M. S.

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No description available.

<p>Electrochemical deposition methods have been developed for the fabrication of organic － inorganic nanocomposite coatings. The methods are based on electrophoretic deposition of ceramic nanoparticles and polymers.</p> <p>EPD method has been developed for the deposition of nanostructured TiO₂ films using new dispersing agents. The stabilization and charging of the nanoparticles in suspensions was achieved using these organic molecules, which belong to catecholate and salicylate families. Anodic deposition was achieved using caffeic acid, 2,3－dihydroxybenzoic acid, 2,6－dihydroxybenzoic acid and 5－sulfosalicylic acid. Cathodic deposition was performed using 2,4 dihydroxycinnamic acid, p－coumaric acid and trans cinnamic acid. The deposition yield has been studied as a function of the additive concentration and deposition time. The deposition mechanism has been investigated. The fundamental adsorption mechanism is based on the complexation of metal ions at the surfaces of oxide nanoparticles. The method enabled the co-deposition of TiO₂ and other oxides and the formation of composite films.</p> <p>Electrophoretic deposition method has been used for the deposition of TiO₂ nanoparticles modified with organic dyes. Alizarin red, alizarin yellow, pyrocatechol violet and Aurintricarboxylic acid dyes were used for the dispersion and charging of TiO₂. The microstructures of the nanocomposite coatings were studied. The deposition yield was investigated under a variety of conditions. Obtained results could pave the way for the fabrication of dye-sensitized TiO₂ films.</p> <p>EPD method has also been developed for the fabrication of (Poly[3-(3-N,N-diethylaminopropoxy)thiophene]) PDAOT－TiO₂, (polyethylenimine) PEI－TiO₂ and PEI－hydrotalcite composite films. The microstructures of the nanocomposite coatings were studied by Scanning Electron Microscopy, Thermogravimetric Analysis, which showed the co－deposition of inorganic nanoparticles and organic polymer. Electrochemical test of the composite film has been conducted. The results showed that PEI film provided corrosion protection of the stainless steel substrates.</p> / Master of Science (MSc)

This dissertation culminates a three year research program investigating the properties and performance of a tubular, ceramic composite component. Eight test specimens were fabricated using an injection molding process with a borosilicate glass matrix reinforced with chopped graphite fibers. These specimens were then tested under quasi-static and cyclic loading at room temperature. Due to the infancy of CMC materials and, especially, CMC components, the program included a very broad-based investigation into many areas which are considered well-established for more conventional materials, and a very extensive and diverse set of achievements were realized. A tubular CMC test specimen representing an engineering component was designed and fabricated. A high temperature multiaxial test facility for ceramic matrix composite components was developed and installed at Virginia Tech. Nondestructive and destructive test methods for CMC components were developed, and a thorough investigation of the failure mechanisms in injection molded CMC tubes subjected to room temperature, quasi-static and cyclic loading was conducted in spite of a very limited quantity of material. As a result of this investigation, performance limiting defects in the injection molded tubes were identified. In addition, a generalized modeling approach was investigated for the analysis of complex, composite components which includes the effects of damage development under static and cyclic loading. All of these topics are discussed in detail in this dissertation. / Ph. D.

Processing of (Ca_0.6, Mg_0.4)Zr₄(PO₄)₆ [CMZP] powder synthesized by sol-gel techniques was investigated. Amorphous powder was cold pressed/sintered and hot pressed. Cold pressing CMZP, followed by controlled drying and sintering, resulted in maximum relative densities of 96% when using 2wt% of a sintering aid (ZnO). When increasing ZnO content to ≥ 5wt%, a second phase ((ZrO)₂P₂O₇) was formed. Hot pressing conditions were optimized to yield the highest room temperature flexure strength. Mechanical properties of the hot pressed CMZP at room temperature were: (1) a four-point flexure strength of 124.77 MPa, (2) an elastic modulus of 118.45 GPa, and (3) a Weibull modulus of 10.7. At 850°C, the flexure strength and elastic modulus were 118.35 MPa and 68.63 GPa while at 1050°C they were 89.57 MPa and 78.27 GPa. Samples tested at 1250°C creeped during loading. The fracture toughness K_c of hot pressed CMZP was determined to be 1.145 MPa·√m by indentation. Breaking multiple-indented bars in a four-point bend resulted in a fracture toughness value of 1.269 MPa·√m. The coefficient of thermal expansion (CTE) on heating from 25°C to 1000°C was 2.64 x 10⁻⁶/°C and did not change on cycling ten times to 1000°C. No thermal expansion hysteresis was observed. Elevated temperature X-ray diffraction (XRD) revealed that the hot pressed CMZP remained single phase when heated to 1200°C and cooled to room temperature. / Master of Science

[ES] La tesis doctoral presenta y analiza la técnica de la cáscara cerámica, desde la creación del modelo en cera hasta la elaboración completa del molde de fundición específico de esta técnica. Se aportan referencias originales históricas y técnicas. Se realizan pruebas de porosidad y resistencia en función de los refractarios empleados y el número de capas, con conclusiones aclaratorias en cada capítulo. / [EN] This doctoral dissertation explains and analyzes the ceramic shell technique as a whole, starting from the creation of the wax model until the elaboration of the casting mold specific for this technique is finished. Original historical and technical references are provided. Different porosity and resistance tests are carried out depending on the refractory materials used and the number of layers. Clarifying conclusions are included in each chapter. / A Mr. David Reid, maestro de la técnica de la cáscara cerámica adaptada al taller de los escultores. Al Dr. Juan Carlos Albaladejo, director de la tesis doctoral, generoso maestro difusor de la técnica en las universidades españolas. Al Departamento de Ingeniería de los materiales (D. José Monzó y D. Pascual Hernández); al Dpto. de Pintura (Dr. Domingo Oliver y D. Manuel Guillén); al Institut de Ciències del Materials de la UV (Dra. Carmen Guillém); al IDM de la UPV (Dr. Ramón Martínez Mañez, Dr. Juan Soto y Dra. Mª Dolores Marcos); y al Departamento de Escultura (Paco P. Benavent y Dr. Pablo Sedeño) A Toni Tomás, Beatriz Piñero, Ángeles Afonso, Soledad del Pino, Mª Mar Caballero, familia Crespo Ricart y a Marian Alonso. / Marcos Martínez, MDC. (2001). Fundición a la cera perdida: Técnica de la Cascarilla Cerámica [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/157239

Yes / Lake-dwellings in the northern Alpine region are renowned for their extraordinary organic preservation. In addition to organic remains, thousands of ceramic sherds are also recovered. This paper addresses ceramic sherds from the Late Bronze Age site Zürich-Alpenquai, and assesses over 2000 sherds for indications of erosion and abrasion in addition to quantifying sherd size and plotting the spatial distribution of these factors. Recording such wear patterns can provide indications of deposition practices in addition to environmental conditions pre- and post-deposition. In this manner the study of ceramic remains from wetland sites for abrasion can complement environmental studies addressing conditions at the time of artefact deposition, and contribute to discussions of influences for lake-settlement abandonment.

Pearly layers in seashells, also known as nacreous layers, are reported to be three orders of magnitude tougher than their primary constituent, aragonite. Their high toughness is attributed to a particular structure of alternating layers of natural ceramic and polymer materials. This work tries to emulate it using engineering materials. The thickness, strength, and stiffness of the ceramic layer; the thickness, stiffness, strength, and toughness of the polymer interface layer; and the number of layers are the factors that contribute to different degrees. Furthermore, understanding the relative contribution of different toughening mechanisms in nacre would enable identification of key parameters to design tough engineered ceramics. As a step towards that, in this thesis, layered ceramic beams replicating nacre were studied analytically, computationally, and experimentally. The insights and findings from these studies were then used to develop a new method to make tough layered ceramics mimicking nacre. Subsequently, the use of layered ceramics for armour applications was evaluated. Based on analytical numerical and experimental studies, we observed that the strength of the layers is a key factor to replicate the high toughness of nacre in engineered ceramics. We also demonstrated that, crack deflection and bridging observed in nacre in studies elsewhere, occur due to the high strength of platelets. Based on these findings, the new method developed in this study uses green alumina-based ceramic tapes stacked with screen printed stripes of graphite. During sintering, graphite oxidizes leaving empty channels in the stack. These channels were filled with tough interface materials afterwards. As a result, a ceramic- polymer composite with more than 2-fold increase in toughness was developed. Subsequently, we evaluated layered ceramics for armour applications based on numerical analysis validated with experiments. Consistent to the trends in literature, we observed that layers degrade the resistance to ballistic impact. However, improved energy absorption is demonstrated in layered ceramics. These conflicting dual trends were not presented and quantified in any earlier studies conducted elsewhere. Another new observation not documented earlier is the effect of interface strength. Using an interface material of sufficient strength, penetration resistance of layered ceramics can be improved beyond monolithic ceramics. Using these findings, new layered ceramic armour can be designed that is cost- effective and better performing than monolithic ceramics.

Made available in DSpace on 2016-12-08T17:19:18Z (GMT). No. of bitstreams: 1 Thais de Jesus Schmitt.pdf: 2052116 bytes, checksum: d868f1a9aaf1f2eadf918c40531c8101 (MD5) Previous issue date: 2012-06-18 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Recently, the traditional ceramics industry has developed great interest in obtaining pigments which may have firing temperature stable, so that the action of molten glass does not interfere with the final product. In the coating industry, whose selection is strongly influenced by the visual appearance of the decorated surface, the color is an important feature. In order to search for new pigments that replace or optimize the old, new synthetic methods has being studied, as well as new systems and the incorporation of pigments alternative raw materials. Thus, this work studied the possibility of use of industrial byproducts, rich in iron, in the synthesis of pigments encapsulated in glassy matrix. The by product from the surface treatment of sheet metal was evaluated and characterized by chemical composition, crystalline phases and morphology of particles. The residue was added to the glassy matrix, homogenized using conventional milling and calcined at temperatures of 700 ° C to 900 ° C for 15 minutes. The characterization of the pigments obtained were performed using XRD and SEM. The pigments were used in ceramic and enamel porcelain paste and observed by optical microscopy and SEM. The results showed that color development becomes effective when the pigment is incorporated into porcelain paste, because it is a less aggressive. Was concluded that the developed color is influenced by oxide content employed, milling conditions and the processing temperature. The results showed that the use of the pigment developed does not interfere in the microstructural characteristics of pigmented material. / Recentemente, na indústria cerâmica tradicional, tem havido um interesse crescente na obtenção da inclusão de pigmentos na qual a temperatura de queima seja estável de tal forma que ação dos vidros fundidos não interfiram no produto final. No setor de revestimento, cuja seleção é fortemente influenciada pelo aspecto visual da superfície decorada, a cor passa a ser uma importante característica. Com o intuito de buscar novos pigmentos que substituam ou otimizem os já conhecidos, novos métodos de síntese estão sendo pesquisados, bem como novos sistemas pigmentantes e a incorporação de matérias primas alternativas. Desta forma, no presente trabalho, procurou-se estudar a possibilidade de aproveitamento de subprodutos industriais, ricos em ferro, na síntese de pigmentos encapsulados em matriz de vidro. O subproduto que é proveniente, do processo de tratamento superficial de chapas metálicas foi avaliado. O subproduto foi caracterizado quanto a sua composição química, fases cristalinas presentes e morfologia das partículas. O resíduo foi adicionado à matriz vítrea, sendo posteriormente homogeneizados, utilizando moagem convencional e seguidos de calcinação nas temperaturas de 700°C até 900°C por 15 minutos. As caracterizações dos pigmentos obtidos foram realizadas através de difratometria de raios X e microscopia eletrônica de varredura. Os pigmentos foram aplicados em esmalte cerâmico e em massa porcelânica. Posteriormente, foram realizadas análises de microscopia ótica e eletrônica de varredura. Os resultados evidenciaram que o desenvolvimento da cor torna-se efetivo quando o pigmento é incorporado em massa porcelânica, por se tratar de um meio menos agressivo. A coloração desenvolvida é influenciada por variáveis como o teor de óxido empregado, condições de moagem e temperatura de processamento. Os resultados mostraram ainda que a utilização do pigmento desenvolvido não interfere nas características microestruturais do material pigmentado.