Ferroelektroelastische Keramiken besitzen aufgrund ihrer elektromechanischen Koppeleigenschaften Bedeutung in der Sensorik und Aktuatorik. Zur Vorhersage der Bauteileigenschaften und Beurteilung der Bauteilfestigkeit werden Materialmodelle benötigt. In der vorliegenden Arbeit wird ein mehrachsiges, ratenunabhängiges Materialmodell für ferroelektroelastische Keramiken einschließlich der zur effizienten Lösung notwendigen numerischen Methoden ausgearbeitet. Dabei erfolgt die Einbeziehung von Ansätzen aus der makroskopischen phänomenologischen und mikroelektromechanischen phänomenologischen Modellierung. Das resultierende Materialmodell stellt einen Versuch dar, die Vorteile beider Betrachtungsweisen zu vereinen und trägt deshalb die Bezeichnung "hybrid". In einem ersten Beispiel wird gezeigt, dass das hybride Materialmodell die für Barium-Titanat-Keramiken experimentell beobachtete Materialantwort reproduzieren kann. In einem zweiten Beispiel erfolgt die Anwendung auf morphotrope PZT-Keramiken. Dabei wird die in jüngerer Vergangenheit entdeckte monokline Phase zusammen mit der elektronenmikroskopisch beobachteten hierarchischen Struktur von Mikro- und Nanodomänen in vereinfachter Weise berücksichtigt. Auf Grundlage der getroffenen Modellannahmen gelingt es, die experimentell gemessene makroskopische Materialantwort der morphotropen PZT-Keramik PIC151 (PI Ceramic GmbH, Lederhose, Deutschland) für ausgewählte Lastfälle mit guter Genauigkeit vorherzusagen. / Ferroelectroelastic ceramics are used in sensor and actuator applications due to their electromechanical coupling properties. In order to predict the behavior of components or to assess their strength, material models are required. In the present work, a multi-axial, rate-independent material model for ferroelectroelastic ceramics is elaborated. This includes the development of efficient numerical solution methods. By incorporating ideas from known macroscopic phenomenological and micro-electromechanical phenomenological models into the novel model, it is attempted to combine the advantages of both approaches. In a first example, it is shown that the hybrid model can reproduce the experimentally observed material response of barium titanate ceramics. In a second example, the model is applied to morphotropic PZT ceramics. In this context, the recently discovered monoclinic phase as well as the hierarchical structure of micro-domains and nano-domains observed by means of electron microscopy are taken into account in a simplified way. Based on the assumptions made, the experimentally measured material response of the morphotropic PZT ceramic PIC151 (PI Ceramic GmbH, Lederhose, Germany) is predicted with reasonable accuracy for selected load cases.

Next generation aerospace vehicles require thermal protection system (TPS) materials that are capable of withstanding the extreme aerothermal environment during hypersonic flight (>Mach 5 [>1700 m/s]). Ultra-high temperature ceramics (UHTC) such as zirconium diboride (ZrB₂) are candidate TPS materials due to their high-temperature thermal and mechanical properties and are often the basis for advanced composites for enhanced oxidation resistance. However, ZrB₂ matrix impurities in the form of boron trioxide (B₂O₃) and zirconium dioxide (ZrO₂) limit the high-temperature capabilities. Electric based sintering techniques, such as spark plasma sintering (SPS), that use joule heating have become the preferred densification method to process advanced ceramics due to its ability to produce high density parts with reduced densification times and limit grain growth. This study focuses on a combined experimental and thermodynamic assisted processing approach to enhance powder purity through a carbo- and borocarbo-thermal reduction of oxides using carbon (C) and boron carbide (B₄C). The amount of oxides on the powder surface are measured, the amount of additive required to remove oxides is calculated, and processing conditions (temperature, pressure, environment) are controlled to promote favorable thermodynamic reactions both during thermal processing in a tube furnace and SPS. Untreated ZrB₂ contains 0.18 wt%O after SPS. Additions of 0.75 wt%C is found to reduce powder surface oxides to 0.12 wt%O. A preliminary Zr-C-O computational thermodynamic model shows limited efficiency of carbon additions to completely remove oxygen due to the solubility of oxygen in zirconium carbide (ZrC) forming a zirconium oxycarbide (ZrCₓOᵧ). Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with atomic scale elemental spectroscopy shows reduced oxygen content with amorphous Zr-B oxides and discreet ZrO₂ particle impurities in the microstructure. Processing ZrB₂ with minimal additions of B₄C (0.25 wt%) produces high purity parts after SPS with only 0.06 wt%O. STEM identifies unique “trash collector” oxides composed of manufacturer powder impurities of calcium, silver, and yttrium. A preliminary Zr-B-C-O thermodynamic model is used to show the potential reaction paths using B₄C that promotes oxide removal to produce high-purity ZrB₂ with fine grains (3.3 𝜇m) and superior mechanical properties (flexural strength of 660MPa) than the current state-of-the-art ZrB₂ ceramics. Due to the desirable properties produced using SPS, there is growing interest to advance processing techniques from lab-scale (20 mm discs) to large-scale (>100 mm). The advancement of SPS technologies has been stunted due to the limited power and load delivery of lab-scale furnaces. We use a large scale direct current sintering furnace (DCS) to address the challenges of producing industrially relevant sized parts. However, current-assisted sintering techniques, like SPS and DCS, are highly dependent on tooling resistances and the electrical conductivity of the sample, which influences the part uniformity through localized heating spots that are strongly dependent on the current flow path. We develop a coupled thermal-electrical finite element analysis model to investigate the development and effects of tooling and current density manipulation on an electrical conductor (ZrB₂) and an electrical insulator, silicon nitride (Si₃N₄), at the steady-state where material properties, temperature gradients and current/voltage input are constant. The model is built based on experimentally measured temperature gradients in the tooling for 20 mm discs and validated by producing 30 mm discs with similar temperature gradients and grain size uniformity across the part. The model aids in developing tooling to manipulate localize current density in specific regions to produce uniform 100 mm discs of ZrB₂ and Si₃N₄.

In this thesis, the fabrication technology of Roman lead glazes were examined using a number of materials science techniques: namely, electron probe microanalysis, X-ray diffraction, and inductively coupled plasma atomic emission spectroscopy. The overall aim of this work was to discern particular technological styles for a wide group of lead glazes by quantifying the chemical and microstructural features of glaze production. Using experimental replication, it was found that two basic methods of glazing could be identified chemically. When applying PbO alone to an earthenware ceramic, the resulting glaze was in equilibrium with the ceramic as indicated by flat compositional profiles obtained along the glaze cross-section. However, when applying PbO·SiO₂ mixtures to earthenware ceramics, gradient profiles indicative of diffusive mass transfer were obtained from the glaze cross-section. On the basis of these chemical criteria, these two methods of glazing were identified in archaeological material. It has been determined that the earliest lead glazes from Anatolia and Italy (approximately 1^st century B.C.) were made using PbO·SiO₂ mixtures applied to calcareous clays with Fe and Cu oxides added as colourants. Later production (post 2^nd century A.D.), seems to have employed PbO alone applied to non-calcareous clays with no intentionally added colourants. The Roman production of lead glazes was compared to both those of Late Antiquity (4^th – 10^th centuries A.D.) which continued to use PbO applied to non-calcareous clays, and to those of Byzantine and Islamic contexts (8^th – 14^th centuries A.D.) which seem to have used PbO·SiO₂ mixtures applied to both calcareous and non-calcareous clays. It is also argued that the technological features of the Byzantine and Islamic glaze production shared more in common with the contemporary Chinese lead glazing tradition (the Sancai wares of the 7^th century A.D.) which also used PbO·SiO₂ mixtures applied to non-calcareous clays, than with the Late Antique glazing tradition.

The current work is part of the EPSRC MUZIC project, which established the collaboration among several universities to carry out a multidiscipline study on the breakaway oxidation of zirconium alloys. The overall goal of the project is to further understand the mechanisms of the oxidation and breakaway process of zirconium alloys. This thesis describes the nano/micro-structural study and nano-analysis of the corroded zirconium alloys using up-to-date TEM and 3D focused ion beam (FIB) slicing and reconstruction techniques. The work mainly focused on the characterization of ZIRLO. The oxide morphology in general comprises an inner columnar layer and an outer equiaxed layer, except for a post-second transition oxide grown on a Zr-Nb-Ti test alloy with a very poor corrosion resistance, which exhibits generally only equiaxed grains throughout the whole oxide scale. Detailed investigation reveals oxides in a slower oxidation stage exhibit better developed columnar grain structure. All the oxides, independent of different corrosion stages and alloy types, contain predominantly monoclinic oxide and a small amount of tetragonal oxide. Defects at different length scales were examined. In stead of a sudden burst of crack nucleation at the kinetic transition, a gradual introduction of cracks parallel to the metal/oxide interface throughout the pre-transition stage is found, suggesting no direction correlation between the formation of cracks and the transition. Besides cracks, the oxide also contains different forms of nano-porosity: isolated pores of 1-3 nm or interconnected pores at grain boundaries. The density of interconnected porosity, especially those along the oxide growth direction, increases towards the oxide surface, evolving over time. It is suggested that the kinetic transition is related to the development of an interconnected porosity down to the metal/oxide interface, providing easy pathways for the transportation of oxidation species. The metal-oxide interface has a wavy morphology both in the micrometer and nanometer scale. The roughness develops to a maximum just before the first kinetic transition. An intermediate suboxide layer with complex 3D morphology between the bulk oxide and the metal substrate is found. Quantitative EELS analysis shows the composition of this layer to be 40-50 at. % oxygen. The suboxide appears to develop in thickness with increasing oxidation time for the pre-transition oxides, while is very thin or absent in the post-, and post-second transition oxides. In the suboxide region, multiple phases including α-Zr, ω-Zr, tetragonal oxide and a phase with an unidentified structure were found, suggesting different structures can coexist in the suboxide layer. Second-phase particles (SSPs) of β-Nb and hexagonal Zr(Fe,Nb)₂ types were found in ZIRLO samples and FCC Zr(Fe,Cr)₂ was the predominant type in Zircaloy-4. The SPPs showed delayed oxidation compared to surrounding Zr. In ZIRLO, those containing high Fe contents were found to be oxidized and transform into an amorphous state much earlier than β-Nb. Hydrides of different types (γ, σ and ε) were observed in the metal and metal/oxide region for both Zircaloy-4 and ZIRLO samples. A higher density of hydrides was seen in post-transition oxides of ZIRLO than in pre-transition oxides.

Crystallographic texture in polycrystalline HCP and cubic materials, often developed during thermomechanical deformations, has profound effects on properties at the macroscopic or component level. Given the respective natures of current detection techniques, a non-destructive, three-dimensional bulk texture detection method for these materials has not yet been developed. This thesis aims to achieve this goal through systematic studies on the relationship between ultrasonic wave velocity and texture. The feasibility of such development is firstly reviewed via the combination of computational and experimental studies on exemplary HCP materials. Numerical results obtained via a representative volume element (RVE) methodology reveal that the wave speed varies progressively and significantly with changing texture, and experimental ultrasound studies combined with EBSD characterisation demonstrate distinguished velocity profiles for samples with different textures. Thus the possibility of the development is demonstrated from these combined results. A novel convolution theorem is then presented, which couples the single crystal wave speed (the kernel function) with polycrystal orientation distribution function to give the resultant polycrystal wave speed function. Firstly developed on HCP and then successfully extended to general anisotropic materials, the theorem expresses the three functions as harmonic expansions thus enabling the calculation of any one of them when the other two are known. Hence, the forward problem of determination of polycrystal wave speed is solved for all crystal systems with verifications on varying textures showing near-perfect representation of the sensitivity of wave speed to texture as well as quantitative predictions of polycrystal wave speed. More importantly, the theorem also presents a solution to the long-standing inverse problem for HCP and cubic materials, with proof of principle established where groups of HCP and cubic textures are recovered solely from polycrystal wave velocities through the theorem and the results show good agreements with the original textures. Therefore the theorem opens up the possibility of developing a powerful technique for bulk texture measurement and wave propagation studies in HCP, cubic materials and beyond.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

There are two principle arguments in this thesis. First, this thesis will show that Félix Bracquemond had a profound impact on late-nineteenth-century and early-twentieth-century ceramics in America. Second, this thesis will illustrate how John Ruskin’s principle that pottery is “more permanent than the Pyramids” encouraged reform of the ceramic arts and shaped the Art Pottery Movement of the late nineteenth century. After this thesis introduces Bracquemond as an innovator in ceramic decoration and the dissemination of Ruskin’s principle, the thesis will examine two instances in the American Art Pottery Movement in which Bracquemond’s and Ruskin’s influence can be detected. The first is Theodore Davis’s 1879 design for the Haviland-Hayes Service, the White House dinner service for Rutherford B. Hayes. The second case study is the Rookwood Pottery of Cincinnati, which represents the apex of Bracquemond’s influence in America and Ruskin’s principle of the permanence of pottery.

Le développement d'une méthode efficace de séparation/purification d'hydrogène représente une nécessité primordiale pour améliorer les rendements de production des systèmes énergétiques futurs. En effet, le procédé de reformage classique de production d'hydrogène conduit à un mélange complexe de gaz à haute température (au-delà de 523 K) qui limite l'utilisation de H2 dans diverses applications. La réalisation de membranes hautement sélectives à l'hydrogène apparaît alors comme un point essentiel pour augmenter la production d'hydrogène. Les membranes à base de silice ont largement été étudiées en vue de répondre à cette problématique. Malgré leurs excellentes performances, elles ne pourraient être compétitives à l'échelle industrielle qu'après amélioration de leur résistance à la vapeur d'eau en température (lixiviation). Des travaux antérieurs menés à l'IEM ont montré les performances de membranes « SiCN » en termes de perméance et de permsélectivité. Sur la base de ces résultats, nous avons développé des membranes non-oxydes autour du quaternaire « SiZrCN ». L'incorporation de Zr avait pour objectif d'améliorer la tenue en température des membranes et de fait leur sélectivité. Ce projet de thèse a été divisé en trois tâches principales : la première a consisté en la synthèse d'un précurseur moléculaire contenant les éléments Si, Zr, C, N ; la seconde a porté sur la préparation par PECVD de membranes denses non oxydes et la dernière partie a permis d'évaluer les performances de ces membranes en séparation de gaz. Un précurseur moléculaire « single source » a été synthétisé avec succès autour du quaternaire « SiZrCN », de tension de vapeur adéquate pour un dépôt par PECVD. Des films minces ont ainsi été déposés sur des supports variés afin d'obtenir des membranes sans défauts de surface conduisant à une perméance à He de 1,7.10-7 mol.m-2.s-1.Pa -1 et à une sélectivité idéale He/N2 (estimée) de 1300 à T = 423 K et Delta p = 1,105 Pa. / The development of an efficient hydrogen separation/purification method represents a tremendous requirement to enhance the production yields of future energy systems. Indeed, the reforming process commonly used for hydrogen production leads to a complex gas mixture at high temperature (beyond 523 K) that limits the H2 use in various applications. The elaboration of highly hydrogen selective membranes appears to be a determining step to expand hydrogen production. Silica-based membranes have been largely studied to respond this problematics. In spite of their excellent performances, they could only be competitive from an industrial point of view after improvement of their low resistance to water vapor at high temperature (lixiviation). Previous works completed at IEM have demonstrated the good performances of “SiZrCN” membranes in terms of permeance and permselectivity. Based on these results, we developed new non-oxide membranes in the quaternary system “SiZCN”. The incorporation of Zr aimed to enhance the temperature resistance of the membranes and then their selectivity. This thesis project was divided into three major tasks : the first one has consisted in the synthesis of a molecular precursor containing the Si, Zr, C, N elements ; the second one was focused on the preparation by PECVD of dense non-oxide membranes and the last one was meant to evaluate the performances of these membranes in gas separation. A single source molecular precursor was successfully obtained in the system “SiZrCN” usable for PECVD. Thin films were thus deposited over various supports to obtain defect free membranes presenting a He permeance of 1,7.10-7 mol.m-2.s-1.Pa-1 and a (estimated) He/N2 ideal selectivity of 1300 at T = 423 K and Delta p = 1.105 Pa.

Japan, as a country with remarkably strong tradition of craftsmanship, undertook significant changes in this area in the 20th century. One of the main areas in this field is a Japanese folk pottery. The aim of this paper is to present how the ceramic craft and all its aspects transformed from the Meiji Restoration to the present. Firstly, it focuses on introducing the styles of folk pottery and the way traditional potters in the Tokugawa period worked, then it focuses on various influences which affected the field and the changes that brought. In the final part, the work focuses on the description of ceramic craft nowadays, the comparison with the past and tries to contemplate on the philosophy of tradition.

This thesis concerns the formation, sintering and humidity dependent electrical behaviour of the spinel ceramic material nickel germanate, Ni(_2)Ge0(_4).Ni(_2)Ge0(_4) has been prepared via the solid state reaction between NiO and GeO(_2) over a range of temperatures, and characterised using a number of techniques. The sintering behaviour of pressed pellets of Ni(_2)Ge0(_4) has also been investigated, together with a characterisation of the microstructure of the sintered bodies. Substitutional doping of Ni(_2)GeO(_4) with Li as a replacement for Ni is found to promote a high degree of shrinkage in the sintering process, probably due to the formation of a liquid phase. XRD revealed that even when 10 % of the Ni atoms were replaced with Li, no change in the crystal structure could be detected. A C. impedance spectroscopy of Ni(_2)Ge0(_4) samples was used to investigate the humidity sensitivity of this material. Equivalent circuit analysis, based on a network of resistors and constant phase elements, shows that the humidity sensitivity is due to conduction in a surface layer of water, in agreement with the models currently popular in the Uterature. Measurement of the water adsorption isotherm of Ni(_2)Ge0(_4) in pellet form indicates that a single monolayer of water is formed at around 20 %R(_H), with an approximately linear increase in water layer thickness up to around 80 %R(_H), after which capillary condensation causes a large increase in the volume of adsorbed water. The information gained on the thickness of this layer of water has been correlated with the resistance of the layer measured by impedance spectroscopy, and subsequently used to provide evidence for a model of the humidity sensitive conduction. The conduction in the surface layer is thought to be due to dissociation of the water, where the amount of dissociation is exponentially dependent on the humidity.