Dissertations / Theses: 'Carbide and nitride precipitation'

1

Sabounchei, S. J. S. Z. "Carbide and nitride clusters." Thesis, University of Liverpool, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.291737.

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2

Fujita, Nobuhiro. "Modelling carbide precipitation in alloy steels." Thesis, University of Cambridge, 2000. https://www.repository.cam.ac.uk/handle/1810/219197.

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3

Razzell, Anthony Gordon. "Silicon carbide fibre silicon nitride matrix composites." Thesis, University of Warwick, 1992. http://wrap.warwick.ac.uk/110559/.

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Silicon carbide fibre/silicon nitride matrix composites have been fabricated using the reaction bonded silicon nitride (RBSN) and sintered reaction bonded silicon nitride (SRBSN) processing routes. A filament winding and tape casting system was developed to produce sheets of parallel aligned fibres within a layer of green matrix ('prepreg') which were cut, stacked and hot pressed to form a plate. This was nitrided and (in the case of SRBSN matrix composites) hot pressed at 1700°C to density the matrix. The magnesia (MgO) and the yttria/alumina (Y2O3/AI2O3) additive SRBSN systems were investigated as matrices for ease of processing and compatibility with the matrix. The MgO additive Si3N4 matrix reacted with the outer carbon rich layer on the surface of the fibres, framing a reaction layer approx. 2pm in thickness. A reaction layer was also observed with the Y2O3/AI2O3 additive matrix, but was thinner (< 0.5um), and was identified as silicon carbide from the electron diffraction pattern. X-ray mapping in the SEM was used to investigate the spatial distribution of elements within the interface region to a resolution < lum, including light elements such as carbon. The 6wt%Y203/ 2wt%Al203 additive SRBSN system was chosen for more detailed investigation, and the majority of characterisation was performed using this composition. Oxidation of composite samples was carried out at temperatures between 1000°C and 1400°C for up to 1000 hours. Little damage was visible after 100 hours for all temperatures, corresponding to a relatively small drop in post oxidation bend strength. After 1000 hours at 1000°C both carbon rich outer layers and the central carbon core of the fibre were removed. Samples were severely oxidised after 1000 hours at 1400°C, having a glass layer on the outer surface and replacement of near surface fibre/matrix interfaces with glass. The post oxidation bend strengths for both conditions were approx.2/3 of the as fabricated strength. Less damage was observed after 1000 hours at 1200°C, and the post oxidation bend strength was higher than the 1000°C and 1400°C samples. Mechanical properties of the SRBSN matrix composite were investigated at room temperature and elevated temperatures (up to 1400°C). The average room temperature values for matrix cracking stress and ultimate strength (in bend) were 651.1 and 713.2 MPa respectively, with corresponding Weibull moduli of 5.7 and 8.7. The stresses are comparable to similar monolithic silicon nitrides. Room temperature tensile matrix cracking and ultimate strength were 232MPa and 413MPa, lower than the bend test results, which were attributed to bending stresses in the sample, lowering the apparent failure stresses. The samples failed in a composite like manner (i.e. controlled rather than catastrophic failure), with a substantially higher woric of fracture than monolithic materials. The average matrix cracking and ultimate bend strength at 1200°C were 516MPa and 554MPa, dropping to 178MPa and 486MPa at 1400°C (the matrix cracking stress was indistinct at 1400°C due to plasticity). The creep and stress rupture properties at 1300°C were investigated in four point bend, using dead-weight loading. The creep rate was KH/s at a stress of 200MPa, lower than a hot pressed silicon nitride with MgO additive, and higher than a hot isostatically pressed Y2O2/SÍO2 additive silicon nitride. A cavitation creep mechanism was deduced from the stress exponent, which was >1. Failure by stress rupture did not have a lower limit, which is also associated with cavitation of the amorphous grain boundary phase.

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4

Gao, Wei. "Oxidation of nitride-bonded silicon carbide (NBSC) and hot rod silicon carbide with coatings." Thesis, University of Strathclyde, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366751.

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5

Tatli, Zafer. "Silicon nitride and silicon carbide fabrication using coated powders." Thesis, University of Newcastle Upon Tyne, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394640.

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6

Turan, Servet. "Microstructural characterisation of silicon nitride-silicon carbide particulate composites." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.627653.

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7

Martinelli, Antonio Eduardo. "Diffusion bonding of silicon carbide and silicone nitride to molybdenum." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40191.

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This study focuses on various aspects of solid-state diffusion bonding of two ceramic-metal combinations, namely: silicon carbide-molybdenum (SiC-Mo), and silicon nitride-molybdenum (Si$ rm sb3N sb4$-Mo). Single SiC-Mo and $ rm Si sb3N sb4$-Mo joints were produced using hot-uniaxial pressing. The microstructure of the resulting interfaces were characterized by image analysis, scanning electron microscopy (SEM), electron probe micro-analysis (EPMA), and X-ray diffraction (XRD). The mechanical properties of the joints were investigated using shear strength testing, depth sensing nanoindentation, and neutron diffraction for residual stress measurement.
SiC was solid-state bonded to Mo at temperatures ranging from 1000$ sp circ$C to 1700$ sp circ$C. Diffusion of Si and C into Mo resulted in a reaction layer containing two main phases: $ rm Mo sb5Si sb3$ and Mo$ sb2$C. At temperatures higher than 1400$ sp circ$C diffusion of C into $ rm Mo sb5Si sb3$ stabilized a ternary phase of composition $ rm Mo sb5Si sb3$C. At 1700$ sp circ$C, the formation of MoC$ rm sb{1-x}$ was observed as a consequence of bulk diffusion of C into Mo$ sb2$C. A maximum average shear strength of 50 MPa was obtained for samples hot-pressed at 1400$ sp circ$C for 1 hour. Higher temperatures and longer times contributed to a reduction in the shear strength of the joints, due to the excessive growth of the interfacial reaction layer. $ rm Si sb3N sb4$ was joined to Mo in vacuum and nitrogen, at temperatures between 1000$ sp circ$C and 1800$ sp circ$C, for times varying from 15 minutes to 4 hours. Dissociation of $ rm Si sb3N sb4$ and diffusion of Si into Mo resulted in the formation of a reaction layer consisting, initially, of $ rm Mo sb3$Si. At 1600$ sp circ$C (in vacuum) Mo$ sb3$Si was partially transformed into $ rm Mo sb5Si sb3$ by diffusion of Si into the original silicide, and at higher temperatures, this transformation progressed extensively within the reaction zone. Residual N$ sb2$ gas, which originated from the decomposition of $ rm Si sb3N sb4,$ dissolved in the Mo, however, most of the gas escaped during bonding or remained trapped at the original $ rm Si sb3N sb4$-Mo interface, resulting in the formation of a porous layer. Joining in N$ sb2$ increased the stability of $ rm Si sb3N sb4,$ affecting the kinetics of the diffusion bonding process. The bonding environment did not affect the composition and morphology of the interfaces for the partial pressures of N$ sb2$ used. A maximum average shear strength of 57 MPa was obtained for samples hot-pressed in vacuum at 1400$ sp circ$C for 1 hour.

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Kim, Hyoun-Ee. "Gaseous corrosion of silicon carbide and silicon nitride in hydrogen /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487327695622538.

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Rohatgi, Aashish. "Detection of vanadium nitride precipitation using a creep technique." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69578.

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Computer programs were developed to perform creep tests on three microalloyed steels, with the aim of determining the precipitation kinetics of VN in austenite in one of the steels. This was a commercial 0.01% Ti- 0.12% V- 0.25% Mo steel. The other two were niobium steels with low (0.04% Nb) and high (0.07% Nb) niobium levels, respectively.
The Ti-V-Mo steel was tested at various stresses between 30 and 50 MPa in the temperature range 850-900$ sp circ$C. A mathematical equation was fitted to the creep strain vs. time curves and the creep strain was expressed as a function of time. The strain rate was determined by differentiating the equation with respect to time and log(strain rate) vs. log(creep strain) or creep strain curves were then plotted for each testing condition. At 850$ sp circ$C and 900 seconds, the strain rate was observed to decrease at a faster rate. This time decreased to 700 seconds at 875$ sp circ$C at the same stress of 36MPa. This effect is attributed to the occurrence of VN precipitation in austenite, which reduces the creep rate. However, precipitation could not be detected by the creep technique at 900$ sp circ$C in this steel.
The 0.07% Nb steel was tested at 950$ sp circ$C under stresses of 42 and 32 MPa. At 32MPa, the strain rate was found to decrease at a faster rate at 250 seconds. The 0.04% Nb steel was tested under stresses of 50 and 40 MPa at 875$ sp circ$C, and under 50 MPa at 850$ sp circ$C. In this steel too, a behaviour similar to that shown by the Ti-V and high Nb steels was observed at 375 seconds, 40MPa (875$ sp circ$C) and at 460 seconds, 50MPa (850$ sp circ$C). This is believed to be due the precipitation of NbCN.

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10

Sundaresan, Siddarth G. "Ultra-fast high temperature microwave processing of silicon carbide and gallium nitride." Fairfax, VA : George Mason University, 2007. http://hdl.handle.net/1920/2851.

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Thesis (Ph.D.)--George Mason University, 2007.
Title from PDF t.p. (viewed Oct. 29, 2007). Thesis director: Mulpuri V. Rao. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Vita: p. 170. Includes bibliographical references (p. 160-169). Also available in print.

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11

Okayama, Taizo. "Performance of devices made of large band-gap semiconductors, SiC and GaN." Fairfax, VA : George Mason University, 2007. http://hdl.handle.net/1920/2935.

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Thesis (Ph. D.)--George Mason University, 2007.
Title from PDF t.p. (viewed Jan. 21, 2008). Thesis director: Mulpuri V. Rao. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Vita: p. 128. Includes bibliographical references (p. 122-127). Also available in print.

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12

Lee, Jaeseob. "Direct bonding of gallium nitride to silicon carbide physical, and electrical characterization /." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-08072003-125025/.

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The direct bonding method is applied to the GaN/SiC system, and the processing conditions for successful direct bonding are clarified. Direct bonding of GaN/SiC is achieved at 900¡ÆC. The direct bonding of GaN to Si-face SiC is very dependent on the choice of chemical treatments, but the bonding of GaN to C-face SiC is less dependent on surface preparation. If a native oxide is present when the bonded interface is prepared, the current through the interface is decreased, which is attributed to an energy barrier due to the presence of charged interface states. TEM images indicate 10nm spaced dislocations at the interface for the GaN/SiC (Si-face), and ~6nm for the GaN/SiC (C-face), which form to accommodate the lattice mismatch (3.4%) and twist (1~2¡Æ) and tilt misfit (0.2¡Æ for Si-face SiC and 3¡Æ for C-face SiC). In some regions (~30%) an amorphous oxide layer forms at the interface, which is attributed to inadequate surface preparation prior to bonding. The strain of the GaN film with a Ga/C interface was ~0.1%, tensile strain, and that of GaN with a Ga/Si interface was ~0.2%, tensile strain. Our analysis indicates that the GaN/SiC thermal misfit dominates the strain of the GaN after bonding. The electrical characteristics of n-p GaN/SiC heterojunctions display diode ideality factors, saturation currents, energy barrier heights, and band offsets of 1.5 ¡¾ 0.1, 10^-13 A/cm² , 0.75 ¡¾ 0.10 eV, and ¥ÄE_c= 0.87 ¡¾ 0.10 eV for the Ga/Si interface and 1.2 ¡¾ 0.1, 10^-16 A/cm² , 0.56 ¡¾ 0.10 eV, and ¥ÄE_c= 0.46 ¡¾ 0.10 eV for the Ga/C interface.

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13

Stodilka, Danielle O. "Silicon carbide MIS and MOS development using alternative nitride and oxide dielectrics." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0013116.

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14

慎護, 中根. "Synthesis and densification of nitride, boride, and carbide by high-pressure technology." Thesis, https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB10353361/?lang=0, 2010. https://doors.doshisha.ac.jp/opac/opac_link/bibid/BB10353361/?lang=0.

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15

Romero, Amy Marie. "Static and Dynamic Characterization of Silicon Carbide and Gallium Nitride Power Semiconductors." Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/93744.

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Wide-bandgap semiconductors have made and are continuing to make a major impact on the power electronics world. The most common commercially available wide-bandgap semiconductors for power electronics applications are SiC and GaN devices. This paper focuses on the newest devices emerging that are made with these wide-bandgap materials. The static and dynamic characterization of six different SiC MOSFETs from different manufacturers are presented. The static characterization consists of the output characteristics, transfer characteristics and device capacitances. High temperature (up to 150 °C) static characterization provides an insight into the dependence of threshold voltage and on-state resistance on temperature. The dynamic characterizations of the devices are conducted by performing the double-pulse test. The switching characteristics are also tested at high temperature, with the presented results putting an emphasis on one of the devices. A comparison of the key characterization results summarizes the performance of the different devices. The characterization of one of the SiC MOSFETs is then continued with a short-circuit failure mode operation test. The device is subjected to non-destructive and destructive pulses to see how the device behaves. The non-destructive tests include a look at the performance under different external gate resistances and drain-source voltages. It is found that as the external gate resistance is increased, the waveforms get noisier. Also, as the drain-source voltage is increased, the maximum short-circuit current level rises. The destructive tests find the amount of time that the device is able to withstand short-circuit operation. At room temperature the device is able to withstand 4.5 μs whereas at 100 °C, the device is able to withstand 4.2 μs. It is found that despite the different conditions that the device is tested at for destructive tests, the energy that they can withstand is similar. This paper also presents the static and dynamic characterization of a 600 V, 2A, normallyoff, vertical gallium-nitride (GaN) transistor. A description of the fabrication process and the setup used to test the device are presented. The fabricated vertical GaN transistor has a threshold voltage of 3.3 V, a breakdown voltage of 600 V, an on-resistance of 880 mΩ, switching speeds up to 97 V/ns, and turn-on and turn-off switching losses of 8.12 µJ and 3.04 µJ, respectively, demonstrating the great potential of this device
MS

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16

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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17

Clauß, Arno Rainer. "Nitriding of Fe-Cr-Al alloys nitride precipitation and phase transformations /." Stuttgart : Max-Planck-Inst. für Metallforschung, 2008. http://d-nb.info/995395918/34.

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18

Holleck, H. [Verfasser]. "Binaere und ternaere Carbide und Nitride der Uebergangsmetalle und ihre Phasenbeziehungen / H. Holleck." Karlsruhe : KIT-Bibliothek, 2012. http://d-nb.info/1190100371/34.

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19

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, 2018
Cataloged 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

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20

Robson, Joseph Douglas. "Modelling of carbide and Laves phase precipitation in 9-12 wt% chromium steels." Thesis, University of Cambridge, 1997. https://www.repository.cam.ac.uk/handle/1810/224753.

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21

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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22

Rey, Tomas. "Investigation of Microstructure and Mechanical Properties in Hot-work Tool Steels." Thesis, KTH, Materialvetenskap, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-210699.

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Hot-work tool steels make up an important group of steels that are able to perform with good strength and toughness properties at elevated temperatures and stresses. They are able to gain this behavior through their alloy composition and heat treatment, which relies on the precipitation of alloy carbides to counter the loss in strength as the tempered material becomes more ductile. As demand grows for materials that are suitable for even harsher applications and that show improved mechanical qualities, the steel industry must continuously investigate the development of new steel grades. Within this context, the present work focuses on examining the mechanical properties and microstructure of two hot-work tool steels, of which one is a representative steel grade (Steel A) and the second a higher-alloyed variant (Steel B), at different tempering conditions. To complement the experimental work, precipitation simulations are used to monitor the progression of secondary carbide precipitation and to examine the predicted microstructural changes through varying the alloy composition. The study finds that Steel B does not actually have improved properties with respect to Steel A and suggests that the precipitation behavior of both steels is virtually identical. Despite this, the simulation work reveals that this behavior can change dramatically to favor more positive hardness contributions by increasing the alloy content of V. In short, with the project being part of an ongoing investigation, there remain several areas of analysis that need to be completed before offering a complete picture that can ultimately play a part in the development of a new hot-work tool steel grade.

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23

Cook, Grant O. III. "Joining Polycrystalline Cubic Boron Nitride and Tungsten Carbide by Partial Transient Liquid Phase Bonding." BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2366.

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Friction stir welding (FSW) of steel is often performed with an insert made of polycrystalline cubic boron nitride (PCBN). Specifically, MS80 is a grade of PCBN made by Smith MegaDiamond that has been optimized for the FSW process. The PCBN insert is attached to a tungsten carbide (WC) shank by a compression fitting. However, FSW tools manufactured by this method inevitably fail by fracture in the PCBN. Permanently bonding PCBN to WC would likely solve the fracturing problem and increase the life of PCBN FSW tools to be economically viable. Partial transient liquid phase (PTLP) bonding, a process used to join ceramics with thin metallic interlayers, was proposed as a method to permanently bond PCBN to WC. PTLP bonding is often performed using three layers of pure elements. On heating, the two thin outer interlayers melt and bond to the ceramics. Concurrently, these liquid layers diffuse into the thicker refractory core until solidification has occurred isothermally. A procedure was developed to reduce the number of possible three-layer PTLP bonding setups to a small set of ideal setups using logical filters. Steps in this filtering method include a database of all existing binary systems, sessile drop testing of 20 elements, and a routine that calculates maximum interlayer thicknesses. Results of sessile drop testing showed that the PCBN grade required for this research could only be bonded with an alloy of Ti, Cu, Mg, and Sb. Two PTLP bond setups were tested using this special coating on the PCBN, but a successful bond could not be achieved. However, a PTLP bond of WC to WC was successful and proved the usefulness of the filtering procedure for determining PTLP bond setups. This filtering procedure is then set forth in generalized terms that can be used to PTLP bond any material. Also, recommendations for future research to bond this grade of PCBN, or some other grade, to WC are presented.

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24

Unal, Ozer. "Interface studies in silicon nitride/silicon carbide and gallium indium arsenide/gallium arsenide systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=case1059501714.

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25

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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26

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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27

Badinier, Guillaume. "The effect of carbon segregation and carbide precipitation on the mechanical response of martensite." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44022.

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The influence of carbon distribution and carbide precipitation on the mechanical properties of the as-quenched and quenched and tempered 300M martensitic steel has been investigated. The microstructure, investigated by transmission electron microscopy (TEM) and three dimensional atom probe tomography (APT) was found to be relatively homogeneous in the as-water-quenched state, but signifi cantly evolved upon tempering and variation of quench rate. This evolution included carbon segregation to dislocations and grain boundaries and carbide precipitation. A simple mean- field precipitation model assuming heterogeneous nucleation onto the dislocations proved to satisfactorily capture the evolution of precipitation upon tempering at 120C and 150C. The material was found to behave, mechanically, as a composite and in accordance, the Bauschinger stress-strain behaviour was successfully modeled using a continuous Masing model. This model, when related to the microstructure, showed that the composite behaviour arose from the mechanical contrast between the laths, this being controlled by the local dislocation density and carbon segregation and/or precipitation onto them. Carbon segregation and carbide precipitation were observed to have a direct impact on alpha in the Taylor-like equation that was shown to control the local yield stress within the laths. When applied to martensites containing various amount of carbon, the model allowed for an empirical assessment of the e ffect of the nominal carbon content on alpha , which was found to be linearly dependent on the nominal carbon content.

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28

Zirkelbach, Frank [Verfasser], and Bernd [Akademischer Betreuer] Stritzker. "Atomistic simulation study on silicon carbide precipitation in silicon / Frank Zirkelbach. Betreuer: Bernd Stritzker." Augsburg : Universität Augsburg, 2012. http://d-nb.info/1077700946/34.

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29

Schwartz, Viviane. "Preparation and Reactivity of Niobium-Containing Hydrotreating Catalysts." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/26368.

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A series of niobium-containing nitride and carbides were prepared by a temperature-programmed synthesis method. The catalysts synthesized comprised a monometallic niobium oxynitride and a new bimetallic oxycarbide supported system, Nb-Mo-O-C/Al₂O₃ (Mo/Nb = 1.2; 1.6; 2.0). In the case of the niobium oxynitride, the progress of formation was analyzed by interrupting the synthesis at various stages. The effect of the heating rate on product properties was also investigated. The solid intermediates and the final niobium oxynitride were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), elemental analysis (CHNS), and gas adsorption techniques. The solid state transformation occurred directly from Nb₂O₅ to NbN_xO_y without any suboxide intermediates. The bimetallic supported oxycarbide materials were also characterized by X-ray diffraction (XRD), gas adsorption techniques, X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS). It was found that the electronic properties of the oxycarbide were modified by the interaction with the Al₂O₃ support, and that most of the oxygen atoms were associated with the niobium rather than the molybdenum atom. All of the niobium-containing catalysts were tested in a three-phase trickle-bed reactor for the simultaneous hydrodenitrogenation (HDN) of quinoline and hydrodesulfurization (HDS) of dibenzothiophene. The niobium oxynitride presented low HDS activity and moderate HDN activity, whereas the supported bimetallic oxycarbide was found to be highly active for both, HDN and HDS, demonstrating higher activities than the commercial sulfided Ni-Mo/Al₂O₃ when compared on the basis of active sites. In addition to these studies a comprehensive investigation of the HDN reaction mechanism was carried out over bulk unsupported Mo₂C, NbC, NbMo₂-O-C, and compared with the mechanism over a sulfide catalyst, MoS₂/SiO₂. For this purpose, a comparison of the HDN rate of a series of isomeric amines was performed, and the reaction occurred mainly through a β-elimination mechanism for all catalysts. Temperature programmed desorption of ethylamine was used to investigate the acid properties of the catalytic surfaces, and a good agreement between the specific rate of reaction and the number of Brønsted acid-sites was obtained. Infrared spectroscopy showed that the amines interacted with acidic centers to form adsorbed quartenary ammonium species. The deamination reaction over the carbide and sulfide catalysts probably occurs by a concerted push-pull mechanism involving basic sulfur species and Brønsted-acidic centers. In order to obtain more insight into the mechanism a study of the pyridine HDN network was carried out.All of the catalysts showed the same activity trend: the reactivity of n-pentylamine was high, while those of piperidine and pyridine were relatively low. The carbide catalysts showed higher selectivity towards HDN products than the sulfide catalyst at the same conversion levels. The higher selectivity was related to the higher ratio (r = k₂/k₁) between the rate constants of the two consecutive reactions, hydrogenation of pyridine (k₁) and ring opening of piperidine (k₂). The order of activity of the carbides and sulfide differed considerably depending on the substrate. However, for the pyridine reaction network the similarity in product distribution suggested that a similar surface composition, a carbosulfide, was attained during the reaction.
Ph. D.

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30

Camurlu, Hasan Erdem. "Carbothermic Production Of Hexagonal Boron Nitride." Phd thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607808/index.pdf.

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Formation of hexagonal boron nitride (h-BN) by carbothermic reduction of B2O3 under nitrogen atmosphere at 1500oC was investigated. Reaction products were subjected to powder X-ray diffraction analysis, chemical analysis and were examined by SEM. B4C was found to exist in the reaction products of the experiments in which h-BN formation was not complete. One of the aims of this study was to investigate the role of B4C in the carbothermic production of h-BN. For this purpose, conversion reaction of B4C into h-BN was studied. B4C used in these experiments was produced in the same conditions that h-BN was formed, but under argon atmosphere. It was found that formation of h-BN from B4C&ndash
B2O3 mixtures was slower than activated C&ndash
B2O3 mixtures. It was concluded that B4C is not a necessary intermediate product in the carbothermic production of h-BN. Some additives are known to catalytically affect the h-BN formation. The second aim of this study was to examine the catalytic effect of some alkaline earth metal oxides and carbonates, some transition metal oxides and cupric nitrate. It was found that addition of 10wt% CaCO3 into the B2O3+C mixture was optimum for increasing the rate and yield of h-BN formation and decreasing the B4C amount in the products and that the reaction was complete in 2 hours. CaCO3 was observed to be effective in increasing the rate and grain size of the formed h-BN. Addition of cupric nitrate together with CaCO3 provided a further increase in the size of the h-BN grains.

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Techaboonanek, Chanachon. "Precipitation during Tempering of Martensite in Fe-Cr-C alloys." Thesis, KTH, Materialvetenskap, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103192.

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The martensite structure is the most important microstructure in tool steel due to its high hardness. However, a lack of ductility is the major drawback. In order to improve the ductility and still maintaining a suitable hardness a tempering process is needed. The tempering process will cause recovery and recrystallization in the matrix, and moreover carbides will precipitate. The specific carbides have different characteristics and thus the type of carbide formed during tempering is very important for the properties of the steel. The simulation software (TC-Prisma) is interesting because it can predict type, size, and amount of carbides. The present study was carried out to investigate both the microstructure, hardness evolution of martensite and precipitation which occurred in Fe-C-Cr steel with different compositions, tempered at 700oC. The experimental results were compared with simulation results. Micro-Vickers hardness test with a load of 100 g was used and the hardness value dropped 40% and 60% in low carbon alloy and high carbon alloy steels, respectively. The significant drop occurred during the first 30 seconds of tempering due to recovery of the matrix. Hardness values slightly decreased and then stabilized during continued tempering. The microstructure of martensite and the morphology of carbides at different tempering times were examined by scanning and transmission electron microscopy in order to study the precipitation of carbides from the nucleation and growth to coarsening. There are three types of carbides which precipitated in the Fe-C-Cr specimens: M7C3, cementite and M3C2 depending on the composition. Fe-0.16C-4.05Cr contained M7C3, Fe-0.95C-1.065Cr contained cementite and M3C2 and Fe-014C-0.983Cr and Fe-0.88C-4.12Cr contained M7C3 and cementite. M7C3 has a faceted shape and precipitates referentially at grain boundaries. On the other hand, cementite has an elongated shape and precipitated mainly at grain boundaries but also intragranulary. M3C2 has a rounded shape and was seen only in very small amounts, and seemed to precipitate at random sites. The trend of carbide growth in experiments is consistent with the simulations using TC-Prisma, but more work is needed to enable quantitative comparisons.

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32

Gasch, Matthew J. "Processing and mechanical properties of silicon nitride/silicon carbide ceramic nanocomposites derived from polymer precursors /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.

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33

Ischenko, Vladislav. "Verwendung molekularer Vorstufen für die Synthese neuartiger Carbide und Nitride der Elemente der IV. Hauptgruppe." [S.l. : s.n.], 2003. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB11244196.

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34

張秀霞 and Sau-ha Cheung. "Growing of GaN on vicinal SiC surface by molecular beam epitaxy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B31243009.

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35

Cheung, Sau-ha. "Growing of GaN on vicinal SiC surface by molecular beam epitaxy /." Hong Kong : University of Hong Kong, 2002. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25212163.

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36

Jordan, Jennifer Lynn. "Shock-activated reaction synthesis and high pressure response of Ti-based ternary carbide and nitride ceramics." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/19674.

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37

Kerkar, Awdhoot Vasant. "Investigation of steric stabilization as a route for colloidal processing of silicon carbide/silicon nitride composites." Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1059055054.

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38

Zhou, Yijian. "Effects of grain boundary and triple line structures on carbide precipitation in type 304L stainless steel." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0019/MQ54131.pdf.

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39

Zaman, Farhana. "Characterization of selective epitaxial graphene growth on silicon carbide: limitations and opportunities." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43624.

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The need for post-CMOS nanoelectronics has led to the investigation of innovative device structures and materials. Graphene, a zero bandgap semiconductor with ballistic transport properties, has great potential to extend diversification and miniaturization beyond the limits of CMOS. The goal of this work is to study the growth of graphene on SiC using the novel method of selective graphitization. The major contributions of this research are as follows - First, epitaxial graphene is successfully grown on selected regions of SiC not capped by AlN deposited by molecular beam epitaxy. This contribution enables the formation of electronic-grade graphene in desired patterns without having to etch the graphene or expose it to any detrimental contact with external chemicals. Etching of AlN opens up windows to the SiC in desirable patterns for subsequent graphitization without leaving etch-residues (determined by XPS). Second, the impact of process parameters on the growth of graphene is investigated. Temperature, time, and argon pressure are the primary growth-conditions altered. A temperature of 1400oC in 1 mbar argon for 20 min produced the most optimal graphene growth without significant damage to the AlN capping-layer. Third, first-ever electronic transport measurements are achieved on the selective epitaxial graphene. Hall mobility of about 1550 cm2/Vs has been obtained to date. Finally, the critical limitations of the selective epitaxial graphene growth are enumerated. The advent of enhanced processing techniques that will overcome these limitations will create a multitude of opportunities for applications for graphene grown in this manner. It is envisaged to be a viable approach to fabrication of radio-frequency field-effect transistors.

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40

Zetterling, Carl-Mikael. "Silicon dioxide and aluminium nitride as gate dielectric for high temperature and high power silicon carbide MOSFETs." Doctoral thesis, KTH, Electronic Systems Design, 1997. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-2514.

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Silicon carbide (SIC) is a wide bandgap semiconductor thathas been suggested as a replacement for silicon in applicationsusing high voltages, high frequencies, high temperatures orcombinations thereof. Several basic process steps need to bedeveloped for reliable manufacturing of long-term stableelectronic devices. One important process step is the formationof an insulator on the silicon carbide surface that may be usedas a) a gate dielectric, b) for device isolation or c) forpassivation of the surface. Silicon dioxide and aluminumnitride have been suggested for these purposes. This thesiscovers the investigation of some formation methods for boththese materials on 4H and 6H silicon carbide, and theelectrical characterisation of the resulting films.

Commercially available n-type and p-type 4H and 6H SICwafers have been used, and both the silicon face and the carbonface have been investigated. Silicon dioxide has been formed byseveral methods: a) dry thermal oxidation with or without theaddition of TCA (trichloroethane), b) wet oxidation inpyrogenic steam or with awater bubbler, c) oxide deposition byPECVD (plasma enhanced chemical vapor deposition) or LPCVD (lowpressure chemical vapor deposition) and d) oxidation of aevaporated or LPCVD deposited sacrificial layer of silicon. Theinfluence of various cleaning methods prior to oxidation hasbeen studied, as well as post-oxidation and post-metallisationannealing. The aluminum nitride films were grown by MOCVD(metal organic chemical vapor deposition) under various processconditions.

Oxidation kinetics have been studied for dry thermaloxidation at 1200 0C. The redistribution of aluminum (p-typedopant in SiC) during dry thermal oxidation has beeninvestigated using SIMS (secondary ion mass spectrometry). Themorphology of the aluminum nitride was determined using x-raydiffraction rocking curves, RHEED (reflection high energyelectron diffraction) and AFM (atomic force microscopy). Thequality of the silicon dioxide used as gate dielectric has beendetermined using breakdown field measurements. High frequencycapacitance-voltage measurements have been used on bothinsulators to a) verify thickness measurements made with othermethods, b) to determine fixed oxide charges by measuring theflatband voltage shifts and c) to quantitatively compare theamount of interface states.

For electrical characterisation either aluminum, titanium ordoped polysilicon circular gate contacts of various sizes wereformed on the insulator surface. Flat MOS capacitors weremainly used for the electrical characterisation. U-grooved MOScapacitors, manufactured by RIE (reactive ion etching), wereused to test the quality of oxides grown on vertical surfaces.Two types of MOSFETs (metal oxide semiconductor field effecttransistors) have been fabricated: vertical U-grooved andlateral devices.

Keywords:silicon carbide, thermal oxidation, silicondioxide, metal organic chemical vapor deposition (MOCVD),aluminum nitride, capacitance-voltage measurements, MOSFET.

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41

Graham, David W. "Corrosion resistant chemical vapor deposited coatings for SiC and Si₃N₄ /." This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09292009-020327/.

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42

Clauß, Arno Rainer [Verfasser]. "Nitriding of Fe-Cr-Al alloys : nitride precipitation and phase transformations / vorgelegt von Arno Rainer Clauß." Stuttgart : Max-Planck-Inst. für Metallforschung, 2008. http://d-nb.info/995395918/34.

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43

Cheng, Leon Man Lung. "Study of the kinetics of precipitation, dissolution and coarsening of aluminum nitride in low-carbon steels." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0029/NQ38867.pdf.

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44

Chan, King-lung, and 陳勁龍. "A study of geometrical properties of SiC and GaN surfaces by auger electron spectroscopy." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2002. http://hub.hku.hk/bib/B2664387X.

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45

Devarapally, Rahul Reddy. "Survey of applications of WBG devices in power electronics." Kansas State University, 2016. http://hdl.handle.net/2097/32665.

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Master of Science
Department of Electrical and Computer Engineering
Behrooz Mirafzal
Wide bandgap devices have gained increasing attention in the market of power electronics for their ability to perform even in harsh environments. The high voltage blocking and high temperature withstanding capabilities make them outperform existing Silicon devices. They are expected to find places in future traction systems, electric vehicles, LED lightning and renewable energy engineering systems. In spite of several other advantages later mentioned in this paper, WBG devices also face a few challenges which need to be addressed before they can be applied in large scale in industries. Electromagnetic interference and new requirements in packaging methods are some of the challenges being faced by WBG devices. After the commercialization of these devices, many experiments are being carried out to understand and validate their abilities and drawbacks. This paper summarizes the experimental results of various applications of mainly Silicon Carbide (SiC) and Gallium Nitride (GaN) power devices and also includes a section explaining the current challenges for their employment and improvements being made to overcome them.

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46

Parikh, Rinku Pankaj. "Simulation-based design, optimization, and control of silicon carbide and gallium nitride thin film chemical vapor deposition reactor systems." College Park, Md. : University of Maryland, 2006. http://hdl.handle.net/1903/3976.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2006.
Thesis research directed by: Chemical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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47

Wang, Li [Verfasser], Florian [Akademischer Betreuer] Pyczak, and Helmut [Akademischer Betreuer] Clemens. "Mechanisms of carbide precipitation and carbon solubility in high Nb containing TiAl Alloys / Li Wang ; Florian Pyczak, Helmut Clemens." Cottbus : BTU Cottbus - Senftenberg, 2014. http://d-nb.info/1114282898/34.

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48

Wang, Li Verfasser], Florian [Akademischer Betreuer] [Pyczak, and Helmut [Akademischer Betreuer] Clemens. "Mechanisms of carbide precipitation and carbon solubility in high Nb containing TiAl Alloys / Li Wang ; Florian Pyczak, Helmut Clemens." Cottbus : BTU Cottbus - Senftenberg, 2014. http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-30392.

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49

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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50

Yao, Mengji Verfasser], Dierk [Akademischer Betreuer] Raabe, and Jochen M. [Akademischer Betreuer] [Schneider. "κ-carbide in a high-Mn light-weight steel : precipitation, off-stoichiometry and deformation / Mengji Yao ; Dierk Raabe, Jochen Michael Schneider." Aachen : Universitätsbibliothek der RWTH Aachen, 2017. http://d-nb.info/1162498366/34.

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Dissertations / Theses on the topic 'Carbide and nitride precipitation'

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