<p dir="ltr">The technological drive of humanity to explore the cosmos, travel at hypersonic speeds, and pursue clean energy solutions requires ceramic scientists and engineers to constantly push materials to their functional, behavioral, and chemical extremes. Ultra-high temperature ceramics, and particularly transition metal carbides, are promising materials to meet the demands of extreme environment materials with their >4000 °C melting temperature and impressive thermomechanical behaviors in extreme conditions. The advent of the 2D version of these transition metal carbides, known as MXenes, added a new direction to design transition metal carbides for energy, catalysis, flexible electronics, and other applications. Toward extreme conditions, although MXenes remain yet unexplored, we believe that the ~1 nm flakes of MXenes gives ceramics scientists and engineers the ability to truly engineer transition metal carbides layer-by-layer at the nanoscale to endure the extreme conditions required by future harsh environment technology. Although MXenes have this inherent promise, fundamental study of their behavior in high-temperature environments is necessary to understand how their chemistry and 2D nature affects the high-temperature stability and phase behavior of MXenes toward application in extreme environments.</p><p dir="ltr">In this dissertation, we investigate the high-temperature phase behavior of 2D MXenes in high temperature inert environments to understand the stability and phase transition behavior of MXenes. In this work, we demonstrate that 1) MXenes’ transition at high-temperatures is to highly textured transition metal carbides is due to the homoepitaxial growth of these phases onto ~1-nm-thick MXenes’ highly exposed basal plane, 2) the MXene to MXene interface plays a major role in the phase behavior of MXenes, particularly toward building layered transition metal carbides using MXenes as ~1-nm-thick building blocks, and 3) Defects are the primary site at which atomic migration begins during phase transition of MXenes into these highly textured transition metal carbides, and these defects can be engineered for different phase stability of MXenes. To do so, we investigate the phase behavior of Ti₃C₂T_<em>x</em>, Ta₄C₃T_<em>x</em>, Mo₂TiC₂T_<em>x</em>, and other MXenes using a combination of <i>in situ</i> x-ray diffraction and scanning transmission electron microscopy and other <i>ex situ</i> methods, such as secondary ion mass spectrometry and x-ray photoelectron spectroscopy, with other methods. By investigating the fundamentals of the high-temperature phase behavior of MXenes, we hope to establish the basic principles behind use of MXenes as the ideal material for application in future extreme environments.</p>

No description available.

This thesis describes the fabrication and characterization of ex situ magnesium diboride (MgB<sub>2<) 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 MgB<sub>2< material with low impurity content and high density. In this work, the key parameters in the production of dense ex situ MgB<sub>2< produced from Alfa Aesar MgB<sub>2< 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 MgB<sub>2< 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 MgB<sub>2< powder to less than 8 wt.% for heat-treatment at 1100°C. MgO content was determined by X-ray diffraction using calibrated standards. MgB<sub>2< 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 MgB<sub>2< 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 MgB<sub>2<.

Este trabalho teve por objetivo desenvolver uma metodologia para fabricação cerâmica de ítria (\'Y IND.2\'O IND.3\') transparente e, em paralelo, desenvolver um sistema de aquecimento que permitisse atingir temperaturas superiores a 1800ºC. Nos últimos 5 anos, cerâmicas transparentes ganharam grande destaque e foram incluídas entre os cinco supermateriais da atualidade. A ítria - \'Y IND.2\'O IND.3\' - apresenta algumas características ópticas promissoras para fabricação de cerâmicas transparentes, dentre as quais podemos destacar: isotropia óptica e ampla faixa de transparência. Além disso, possui elevada condutividade térmica, o que confere potencialidade para aplicações em sistemas lasers de alta potência. Neste trabalho são apresentados os resultados de estudos sistemáticos relacionados à síntese, compactação e sinterização do óxido de ítria. As amostras foram sintetizadas por reação do estado sólido, usando óxido de zircônio como aditivo para o processo de sinterização. As condições de compactação das pastilhas à verde foram investigadas e permitiu a obtenção de corpos cerâmicos com densidade relativa à verde de ~55%, com uso de prensagem uniaxial seguido de prensagem isostática. As cerâmicas foram sinterizadas utilizando-se programas de temperaturas específicos sob duas condições quanto ao aquecimento: em forno elétrico e em atmosfera aberta e em forno de indução, desenvolvido nesse trabalho, em condições de vácuo dinâmico. As caracterizações físicas das amostras foram feitas por difração de raios X, microscopia eletrônica de varredura e espectroscopia óptica. Os resultados mostraram que temperaturas superiores a 1800ºC combinado com o efeito do vácuo são indispensáveis para obtenção de ítria transparente pelo método de sinterização convencional; o sistema de aquecimento desenvolvido apresentou eficiência em atingir a temperatura desejada, porém apresentou algumas limitações que impossibilitou o controle e reprodutibilidade do processo. Por meio da metodologia desenvolvida foi possível a obtenção de cerâmica de ítria com transmissão na região do visível do espectro eletromagnético (400-700 nm) de até 42%, quando comparado a um monocristal. Avançou-se na fabricação de cerâmicas transparentes, porém, ainda será necessário otimizar o controle do sistema de aquecimento do forno desenvolvido, de modo a eliminar os poucos centros espalhadores de luz existentes. / The focus of this work was to develop a methodology for manufacture of transparent Yttria (\'Y IND.2\'O IND.3\') and in addition develop a heating system that operates in temperatures above 1800ºC. In the last 5 years, transparent ceramics featured among the five supermaterials of the present. Yttria - \'Y IND.2\'O IND.3\' - presents a few optical characteristics promising to manufacture transparent ceramics, such as: optical isotropy and wide range of transparency. Besides, it has high thermal conductivity, which gives potential for applications in high power laser systems. In the work presented here, the results of a systematic study of the synthesis, compaction and sintering of yttria oxide are presented. The samples were prepared by solid state reaction, using zircon oxide as an additive to the sintering process. The compaction conditions of the green tablets were investigated and allowed the obtainment of ceramic bodies with relative density around 55%, by using uniaxial pressing followed by isostatic pressing. The ceramics were sintered using specific temperature programs under two heating conditions: electric furnace and open atmosphere and under induction furnace, developed in this work, under dynamic vacuum conditions. The physical characterizations of the samples were made by X-ray diffraction, scanning electron microscopy and optical spectroscopy. The results showed that temperatures above 1800ºC combined with the effect of vacuum are necessary to obtain transparent Yttria by conventional sintering method; the heating system developed was efficient in reaching the desired temperature, however had some limitations that prevented the control and reproducibility of the process. By means of the methodology developed it was possible to obtain ceramic yttria with transmission in the visible region of the electromagnetic spectrum (400-700) up to 42% compared to single crystal yttria. Progress was made in manufacture of transparent ceramics, however, it is necessary to optimize the control of the heating system of the furnace developed, in order to eliminate the few existing light scattering centers.

High dielectric constant materials are of technological importance as they lead to the miniaturization of the electronic devices. In this context, the observation of anomalously high dielectric constant (>104) in the body-centered cubic perovskite-related (Space group Im3) material Calcium Copper Titanate ((CaCu3Ti4O12)(CCTO)) over wide frequency (100 Hz – 1MHz at RT) and temperature (100 – 600 K at 1 kHz ) ranges has attracted a great deal of attention. However, high dielectric constant in CCTO is not well understood yet, though internal barrier layer capacitor (IBLC) mechanism is widely been accepted. Therefore, the present work has been focused on the preparation and characterization of CCTO ceramic and to have an insight into the origin of high dielectric constant. Influence of calcination temperature, processing conditions, microstructure (and hence grain size), composition, doping etc on the electrical characteristics of CCTO ceramics were investigated. Electrical properties were found to be strongly dependent on these parameters. The dielectric constant in CCTO was observed to be reduced considerably on substituting La+3 on Ca+2 site. The formation temperature of CCTO was lowered substantially (when compared to conventional solid-state reaction route) by adopting molten-salt synthesis. The dielectric loss in CCTO was reduced by incorporating glassy phases at the grain boundary. Potential candidates for the practical applications such as charge storage devices, capacitors etc, with dielectric constant as high as 700 at 300 K was accomplished in a three-phase percolative composite fabricated by incorporating Aluminium particle into CCTO-epoxy composite. Polycrystalline CCTO thin films with dielectric constant as high as ~ 5000 (1 kHz and 400 K) were fabricated on Pt(111)/Ti/SiO2/Si substrates using radio frequency magnetron sputtering. Effect of sintering conditions on the microstructural, ferroelectric and varistor properties of CCTO and LCTO ceramics belonging to the high and low dielectric constant members of ACu3M4O12 family of oxides were investigated in detail and are compared. Ferroelectric-like hysteresis loop (P vs E) and weak pyroelectricity were observed in CCTO and plausible mechanisms for this unusual phenomenon have been proposed.

Made available in DSpace on 2016-12-08T17:19:16Z (GMT). No. of bitstreams: 1 CAPA-INTRO.pdf: 65338 bytes, checksum: 29ebb2d21aacfe78d6df0edf9d832a57 (MD5) Previous issue date: 2012-02-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The aim of this work is evaluate the effect of incorporation of waste printed circuit boards (WPCB) in physical and mechanical properties of triaxial ceramics for coating. Through the technique of experiment with mixtures seven formulations were developed with clay (40, 53, 60 e 80%); phyllite (20, 33, 40 e 60%) and waste (0, 14, 20 e 40%). The WPCB was characterized by their particle size, chemical composition and thermal behavior. The mixtures were processed by wet milling, drying, granulation, uniaxial compaction and sintering at 1180 ° C. Properties measured were dried modulus of rupture (DMoR), linear firing shrinkage (LFS), fired modulus of rupture (FMoR) and water absorption (WA). Microstructures were analyzed by SEM and XRD. The thermal behavior was also studied. The WPCB showed melting behavior in the sintering process, but its addition to the material prejudice the DMoR. After firing, the FMoR is improved if are added moderate amounts of waste, but it decreases when there is an excess of waste. Was observed that the interaction between the phyllite and the waste increases the LFS, what is linked to the closing of the pores in the samples, and hence the flux characteristics of these materials. The WA also refers to this conclusion, since the addition of the waste decreases the absorption of 8.0 to 0.5%. Due the found behavior, it is possible to say that there are mixtures of clay-phyllite-WPCB, in certain proportions, that can be classified according to NBR 13818:1997 as stoneware. Microstructural characterization showed that the addition of the waste improves the sinterability of the material, however, in excess are formed glassy phase, not desired, weakening the material. The main phases present, verified by XRD are quartz and mullite, showing that the addition of the waste does not affect the formation of the main phases of interest ceramic. Thermal analysis showed that there is mass loss to 600 ° C, which can be related to the fraction of the polymer in the waste and the loss of water of constitution of the ceramics. In all cases there was an exothermic peak above 950 ° C which is related to the phase transformation of the ceramic material during sintering. / Este trabalho tem como objetivo avaliar o efeito da incorporação de resíduos de placas de circuito impresso (RPCI) nas propriedades físicas e mecânicas de misturas cerâmicas triaxiais para revestimento. Por meio da técnica de experimento com misturas foram desenvolvidas sete formulações com teor de argila de 40, 53, 60 e 80%, teor de filito de 20, 33, 40 e 60% e teor de resíduo de 0, 14, 20 e 40%. O resíduo foi caracterizado quanto à sua granulometria, constituição química e comportamento térmico. As misturas foram processadas por moagem à úmido, secagem, granulação, compactação uniaxial e sinterização a 1180°C. Foram medidas as propriedades de resistência mecânica a seco (RMS), retração linear no sinterizado (RLSi), resistência mecânica do sinterizado (RMSi) e absorção de água (AA). A verificação das microestruturas obtidas foi realizada por MEV, DRX e o comportamento térmico também foi analisado. O RPCI apresentou comportamento fundente no processo de sinterização, mas sua adição ao material prejudica a RMS. Após a sinterização, a RMSi é melhorada desde que sejam adicionadas quantidades moderadas de resíduo, pois este em excesso fragiliza o material. Observou-se que a interação entre o filito e o resíduo aumenta a RLSi, fato ligado ao fechamento dos poros nas amostras, e, portanto, às características fundentes desses materiais. A AA também remete a esta conclusão, pois a adição do resíduo diminui a absorção de 8,0 para 0,5%. Devido ao comportamento encontrado, verificou-se que a mistura de argila-filito- RPCI, em determinadas proporções, pode ser classificada, segundo a NBR 13818 : 1997 como semi-grês ou grês. A caracterização microestrutural mostrou que a adição do resíduo melhora a sinterabilidade do material, no entanto, em excesso, há formação de fase vítrea além do desejado, fragilizando o material. As principais fases presentes, verificadas por DRX, são quartzo e mulita, evidenciando que a adição do resíduo não prejudica a formação das principais fases de interesse cerâmico. A análise térmica mostrou que há perda de massa até 600°C, o que pode estar relacionado à fração polimérica do RPCI e à perda da água de constituição das cerâmicas. Para todos os casos ocorreu um pico exotérmico acima de 950°C, que está relacionado à transformação de fase do material cerâmico durante a sinterização.

Este trabalho teve por objetivo desenvolver uma metodologia para fabricação cerâmica de ítria (\'Y IND.2\'O IND.3\') transparente e, em paralelo, desenvolver um sistema de aquecimento que permitisse atingir temperaturas superiores a 1800ºC. Nos últimos 5 anos, cerâmicas transparentes ganharam grande destaque e foram incluídas entre os cinco supermateriais da atualidade. A ítria - \'Y IND.2\'O IND.3\' - apresenta algumas características ópticas promissoras para fabricação de cerâmicas transparentes, dentre as quais podemos destacar: isotropia óptica e ampla faixa de transparência. Além disso, possui elevada condutividade térmica, o que confere potencialidade para aplicações em sistemas lasers de alta potência. Neste trabalho são apresentados os resultados de estudos sistemáticos relacionados à síntese, compactação e sinterização do óxido de ítria. As amostras foram sintetizadas por reação do estado sólido, usando óxido de zircônio como aditivo para o processo de sinterização. As condições de compactação das pastilhas à verde foram investigadas e permitiu a obtenção de corpos cerâmicos com densidade relativa à verde de ~55%, com uso de prensagem uniaxial seguido de prensagem isostática. As cerâmicas foram sinterizadas utilizando-se programas de temperaturas específicos sob duas condições quanto ao aquecimento: em forno elétrico e em atmosfera aberta e em forno de indução, desenvolvido nesse trabalho, em condições de vácuo dinâmico. As caracterizações físicas das amostras foram feitas por difração de raios X, microscopia eletrônica de varredura e espectroscopia óptica. Os resultados mostraram que temperaturas superiores a 1800ºC combinado com o efeito do vácuo são indispensáveis para obtenção de ítria transparente pelo método de sinterização convencional; o sistema de aquecimento desenvolvido apresentou eficiência em atingir a temperatura desejada, porém apresentou algumas limitações que impossibilitou o controle e reprodutibilidade do processo. Por meio da metodologia desenvolvida foi possível a obtenção de cerâmica de ítria com transmissão na região do visível do espectro eletromagnético (400-700 nm) de até 42%, quando comparado a um monocristal. Avançou-se na fabricação de cerâmicas transparentes, porém, ainda será necessário otimizar o controle do sistema de aquecimento do forno desenvolvido, de modo a eliminar os poucos centros espalhadores de luz existentes. / The focus of this work was to develop a methodology for manufacture of transparent Yttria (\'Y IND.2\'O IND.3\') and in addition develop a heating system that operates in temperatures above 1800ºC. In the last 5 years, transparent ceramics featured among the five supermaterials of the present. Yttria - \'Y IND.2\'O IND.3\' - presents a few optical characteristics promising to manufacture transparent ceramics, such as: optical isotropy and wide range of transparency. Besides, it has high thermal conductivity, which gives potential for applications in high power laser systems. In the work presented here, the results of a systematic study of the synthesis, compaction and sintering of yttria oxide are presented. The samples were prepared by solid state reaction, using zircon oxide as an additive to the sintering process. The compaction conditions of the green tablets were investigated and allowed the obtainment of ceramic bodies with relative density around 55%, by using uniaxial pressing followed by isostatic pressing. The ceramics were sintered using specific temperature programs under two heating conditions: electric furnace and open atmosphere and under induction furnace, developed in this work, under dynamic vacuum conditions. The physical characterizations of the samples were made by X-ray diffraction, scanning electron microscopy and optical spectroscopy. The results showed that temperatures above 1800ºC combined with the effect of vacuum are necessary to obtain transparent Yttria by conventional sintering method; the heating system developed was efficient in reaching the desired temperature, however had some limitations that prevented the control and reproducibility of the process. By means of the methodology developed it was possible to obtain ceramic yttria with transmission in the visible region of the electromagnetic spectrum (400-700) up to 42% compared to single crystal yttria. Progress was made in manufacture of transparent ceramics, however, it is necessary to optimize the control of the heating system of the furnace developed, in order to eliminate the few existing light scattering centers.

Abstract In the first part of the thesis, novel glass-ceramic compositions based on Al2O3 and BaTiO3 and bismuth-zinc borosilicate (BBSZ) glass, sintered at ultra-low temperatures, were researched. With adequate glass concentration, dense microstructures and useful dielectric properties were achieved. The composite of BaTiO3 with 70 wt % BBSZ sintered at 450 &#176;C exhibited the highest relative permittivity, &#949;r, of 132 and 207 at 100 kHz and 100 MHz, respectively. Thus, the dielectric properties of the composites were dominated by the characteristics of glass, BaTiO3, and Bi24Si2O40 phase, especially the contribution of Bi24Si2O40 for the samples with 70-90 wt % glass. Actually, the existence of the secondary phase Bi24Si2O40 may not hinder but enhance the dielectric properties. The Al2O3-BBSZ composition samples showed a similar situation, not only for densification but also for their microstructures and phases (Al2O3, BBSZ, Bi24Si2O40), explaining the achieved dielectric properties. The second part of the thesis mainly discusses the composite of BaTiO3 with 50 wt % BBSZ with different thermal treatments. After sintering at 720 &#176;C, dense microstructures and the existence of Bi4BaTi4O15, BaTiO3, Bi24Si2O40 phases were observed. The results also showed that the size of glass powder particles did not influence the dielectric properties (&#949;r = 263-267, tan &#948; = 0.013 at 100 kHz) of sintered samples, but the addition of LiF degraded the dielectric properties due to the features and amount of Bi4BaTi4O15. These results demonstrate the feasibility of the BBSZ based composites for higher sintering temperature technologies as well. At the end, a novel binder system, which enables low sintering temperatures close to 300 &#176;C, was developed. A dielectric multilayer module containing BaTiO3-BBSZ and Al2O3-BBSZ composites with silver electrodes was co-fired at 450 &#176;C without observable cracks and diffusions. These results indicate that these glass-ceramic composites provide a new horizon to fabricate environmentally friendly ULTCC materials, as well as multilayers for multimaterial 3D electronics packages and high frequency devices. / Tiivistelmä Väitöstyön ensimmäisessä osassa tutkittiin ja kehitettiin uudentyyppisiä, ultramatalissa sintrauslämpötiloissa (ULTCC) valmistettuja lasi-keraami komposiitteja käyttäen vismuttisinkkiborosilikaatti -pohjaista lasia (BBSZ). Täyteaineina olivat alumiinioksidi (Al2O3) ja bariumtitanaatti (BaTiO3). Materiaaleille saatiin riittävän suuren lasipitoisuuden avulla tiheät mikrorakenteet ja sovelluskelpoiset dielektriset ominaisuudet. BaTiO3:n komposiitti, joka sisälsi 70 p-% BBSZ lasia, saavutti 450 &#176;C lämpötilassa sintrattuna korkeimman suhteellisen permittiivisyyden: &#949;r=132 (@100 kHz) ja &#949;r=207 (@100 MHz). Komposiittien dielektrisiä ominaisuuksia määrittivät tällöin lasi-, BaTiO3- ja Bi24Si2O40- faasien ominaisuudet ja erityisesti Bi24Si2O40 -faasi näytteissä, joissa on 70-90 p-% lasia. Sekundäärinen faasi Bi24Si2O40 ei välttämättä heikentänyt, vaan jopa paransi dielektrisiä ominaisuuksia. Vastaavilla Al2O3-BBSZ –komposiiteilla saavutettiin samanlaisia tuloksia tihentymisen, mikrorakenteiden ja faasien (Al2O3, BBSZ, Bi24Si2O40) suhteen. Lisäksi tässä tapauksessa saavutetut dielektriset ominaisuudet voidaan selittää näiden kolmen faasin yhdistelmän olemassaololla. Väitöstyön toinen osa käsitteli pääasiassa eritavoin lämpökäsiteltyjä BaTiO3:n komposiitteja, joissa on 50 p-% BBSZ-lasia. Näillä saavutettiin tiheä mikrorakenne sintrattaessa 720 &#176;C lämpötilassa ja havaitiin Bi4BaTi4O15-, Bi24Si2O40-faasien muodostuminen BaTiO3 lähtöfaasin rinnalle. Tulokset osoittivat myös, että lasijauheen partikkelikoko ei vaikuttanut sintrattujen näytteiden dielektrisiin ominaisuuksiin (&#949;r = 263-267, tan &#948; = 0.013 (@100 kHz)). LiF -lisäys sen sijaan heikensi dielektrisiä ominaisuuksia ja vähensi Bi4BaTi4O15 faasin muodostumista. Tämä aiheutui Bi4BaTi4O15-faasin ominaisuuksista ja oli riippuvainen kyseisen faasin määrästä. Nämä tulokset osoittivat BBSZ -pohjaisten komposiittien käytettävyyden myös korkeampien sintrauslämpötilojen teknologioihin. Viimeisenä kehitettiin uudentyyppinen sideainesysteemi, joka mahdollistaa ultramatalien keraamien yhteissintraamisen jopa noin 300 &#176;C lämpötilassa. Hyödyntäen kehitettyä sideainesysteemiä monikerrosrakenne, jossa käytettiin dielektrisiä BaTiO3-BBSZ- ja Al2O3-BBSZ-komposiitteja ja hopeaelektrodeja, yhteissintrattiin 450 &#176;C lämpötilassa. Valmistetuissa rakenteissa ei havaittu murtumia eikä diffuusioita. Tulokset osoittavat, että kehitetyt lasi-keraami komposiitit mahdollistavat ympäristöystävällisten ULTCC -materiaalien valmistuksen. Lisäksi osoitettiin kehitettyjen materiaalien soveltuvuus monikerroksisten rakenteiden käyttöön monimateriaali-3D-elektroniikan pakkauksissa ja suurtaajuuskomponteissa.

Theese objects from burned clay are representing the sublimation of traditional technologies and materials with contemporary visual technologies such as 3D.

Transparent polycrystalline aluminum oxide is a promising optical material, particularly in applications that require ballistic protection. However, the rhombohedral crystal structure of alumina limits its transparency due to birefringent scattering. One method of reducing birefringent scattering is to align the particles along the same crystallographic direction, minimizing the refractive index mismatch. This dissertation explores the use of high aspect-ratio platelet-morphology alumina powder in order to process a crystallographically aligned polycrystalline alumina part, with improved optical properties. The optimal hot-pressing parameters of non-pre-aligned platelet alumina were explored, showing that a low pre-load pressure (0MPa), a high maximum temperature (1800°C), a low maximum pressure (10MPa), and a long isothermal hold time (>5hrs) yields dense, transparent parts. These parameters resulted in samples with a high in-line transmission (>65%) despite a large grain size (>60μm). This is due to a high degree of crystallographic orientation, which minimizes the refractive index mismatch between grains, reducing birefringent scattering. Pre-alignment resulted in a further increase in crystallographic orientation, indicating that the pre-alignment procedure effectively aligns the platelets along the same crystallographic orientation. However, pre-alignment resulted in a minimal improvement in optical properties due to the pre-aligned platelets decreasing the densification. Mechanical properties were characterized, resulting in a flexure stress and Vickers hardness of approximately 175MPa and 17GPa, respectively. These low mechanical properties are due to the large grain size. The Vickers hardness was also characterized along different alignment/hot-pressing directions, showing that the hardness matches that of sapphire along corresponding crystallographic directions. Modifications to the Rayleigh-Gans-Debye model were made, accounting for crystallographic orientation. The modified model more closely matches the experimental optical data, illustrating the importance of accounting for crystallographic alignment. This dissertation emphasizes the importance of characterizing optical losses in transparent ceramics and how they relate to the microstructure, as well as the significance of crystallographic alignment in a birefringent transparent ceramic like alumina.