Dissertations / Theses on the topic 'Ceramics processing'
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Yakimov, Audrey-Olga. "Processing of fibrous monolithic ceramics." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0020/NQ45653.pdf.
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Greener, James. "Elongational flow in ceramics processing." Thesis, Brunel University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294511.
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Pethybridge, Guy David. "Sol-gel processing of dielectric ceramics." Thesis, University of Oxford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318872.
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Walker, Luke Sky. "Processing of Ultra High Temperature Ceramics." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/228496.
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For hypersonic flight to enable rapid global transport and allow routine space access thermal protection systems must be developed that can survive the extreme aerothermal heating and oxidation for extended periods of time. Ultra high temperature ceramics (UHTCs) are the only potential materials capable of surviving the extreme hypersonic environment however extensive research in processing science and their oxidation properties are required before engineering systems can be developed for flight vehicles. Investigating the role of oxides during processing of ultra high temperature ceramics shows they play a critical role in both synthesis of ceramic powders and during densification. During spark plasma sintering of UHTCs the oxides can result in the formation of vapor filled pores that limit densification. A low temperature heat treatment can remove the oxides responsible for forming the vapor pores and also results in a significant improvement of the densification through a particle surface physical modification. The surface modification breaks up the native continuous surface oxide increasing the surface energy of the powder and removing the oxide as a barrier to diffusion that must be overcome before densification can begin. During synthesis of UHTCs from sol-gel the B₂O₃ phase acts as the main structure of the gel limiting the transition metal oxide network. While heat treating to form diborides the transition metal oxide undergoes preferential reduction forming carbides that reduce B₂O₃ while at high temperature encourage particle growth and localized extreme coarsening. To form phase pure borides B₂O₃ is required in excessive quantities to limit residual carbides, however carbide reduction and grain growth are connected. When the UHTC systems of ZrB₂-SiC are exposed to oxidation, either as dense ceramics or coatings on Carbon-Carbon composites, at high temperatures they undergo a complex oxidation mechanism with simultaneous material transport, precipitation and evaporation of oxide species that forms a glass ceramic protective oxygen barrier on the surface. The composite effect observed between the oxides of ZrB₂-SiC enables them to survive extreme oxidizing environments where traditional SiC oxidation barrier coatings fail.
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Pham, David, and David Pham. "Processing High Purity Zirconium Diboride Ultra-High Temperature Ceramics: Small-to-Large Scale Processing." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621315.
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Next generation aerospace vehicles require thermal protection system (TPS) materials that are capable of withstanding the extreme aerothermal environment during hypersonic flight (>Mach 5 [>1700 m/s]). Ultra-high temperature ceramics (UHTC) such as zirconium diboride (ZrB₂) are candidate TPS materials due to their high-temperature thermal and mechanical properties and are often the basis for advanced composites for enhanced oxidation resistance. However, ZrB₂ matrix impurities in the form of boron trioxide (B₂O₃) and zirconium dioxide (ZrO₂) limit the high-temperature capabilities. Electric based sintering techniques, such as spark plasma sintering (SPS), that use joule heating have become the preferred densification method to process advanced ceramics due to its ability to produce high density parts with reduced densification times and limit grain growth. This study focuses on a combined experimental and thermodynamic assisted processing approach to enhance powder purity through a carbo- and borocarbo-thermal reduction of oxides using carbon (C) and boron carbide (B₄C). The amount of oxides on the powder surface are measured, the amount of additive required to remove oxides is calculated, and processing conditions (temperature, pressure, environment) are controlled to promote favorable thermodynamic reactions both during thermal processing in a tube furnace and SPS. Untreated ZrB₂ contains 0.18 wt%O after SPS. Additions of 0.75 wt%C is found to reduce powder surface oxides to 0.12 wt%O. A preliminary Zr-C-O computational thermodynamic model shows limited efficiency of carbon additions to completely remove oxygen due to the solubility of oxygen in zirconium carbide (ZrC) forming a zirconium oxycarbide (ZrCₓOᵧ). Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with atomic scale elemental spectroscopy shows reduced oxygen content with amorphous Zr-B oxides and discreet ZrO₂ particle impurities in the microstructure. Processing ZrB₂ with minimal additions of B₄C (0.25 wt%) produces high purity parts after SPS with only 0.06 wt%O. STEM identifies unique “trash collector” oxides composed of manufacturer powder impurities of calcium, silver, and yttrium. A preliminary Zr-B-C-O thermodynamic model is used to show the potential reaction paths using B₄C that promotes oxide removal to produce high-purity ZrB₂ with fine grains (3.3 𝜇m) and superior mechanical properties (flexural strength of 660MPa) than the current state-of-the-art ZrB₂ ceramics. Due to the desirable properties produced using SPS, there is growing interest to advance processing techniques from lab-scale (20 mm discs) to large-scale (>100 mm). The advancement of SPS technologies has been stunted due to the limited power and load delivery of lab-scale furnaces. We use a large scale direct current sintering furnace (DCS) to address the challenges of producing industrially relevant sized parts. However, current-assisted sintering techniques, like SPS and DCS, are highly dependent on tooling resistances and the electrical conductivity of the sample, which influences the part uniformity through localized heating spots that are strongly dependent on the current flow path. We develop a coupled thermal-electrical finite element analysis model to investigate the development and effects of tooling and current density manipulation on an electrical conductor (ZrB₂) and an electrical insulator, silicon nitride (Si₃N₄), at the steady-state where material properties, temperature gradients and current/voltage input are constant. The model is built based on experimentally measured temperature gradients in the tooling for 20 mm discs and validated by producing 30 mm discs with similar temperature gradients and grain size uniformity across the part. The model aids in developing tooling to manipulate localize current density in specific regions to produce uniform 100 mm discs of ZrB₂ and Si₃N₄.
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Hirano, Shin-ichi, Toshinobu Yogo, Wataru Sakamoto, Ko-ichi Kikuta, Kazumi Kato, Yoshikuni Takeichi, Yasushi Araki, et al. "Chemical processing and properties of functional ceramics." IEEE, 1999. http://hdl.handle.net/2237/6125.
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Paul, Anish. "Processing and properties of nanostructured zirconia ceramics." Thesis, Loughborough University, 2009. https://dspace.lboro.ac.uk/2134/11995.
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The term nanoceramics is well known in the ceramic field for at least two decades. Even though there are many reports that nanoceramics are superior in terms of mechanical and other properties, no comprehensive and conclusive study on the grain size dependent variation in mechanical properties. So this study was an attempt to study the property variation with grain size and yttria content for a well known ceramic, yttria stabilised zirconia. High solids content but low viscosity YSZ nanosuspensions have been slip cast into -52% dense, very homogeneous green bodies in sizes up to 60 mm in diameter. Sintering cycles have been optimised using both hybrid and conventional two-step heating to yield densities >99.5% of theoretical whilst retaining a mean grain size of <100 nm. The sintered samples have been characterised for hardness, toughness, strength, wear resistance and hydrothermal ageing resistance. The results have been compared with that of a submicron zirconia ceramic prepared using a commercial powder. The strength of the nanoceramics has been found to be very similar to that of conventional submicron ceramics, viz. -10Pa, although the fracture mechanism was different. Two toughness measurement approaches have been used, indentation and surface crack in flexure. The results indicate that the nano 1.5YSZ ceramics may be best viewed as crack, or damage, initiation resistant rather than crack propagation resistant; indentation toughness measurements as high as 14.5 MPa m 112 were observed. Micro-Raman mapping was demonstrated to be a very effective technique to map the phase transformations in zirconia. The wear mechanism of nanozirconia has been observed to be different compared to that in conventional, submicron YSZ and the wear rates to be lower, particularly under wet conditions. In addition, and potentially most usefully, the nan03YSZ ceramics appear to be completely immune to hydrothermal ageing for up to 2 weeks at 245°C & 7 bar; conditions that see a conventional, commercial submicron ceramic disintegrate completely within 1 hour.
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Kara, Ferhat. "Processing and characterisation of mullite based ceramics." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.319362.
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Ghanizadeh, Shaghayegh. "Synthesis and processing of nanostructured alumina ceramics." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/13504.
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The term Nanoceramics is well known in the ceramic field for at least two decades. In this project a detailed study was performed on the synthesis of α-alumina nanopowders. High solids content nanoalumina suspensions were prepared and used to form green bodies using both wet and dry forming routes. The green bodies were then sintered using both conventional single and two-step sintering approaches. Synthesis: Two different synthesis methods, viz. precipitation and hydrothermal treatment, were used to synthesize fine α-alumina powders from aluminium chloride, ammonia solution and TEAH (Tetraethyl ammonium hydroxide). XRD, TEM and FEG-SEM were used to characterise the powders produced. The presence of commercial α-alumina powder as seed particles did not affect the transformation to α-alumina phase during the hydrothermal treatment at 220˚C in either basic or acidic environments. The results obtained from the precipitation route showed that the combined effect of adding α-alumina seeds and surfactants to the precursor solution could lower the transformation temperature of α-alumina from about 1200˚C for unseeded samples to 800˚C, as well as reducing the level of agglomeration in the alumina powders. The difference in transformation temperature mainly resulted from the nucleation process by the α-alumina seeds, which enhanced the θ → α transformation kinetics. The lower level of agglomeration present in the final powders could be due to the surface modifying role of the surfactants preventing the particles from growing together during the synthesis process. By introducing a further high-temperature step for a very short duration (1 minute) to the low-temperature heat treatment route (800˚C/12 h), the unseeded sample with added surfactant transformed into pure α-alumina phase. The newly-added step was shown to be an in-situ seeding step, followed by a conventional nucleation and growth process. The best final powder was compared with a commercial α-alumina nanopowder. Processing of alumina ceramics: The effect of low-molecular weight ammonium dispersants including Dispex-A40, Darvan-C and Dolapix-CE64, on high solids content nanoalumina suspensions was investigated. The nanosuspension prepared using the most suitable dispersant, Dolapix-CE64, was slip cast into ~53% dense, very homogeneous green bodies. This nanosuspension was also spray freeze dried into crushable granules using Freon as a foaming agent. Green compacts with density of ~53.5% were then formed by dry pressing the 2 vol% Freon-added spray freeze dried granules at 40 MPa. Both slip cast and die pressed green bodies were sintered using conventional single-step and two-step routes followed by characterising the density and grain size measurement of final dense compacts. The results have been compared with that of a submicron alumina ceramic prepared using a commercial α-alumina suspension. Highly dense alumina with an average grain size of ~0.6 μm was fabricated by means of spark plasma sintering at 1200˚C. The application of 500 MPa allowed achieving almost fully dense alumina at temperature as low as 1200˚C for 30 minutes with no significant grain growth.
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Nel, Jacqueline Margot. "Processing and properties of silicon nitride ceramics." Master's thesis, University of Cape Town, 1993. http://hdl.handle.net/11427/21682.
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Bibliography: pages 129-139.Silicon nitride, Si₃N₄, ceramics were produced using either silicon or silicon nitride powder. The silicon was reaction bonded in nitrogen atmosphere to form reaction bonded Si₃N₄,which was then sintered between 1700°C and 1800°C to form a dense Si₃N₄ ceramic. The silicon nitride powder compacts were also sintered between 1700°C and 1800°C. In order to achieve densification Y₂O₃-A1₂O₃ additive combination was used in both processing routes. The physical and mechanical properties of the Si₃N₄ materials was found to be dependent on the processing conditions. The post sintered reaction bonded Si₃N₄ materials had the highest densities and hardness values, while the sintered Si3N4 materials had the highest strength and toughness values. The microstructure was also influenced to a great extent by the processing conditions, and this in tum influenced the mechanical properties of the ceramics.
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He, Jingyan. "Processing and characterisation of submicron/nanometre alumina ceramics and alumina matrix nanocomposite ceramics." Thesis, University of Birmingham, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633127.
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The microstructure and properties of alumina and alumina-matrix nanocomposites are strongly affected by the raw powders and the processing route. The significant effect of hydrothermal synthesis condition on the morphology of boehmite particle was observed. UF-SiC has more controllable oxidation behaviour for the preparation of nanometer SiC/mullite/alumina composites than P-SiC. Due to the crystallization and agglomeration of SiC at high temperature, oxidation at low temperature is suggested. The properties of the compacts prepared by pressure filtration were closely related to the state of the starting slurry, the particle size and morphology and the applied pressure. A desired slurry can be obtained by the controlling of pH value, the ionic strength and the addition of suitable dispersant. Due to the non-uniform distribution of the liquid pressure and solid pressure across the compact during pressure filtration, the density of the compacts is not uniform as well. Gradually increasing the pressure to the desired level is suggested in order to obtain a more homogeneous compact density. Cracking upon unloading after pressure filtration and during drying became severe for mono and binary boehmite system due to the high stress caused by its very small particle size. Drying rate and stress, hence cracking can be somehow controlled by the drying condition. All the sintered materials from the pressure filtered compacts of submicron/nanometer alumina and alumina-matrix composite show very homogeneous microstructures with fine grain size, confirming that colloidal pressure filtration is a good way to produce advanced materials
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Dancer, Claire E. J. "Ceramic processing of magnesium diboride." Thesis, University of Oxford, 2008. http://ora.ox.ac.uk/objects/uuid:40e122d4-5bdf-4cf4-b23b-5d7286ede4c0.
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This thesis describes the fabrication and characterization of ex situ magnesium diboride (MgB2<) bulk material to study its sintering behaviour. Since the discovery of superconductivity in magnesium diboride in 2001, many research studies have identified the attractive properties of this easy-to-fabricate, low cost superconductor which can attain high critical current density even without heat-treatment. However there is little consensus in the literature on the processing requirements to produce high quality MgB2< material with low impurity content and high density. In this work, the key parameters in the production of dense ex situ MgB2< produced from Alfa Aesar MgB2< powder are established by examining the effect of modifying the characteristics of the starting material and the processing parameters during pressureless and pressure assisted heat-treatment. The particle size distribution, impurity content and particle morphology of Alfa Aesar MgB2< powder were determined using laser dffraction, X-ray diffraction, X-ray photoelectron spectroscopy, electron dispersive spectroscopy, scanning electron microscopy and transmission electron microscopy. This powder was also modified by separation (sieving and sedimentation) and milling (ball milling and attrition milling), with changes made to the powder determined by the same techniques. A pressureless heat-treatment method using a magnesium diboride powder bed was developed. This minimised MgO formation in samples produced from as-purchased MgB2< powder to less than 8 wt.% for heat-treatment at 1100°C. MgO content was determined by X-ray diffraction using calibrated standards. MgB2< bulk material was produced from as-purchased and modified powders by pressureless heat-treatment under Ar gas, and characterized using Archimedes' density method, X-ray diffraction, Vickers hardness testing, scanning electron microscopy, and magnetization measurements. Very limited densification was observed for all samples prepared by pressureless heat-treatment, with only limited increases in connectivity observed for some samples heat-treated at 1100°C. Pressure-assisted bulk samples were prepared from as-purchased MgB2< and selected modified powders using resistive sintering, spark plasma sintering, and hot pressing. These were characterized using the same techniques, which indicated much more extensive densification with similar levels of impurity formation as for pressureless heat-treatment at 1100°C. The results indicate that densification and applied pressure are strongly correlated, while the effect of temperature is less significant. The optimum processing environment (inert gas or vacuum) was dependent on the technique used. These results indicate that pressure-assisted heat-treatment is required in order to produce dense bulk MgB2<.
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Aydogan, Eda. "Processing And Characterization Of Textured Barium Ferrite Ceramics." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614465/index.pdf.
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Technological advances results in the fact that quite a large number of electronic equipment interacts with its environment leading to the malfunction of the devices. This brings about the necessity of using proper electromagnetic (EM) wave absorbers/shields to avoid such interactions. In order to absorb EM waves in a large frequency band from several MHz to GHz, barium hexaferrite (BaHF) ceramics which are produced as textured ceramics as well as in multilayered form can be used. Textured ceramics are processed by tape casting using templated grain growth (TGG) phenomenon. In order to obtain textured ceramics, BaHF powders and platelets are required as raw materials in such a way that during sintering small size powders are directioned by large platelet surfaces. In this study, ferrite powders were synthesized by mixed oxide technique while the platelets were produced by both molten salt synthesis (MSS) and reactive templated grain growth (RTGG) methods. In the case of platelet synthesis by MSS, effects of calcination temperature and time as well as type and composition of the flux on the formation and morphology of platelets were investigated based on the XRD and SEM results. Studies have shown that KCl flux led to the formation of sharper platelet morphology, while NaCl resulted in more round shapes. However, extent of BaHF formation in the case of NaCl was higher when compared to KCl flux due to its higher wettability characteristic, and hence faster interaction with the raw materials. Since the aspect ratio of the synthesized platelets was only ca. 2-4, these platelets were not efficient for further TGG studies. Alternatively, BiFeO3 (BiF) particles having ~30-40 &mum average size were synthesized as seed crystals for the synthesis of BaHF platelets by RTGG method. After the washing of these platelets with dilute HNO3, pure BaHF powders and platelets were directed by tape casting which was followed by sintering using TGG phenomenon. Degree of achieved texturing in the processed ceramics was studied using Rietveld analysis, pole figure measurement and electron backscattered diffraction (EBSD).
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Mallinson, Phillip Martin. "Perovskite Microwave Dielectric Ceramics: Structure, Properties and Processing." Thesis, University of Liverpool, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490899.
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Perovskite Microwave Dielectric Ceralnics: Structure, Properties and Processing PhD thesis, Phillip M. Mallinson, University of Liverpool This thesis describes the synthesis and characterisation of several new hexagonal perovskite materials and the investigation into the processing of a commercial microwave dielectric. Chapter 1 is in two parts, the first gives an introduction to the perovskite and hexagonal perovskite structural types, and reviews the structure and properties of reported hexagonal perovskites with the AnBn-\03n general formula. The second part reviews the literature on the microwave dielectric material Ba3ZnTa209 (BZT). In Chapter 2 the details of the synthetic and analytical techniques employed are described. Chapter 3 describes the synthesis and characterisation of a number of new hexagonal perovskite materials. The eight layer compounds BagCoNb60 24 and BagCoTa6024 were found to crystallise with different structures in the space groups P 3ml and P63c11l respectively. A detailed structural description and comparison of the structures of the materials is given along with the dielectric and magnetic properties. The structure and dielectric properties of the six layer material Ba6Ca1l3Nb\4/30\g are also presented. Chapter 4 describes the synthesis and characterisation of two isostructural ten layer hexagonal perovskites with the formulas BalOMgo.25Ta7.903o and BaIOCoO.25Ta7.903o. Refinement of combined synchrotron X-ray and neutron powder diffraction data is used to determine the structures of the materials. The dielectric properties of the materials are reported and the links between dielectric loss and ordering and microstructure discussed. In Chapter 5 the results of an in-situ X-ray powder diffraction study of the ordering and domain growth ofBZT at temperatures between 1200 and 1500 °C is presented. The degree of ordering is quantified using two different methods and a rate of ordering calculated at each of the temperatures studied, from the rates of ordering the activation energy for cation transport is calculated. The ordered domain size is also quantified from the diffraction data and the dynamics compared to domain growth in other systems. Supplied by The British Library - 'The world's knowledge'
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Daga, Amit Kumar. "Characterization and processing of [beta]-lactoglobulin gelcast ceramics." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0013104.
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Klesner, Catherine Elizabeth, and Catherine Elizabeth Klesner. "Reverse Engineering of Corinthian Pigment Processing and Firing Technologies on Archaic Polychrome Ceramics." Thesis, The University of Arizona, 2017. http://hdl.handle.net/10150/625903.
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Decorative, polychrome ceramics from Corinth, Greece, produced during the 8th-6th centuries B.C.E. are luxury goods that were widely traded throughout Greece and the Mediterranean. The decorated ceramics were produced in a variety of shapes, including aryballos, alabastron, and olpe. They were decorated with slip-glazes in distinctive white, black, red, yellow, and purple colors, and in a variety of surface finishes, matte, semi-matte and glossy. Artisans in Corinthian workshops experimented to change the colors of the slips by varying the type and amount of iron-rich raw materials. They also varied the composition of the clay used as a binder and the amount of flux used as a sintering aid to promote glass formation. This research reconstructs the technology used by the Corinthian craftsmen to produce the Archaic polychrome ceramics, and shows how these technologies differed from the production of better known, more prestigious Athenian black-figure and red-figure ceramics. Through microstructural examination of archaeological samples and replication experiments, this thesis proposes that the purple iron oxide pigment is the result of acid treatment and oxidation of iron metal. The firing temperature range of the Corinthian polychrome ceramics was determined experimentally to be 925-1025° C, which is higher than previously reported and similar to that reported for Corinthian transport amphoras. The firing range is higher by 50-150° C than the Athenian black-figure and red-figure ceramics. Samples of Corinthian polychrome and Athenian black-figure ceramics from the Marie Farnsworth collection at the University of Arizona were tested and compared to Corinthian clay collections. Analytical techniques included Fourier-transform infrared spectroscopy (FTIR), scanning-electron microscopy with energy-dispersive spectroscopy (SEM-EDS), micro-Raman spectroscopy, and wavelength-dispersive electron microprobe (EPMA with BSE-SEM).
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Cox, Sarah. "Processing and Characterization of Continuous Basalt Fiber Reinforced Ceramic Matrix Composites Using Polymer Derived Ceramics." Master's thesis, University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6259.
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The need for high performance vehicles in the aerospace industry requires materials which can withstand high loads and high temperatures. New developments in launch pads and infrastructure must also be made to handle this intense environment with lightweight, reusable, structural materials. By using more functional materials, better performance can be seen in the launch environment, and launch vehicle designs which have not been previously used can be considered. The development of high temperature structural composite materials has been very limited due to the high cost of the materials and the processing needed. Polymer matrix composites can be used for temperatures up to 260°C. Ceramics can take much higher temperatures, but they are difficult to produce and form in bulk volumes. Polymer Derived Ceramics (PDCs) begin as a polymer matrix, allowing a shape to be formed and cured and then to be pyrolized in order to obtain a ceramic with the associated thermal and mechanical properties. The use of basalt in structural and high temperature applications has been under development for over 50 years, yet there has been little published research on the incorporation of basalt fibers as a reinforcement in the composites. In this study, continuous basalt fiber reinforced PDCs have been fabricated and tested for the applicability of this composite system as a high temperature structural composite material. The oxyacetylene torch testing and three point bend testing have been performed on test panels and the test results are presented.M.S.M.S.E.
Masters
Materials Science Engineering
Engineering and Computer Science
Materials Science and Engineering
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Gai, Fangyuan, and Fangyuan Gai. "Processing and Microstructural Characterization of Ultra-High Temperature Ceramics." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/626334.
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Spark plasma sintering (SPS), also known as direct current sintering (DCS) is an advanced sintering technique that and uses a continuous pulsed direct current to rapidly process materials through Joule heating and offers significant advantages and versatility over conventional sintering methods. The technique features in energy saving owing to high heating rates and is very suitable for consolidation as well as diffusion bonding of electrical conductive advanced ceramic materials such as ultra high temperature ceramics (UHTCs). However, cooling rate in SPS also plays an important role as it directly influences the generation of residual stress especially for specimens consist of dissimilar phases such as composites and laminates primarily due to CTE mismatch. Therefore, in order to produce high quality materials, a zirconium diboride with addition of silicon carbide (ZrB2-SiC) ultra high temperature ceramic composite is selected to investigate the effect of cooling rate in SPS on microstructure and mechanical properties. After being densified at the target temperature, ZrB2-25vol%SiC specimens are cooled from 1800°C using controlled cooling rates of 10 °C/minute to ~225.5 °C/minute (free cooling). A time dependent finite element analysis (FEA) model is used to simulate the temperature gradients across the specimens at dwell times and during the cooling processes. The residual stress within the specimens are experimentally verified using X-ray diffraction (XRD) and Raman spectrometry, and found maximum residual stress within the specimen cooled at 225.5 °C/minute. Peak Hardness and moderate elastic modulus is found for specimen sintered at 1800 °C and cooled at 100 °C/minute, which make this temperature and cooling rate appropriate conditions for future fabrication of UHTCs with similar thermal and electrical properties. These materials are of great interest for their excellent high-temperature capabilities, wear and corrosion resistance, and are regarded as material candidates for engineering applications in extreme environments. Therefore, development of an effective joining technique is important since near-net shape fabrication is challenging, and joints formed by brazing or conventional solid-state diffusion bonding limit the mechanical strength and high temperature applications of the base materials. Using SPS we have rapidly and successfully joined ZrB2 to hafnium diboride (HfB2) at 1750 and 1800 °C within a minute through electric current assisted solid-state diffusion bonding. The electric current enables localized Joule heating as well as plastic deformation of the mating surface asperities, and enhances the elemental interdiffusion process at the HfB2/ZrB2 interfaces owing to electromigration, which leads to the formation of ZrxHf1-xB2 solid solution. A series of characterization and analytical techniques including scanning electron microscopy (SEM), wavelength dispersive spectroscopy (WDS), electron backscatter diffraction (EBSD), and scanning transmission electron microscopy (S/TEM) are employed to study the microstructure and chemical composition at of the HfB2/ZrB2 interfaces. Apart from enhanced diffusion as a result of electromigration, the applied electric current can also be use to promote plastic deformation in ZrB2, which does not go through gross plastic deformation due to its extremely high melting point and brittle nature even when elevated temperature and pressure are applied. Through “electroplastic effect” (an effect based on electromigration) the mobility and multiplication of the existing dislocations in ZrB2 is enhanced, and a “metal-like” primary recrystallization phenomenon in the ZrB2 is observed meaning the material has experienced a sufficient amount of plastic deformation and reached the critical dislocation density and configuration for nucleation of “strain-free” grains. The average grain size of the recrystallized grain is only ½ of its original value. These findings suggest great potentials in microstructural tailoring and grain refinement of conductive advanced ceramics using SPS, and provide promising ideas for future fabrications and applications.
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Coimbra, David. "AFM and rheological investigations on colloidal processing of ceramics." Thesis, Keele University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368984.
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Hoad, Oliver John. "Epoxy functional dispersants for the processing of alumina ceramics." Thesis, University of Sussex, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357644.
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Nogueira, Ricardo Emilio Ferreira Quevedo. "Processing and properties of moulded alumina bodies." Thesis, Brunel University, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305112.
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Smith, R. T. "The processing of engineering ceramic foams." Thesis, University of Nottingham, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.250759.
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Schnittker, Kimberlin, and Kimberlin Schnittker. "Processing of Silicon Nitride Ceramics Produced by Spark Plasma Sintering." Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625918.
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Four silicon nitride powder blends vary in starting powder characteristics, glass chemistry, and phase composition. This work focuses on how these properties influence densification behavior, microstructural development, and the resulting mechanical performance of dense ceramics. Previous work completed on alpha-rich, low oxide containing (8 wt%), and fine silicon nitride powder (GS-44) showed high hardness equiaxed with grained ceramic. GS-44 served as an excellent precursor for the matrix phase material in graphene reinforced composites, which resulted in 235% increase in toughness and high hardness retention [1] with the addition of 1.5 vol% graphene. As the GS-44 powder is no longer in production, investigative work into other commercial powders and customization of powder blends was initiated. Commercial blends were selected based on availability, high alpha content, fine particle size, and additive chemistry (Al2O3, MgO, and Y2O3). The objective was to understand which powder characteristics led to a ceramic design that contained high hardness, strength, and toughness properties in order to increase the use of silicon nitride in extreme temperature environments. One such example is aerospace and structural applications that require a high-performance material that is lightweight and good thermal stability.
Strong covalent bonding in silicon nitride make densification of powders extremely difficult; thereby, sintering additives are necessary to promote liquid phase sintering processes. Compaction of ceramic powders was carried out using a spark plasma sintering (SPS) furnace by utilizing a pulsed direct current through a conductive graphite die that encapsulates the sample powder. SPS was preferred over other conventional sintering methods owing to its high heating rate and short dwell times at the sintering target temperature. Thus, SPS provides superior control for tailoring the final silicon nitride properties by producing a hard alpha-phase and tough beta-phase microstructures.
The custom blend developed had an appreciable amount of media wear included during the milling process that increased the additive content. Development of the custom blend was used to understand the effect of a larger additive content. Commercial GS-44 blend was used as the control to track the effect of adjusting specific surface area and oxide content in silicon nitride powder systems (HCS-M, C-R3, and UA-SN). The mechanical results for the four matrix systems, showed that toughness increased with grain coarsening and minimization of alumina content in beta silicon nitride. Based on these findings it is important to determine tradeoffs (i.e. balance of high hardness, toughness, and strength) to engineer an optimal ceramic that can be used for structural and aerospace applications.
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Inostroza, Pilar Angelica Sepulveda. "Processing of cellular ceramics synthesised by gel casting of foams." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.301868.
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Shaw, N. J. "Structure and grain coarsening during the processing of engineering ceramics." Thesis, University of Leeds, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378400.
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Ramanujam, Prabhu. "Synthesis and processing of nanocrystalline YAG (Yttrium Aluminium Garnet) ceramics." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/16651.
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Transparent ceramics are used in a variety of applications such as protective visors, thermo-graphic lens, night vision devices and windowpane of an armed vehicle, missile domes and in aircrafts. Yttrium Aluminium Garnet (YAG, Y3Al5O12) exhibits uniform index of refraction without birefringence owing to its cubic crystal structure and offers a range of optical and mechanical properties that makes it suitable for transparent applications.
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Cordero, Cabrera Mario César. "Sol-gel processing and fabrication of lead zirconate titanate ceramics." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.615260.
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Santa, Cruz Hernán. "Processing and properties of macroporous nanocrystalline yttria stabilised zirconia ceramics." Berlin dissertation.de, 2009. http://d-nb.info/993571190/04.
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Ikuhara(Hayami), Yumi. "Processing and microstructure of functional oxide ceramics with oriented structure." 京都大学 (Kyoto University), 2004. http://hdl.handle.net/2433/147669.
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Kirby, Nigel Matthew. "Barium zirconate ceramics for melt processing of barium cuprate superconductors." Thesis, Curtin University, 2003. http://hdl.handle.net/20.500.11937/1364.
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The widespread use of high temperature superconductors through improved understanding of their underlying physics is in part dependent on the synthesis of large, high quality single crystals for physical research. Crucible corrosion is an important factor hindering the routine synthesis of large, high purity rare-earth barium cuprate superconductor single crystals. Molten BaCuO2-CuO fluxes required for the growth of such crystals are highly corrosive to substrate materials, and corrosion products may lead to chemical contamination of crystals and other practical difficulties. BaZrO3 is known to be inert to BaCuO2-CuO melts, but its use has remained restricted to a very small number of laboratories worldwide because it is very sensitive to the effects of off- stoichiometric or residual secondary phases which degrade its performance. BaZrO3 suitable for sustained melt containment is difficult to produce due to kinetic limitations of phase purity, difficulty in sintering to adequate density, and very narrow stoichiometry tolerances of finished ceramics. The existing literature provided a guide to the production of high quality BaZrO3, but was not sufficiently complete to readily allow production of crucibles suitable for this application. The two basic aims of this project were: To provide a comprehensive and quantitative description of the necessary attributes of crucibles for barium cuprate melt processing and to expand the knowledge of solid-state BaZrO3 processing to encourage its widespread application to crucible manufacture; To explore the application of solution chemical processes whose potential benefits could lead to routine application of BaZrO3 through improved ceramic quality and processing properties.Based primarily on solid-state processing research, the optimal stoichiometry for corrosion resistant crucibles was observed over the narrow range of 1.003±0.003 Ba : (Zr + Ht) mole ratio. Residual ZrO2 must be strictly avoided even at very low levels because severe localized expansion of Z a grains during reaction with the melt severely reduces corrosion resistance. Although the effect of Ba-rich phases are less severe, their abundance must be suppressed as much as allowed by the production process. Solid-state derived crucibles with a large barium excess were unstable and readily attacked by water. TEM analysis clearly showed residual Zr02 was present as discrete grains and not as grain boundary films, and also the prevalence of intragranular defects in Ba-rich ceramics. Quantitative knowledge of the narrow range of required stoichiometry is critical for developing successful solid-state and solution chemical processes. Reliably achieving the required stoichiometry and phase purity is experimentally challenging and beyond the capability of many processing systems. Systematic investigation revealed sharp changes in physical properties of processed powders across the phase boundary. The resistance of BaZrO3, of the desired stoichiometry to grain growth during powder processing has not previously been reported in the available literature. At the desired stoichiometry for corrosion resistance, powder grain growth resistance combined with very precise control over stoichiometry makes the solid-state process more competitive with solution-based processes than previously acknowledged in the literature. The development of solution processes for BaZr03 precursors is complicated by aqueous chemistry of zirconium compounds.This project developed the first chemically derived precursor process demonstrated to produce a ceramic of adequate quality for sustained barium cuprate melt containment. The barium acetate / zirconium oxychloride / ammonium oxalate system provided control over stoichiometry without requiring elevated solution temperatures, a large excess of barium reagents, or reagents containing alkalis. Despite showing the capability to supersede the solid-state process, the oxalate process still requires further refinement to more reliably achieve high sintered densities. Although the attributes required for sustained barium cuprate melt containment are now clear, its routine mass production remains reliant on further development of solution chemical techniques or improvements to the kinetics of solid-state processing. This project advanced ceramic design and processing technology in the BaZrO3 system and provided new approaches in meeting the challenging analytical needs of research and process control for high quality production of this compound.
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Kirby, Nigel Matthew. "Barium zirconate ceramics for melt processing of barium cuprate superconductors." Curtin University of Technology, Department of Applied Physics, 2003. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16216.
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The widespread use of high temperature superconductors through improved understanding of their underlying physics is in part dependent on the synthesis of large, high quality single crystals for physical research. Crucible corrosion is an important factor hindering the routine synthesis of large, high purity rare-earth barium cuprate superconductor single crystals. Molten BaCuO2-CuO fluxes required for the growth of such crystals are highly corrosive to substrate materials, and corrosion products may lead to chemical contamination of crystals and other practical difficulties. BaZrO3 is known to be inert to BaCuO2-CuO melts, but its use has remained restricted to a very small number of laboratories worldwide because it is very sensitive to the effects of off- stoichiometric or residual secondary phases which degrade its performance. BaZrO3 suitable for sustained melt containment is difficult to produce due to kinetic limitations of phase purity, difficulty in sintering to adequate density, and very narrow stoichiometry tolerances of finished ceramics. The existing literature provided a guide to the production of high quality BaZrO3, but was not sufficiently complete to readily allow production of crucibles suitable for this application. The two basic aims of this project were: To provide a comprehensive and quantitative description of the necessary attributes of crucibles for barium cuprate melt processing and to expand the knowledge of solid-state BaZrO3 processing to encourage its widespread application to crucible manufacture; To explore the application of solution chemical processes whose potential benefits could lead to routine application of BaZrO3 through improved ceramic quality and processing properties.Based primarily on solid-state processing research, the optimal stoichiometry for corrosion resistant crucibles was observed over the narrow range of 1.003±0.003 Ba : (Zr + Ht) mole ratio. Residual ZrO2 must be strictly avoided even at very low levels because severe localized expansion of Z a grains during reaction with the melt severely reduces corrosion resistance. Although the effect of Ba-rich phases are less severe, their abundance must be suppressed as much as allowed by the production process. Solid-state derived crucibles with a large barium excess were unstable and readily attacked by water. TEM analysis clearly showed residual Zr02 was present as discrete grains and not as grain boundary films, and also the prevalence of intragranular defects in Ba-rich ceramics. Quantitative knowledge of the narrow range of required stoichiometry is critical for developing successful solid-state and solution chemical processes. Reliably achieving the required stoichiometry and phase purity is experimentally challenging and beyond the capability of many processing systems. Systematic investigation revealed sharp changes in physical properties of processed powders across the phase boundary. The resistance of BaZrO3, of the desired stoichiometry to grain growth during powder processing has not previously been reported in the available literature. At the desired stoichiometry for corrosion resistance, powder grain growth resistance combined with very precise control over stoichiometry makes the solid-state process more competitive with solution-based processes than previously acknowledged in the literature. The development of solution processes for BaZr03 precursors is complicated by aqueous chemistry of zirconium compounds.
This project developed the first chemically derived precursor process demonstrated to produce a ceramic of adequate quality for sustained barium cuprate melt containment. The barium acetate / zirconium oxychloride / ammonium oxalate system provided control over stoichiometry without requiring elevated solution temperatures, a large excess of barium reagents, or reagents containing alkalis. Despite showing the capability to supersede the solid-state process, the oxalate process still requires further refinement to more reliably achieve high sintered densities. Although the attributes required for sustained barium cuprate melt containment are now clear, its routine mass production remains reliant on further development of solution chemical techniques or improvements to the kinetics of solid-state processing. This project advanced ceramic design and processing technology in the BaZrO3 system and provided new approaches in meeting the challenging analytical needs of research and process control for high quality production of this compound.
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Kwan, Y. B. P. "Processing and fluid flow characteristics of hot isostatically pressed porous alumina for aerostatic bearing applications." Thesis, Cranfield University, 1996. http://dspace.lib.cranfield.ac.uk/handle/1826/3690.
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Despite their well known superior load and stiffness characteristics, the wide-spread use of porous aerostatic bearings in preference to other bearing types has been hampered by difficulties in controlling the permeability of the porous material during manufacture and machining, in addition to instability problems caused by the additional volume of air trapped amongst the pores. Recent development in porous aerostatic bearings centres around the use of a thin dense surface layer to overcome the stability problem. The production of single and two-layered porous ceramic structures for aerostatic bearing applications have been investigated using the free-capsule hot isostatic pressing process, and in conjunction with slip and tape castings. The influence of various process parameters on open porosity, and the empirical relationships between porosity, particle size and the resulting fluid flow and structural properties were determined from experimental data. The measurement accuracy and uniformity of temperature within the furnace are identified as the most important factors affecting consistency and predictability of the permeability of the porous substrate. Prototype bearings were produced and tested, based on the above materials. The single-layer bearing was, not unexpectedly, found to be unstable over a wide operating range. The use of a two-layeredb earingm ateriale liminatedth e stabilityp roblem. Initial measurements of the slip coefficient of the porous material in air and at small gaps indicated significant deviation from the Beavers' theory. The effect of velocity slip was found to be significant in both test bearings, and was allowed for by the addition of an equivalent clearance to the bearing gap. The value of the equivalent clearance was deduced from experimental data. The static load characteristics and the pressure profile of both test bearings agreed well with published theories, once the above-mentioned correction for slip was applied.
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Davies, Jason. "Plastic forming of alumina via colloidal powder processing." Thesis, University of Nottingham, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283400.
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Farahi, Elham. "Advanced calcareous ceramics via novel green processing and super-critical carbonation." Thesis, University of Warwick, 2008. http://wrap.warwick.ac.uk/2270/.
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The work presented in this thesis is aimed at evaluating the potential for using supercritical carbonation (SCC) in conjunction with novel processing techniques, to fabricate new blended calcareous matrix composites with superior engineering properties and lower environmental impacts than conventional cement-based materials. Taking combinations of waste materials such as steel slag (SS) and fuel ash (PFA), binders such as hydrated and cement and various aggregate types to manufacture green forms and exposing them to supercritical carbon dioxide has produced a number of promising ceramic materials. The project looked at novel ways to process the ‘green forms’ from these composites, such as dry- and wet-compression moulding, 3-D printing and hand lay up technique that was adapted from the fibre-reinforced polymer industry. Work concentrated on optimising mix designs, green processing and SCC conditions to produce the highest strength materials. Three main avenues were explored. The effects of mix design, different curing regimes and SCC treatment, on the microstructure and chemistry of the composites was investigated using SEM, TSP, DTA, XRD, helium pycnometry and other techniques. Investigation showed that SCC process significantly enhances the mechanical and microstructural properties of carbonated products. It was shown that SCC treatment activates materials such as steel slag, that in the unground state are not activated by high temperature curing, to form useful composites. It was revealed that the relationship between the ‘degree of carbonation’ and strength is not straightforward and the order in which the various phases in the concrete react is important. Microstructural investigations hinted that the bond between carbonate limestone aggregate and the carbonated matrix was much stronger and more intimate (less porous) than for other aggregates. Chemical analysis also determined how much carbon dioxide could be ‘locked-up’ in the samples and this data was then used in the life-cycle assessment (LCA) of potential products. LCA was used to assess the green credentials of the SCC process and results were encouraging; a net reduction in CO2 emission of around 50% can potentially be achieved. Overall, the project has made many significant advances both in the practical application of SCC to ceramic composite manufacture and in the science of the reaction between sc-CO2 and cementitious phases. The technology could now be exploited by the manufacturing industry as a lowtemperature, rapid, low raw material cost and a sustainable route for manufacture of a wide range of ceramics.
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Benkert, Katrin Sabine. "Processing and properties of novel pb(Zr1-xTix)O3-based ceramics." Thesis, University of Manchester, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685300.
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The investigation comprised three main sections: first, the development of an aqueous slurry system for tape casting PZT ceramics, second, examination of the doping influence on the sintering behaviour and on the piezoelectric properties of PZT ceramics and thirdly, the fabrication of multilayer actuators with silver-based inner electrodes, in order to investigate the influence of co-firing with inner electrodes on the sintering behaviour and the piezoelectric properties of the ceramics.
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Otieno, Geoffrey. "Processing and properties of aligned carbon nanotube/glass ceramic composite." Thesis, University of Oxford, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.560925.
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Previous attempts to produce carbon nanotube (CNT) ceramic composites have resulted in poorly dispersed, unaligned and non-continuous CNTs in the composites with modest improvements in properties. The research presented in this thesis pertains to the production of dense aluminoborosilicate (ABS) glass matrix composites containing aligned and continuous multi- walled carbon nanotubes (MWCNT) of millimetre lengths. This was achieved by infiltrating CVD grown MWCNT preforms using a precursor sol and sintering which achieved 80 ± 2% dense composites. Focused ion beam milling together with image analysis showed that the composites contained 20 ± 2 vol.% MWCNTs, which are aligned and continuous within the glass matrix. Indentation studies showed greater damage tolerance in the composite compared to unreinforced ABS glass. Under compression, there is no significant change in the compressive strength between the composite and the unreinforced glass. The bend strength of microcantilever beams were 1.4 to 1.3 GPa for the composite and glass respectively. Elastic modulus of 84 GPa and fracture toughness (Kic of up to 2.4 MPa √m were obtained for the composite. The elastic modulus and fracture toughness results are an improvement of 30 % and 240 % over that of unreinforced ABS glass. Fracture surfaces showed apparent MWCNT pullout lengths of up to ~ 1 urn. Analysis indicates that crack bridging by intact MWCNTs provides the majority of the improvement in fracture toughness. Interlayer sliding of the MWCNTs and "sword in' sheath" failure mechanism of the MWCNTs prevented the maximum potential performance, with respect to elastic modulus and fracture toughness, from being achieved. Electrical conductivity in the alignment direction of the CNTs showed improvements by a factor of 106 compared to unreinforced ABS glass. Furthermore, improvement of a factor of ~ 10 in the thermal conductivity was obtained for the composite over that of ABS glass.
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Stroyan, Jared James. "Processing and characterization of PVDF, PVDF-TrFE, and PVDF-TrFE-PZT composites." Online access for everyone, 2004. http://www.dissertations.wsu.edu/Thesis/Fall2004/j%5Fstroyan%5F121704.pdf.
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Luo, Hongyu Shih Wei-Heng Shih Wan Y. "Colloidal processing of PMN-PT thick films for piezoelectric sensor applications /." Philadelphia, Pa. : Drexel University, 2005. http://dspace.library.drexel.edu/handle/1860/500.
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Sun, Xudong. "Aspects of the processing and properties of nickel particle toughened alumina." Thesis, University of Surrey, 1993. http://epubs.surrey.ac.uk/804932/.
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MESQUITA, RODRIGO M. "Desenvolvimento de ceramicas porosas a base de nitreto de silicio." reponame:Repositório Institucional do IPEN, 2009. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11517.
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Made available in DSpace on 2014-10-09T12:52:46Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:02:42Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP
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Ji, Ying. "Aspects of the processing and properties of chromium particle-alumina matrix composites." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/843905/.
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This work is concerned with the processing and properties of chromiuni reinforced alumina ceramics with the Cr particles in both the micro- and nano-scale ranges. The influence of processing and microstructure on the mechanical properties has been studied. Al2O3-20vol%Cr micro-composites have been fabricated using both sintering and hot pressing techniques. Sintering environment has a crucial influence on the microstructural development of the pressureless sintered Al2O3-Cr composites. It was found that too little or too much oxygen is detrimental to Al2O3/Cr interfacial bonding. Attempts have been made to improve the Al2O3/Cr interfacial bonding by sintering in a graphite powder bed in order to control the oxygen partial pressure. The fracture toughness of the composite with strengthened interfaces was the highest of all the sintered samples. However, the improvement is limited by the brittle fracture of Cr. This may be caused by the high carbon content associated with Cr particles in the composite. The ductility of Cr was higher in the hot-pressed Al2O3-Cr samples. The possibility of further toughening Al2O3 by Cr80Ni20 and Cr20Ni80 alloys with higher ductility was explored. It was shown that 20 wt% of Ni present in the alloying phase did not change the ductility, but when the Ni content increased to 80 wt% the crystal structure changed to fc.c., giving a inherently ductile metal. However, the large thermal mismatch between Al2O3 and Ni/Cr alloys led to a high density of microcracks at the interfaces. The composites with different metallic phases had similar' fracture toughness values as measured by double cantilever beam testing. Among the Al2O3-CrxNi1-x composites, the highest fracture toughness, 5.8 MPa m1/2, was achieved by the hot pressed Al2O3-Cr composite. This value is comparable to values measured for other alumina-metal systems. The poor bonding at the alumina/metal interface is the main limitation to toughening in these composites. Thus, it may not be possible to have a strongly bonded and ductile reinforcement. The pressureless sintered Al2O3-Cr composites with different particle sizes showed different thermal shock behaviour. The composite with fine Cr particles exhibited a thermal shock behaviour which is typical of engineering ceramics, but with an improved critical temperature difference compared to sintered Al2O3. The specimen with a larger Cr particle size showed gradual strength degradation with increasing temperature difference. The increased fracture toughness, low initial strength and low Young's modulus of the composite are the primary reasons for the greater strength retention following quenching. Although Al2O3 was toughened by Cr and Cr/Ni alloys, the strength of the micro-composites was not improved as the metal particles acted as large flaws. In order to reduce the flaw size nano-composites were investigated. Al2O3-5vol% Cr nanocomposites were fabricated using a chemical method. Optimisation of the processing procedure led to a desirable microstructure and significantly increased strength. Among the nanocomposites, the highest strength, 736+/-29 MPa, was achieved by hot pressing at 1450°C. The improved strength of the nanocomposites is the consequence of the microstructure refinement by homogeneously distributed nano-sized Cr particles. The nanocomposites are slightly tougher than the parent Al2O3, although the values of the fracture toughness are lower than those for the 20vol% micro-scale particle toughened Al2O3. Thus, a small degree of toughening and significant strengthening have been achieved by Al2O3-Cr nanocomposites.
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He, Xing. "Processing of porous and dense ceramics using natural polymer binders for biomedical applications." Thesis, University of Bristol, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.503879.
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Ceramics have long been used in different biomedical applications. Examples include biodegradable porous ceramic scaffolds and bioactive dense ceramic implants and prostheses. For the fabrication of different forms of ceramics, polymer binders, organic solvents and hazardous processing aids have often been used. Some of them, e.g. acrylamide monomers used in the conventional gelcasting processing. are even toxic. There is a compelling need to develop eco-friendly processing of ceramics. In this work, an environmentally-friendly protein system - egg white protein - has been employed to fabricate porous and dense ceramics to take the advantage of the well-known foaming and gelling capabilities of egg white protein.
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Pascual-Gonzalez, Cristina. "Processing-composition-structure effects on the optical band gap of KNbO3-based ceramics." Thesis, Sheffield Hallam University, 2017. http://shura.shu.ac.uk/18746/.
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This present work is focused on band-gap engineering of solid-solutions based on KNbO3, which was proposed as a promising photoferroelectric (Grinberg et al., 2013). The strategy to narrow the band-gap of the parent KNbO3 (3.22 eV), relies on replacing Nb5+ by lower valence transition metals (Me3+) and K+1 by cations which maintain the compositions stoichiometric. Ceramic processing of KNbO3 by conventional route was optimised in order to minimise K losses, which leads to the formation of a hygroscopic secondary phase, K4Nb6O17. This phase impairs the structural integrity of the samples. In addition, single-phase KNbO3 ceramics have the tendency to absorb moisture from the environment, increasing its conductivity near room temperature. Subsequently, all solid-solutions presented in this work, (1-x) KNbO3-x Ba0.5Bi0.5Nb0.5Zn0.5O3 and (1-x) KNbO3-x BiMeO3 (Me= Mn, Co and Ni) systems in a compositional range of 0≤x≤0.25, 0.90 KNbO3-0.1 BaNb0.5Ni0.5O3 and 0.98 K0.5Na0.5NbO3-0.02 BaNb0.5Ni0.5O3 compounds, were prepared by the same route as KNbO3. X-Ray Diffraction (XRD), Raman spectroscopy and Scanning Electron Microscopy (SEM) revealed compositionally inhomogeneities, suggesting difficulties in cation diffusion for low concentration of solutes by conventional routes. The systems evolve from orthorhombic (x=0) to pseudo-cubic symmetry with an increase of x, suggested by XRD, Raman spectroscopy, ferroelectric and dielectric response. Indeed, these two symmetries seem to coexist for intermediary concentrations. A solubility limit for orthorhombic KNbO3 phase is determined for each system. In addition, a continuous band-gap narrowing was observed in all systems. Nevertheless, (1-x) KNbO3-x BiFeO3 (0≤x≤0.25) system maintained the polar phase up to x=0.25 and its band-gap was narrowed down to 2.22 eV. Indeed, a photocurrent of 0.24 μA/cm2 was measured for 0.75 KNbO3- 0.25 BiFeO3 which is higher than reported for the controversial 0.90 KNbO3-0.1 BaNb0.5Ni0.5O3 compound (Grinberg et al., 2013). The literature does not agree about its band-gap value, which varies from 1.3 eV to 3 eV. Hypothetically, the impossibility of preparing chemically homogenised samples by solid-state reaction may lead to the occurrence of intraband states, which can be misinterpreted. Similar conclusions are reached for 0.98 K0.5Na0.5NbO3-0.02BaNb0.5Ni0.5O3.
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Atanga, Valetine Kubong Verfasser], and Michael [Akademischer Betreuer] [Scheffler. "Processing and properties of alumina reinforced mullite ceramics / Valetine Kubong Atanga. Betreuer: Michael Scheffler." Magdeburg : Universitätsbibliothek, 2013. http://d-nb.info/1054420653/34.
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Feng, Jian-Huei. "Colloidal processing, tape casting and sintering of PLZT for development of piezoceramic/polymer interlayered composites /." Thesis, Connect to this title online; UW restricted, 2000. http://hdl.handle.net/1773/10577.
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Phule, Pradeep Prabhakar. "Chemical processing and structural simulations of electronic materials in the barium-oxide - titanium-dioxide system." Diss., The University of Arizona, 1989. http://hdl.handle.net/10150/184672.
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Novel low temperature wet chemical processes for the synthesis of gels and ultrafine powders of BaTiO₃ and BaTi₄O₉ were developed. Under acidic conditions a titanyl acylate precursor was obtained by molecular modification of titanium isopropoxide. In the sol-gel process, amorphous BaTiO₃ gels obtained under acidic conditions were heat treated at ≈950-1000°C yielding fine (≈ 1-3 μm), high purity (99.9%) stoichiometric (Ba/Ti = 0.99) BaTiO₃ powders. In the sol-precipitation process, ultrafine (≈ 10 nm) crystalline BaTiO₃ powders were directly precipitated at low temperatures (<100°C) from a stoichiometric titanium acylate- barium acetate sol (pH > 13.5). Precursor powders obtained by hydrolytic decomposition of barium and titanium alkoxides were heat treated at 1100°C to obtain high purity, homogeneous, single phase BaTi₄O₉ powders. Atomistic pathways for the evolution of crystalline phases from amorphous gels and powders were investigated. The microstructure and electrical properties of sintered BaO-TiO₂ ceramics were studied and correlated with the powder processing conditions. The structures of crystalline and amorphous forms of some materials in the BaO-TiO₂ system were simulated using molecular dynamics computer techniques to develop a fundamental understanding of structure-property relationships for BaTiO₃ and TiO₂ containing glasses.
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Chiu, Raymond Chi Hing. "Drying of granular ceramic films." Thesis, Ceramics Processing Research Laboratory, Massachusetts Institute of Technology, Materials Processing Center, 1991. http://hdl.handle.net/1721.1/13045.
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Srivastava, Deepanshu. "Effect of processing conditions and second-phase additives on thermoelectric properties of SrTiO3 based ceramics." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/effect-of-processing-conditions-and-secondphase-additives-on-thermoelectric-properties-of-srtio3-based-ceramics(ff3c590e-4fc5-4c5d-b47b-823369ae369d).html.
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Oxide ceramics have been increasingly researched for high temperature thermoelectric (TE) applications. SrTiO3 based materials are promising candidates due to its chemical and thermal stability. In this study, oxide ceramics of composition (1-x)SrTiO3-(x)La1/3NbO3 (0 smaller or equal to x smaller or equal to 0.3) were prepared by single-step solid state sintering in Ar/5%H2 at 1700 K. The density of all the samples prepared was above 90%. All the samples were predominantly single-phase compositions crystallised with a cubic structure in Pm ̅3m space group. The impact of oxygen deficiency, A-site vacancies and mixed oxidation states of Ti3+/Nb4+ on electrical and thermal transport properties was assessed. Optimum TE properties were obtained for x=0.2 (Sr0.8La0.067Ti0.8Nb0.2O(3-delta) = L2), which has 13.4% A-site vacancies. The ZT values improved from 0.2 to 0.27 at 1000 K, with an increase in sintering time from 8 hours to 48 hours, due to increased carrier concentration. Complex interplay of oxygen vacancies and excess donor substitution on A/B-sites of L2 (substituting 5-10% Sr/Ti with La/Nb) exhibited 35% improvement in ZT values, whilst maintaining the A-site vacancies and core-shell structures within grains, which reduced the thermal conductivity by ~50% compared to undoped SrTiO3 samples, due to strong phonon scattering. A facile method to incorporate metallic inclusions (2.5 wt% Fe/Cu) at grain boundaries in L2 ceramics is demonstrated. The modified compositions displayed a maximum ZT of ~0.37 at 1000 K for L2 samples containing metallic inclusions due to increased carrier concentration (5.5 x 10^21 carriers/cm^3) and carrier mobility (2.4 cm^2/(V.s).The addition of graphene/Graphene Oxide (GO) flakes in L2 ceramics has been investigated to improve the electrical conductivity of L2 composites without significantly increasing the thermal conductivity. Spark plasma sintering (SPS) of the composite powders at 1473 K and 50 MPa produced dense samples (>95% relative density) with a homogeneous dispersion of graphene/GO flakes, for loadings smaller or equal to 1.0 wt%. The effect of interaction and distribution of graphene/GO flakes within the ceramics on TE properties is investigated. The composite samples demonstrate anisotropic ZT values, with 20% improvement in the direction normal to the orientation of graphene flakes. A novel sintering method has been proposed which has strong industrial potential. The L2 based composites were sintered in Air at 1700 K (ramp rate: ±300 K/min), whilst samples were covered uniformly. Strong reducing conditions and evolution of secondary phases in the microstructure helped achieve, the very low electrical resistivity of ~3.0 x 10^(-6) ohm.m at room temperature. Secondary phases, sub-micron voids in the grains and A-site vacancies reduced the lattice thermal conductivity (~2.0 W/m.K), comparable to the lowest lattice thermal conductivity achievable (~1.5 W/m.K) at 1000 K and obtain a maximum ZT of 0.4 at 1000 K for L210G-Air/C composites.
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Harrison, Robert. "Processing and characterisation of ZrCxNy ceramics as a function of stoichiometry via carbothermic reduction-nitridation." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/24810.
Full textAbstract:
Carbothermal reduction-nitridation of ZrO2 has been studied in the context of application of non-oxide zirconium ceramics as fuel components in advanced nuclear fuels. Varying processing parameters of nitridation of ZrCx (where 0.7 x 1) powders revealed the rate increased with dwell time, dwell temperature and higher carbon content of the starting ZrCx powders. A novel mechanism is reported whereby nucleation of small ( 500 nm) ZrN containing crystals occurs on the surface of the ZrCx powder particles, growing separate to the carbide particle and resulting in mixed phases. Sintering of the ZrCxNy powders by hot pressing resulted in higher densities than commercially-available ZrC powders suggesting nitrogen content improves the sinterability of ZrC containing ceramics. Thermal and electrical conductivity of the ZrCxNy ceramics were all higher than the ceramics produced from commercially-available ZrC and ZrN powders. Room temperature thermal conductivities of the ZrCxNy ceramics were found to be 35 and 43 Wm-1K-1 for the lowest and highest N-containing ZrCxNy ceramics and increased with temperature to 45 and 55Wm-1K-1 respectively at 2073 K. Electrical conductivities were in the range 250-450 x 104 -1m-1 for the ZrCxNy ceramics (at 298 K) and again increased with increasing nitrogen content. The increase in thermal conductivity of ZrCxNy with nitrogen content is due to the increase in electrical conductivity. Oxidation studies of ZrN revealed oxidation begins at around 773 K with an initial destabilisation of ZrN occurring at around 673 K. A decrease in oxidation rate was observed between lower (973-1073 K) and higher temperatures (1173-1273 K). This is attributed to dense protective oxide scales forming at higher temperature (1173-1273 K) compared to porous oxide scales forming at lower temperature ( 1073 K). However, this protective layer fails at higher temperature (1373 K), attributed to increased oxygen diffusion through the oxide layer.
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Stackpoole, Margaret Mary. "Reactive processing and mechanical properties of polymer derived silicon nitride matrix composites and their use in coating and joining ceramics and ceramic matrix composites /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/10564.
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