Advanced ceramic materials have found many new applications in the automotive and other industries. To satisfy demands of higher temperatures and inert surfaces, new lubrication methods for these ceramics need explored and evaluated. This thesis focuses on a boundary lubrication method termed tribopolymerization -- the formation of polymers at the tribological interphase. The research evaluated new high-temperature classes of anti-wear additives. The work involved experiments on steel and alumina material pairs with a pin-on-disk tribometer used to explore the anti-wear capabilities of selected additives in the liquid phase at concentrations of 1% by weight in hexadecane. New additives included aromatic compounds with various pendant groups adding the design functionality necessary for in-situ polymerization. The amino, hydroxyl, acid, and ester functional groups underwent studies across several aromatic molecular compositions while new heterocyclic additives, in particular the readily available lactams, underwent exploratory tests as a new class under the tribopolymerization design approach. In concentrations of 1%, additives showed significant wear reductions of up to 99.9 %. Anti-wear behavior persisted in select cases at concentrations as low as 0.1% by weight. Compounds from two new classes demonstrated anti-wear behavior at 6x the frictional heat generation of standard exploratory conditions. This surprising effect partially filled a void in the effective range of operating conditions between 0.25 m/s, 40 N and 1.0 m/s, 160 N. Earlier work by Tritt found a complete absence of anti-wear behavior for the previous additive classes at the high-speed conditions. In addition, several individual compounds constituent to an A-R-A + B-R'-B condensation polymerization reaction demonstrated significant anti-wear behavior when used alone. In particular, the compound BTDA from DuPont's Kapton® exhibited higher wear reductions than any other new additive. These findings support tribopolymerization as an effective approach to boundary lubricant design. Low wear was often associated with an attached reaction debris layer. This finding is consistent with previous work involving tribopolymerization anti-wear additives with ceramics. Further research into the roles of the debris layer and tribochemistry will help in understanding the complex anti-wear behavior of these new high-temperature additive classes. / Master of Science

This thesis presents the results of a study done on the damage accumulation process in poly(ether ketone ketone) and its AS4 carbon fiber reinforced composites. The damage accumulation process was studied as a function of applied heat treatment. This study is the result of a project funded by duPont and was done in part to explain the dramatic change in fatigue properties observed at duPont as the applied heat treatment is changed. The mechanical properties were characterized using a battery of tests. The quenched composite systems have lower moduli, but higher toughness and elongations. The quenched systems also have the best fatigue performance and therefore, it can be concluded that the quenched composite systems have the best potential as far as industrial applications are concerned. Quenching has other advantages in industrial applications. These include decreased chances of operator error, and decreased processing times. The damage accumulation process was characterized using the acoustic emission method and also the drop in stiffness during flexure testing. It has been observed that the ultimate mechanical properties show a weak dependence on the applied heat treatment, whereas the damage accumulation process changes dramatically. A model has been developed to simulate the damage accumulation process. This model has then been used to predict the fatigue S-N curve in stroke control and to qualitatively relate it to the available fatigue data in stress control. / Master of Science

Lightweight (Ca,Mg)Zr₄(PO₄)₆(CMZP) ceramics have been fabricated with relative densities (P_lightweight/p_dense) of less than 0.35 by the polymer foam technique, and higher than 0.35 by the polymer powder technique. The polymer powder method forms an inhomogeneous pore structure having average pore sizes of 30-80 μm compared with the polymer foam method, which yields a large and uniform pore structures with pores 250-300 μm in diameter. The thermal expansion of the lightweight CMZP ceramics varies from positive (+2.7x1 0⁻⁶/â C) to negative (-2.6x10⁻⁶/ â C) with increasing grain size. The lightweight CMZP ceramics exhibit an excellent thermal shock resistance and this resistance is improved by increasing porosity. Mechanical properties including tensile strength, compressive strength, Modulus of rupture (MOR), and Young's moduli have been determined and vary exponentially with porosity. The strengths of the lightweight CMZP ceramics are superior to those of lightweight Zr0₂ with the same bulk density. Young's moduli, which were determined using a sonic velocity technique, range from about 5 GPa to 30 GPa, depending on the composition and the relative density. Furthermore, corrosion studies show that lightweight CMZP ceramics possess high resistance to acid corrosion at ambient temperature. / Master of Science

Equilibrium conditions in the CaO-Al₂O₃-SiO₂ ternary system as shown by the equilibrium diagram were established by allowing the solid phases to crystallize out of a liquid phase at specific temperatures. The purpose of this investigation was to determine whether equilibrium was attained or was closely approached when certain compositions of the anorthite-mullite-cristobalite and the anorthite-gehlenite-corundum compatibility triangles were fired to 1400° C. The effect on equilibrium of different raw materials used to form the compositions was also studied. Based on the results of the present investigation the following conclusions seem justified: (1) Equilibrium is attained by compositions in the anorthite-gehlenite-corundum compatibility triangle when held for twelve hours at 1400°C. (2) Equilibrium is closely approached but is not attained by compositions in the anorthite-mullite-cristobalite compatibility triangle when held for twelve hours at 1400°C. (3) The reactions in the anorthite-gehlenite-corundum sub-system take place essentially in the solid state. (4) The transitory compounds that are formed at temperatures below 1400°C progress from the binary compounds of dicalcium silicate and calcium aluminate to binary compounds of higher silica and alumina contents, respectively, until gehlenite and anorthite are formed. (5) The introduction of incompatible phases such as wollastonite and mullite does not deter the attainment of equilibrium in the anorthite-gehlenite-corundum triangle. (6) Absorption and bulk density are not good indicators of the attainment of equilibrium in the compositions studied, but serve to show the marked differences in physical properties of samples having the same ultimate composition but made from different raw materials. / Master of Science

No / Not available

Yes / Diffusion brazing of SiC ceramic to IN738 using an Ag-Cu-Ti powder-mixture as an interlayer was carried out for the first time. The impact of the bonding time (30 and 45 min) on metallurgical features and shear strength of the joints was assessed. The results revealed that raising the bonding time resulted in expanding of the brazing layer from 46.98 µm to 55.31 µm. Besides, increasing the bonding time also enhanced the shear strength of the SiC/Ag-Cu-Ti/IN738 joints.

Crack-microstructure interactions occurring during the flaw introduction process were studied in a model brittle composite, a cordierite glass-ceramic. Microstructural effects associated with the repropagation of the introduced flaws under the imposition of a mechanical load were also examined. Two general types of crystallized microstructures were investigated for samples heat-treated from the original glass: a fine structure composed of a uniform precipitation of very small (< 0.1 µm) crystallites, and a coarser structure characterized by crystallites, and a coarser structure characterized by crystallites ~ 1-2 µm in diameter dispersed within a much finer-grained (< 0.1 µm) crystalline matrix. Surface damage was simulated by the Vicker's microhardness technique, with indentations being made over a wide load range to duplicate varying degrees of severity in the contact events. Direct measurement of the indentation flaws was made by calibrated scanning electron microscopy. Fracture toughness values were determined by direct calculation from the indentation parameters. The repropagation of the indentation flaws was investigated by strength tests performed in biaxial flexure. The results indicated that flaw introduction, as well as strength, fracture toughness, and the magnitude of strength loss sustained from surface damage, were all significantly affected by crack interactions with the crystallites in the glass-ceramic samples. The crack-crystallite interactions were extensive in the coarse microstructure samples. Crack pinning by the dispersed phase crystallites occurred at flaw sizes approximately equal to the mean free path distance between the dispersions, while at larger flaw sizes, crack deflection around the dispersed crystallites took place. Crack-microstructure interactions were absent in these same samples at flaw sizes less than the mean free path distance, and were not observed at all in the original glass or in samples heat-treated to yield only the fine microstructure. In the coarse microstructure samples, the size of flaws introduced by surface contact was found to be limited by the crack pinning interaction, thus confirming the basic concept of the dispersion-strengthening model for brittle composites. A substantial toughening effect in these same samples was realized from the crack deflection. Fracture toughness for the coarse microstructure samples exhibited a crack size-dependency, with toughness values corresponding to that of the matrix measured at small flaw sizes, and to that of the composite, at larger flaw sizes. The phenomenon was not present in either the original glass or in the fine microstructure samples. The crack-crystallite interactions occurring in the coarse microstructure samples greatly improved mechanical performance. The combination of decreased flaw size from crack pinning and increased fracture toughness from crack deflection resulted in strength values which were superior to those of the original glass. The crack size dependent fracture toughness enhanced the ability of the coarse microstructure samples to avoid potential strength losses following surface contact. / Ph. D.

Additive Manufacturing (AM, also known as 3D printing) can produce novel three-dimensional structures using low-loss dielectric materials. This enables the construction of dielectrics with complex shapes that enable innovative microwave applications such as resonators, filters, and metamaterial lenses. This thesis addresses the production and characterization of cellular structures of various designed densities created with a low loss ceramic material, alumina (aluminum oxide), via vat photopolymerization. The permittivity of these printed structures is variable over roughly an octave, with a range of relative permittivites from 1.78 to 3.60, controlled via part geometry. Two additional materials, ferrite and nickel, have been explored for inclusion within these dielectric structures to enable the production of multi-material electromagnetic structures with conductive, magnetic, and dielectric elements. / Master of Science / Additive Manufacturing (AM, also known as 3D printing) has unique manufacturing capabilities. 3D printing can create structures that cannot be produced using traditional manufacturing methods. For example, sponge like structures, with internal voids inaccessible from the outside of the structure, can be created out of a variety of materials. Such structures, known as cellular structures, can be used to create new advanced materials. Ceramic cellular structures can be produced using 3D printing. Ceramics possess many advantages over other materials for use in high frequency radio systems, such as those used for radar and communications. Notably, ceramics are known as low-loss materials, meaning that when electromagnetic waves travel through them they lose less energy than other materials. Cellular structures can be used to vary a material property known as the dielectric constant. Creating cellular structures with designed dielectric constants will enable the creation of new and useful electromagnetic structures. Measuring how this material property changes with the geometry of the cellular structures is important to enable their use. These measurements are described in this work. Additionally, other materials are printed into the ceramic structures. Ferrite, a magnetic material, is extruded as a paste from a nozzle into the ceramic structures. This material is also important for radio systems. Nickel, a good conductor, has also been embedded into the ceramic to provide the ability to create electrically conductive paths inside the part.

Vários compostos de fórmula AMO3 (A = Sr, Ca, Ba; M = Ru, Ti, Hf), com estrutura de perovskita foram sintetizados. Realizou-se uma análise estrutural dos compostos, usando difração de raios X, de fonte convencional e síncrotron, e difração de nêutrons em material policristalino. Para esta análise usaram-se dois dos programas mais reconhecidos internacionalmente para o método de Rietveld: DBWS e GSAS. Todas as estruturas analisadas foram classificadas segundo o sistema de inclinação dos octaedros de Glazer e representadas graficamente com o programa Atoms. A estrutura do SrHfO3 foi determinada por difração de nêutrons e raios X em material policristalino. Foi estudada a dependência da estrutura desses compostos com a temperatura e, com a composição, no caso das soluções sólidas SrTi1-xRuxO3 (O&#8804; x&#8804;1). Duas transições estruturais de fase com a temperatura foram encontradas nos compostos SrRuO3 e SrHfO3. Nas soluções sólidas SrTi1-xRuO3 foi estudada a correlação da estrutura com as propriedades elétricas e com a estrutura eletrônica / Several compounds whose general formula was AMO3 (A = Sr, Ca, Ba; M = Ru, Ti, Hf) and which present the perovskite structure were synthesized. A structural analysis of the compounds by conventional and synchrotron X ray and neutron powder diffraction was performed. For this study was used the internationally accepted software for Rietveld analysis DBWS and GSAS. A11 of the structures analyzed were classified according to the octahedral tilt classification system of Glazer and represented with the program Atoms. The structure of SrHfO3 was determined by neutron and X ray powder diffraction. The dependence of the structure of severa1 compounds with temperature was studied. Two different structural phase transitions were found in the compounds SrRuO3 and SrHfO3. In the case of the solid solutions SrTi1-xRuxO3 (O&#8804; x &#08804;1) the dependence of the structure with the composition and the correlation with electric properties and the electronic structure was studied

As fontes históricas disponíveis para área dos rios Nhamundá-Trombetas, no baixo Amazonas, relatam à existência de assentamentos populosos, formas hierarquizadas de organização social e cultos religiosos, indicando a existência de sociedades complexas a época dos primeiros contatos. Na segunda metade do século XIX, foram descobertas nessa área cerâmicas elaboradas e ídolos de pedra. Esses elementos associados aos relatos históricos induziram à hipótese sobre a existência de complexidade cultural nessa região desde antes do contato. Nesse contexto, a região do rio Trombetas adquiriu visibilidade para arqueologia da Amazônia. Estudos arqueológicos na região de Porto Trombetas realizados na década de 1970 demostratam a existência de duas ocupações ceramistas situadas ao longo dos rios e lagos: uma mais antiga - Pocó; e outra mais recente - Konduri. Pesquisas recentes na mesma região, realizadas no âmbito da arqueologia de contrato, permitiram identificar sítios com características distintas daqueles situados nas margens dos rios relacionados a ocupação Konduri. O estudo e a comparação entre os sítios ribeirinhos e do interflúvio irá mostrar que as sociedades pré-históricas daquela região exploravam e dominavam ambos os ambientes. / The available historical sources for the area of the Nhamundá-Trombetas rivers, in the lower Amazon, report the existence of populous settlings, hierarchical forms of social organization and religious cults, indicating the existence of complex societies during the time of the first contacts. In the second half of the 19th century, elaborated ceramic and stone idols were discovered in this area. These elements associated with the historical reports led to the hypothesis of the existence of cultural complexity in this region previous to the contact. In this context, the region of the Trombetas river acquired visibility for Amazon archaeology. Archaeological studies carried out in the Porto Trombetas region in the 1970s demonstrated the existence of two ceramist occupations spread along the rivers and the lakes: an older one - Pocó; and a more recent one - Konduri. Recent research, in the same region, carried out in the scope of contract archaeology, allowed the identification of small sites showing distinct characteristics from those located in the edges of the rivers and associated with Konduri occupation. The study and comparison between the sites located in the edges of the rivers and in the interfluve zone will show that the prehistoric societies from that region exploited and dominated both environments.