Dissertations / Theses on the topic 'Ceramic materials'
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1
Adicks, Michael Kent. "Strength characterization of thin-wall hollow ceramic spheres from slurries." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/9318.
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Katti, Kalpana Shastri. "Microstructure and local dielectric function in barium titanate based electroceramics /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/10590.
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Pemberton, Sonya Rachel. "Toughening ceramics : optimising the fracture behaviour of metallic fibre reinforced ceramic matrix composites (MFCs)." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607820.
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Ceseracciu, Luca. "Contact Damage on Ceramic Laminates." Doctoral thesis, Universitat Politècnica de Catalunya, 2008. http://hdl.handle.net/10803/6057.
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La difusión de los materiales cerámicos en muchos campos de la industria es amplia y está en fuerte expansión, debido a las excelentes propiedades de estos materiales, ya sean mecánicas, térmicas, tribológicas o biológicas. Sin embargo, su fragilidad intrínseca y falta de fiabilidad limitan una mayor difusión en esas aplicaciones donde se precisa alta resistencia estructural. La producción de composites multilaminares es un camino prometedor para aumentar la fiabilidad de los cerámicos. Los cerámicos multicapa permiten que las propiedades mecánicas sean mejores que las de los componentes, debido a la presencia en la superficie de tensiones residuales de compresión provocadas diferencias de expansión térmica entre las capas.Las aplicaciones óptimas de estos materiales son las que están relacionadas con las propiedades superficiales; por eso la respuesta a las cargas por contacto son especialmente importantes para caracterizar las propiedades mecánicas y para mejorar el diseño de cerámicos composites avanzados.
Las técnicas de indentación Hertziana son herramientas muy útiles para estudiar este tipo de carga, que por otro lado es difícil de caracterizar por ensayos mecánico tradicionales. El daño por contacto en materiales frágiles aparece principalmente como grietas anillo en la superficie, que pueden desarrollarse como grietas cono, características de este tipo de carga. Este agrietamiento es perjudicial para la funcionalidad del material, y puede llevar al fallo de la pieza. Las cerámicas tenaces, por otro lado, pueden presentar un daño, cuasi-plástico, que se genera debajo la superficie en forma de microagrietamento, y que es causa de deformación inelástica.
En esta tesis, se caracteriza la resistencia al daño por contacto materiales cerámicos en base alúmina, incluyendo todos los aspectos de ese daño, desde la aparición de fisuras superficiales, a la propagación de grietas frágiles en la primera capa y su influencia sobre la resistencia del material, hasta el fallo inducido por carga de contacto. Se comparan medidas experimentales con análisis a los Elementos Finitos de los parámetros involucrados en cada caso, lo que permite formular pautas para una correcta caracterización y diseño de cerámicas multicapas avanzados.
Se vio que la presencia de tensiones residuales es efectiva en mejorar la resistencia a la formación de grieta anillo, sea generada por cargas monotónicas, cíclicas o estáticas.
La alta resistencia frente a este último tipo de carga revela que existen mecanismos de puenteo intergranular que se oponen a la formación de grietas, lo que era inesperado por el tamaño de grano fino, y que se atribuye a un efecto de grieta corta, comparada con la microestructura. Ensayos cíclicos de larga duración mostraron, por otro lado, que en los materiales multicapas aparece daño superficial más severo que en los monolíticos, lo que sugiere un cambio del daño predominante hacía una degradación superficial producida por cuasi-plasticidad.
Las tensiones residuales afectan tanto la longitud como el ángulo de la grieta cono. Se modeló el problema mediante Elementos Finitos y algoritmos de propagación de grieta, lo que permitió predecir el crecimiento de grieta en función tanto de las tensiones residuales, como de otros parámetros microestructurales, y determinar del ángulo de la grieta cono en materiales policristalinos.
La respuesta a cargas remotas de materiales indentados, en otras palabras la degradación de la resistencia, se ve afectada por la geometría de la grieta cono, y por otros factores que son consecuencia de la estructura laminar, tales como las tensiones residuales y la redistribución de carga por el desajuste elástico entre capas. Asimismo, la resistencia por contacto, o sea la resistencia a compresión roma localizada, se ve mejorada en materiales laminares, como consecuencia de las tensiones residuales. Sin embargo, se evidenció que existe el riesgo de que se genere tensión elevada en las capas interiores bajo ambos tipos de carga, y se propusieron consideraciones generales sobre el diseño de materiales laminares.
En definitiva, se consiguió una caracterización exhaustiva de las propiedades de contacto mecánico de los materiales estudiados, y se amplió y mejoró el conocimiento de la propagación de grieta en materiales frágiles policristalinos.
The use of ceramic materials in many industrial fields is spread and ever-increasing, for their excellent properties, either mechanical, thermal, tribological or biological. However, their intrinsic brittleness and lack of reliability are obstacles to further spreading these materials in applications where structural resistance is required. To build multilayered composite structures is a promising way which aims to increase the reliability of ceramics. As it is common in composite materials, layered materials allow the mechanical properties to be superior to those of the constituent materials, in the studied case due to the presence of compressive residual stress in the surface.
The best applications for such materials are those related to the surface properties; for this reason the response to contact loading is especially important to characterize the mechanical properties and to assist in the design of advanced ceramic composites. Hertzian indentation techniques provide a powerful tool to study such type of loading, which is otherwise difficult to characterize with the traditional mechanical testing methodologies.
Contact damage in brittle materials appears mainly as surface ring-cracks, which can develop in a characteristic cone crack. Such fissuration is detrimental to the functionality of the material, and can lead to the failure of the component. Tough ceramics often present another type of damage, the so-called quasi-plasticity, generated as subsurface microcracking and which is cause of inelastic deformation.
In this thesis, alumina-based ceramic laminates were characterized in their resistance to contact damage in all its aspects, starting from the appearance of surface fissures, to the propagation of brittle cracks in the first layer and its influence on the material strength, to the contact loadinginduced failure. Experimental measurements were coupled with Finite Element analysis of the involved parameters, which assisted in formulating comprehensive guidelines for the correct characterization and the design of advanced multilayered ceramics.
The presence of residual stress in ceramic laminates proved to be effective in improving the material resistance to the ring cracking, generated by monotonic, cyclic and longlasting tests.
The better resistance to these latter revealed the existence of grain bridging hindering the crack formation, unexpected in fine-grained alumina and which was related to the small crack character of the ring crack. Longer lasting cyclic tests showed that more severe damage appears in the multilayered materials than in the monolithic one, suggesting a modification of the redominant damage mode to quasi-plastic-derived surface degradation.
Propagation of long cone cracks is affected by residual stress in both the length and angle. An automatic Finite Element model of crack propagation allowed to predict crack growth as a function of both the extrinsic residual stresses and of microstructural parameters, which helped address the long-open question of the cone crack angle on polycrystalline materials.
The response to remote loading of indented materials, in other words the strength degradation, is conditioned by the cone crack geometry, as well as by other factors deriving from the laminated structure, such as the presence of residual stress itself and the load redistribution due to the elastic mismatch between layers. Similarly, the contact strength, i.e. the resistance to local blunt compression, is improved in the composite materials as a consequence of the residual stresses. Nevertheless, the risk of high stress in the lower tensile layers was highlighted for both types of loading and general consideration on the design of laminated materials were proposed.
In the overall, a comprehensive characterization of the contact properties of the studied materials was achieved, and the understanding of crack propagation on brittle polycrystalline materials was broadened and improved.
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Stanciu, Lia Antoaneta. "Field assisted sintering of ceramic materials /." 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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Louie, Beverly. "Permeation of fluids through ceramic materials." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259809.
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Thoe, T. B. "Ultrasonic Contour Machining of Ceramic Materials." Thesis, University of Birmingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.525493.
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Hassani, Seyed Khosrow Seyed. "Isostatic bonding of pressed ceramic materials." Thesis, Queen's University Belfast, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334709.
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Kryvobok, R. V., G. Lisachuk, A. Zakharov, E. Fedorenko, and M. Prytkina. "Development of radio transparent ceramic materials." Thesis, The American Ceramic Society, 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/26130.
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Wallace, Andrew. "Cathodic precipitation of ceramic precursor materials." Thesis, Loughborough University, 1997. https://dspace.lboro.ac.uk/2134/10989.
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An electrochemical technique has been developed for the production of precursors to ceramic films on hydrogen sorbing metal substrates. It involves the electrolysis of aqueous metal salt solutions which yields hydrogen at the cathode, resulting in local generation of base (hydroxide ions) around this electrode. Such conditions promote the precipitation of metallic hydroxides from a suitable electrolyte. If the local alkaline environment is not disrupted by convective or other forces, then a solid phase accumulates near the cathode, and forms an adherent gel-like structure on its surface. In order to maintain deposition, it is essential that gaseous hydrogen evolution is minimised, and preferably eliminated. This can be achieved by use of a hydrogen sorbing cathode material, such as palladium. The electrode, and adherent film (or, in appropriate circumstances, the deposit alone) can then undergo a subsequent calcination treatment to yield the ceramic layer. It is possible to generate both porous and compact structures by this method, depending on the potential programme employed during deposition. Research has been conducted into the understanding of mechanisms involved in porosity control of films deposited during different potential regimes, with view to establishing routes to layers of predetermined physical structure. In-situ optical methods were employed to complement the electrochemical techniques, providing valuable insight into the initial mechanisms of film formation and the subsequent thickening processes. The utility of the precipitation process was illustrated by the fabrication of films which demonstrated a variable conductivity over a range of humidities appropriate to sensing application. Investigation into the use of a bipolar palladium electrode as an aid to generating thick film deposits was carried out. The device comprised a palladium plate, operated as a bipolar electrode in aqueous electrolyte. Under suitable conditions, the negative face of this electrode can be made to generate and absorb hydrogen, whilst simultaneously, the positive face oxidises hydrogen transported across the bipolar substrate by diffusion. Thus the cathode face is a non-gassing electrode on which thick deposits of metal hydroxide can be grown. This line of research lead to the realisation of a self-feeding hydrogen anode at the electrode's positive face. Further research was undertaken to assess the electrochemical properties of this anode. The effective operating window for hydrogen oxidation was investigated, and the effect of prolonged potential cycling, elevated temperature and bipolar plate thickness on this region was also considered.
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Ricci, Giulia <1985>. "Archaeometric studies of historical ceramic materials." Doctoral thesis, Università Ca' Foscari Venezia, 2016. http://hdl.handle.net/10579/10321.
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The aim of the PhD research was to define a scientific methodology able to correlate the production techniques and the chemical and physical characteristics of traditional ceramic materials. The methodological approach considered traditional techniques employed in archaeometric research, and the use of innovative methods only recently applied in CH material investigation, in order to develop an effective and innovative methodology for the study of this kind of materials.
The research was performed at first by studying the relationship between raw material composition, firing temperatures and the final chemical-physical features of raw ceramic samples ad hoc made in laboratory, following traditional methods and using different kinds of raw clay materials and firing temperatures. Subsequently, through the reverse process, potteries of different provenance and age were analysed in order to verify the correlation between the production techniques and the characteristics of the ceramic materials. Archaeological potteries from Torcello, one of the first settled islands on the northern Venetian lagoon, alongside historical ceramic sherds from Central and Eastern German sites, never investigate before, were selected as interesting case studies for the research project.
The ceramic samples were studied using chemical, physical and petrological techniques, with the joint use of traditional and non-traditional methods. Chemical composition, mineral phases, microstructure as well as morphology of pottery depend on the native material composition, technology and conservation state. Considering these distinctive properties, the samples were investigated by a multi-analytical approach by optical e morphological studies (Polarizing Microscopy (OM), Scanning Electron Microscopy (SEM)), chemical characterization (X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FT-IR), micro-Raman spectroscopy, X-ray Fluorescence (XRF)) and microstructural analysis by Mercury Intrusion Porosimetry (MIP).
The proposed innovative approach included chemical and morphological analysis, encouraging the use of non-destructive techniques. UV-Vis spectrophotometry, Laser Induced Fluorescence (LIF) and the micro-destructive Laser Induced Breakdown Spectroscopy (LIBS) were applied to deepen the chemical characterization and the production techniques of the ceramic glaze present in the historical potteries. LIF technique was applied to study both the ceramic glaze and matrix composition of the potteries exploiting the mineral luminescence. The results were integrated and combined with those obtained by UV-Vis spectrophotometry, XRF and LIBS, which was able to provide highly sensitive qualitative elemental data. Morphological studies were carried out by X-ray micro-Computed Tomography (μ-CT), which provided a complementary microstructural investigation of the ceramics respecting the integrity of the artefact. UV-Vis spectrophotometry, LIF and μ-CT, only recently applied within conservation science but not yet widely employed within archaeology, offer the advantage of being non-destructive. Despite the fact that LIBS technique is micro-destructive (with a minimal loss of material and order of fractions of micrograms), its ability to analyse materials in laboratory or in situ conditions is highly appreciated.
The obtained results encourage the application of the laser techniques in archaeological and historical ceramics. Furthermore, X-ray μ-CT permited the implementation of the data previously obtained by traditional techniques, offering the possibility to investigate the role of close porosity and its behaviour during the firing processes.
Furthermore, this research has been able to collect innovative results in order to estimate the firing temperature and technology of the ceramic sherds, thus expanding the knowledge upon pottery production in Torcello and in central-Eastern Germany.
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Chung, Jae Hoon. "Compressive mechanical behavior of hollow ceramic spheres and bonded-sphere forms." Diss., Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/9984.
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Papageorge, Marc Vasilios. "Characterization of metal/ceramic interfaces on aluminum nitride." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/9352.
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Rosenthal, Matthew E. (Matthew Eric) 1971. "Ceramic microforming process." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50627.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1998.Includes bibliographical references (leaves 110-113).
A forming process for creating MEMS and mesoscale ceramic parts with micron scale features has been developed. This micromolding process takes advantage of clean room compatible techniques to create silicon etchings, which are used to create a silicone transfer mold. The silicone molds are used to make numerous sacrificial mold into which ceramic slurry is cast. The wax molds are sacrificed leaving green ceramic parts which are fired to produce the final component. The process was found to reproduce features as small as 2 gm with a tolerance of ± 0.8 pm over about a 100 pm length scale. The production of several parts are examined, demonstrating the ability to make stand alone MEMS and mesoscale parts with complex geometries. A non-ceramic application involving precise particle arrangement is also discussed. Observations regarding part quality, defect formation, yield issues, and process enhancement are made, along with a characterization of the dimensional stability of the process. The costs associated with processing silicon molds are also compared to competing processing techniques. This technique has generated excellent results and has potential to become a major forming tool to fill the materials selection gap in MEMS and mesoscale component design.
by Matthew E. Rosenthal.
S.M.
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Senapati, Rajeev. "Discrete element modelling of silicon nitride ceramics crack formation and propagation in indentation test and four point bending test /." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
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Cai, Bing. "Ceramic Materials for Administration of Potent Drugs." Doctoral thesis, Uppsala universitet, Tillämpad materialvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-245031.
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This thesis aimed to investigate and document the potential of applying ceramics in two specific drug delivery applications: tamper-resistant opioid formulations and transdermal enhancement protrusions. Geopolymers were developed into the matrix for a tamper-resistant formulation, aiming to protect drug substances from non-medical abuse. The synthesis conditions and excipients composition of the geopolymer-based formulation were modified in this work to facilitate a stable and extended drug delivery. Results showed that 37ºC 100% humidity for 48 hours were applicable conditions to obtain geopolymer with suitable mechanical strength and porosity. Moreover, it was found that the integration of poly(methyl acrylate) into the geopolymer-based formulation could reduce the drug release at low pH and, meanwhile, maintain the mechanical strength. Therefore, the geopolymer-based drug formulations concluded from these studies were applied in oral and transdermal delivery systems. Evidence of the tamper-resistance of geopolymer-based oral and transdermal formulations was documented and compared to the corresponding commercial opioid formulations. The results provided experimental support for the positive effects of geopolymers as drug carriers for the tamper-resistance of oral and transdermal delivery systems. Self-setting bioceramics, calcium phosphate and calcium sulfate were fabricated into transdermal enhancement protrusions in this work for the first time. Results showed that, under mild conditions, both bioceramics could form pyramid-shaped needles in the micron size. The drug release from these needles could be controlled by the bulk surface area, porosity and degradation of the bioceramics. An in vitro insertion test showed that the bioceramic microneedles had enough mechanical strength to insert into skin. Further optimization on the geometry of needles and the substrate material was also performed. The higher aspect-ratio needles with a flexible and self-swellable substrate could release most of the drug content within 4 hours and could penetrate through the stratum corneum by manual insertion. This study explored the potential application of bioceramics in transdermal enhancement protrusions and showed promising indication of their future developments.
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Cai, Andrew. "CHEMICAL EXPANSIVITY IN CERAMIC OXYGEN TRANSPORT MATERIALS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=case159439738367673.
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Naik, Kiran Suresh. "Sintering of Ceramic Materials Under Electric Field." Doctoral thesis, University of Trento, 2014. http://eprints-phd.biblio.unitn.it/1301/1/Kiran_Naik_PhD_Thesis.pdf.
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The remarkable discovery of flash sintering came across during the early work of Cologna et al. and emerged as an attractive technique in the field of ceramic processing. In this technique the applied electric field initiates the “flash” event, while the densification is controlled by the current density set. Sintering occurs in less than 5 s at a threshold temperature for a given applied field.
The objective of this thesis is to analyse the phenomena of flash sintering with different ceramic oxides; such as alumina-zirconia composite, hydroxyapatite and doped-alumina. The technique involved the application of constant electric field to a dog bone shaped specimen by means of two platinum electrodes while heating. Experiments were performed either in constant heating rate or in Isothermal condition. For the two-phase 3YSZ-alumina ceramic flash sintering was studied by constant heating rate (CHR) and isothermal sintering experiments. In CHR experiment the 50 vol% 3YSZ-alumina composite was shown to flash sinter at a furnace temperature of 1060°C under an electrical field of 150 V cm−1. Conversely, undoped single-phase alumina remains immune to sintering under fields up to 1000 V cm−1, although single-phase 3YSZ flash sinters at 750°C (furnace temperature). The mechanisms of field assisted sintering are divided into two regimes. At low fields the sintering rate increases gradually (FAST), while at high fields sintering occurs abruptly (FLASH). Interestingly, alumina/zirconia composites show a hybrid behaviour such that early sintering occurs in FAST mode, which is then followed by flash-sintering. The specimens held in the flashed state, after they had sintered to nearly full density, show much higher rate of grain growth than in conventional experiments. These results are in contrast to earlier work where the rate of grain growth had been shown to be slower under weak electrical fields.
In the case of isothermal field-assisted sintering of two-phase, 50 vol% 3YSZ-alumina, the composites exhibit an incubation time for the onset of the flash event. Weaker applied fields and lower temperatures lengthen the incubation period. The effect is highly non-linear. For example at 1300°C and 150 V cm–1 the flash occurs nearly instanteously (in 10 s), but extends to two hours at 1275°C and 65 V cm–1. This behaviour is reminiscent of nucleation and growth phenomena in chemically driven experiments involving phase transformations in the solid state. Here, a model for nucleation under electrical driving forces, based upon the growth of embryos of colossal permittivity is presented. The flash sintering was also studied for composites with in-creasing volume faction of alumina in zirconia (10-50 vol%). The flash onset temperature or the incubation time for the 3YSZ-alumina composites increases with increasing the alumina volume fraction.
In case of CHR experiments of hydroxyapatite, flash effect was shown at 840°C for an applied field of 2000 V cm-1. All the flash sintered samples show stable hydroxyapatite phase. However the sample sintered at 500 V cm-1 requires higher sintering temperature and shows enhanced preferred orientation due to higher diffusivity along c-axis.
In case of alumina, field in excess to 1000 V cm-1 are re-quired to induce flash effect, whereas doped alumina shows flash sintering at 1000 V cm-1.
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Paduano, Andrea. "Development of innovative ceramic materials for electrocatalysis." Doctoral thesis, Università degli studi di Padova, 2017. http://hdl.handle.net/11577/3424928.
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The main goal of this work is to synthetize and characterize new and innovative ceramic materials that can be used for energetic catalysis. The work is split in two main branches, the first one focused on TiOxCy ceramics, the second one on Max phases. Both of them appear to be excellent anodic materials for fuel cells, with the first one specifically developed within the European DECORE Project.
The titanium oxycarbide was developed to work at the anode of direct ethanol fuel cells because of its predicted stability in acidic and moderate high temperature ambient. The initial requirements that have to be satisfied for the European project were to have a pure powder with high surface area, that can be scaled easily to industrial scale. Several and different paths were used to satisfy and outdo the starting requirements, obtaining a process and the resulting powder that show excellent results in terms of purity, surface area, reproducibility and scalability. All of the requirements were fully satisfied. New catalysts were also synthetized to optimize the efficiency of the anode, using platinum and platinum-tin nanoparticles. Especially the latter showed very promising results, that have to be further analysed with more complete and in-depth experiments.
The Max phases are a class of innovative ceramics with nanolamitated structures. They mix the best properties of the ceramics, like acid and high temperature resistance, with the best ones of the metals, as electrical conductivity and malleability. They were studied in the last two decades, but few works aimed to discover their utility in fuel cells. Due to their very promising qualities we tried to produce them for future works aimed to use them as catalyst support. We concentrated our work on Ti3SiC2, Ti2AlC and Ti3AlC2 due to their ease of synthesis, but we obtained pure powders barely, so additional and further studies are needed. On that powders, we made a preliminary study on the feasibility of decoration with platinum nanoparticles and on the electrochemical behaviour in mild conditions. The results were promising, but require more experiments.L'obiettivo principale di questo lavoro è la sintesi e la caratterizzazione di nuovi ed innovativi materiali ceramici che possono essere utilizzati per catalisi energetica. Il lavoro è diviso in due rami principale, il primo focalizzato sulle ceramiche TiOxCy, il secondo sulle Max Phases. Entrambe sembrano essere ottimi supporti anodici per celle a combustibile, con il primo sviluppato espressamente all'interno del progetto europeo DECORE. L'ossicarburo di titanio è stato sviluppato per lavorare all'anodo di celle a combustibile a etanolo per la sua stabilità in ambienti acidi e a medie-alte temperature. Le richieste iniziali da soddisfare per il progetto europeo erano di avere una polvere pura con grande area superficile, che può essere prodotta in grande scala facilmente. Differenti e varie strade sono state percorse per soddisfare e superare gli obiettivi iniziali, ottenendo un processo e una polvere finale che mostrano eccellenti risultati in purità, area superficiale, riproducibilità e scalabilità. Tutte le richieste sono state soddisfatte. Nuovi catalizzatori sono stati sintetizzati per ottimizzare l'efficienza dell'anodo, usando nanoparticelle di platino e di platino-stagno. Le ultime in particolare hanno mostrato risultati promettenti che devono essere analizzati ulteriormente con studi più completi e dettagliati. Le MAX phases sono una classe di ceramici innovativi con strutture nanolaminate. Uniscono le migliori proprietà dei metalli, come la conducibilità elettrica e malleabilità, con quelle dei ceramici, come la resistenza agli acidi e alle alte temperature. Sono state studiate negli ultimi venti anni, ma pochi lavori si sono focalizzati sul loro uso nelle celle a combustibile. Ci siamo concentrati su Ti3SiC2, Ti2AlC e Ti3AlC2 per la loro facilità di sintesi, ma abbiamo ottenuto scarsi risultati. Per questo sono richiesti ulteriori studi. Sulle polveri ottenute abbiamo svolto uno studio preliminare per la decorazione con nanoparticelle di platino e per il comportamento elettrochimico in condizioni blande. I risultati sono incoraggianti, ma richiedono un studio più approfondito.
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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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Krug, Steffen. "Large section ceramic injection moulding." Thesis, Queen Mary, University of London, 2000. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1852.
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Ceramic injection moulding is already established as a production technique for complex shaped ceramic components. However the process is limited to thin section mouldings generally not exceeding a wall thickness of 10 mm. The global objective of this work is to describe and understand the aetiology of defects which preferentially appear in thick injection moulded ceramics, and to find ways to overcome these problems. The following stages are examined mould-filling, solidification, binder removal and sintering. Different moulding techniques; conventional moulding, modulated pressure moulding, insulated sprue moulding and low hold pressure moulding were applied. Moulding thicknessw as systematicallyv aried (15,20,25, and 35 mm).. Hold pressures and times were closely controlled and found to be decisive processing parameters for defect creation. The use of insulated sprue moulding prevented void formation in 25 nun thick mouldings and the application of low and constant hold pressures (>5 MPa) led to a reduction of residuals tressesin the mouldings. An intensive study was carried out on the binder removal stage in which the catalytic removal of the polyacetal binder enabled removal of the binder from sections of 35 nun thickness. The reaction and transport kinetics during binder removal were studied and close observations were made out on various defects which could appear during interrupted binder removal. Differential shrinkage of the ceramic components during sintering was studied and could be tracked back to flow-induced particle alignment during mould filling. The sintering behaviour of the alumina feedstock used in this study was compared with an equiaxed zirconia powder injection moulding suspension. The phenomenon of jetting in large section mouldings and the creation of spherulites during solidification of the polymer were found to influence moulding structure.
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Bucella, Stefania <1971>. "Synthesis and chemical-physical characterisation of hybrid, ceramic and glass ceramic luminescent materials." Doctoral thesis, Università Ca' Foscari Venezia, 2005. http://hdl.handle.net/10579/670.
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Tran, Duc Khanh. "Experimental and numerical study of crack bridging in polycrystalline ceramics at room and elevated temperatures /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/7042.
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Chan, Vanessa Zee-Haye 1973. "Ceramic nanostructures for block copolymers." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/9132.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000.Vita.
Includes bibliographical references (leaves 224-234).
The field of nanotechnology has received burgeoning interest in recent years as the characteristic dimensions for many applications (such as integrated circuits and magnetic storage media) become smaller and smaller. In this work, block copolymers are harnessed in order to produce both porous and relief nanostructures. The interest in using these materials is due to the unique morphologies that block copolymers form and the fact that these nanostructures do so by self assembly. With careful selection of the relative volume fraction and phases, nanostructures with highly ordered and complex pore structures with a vast range of different symmetries can be produced; structures that are not attainable by more conventional processing techniques such as lithography. In this thesis, we have produced porous and relief ceramic nanostructures from self-assembling (template free) block copolymer precursors using a one-step, room temperature technique. To accomplish this, a silicon containing block copolymer system was used where upon exposure to an oxidation process the material undergoes two steps 1) the selective removal of the hydrocarbon block and 2) the formation of a ceramic from the inorganic containing block, resulting in nanoporous and nanorelief ceramics. These structures have potential to be used at temperatures far above the T 8 of traditional nanoporous or nanorelief polymers. By choosing the appropriate morphologies and parent block copolymers, 30 nanostructured ceramics with interfacial areas of-40 m2/g, masks for one-step lithography with a density of-5 x 1011 dots/cm2 or templates for the next generation of nanomagnets can be produced. In addition to these applications, it is envisioned that these structures can be used as photonic band gap materials, high temperature membranes and low dielectric constant materials. Specifically, the formation of both nanoporous and nanorelief structures from an ABA triblock copolymer system of poly(pentamethyldisilylstyrene) P(PMDSS) with polyisoprene was studied. The focus of this thesis is on the oxidation of the double gyroid and ''inverse" double gyroid morphologies using either ozone/uv and oxygen plasma techniques. By transmission electron microscopy (TEM) and atomic force microscopy (AFM), it is shown that the PI can be preferentially removed by oxidation resulting in a nanoporous material in the case of the double gyroid morphology and a nanorelief material in the case of the inverse double gyroid morphology. Oxidation of the P(PMDSS) homopolymer was also studied chemically using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), Fourier Transform Infra-red Spectroscopy (FTIR), Rutherford Backscattering Spectrometry (RBS) and Forward recoil Spectrometry (FRES) and morphologically by AFM. Through these chemical analysis techniques, it is demonstrated that the ozone + uv and uv only oxidation processes converts thin films of P(PMDSS) to a ceramic, specifically silicon oxycarbide, that is far more stable than the parent homopolymer.
by Vanessa Zee-Haye Chan.
Ph.D.
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Hopkinson, Andrew Christopher Graham. "Cracking of drying ceramic dispersions." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608101.
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Allahverdi, Mehdi. "Melt extraction of oxide ceramic fibers." Thesis, McGill University, 1995. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28980.
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Ceramic fibers are one of the most important categories of reinforcements for composite materials. This study deals with a novel melt extraction system which has been developed to produce fine oxide ceramic fibers. Four oxide compounds were selected for the production of fibers and characterization of the extraction system. These compounds were CaO-$ rm Al sb2O sb3$ (CA), ZrO$ sb2$-$ rm Al sb2O sb3$ (ZA), ZrO$ sb2$-$ rm Al sb2O sb3$-SiO$ sb2$ (ZAS), and ZrO$ sb2$-$ rm Al sb2O sb3$-TiO$ sb2$ (ZAT). Using a 150 W CO$ sb2$ laser, these materials were melted to obtain a small molten drop, and through shallow contact with a sharpened and bevelled molybdenum wheel, fibers were extracted at various wheel velocities. At low speeds (v 000$ sp circ$C) was measured using a novel technique. Various parameters such as laser power (temperature), wheel tip radius and feed rate have been studied and their effects on the extracted fiber dimensions were investigated. It is suggested that momentum transfer controls the extracted layer thickness and fiber dimensions. The viscosity of the liquid ceramics is a crucial factor in the system, and is estimated to be $<$0.5 poise (0.05 Pa$ cdot$s) at ${ approx}2400 sp circ$C.Due to the fine fiber dimensions and strong conductive cooling of the molybdenum wheel, the extracted liquid layer was rapidly solidified, and fibers with amorphous, partially crystalline and/or metastable phases were formed. Uniform diameter fibers were amorphous, transparent, flexible and exhibited excellent tensile properties. Fine fibers with a diameter of ${ approx}$10 $ mu$m showed tensile strengths up to 3300 MPa, however, only moderate elastic moduli were achieved (95-143 GPa) due to the amorphous nature of the fibers. The rapidly solidified fibers were thermodynamically metastable, and as shown by differential thermal analysis (DTA), they devitrified in the temperature range of 930-980$ sp circ$C. Heating the fibers at higher temperatures resulted in the formation of various crystalline phases and the development of different grain morphologies.
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Chi, Xiaopeng. "Micro-extrusion of fine ceramic latticework." Thesis, Queen Mary, University of London, 2008. http://qmro.qmul.ac.uk/xmlui/handle/123456789/447.
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Microextrusion freeforming of ceramic lattices from high solids ceramic pastes is a method for forming complex multi-scale hierarchical porous structures. It has the advantages of low shrinkage stress, high sintered density and environmental compatibility. A user friendly graphical user interface (GUI) was created so that the micro-extrusion freeforming worktable could be made very easy to manipulate even for a beginner. A solvent-based approach to paste preparation for extrusion freeforming was established, involving selection of solvent, polymer and dispersant. The parameters in the process such as solid fraction in the paste, paste viscosity, extrusion rate, X, Y table velocity, filament diameter and the volatilization of the solvent were studied. A substrate material which provided sufficient adhesion to resist shrinkage efficiently and also allowed the extruded lattice to be easily detachable was selected. The extrusion pressure in the alumina paste was monitored and was found to be useful in predicting and optimizing the extrusion behaviour. Hydroxyapatite (HA)/ tricalcium phosphateTCP and alumina lattices were directly fabricated using 80-500 μm diameter filaments. This thesis reports the implementation of design and fabrication of these scaffolds for tissue engineering, band gap materials and micro-fluidic devices. Multi-scale hierarchical void structures were fabricated and tested in vivo for regenerative medical applications. A co-extrusion nozzle assemble was design to produce tubular alumina lattice.
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Guillou, Marie-Odile. "Indentation deformation and fracture of hard ceramic materials." Thesis, University of Exeter, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317433.
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Scott, J. A. "Plane form grinding of silicon nitride ceramic materials." Thesis, University of Bristol, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.317964.
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Aoki, Yasuyuki. "Development of highly porous carbon and ceramic materials." Thesis, University of Bath, 1993. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760638.
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Brach, Ann M. (Ann Margaret) 1962. "The potential for advanced ceramic materials in construction." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/44659.
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Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Civil Engineering, 1987.Supervised by Michael J. Markow. Vita.
Includes bibliographical references.
by Ann Margaret Brach.
M.S.
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HUSSAIN, AZHAR. "INNOVATIVE CERAMIC MATERIALS AND PROCESSES FOR AERONAUTIC APPLICATIONS." Doctoral thesis, Politecnico di Torino, 2015. http://hdl.handle.net/11583/2588266.
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In the field of aerospace, aircrafts are the most dominant element with other spacecrafts and research satellites finding a limited usage. All the space vehicles are run by the highly efficient engines to make them escape the gravity in case of spacecraft or enable them to carry heavy loads and move quickly to the long destination as achieved by the civil and military planes. To achieve the excellence in transportation in the space, air vehicles are fitted with the engines (rocket or jet engines), these are termed as the power houses and are operated at extremely high temperature and pressure. Such a high temperature achievement and sustainment over the passage of time has put the challenges to the manufacturers and material producers. Spacecrafts and other research crafts which are specifically designed to achieve supersonic flights use special type of non-air breathing engines (rocket engine or scramjet/ramjet) and materials and comprise only up to 10% of the aeronautical industry. All other planes used by the airliners or being used as military planes rely on the air-breathing engines (jet engines).
Depending upon the function and role of a plane these jet engines have different modifications but the operating unit and principle of all these engines remain same and is a variant of gas generator. Common goal of achieving the maximum fuel efficiency (thermal efficiency) in all the planes still remain same.
Achievement of high thermal efficiency led to the development of materials and new methods to extract the maximum possible effectiveness of the materials. Simultaneously, new techniques also emerged to boost the overall operation. One such milestone was the development of superalloys and evolve of the process to fabricate superalloyed blades from equiaxed to single crystal. And introduction of cooling channels and thermal barrier coatings has carried this to limits of the current systems.
With the metals and existing technology reaching the limit, focus is placed on the development of ceramic materials. Most of the technical (high temperature) ceramics are brittle and difficult to fabricate, Si3N4 one among this class is overlapping with metals in terms of toughness but production of this material into useful components is challenging. There are some derivatives of Si3N4 which are easy to produce (develop) into components but their development is limited to few special ceramic processing techniques. These derivatives are α-Sialon and β-Sialon later is easy to fabricate and develop into the components but is very soft, the former is hard and strong and impossible to be synthesized without the use of hot isostatic pressing (HIP), hot pressing and spark plasma sintering (SPS). All of these methods limit the size and geometry of the object to be produced. Machining of these hard materials at cost of diamond to make useful shapes is another restriction; additionally highly machined components may get notches and other fabrication defects which limit the mechanical properties.
Production of Si3N4 based materials, Sialons, using the colloidal processing and pressure less consolidation (sintering) technique has been the challenge. Composition of the pure α-Sialon material was modified with another material, aluminosilicate (β-Sialon former) and this system could be sintered without applying pressure. Modification of this system (material-method) as influenced by the other useful additives like MgO, Spinel and Ce2O3 was also observed.
Hence a new material system capable to be processed by shaping and forming methods linked to colloidal processing was designed
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Touryan, Lara A. "Permeability of millimeter sized consolidated hollow ceramic spheres." Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/16873.
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Antti, Marta-Lena. "All-oxide ceramic matrix composites." Doctoral thesis, Luleå, 2001. http://epubl.luth.se/1402-1544/2001/34/index.html.
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Yun, Jeong Woo. "Permeability analysis for thermal binder removal from green ceramic bodies." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4806.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on October 16, 2007) Vita. Includes bibliographical references.
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Peng, Fei. "Pressureless sintering and oxidation resistance of zrb2 based ceramic composites." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28208.
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Thesis (M. S.)--Materials Science and Engineering, Georgia Institute of Technology, 2009.Committee Chair: Robert F. Speyer; Committee Member: George Kardomateas; Committee Member: Preet Singh; Committee Member: Robert L. Snyder; Committee Member: Thomas H. Sanders, Jr.
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English, Jennifer M. "Wireless micromachined ceramic pressure sensors for high termperature environments." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/15790.
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Wang, Jian. "Combinatorial ink-jet printing for ceramic discovery." Thesis, Queen Mary, University of London, 2006. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1759.
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An aspirating and dispensing printer established inside a robot gantry equipped with furnace and measurement table is used to prepare thick-film combinatorial libraries. Implementation of series of screening tests for ceramic inks that address stability against sedimentation, evaporation and particle segregation during drying, has provided a series of calibration inks can be used for calibration of this printer. The instrument can assemble ceramic mixtures with compositional accuracy of 1-3 wt %. By changing the amount of dispersant used in the inks or by printing onto a porous substrate, the geometry of residues from dried ceramic ink droplets can be modified to facilitate property measurements and uniform composition, as planned, can be achieved. The same material prepared in three ways, in the form of dried ink, ink-jet printed as for a combinatorial sample and by conventional compaction gave similar dielectric measurements. A combinatorial system has been developed so that combinatorial libraries can be printed, fired and screened automatically. A ternary A1203-TiO2-ZrO2 system was first studied using the developed combinatorial method. The particle segregation during drying of multi-component ceramic ink drops is not due to preferential sedimentation unless dispersant addition is restricted. The segregation is due to the partitioning of particles between the growing peripheral 'foot' that develops during drying and the diminishing liquid pool which contains vigorous recirculation flows. Better dispersed particles remain in the pool and hence are found in excess on the upper surface of residues. Less well dispersed particles join the 'foot' earlier in the drying process. The contact angle and height of droplets containing large amounts of dispersant, steadily reduced during drying until a minimum value was reached; the contact diameter being almost unchanged during drying. These droplet residues retained a dome shape. Droplets of suspensions containing small additions of dispersant terminated in a 'doughnut' shaped residue.
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Howie, Philip Robert. "Measuring plasticity in brittle materials." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610682.
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Rickles, Stacey A. "Microstructural and compressive properties of a metal/ceramic syntactic foam." Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/19677.
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Simha, Chityalla Harimanoj. "High rate loading of a high purity ceramic : one dimensional stress experiments and constitutive modeling /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Jia-fong, Hon, and 洪佳豐. "Investigations of Porous Bioglass-Ceramic Materials." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/43896305363588061257.
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碩士大葉大學
機械工程研究所碩士班
95
The bioglass powders of MgO-CaO-Al2O3-SiO2-P2O5 system produced in this study were each mixed with stearic acid, pressed into shape and sintered in air, respectively. The bioglass with chemical composition of MgO 3.0%, CaO 35.0%, Al2O3 8.6%, SiO2 41.4% and P2O5 12.0% was studied. The results respectively showed that after a heat treatment at 960℃ and 1060℃ for one hour in air ; the crystallized phases of apatite and anorthite in the specimen were determined by X-ray diffraction. In the present study three different particle sizes and contents of stearic acid additive were used to produce porous structures. The pore size and open porosity of the produced specimens were measured by scanning electron microscopy and Archimede’s methods. The green bodies (content of 50vol%) were sintered at 960℃ for one hour. As a result, porous specimens with the open porosity of 29.94±1.14%, 27.67±0.94%, 18.67±0.97% and with the macropore size of 448±67μm, 251±42μm, 59±12μm were fabricated. Porous specimens are fabricated in the total porosity range from 26.96±1.03 to 45.89±0.17% after sintering. Elastic modulus and bending strength at the total porosity of 26.96±1.03% are found to be similar to those of human cortical bone. Regarding mechanical properties of the other specimens could be ranged between cortical and cancellous bone. Formation of the crystals on porous bioglass-ceramic surfaces in simulated body fluid after 30 days was investigated. Besides, SA50P1 was shown to be a good biocompatibility by MTT assay.
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"Modeling & processing of ceramic and polymer precursor ceramic matrix composite materials." STATE UNIVERSITY OF NEW YORK AT STONY BROOK, 2008. http://pqdtopen.proquest.com/#viewpdf?dispub=3299726.
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Zhang, Zong-Ying, and 張宗穎. "Research and Application of SiAlON Ceramic Materials." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/y8uenc.
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碩士中原大學
化學研究所
105
SiAlON ceramic materials are composed of Si,Al,O,N elements. In fact, it is a solid solution family of Si3N4 and Al2O3, in which the Si and N elements in Si3N4 are replaced by Al or M element (M may be Y, Li, Mg, Ca and other rare-earth metals such as Nd, Sm, Dy, Er, Yb, and etc.) and O element, respectively. With its exceptional mechanical and chemical properties, SiAlON has become an important family of materials since 1972 after Jack K. H. and Oyama Y. discovered the formation of SiAlON ceramics. This technical report focus on the analysis and study on the behaviors of the high hardness α-SiAlON and high strength β-SiAlON in the SiAlON family. It discusses the variation of mechanical properties of SiAlON due to processing conditions. The effect of sintering aids, temperature control and seeds addition for sintering processes are analyzed. These factors affect the morphology of grains of SiAlON ceramic and therefore their mechanical properties. By properly controlling of the grain growth and morphology formation can improve its mechanical strength significantly. For example, a mixture of α-SiAlON and β-SiAlON can form a complex material with both high hardness and high strength superior than the original single phase material. The applications of SiAlON ceramics on grinding of superalloy, e.g. Inconel 718, making high wear resistant tools and manufacturing some non-ferro metallic material melting furnace are all beneficial.
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Lamuta, Caterina, Franco Furgiuele, and Leonardo Pagnotta. "Development and characterization of advanced ceramic materials." Thesis, 2017. http://hdl.handle.net/10955/1885.
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Dottorato di Ricerca in Ingegneria Civile e Industriale. Ciclo XXIXIl presente lavoro di tesi è incentrato sullo sviluppo e la caratterizzazione di materiali ceramici avanzati. In particolare, tre diversi materiali sono stati prodotti e analizzati, e i risultati ottenuti sono stati presentati in tre differenti capitoli. Il primo capitolo si focalizza sullo studio di rivestimenti ceramici nanostrutturati di zirconia parzialmente stabilizzata con yttria (YSZ), realizzati mediante un processo di Air Plasma Spray (APS). Tali rivestimenti sono stati prodotti presso il centro ricerche ENEA di Brindisi e sono stati caratterizzatti nei laboratori del Dipartimento di Ingegneria Meccanica dell’Università della Calabria. L’obiettivo dell’attività di ricerca svolta è stato quello di analizzare l’influenza di alcuni parametri di processo sulle proprietà microstrutturali, meccaniche e tribologiche dei suddetti rivestimenti. E’ stato dimostrato che, modificando in maniera opportuna tali parametri, è possibile controllare la percentuale di aree nanostrutturate contenute all’interno del materiale e quindi conferire al rivestimento proprietà differenti. In tal modo si possono quindi ingegnerizzare tali rivestimenti in funzione dei diversi campi di applicazione, che spaziano dalle produzione di barriere termiche a quella di rivestimenti abradibili, utilizzati per ridurre i flussi di bypass tra le pale e lo statore dei motori a turbina degli aerei. La microstruttura dei rivestimenti prodotti è stata analizzata mediante acquisizioni SEM (Scanning Electron Microscopy), mentre per la caratterizzazione meccanica e ad usura sono stati realizzati test di indentazione e test tribologici, rispettivamente. Mentre la zirconia può essere considerata un materiale ceramico avanzato ben noto, il materiale analizzato all’interno del secondo capitolo, una malta geopolimerica a base di metacaolino, è presentato come materiale ceramico avanzato per la prima volta nel presente lavoro di tesi. Tale materiale è stato interamente prodotto e caratterizzato presso i laboratori di Ingegneria Meccanica e Chimica dell’Università della Calabria. I geopolimeri sono materiali ceramici consolidati a freddo, ottenuti dall’attivazione alcalina di precursori alluminosilicati. Tali materiali, sviluppati nel 1970 come alternativa al cemento Portland, pur essendo più ecosostenibili rispetto a quest’ultimo presentano proprietà meccaniche e applicazioni simili a quelle del comune cemento. Non trovando impiego nell’ambito di applicazioni high-tech, i geopolimeri sono sempre stati annoverati tra i materiali ceramici tradizionali. La scoperta di un effetto piezoelettrico diretto all’interno di tali materiali, proposta per la prima volta nella presente trattazione, ha però il potere di trasformare i geopolimeri in materiali ceramici avanzati. Nuove ed interessanti applicazioni derivano infatti da questa scoperta, sia nell’ambito della sensoristica che in quello dell’ energy harvesting. In particolare, è stato proposto un nuovo modello chimico-fisico per la descrizione dell’effetto piezoelettrico osservato all’interno dei geopolimeri. Per la prima volta l’attività piezoelettrica è stata ricondotta ad un fenomeno di mobilità ionica anziché alla deformazione di una struttura cristallina non centro-simmetrica. Il coefficiente di carica misurato per le malte geopolimeriche prodotte varia da 4 pC/N a 40 pC/N, in base alla quantità di acqua contenuta all’interno del materiale. Oltre alla caratterizzazione piezoelettrica, sono state proposte anche una caratterizzazione piezoresistiva e meccanica. Quest’ultima in particolare, è stata condotta a diverse scale. Per la caratterizzazione alla nano e alla micro scala, sono state realizzate prove di indentazione, mentre per la caratterizzazione alla macroscale, è stata sviluppata ed ottimizzata una nuova metodologia, caratterizzata dalla combinazione della correlazione digitale delle immagini (DIC) e del Brazilian Disk Test. Il coefficiente piezoelettrico misurato per le malte geopolimeriche prodotte risulta essere sufficientemente elevato per applicazioni sensoristiche; tuttavia, alcune applicazioni, soprattutto nell’ambito dell’ energy harvesting, richiedono spesso coefficienti più elevati. Con lo scopo di incrementare le prestazioni elettro-meccaniche dei geopolimeri analizzati, si è deciso di utilizzare nanoplatelets di grafene (GNPs) come fillers all’interno delle malte prodotte. I risultati relativi alla produzione e alla caratterizzazione chimica, meccanica, ed elettromeccanica di tali nanocompositi sono stati presentati all’interno del terzo ed ultimo capitolo. Mentre l’aggiunta di GNPs sembra non aver modificato in maniera incisiva le proprietà meccaniche dei geopolimeri, sono stati misurati promettenti incrementi del gauge factor e del coefficiente piezoelettrico (pari al 20% e al 198%, rispettivamente) in seguito all’aggiunta dell’1% in peso di grafene. Ulteriori analisi sono tuttavia necessarie per la formulazione di un modello fisico in grado di chiarire il ruolo del grafene nell’ambito dell’attività elettro-meccanica dei geopolimeri. Nella seconda parte del terzo capitolo, alcuni isolanti topologici (Bi2Te3, Bi2Se3 e SnSe) sono stati proposti come nanofillers alternativi per l’incremento delle performances elettro-meccaniche dei geopolimeri. Gli isolanti topologici, noti anche come “graphene like materials”, pur essendo semiconduttori nel bulk, sono caratterizzati da un’eccellente conducibilità elettrica in superficie, paragonabile a quella del grafene. Rispetto a quest’ultimo inoltre, presentano una conducibilità priva di dissipazioni in presenza di difetti superficiali e possono essere prodotti tramite processi relativamente economici. La conoscenza delle proprietà meccaniche di tali materiali è tuttavia estremamente limitata e i pochi lavori presenti in letteratura sono quasi interamente di carattere teorico e computazionale. A tal proposito, il Bi2Te3, il Bi2Se3 e lo SnSe sono stati caratterizzati mediante prove di indentazione strumentata e simulazioni DFT (Density Functional Theory), tenendo in considerazione l’anisotropia meccanica che tali materiali presentano. I risultati ottenuti sono di fondamentale importanza per tutti gli studi futuri incentrati sulla produzione e la caratterizzazione di nanocompositi geopolimerici rinforzati con nanofillers di Bi2Te3, Bi2Se3 e SnSe. “Ingegnerizzare”, “concepire” e “migliorare” un materiale ceramico avanzato sono quindi i tre differenti approcci proposti all’interno dei tre differenti capitoli del presente lavoro di tesi.
Università della Calabria.
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Rana, Shambhu bhusan. "Development of ceramic tiles using waste materials." Thesis, 2014. http://ethesis.nitrkl.ac.in/6102/1/110CR0033.pdf.
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Red mud from aluminium industry and Fly ash from the thermal power plant were regarded as hazardous industry waste all over the world.The present study emphasizes the development of ceramic tiles utilizing red mud and fly ash as raw materials. The bulk density,apparent porosity, wt. loss on sintering, linear shrinkage, water suction, water absorption properties of the developed products are studied carefully. The study showed that tailoring the composition ceramic tiles could be made utilizing up to 50% red mud when used along with clay and up to 80% west utilization when used in combination (red mud and fly ash together) with clay.
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Silva, Cristina Santos. "Wear behavior of glass-ceramic and polymer-infiltrated ceramic materials for dental applications." Master's thesis, 2018. http://hdl.handle.net/1822/71286.
Full textAbstract:
Dissertação de mestrado integrado em Engenharia Biomédica (área de especialidade em Biomateriais, Reabilitação e Biomecânica)Wear of teeth and restorative materials has been often reported by general dental practitioners and researchers. Wear can occur at tooth-tooth, restoration-tooth, or restoration-restoration contacting surfaces, depending on the properties of the related synthetic and natural materials. All-ceramic restorations are the most popular type of dental restorations due to their optical and mechanical properties. However, the abrasiveness of ceramic materials results in progressive wear of contacting surfaces such as resin composite or tooth enamel. Concerning aaesthetics, strength, and wear, new glass ceramics and composites have been commercially introduced in the field of dentistry. The objective of the present work is to study the tribological behavior of a zirconia-reinforced lithium silicate glass-ceramic and a polymer-infiltrated ceramic. Samples were tested on a reciprocating ball-on-plate tribometer at 30 N applied load, 1 Hz and stroke length of 2 mm. The wear sliding tests were carried out against an alumina ball in artificial saliva at 37 ºC. Additionally, micro-scale abrasion tests were also performed in the presence of abrasive particles to simulate three-body abrasion conditions. The micro-scale abrasion tests were performed at 60 rpm with a normal load of 0.8 N for 600 revolutions of a stainless-steel ball in contact with a suspension of hydrated silica particles. After wear tests, the worn surfaces were inspected by scanning electron microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS). The main wear mechanism found during the tests was abrasion. However, the hybrid ceramic, during the reciprocating tests, presented an unstable adhesive tribo-layer, associated with a delamination process. Congruently, the wear volume obtained during the micro-abrasion tests were higher for the polymer infiltrated ceramic than for the glass-ceramic, 1.44x10-1 mm3, and 9.89x10-2 mm3, respectively. The same happened to the specific wear rate for sliding tests where the hybrid ceramic obtained 5.33x10-5 mm3/N.m and the glass-ceramic 3.17x10-5 mm3/N.m. For all test conditions, zirconia reinforced glass-ceramic, presented higher wear resistance than hybrid ceramic, combined with lower friction coefficient against alumina, which indicates the potential of this reinforced glass-ceramic for application in dental restorations.
O desgaste dos dentes e materiais de restauro, tem sido referenciado muitas vezes por médicos dentistas e investigadores. O desgaste pode ocorrer na interação de superfícies em contacto, dente-dente, restauro-dente, ou mesmo restauro-restauro, dependendo das propriedades dos materiais sintéticos e naturais. Os restauros totalmente cerâmicos são o tipo mais popular de restauros dentários, devido às suas propriedades óticas e mecânicas. No entanto, a abrasividade dos materiais cerâmicos resulta no desgaste progressivo das superfícies em contacto como resinas compósitas ou esmalte dentário. Tendo em conta a estética, resistência e desgaste, novos vitrocerâmicos e compósitos têm sido introduzidos no campo da dentária. O objetivo do presente trabalho é o estudo do comportamento tribológico de um vitrocerâmico de silicato de lítio reforçado com zircónia e de uma cerâmica infiltrada com polímero. As amostras foram testadas num tribómetro esfera-placa em deslizamento linear alternativo, com uma carga aplicada de 30 N, 1 Hz e 2 mm de amplitude. Estes testes foram realizados contra uma esfera de alumina em saliva artificial a 37 ºC. Além disso, foram realizados testes de abrasão em micro-escala, na presença de partículas abrasivas para simular condições de abrasão a três corpos. Os testes de micro-abrasão foram realizados a 60 rpm e com uma carga normal fixa de 0,8 N para 600 rotações da esfera em aço, usando uma suspensão de sílica hidratada. Após os testes tribológicos, as superfícies desgastadas foram inspecionadas por microscopia eletrónica de varrimento (SEM) e por espetroscopia de energia dispersiva (EDS). O principal mecanismo de desgaste encontrado durante os ensaios foi a abrasão. Porém, o cerâmico hibrido, apresentou uma tribo-camada adesiva e instável, associada a um processo de delaminação. Congruentemente, o volume de desgaste obtido durante os testes de microabrasão foi maior para o cerâmico infiltrado com polímero do que para o vitrocerâmico, 1,44x10-1 mm3 e 9,89x10-2 mm3, respetivamente. O mesmo aconteceu com a taxa de desgaste específica para testes de deslizamento em que a cerâmica híbrida resultou em 5,33x10-5 mm3/N.m e a vitrocerâmica 3,17x10-5 mm3/N.m. Para todas as condições de teste, o vitrocerâmico reforçado com zircónia apresentou maior resistência ao desgaste do que o cerâmico híbrido, combinando com menor coeficiente de atrito contra a alumina, o que indica o potencial de aplicação deste vitrocerâmico reforçado em restaurações dentárias.
This work was supported by the Portuguese Foundation of Science and Technology through the projects: POCI-01-0145-FEDER-006941 and UID/EEA/04436/2013
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"Synthesis of fine ceramic powders and the making of ceramic matrix composite materials =: 精細陶瓷粉末之合成及以陶瓷為基質的複合材料之製造." 1998. http://library.cuhk.edu.hk/record=b5896318.
Full textAbstract:
by Fung-luen Kwong.Thesis submitted in: August 1998.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1999.
Includes bibliographical references (leaves 130-131).
Text in English; abstract also in Chinese.
by Fung-luen Kwong.
Acknowledgements --- p.i
Abstract --- p.ii
Chapter 1 --- Introduction --- p.1
Chapter 1.1 --- Development of ceramic materials --- p.1
Chapter 1.2 --- Alumina-Zirconia advanced ceramics --- p.2
Chapter 1.3 --- About this thesis --- p.3
Chapter 2 --- Related work and Motivation --- p.6
Chapter 2.1 --- Introduction --- p.6
Chapter 2.2 --- Powder synthesis --- p.7
Chapter 2.2.1 --- Mechanical milling --- p.7
Chapter 2.2.2 --- Sol-gel methods --- p.8
Chapter 2.2.3 --- CVD methods --- p.12
Chapter 2.2.4 --- Hydrothermal processing --- p.12
Chapter 2.2.5 --- Wear of Zr02 milling media --- p.14
Chapter 2.3 --- Powder fabrication --- p.14
Chapter 2.3.1 --- Dry pressing --- p.14
Chapter 2.3.2 --- Isostatic pressing --- p.19
Chapter 2.3.3 --- Hot pressing --- p.23
Chapter 2.4 --- Sintering mechanism --- p.26
Chapter 2.4.1 --- Solid state sintering --- p.26
Chapter 2.4.2 --- Liquid state sintering --- p.36
Chapter 2.5 --- Toughening mechanism --- p.39
Chapter 2.5.1 --- Stress-induced transformation toughening --- p.39
Chapter 2.5.2 --- Microcrack toughening --- p.42
Chapter 2.6 --- Motivation --- p.42
Chapter 3 --- Experiments --- p.45
Chapter 3.1 --- Methodology --- p.45
Chapter 3.1.1 --- Procedures --- p.45
Chapter 3.1.2 --- Verified parameters and potential difficulties --- p.53
Chapter 3.2 --- Instrumentation --- p.56
Chapter 3.2.1 --- Electronic balance --- p.56
Chapter 3.2.2 --- Instron 4486 loading machine --- p.60
Chapter 3.2.3 --- High temperature furnace --- p.63
Chapter 3.2.4 --- Scanning electron microscope (SEM) --- p.65
Chapter 3.2.5 --- Hardness tester --- p.67
Chapter 3.2.6 --- X-ray powder diffraction --- p.69
Chapter 4 --- Results ´ؤ The effects of conditions in fabrication --- p.71
Chapter 4.1 --- Wet chemical reaction --- p.71
Chapter 4.2 --- Pressure dependence analysis --- p.75
Chapter 4.3 --- Sintering behavior --- p.80
Chapter 4.3.1 --- Sintering temperature analysis --- p.80
Chapter 4.3.2 --- Sintering duration analysis --- p.85
Chapter 4.3.3 --- Program for counting pores --- p.94
Chapter 5 --- Results ´ؤ The effects of Additives to Al203 - ZrO2 --- p.96
Chapter 5.1 --- Introduction --- p.96
Chapter 5.1.1 --- Effects of adding metal aluminum --- p.97
Chapter 5.1.2 --- Effects of adding magnesium oxide --- p.103
Chapter 6 --- Conclusions --- p.108
Source code of the programs for counting pores --- p.111
TIFF 6.0 --- p.124
Bibliography --- p.131
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Vurovecz, Candice. "Hilda Ditchburn : a teacher and pioneer of stoneware ceramics in Southern Africa." Thesis, 2008. http://hdl.handle.net/10413/293.
Full textAbstract:
The candidate's investigation of Hilda Ditchburn (nee Rose) (1917 - 1986) attempts to
historically place the subject as a teacher and pioneer of stoneware ceramics within the
context of studio ceramics in South Africa in the second half of the 20th Century.
Through an analysis, discussion and documentation of Ditchburn's life and works on a
personal, technical and professional level, her discoveries and advances in studio
ceramics in South Africa in the 1950's and 60's will be determined.
In the light of Ditchburn's ceramic background, I shall discuss the ceramic pieces she
made from the 1940's to late 1970's, focusing on selected stoneware pieces, and
including examples of her earthenware and porcelain pieces. I shall discuss her
experiments and discoveries with glaze chemistry and clay bodies as well as their
different firing methods. I shall highlight her achievement in being the first studio potter
in South Africa to design and build an oil fired kiln for high fired stoneware. This kiln
was successfully fired in 1954, a time when stoneware was not being made in South
Africa, thus predating any stoneware kiln made by a studio potter in the country and
pioneering the growth of stoneware ceramics in South Africa.
This dissertation is divided into four chapters, each with sub-headings pertaining to the information contained. The first and second chapters give background and foundational information for placing Hilda in context. The third and fourth chapters map out Hilda's personal, academic and professional
information. This includes archival material and Hilda's works of art.Thesis (M.A.)-University of KwaZulu-Natal, Pietermaritzburg, 2008.
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Tsai, Yao-Kun, and 蔡耀坤. "Applications of Piezoelectric Ceramic Materials to 3C Products." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/16742483206424473016.
Full textAbstract:
博士國立交通大學
機械工程學系
99
The thesis focuses on three applications of piezoelectric ceramic materials: optimization of the piezoelectric panel speakers, touch panel application based on time-reversal approach and optimized design of the energy harvester. The first application deals with the optimized design of the piezoelectric panel speaker, two piezoelectric ceramic plates serve to excite the diaphragm is adopted in the panel speaker design. In light of an optimization procedure, the optimal position on the diaphragm to mount the piezoelectric ceramic plates is determined. In the system modeling stage, a finite element model (FEM) is established using the energy method, where the electrical system, mechanical system and acoustic loading of the transducer are considered as a coupled system. The simulated annealing (SA) algorithm is exploited to attain a design that enables low fundamental resonance frequency and high acoustic output. Experiments are conducted to verify the numerical model. The experimental results are in good agreement with the numerical prediction, in which the performance of the optimized configuration is found to be significantly improved over the non-optimal design. In the second application, a combined impact localization and haptic feedback system presented for the touch panel application is presented in the thesis. Theoretical impulse responses are derived based on propagation of bending waves in a thin elastic plate. On the basis of the impulse responses, the time reversal technique is exploited to localize the impact location as well as to generate haptic feedback. The chief advantage of the time reversal technique lies in its robustness of tackling broadband sources in a reverberant environment. Piezoelectric ceramic plates and voice-coil motors are used as sensors for localization, whereas only voice-coil motors are used as the actuator for haptic feedback. Experimental results demonstrated that the proposed system is effective in impact localization for a thin panel, while haptic feedback that is also implemented using time reversal principle can generate an impulse at the previously touched position. The combined impact localization and haptic feedback system effectively enhances the sensation of interaction in real time fashion. Energy harvester is the last device studied in the thesis. The thesis presents a piezoelectric energy harvester by which the vibration energy induced by a moving mass is converted to electrical energy through the piezoelectric effect. An electromechanically coupled FEM based on the Euler-Bernoulli beam theory is employed to estimate the electrical energy that can be generated by the energy harvester. The effects of mass ratio, beam length, travel time and load resistance on the energy output are examined. As indicated by the simulation and experiment results, it is observed that the numerical model can successfully predict the dynamics of the couple system based on the selected electrical load resistance. In the design stage, the nonlinear conjugate gradient (CG) algorithm is applied for calculation to maximize the energy throughput from the energy harvester. Results have shown that the harvested energy depends heavily upon the optimal choice of load resistance and travel time of the moving mass. In addition, the longer beam or the higher mass ratio, the higher energy throughput can be achieved.