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1
Tengstrand, Olof. "Transition metal carbide nanocomposite and amorphous thin films." Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-104929.
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This thesis explores thin films of binary and ternary transition metal carbides, in the Nb-C, Ti-Si-C, Nb-Si-C, Zr-Si-C, and Nb-Ge-C systems. The electrical and mechanical properties of these systems are affected by their structure and here both nanocomposite and amorphous thin films are thus investigated. By appropriate choice of transition metal and composition the films can be designed to be multifunctional with a combination of properties, such as low electric resistivity, low contact resistance and high mechanical strength. Electrical contacts are one example of application that has been of special interest in this thesis. Since some industrially important substrates used in electrical contacts soften at higher temperature, all films were deposited with dc magnetron sputtering at a low substrate temperature (200-350 °C). I show that the electrical resistivity and mechanical properties of composites consisting of nanocrystalline NbC grains (nc-NbC) in a matrix of amorphous C (a-C) depend strongly on the amount of amorphous C. The best combination of hardness (23 GPa) and electrical resistivity (260 μΩ*cm) are found in films with ~15 at.% a-C phase. This is a higher hardness and lower resistivity than measured for the more well studied Ti-C system if deposited under similar conditions. The better results can be explained by a thinner matrix of amorphous C phase in the case of NbC. The nc-NbC/a-C is therefore interesting as a material in electrical contacts. Si can be added to further control the structure and thereby the properties of binary Me-C systems. There are however, different opinions in the literature of whether Si is incorporated on the Ti or C site in the cubic NaCl (B1) structure of TiC. In order to understand how Si is incorporated in a Me-Si-C material I use a model system of epitaxial TiCx (x ~0.7). In this model system a few atomic percent of Si can be incorporated in the cubic TiC structure. The experimental results together with theoretical stability calculations suggest that the Si is positioned at the C sites forming Ti(Si,C)x. The calculation further shows a strong tendency for Si segregation, which is seen at higher Si contents in the experiments, where Si starts segregate out from the TiCx to the grain boundaries causing a loss of epitaxy. If Si is added to an Nb-C nanocomposite, it hinders the grain growth and thus a reduced size of the NbC grains is observed. The Si segregates to the amorphous matrix forming a-SiC. At the same time the resistivity increases and the hardness is reduced. With even higher amounts of Si (>25 at.%) into the Nb-Si-C material, grain growth is no longer possible and the material becomes amorphous. In order to separate between effects from the addition of Si and the choice of transition metal I compare the Nb-Si-C system to already published results for the Zr-Si-C system. I find that the hardness of the material depends on the amount of strong Si-C bonds rather than the type of transition metal. The reduced elastic modulus is, however, dependent on the choice of transition metal. I therefore suggest that it is possible to make Me-Si-C films with high wear resistance by an appropriate choice of transition metal and composition. Electron microscopy was of importance for determining amorphous structures of Nb-Si-C and Zr-Si-C at high Si contents. However, the investigations were obstructed by electron beam induced crystallization. Further investigations show that the energy transferred from the beam electrons to C and Si atoms in the material is enough to cause atomic displacements. The displacements cause volume fluctuations and thereby enhance the mobility of all the atoms in the material. The result is formation of MeC grains, which are stable to further irradiation. Finally, I have studied substitution of Ge for Si in a ternary system looking at Nb-Ge-C thin films. I show that the films consist of nc-NbC/a-C/a-Ge and that Ge in a similar way to Si decreases the size of the crystalline NbC grains. However, a transition to a completely amorphous material is not seen even at high Ge contents (~30 at.%). Another dissimilarity is that while Si bonds to C and forms a matrix of a-SiC, Ge tends to bond to Ge.
2
Garg, Aaron R. "Transition metal carbide and nitride nanoparticles with Noble metal shells as enhanced catalysts." Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/121890.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2018Cataloged from PDF version of thesis. Page 157 blank. Vita.
Includes bibliographical references (pages 137-153).
Core-shell nanostructures represent a promising and versatile design platform for enhancing the performance of noble metal catalysts while reducing the cost. Early transition metal carbides (TMCs) and nitrides (TMNs) have been identified as ideal core materials for supporting noble metal shells owing to their earth-abundance, thermal and chemical stability, electrical conductivity, and their ability to bind strongly to noble metals while still being immiscible with them. Unfortunately, the formation of surface oxides or carbon on TMCs and TMNs presents a difficult synthetic challenge for the deposition of atomically thin, uniform noble metal layers. Recent advances have enabled the synthesis of TMC core nanoparticles with noble metal shells (denoted as NM/TMC), although applicability toward TMN cores has not been previously demonstrated. Furthermore, the complete properties of these unique materials are still unknown.
This thesis conducts a detailed investigation of the synthesis, characterization, and catalytic performance of NM/TMC and NM/TMN core-shell nanoparticles to provide a comprehensive understanding of their material properties and the underlying phenomena. First, in-situ studies yielded insight into the mechanism behind the high temperature self-assembly of NM/TMC particles, indicating the presence of a metallic alloy phase preceding the formation of the core-shell structure upon insertion of carbon into the lattice. Next, the synthesis of NM/TMN nanoparticles was demonstrated via nitridation of a parent NM/TMC, and the structural and electronic properties of both core-shell materials were examined through in-situ X-ray absorption spectroscopy (XAS). The analysis revealed significant alterations to the electronic structure of the noble metal shell due to bonding interactions with the TMC and TMN cores, which led to weakened adsorbate binding energies.
Finally, the materials displayed improved performance for the oxygen reduction reaction (ORR), a critical challenge for fuel cell technologies. Notably, particles with complete, uniform shells exhibited unprecedented stability during electrochemical ageing at highly oxidizing conditions, highlighting the great potential of core-shell architectures with earth-abundant TMC and TMN cores for future ORR applications. Overall, this work will provide new opportunities toward the design of enhanced noble metal catalysts and enable further optimization of their performance.
by Aaron R. Garg.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineering
3
Tan, Keng Ean. "Quantum mechanical modelling of refractory transition metal carbide films." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294188.
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Lai, Chung-Chuan. "Phase Formation of Nanolaminated Transition Metal Carbide Thin Films." Doctoral thesis, Linköpings universitet, Tunnfilmsfysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-137367.
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Research on inherently nanolaminated transition metal carbides is inspired by their unique properties combining metals and ceramics, such as higher damage tolerance, better machinability and lower brittleness compared to the binary counterparts, yet retaining the metallic conductivity. The interesting properties are related to their laminated structure, composed of transition-metalcarbide layers interleaved by non-transition-metal (carbide) layers. These materials in thin-film form are particularly interesting for potential applications such as protective coatings and electrical contacts. The goal of this work is to explore nanolaminated transition metal carbides from the aspects of phase formation and crystal growth during thin-film synthesis. This was realized by studying phases in select material systems synthesized from two major approaches, namely, fromdirect-deposition and post-deposition treatment. The first approach was used in studies on the Mo-Ga-C and Zr-Al-C systems. In the former system, intriguing properties have been predicted for the 3D phases and their 2D derivatives (socalled MXenes), while in the latter system, the phases are interesting for nuclear applications. In this work, the discovery of a new Mo-based nanolaminated ternary carbide, Mo2Ga2C, is evidenced from thin-film and bulk processes. Its structure was determined using theoretical and experimental techniques, showing that Mo2Ga2C has Ga double-layers in simple hexagonal stacking between adjacent Mo2C layers, and therefore is structurally very similar to Mo2GaC, except for the additional Ga layers. For the Zr-Al-C system, the optimization of phase composition and structure of Zr2Al3C4 in a thin-film deposition process was studied by evaluating the effect of deposition parameters. I concluded that the formation of Zr2Al3C4 is favored with a plasma flux overstoichiometric in Al, and with a minimum lattice-mismatch to the substrates. Consequently, epitaxial Zr2Al3C4 thin film of high quality were deposited on 4H-SiC(001) substrates at 800 °C. With the approach of post-deposition treatment, the studies were focused on a new method of thermally-induced selective substitution reaction of Au for the non-transition-metal layers in nanolaminated carbides. Here, the reaction mechanism has been explored in Al-containing (Ti2AlC and Ti3AlC2) and Ga-containing (Mo2GaC and Mo2Ga2C) phases. The Al and Ga in these phases were selectively replaced by Au while the carbide layers remained intact, resulting in the formation of new layered phases, Ti2Au2C, Ti3Au2C2, Mo2AuC, and Mo2(Au1-xGax)2C, respectively. The substitution reaction was explained by fast outward diffusion of the Al or Ga being attracted to the surface Au, in combination with back-filling of Au, which is chemically inert to the carbide layers,to the vacancies. The substitution reaction was further applied to Ga-containing nanolaminated carbides, (Cr0.5Mn0.5)2GaC and Mo2GaC, motivated by development of novel magnetic nanolaminates. The former experiment resulted in the formation of (Cr0.5Mn0.5)2AuC, where the retained (Cr0.5Mn0.5)2C layers allowed a comparative study on the magnetic properties under the exchange of Ga for Au. After Au substitution, reduction in the Curie temperature and the saturation magnetization were observed, showing a weakened magnetic exchange interaction of the magnetic (Cr0.5Mn0.5)2 Clayers across the Au. In the Mo2GaC case, an Fe-containing MAX phase, Mo2AC with 50 at.% of Fe on the A site, was synthesized through selective substitution of Au-Fe alloy for the Ga layers, showing the first direct evidence for Fe in the MAX-phase structure. The substitution of Fe did not take place on another Mo2GaC sample tested for Fe exchange only, indicating the essential role of Au in catalyzing the Fe-substitution reaction. The knowledge gained from this thesis work contributes to improved approaches for attaining thin films of nanolaminated transition metal carbides with desired phase composition and crystal quality. The reports on the new nanolaminated phases through exchange interactions are likely to expand the family of nanolaminated carbides and advance their properties, and trigger more studies on related (quasi-) 2D materials.
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Hunt, Sean Thomas. "Engineering carbide nanoparticles coated with noble metal monolayers for catalysis." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104207.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 231-249).
The noble metals (NMs) comprise ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), osmium (Os), iridium (Ir), platinum (Pt), and gold (Au). Together, these corrosion-resistant elements serve as nature's universal catalysts by binding reactant molecules neither too strongly nor too weakly. This allows for rapid catalytic transformations of reactants into useful products. Modern society, its current technologies, and its emerging renewable energy technologies are underpinned by precious metal catalysts. However, the noble metals are the least abundant elements in the lithosphere, making them prohibitively scarce and expensive for future global-scale technologies. Furthermore, the traditional catalyst engineering toolkit is ill-equipped to optimize the reactivity, stability, and loading of NM catalysts. The technologies developed in this thesis have two overarching implications. First, a method is developed to engineer non-sintered and metal-terminated transition metal carbide (TMC) nanoparticles. Featuring "noble metal-like" surface reactivity, TMCs are earth-abundant and exhibit many useful catalytic properties, such as carbon monoxide and sulfur tolerance. By designing TMC nanoparticles with controlled surface properties, this thesis offers new avenues for replacing noble metal catalysts with inexpensive alternatives. Second, a method is developed to synthesize TMC nanoparticles coated with atomically-thin noble metal monolayers. This offers new directions for improved catalyst designs by substantially enhancing reactivity and stability while reducing overall noble metal loadings. These synthetic achievements in nanoscale core-shell catalyst engineering were guided by computational quantum chemistry, model thin film studies, and advanced spectroscopic techniques. Examination of the catalytic utility of these new materials was performed in the context of water electrolysis, proton exchange membrane fuel cells, direct methanol fuel cells, and high temperature thermal reforming.
by Sean Thomas Hunt.
Ph. D.
6
Sallom, Zuhair Kamil. "Evolution of particle characteristics in sintered hard metal." Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236236.
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Kieschke, Robert Richard. "The interface region in titanium reinforced with silicon carbide monofilaments." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.335165.
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Al-Motin, Md Abdulla Materials Science & Engineering Faculty of Science UNSW. "Effects of metastable carbide destabilization on metal dusting of ferritic iron." Awarded by:University of New South Wales. Materials Science & Engineering, 2008. http://handle.unsw.edu.au/1959.4/41514.
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Metal dusting corrosion has been known for more than a 100 years as an industrial problem. As a result of extensive research over the last five decades several mechanisms have been evolved involving ferritic materials. However, a complete understanding is yet lacking. One of the most referred models, developed by Hochman-Grabke, suggests that formation of metastable cementite and its subsequent decomposition is the central aspect of the process. To verify this hypothesis, an Fe-Si model was designed based on silicon's ability to retard cementite formation. However, this strategy was unsuccessful because silicon oxidized and amount of silicon remaining after silica formation was not sufficient to suppress cementite. On the other hand, germanium does not form a stable oxide in the conditions employed. A alloying with germanium did prevent Fe3C formation, but not dusting, which resulted from an alternative mechanism. Dusted particles were confirmed to be cementite for pure iron specimens (where cementite scale formed) and ferrite for alloys that did not form cementite. These observations are inconsistent with the prior model. In addition, the general features of metal dusting corrosion have been characterized. Kinetics of coking and metal wastage for ferritic materials (Fe, Fe-Si, Fe-Ge and Fe-Ge-Ni) were found to be linear in nature, though respective rates may vary due to the differences in alloy catalytic activity and reaction morphologies. The carbon diffusion coefficient in cementite was evaluated from Fe3C scaling rates. Crystallographic orientations of different forms of cementite were established. Internal cementite precipitates in pure iron accounted for by a very high degree of supersaturation with respect to carbon, indicating a non-equilibrium situation. Coking and dusting rates were found to be strongly correlated and their gas composition dependence indicate the contribution of the Boudouard reaction. Reactions with fixed carbon activity gases demonstrated that kinetics rather than thermodynamics control the reaction rates. However, at a particular temperature, these rates increase with carbon activity. Activation energies for coking and dusting are equal for a given alloy, meaning that the same process controls them. For Fe-lOGe alloy, in the early stages of reaction, grains with near (001) surfaces were more susceptible to graphitization than grains having near (110) surfaces, but the underlying cause has not been revealed.
9
Kinzer, Raymond Edward. "Fourier transform infrared spectroscopy study of small transition-metal carbide clusters." [Fort Worth, Tex.] : Texas Christian University, 2009. http://etd.tcu.edu/etdfiles/available/etd-10152009-103514/unrestricted/kinzer.pdf.
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Rubiano, Rodrigo R. (Rubiano Ray). "Low temperature deposition of metal carbide films from single source precursors." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34692.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1994, and Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Materials Science & Engineering, 1994.Includes bibliographical references (leaves 71-73).
by Rodrigo R. Rubiano.
B.S.
M.S.
11
Lee, Wai Yee. "The control of metal-silicon carbide contacts using a silicon interlayer." Thesis, Swansea University, 2004. https://cronfa.swan.ac.uk/Record/cronfa42768.
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The effect of Si interlayers within Ni-SiC contacts was studied using X- ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM). Firstly an atomically clean surface was successfully obtained by depositing a 40A layer of Si onto the SiC surface, followed by an immediate anneal at 1000°C to re-evaporate the Si and remove surface contaminants. The interlayer was formed in ultra-high vacuum (UHV) conditions by depositing a known thickness of Si onto the clean SiC surface at room temperature. The metal contact was then produced by a sequential deposition of various Ni thicknesses onto the interlayer so that contact formation could be accurately monitored. These contacts were then annealed sequentially from 400°C to 1200°C. At each stage the process was characterised by XPS. Si interlayer thicknesses of 20A, 40A and 60A were tested. Results show that the consumption of Si atoms occurs, either from the Si interlayer or from the bulk SiC, with the evolution of Ni silicides and a Ni-Si-C ternary compound. In addition, chemical shifts associated with the formation of silicides and Fermi shifts (indicative of surface band bending) were also observed. When annealed at temperatures up to 1000°C, rapid formation of silicides is observed in the Si spectra, whilst the C spectra consisted of only bulk C and a small amount of free C. Conversely, for the Ni-SiC interface without a Si interlayer, the C spectra consisted of large amount of free C and hydrocarbon. As a result of annealing the interlayer samples, chemical shifts were observed as well as downward band bending, indicative of barrier lowering and complimentary to the generation of an Ohmic contact at these elevated temperatures. At 1200°C, all silicides had been re-evaporated leaving a carbon-rich surface, plus the formation of graphite on the surface. The electrical properties of the Ni-SiC contacts with and without Si interlayer were assessed using current-voltage (I/V) measurements. The contacts with a Si interlayer exhibit various behaviour from Schottky to Ohmic depending on the thickness of the Si interlayer. An Ohmic contact, which required no annealing was obtained when using a thick Si interlayer of 60A. However, Ni-Si-SiC Schottky contacts formed with 20A and 40A thick Si interlayers were shown to be able to operate, with Schottky barriers of ~1.7eV, up to 400°C higher than the normal Ni-SiC contact, indicating the superior control of these interfaces when Si is used as an interlayer.
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Johnson, Peter Kenneth. "The interaction between liquid aluminium and silicone carbide in metal composites." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46370.
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Brungs, A. J. A. "Transition metal carbides as catalysts for methane reforming." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365881.
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Cheong, Kuan Yew, and n/a. "Silicon Carbide as the Nonvolatile-Dynamic-Memory Material." Griffith University. School of Microelectronic Engineering, 2004. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20050115.101233.
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This thesis consists of three main parts, starting with the use of improved nitridation processes to grow acceptable quality gate oxides on silicon carbide (SiC)[1][7], to the comprehensive investigation of basic electron-hole generation process in 4H SiC-based metaloxidesemiconductor (MOS) capacitors [8], [9], and concluding with the experimental demonstration and analysis of nonvolatile characteristics of 4H SiC-based memory devices [10][15]. In the first part of the thesis, two improved versions of nitridation techniques have been introduced to alleviate oxide-growth rate and toxicity problems. Using a combination of nitridation and oxidation processes, a sandwich technique (nitridationoxidationnitridation) has been proposed and verified to solve the lengthy and expensive oxide-growing process in direct nitric oxide (NO) gas [1]. The nitrogen source from the toxic-NO gas has been replaced by using a nontoxic nitrous oxide (N2O) gas. The best combination of process parameters in this gas is oxide-growing temperature at 1300oC with 10% N2O [2], [3]. The quality of nitrided gate oxides obtained by this technique is lower than the sandwich technique [6], [13]. Using 4H SiC-based MOS with nitrided gate oxides grown by either of the abovementioned nitridation techniques, the fundamentals of electron-hole generation have been investigated using high-temperature capacitancetransient measurements. The contributions of carrier generation, occurring at room temperature, in the bulk and at the SiCSiO2 interface are evaluated and compared using a newly developed method [8], [9]. The effective bulk-generation rates are approximately equal for both types of nitrided oxides, whereas the effective surface-generation rates have been shown to exhibit very strong dependencies on the methods of producing the nitrided gate oxide. Based on analysis, the prevailing generation component in a SiC-based MOS capacitor with nitrided gate oxide is at SiCSiO2 interface located below the gate. Utilizing the understanding of electron-hole generation in SiC, the nonvolatile characteristics of memory device fabricated on SiC have been explored. The potential of developing a SiC-based one-transistor one-capacitor (1T/1C) nonvolatile-dynamic memory (NDM) has been analyzed using SiC-based MOS capacitors as storage elements or test structures. Three possible leakage mechanisms have been evaluated [10][16]: (1) leakage via MOS capacitor dielectric, (2) leakage due to electron-hole generation in a depleted MOS capacitor, and (3) junction leakage due to generation current occurred at a reverse-biased pn junction surrounding the drain region of a select metaloxide semiconductor fieldeffecttransistor (MOSFET). Among them, leakage through capacitor oxide remains an important factor that could affect the nonvolatile property in the proposed device, whereas others leakage mechanisms are insignificant. Based on the overall results, the potential of developing a SiC-based 1T/1C NDM is encouraging.
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Demir, Adem. "Silicon carbide fibre reinforced #beta#-sialon ceramics." Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391291.
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Haron, Che Hassan Che. "Machining of titanium alloys with coated and uncoated carbide tools." Thesis, Coventry University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262998.
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Pilz, Adrian Take. "Transient liquid phase diffusion bonding of reaction bonded silicon carbide." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241960.
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Glatzel, Stefan. "Cellulose based transition metal nano-composites : structuring and development." Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2013/6467/.
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Cellulose is the most abundant biopolymer on earth. In this work it has been used, in various forms ranging from wood to fully processed laboratory grade microcrystalline cellulose, to synthesise a variety of metal and metal carbide nanoparticles and to establish structuring and patterning methodologies that produce highly functional nano-hybrids.
To achieve this, the mechanisms governing the catalytic processes that bring about graphitised carbons in the presence of iron have been investigated. It was found that, when infusing cellulose with an aqueous iron salt solution and heating this mixture under inert atmosphere to 640 °C and above, a liquid eutectic mixture of iron and carbon with an atom ratio of approximately 1:1 forms. The eutectic droplets were monitored with in-situ TEM at the reaction temperature where they could be seen dissolving amorphous carbon and leaving behind a trail of graphitised carbon sheets and subsequently iron carbide nanoparticles. These transformations turned ordinary cellulose into a conductive and porous matrix that is well suited for catalytic applications. Despite these significant changes on the nanometre scale the shape of the matrix as a whole was retained with remarkable precision. This was exemplified by folding a sheet of cellulose paper into origami cranes and converting them via the temperature treatment in to magnetic facsimiles of those cranes. The study showed that the catalytic mechanisms derived from controlled systems and described in the literature can be transferred to synthetic concepts beyond the lab without loss of generality.
Once the processes determining the transformation of cellulose into functional materials were understood, the concept could be extended to other metals and metal-combinations. Firstly, the procedure was utilised to produce different ternary iron carbides in the form of MxFeyC (M = W, Mn). None of those ternary carbides have thus far been produced in a nanoparticle form. The next part of this work encompassed combinations of iron with cobalt, nickel, palladium and copper. All of those metals were also probed alone in combination with cellulose. This produced elemental metal and metal alloy particles of low polydispersity and high stability. Both features are something that is typically not associated with high temperature syntheses and enables to connect the good size control with a scalable process. Each of the probed reactions resulted in phase pure, single crystalline, stable materials.
After showing that cellulose is a good stabilising and separating agent for all the investigated types of nanoparticles, the focus of the work at hand is shifted towards probing the limits of the structuring and pattering capabilities of cellulose. Moreover possible post-processing techniques to further broaden the applicability of the materials are evaluated.
This showed that, by choosing an appropriate paper, products ranging from stiff, self-sustaining monoliths to ultra-thin and very flexible cloths can be obtained after high temperature treatment. Furthermore cellulose has been demonstrated to be a very good substrate for many structuring and patterning techniques from origami folding to ink-jet printing. The thereby resulting products have been employed as electrodes, which was exemplified by electrodepositing copper onto them. Via ink-jet printing they have additionally been patterned and the resulting electrodes have also been post functionalised by electro-deposition of copper onto the graphitised (printed) parts of the samples. Lastly in a preliminary test the possibility of printing several metals simultaneously and thereby producing finely tuneable gradients from one metal to another have successfully been made. Starting from these concepts future experiments were outlined.
The last chapter of this thesis concerned itself with alternative synthesis methods of the iron-carbon composite, thereby testing the robustness of the devolved reactions. By performing the synthesis with partly dissolved scrap metal and pieces of raw, dry wood, some progress for further use of the general synthesis technique were made. For example by using wood instead of processed cellulose all the established shaping techniques available for wooden objects, such as CNC milling or 3D prototyping, become accessible for the synthesis path. Also by using wood its intrinsic well defined porosity and the fact that large monoliths are obtained help expanding the prospect of using the composite. It was also demonstrated in this chapter that the resulting material can be applied for the environmentally important issue of waste water cleansing. Additionally to being made from renewable resources and by a cheap and easy one-pot synthesis, the material is recyclable, since the pollutants can be recovered by washing with ethanol. Most importantly this chapter covered experiments where the reaction was performed in a crude, home-built glass vessel, fuelled – with the help of a Fresnel lens – only by direct concentrated sunlight irradiation. This concept carries the thus far presented synthetic procedures from being common laboratory syntheses to a real world application.
Based on cellulose, transition metals and simple equipment, this work enabled the easy one-pot synthesis of nano-ceramic and metal nanoparticle composites otherwise not readily accessible. Furthermore were structuring and patterning techniques and synthesis routes involving only renewable resources and environmentally benign procedures established here. Thereby it has laid the foundation for a multitude of applications and pointed towards several future projects reaching from fundamental research, to application focussed research and even and industry relevant engineering project was envisioned.Die vorliegende Arbeit beschäftigt sich mit der Synthese und Strukturierung von Nanokompositen, d.h. mit ausgedehnten Strukturen, welche Nanopartikel enthalten. Im Zuge der Arbeit wurde der Mechanismus der katalytischen Graphitisierung, ein Prozess, bei dem ungeordneter Kohlenstoff durch metallische Nanopartikel in geordneten (graphitischen) Kohlenstoff überführt wird, aufgeklärt. Dies wurde exemplarisch am Beispiel von Zellulose und Eisen durchgeführt. Die untersuchte Synthese erfolgte durch das Lösen eines Eisensalzes in Wasser und die anschließende Zugabe von so viel Zellulose, dass das die gesamte Eisensalzlösung aufgenommen wurde. Die so erhaltene Mischung wurde anschließend unter Schutzgas innerhalb kürzester Zeit auf 800 °C erhitzt. Hierbei zeigte sich, dass zu Beginn der Reaktion Eisenoxidnanopartikel (Rost) auf der Oberfläche der Zellulose entstehen. Beim weiteren Erhöhen der Temperatur werden diese Partikel zu Eisenpartikeln umgewandelt. Diese lösen dann kleine Bereiche der Zellulose auf, wandeln sich in Eisenkarbid um und scheiden graphitischen Kohlenstoff ab. Nach der Reaktion sind die Zellulosefasern porös, jedoch bleibt ihre Faserstruktur vollkommen erhalten. Dies konnte am Beispiel eines Origamikranichs gezeigt werden, welcher nach dem Erhitzen zwar seine Farbe von Weiß zu Schwarz verändert hatte, ansonsten aber seine Form vollkommen beibehält. Aufgrund der eingebetteten Eisenkarbid Nanopartikel war der Kranich außerdem hochgradig magnetisch. Basierend auf dieser Technik wurden außerdem winzige metallische Nanopartikel aus Nickel, Nickel-Palladium, Nickel-Eisen, Kobalt, Kobalt-Eisen und Kupfer, sowie Partikel aus den Verbundkarbiden Eisen-Mangan-Karbid und Eisen-Wolfram-Karbid, jeweils in verschiedenen Mischungsverhältnissen, hergestellt und analysiert. Da die Vorstufe der Reaktion flüssig ist, konnte diese mit Hilfe eines einfachen kommerziellen Tintenstrahldruckers strukturiert auf Zellulosepapier aufgebracht werden. Dies ermöglicht gezielt Leiterbahnen, bestehend aus graphitisiertem Kohlenstoff, in ansonsten ungeordnetem (amorphen) Kohlenstoff zu erzeugen. Diese Methode wurde anschließend auf Systeme mit mehreren Metallen übertragen. Hierbei wurde die Tatsache, dass moderne Drucker vier Tintenpatronen beherbergen, ausgenutzt um Nanopartikel mit beliebigen Mischungsverhältnisse von Metallen zu erzeugen. Dieser Ansatz hat potentiell weitreichende Auswirkungen im Feld der Katalyse, da hiermit hunderte oder gar tausende Mischungen simultan erzeugt und getestet werden können. Daraus würden sich große Zeiteinsparungen (Tage anstelle von Monaten) bei der Entwicklung neuer Katalysatoren ergeben. Der letzte Teil der Arbeit beschäftigt sich mit der umweltfreundlichen Synthese der obengenannten Komposite. Hierbei wurden erfolgreich Altmetall und Holzstücke als Ausgangstoffe verwandt. Zusätzlich wurde gezeigt, dass die gesamte Synthese ohne Verwendung von hochentwickeltem Equipment durchgeführt werden kann. Dazu wurde eine sogenannte Fresnel-Linse genutzt um Sonnenlicht zu bündeln und damit direkt die Reaktionsmischung auf die benötigten 800 °C zu erhitzen. Weiterhin wurde ein selbst gebauter Glasreaktor eingesetzt und gezeigt, wie das entstehende Produkt als Abwasserfilter genutzt werden kann. Die Kombination dieser Ergebnisse bedeutet, dass dieses System sich beispielsweise zum Einsatz in Katastrophenregionen eignen würde, um ohne Strom und besondere Ausrüstung vor Ort Wasserfilter herzustellen.
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Malin, Leijon Lind. "An investigation of metallic glass as binder phase in hard metal." Thesis, Linköpings universitet, Tunnfilmsfysik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-116475.
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In this study, the possibilities to produce metallic glass as binder phase in hard metal by means of powder metallurgical methods have been investigated. The aim of the study was to do an initial investigation about metallic glass as alternative binder phase to cobalt in hard metal. Production of samples with metallic glass forming alloys and an amorphous powder as binder phase in hard metal by means of quenching and hot pressing have been performed. Moreover, mechanical alloying of metallic glass forming powder to achieve amorphicity has been performed. The samples and powders were analyzed by means of XRD, LOM, STA, SEM and EDS. The results showed that no glass formation of the binder phase was achieved by quenching, hot pressing or mechanical alloying. However, interesting information about glass formation by means of metallurgical methods was obtained. The main conclusion was that production of metallic glass by means of metallurgical methods is complicated due to changes in the binder phase composition throughout the production process as well as requirements of high cooling rates when quenching and high pressures when hot pressing.
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Okeke, Christopher Igwedinma. "Threading and turning of aerospace materials with coated carbide inserts." Thesis, London South Bank University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297919.
Full textAbstract:
The first part of this study involve an evaluation of the performance of TiN and AlZ03 single layer coated cemented carbide tools when threading inclusion modified, 708M40T (En 19T) 817M40T (En 24T) and Jethete steels at high cutting conditions by monitoring tool wear, failure modes, post threading workpiece properties, micro and macro-surface alterations and subsurface microhardness variation of threaded surfaces. Test results show that flank wear was the dominant failure mode, increasing rapidly when machining at the top speed of 225 m min,l due to the high temperature generated which accelerates thermally related wear mechanisms. Tool life, surface finish, hardness variation and component forces during threading were influenced by the geometry of the cutting edge, shape of wear/length of wear along tool nose/cutting edge after threading. Formation of flake-like oxide debris on the worn inserts was found to increase with nickel content in the workpiece material. The Al20) coated carbide inserts with K05 - K20 substrate gave longer tool life, lower cutting forces, better surface finish! damages as well as minimum hardness variation after threading compared with the TiN coated VSX grade with P20-P30 substrates. This can be related to their superior hardness, density, transverse rupture strength as well as the unalloyed WC fine grained substrate (1/lm) in addition to the high hot hardness, excellent chemical stability and low thermal conductivity of the AlZ03 coating at elevated temperatures. A formula for tool rejection was also developed during this study based on the average flank wear (VBb) and growth in thread root (GTR) in order to establish a scientific basis for assessing wear of threading tools. The second part of this study involve single point turning of a nickel base, G263, alloy using rhomboid-shaped PVD coated (TiN/TiCN/TiN, TiAIN and TiZrN) carbide tools at high speed cutting conditions. The worn tool edges revealed adhesion of a compact fin-shaped structure of hardened burrs with saw-tooth edges. The compact structure also formed on the cut surface of the workpiece material. The use of coolant during machining tend to work harden the root of the burr thereby restricting tool entry at the cutting zone leading to the generation of excessive feed force which subjects the tool edge to premature fracture and consequently lower tool life. The serrated/saw-tooth like edges of the burr encourages abrasion wear on the tool flank face and the formation of shallow cavities/lateral cracks where fragments of hardened workpiece material are deposited causing deterioration of the machined surfaces. Tool life was generally influenced by the cutting conditions employed as well as the insert geometry. Increasing cutting conditions (speed, feed and depth of cut) led to chipping of the cutting edge and/or flaking of coating layers as well as notching and fracture of the cutting edge. These failure modes jointly contributed to lowering tool life during machining. The TiN/TiCN/TiN coated KC732 (Tool A) inserts with positive sharp edges gave overall performance at the optimum cutting conditions established under finishing operation. This is followed by the TiN/TiCN/TiN coated KC732 (Tool B), TiAlN coated KC313 (Tool C) and lastly the TiZrN coated KC313 (Tool D) inserts' with razor sharp edges. Under roughing operation, the ranking order of tool performance is the TiZrN coated KC313 (Tool D), TiN/TiCN/TiN coated KC732 (Tool A), TiAlN coated KC313 (Tool C) and lastly the TiN/TiCN/TiN coated KC732 {Tool B). The difference in tool geometry and coating materials contributed to the relative order of tool performance.
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Rees, Eric John. "The role of synthesis conditions for metal-carbide electrocatalysts in fuel cells." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609023.
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Rix, Michael V. "Development of silicon carbide monofilaments for the reinforcement of metal matrix composites." Thesis, University of Surrey, 2018. http://epubs.surrey.ac.uk/848794/.
Full textAbstract:
Silicon carbide (SiC) monofilaments are high strength, continuous ceramic fibres produced through chemical vapour deposition (CVD) and used to reinforce metal matrix composites. Such composites have excellent mechanical properties. However, they are expensive to manufacture and the monofilaments must be highly reproducible to ensure reliability of the resulting composite. TISICS Ltd are the sole producers of the material outside of the United States of America and have recently developed two new monofilaments, SM3256 (140 μm diameter) and SM3240 (100 μm diameter) with enhanced mechanical properties and reduced cost of production. These monofilaments and composite panels have been evaluated through tensile testing. They have been found to be highly reproducible over three years of production with the monofilaments possessing an average tensile strength of 4.0±0.2 GPa with a Weibull modulus of 50±10. Recent advances in plasma focussed ion beam (PFIB) milling techniques and scanning transmission electron microscopy (STEM) have been exploited to produce specimens revealing the interior of the monofilaments with unparalleled detail and precision. Raman spectroscopy and Auger spectroscopy have been used to characterise the microstructure and composition of the monofilaments and inform their development. The process for depositing a protective coating on the monofilaments has been improved, resulting in a 17% decrease in the total cost of CVD feedstock chemicals required. Previously unobserved nanoscale voids in the tungsten filament substrate have been identified as a critical process variable potentially responsible for the narrow strength distribution of the monofilaments. Analysis of the monofilament microstructures has indicated the potential for increasing the production speed of SM3256. Experimental trials have resulted in up to 75% faster production however a resulting decrease in performance demonstrates that further work is necessary. This research has resulted in significant cost reductions and has improved the economic viability of the monofilaments. The demonstration of reproducibility of the material properties has contributed to ongoing qualification for their use in aerospace components. The potential for further fundamental improvements to the process has been identified.
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McDermid, Joseph Robert. "The joining of reaction bonded silicon carbide to inconel 600 /." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63772.
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Bretzler, Patrick [Verfasser]. "Tungsten Carbide as Alternative for Precious Metal Based Hydrogenation- and Electrocatalysts / Patrick Bretzler." München : Verlag Dr. Hut, 2020. http://d-nb.info/1219476544/34.
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Koh, A. "Investigation of thermal oxidation on silicon carbide for power metal-oxide-semiconductor devices." Thesis, Swansea University, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637818.
Full textAbstract:
The rapid progress in the semiconductors technology and the increasing demand in performance for the high power and high frequency semiconductor devices have prompt for the search of a new semi-conducting material to meet the needs in the new millennium. Silicon Carbide (SiC), a wide band gap compound semiconductor is deemed to be the most likely candidate for its unique ability to thermally oxidise, forming Silicon Dioxide (SiO2). This advantage allows the fabrication of Metal-Oxide-Semiconductor (MOS) devices on SiC, thus has been a focus in the semiconductor research arena with a drastic increase in world-wide research activities particularly during the last two years. The research work in this thesis focuses on the basics of the thermal oxidation on Silicon Carbide, investigating on the physics behind the problems hampering the ability to grow oxide of acceptable quality of MOS device application. This is achieved by providing experimental results supporting initial hypothetical "Carbon Cluster Model" phenomenon described by Bassler et, al. observed in SiC/SiO2 interface. This is of vital importance as the success of fabricating a SiC MOS device would ultimately depends on the ability to produce high quality oxide with low SiC/SiO2 interface states density and other oxide trap charges. The work also includes a comparative study on the different methods of thermal oxidation on SiC such as conventional wet and dry thermal oxidation on SiC, and Sacrificial Silicon Oxidation (SSO) and SiC, which utilises the advantage of temperature differences between thermally oxidising Silicon (Si) and SiC. This has yield promising results. Consequently the results also suggest that the SSO technique, when optimised can be further utilised as a form of surface preparation of SiC.
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Im, Hsung Jai. "Metal contacts to silcon carbide and galliumnitride studied with ballistic electron emission microscopy." Connect to this title online, 2001. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1000844302.
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Thesis (Ph. D.)--Ohio State University, 2001.Title from first page of PDF file. Document formatted into pages; contains xiii, 165 p.; also contains graphics (some col.). Includes abstract and vita. Advisor: Jonathan P. Pelz, Dept. of Physics. Includes bibliographical references (p. 160-165).
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Pajares, Rojas Arturo Javier. "Study of transition metal carbide catalysts of group 5 in the RWGS reaction." Doctoral thesis, Universitat de Barcelona, 2021. http://hdl.handle.net/10803/672225.
Full textAbstract:
Nowadays there is a growing interest in the capture and utilization of CO2 because of the increase of its concentration in the atmosphere. Captured CO2 can be recycled through different processes to obtain several value-added products, such as fuels. Current processes for the production of synthetic fuel and of some other products use syngas, a mixture of CO and H2 of varying composition, as feedstock. Syngas can be obtained by the catalytic reduction of CO2 to CO using an excess of H2 through the reverse water gas shift (RWGS) reaction. The RWGS reaction is endothermic and to reach appropriate conversion values, needs high temperature and the presence of a catalyst. Suitable catalysts should present not only high activity and selectivity, but also a good stability and low cost. In this context, transition metal carbides (TMCs) have been proposed as a good alternative to conventional catalysts to be used in the RWGS reaction. Theoretical and experimental investigations have shown that molybdenum carbide presents good catalytic behavior in the RWGS reaction. However, very few investigations about the use of TMCs of group 5 as catalysts in this reaction have been reported.
The main objective of this work is the study of the CO2 reduction to CO under RWGS conditions over catalysts based on transition metal carbides of group 5 (G5TMC=VC, NbC and TaC). Additionally, some of these materials have been tested as catalysts in the methanol steam reforming (MSR). The catalysts have been characterized before and after reaction by means of different techniques, such as, X-ray diffraction, N2 adsorption-desorption isotherms, Raman spectroscopy, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, scanning and transmission electron microscopy, and precession electron diffraction. In addition, studies of CO2 adsorption and reactivity have been carried out using thermogravimetry, calorimetry and in-situ diffuse reflectance infrared spectroscopy.
The preparation of bulk and, ɣ-Al2O3-, TiO2-, SBA-15-, SiO2-, CeO2-, ZrO2- and activated carbon-supported catalysts, based on G5TMC has been performed avoiding the use of carburizing methods. A sol-gel method using 4,5-
dicyanoimidazole as carbon source, metal chloride and alkoxide as metal precursors, and different thermal treatments has been developed. The use of metal alkoxides resulted in the preparation of bulk G5TMCs with smaller crystallite size compared to that obtained when metal chloride was used. Moreover, for metal alkoxide precursors, a decrease of the crystallite size of G5TMC was observed when the 4,5-dicyanoimidazole/metal precursor molar ratio was increased. An increase of the temperature of treatment led to a higher crystallite size of the G5TMCs. For supported vanadium carbide catalysts, VCx with different crystallite sizes were obtained as a function of the support and/or method of preparation used.
The catalysts were tested under RWGS conditions, CO2/H2=1/3 in the 573- 873 K range. The catalysts based on vanadium carbide were active and highly CO selective, reaching values of CO selectivity near to 100% above 773 K. The samples based on niobium carbide and tantalum carbide were inactive under the experimental conditions used.
For bulk vanadium carbide catalysts, the coexistence of two different phases, VC (stoichiometric), and V8C7 (C deficient) was determined. The presence of a higher amount of V8C7 phase was related with a smaller VCx crystallite size and a higher CO2 adsorption energy. The catalyst, which presented a higher presence of V8C7, showed a better catalytic behavior in all the temperature range studied.
The experimental results obtained in this work have been interpreted in the light of theoretical studies performed in the group of Prof. Illas (University of Barcelona) in a frame of a collaborative research. The dissociative adsorption of CO2 to CO+O over G5TMC is proposed; a subsequent surface oxy-carbide species formation and CO release would take place. The presence of C vacancies in vanadium carbide catalysts allows the reactants to absorb more strongly, lowering the energy barrier for both H2 and CO2 dissociation steps. VC- based catalysts with smaller VCx crystallite size, showed lower activation energy in the RWGS reaction under the conditions used.
Supported vanadium carbide catalysts produced a higher amount of CO per mol of V than the corresponding bulk catalyst. VC/Al2O3, VC/SiO2 and VC/AC,
which had the smallest crystallite sizes of VCx phase showed the best catalytic behavior in the RWGS reaction.
Some catalysts have been tested in the RWGS during 4 days, showing a high stability under the reaction conditions used.
Finally, several bulk and supported G5TMC catalysts were tested under MSR conditions (CH3OH/H2O=1/1, 573-723 K). CH4 was the main product found when vanadium carbide catalysts were used; this is related with the methanol decomposition. On the other hand, for niobium carbide and tantalum carbide catalysts, HCHO was the main product, which could be formed via methanol dehydrogenation. After MSR catalytic tests, the characterization of used catalysts revealed a high SBET reduction and the presence of abundant carbon deposits, which is associated with the high deactivation of the catalysts observed under the reaction conditions used.El principal objetivo de este trabajo es el estudio de catalizadores basados en carburos de metales de transición del grupo 5 (CMTG5=VC, NbC and TaC) en la reducción selectiva de CO2 a CO bajo condiciones de reacción inversa de desplazamiento de agua (RWGS por sus siglas en inglés). Adicionalmente, algunos de estos materiales se han probado como catalizadores en el reformado de metanol con vapor (MSR por sus siglas en inglés). Los catalizadores se han caracterizado adecuadamente antes y después de su uso en reacción mediante diversas técnicas físico-químicas. Asimismo, se han llevado a cabo estudios de adsorción y reactividad de CO2 mediante termogravimetría, calorimetría y espectroscopia infrarroja en modo reflectancia difusa in situ. Se han ensayado los diferentes materiales bajo condiciones de RWGS, CO2/H2=1/3 en el rango de 573-873 K. Los catalizadores basados en carburo de vanadio fueron activos y altamente selectivos a CO alcanzando valores cercanos al 100% a partir de 773 K. Los materiales basados en carburo de niobio y carburo de tántalo fueron inactivos bajo las condiciones experimentales usadas. En los catalizadores de carburo de vanadio másico se pudo determinar la coexistencia de dos fases, una estequiométrica VC, y otra deficiente en C, V8C7. La presencia de una mayor cantidad de la fase V8C7 se relaciona con el menor tamaño de cristalito y se refleja en una mayor energía de adsorción de CO2. El catalizador que presentó mayor presencia de la fase V8C7 mostró el mejor comportamiento catalítico en todo el rango de temperatura estudiado. Todos los catalizadores soportados de carburo de vanadio produjeron una mayor cantidad de CO por mol de V que el catalizador másico correspondiente. Los catalizadores soportados, VC/Al2O3, VC/SiO2 y VC/AC, que tuvieron los menores tamaños de cristalito de la fase VCx mostraron el mejor comportamiento catalítico. Algunos catalizadores se ensayaron en la RWGS durante 4 días, mostrando una elevada estabilidad bajo las condiciones de reacción utilizadas. Finalmente, diversos catalizadores másicos y soportados de CMTG5 se ensayaron bajo condiciones de MSR, CH3OH/H2O=1/1 en el rango de 573-723 K. Con los catalizadores de carburo de vanadio se obtuvo como producto mayoritario CH4. Por otra parte, con los catalizadores de carburo de niobio y carburo de tántalo, se obtuvo mayoritariamente HCHO. La caracterización de los catalizadores usados en el MSR reveló una gran reducción del área superficial SBET y la presencia de abundantes depósitos carbonosos, lo que se asocia con la elevada desactivación observada bajo las condiciones de reacción utilizadas.
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Kothari, Mitul Arvind. "Welding of cast A359/SiC/10p metal matrix composites." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2699.
Full textAbstract:
Welding of metal matrix composites (MMCs) is an alternative to their
mechanical joining, since they are difficult to machine. Published literature in fusion
welding of similar composites shows metallurgical problems. This study investigates the
weldability of A359/SiC/10p aluminum SiC MMC. Statistical experiments were
performed to identify the significant variables and their effects on the hardness, tensile
and bending strengths, ductility, and microstructure of the weld. Finite Element
Analysis (FEA) was used to predict the preheat temperature field across the weld and the
weld pool temperature.
Welding current, welding speed, and the preheat temperature (300-350??C)
affected the weld quality significantly. It was seen that the fracture of the welded
specimens was either in the base MMC or in the weld indicating a stronger interface
between the weld and the base MMC. Oxides formation was controlled along the weld
joint. Low heat inputs provided higher weld strengths and better weld integrity. It was
found that the weld strengths were approximately 85% of the parent material strength.
The weld region had higher extent of uniform mixing of base and filler metal when
welded at low currents and high welding speeds. These adequate thermal conditions
helped the SiC particles to stay in the central weld region. The interface reaction
between the matrix and SiC particles was hindered due to controlled heat inputs and
formation of harmful Al4C3 flakes was suppressed. The hardness values were found to
be slightly higher in the base metal rich region. There was no significant loss in the
hardness of the heat affected zone. The ductility of the weld was considerably increased
to 6.0-7.0% due to the addition of Al-Si filler metal.
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Nygren, Kristian. "Magnetron Sputtering of Nanocomposite Carbide Coatings for Electrical Contacts." Doctoral thesis, Uppsala universitet, Oorganisk kemi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302063.
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Today’s electronic society relies on the functionality of electrical contacts. To achieve good contact properties, surface coatings are normally applied. Such coatings should ideally fulfill a combination of different properties, like high electrical conductivity, high corrosion resistance, high wear resistance and low cost. A common coating strategy is to use noble metals since these do not form insulating surface oxides. However, such coatings are expensive, have poor wear resistance and they are often applied by electroplating, which poses environmental and human health hazards. In this thesis, nanocomposite carbide-based coatings were studied and the aim was to evaluate if they could exhibit properties that were suitable for electrical contacts. Coatings in the Cr-C, Cr-C-Ag and Nb-C systems were deposited by magnetron sputtering using research-based equipment as well as industrial-based equipment designed for high-volume production. To achieve the aim, the microstructure and composition of the coatings were characterized, whereas mechanical, tribological, electrical, electrochemical and optical properties were evaluated. A method to optically measure the amount of carbon was developed. In the Cr-C system, a variety of deposition conditions were explored and amorphous carbide/amorphous carbon (a-C) nanocomposite coatings could be obtained at substrate temperatures up to 500 °C. The amount of a-C was highly dependent on the total carbon content. By co-sputtering with Ag, coatings comprising an amorphous carbide/carbon matrix, with embedded Ag nanoclusters, were obtained. Large numbers of Ag nanoparticles were also found on the surfaces. In the Nb-C system, nanocrystalline carbide/a-C coatings could be deposited. It was found that the nanocomposite coatings formed very thin passive films, consisting of both oxide and a-C. The Cr-C coatings exhibited low hardness and low-friction properties. In electrochemical experiments, the Cr-C coatings exhibited high oxidation resistance. For the Cr-C-Ag coatings, the Ag nanoparticles oxidized at much lower potentials than bulk Ag. Overall, electrical contact resistances for optimized samples were close to noble metal references at low contact load. Thus, the studied coatings were found to have properties that make them suitable for electrical contact applications.
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Hicks, Kevin Paul. "A study of magnesium and magnesium alloy composites containing alumina and silicon carbide-based fibres." Thesis, University of Bath, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359089.
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Im, Hsung J. "Metal Contacts to Silicon Carbide and Gallium Nitride Studied with Ballistic Electron Emission Microscopy." The Ohio State University, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=osu1000844302.
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Im, Hsung Jai. "Metal contacts to silicon carbide and gallium nitride studied with ballistic electron emission microscopy /." The Ohio State University, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=osu1486402957194756.
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Hass, Joanna R. "Structural characterization of epitaxial graphene on silicon carbide." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26654.
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Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2009.Committee Co-Chair: Conrad, Edward; Committee Co-Chair: First, Phillip; Committee Member: Carter, Brent; Committee Member: de Heer, Walter; Committee Member: Zangwill, Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Bawane, Kaustubh Krishna. "Silicon Carbide - Nanostructured Ferritic Alloy Composites for Nuclear Applications." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/96403.
Full textAbstract:
Silicon carbide and nanostructured ferritic alloy (SiC-NFA) composites have the potential to maintain the outstanding high temperature corrosion and irradiation resistance and enhance the mechanical integrity for nuclear cladding. However, the formation of detrimental silicide phases due to reaction between SiC and NFA remains a major challenge. By introducing a carbon interfacial barrier on NFA (C@NFA), SiC-C@NFA composites are investigated to reduce the reaction between SiC and NFA. In a similar way, the effect of chromium carbide (Cr3C2) interfacial barrier on SiC (Cr3C2@SiC) is also presented for Cr3C2@SiC-NFA composites. Both the coatings were successful in suppressing silicide formation. However, despite the presence of coatings, SiC was fully consumed during spark plasma sintering process. TEM and EBSD investigations revealed that spark plasma sintered SiC-C@NFA and Cr3C2@SiC-NFA formed varying amounts of different carbides such as (Fe,Cr)7C3, (Ti,W)C and graphite phases in their microstructure. Detailed microstructural examinations after long term thermal treatment at 1000oC on the microstructure of Cr3C2@SiC-NFA showed precipitation of new (Fe,Cr)7C3, (Ti,W)C carbides and also the growth of existing and new carbides. The results were successfully explained using ThermoCalc precipitation and coarsening simulations respectively.
The oxidation resistance of 5, 15 and 25 vol% SiC@NFA and Cr3C2@SiC-NFA composites at 500-1000oC temperature under air+45%water vapor containing atmosphere is investigated. Oxidation temperature effects on surface morphologies, scale characteristics, and cross-sectional microstructures were investigated and analyzed using XRD and SEM. SiC-C@NFA showed reduced weight gain but also showed considerable internal oxidation. Cr3C2@SiC-NFA composites showed a reduction in weight gain with the increasing volume fraction of Cr3C2@SiC (5, 15 and 25) without any indication of internal oxidation in the microstructure. 25 vol% SiC-C@NFA and 25 vol% Cr3C2@SiC-NFA showed over 90% and 97% increase in oxidation resistance (in terms of weight gain) as compared to NFA. The results were explained using the fundamental understanding of the oxidation process and ThermoCalc/DICTRA simulations.
Finally, the irradiation performance of SiC-C@NFA and Cr3C2@SiC-NFA composites was assessed in comparison with NFA using state-of-the-art TEM equipped with in-situ ion irradiation capability. Kr++ ions with 1 MeV energy was used for irradiation experiments. The effect of ion irradiation was recorded after particular dose levels (0-10 dpa) at 300oC and 450oC temperatures. NFA sample showed heavy dislocation damage at both 300oC and 450oC increasing gradually with dose levels (0-10 dpa). Cr3C2@SiC-NFA showed similar behavior as NFA at 300oC. However, at 450oC, Cr3C2@SiC-NFA showed remarkably low dislocation loop density and loop size as compared to NFA. At 300oC, microstructures of NFA and Cr3C2@SiC-NFA show predominantly 1/2<111> type dislocation loops. At 450oC, NFA showed predominantly <100> type loops, however, Cr3C2@SiC-NFA composite was still predominant in ½<111> loops. The possible reasons for this interesting behavior were discussed based on the large surface sink effects and enhanced interstitial-vacancy recombination at higher temperatures. The molecular dynamics simulations did not show considerable difference in formation energies of ½<111> and <100> loops for NFA and Cr3C2@SiC-NFA composites. The additional Si element in the SiC-NFA sample could have been an important factor in determining the dominant loop types. SiC-C@NFA composites showed heavy dislocation damage during irradiation at 300oC. At 450oC, SiC-C@NFA showed high dislocation damage in thicker regions. Thinner regions near the edge of TEM samples were largely free from dislocation loops. The precipitation and growth of new (Ti,W)C carbides were observed at 450oC with increasing irradiation dose. (Fe,Cr)7C3 precipitates were largely free from any dislocation damage. Some Kr bubbles were observed inside (Fe,Cr)7C3 precipitates and at the interface between α-ferrite matrix and carbides ((Fe,Cr)7C3, (Ti,W)C). The results were discussed using the fundamental understanding of irradiation and ThermoCalc simulations.Doctor of Philosophy
With the United Nations describing climate change as 'the most systematic threat to humankind', there is a serious need to control the world's carbon emissions. The ever increasing global energy needs can be fulfilled by the development of clean energy technologies. Nuclear power is an attractive option as it can produce low cost electricity on a large scale with greenhouse gas emissions per kilowatt-hour equivalent to wind, hydropower and solar. The problem with nuclear power is its vulnerability to potentially disastrous accidents. Traditionally, fuel claddings, rods which encase nuclear fuel (e.g. UO2), are made using zirconium based alloys. Under 'loss of coolant accident (LOCA) scenarios' zirconium reacts with high temperature steam to produce large amounts of hydrogen which can explode. The risks associated with accidents can be greatly reduced by the development of new accident tolerant materials. Nanostructured ferritic alloys (NFA) and silicon carbide (SiC) are long considered are leading candidates for replacing zirconium alloys for fuel cladding applications. In this dissertation, a novel composite of SiC and NFA was fabricated using spark plasma sintering (SPS) technology. Chromium carbide (Cr3C2) and carbon (C) coatings were employed on SiC and NFA powder particles respectively to act as reaction barrier between SiC and NFA. Microstructural evolution after spark plasma sintering was studied using advanced characterization tools such as scanning electron microscopy (SEM), electron backscattered diffraction (EBSD), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) techniques. The results revealed that the Cr3C2 and C coatings successfully suppressed the formation of detrimental reaction products such as iron silicide. However, some reaction products such as (Fe,Cr)7C3 and (Ti,W)C carbides and graphite retained in the microstructure. This novel composite material was subjected to high temperature oxidation under a water vapor environment to study its performance under the simulated reactor environment. The degradation of the material due to high temperature irradiation was studied using state-of-the-art TEM equipped with in-situ ion irradiation capabilities. The results revealed excellent oxidation and irradiation resistance in SiC-NFA composites as compared to NFA. The results were discussed based on fundamental theories and thermodynamic simulations using ThermoCalc software. The findings of this dissertation imply a great potential for SiC-NFA based composites for future reactor material designs.
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Giordano, Cristina [Verfasser], and Peter [Akademischer Betreuer] Strauch. "A neglected world: transition metal nitride and metal carbide based nanostructures : novel synthesis and future perspectives / Cristina Giordano ; Betreuer: Peter Strauch." Potsdam : Universität Potsdam, 2015. http://d-nb.info/1218792590/34.
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Rösth, Eric. "Ageing tests of cemented carbide powders : An investigation for increased quality of metal cutting inserts." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-355320.
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In this study, the ageing effects on powder used for cemented carbide insert production are examined. Ageing is throughout this study, defined as the time dependent change of the magnetic properties: coercive field strength and saturation magnetization. Testing is done using eight different powder compositions stored in both air and in an argon cabinet for 10 weeks, where sampling is done at specific intervals. Samples are stored in vacuum sealed bags for a combined sintering at the last phase of the test. Magnetic properties are assumed to be dependent on the amount of oxides needed to be reduced by taking carbon from the material itself during the vacuum stage of the sintering. To achieve interpretive results, this study also tested available sintering furnaces (DMK and DEK) by sintering trays with patterns of test pieces. This shows that DEK furnaces are much better for the ageing tests performed in this study, since less variation of the magnetic properties are measured because of the symmetrical heat gradient over each tray. Ageing tests strongly suggest that the cause of ageing comes from water absorbed by the PEG in the powder composition. Changing the molecular weight of the PEG seems to have an effect on the powder's ageing sensitivity. Measurements performed in this study show less ageing for Cr-rich DA-powders than for cubic carbide rich DQ-powders.
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Gao, Qin. "First-Principles Study of Bismuth at Transition Metal Surfaces, Interfaces and Boron Carbide Bulk Thermodynamics." Research Showcase @ CMU, 2015. http://repository.cmu.edu/dissertations/978.
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With the help of density functional theory (DFT) and powerful computers, firstprinciples computation of solid state systems can be performed to accurately explain and predict nanoscale phenomena. This thesis focuses on our first-principles investigation of bismuth on the Ni(111) surface, at transition metal interfaces, and describes our study of boron carbide bulk thermodynamics combining DFT calculations, machine learning methods and Monte Carlo simulations. Our Bi on Ni(111) surface study confirms the stability of odd-layer Bi films, proposes specific stable atomic structures, and explains their stability with covalent chemical bonding. Our research of Bi at transition metal grain boundaries verifies the stability of bilayer films, explains the difference between transition metals, and proposes a model for bilayer stability on general grain boundaries. Although DFT calculations are accurate, they can be time consuming and scale badly with system size. Our DFT-based machine learning interaction models are used to capture certain non-linear effects associated with many-body interactions blue which reduce the error of prediction by 20 − 33% comparing to a linear model. We utilize these models to evaluate the thermodynamics of boron carbide in Monte Carlo simulations and identify three boron carbide phases.
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Wakisaka, Takuo. "Rational Syntheses of New Metal Nanoparticles and Investigation of Catalytic Activity." Kyoto University, 2020. http://hdl.handle.net/2433/253114.
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Sobiyi, Kehinde Kolawole. "Machining of powder metal titanium." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6852.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: The purpose of this study is to investigate the machinability of commercially pure (CP) titanium, manufactured using the press-and-sinter PM process. To this end, CP titanium powder (-200 mesh) was compacted and sintered in vacuum (10-4 torr) for two hours at 1200°C. Small cylindrical samples were compacted at pressures varying from 350 to 600 MPa in order to determine the compressibility of the powder. Following these tests, four larger stepped-cylinder samples were compacted at pressures close to 400 MPa and sintered under similar conditions. These samples had sintered densities varying between 3.82 and 4.41 g/cm3. They were used to evaluate the machinability of the sintered titanium using face turning machining tests. The samples were machined dry, using uncoated carbide (WC-Co) cutting tool. Cutting speeds between 60-150 m/min were evaluated while keeping the feed rate and depth of cut constant at 0.15 mm/rev and 0.5 mm, respectively. The final machined surface finish and the tool wear experienced during the face turning machining tests were monitored in order to evaluate PM titanium’s machining performance. This study showed that it is possible to use the press-and-sinter PM process with CP titanium powder, with a particle size of less than 75 μm (-200 mesh), to manufacture sintered titanium. However, particle shape influences the compressibility of the powder and pressing parts of larger volume, such as the machining test sample shape, is challenging when using such small particle size powder. Processing conditions, such as compaction pressure, sintering temperature and sintering time, influence the sintered density. Results from the machinability tests show that tool wear increases with a decrease in the porosity of the sintered titanium. A more porous sintered material has both lower strength and thermal conductivity. As these factors have opposing effects on the machinability of materials, it is concluded that the strength of the sintered titanium has a stronger influence on its machinability than the thermal conductivity. The cutting tool wear was uniform but showed indications of crater wear. The machined surface of the denser parts had minimal defects compared to less dense parts. Chip shape is long for the dense parts, and spiral for the less dense parts. The chips formed were all segmented, which is typical for titanium. The machinability of the sintered CP titanium was compared to that of wrought titanium alloys. As expected, it was found that the machinability of the sintered titanium was poor in comparison.
AFRIKAANSE OPSOMMING: Die doel van hierdie studie is om die masjineerbaarheid van kommersieel suiwer (KS) titaan, wat deur die pers-en-sinter poeiermetallurgie (PM) metode vervaardig word, te ondersoek. Om hierdie doel te bereik, is KS titaan poeier (-200 ogiesdraad) gekompakteer en gesinter in ‘n vakuum (10-4 torr) teen 1200°C vir 2 ure. Klein silindriese monsters is tussen drukke van 350en 600 MPa gekompakteer om die samedrukbaarheid van die poeier te bepaal. Na aanleiding van hierdie toetse, is vier groter trapvormige-silinder monsters by drukke naby aan 400MPa gekompakteer en onder soortgelyke omstandighede gesinter. Hierdie monsters het gesinterde digthede tussen 3.82 en 4.41 g/cm3 gehad. Hulle is gebruik om die masjineerbaarheid van die gesinterde titaan te ondersoek deur middel van vlak-draai masjineringstoetse. Die monsters is sonder smeermiddel gemasjineer met onbedekte karbied (WC-Co) snygereedskap. Snysnelhede tussen 60 – 150 m/min is geëvalueer terwyl die voertempo en diepte van die snit konstant by 0.15 mm/rev en 0.5 mm, onderskeidelik, gehou is. Die finale gemasjineerde oppervlak afwerking en gereedskapsslytasie tydens die vlak-draai masjinering toets is van die faktore wat gemonitor is sodat PM titaan se optrede tydens masjinering geëvalueer kan word. Hierdie studie wys dat diepers-en-sinter metode wel met KS titaan poeier, met ‘n partikel grootte van minder as 75 μm (-200 maas), gebruik kan word om gesinterde titaan te vervaardig. Die partikelgrootte beïnvloed wel die samedrukbaarheid van die poeier. Die samedrukking van parte met groter volume, soos bv die masjinerings toetsmonster, is uitdagend wanneer klein partikelgrootte poeier gebruik word. Proses omstandighede, soos kompaksie druk, sinteringstemperatuur en sinteringstyd, beïnvloed die gesinterde digtheid. Resultate van die masjineerbaarheidstoetse wys dat beitelslytasie toeneem met ‘n afname in porositeit van die gesinterede titaan. ‘n Meer poreus gesinterde materiaal het beide laer sterkte en termiese geleidingsvermoë. Aangesien hierdie faktore teenoorgestelde uitwerkings op masjineerbaarheid het, word dit dan afgelei dat die sterkte van gesinterde titaan ‘n groter invloed het op sy masjineerbaarheid as die termiese geleidingsvermoë. Die beitel se slytasie is hoofsaahlik, maar het tekens van kraterslytasie getoon. Die gemasjineerde oppervlak van die meer digte onderdele of toetsmonters het min gebreke gehad in vergelyking met die minder digte dele. Die vorm van die spaanders is lank vir digte parte, en spiraalvormig vir minder digte toetsmonsters. Die spaanders wat gevorm het, was almal gesegmenteerd, wat tipies is vir titaan. Die masjineerbaarheid van die gesinterde KS titaan is met dié van gesmede titaanallooie vergelyk. Soos verwag is, is gevind dat die masjineerbaarheid van die gesinterde titaan in vergelyking swak is.
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Karakas, Mustafa Serdar. "Effect Of Aging On The Mechanical Properties Of Boron Carbide Particle Reinforced Aluminum Metal Matrix Composites." Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/2/12608944/index.pdf.
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Metal matrix composites (MMCs) of Al - 4 wt.% Cu reinforced with different volumetric fractions of B4C particles were produced by hot pressing. The effect of aging temperature on the age hardening response of the composites was studied and compared with the characteristics exhibited by the matrix alloy. Reinforcement addition was found to considerably affect the age hardening behavior. Detailed transmission electron microscopy and differential scanning calorimetry observations were made to understand the aging response of the composites. The low strain rate and high strain rate deformation behavior of the MMCs were determined utilizing low velocity transverse rupture tests and true armor-piercing steel projectiles, respectively. Increasing the volume fraction of B4C led to a decrease in flexural strength. The flexural strength vs. strain rate plots showed a slight increase in strength followed by a decrease for all samples. The mechanical performance of the composites and the unreinforced alloy were greatly improved by heat treatment. The MMCs were found to be inferior to monolithic ceramics when used as facing plates in armors.
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Lobley, Christopher Marcus. "Tape casting as a novel processing route for silicon carbide fibre-reinforced titanium metal matrix composites." Thesis, Queen Mary, University of London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298249.
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Herbst, Stephan. "Investigation of a ceramic metal matrix composite functional surface layer manufactured using gas tungsten arc welding." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9191.
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Wear resistant surfaces with high toughness and impact resistant properties are to be created to improve the life cycle cost of brake discs for trains. A potential solution to this industrial problem is to use an arc cladding process. This work describes the application of gas tungsten arc welding (GTAW) for a structural ceramic Metal Matrix Composite (MMC) on steel. The structure of the two ceramics examined indicates the possibility of development of a wear resistant surface, which would extend the life of the brake disc. Silicon Carbide (SiC) and Tungsten Carbide (WC) ceramics were studied to embed them in a steel matrix by an advanced GTAW method. WC particles penetrated the liquid weld pool and also partially dissolved in the steel matrix, whereas, SiC because of the physical properties never penetrated deeper into the weld pool but segregated on the surface. Successful embedding and bonding of WC led to the decision to exercise an in-depth analysis of the bonding between the WC particles and the matrix. Chemical analysis of the matrix revealed more WC dissolution as compared to particle form within the clad. It was observed that WC reinforcement particles built a strong chemical bond with the steel matrix. This was shown by electron backscatter diffraction (EBSD) analysis. The hard clad layer composed of WC reinforced steel matrix gave an matching friction coefficient to high-strength steel in cold wear conditions through Pin-on-Disc wear and friction testing. A prototype railway brake disc was created with the established GTAW parameters to find out the difficulties of producing industrial scale components.
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Köksal, Sakip. "Face milling of nickel-based superalloys with coated and uncoated carbide tools." Thesis, Coventry University, 2000. http://curve.coventry.ac.uk/open/items/86a6b065-704a-475b-b805-9d3397487ddf/1.
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Face milling machinability investigation of two difficult-to-machine nickel-based superalloys, namely Inconel 718 and Waspaloy, has been carried out with four different types of tungsten carbide tools under various cutting conditions. The tools comprised of one double-layer CVD-TiCN+Al2O3 coated (KC994M), two PVD-TiN coated (KC720 and KC730) and one uncoated (KMF) tungsten carbide tools. The objectives of the study include investigation of tool performance, failure modes and wear mechanisms under the cutting conditions employed. In addition, surface integrity of the machined surfaces, with regard to surface finish, subsurface microhardness and metallographic examination of the subsurface microstructure, was investigated. CVD-coated KC994M gave the best overall performance in terms of tool life at low and high cutting conditions on both workpieces. The second best-performing tool was the uncoated KMF grade which gave as high tool lives as KC994M at lower cutting speeds. However at higher cutting speeds, KMF was generally outperformed by PVD-TiN coated tools. Short tool lives were obtained at higher cutting speeds of 75 and 100 m/min due to premature failure by chipping. Tool wear at low cutting speed range was due to a combination of progressive microchipping and plucking through a fracture/attrition related wear mechanism associated with cyclic workpiece adhesion and detachment and abrasion/diffusion-related flank wear. Plucking and microchipping were the dominant wear mechanisms. Coating layers on the rake face of both CVD and PVD coated tools were almost completely removed within the first few seconds of cutting at all cutting speeds tested, thus becoming ineffective. On the flank face, however, they remained intact for a longer period and hence increasing tools performance at the medium cutting speed range. Analysis of the subsurface microstructures and microhardness measurements showed that plastic deformation was the predominant effect induced onto the machined surface, the degree of which influenced by the cutting speed, tool wear and prolonged machining. In addition surface irregularities in the form of tearing and embedded hard particles were found to occur which was mainly associated with the chipping dominated wear mode.
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Morrison, Dominique Johanne. "The fabrication and characterisation of 4H-SiC Schottky barrier diodes." Thesis, University of Newcastle Upon Tyne, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324784.
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Liu, Wei. "Electro-thermal simulations and measurements of silicon carbide power transistors." Doctoral thesis, Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-86.
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Larsson, Niklas. "Gradient formation in cemented carbides with 85Ni:15Fe-binder phase." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-256503.
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In today’s inserts used for metal cutting the binder phase consists of cobalt (Co).However, EU’s REACH programme and the U.S’s National Toxicity Programme(NTP) classified Co as toxic/carcinogenic. Therefore, there is a strong need toinvestigate alternative binder phases. This thesis covers sintering and characterisationof cemented carbide with a binder phase consisting of nickel (Ni) and iron (Fe) withthe composition of 85Ni:15Fe. The aim was to study the gradient formation of turninginsert and find sintering processes to achieve a gradient structure with the targetedthickness of 26 microns. Simulations in ThermoCalc provided a suitable composition and a starting point forsintering parameters. The influences of sintering process parameters, such as holdingtime, temperature and counter pressure on the formation of the gradient zone wereinvestigated. Hot isostatic pressing (HIP) sintering was done in order to study thegradient formation as well as to reduce the porosity when needed. Sintered insertswere analysed by light optical microscopy. It was found that there are at least three possible ways to control the formation ofthe gradient: sintering in vacuum with a holding time of 20 min at 1450°C, sintering at1450°C with a counter pressure of 5 mbar nitrogen, and sintering with a counterpressure of 11.5 mbar followed by a double sinter-hip with 55 bar argon atmosphere.However, only the last process fulfilled the microstructure criteria in terms ofporosity and binder phase distribution. It is clear that the formation of gradient zonesin 85Ni:15Fe can be predicted, however calculations and simulations need to beoptimized in order to get more accurate results.
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Joshi, Kunal J. "OPTIMIZATION OF CUTTING CONDITIONS FOR SUSTAINABLE MACHINING OF SINTERED POWDER METAL STEELS USING PCBN AND CARBIDE TOOLS." UKnowledge, 2006. http://uknowledge.uky.edu/gradschool_theses/379.
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Powder metals are becoming a popular choice in the automotive and other manufacturing industries because of their ability to meet wide ranging product functional requirements without compromising the performance of the product. They offer various advantages, including weight reduction, near net-shape processing capability, and their ability to be sintered to achieve desired properties in the end-product. However, in order to satisfy the product design requirements during manufacturing, they need to be machined to the required tolerances. Machining of powder metals is quite different to machining of traditional metals because of their specific properties, including porosity. This thesis work deals with the finish machining of powder metal steels in automotive applications, for increased tool-life/reduced tool-wear. Tool-life is affected by a variety of factors such as tool grade selection, tool coating, cutting conditions and tool geometry including cutting edge geometry. This work involves optimization of cutting conditions for plunge cutting and boring operations of automotive powder metal components using PCBN and carbide tools. The cycle time of the process introduces an additional constraint for the optimization model along with the tool-wear criterion. Optimized cutting conditions are achieved for maximum tool-life.
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Lacerda, Felipe Soares. "Contribuição à usinagem de peças de metal duro sinterizado." Universidade de Taubaté, 2015. http://www.bdtd.unitau.br/tedesimplificado/tde_busca/arquivo.php?codArquivo=767.
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A necessidade de se usinar materiais de alta dureza e garantir bom acabamento superficial é um desafio para as atuais indústrias metal/mecânica. Além disso, coloca-se também a necessidade de fazê-lo de forma técnica e economicamente viável. Diante desse desafio o torneamento duro surge como uma
opção. Com o uso dos parâmetros (velocidade de corte, avanço e profundidade de corte) e ferramentas adequadas o torneamento duro possibilita uma adequada rugosidade superficial e pode substituir a necessidade de retificação, simplificando e reduzindo custos no processo de fabricação. Para que seja possível alcançar tais resultados, é necessária a pesquisa e validação de parâmetros que permitam a
execução do torneamento de materiais de alta dureza. Por meio de ensaios, de desbaste interno, realizados com peças de metal duro H11N e com ferramentas de diamante, foram feitos testes preliminares com o uso da ferramenta de projeto de
experimentos (DOE), para selecionar os melhores conjuntos de parâmetros (velocidade de corte e avanço). Foi realizado um segundo grupo de testes, finais, para garantir estatisticamente os melhores resultados, as informações obtidas foram
rugosidade, desgaste e número de passes. Com a análise dos resultados preliminares obtidos utilizando a ferramenta estatística de projeto de experimentos (DOE), foi identificado alta quebra de ferramentas (54%). Com a realização de
micrografias, a possibilidade do problema estar relacionado com a estrutura do material e ou com o tamanho do grão foi descartada. Foram detectadas ainda, marcas na superfície usinada dos corpos de prova que são indicadores da existência
de vibrações durante o processo, o que justifica o número elevado de quebras das arestas de corte de forma prematura. Os testes finais não apresentaram quebra prematura de ferramentas, e sim uma vida maior que o esperado. Foi estabelecido parâmetros viáveis para o processo, velocidade de corte de 22,1 m/min e avanço de 0,09 mm/rev. Através da análise do desgaste foi possível estabelecer um critério
para troca de ferramenta, que foi o desgaste de flanco (Vb) de 0,2mm.The necessity of machining materials with high hardness to ensure a good surface finish is a challenge for metal mechanic industries these days. Furthermore, it has the necessity to achieve this goal in a technical way and be economically viable. An option to tackle this challenge is hard turning. Through the use of parameters (speed cutting, feed rate and cut depth) and adequate tools, the hard turning enables a good surface roughness and can replace the need for grinding, making the fabrication process simpler and reducing the cost. In order for these results to be achieved, research is required and validation of parameters, which allow the realization of turning materials with high hardness. Through trials of internal thinning, with pieces made of H11N material and diamonds tools, Design of experiments (DOE) preliminary tests were carried out to select the best parameters group (cutting speed and feed rate). Secondary tests were done to ensure statically the best results in this case, the data obtained was of roughness, wear and tool life. When analyzing the preliminary results obtained using the statistic tool, design of experiments (DOE), it was identified that a high breakage of tools was occurring (54%). Through micrograph tests, the possibility of the problem being with the material structure and grain size was discarded. Traces were detected in the machining surface on the machined piece, these are indicators of the chance of vibration during the process, which can justify the high premature tool breakage. The final tests didnt show premature tool breakage, they showed the life span of the tool was longer than what was expected. Viable parameters were established for this process, cutting speed of 22.1 m/min and feed rate of 0.09 mm/rev. Through the wear analysis it was possible to establish a criterion of tool change, it was flank wear (Vb) of 0.02mm.
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Posada, Pérez Sergio. "Heterogeneous catalysis of green chemistry reactions on molybdenum carbide based catalysts." Doctoral thesis, Universitat de Barcelona, 2018. http://hdl.handle.net/10803/552405.
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Our society has a problem with the use of fossil fuels, due to the vast and exceeding emissions derived from human activities. Two ways could be consider to mitigate these harmful effects. On the one hand, the capture, activation, and conversion of these hazardous gases towards valuable compounds, and on the other hand, the substitution of fossil fuels for renewable energies. This thesis encompasses the study of two different green chemistry reactions to convert the most abundant greenhouse gas in Earth's atmosphere and the production of a new environmental friendly fuel, the hydrogen.
In the current search for new catalysts, Transition Metal Carbides (TMCs) have arisen as an appealing alternative, because their exhibit broad and amazing physical and chemical properties and their low cost. In particular, titanium carbide (001) was proposed from experimental and theoretical points of view as active catalyst and support of small metal particles for CO2 hydrogenation to methanol and water gas shift reaction. However, given that titanium carbide is a cumbersome support to be used in applications due to the difficulty of obtaining nanoparticles on working conditions, we have carried out these reactions on cubic δ-MoC (001) and orthorhombic β-Mo2C (001) surfaces.
The adsorption and activation of a CO2 molecule on cubic δ-MoC (001) and orthorhombic β-Mo2C (001) surfaces have been investigated by means of periodic density functional theory based calculations using the Perdew-Burke-Ernzerhof exchange-correlation functional showing that both surface are promising catalyst for CO2 conversion because they are able to activate and bend the CO2 molecule. The β- Mo2C (001) surface is able to dissociate the CO2 molecule easily, with a low energy barrier, whereas δ-MoC (001) surface activates CO2 but it does not promote its direct dissociation. Experiments accomplished by the group of Dr. Jose Rodriguez revealed that CO and methane are the main products of the CO2 hydrogenation using β-Mo2C
(001) as catalyst, and the amount of methanol is lower. On the other hand, only CO and methanol are produced using δ-MoC (001).
Experiments revealed that the deposition of small copper particles on the carbide surfaces increase drastically the catalysts' activity and selectivity, which was demonstrated by theoretical calculations. On β-Mo2C, the amount of CO and methanol
increase whilst the amount of methane decrease, since copper blocks reactive sites on surface. This is a positive fact since copper avoid the excessive oxygen deposition, which deactivated the catalysts. On the other hand, the deposition of copper on δ-MoC
(001) increases a lot the amount of CO and methanol. In summary, our combining DFT- experimental study proposed the Cu/δ-MoC as promising catalyst for CO2 hydrogenation due to its activity (the amount of products is superior than other TMCS, metals, and the model of commercial catalysts), selectivity (only CO and methanol are produced), and stability ( this catalysts is not deactivated by the oxygen deposition).
The results obtained in the first part of the thesis were used to study the water gas shift reaction. Given that the excellent features, experiments proposed Au supported on δ-MoC (001) as catalysts. Our theoretical calculations demonstrated that clean δ-MoC (001) is not a good catalysts for WGS, due to the fact that the reverse reactions are favorable respect the direct ones, which implies that the amount of products is lower. Nevertheless, the deposition of Au clusters change the reaction mechanism, favoring the direct barriers instead of reverse ones, and increasing the amount of produced H2.
In summary, this thesis has displayed the prominent role of molybdenum carbides as support of small metal particles to catalyze green chemistry reactions.En aquesta tesi es mostra un treball computacional sobre l'ús de catalitzadors econòmics per a la conversió de CO2, un perillós gas d'efecte hivernacle i també per a la producció d'hidrogen, el combustible del futur. En la recerca actual de nous catalitzadors, els carburs de metalls de transició (TMC) han sorgit com una alternativa atractiva pel el seu baix cost i per exhibir excel·lents propietats físiques i químiques. En aquest treball utilitzarem com a catalitzadors les superfícies cúbica δ-MoC (001) i ortoròmbica β-Mo2C (001). L'adsorció de la molècula de CO2 mostra que ambdues superfícies són capaces d'activar i doblegar la molècula. La superfície β-Mo2C (001) és capaç de dissociar fàcilment la molècula de CO2, mentre que la superfície δ-MoC (001) activa CO2 però no la dissocia. Els experiments realitzats pel grup del Dr. Jose Rodriguez van revelar que el CO i el metà són els principals productes de la hidrogenació de CO2 utilitzant β-Mo2C (001) com a catalitzador, i la quantitat de metanol és menor. D'altra banda, només es produeixen CO i metanol utilitzant δ-MoC (001). La deposició de partícules de coure a les superfícies del carbur augmenta dràsticament l'activitat dels catalitzadors, cosa que es va demostrar mitjançant càlculs teòrics. A la superfície β-Mo2C, la quantitat de CO i metanol augmenten mentre que la quantitat de metà disminueix. D'altra banda, la deposició de coure a δ-MoC (001) augmenta molt la quantitat de CO i metanol. En resum, el nostre estudi proposa el Cu/δ-MoC com a prometedor catalitzador de la hidrogenació de CO2 a causa de la seva activitat (la quantitat de productes és superior a la resta de TMCS, metalls i el model de catalitzadors comercials), selectivitat (només el CO i el metanol es produeixen) i l'estabilitat (aquests catalitzadors no es desactiven per la deposició d'oxigen). Tenint en compte els resultats previs, es va proposar la deposició d'or en la superfície δ-MoC per a la producció d'hidrogen. Els càlculs teòrics demostren que la superfície δ-MoC (001) no és un bon catalitzador per WGS, però la deposició dels clústers d'or canvia el mecanisme de reacció i augmenta la quantitat d'H2 produïda.
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Bojestig, Eric. "Adhesion of CVD coatings on new cemeted carbides." Thesis, Uppsala universitet, Tillämpad materialvetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-298648.
Full textAbstract:
Steel turning inserts cemented carbides have a binder phase consisting of cobalt (Co). However, in recent years a study from the United States National Toxicity Program (NTP) found that cobalt powder is carcinogenic upon inhalation. The European Union's REACH have therefore also classified cobalt powder as carcinogenic upon inhalation. The worldwide search to find a replacement has therefore lately intensified. It is important that the alternative binder phase has no negative effects on the properties of the insert. In this thesis the adhesion between a multilayer ceramic chemical vapor deposition (CVD) coating and a cemented carbide with the alternative binder phases consisting of iron (Fe), nickel (Ni) and cobalt (Co) has been studied. First of all, the fracture surfaces showed that the CVD coating was able to grow on all cemented carbides, regardless of which binder phase. To evaluate the adhesion, scratch tests were performed on all samples. The results from the scratch tests were not as expected. No chipping of the coating down to the cemented carbide occurred on any of the samples and the samples with the hardest cemented carbide did not get the highest critical load, which it should according to the literature if all other parameters were the same. Instead the sample with the binder phase consisting of 73 wt% iron and 27 wt% nickel had the highest critical load. This is thought to be due to that during the scratch test the binder phase in this cemented carbide would most likely transform into deformation martensite.