In this work, the development of theoretically-dense, clean grain boundary, high hardness solid-state sintered silicon carbide (SiC) armor was pursued. Boron carbide and graphite (added as phenolic resin to ensure the carbon is finely dispersed throughout the microstructure) were used as sintering aids. SiC batches between 0.25-4.00 wt.% carbon were mixed and spray dried. Cylindrical pellets were pressed at 13.7 MPa, cold-isostatically pressed (CIP) at 344 MPa, sintered under varying sintering soaking temperatures and heating rates, and varying post hot-isostatic pressing (HIP) parameters. Carbon additive amounts between 2.0-2.5 wt.% (based on the resin source), a 0.36 wt.% B4C addition, and a 2050°C sintering soak yielded parts with high sintering densities (~95.5-96.5%) and a fine, equiaxed microstructure (d50 = 2.525 µm). A slow ramp rate (10°C/min) prevented any occurrence of abnormal grain growth. Post-HIPing at 1900°C removed the remaining closed porosity to yield a theoretically-dense part (3.175 g/cm3, according to rule of mixtures). These parts exhibited higher density and finer microstructure than a commercially-available sintered SiC from Saint-Gobain (Hexoloy Enhanced, 3.153 g/cm3 and d50 = 4.837 µm). Due to the optimized microstructure, Verco SiC parts exhibited the highest Vickers (2628.30 ± 44.13 kg/mm2) and Knoop (2098.50 ± 24.8 kg/mm2) hardness values of any SiC ceramic, and values equal to those of the "gold standard" hot-pressed boron carbide (PAD-B4C). While the fracture toughness of hot-pressed SiC materials (~4.5 MPa m1/2) are almost double that of Verco SiC (2.4 MPa m1/2), Verco SiC is a better performing ballistic product, implying that the higher hardness of the theoretically-dense, clean-grain boundary, fine-grained SiC is the defining mechanical property for optimization of ballistic behavior.

Zirconium diboride (ZrB₂) is a ceramic material possessing ultra-high melting temperatures. As such, this compound could be useful in the construction of thermal protection systems for aerospace applications. This work addresses a primary shortcoming of this material, namely its propensity to destructively oxidize at high temperatures, as well as secondary issues concerning its heat transport properties.To characterize and improve oxidation properties, thermogravimetric studies were per- formed using a specially constructed experimental setup. ZrB₂-SiC two-phase ceramic composites were isothermally oxidized for ∼90 min in flowing air in the range 1500-1900°C. Specimens with 30 mol% SiC formed distinctive reaction product layers which were highly protective; 28 mol% SiC - 6 mol% TaB₂ performed similarly. At higher temperatures, specimens containing lower amounts of SiC were shown to be non-protective, whereas specimens containing greater amounts of SiC produced unstable oxide layers due to gas evolution. Oxide coating thicknesses calculated from weight loss data were consistent with those measured from SEM micrographs. In order to characterize one aspect of the materials' heat transport properties, the thermal diffusivities of ZrB₂-SiC composites were measured using the laser flash technique. These were converted to thermal conductivities using temperature dependent specific heat and density data; thermal conductivity decreased with increasing temperature over the range 25-2000°C. The composition with the highest SiC content showed the highest thermal conductivity at room temperature, but the lowest at temperatures in excess of ∼400°C, because of the greater temperature sensitivity of the thermal conductivity of the SiC phase, as compared to more electrically-conductive ZrB₂. Subsequent finite difference calculations were good predictors of multi-phase thermal conductvities for the compositions examined. The thermal conductivities of pure ZrB₂ as a function of temperature were back-calculated from the experimental results for the multi-phase materials, and literature thermal conductivities of the other two phases. This established a relatively constant thermal conductivity of 88-104 W/m·K over the evaluated temperature range. Further heat transport characterization was performed using pre-oxidized, directly resistively heated ZrB₂-30 mol% SiC ribbon specimens under the observation of a spectral radiometer. The ribbons were heated and held at specific temperatures over the range 1100- 1330°C in flowing Ar, and normal spectral emittance values were recorded over the 1-6 μm range with a resolution of 10 nm. The normal spectral emittance was shown to decrease with loss of the borosilicate layer over the course of the data collection time periods. This change was measured and compensated for to produce traces showing the emittance of the oxidized composition rising from ∼0.7 to ∼0.9 over the range of wavelengths measured.

The use of geochemical analysis for characterization studies of archaeological material has been increasing for decades. In recent years, advancements in X-ray fluorescence (XRF) instrumentation have led to hand-held portable XRF (pXRF) instruments capable of on-site, rapid, non-destructive analysis. The addition of pXRF to the archaeologist's toolkit has the potential to revolutionize geochemical characterization studies as research design can be informed by field analysis, once off-limits museum collections may now be analyzable, and data can be gathered on in-situ objects without disturbing their context. This new instrumentation has shown promise in characterization studies on a variety of archaeological materials, including ceramics. Particularly, it has been shown to generate data useful in distinguishing the geochemical provenance of artifacts. While most existing provenance studies that employ pXRF involve obsidian, it is possible that pXRF is a suitable analytical tool for ceramics as well, since instrumental neutron activation analysis (INAA) and laboratory XRF have both been used in provenance studies of obsidian and ceramics. This thesis reports research that utilized a Bruker hand held pXRF analyzer to study ceramics and plaster floors from Classic Period (ca. AD 250-1000) archaeological sites in southeast Mesoamerica. The data gathered from this analysis are used to examine the ability of pXRF to address archaeological questions of archaeological provenance on ceramic material and human activity patterns on archaeological plaster. The data gathered on ceramic material is analyzed to determine if "valley profiles" (or "chemical fingerprints") can be created for samples excavated in the same valley and to investigate inter-valley trade. Data from the plaster samples is examined to determine if pXRF can detect human activity patterns on plaster floors and, if so, if the activity is identifiable. The results suggest that, while pXRF results can be used to create "valley profiles" for provenance research, it is difficult to ascertain if it can be used to identify items of trade. This investigation also shows that, while pXRF data can identify human activity on plaster, it is difficult to determine what those activities were. This leads to the conclusion that pXRF has potential for both provenance and prospection studies on earthen materials. However, methodological development is necessary to fine tune research design. This thesis contributes to a greater understanding of the potentials and limitations of pXRF instrumentation in characterization studies of archaeological materials as well as understanding cultural-historical details in Classic southeast Mesoamerica.

This thesis examines the extent to which the 1960s process art strand of post-Minimalism can provide an analytical template for critical writing around contemporary ceramic art. A dearth of critical writing is an acknowledged problem in all types of ceramics practice and some of the reasons for this situation will be explored. In the past decade frequent calls have been made by artists, critics, academics, and curators for a body of critical writing to underpin contemporary work and connect with wider cultural debates. During this period, artists have begun to use the process of making the work to form part of the content. Such work has no relationship to traditional studio pottery, and critics have described it as difficult to write about and classify in normative ceramic terms. However, this area of ceramic practice shares characteristics with post-Minimalism, a movement of the 1960s that emphasised the behaviour of materials and the act of making. In The Archaeology of Knowledge the French philosopher Michel Foucault suggests that a new critical language may emerge from the appropriation of other discourses, providing new interpretations for subject areas not yet theoretically mapped out. Foucault’s notions on the formation of discourse are used as a methodological approach to investigate how process-led sculptural ceramics may be articulated by an understanding of post-Minimalist critical writings. A substantial body of critical writing developed around post-Minimalist process art, providing a context for radical new approaches which broke with modernist traditions and which expanded and changed traditional definitions of sculpture. Key post-Minimalist texts are investigated as an analytical template for a new critical discourse for process-led ceramic art. A study of the sculptural ceramics of Richard Deacon and Kosho is undertaken as a means of identifying process-led tendencies and the possibility of a re-conceptualisation from a post-minimalist perspective. An analysis of the role of process within my own practice is used to provide visual evidence of contemporary ceramic work that can be re-conceptualised from a post-Minimalist perspective. After twenty years of stagnant debate in the ceramics field, this research might provide a new critical context for process-led ceramic art. The project shows a way that artists may be empowered to develop a critical literacy in a field that has traditionally lacked a research based approach. It is hoped that it may well encourage other ceramics practitioners to explore new ways of presenting an academic critique of their own area of practice. The contribution to knowledge identifies a new critical context and approach to writing for the process-led area of ceramics practice that is currently described as being difficult to write about, as having no appropriate critical language of its own, and of being difficult to categorise in standard ceramic terms.

Uppdragsgivaren Precer Group erbjuder tekniska lösningar för produktion av el genom ren förbränning av olika typer av fasta bränslen. Tekniken är anpassningsbar för att användas som återladdningskälla i olika typer av hybridfordon samt för produktion av el till bostäder och fritidshus. Arbetet har som syfte att presentera keramiska material till två olika zoner i Precers generation 2 drivlina där metallbränslen förbränns i en temperatur på 1800 °C. I Zon1 ska keramen klara en maximal temperatur på 2300°C och ha isolationsegenskaper. Till Zon2 önskas förmågan att motstå vidhäftning av heta partiklar och materialet ska kunna appliceras som ytbeläggning på befintligt rostfritt stål. Maximal temperatur i denna zon är 1100°C. Av de material som presenteras i arbetet är fullt stabiliserad Zirkoniumoxid (ZrO2) det enda materialet som klarar temperaturskravet i Zon1. ZrO2 har en låg värmeledningsförmåga på 2W/m*°C vilket resulterar i en god isolationsförmåga. Stora delar av arbetet är riktat till Zon2 där tester påvisar att keramiska material har en bättre förmåga att motstå vidhäftning av heta metallpartiklar än det befintliga rostfria stålet. De tre ytbeläggningar som testades var aluminiumoxid, zirkoniumoxid, och aluminia. Väljs istället att använda solida keramiska material ökar utbudet och material så som kiselkarbid( SiC), aluminiumtitanat(Al2TiO2), och kiselnitrid (Si3N4) är också tänkbara. Ett slutgiltigt materialval ansågs vara svårbedömt då konstruktionsunderlag saknades. / The Client Precer Group offers technical solutions for the production of electricity through clean combustion of various types of solid fuels. The technology is adaptable for use as a recharge source in different types of hybrid vehicles and for the production of electricity to homes. The aim of this exam paper is to examine the possibility to use ceramics in Precers new drivetrain where metal fuels are burned at a temperature of 1800 °C. There are two different zones to examine. In Zon1, the ceramic should withstand a maximum temperature of 2300°C and have insulation properties. The ability to resist adhesion of hot metall particles is desirable in Zone 2, where the maximum temperature is 1100°C. There is also a request that the ceramic is to be applied as a coating. Of the materials that where found, fully stabilized zirconia (ZrO2) is the only material that can withstand the demanding temperature in Zone1. The material has a low thermal conductivity at 2W/m°C that results in good insulation. The ability to withstand adhesion was estimated and the results indicate that ceramic materials have a higher capacity to withstand adhesion of hot metall particles than the existing stainless steel. The three coatings tested where pure Alumina, Zirconia, and Alumina 3% Titania. If solid ceramics are to be used instead, the range of materials is increased. Materials such as Silconcarbide (SiC), Aluminimtitanate (Al2TiO2) and siliconnitride (Si3N4) are also possible candidates. A final choice of materiel was considered to be hard because the lack of design documentation.

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No description available.

In the present study, a computational method was developed, validated and applied for the determination of parameters of a constitutive model for a ceramic material. An optimization algorithm, based on a direct search method, was applied to the determination of the load-displacement response of the specimen, and for the identification of the parameters of the constitutive model.A one-dimensional nonlinear initial-boundary value problem of wave propagation in a composite bar made of dissimilar materials was formulated and solved numerically. Convergence of the numerical scheme was studied, and range of convergence was established. Numerical scheme was validated for a number of benchmark problems with known analytical solutions, and for the problems solved using finite element method. Investigation of the accuracy of the displacement and strain responses was conducted; known limitations of the Kolsky's method for split Hopkinson pressure bar were revealed. For numerical examples considered in the present study, comparison of performance of the optimized finite-difference solver and of the finite element code LS-DYNA showed that the finite-difference code is about 10 times faster.Developed method and solutions were applied for the identification of the parameters of the Johnson-Holmquist constitutive model for five sets of experimental data for aluminum oxide AD995. Results of analysis revealed significant sensitivity of stress response to variation of fractured strength model parameters and damage model parameters.For the determined values of parameters, detailed parametric study of stress field, damage accumulation, and velocity field, was conducted with the help of the finite element method.It was found that the accuracy of the simulation using the JH-2 constitutive model changes with the rate of damage accumulation in the ceramic material.The damage patterns and history of damage development, obtained numerically, agreed qualitatively with the fracture history and its patterns, observed in the recovered Macor ceramics available in the literature.A method for image analysis of the photographic images of the lateral sides of the recovered specimen was proposed. It was used to quantify density of the damage in the specimen and to establish a better integral approach to predict amount of damage inside the specimen.

The primary goal of this dissertation is to present an outline of the culture history of the site of La Milpa and its immediate sustaining area through the elaboration and elucidation of a ceramic chronology and typology. However, an equally important aspect of this dissertation is a thorough critique of the type-variety/mode (T-V) system of classification upon which Maya ceramic analysis has been based over the last forty years. The analysis presented here was completed using a relational database (Microsoft Access). By using this database program, it became clear that it is necessary to rethink the basis and use of the type-variety system and how (or whether) it can be adapted as a tool for use in database driven analysis.

Waste is one of the biggest problems in every European country. Formation of waste reveals technological level of a country and creates costs to a society from the economical and ecological point of view. In Europe waste is usually collected and loaded in dumps. Recently, amounts of waste burning are increasing. The effects of waste burning and dumps are obvious: during burning the pollution spreads to an environment, affecting global climate warming; also extremely toxic pollutants (dioxins and furans) and their volatile derivatives form. At present the major part of waste in Lithuania is taken to dumps. Most of dumps in the country do not satisfy even the environmental and sanitary-hygienic requirements. Stiffening the ecological requirements, applying directives of European Union, most dumps will be closed. The waste at the moment ending in dumps may be processed and recycled in future. The integrated application of local raw materials together with various wastes may solve many environmental problems in Lithuania and may affect positively the European ecological balance. To investigate the possibilities to apply the waste, causing the most problems in our country, to the production of building ceramics made of local easily fusible hydro-micous clays. To determine the most optimal quantities of additives such as oil industry waste (used catalyst of GP534 grade, Russia) and shredded rubber of auto tyres, to select the most suitable burning regimes, to analyse the... [to full text]