluções de silicato de sódio solúvel (vidrolíquido) e de soluções aquosas de nitrato de crômio em pH 4 ou 9 previamente ajustado, ou em 4 após a mistura das soluções. O gel foi caracterizado por espectroscopia eletrônica de absorção no ultravioleta -visível e por microscopia eletrônica de transmissão. A morfologia dos géis de sílica e de sílica contendo crômio é dependente do valor de pH e da ordem de mistura dos reagentes. Este efeito é atribuído às espécies poliméricas do crômio diferenciadas presentes na solução que controlam a forma da partícula. Partículas esféricas podem ser obtidas pelo colapso de microgel com alto grau de ligação cruzada. A outra parte do trabalho consiste na preparação de sílica contendo crômio por dois métodos: aquecimento convencional e banho de ultra-som nas temperaturas de 50 e 80oC. O gel obtido foi tratado por extrações com soluções ácidas, extrações com água e diálise, e seco em forno de microondas. As amostras de sílica/crômio em pó foram submetidas ao tratamento térmico em temperaturas de 200 a 1400oC, com intervalos de 200oC, sob atmosfera...
Chromium-containing silica belongs to an important class of materials having technological applications such as polymerization and oxidation catalyses, lasers, pigments and optical fibers. The chromium-containing silica and pure silica gels were obtained by mixing solutions of soluble sodium silicate (water glass) and chromium nitrate with adjusted pH 4 or 9 previously. Other method to prepare the gels was carried out by mixing water glass and chromium nitrate solutions and then the pH 4. The gel was characterized by ultraviolet-visible spectroscopy and transmission electron microscopic. The gel morphology is dependent on the pH value and the order of mixture of reagents. This effect is due to the nature of polymeric shape of chromium species in solution. Spherical particles can be obtained from microgel collapsing with high degree of cross linking . The second part of this work deals with powders obtained from gels. The chromium-containing silica and silica powders were obtained from gel by two methods: i) conventional heating at temperatures of 80 and 50oC and ii) sonication and heating at 80 and 50oC. The resultant colloidal silica was treated by continuous extraction acid solution in followed by extraction in distilled water and then dialyzed against distilled water and dried in microwave oven. The samples were...(Complete abstract, click electronic access below)
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Martines, Marco Antonio Utrera. "Propriedades espectroscópicas de sílica contendo crômio /." Araraquara : [s.n.], 1997. http://hdl.handle.net/11449/105812.
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Resumo: Sílica contendo crômio faz parte de uma classe importante de materiais devido às aplicações como catalisador de polimerização e de oxidação, fibras ópticas, laseres e preparação de pigmentos. Este trabalho está dividido em duas partes. A primeira refere-se ao gel úmido e seco de sílica contendo crômio. Os géis foram preparados fazendo-se a mistura das soluções de silicato de sódio solúvel (vidrolíquido) e de soluções aquosas de nitrato de crômio em pH 4 ou 9 previamente ajustado, ou em 4 após a mistura das soluções. O gel foi caracterizado por espectroscopia eletrônica de absorção no ultravioleta -visível e por microscopia eletrônica de transmissão. A morfologia dos géis de sílica e de sílica contendo crômio é dependente do valor de pH e da ordem de mistura dos reagentes. Este efeito é atribuído às espécies poliméricas do crômio diferenciadas presentes na solução que controlam a forma da partícula. Partículas esféricas podem ser obtidas pelo colapso de microgel com alto grau de ligação cruzada. A outra parte do trabalho consiste na preparação de sílica contendo crômio por dois métodos: aquecimento convencional e banho de ultra-som nas temperaturas de 50 e 80oC. O gel obtido foi tratado por extrações com soluções ácidas, extrações com água e diálise, e seco em forno de microondas. As amostras de sílica/crômio em pó foram submetidas ao tratamento térmico em temperaturas de 200 a 1400oC, com intervalos de 200oC, sob atmosfera...(Resumo completo, clicar acesso eletrônico abaixo)Abstract: Chromium-containing silica belongs to an important class of materials having technological applications such as polymerization and oxidation catalyses, lasers, pigments and optical fibers. The chromium-containing silica and pure silica gels were obtained by mixing solutions of soluble sodium silicate (water glass) and chromium nitrate with adjusted pH 4 or 9 previously. Other method to prepare the gels was carried out by mixing water glass and chromium nitrate solutions and then the pH 4. The gel was characterized by ultraviolet-visible spectroscopy and transmission electron microscopic. The gel morphology is dependent on the pH value and the order of mixture of reagents. This effect is due to the nature of polymeric shape of chromium species in solution. Spherical particles can be obtained from microgel collapsing with high degree of cross linking . The second part of this work deals with powders obtained from gels. The chromium-containing silica and silica powders were obtained from gel by two methods: i) conventional heating at temperatures of 80 and 50oC and ii) sonication and heating at 80 and 50oC. The resultant colloidal silica was treated by continuous extraction acid solution in followed by extraction in distilled water and then dialyzed against distilled water and dried in microwave oven. The samples were...(Complete abstract, click electronic access below)
Orientador: Marian Rosaly Davolos
Coorientador: Miguel Jafelicci Junior
Doutor
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Szczepan, Victor. "Modélisation et étude expérimentale de la corrosion d’un alliage chromino-formeur par des liquides silicatés." Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0169.
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La corrosion haute température d’alliages par les verres fondus est un problème rencontré dans plusieurs procédés industriels tels que la vitrification des déchets nucléaires ou encore la production de la fibre de verre. Les alliages base nickel contenant une grande quantité de chrome sont particulièrement intéressants pour ces applications, notamment grâce à leur bonne résistance à la corrosion due à leur capacité à développer une couche homogène et couvrante de chromine (Cr2O3) lors d’une oxydation à haute température. De par la faible solubilité de l’oxyde dans les silicates fondus, cette couche protège l’alliage d’une corrosion rapide par le verre. Lors de la mise en contact avec le milieu corrosif à haute température, la couche de chromine est soumise à une compétition entre sa dissolution par le verre fondu et à sa formation simultanée par oxydation de l’alliage. La dissolution totale de la couche est appelée dépassivation et est néfaste car elle conduit à une corrosion accélérée de l’alliage par remise en contact direct avec le liquide. La stabilité de la couche d’oxyde au contact du verre est donc un point clé pour optimiser la durée de vie des matériaux. Ainsi, il convient de comprendre les phénomènes assurant ou non la stabilité de cette couche d’oxyde. In fine, le développement d’outils prédictifs permettrait l’optimisation des matériaux et des conditions opératoires des procédés industriels. Pour répondre à cette problématique, l’alliage modèle Ni-30Cr a été sélectionné de même que des compositions de verres binaires Na2O-SiO2 et borosilicatés Na2O-B2O3-SiO2. L’approche consiste en une étude expérimentale visant à déterminer les conditions de température et de composition assurant la stabilité de la couche d’oxyde développée sur l’alliage immergé. Une modélisation de la corrosion de l’alliage est ensuite proposée afin de définir les paramètres prédisant la stabilité de la couche d’oxyde. L’étude de ce modèle révèle que la dépassivation est liée à un manque d’O2 dans liquide, ce qui limite la cinétique de formation de l’oxyde. La confrontation du modèle aux résultats expérimentaux permet valider cette conclusionHigh temperature corrosion of alloys induced by molten glasses is an issue encountered in several industrial processes such as nuclear waste vitrification or glass fiber production. Nickel-based alloys containing a large amount of chromium are especially interesting for these applications, notably due to their good corrosion resistance thanks to their ability to develop an homogeneous and covering chromia (Cr2O3) layer through high temperature oxidation Due to its low solubility in molten silicates, this layer protects the alloy from a fast corrosion induced by the glass. When put in contact with the corrosive medium at high temperature, the chromia layer is submitted to a competition between its dissolution by the molten glass and its simultaneous formation by oxidation of the alloy. The complete dissolution of the scale is called depassivation and is detrimental because it leads to an accelerated corrosion of the alloy due to a direct contact with the melt. The stability of the oxide scale is the key point for optimizing the materials lifetime. Thus, the phenomena ruling the stability or not of the oxide scale must be fully understood. In fine, the development of forecasting tools might allow to optimize the materials and the operating conditions of the industrial processes. To answer to these issues, the Ni-30Cr model alloy was selected so as binary Na2O-SiO2 and ternary Na2O-B2O3-SiO2 glass compositions. The conditions (temperature and composition) ensuring the stability of the oxide scale developed on the immersed alloy are studied through an experimental approach. A modelling of the alloy corrosion is then proposed, which allows to define the parameters forecasting the oxide scale stability. The study of the model reveals that the depassivation is linked to a lack of O2 in the liquid, which limits the formation kinetic of the oxide. The model is validated after comparison with experimental results
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McLean, Michael M. "Phenyl Functionalized Sol-gel Silica Sorbent for Capillary Microextraction and Chromia-Based Sol-gel Ucon Stationary Phase for Capillary Gas Chromatography." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5374.
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The first chapter of this thesis presents an introduction to sol-gel methodology whose usefulness as a synthetic route will be demonstrated with two applications in chromatography. The first application involves the fabrication of a capillary micro-extraction (CME) device by coating a phenyl functionalized extracting phase on the inner surface of a fused silica capillary for analyte pre-concentration. The device was coupled on-line to a RP-HPLC system and practicality was demonstrated using allergens as target analytes. The allergens chosen as model analytes are typically found in fragrance products and food. Most of the 26 fragrance allergens that are monitored by various government authorities have a phenyl organic moiety (a strong chromophore), thus making them appropriate probes for exploring the extraction efficiency of the coating using a UV detector. The CME device showed ppt level limit of detection which makes it suitable for trace analyses of allergens and similar compounds in a variety of matrices.
The second application explores the feasibility of using sol-gel derived chromia-based stationary phase in gas chromatographic columns. The organic moiety of the stationary phase was derived from Ucon 75-H-90,000 while the inorganic backbone was prepared using chromium(III) dichloride hydroxide - methacrylic acid - aqua complex, 40% in isopropanol/acetone . Usefulness of prepared chromia-based GC stationary phase was examined for petrochemical application. Promising results were obtained using aliphatic-aromatics, polyaromatic hydrocarbons, BTEX test mixture, cycloalkanes, branched alkanes and akylbenzenes. The column was able to perform without degradation despite being rinsed multiples times sequentially with the following solvents: dichloromethane, methanol, water and finally methanol again. Maximum theoretical plate number calculated is around 2,400 plates/m. The plate number clearly needs improvement but is a promising result for the newly explored chromia-based stationary phase. The maximum programmable temperature is 250oC which is comparable with similar commercially available polar stationary phases.
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MANOSSO, HELENA C. "Utilizacao dos trocadores inorganicos ZrP e TiP no tratamento de rejeitos industriais e radioativos." reponame:Repositório Institucional do IPEN, 2001. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10919.
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Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Brunner, David R. "The Composition and Distribution of Coal-Ash Deposits Under Reducing and Oxidizing Conditions From a Suite of Eight Coals." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2642.
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Eighteen elements, including: carbon, oxygen, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, potassium, calcium, titanium, chromium, manganese, iron, nickel, strontium, and barium were measured using a scanning electron microscope with energy dispersive spectroscopy from deposits. The deposits were collected by burning eight different coals in a 160 kWth, staged, down-fired, swirl-stabilized combustor. Both up-stream and down-stream deposits from an oxidizing region (equivalence ratio 0.86) and reducing region (equivalence ratio 1.15) were collected. Within the deposits, the particle size and morphology were studied. The average particle cross-sectional area from the up-stream deposits ranged from 10 - 75 µm2 and had a standard deviation of 36 - 340 µm2. These up-stream particles were of various shapes: spherical, previously molten particles; irregular particle that had not melted, hollowed spherical shells; and layered or strands of particles. These particles were a mixture of burned and unburned coal being deposited at various stages of burnout and having completed some burnout after deposition. The average particle cross-sectional area from the down-stream deposits ranged 0.9 - 7 µm2 and the standard deviation range of 2.6 - 30 µm2. The shape of the particles on the bottom sleeves are typically spherical indicating melting prior to deposition. Particles contained a distribution of elemental compositions that were not tightly grouped on ternary phase diagrams. This indicated that particles were not single compounds or phases but each particle contained a mixture of multiple compounds. Coals' deposit sulfur was strongly correlated with the calcium and iron content of the ASTM ash analysis. The low rank sub-bituminous and lignite coals that had high calcium content produced high sulfur deposits, particularly in the oxidizing region, down-stream deposits. The high iron bituminous coals, also produced high sulfur deposits, but more so in the reducing region, up-stream deposits. The low calcium and low iron coals produced low sulfur deposits. Mahoning was an exception being high in iron content but remaining low in sulfur content in the deposit. Gatling coal showed numerous deposit particles that contained only iron and sulfur consistent with the high pyrite content of Gatling coal. The average concentration of chlorine was insignificant in all of the deposits with the concentration being less than 100 ppm. Individual particles containing chlorine were found and were associated with potassium, sodium, and iron.
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Monteiro, Fabricio Malheiros de Miranda. "Efeito da aplicação de carga em coroas de diferentes materiais, confeccionadas sobre implantes unitários curtos e com diferentes diâmetros nas deformações da crista óssea : análise in vitro e in silico." São José dos Campos, 2018. http://hdl.handle.net/11449/154540.
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Orientador: Lafayette Nogueira JuniorBanca: Guilherme de Siqueira Ferreira Anzaloni Saavedra
Banca: Dárcio Kitakawa
Resumo: O intuito deste estudo in vitro e in silico, foi analisar as microdeformações, geradas pela aplicação de carga vertical, sobre coroas de 3 tipos de materiais restauradores diferentes (Zircônia, Dissilicato de Lítio e Cromo Cobalto), que foram selecionadas, através da biblioteca do software SMART DENT/Exocad (Darmstadt - Germany) e confeccionadas, através da tecnologia cad/cam, suportadas por implantes curtos (8mm), conexão cone morse, com diversos diâmetros (3,5 mm; 4,0 mm e 5,0 mm). Os implantes foram instalados 2mm infraósseo para análise através de elementos finitos e da extensometria. Foram confeccionados 3 blocos de poliuretano: bloco 1 (grupo experimento) no qual foi colocado um implante Titamax CM Neodent 3,5 X 08 mm, bloco 2 (grupo controle) no qual foi colocado um implante titamax CM Neodent 4,0 X 08 mm e bloco 3 (grupo controle) no qual foi colocado um implante titamax CM Neodent 5,0 X 08 mm. Pilares protéticos retos (Base de Titânio 4,5 - Neodent) foram instalados sobre os respectivos implantes sendo instalados 4 extensômetros, na região superior dos blocos ao redor dos implantes. Foi aplicada uma carga vertical de 300N ao redor da abertura de acesso do parafuso protético das coroas. Para a análise por elementos finitos (FEA), o mesmo bloco foi modelado e analisado sob a mesma carga de 300N. Os valores de tensão e deformação foram analisados quanto à correlação com a extensometria. A estatística inferencial consistiu no teste de análise de variância de Friedmann, u... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The aim of this in vitro and in silico study was to analyze the microdeformations generated by the application of vertical load on crowns of 3 different types of restorative materials (Zirconia, Lithium Dissilicate and Cobalt Chromium) that were selected through the software library SMART DENT / Exocad (Darmstadt - Germany), and made using cad / cam technology, supported by short implants (8 mm), cone morse connection with various diameters (3.5 mm, 4.0 mm and 5.0 mm). These were installed 2 mm subcrestal for finite element analysis and extensometry. Three blocks of polyurethane were made; block 1 (experimental group) in which a Titamax CM Neodent 3.5 X 08 mm implant, block 2 (control group) was implanted in which a CM Neodent 4.0 X 08 mm titamax and block 3 (control group) were implanted in which an implant was placed titamax CM Neodent 5.0 X 08 mm. Straight prosthetic abutments (Titanium Base 4.5 - Neodent) were installed on the respective implants and 4 extensometers were installed, in the upper region of the blocks around the implants. A vertical load of 300N was applied around the access opening of the crown prosthetic screw. For the finite element analysis (FEA), the same block was modeled and analyzed under the same 300N load. The stress and strain values were analyzed for correlation with extensometry. The inferential statistics consisted of Friedmann's analysis of variance, a fixed effect factor. For the level of significance, the conventional value of 5% was chosen.... (Complete abstract click electronic access below)
Mestre
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Carter, Donald F. Stiegman Albert E. "Spectroscopic studies of vanadium and chromium in crystalline and amorphous silica matrices." 2004. http://etd.lib.fsu.edu/theses/available/etd-07162004-131013.
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Thesis (Ph. D.)--Florida State University, 2004.Advisor: Dr. Albert E. Stiegman, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed Sept. 27, 2004). Includes bibliographical references.
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Brown, Carole E. Stiegman Albert E. "Charaterization [sic] of the reaction of silica bound chromium(VI) sites with aniline." 2004. http://etd.lib.fsu.edu/theses/available/etd-04122004-145720.
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Thesis (M.S.)--Florida State University, 2004.Advisor: Dr. Albert E. Stiegman, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed June 17, 2004). Includes bibliographical references.
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Lin, Jin-Hsiang, and 林經祥. "Interfacial Reactions of Vanadium and Chromium Metal Thin Films on Silicon." Thesis, 1995. http://ndltd.ncl.edu.tw/handle/38493753630315693491.
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Jiang, Yan-Yu, and 江晏瑜. "Interfacial compound formation between silicon germanium alloy and chromium during diffusion bonding." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/36899380480595630568.
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碩士國立中興大學
材料科學與工程學系
96
The silicon germanium is well known as one of the best thermoelectric materials under the high-temperature environment. However, whether a thermoelectric device performs well or not is strongly related to the property of its electrode. In this research, chromium metal, used as the electrode, is jointed with silicon germanium alloy. The research goal is to understand the interfacial compound formation during joining silicon germanium and chromium, such as the composition, structure of compound, and activation energy of compound growth. In this study, the bulk of silicon germanium alloy was processed by vacuum arc melting, and then joined with chromium by hot pressing. The microstructure, composition and crystalline structure were determined by means of scanning electron microscopy, electron probe microanalysis and X-ray diffraction, respectively. Finally, the average thickness was measured and activation energy of formation was computed. The results showed that the intermetallic compounds formed are Cr3Ge, Cr(Six Ge1-x)3 and CrSi2, and the activation energy of growth were calculated. The possible reasons for the defect formation and the growing sequence are also conjectured.
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Lin, Wan-Jhen, and 林琬禎. "Dynamic Study of The Growth Behaviors in Chromium Silicide/Silicon Heterostructure Nanowires." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/54sc86.
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碩士國立交通大學
材料科學與工程學系奈米科技碩博士班
105
Transition metal silicide nanowires exhibit low resistivity, great thermal stability and excellent mechanical strength, thus can be applied as interconnect and contact materials for future integrated circuits devices. In this work, we successfully fabricated three kinds of chromium silicide/silicon heterostructure nanowires through solid state reaction ─ bare Si/Cr3Si nanowires, Si/SiO2 core-shell/Cr3Si nanowires and Si/Al2O3 core-shell/Cr5Si3 nanowires. The growth behaviors and diffusion mechanisms of these three kinds of silicide heterostructure nanowires were observed by in-situ TEM at 700℃, and calculate the growth rate and thermal expansion of these chromium silicide nanowires. During the growth of chromium silicide nanowires, Si-rich phase would form first in front of silicide nanowires. We also find that oxide-shell can control the diffusion process in silicon nanowire. When oxide-shell applied, suppression stress would restrain radial direction growth of chromium silicide and accelerate its axial direction growth rate. In addition, Al2O3 shell was found to reduce the radial expansion of chromium silicide nanowires and hinder Cr-rich phase, then Cr5Si3 eventually wins out as the first phase. Furthermore, we studied the crystal structure of Cr3Si and Cr5Si3 nanowires, and confirmed the single-crystalline A15 and D8m type structure of the intrinsic Cr3Si nanowires and Cr5Si3 nanowires respectively. In addition to fundamental science, the significant study would be helpful for future processing techniques in nanotechnology and related applications.
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Filonenko, Olga [Verfasser]. "Structural investigations of thin chromium disilicide films on silicon / vorgelegt von Olga Filonenko." 2004. http://d-nb.info/975368362/34.
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Lee, Tung-Yeh, and 李東曄. "A Study of Nickel-Chromium-Silicon thin films Deposited by DC magnetron sputtering system." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/16935108629823895852.
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碩士國立高雄應用科技大學
機械與精密工程研究所
98
The objective of this experiment is to make a series study of the Ni-Cr-Si thin film material which is fabricated on the glass and Al2O3 substrates by DC magnetron sputtering process. With the fixed sputtering power 500 W, several different deposition time, working pressure and annealing temperature parameters are investigated and tried to find the relationship between the microstructure and electric properties. The results show that the amorphous structure or micro-crystal sturcture were observed on the surface morphology and microstructure by FE-SEM, XRD and TEM before annealing process. The composition amout of oxygen in the surface was found more than internal by ESCA check. Atomic percentage ratio of the deposition at the surface of nickel, chromium, silicon of approximately were 36 %, 31 %, 33 % and the internal ratio were 48 %, 26 %, 26 %. At the fixed working pressure parameter, the sheet resistance is decreased with increasing deposition time. At the fixed deposition time parameter, the sheet resistance is increased with increasing working pressure. The material resistivity is about 300~500 uΩ-cm after the various experimental checked. After annealing temperature of 350 ℃/3h, the small crystal ring structure was found on the surface by using FE-SEM observation. In the condition of the working pressure 1.6×10-3 torr, deposition time 60 sec, annealing temperature 350 ℃/3h, the crystal structure was detected by TEM, but there is no diffraction peak produced by XRD checked. The temperature coefficient resistance (TCR) is increasing with the annealing temperature increased from negative to positive. The thinner thickness film was annealed, the higher TCR was shown after the same anneling temperature. The thicker film was required for TCR to zero with the higher annealing temperature required, and the TCR of the thicker film is more stable than thinner film as the temperature increasing. The deposition time was the key parameter for the TCR results after annealing temperature.
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Filonenko, Olga. "Structural Investigations of Thin Chromium Disilicide Films on Silicon: Strukturuntersuchungen an dünnen Chromdisilicideschichten auf Silicium." Doctoral thesis, 2004. https://monarch.qucosa.de/id/qucosa%3A18300.
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In der vorliegenden Arbeit wurden Röntgentechniken benutzt um die Struktur von dünnen (etwa 40 nm) CrSi2-Schichten, die unter UHV-Bedingungen mittels reaktive Koabscheidung und template-Verfahren auf Si(001) hergestellt wurden, zu charakterisieren. Die Ergebnisse wurden mit TEM-, SEM- und RBS-Untersuchungen korreliert und ergänzt.
Die XRD-Analysen zeigen, dass die beiden Abscheideverfahren immer zur Bildung der CrSi2-Phase führen, wobei die Kristallite mit einer bevorzugten Orientierungsbeziehung CrSi2(001)[100] || Si(001)[110] wachsen. Im ersten Teil der Arbeit wurde die Cr-Si-Koabscheidung benutzt um die Prozessparameter zu bestimmen, die zum Wachstum epitaktischer Schichten führen können. Die Strukturuntersuchungen zeigen, dass nur bei einer Substrattemperatur von 700°C nahezu geschlossene Schichten mit Kristalliten, welche lateral eine Größe bis zu 300 nm haben und neben der bevorzugten noch andere Orientierungen zum Substrat aufweisen, entstehen.
Als zweite Herstellungsmethode wurde das template-Verfahren verwendet, wo die Cr-Si-Koabscheidung auf ein vorher in-situ präpariertes ultradünnes CrSi2-template erfolgt. Die Morphologie und die Stärke der bevorzugten Orientierung der CrSi2-Schichten sind stark von der template-Dicke abhängig. Die Abscheidung auf CrSi2-templates, welche aus einer Cr-Schicht mit nominaler Dicker von 0,35 nm bis 0,52 nm entstehen, führt zum Wachstum weitgehend geschlossener, homogener und epitaktischer CrSi2-Schichten. Ein Modell, das den Einfluss der template-Dicke auf die Qualität der CrSi2-Schichten erklären kann, wird vorgeschlagen.
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Ding, Tzu-Wei, and 丁祖瑋. "Fabrication and Measurement of Ferroelectric Varactors with Through Substrate Vias on Silicon and Chromium Silicide Thin-Film Resistors." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/u6m54h.
Full textAbstract:
碩士國立中央大學
電機工程學系
105
In this work, we continue the efforts of our lab on the development of a ferroelectric-based integrated passive device (IPD) process. We improve the fabrication process for the ferroelectric varactors with through substrate vias (TSVs) on silicon and also develop the fabrication process for chromium silicide thin-film resistors. The advantages of ferroelectric varactors that adopt parallel-plate structure include high capacitance density, high tunability, and low bias voltage. However, their quality factors are limited by the thin bottom electrodes. We previously developed ferroelectric varactors with TSVs on high-resistivity silicon. The approach is to expose the bottom electrodes of the ferroelectric varactors by etching silicon substrate from backside and then thicken the bottom electrodes by gold electroplating. However, the measured quality factor is not as high as expected and the yield of the process is low. One of the reasons that result in the low quality factor is that the high-resistivity silicon substrate does not exhibit the expected high-resistivity property. Consequently, the microwave loss caused by the GSG (ground-signal-ground) pad becomes unexpectedly high. As for the low yield, the major reason is the poor uniformity of the backside vias. From previous literatures, it is known that there is a mobile electron layer beneath the native oxide of a high-resistivity silicon substrate, causing that the resistivity is not as high as expected in practice. It is also known that, by bombarding the substrate surface with argon ions, the silicon surface would become amorphous. As a result, the mobile electron layer would not be formed and therefore the microwave loss of the GSG pad is reduced. By adopting the technique of dosing argon, we increase the resistivity of the silicon substrate from 45 Ω-cm to 150 Ω-cm. As for the improvement of the fabrication process for the backside vias, our original recipe for silicon etching only contains one KMPR 1025 photoresist layer. Unfortunately, it is proven difficult to completely remove the photoresist. Because of the photoresist residue, the surface becomes quite rough. In this work, we spin on a layer of LOR 5A photoresist prior to the KMPR 1025. By doing so, we can completely strip off the photoresists, thereby reducing the surface roughness and improving the uniformity of the backside vias. Finally, we also develop a fabrication process for chromium silicide thin-film resistors, which are commonly used for bias resistors in microwave circuits. The chromium silicide thin films are deposited using RF sputtering and the target used in the sputter is CrSi2. Measurement results show that the sheet resistance of 50-nm chromium silicide thin film is around 1–1.5 kΩ/□. From the measured data of the resistors with film thickness of 50 nm, 100 nm, and 200 nm, calculated that the resistivity of the chromium silicide thin film we deposit is around 4000–6000 μΩ-cm. In this thesis, we successfully reduce the microwave loss caused by the GSG pads by dosing Ar in the high-resistivity silicon substrate. We also successfully improve the uniformity of the TSVs on silicon. Finally, we develop the process for fabricating chromium silicide resistors. Through these advances in the fabrication process, we make the ferroelectric IPD process developed by our lab more complete.
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Patel, J., S. Lal, K. Nuss, Stacy-Paul Wilshaw, Rechenberg B. von, R. M. Hall, and J. L. Tipper. "Recovery of low volumes of wear debris from rat stifle joint tissues using a novel particle isolation method." 2018. http://hdl.handle.net/10454/15561.
Full textAbstract:
YesLess than optimal particle isolation techniques have impeded analysis of orthopaedic wear debris in vivo. The purpose of this research was to develop and test an improved method for particle isolation from tissue. A volume of 0.018 mm3 of clinically relevant CoCrMo, Ti-6Al-4V or Si3N4 particles was injected into rat stifle joints for seven days of in vivo exposure. Following sacrifice, particles were located within tissues using histology. The particles were recovered by enzymatic digestion of periarticular tissue with papain and proteinase K, followed by ultracentrifugation using a sodium polytungstate density gradient. Particles were recovered from all samples, observed using SEM and the particle composition was verified using EDX, which demonstrated that all isolated particles were free from contamination. Particle size, aspect ratio and circularity were measured using image analysis software. There were no significant changes to the measured parameters of CoCrMo or Si3N4 particles before and after the recovery process (KS tests, p > 0.05). Titanium particles were too few before and after isolation to analyse statistically, though size and morphologies were similar. Overall the method demonstrated a significant improvement to current particle isolation methods from tissue in terms of sensitivity and efficacy at removal of protein, and has the potential to be used for the isolation of ultra-low wearing total joint replacement materials from periprosthetic tissues.
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Von, Below Michael Anton. "The market for South Africa's ferrous metals and ferro-alloys." Thesis, 2014. http://hdl.handle.net/10210/9876.
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M.Phil. (Natural Economics)Due to the overwhelming influence of gold on the national economy of South Africa, the importance of the other mineral resources are often underestimated. South Africa is the largest exporter of metals essential to the modern World industry - metals such as chrome, manganese and vanadium. Our vast reserves of these and other ferrous metals might yet prove to provide this country with substantial political and economic powers in years to come. The importance of the availability of ferrous metals for the continued existence of the modern global civilization is not always realised. These metals, in the form of various steels and other alloys, form an integral part of our daily lives in modern communities. This important role and the numerous problems faced by the global ferrous metals industry provided me with a challenging field of study. The phenomenon of cyclical volatility is inherent in mineral commodity markets and is eminently present in the markets for steel and related alloys, due mainly to the sensitivity of these markets to general economic welfare. In turn, and due to the derived demand relationship that exists between these metals and steel, the ferrous metals are particularly susceptible to economic prosperity and depression. More often than not, a period of economic prosperity is characterised by ferrous metal supply shortages, while excess supply is typical during periods of economic recession. Interest in the study of the complexities of ferrous metal markets was kindled whilst in the employ of the Minerals Bureau of the Department of Mineral and Energy Affairs.
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Van, Niekerk Ferdinand. "Method development and validation for the analysis of silicon, phosphorus, sulphur, chromium and metal oxides in charge chrome ferro-alloy by x-ray fluorescence spectroscopy." Thesis, 2010. http://hdl.handle.net/10539/8620.
Full textAbstract:
High-carbon ferrochrome, also known as charge chrome can be used in the production of stainless steel of various grades. For charge chrome to be used as a raw material for stainless steel production, it is essential to know the chemical composition of the alloy.
Charge chrome is currently analysed by X-ray fluorescence spectroscopy (XRF) in the form of a button sample and the slags (oxides forming during the reduction process in charge chrome production) are analysed in the form of a briquette. The main aim during this study was to develop an XRF method for the analysis of charge chrome as a powder briquette and to develop a method for the analysis of the oxides.
During XRF analysis interference effects such as spectral overlaps and matrix effects (mainly in the form of absorption) must be compensated for to ensure accurate analysis. The general composition of the sample matrices, especially with regard to the oxides, is known. The possibility of matrix matching between calibration standards and samples was investigated to see if the necessity of corrections in terms of overlaps and interferences can be eliminated. After setting up calibration lines using production samples analysed by an alternative validated analytical technique (Inductively Coupled Plasma – Optical Emission Spectroscopy) for the elements and oxides (indirectly as elements), no corrections on the calibration lines were made using relevant mathematical correction algorithms.
The method development phase was followed by a complete validation of all the necessary parameters to ensure an accurate XRF analytical technique. The validation of the technique showed that the method is capable of yielding accurate and trustworthy results. This confirmed the theory that matrix matching between calibration standards and samples can compensate for the necessity to make any corrections for spectral overlaps and spectral interferences. The preparation of samples as powder briquettes was also investigated to determine the optimum conditions for sample preparation. The main parameter studied was the influence of particle size on analysis. The optimum sample preparation conditions were determined and confirmed by validating the analytical results obtained when the powder briquette was analysed using the validated XRF method.
After research, the conclusions were made that charge chrome can be analysed in briquette form and that matrix matching between calibration standards and samples eliminates the need for any correction with regard to spectral overlaps and matrix effects.
The newly developed and validated methods for the analysis of Si, P, S and Cr in charge chrome metal and the oxide content in charge chrome slag will be implemented to assist in the daily routine analysis of charge chrome production samples.
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薛彬佑. "A correlation study between the chromium returns-ratio and the content of silicon/aluminum for 15-5PH(V) in the electric are furnace using the Artificial Neural Network method." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/65273720869551577442.
Full textAbstract:
碩士建國科技大學
自動化工程系暨機電光系統研究所
99
Abstract This study applies the artificial neural network (ANN) to analyze the influence on the recovery of silicon and aluminum components of high and low levels after the melting of 15-5PH(V) in EAF to look for the best recovery of chromium. First, the experiment is to take scrap to measure chrome content before EAF’s melting. After the melting, the recovery is achieved by measuring chrome in steel water, and the experimental data are trained by using Back propagation (BP). Also, the content of silicon and aluminum are used as variables to obtain the best model. The accuracy of ANN is confirmed by using root-mean-square (RMS) and mean relative error to reach the best chrome recovery by predicting the control value of silicon and aluminum components. The result shows that by using ANN, the RMS is 1.51%, and the mean relative error is 1.43%, which proves that the ANN model can predict the recovery effectively. Moreover, the best chrome recovery during the EAF process can be achieved through controlling the content of silicon. Keywords: Artificial neural network, Electric arc furnace, Root mean square error, Mean relative error
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Yossapol, Netnapid. "Remediation of chromium contaminated soils with colloidal silica." Thesis, 2002. http://library1.njit.edu/etd/fromwebvoyage.cfm?id=njit-etd2002-085.
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Moisii, Cristina. "Vibrational spectroscopy of silica supported vanadium and chromium catalyst systems." 2006. http://etd.lib.fsu.edu/theses/available/etd-11082006-134504/.
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Thesis (Ph. D.)--Florida State University, 2006.Advisor: Albert E. Stiegman, Florida State University, College of Arts and Sciences, Dept. of Chemistry and Biochemistry. Title and description from dissertation home page (viewed May 20, 2008). Document formatted into pages; contains xiii, 151 pages. Includes bibliographical references.
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Li, Kun-Yu, and 李坤禹. "Synthesis and Characterization of Kaolinite / Silica and Zero-valent Iron Nanocomposites for Remediation of Cobalt, Copper, and Chromium-contaminated Wastewaters." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/11906592431768407119.
Full textAbstract:
碩士元智大學
化學工程與材料科學學系
97
The main objectives of the present study were to prepare surface-modified zero-valent iron nanoparticles (SMZVINs) for the remediation of cobalt, copper and chromium ions from wastewater. Experimentally, synthesis of the material, identification and application to treat cobalt, copper and chromium contaminated wastewater were conducted. SMZVINs were prepared using kaolinite clay and coating silica nanofilms. The synthesized kaolinite supported zero valent iron nanoparticles was mixed with iron(II) sulfate heptahydrate in same mass ratio of kaolinite, after using the borohydride reduction method at room temperature and ambient pressure. Tetraethoxysilane (TEOS) was used as the precursors to synthesize SiO2/zero-valent iron nanocomposites for coating. Characterization of kaolinite /Fe(0) and SiO2/Fe(0) reacted with Co(II), Cu(II), and Cr(VI) contaminated wastewater were also investigated by TEM, FESEM, XRD, XPS, FTIR, BET N2 isotherms, and XANES/EXAFS techniques. In addition, this study was also carried out to provide information concerning the removal efficiencies and mechanism in the chemical reductive treatment processes for Co(II), Cu(II), and Cr(VI) wastewaters. By FE-SEM and TEM analyses, The presence of kaolinite resulted in decreased aggregation of zero-valent iron nanoparticles, yielding composites with a iso-electric point (IEP) of 6. Kaolinite/Fe(0) has characteristic peaks of kaolinite and Fe(0) at 2θ = 24.88, 35.9, 38.52, 54.94, 70.08°, and 2θ = 44.5 and 64.62°, respectively analyzed by XRD. The surface area measured by BET N2 isotherms was 17 m2/g. From ESCA spectra, the main species on the surface of kaolinite/Fe(0) nanoparticles were Fe and α-FeOOH. By using a TEOS as the precursor, SiO2/Fe(0) nanocomposites were synthesized. From TEM and SEM analyses, the core of SiO2/Fe(0) nanocomposite has a diameter around 50 nm and the shell of SiO2/Fe(0) nanocomposites relatively looses and possesses aperture structure. SiO2/Fe(0) nanocomposites have characteristic peaks of SiO2 and Fe(0) at 2θ = 22° and 2θ = 44.96° and 65.36° respectively analyzed by X-Ray diffraction. SMZVINs reacted with Co(II), Cu(II), and Cr(VI) solutions and the concentrations of solutions determined by AAS decreased with increasing reaction times. Kinetics analyses from batch studies revealed that the removal of Co(II), Cu(II), and Cr(VI) from aqueous reaction with SMZVINs appeared to be a pseudo first-order with respect to metal contaminants. Metal-adsorbed Fe(0) nanoparticles were observed using FE-SEM and XRD and the comparison was found abnormally. It was possible that parts of Fe(0) nanoparticles were oxidized in the adsorption process. This study exemplifies the utilization of XRD and XPS to reveal the speciation and possible reaction pathway in a very complex adsorption and redox reaction process. Moreover, XANES spectra and EXAFS data also showed that Cr(VI) reduced to Cr(III). The Cr atoms in SMZVINs have the first shell of Cr-O bonding with a bond distance of 1.98 Å and a coordination number of 3.61.