Electrochemical supercapacitors (ESs) are currently under development for electronics and automotive applications due to their hybrid properties inherited from batteries and capacitors. ESs exhibit higher power densities than batteries and energy densities than capacitors, and offer long cyclic life and rapid charge-discharge suitable for many applications. A promising candidate of electrode materials is manganese dioxide (MnO2), which has the advantages of high theoretical capacitance, low cost and environmentally friendly. However, the low electronic and ionic conductivities of MnO2 have limited its performance for practical applications. It has been demonstrated in literature that composite materials, which consist of conductive additives such as multi-walled carbon nanotubes (MWCNTs) and MnO2 can address this problem, however further investigations are required to produce ESs with superior performance for real-world applications. In this dissertation, novel colloidal fabrication techniques have been developed and advanced dispersants were employed to fabricate advanced nanocomposite electrodes. MnO2-MWCNTs composite electrode was fabricated with use of multifunctional dispersant. The multifunctional dispersant cetylpyridinium chloride (CPC) showed good dispersion of MWCNTs and capability of forming complex with the precursor of MnO2, which improved the homogeneity of the composite and generated unique morphology. The MnO2-MWCNTs composite electrode fabricated exhibited remarkable areal capacitance at high active mass loadings. New scalable fabrication technique was developed for MnO2-MWCNTs by using high solubility sodium permanganate (NaMnO4) precursor. The fabricated composite electrode showed superior performance compared to electrodes fabricated by other colloidal techniques at similar mass loading. Liquid-liquid extraction was employed to address the problem of particles agglomeration upon drying. Bio-inspired advanced extractor lauryl gallate (LG) was used for liquid-liquid extraction of particles. LG has organic catechol group allowed for strong adsorption on inorganic particles. Using LG as an advanced extractor has facilitated the transfer of particles from aqueous to organic phase to prevent agglomeration associated with drying procedure and improved mixing with MWCNTs. Advanced dispersants from bile acid salts and charged aromatic dyes families such as sodium taurodeoxychloate (TDS) and tolonium chloride (TL) were used as MWCNTs dispersants, to fabricate composite electrode with alternative metal oxides such as Mn3O4 and V2O3. Furthermore, 3,4-dihydroxybenzaldhyde (DHB) was investigated as a dispersing agent for Mn3O4 and used to fabricate Mn3O4-MWCNTs composite electrode with TL by Schiff base formation. Mn3O4 offers the advantages of small particle size compared to MnO2, and can be converted to MnO2 by electrochemical cycling to enhance capacitive performance. V2O3 was considered as an alternative to MnO2 due to its metallic conductivity at room temperature. An activation procedure has been developed, which promoted the formation of capacitive V2O5 surface layer on conductive V2O3 to increase capacitance. The advanced dispersants have shown excellent dispersion of MWCNTs in aqueous solutions at low concentrations and facilitated the formation of homogeneous composite with Mn3O4 and V2O3. Activation procedures were developed for the Mn3O4 and V2O3 composite electrodes, and the electrodes with high active mass loadings showed exceptional performance after activation. / Thesis / Doctor of Philosophy (PhD) / In modern society, the demand for clean and renewable energy have grown drastically and there is a need in development of advanced energy storage devices. Currently, the most common energy storage devices are batteries or conventional capacitors. Batteries can store a large amount of energy, however they are limited by their low power performance. Capacitors can charge and discharge rapidly, but the amount of energy stored is relatively low. Other than batteries and capacitor, electrochemical supercapacitors are emerging energy storage devices that offer the advantages of high power and energy density, fast charge-discharge and long lifetime. The objective of this work was to develop advanced nanocomposite electrode materials for electrochemical supercapacitor applications. New colloidal processing strategies have been developed and advanced dispersants were employed for the fabrication of high performance nanocomposites for electrochemical supercapacitor applications. The results presented in this work showed exceptional performances compared to literature data and paved a new way for further developments.

The texturing of ultra-high temperature ceramics (UHTCs) using weak magnetic fields is studied and developed for the first time. Textured UHTCs were prepared by magnetically assisted slip casting (MASC) in weak magnetic field (B ~ 0.5 T). Analytical calculations describing the balance of torques acting on the suspended particles suggested that texture would form at such low magnetic fields. The calculations include a novel contribution of Stokes drag arising from the inhomogeneous velocity profile of the fluid during slip casting. Experimental proof-of-concept of the theoretical calculations was successfully demonstrated. Calculations of Lotgering orientation factor (LOF) based on the intensities of the (00l) family of peaks measures by XRD revealed strong c-axis crystalline texture in TiB2 (LOF = 0.88) and ZrB2 (LOF = 0.79) along the direction of the magnetic field. Less texture was achieved in HfB2 (LOF = 0.39). In all cases, the density of the textured materials was less than that of control untextured materials, indicating that texturing hindered the densification. The findings from this work confirm the potential for more cost-effective, simple, and flexible processes to develop crystalline texture in UHTCs and other advanced ceramics and give new insight into the mechanisms of magnetic alignment of UHTCs under low magnetic fields. The microstructural evolution during slip casting and pressureless sintering is investigated. The interplay between magnetic alignment and particle packing was investigated using XRD and SEM. During MASC, the suspended particles rotate into their aligned configuration. Particles that deposit at the bottom of the mold near the plaster of Paris substrate have their alignment slightly disrupted over a ~220 μm-thick region. The aligned suspended particles lock into an aligned configuration as they consolidate, leading to a uniform degree of texturing across the entire sample height of several millimeters upon full consolidation of the particle network. If the magnetic field is removed before the particles fully consolidate, the suspended particles re-randomize their orientation. Grain size measurements done using the ASTM E112 line counting method on SEM images revealed anisotropic microstructures in green and sintered textured ZrB2 materials. Smaller effective grain sizes were observed in the direction of c-axis texture than the directions perpendicular to the texture. Grain aspect ratios of 1.20 and 1.13 were observed in materials where the c-axis texture directions were parallel (PAR) and perpendicular (PERP) to the slip casting direction, respectively. Constraint of the preferred a-axis grain growth direction in the textured materials inhibited their densification compared to the untextured material. The PERP material with the preferred grain growth direction constrained along the casting direction had smaller average grain sizes than the PAR material which contained the preferred grain growth directions in the circular plane normal to the casting direction. Compression testing suggests a trend towards higher strength and stiffness in materials with higher density. Classical catastrophic brittle failure was observed in the untextured materials, but in the textured materials some samples exhibited a multiple failure mode. The PERP material tended to exhibit superior strength and stiffness to the PAR material in the classical brittle failure mode due to the orientation of the stiffer a-axis along the loading direction and smaller average grain size in the plane normal to the loading direction in the PERP condition. In the multiple failure mode, the PAR material tended to reach higher strength values after the initial failure and reach slightly higher strains before ultimate failure due to the orientation of the compliant c-axis along the loading direction and ability of the grains elongated in the plane normal to the loading direction to rearrange themselves after initial failure(s). Regardless of density or texture condition, all ZrB2 samples survived thermal shock resistance (TSR) testing. Samples were heated to 1500°C in air, held for 30 minutes, then quenched in room temperature air. After TSR testing, oxide layers formed on the surface of the materials. The specific mass gain and oxide layer thickness tended to increase with increasing porosity and were dramatically increased when open porosity was dominant as in the CTRL 1900 condition. After TSR testing, the compressive strength and strain at failure were both higher compared to the as-sintered materials. The increases in the average compressive strength were 20%, 76%, and 57% in the CTRL, PAR, and PERP conditions, respectively. The combination of the presence of the oxide layer shifting the onset of macroscale damage to higher strain values, the dissipation of load in the more porous region near the oxide layer, and the constraining effect of the oxide layer acting against the expansion of the material contributed to reinforcement of the samples after TSR testing. The CTRL material outperformed the textured materials on average in terms of strength and stiffness due to the higher density. The results suggest that reinforcement was more effective in the PAR condition than the PERP, which may be caused by the formation of a homogenous oxide layer on the PAR while the PERP formed an anisotropic layer. The work presented in this dissertation lays the foundation for affordable, energy efficient preparation of UHTCs and other ceramic materials. Equipment costs are reduced by 3 orders of magnitude, and the operating costs and energy consumption are greatly reduced. Facilitation of the preparation of textured materials opens the door to renewed investigations into their processing and performance. This work describes in detail for the first time the relationships between processing, microstructure, and properties of a textured UHTC part, providing a model for future research. Finally, the findings in this work can be used to guide process optimization, exploration of complex shapes and microstructures, and design of manufacturing schemes to create specialty textured parts for demanding structural and functional applications. / Doctor of Philosophy / Textured ultra-high temperature ceramics (UHTCs), special materials with melting temperatures above 3000°C and potential for use in thermal protection of Mach 5+ aircraft and spacecraft, were prepared by magnetically assisted slip casting (MASC) in a weak magnetic field for the first time. The magnetic field was supplied by commercially available permanent magnets which was applied to a liquid-like slurry with UHTC particles floating in it to orient the UHTC particles with their c-crystal axis along the magnetic field direction. Calculations which described the balance of rotational forces acting to align or misalign the suspended particles suggested that the UHTC particles would align in the weak magnetic field. This prediction was realized. After the liquid in the slurry was removed during MASC to leave behind an aligned particle network, the samples were densified by heating in the absence of air to 2100°C for one hour. In titanium diboride (TiB2) and zirconium diboride (ZrB2), two of the most relevant UHTC materials, strong texture was achieved; 88% and 79% of the crystals in the material were aligned along the original magnetic field direction. This is the first time that this has been reported in the scientific literature. In hafnium diboride (HfB2), only 39% of the grains were aligned. The textured materials all had lower density than the untextured materials prepared alongside them using conventional slip casting. The relationship between magnetic alignment and particle packing was investigated by observing the microstructure. During MASC, the suspended particles rotate into their aligned configuration. Particles that deposit at the bottom of the mold near the plaster of Paris substrate have their alignment slightly disrupted over a ~220 μm-thick region. The aligned suspended particles lock into an aligned configuration as they consolidate, leading to a uniform degree of texturing over across the entire sample height of several millimeters upon full consolidation of the particle network. If the magnetic field is removed before the particles fully consolidate, the suspended particles re-randomize their orientation. The findings from this work confirm the potential for more cost-effective, simple, and flexible processes to develop crystalline texture in UHTCs and other advanced ceramics and give new insight into the mechanisms of magnetic alignment of UHTCs under low magnetic fields. Because of the magnetic alignment of the particles, it is expected that the microstructure would show some difference along and across the direction that the alignment formed along the applied magnetic field. In order to determine that, the size of the grains (particles joined to each other during densification) in the materials are measured along different directions in the sample chosen for their orientational relationship to the magnetic field and casting directions. Smaller effective grain sizes were observed along the direction of magnetically aligned crystalline texture than the directions perpendicular to the texture. Because of how the crystal axes of the particles are aligned, there are differences in how the particles join each other during densification, and that results in an anisotropic microstructure where different grain sizes as a function of the magnetic field direction and the texture direction. Compression testing conducted by squeezing the samples at a fixed rate suggests a trend that indicates the samples are stronger and stiffer when the density is higher, as expected. Untextured samples abruptly failed after reaching their maximum strength value in a manner typical of brittle ceramics. Some textured samples failed in this way, but some failed at low strength values then climbed back up in strength repeatedly until they eventually gave out completely, in a crumbly mode. In the classical brittle failure mode, the PERP material with c-axis texture aligned along the sample diameter, perpendicular to the loading direction, tended to exhibit superior strength and stiffness to the PAR material with c-axis texture oriented along the height and loading directions of the sample because the stiffer crystal axis was oriented along the loading direction and the average grain size seen by the load head was smaller. In the crumbly mode, the PAR material tended to reach higher strength values after initial failure and ultimately fail later in a crumblier mode because the more compliant crystal axis was oriented along the loading direction and the grains elongated in the plane perpendicular to the loading direction could rearrange themselves better after initial failure(s) to bear more load. Regardless of density or texture condition, all ZrB2 samples survived thermal shock resistance (TSR) testing, meaning that the samples remained fully intact after experiencing a big difference in temperature in very short time. Samples were heated in a furnace to 1500°C in air, held for 30 minutes, removed from the furnace, and cooled in air. After TSR testing, the samples developed an oxide layer on the outside, in a similar manner to rust forming on a piece of metal. How much it oxidized per unit area and how thick that oxide layer was increased with increasing porosity. These quantities increased dramatically when the pores connected the interior of the sample to the outside, as in the CTRL 1900 condition. After TSR testing, the samples were stronger by 20%, 76%, and 57% in the CTRL, PAR, and PERP conditions, respectively, indicating that the oxide layer was responsible for an enhancement in strength. The results suggest that increase of strength of the oxide layer was more effective in the PAR condition than the PERP, which is believed to be caused by the formation of a homogenous oxide layer on the PAR while the PERP formed an anisotropic layer. The work presented in this dissertation reduces the start-up equipment costs associated with magnetic alignment processes by 1000 times and lays the foundation for affordable, energy efficient preparation of UHTCs and other ceramic materials. The simplicity of this technique makes it easier for future researchers to study textured materials. This work describes in detail for the first time the relationships between processing, microstructure, and properties of a textured UHTC part, providing a model for future research. Finally, the findings in this work can be used to guide process optimization, exploration of complex shapes and microstructures, and design of manufacturing schemes to create specialty textured parts for demanding applications.

A ítria vem sendo muito utilizada como material luminescente e estrutural resistente a altas temperaturas, devido às suas excelentes características ópticas e refratárias. No processamento coloidal da ítria, o controle da estabilidade da suspensão consiste em uma importante etapa quando se objetiva produzir componentes reprodutivos, com densidade controlada, microestrutura homogênea e estabilidade estrutural. Desta maneira, os estudos envolvendo o comportamento de superfície, as condições de estabilidade das suspensões e o comportamento frente às condições de conformação (fluxo), fornecem importantes subsídios para controle dos processos na fabricação de componentes cerâmicos para queimadores de gás. Neste sentido, realizaram-se estudos sobre o comportamento de superfície, de estabilidade e reológico de suspensões aquosas de ítria e do concentrado de terras raras contendo ítria a fim de adequá-las para o processo de conformação por impregnação, onde foram testados diferentes materiais orgânicos como matrizes de réplica, para a confecção de membranas porosas para queimadores de gás. Neste estudo foram avaliados os parâmetros como: pH do meio, concentrações de dispersante, sólidos e ligante na estabilidade e no comportamento ao fluxo das suspensões cerâmicas, e também os aspectos dos distintos materiais orgânicos selecionados como matrizes de réplica para impregnação com as suspensões cerâmicas otimizadas. Os resultados obtidos indicam que se pode confeccionar membranas cerâmicas porosas pelo método de réplica a partir das suspensões aquosas de ítria e do concentrado de terras raras contendo ítria, utilizando-se pH alcalino, polieletrólito aniônico e uma tela mista de nylon-algodão como matriz de réplica. / Yttria has been used very much as luminescent and high temperature material due to its excellent optical and refractory characteristics. In yttria colloidal processing, the control of the stability of suspension is an important step in the fabrication of reproducible products with controlled density, homogeneous microstructure and structural stability. So, the studies concerning surface behavior, stability conditions of the suspensions and the behavior under conformation conditions (flow), give important information for the control of fabrication process of ceramic components for gas burners. In this way, studies concerning surface behavior, stability and rheology of aqueous suspensions of yttria and rare earth concentrate containing yttria were carried out, in order to adequate them for impregnation method, where different organic materials were tested as replica matrix to fabricate porous membranes for gas burners. In this study, the effect of some parameters as pH and concentrations of dispersant, solids and binder on stability and flow behavior of ceramic suspensions were evaluated, and also, different kinds of organic materials selected as replica matrix for impregnation method using optimized ceramic suspensions. The results show that porous ceramics membranes can be produced by replica using yttria and rare earth concentrate containing yttria, using alkaline pH, anionic polyelectrolyte and a nylon-cotton cloth as replica matrix.

A ítria vem sendo muito utilizada como material luminescente e estrutural resistente a altas temperaturas, devido às suas excelentes características ópticas e refratárias. No processamento coloidal da ítria, o controle da estabilidade da suspensão consiste em uma importante etapa quando se objetiva produzir componentes reprodutivos, com densidade controlada, microestrutura homogênea e estabilidade estrutural. Desta maneira, os estudos envolvendo o comportamento de superfície, as condições de estabilidade das suspensões e o comportamento frente às condições de conformação (fluxo), fornecem importantes subsídios para controle dos processos na fabricação de componentes cerâmicos para queimadores de gás. Neste sentido, realizaram-se estudos sobre o comportamento de superfície, de estabilidade e reológico de suspensões aquosas de ítria e do concentrado de terras raras contendo ítria a fim de adequá-las para o processo de conformação por impregnação, onde foram testados diferentes materiais orgânicos como matrizes de réplica, para a confecção de membranas porosas para queimadores de gás. Neste estudo foram avaliados os parâmetros como: pH do meio, concentrações de dispersante, sólidos e ligante na estabilidade e no comportamento ao fluxo das suspensões cerâmicas, e também os aspectos dos distintos materiais orgânicos selecionados como matrizes de réplica para impregnação com as suspensões cerâmicas otimizadas. Os resultados obtidos indicam que se pode confeccionar membranas cerâmicas porosas pelo método de réplica a partir das suspensões aquosas de ítria e do concentrado de terras raras contendo ítria, utilizando-se pH alcalino, polieletrólito aniônico e uma tela mista de nylon-algodão como matriz de réplica. / Yttria has been used very much as luminescent and high temperature material due to its excellent optical and refractory characteristics. In yttria colloidal processing, the control of the stability of suspension is an important step in the fabrication of reproducible products with controlled density, homogeneous microstructure and structural stability. So, the studies concerning surface behavior, stability conditions of the suspensions and the behavior under conformation conditions (flow), give important information for the control of fabrication process of ceramic components for gas burners. In this way, studies concerning surface behavior, stability and rheology of aqueous suspensions of yttria and rare earth concentrate containing yttria were carried out, in order to adequate them for impregnation method, where different organic materials were tested as replica matrix to fabricate porous membranes for gas burners. In this study, the effect of some parameters as pH and concentrations of dispersant, solids and binder on stability and flow behavior of ceramic suspensions were evaluated, and also, different kinds of organic materials selected as replica matrix for impregnation method using optimized ceramic suspensions. The results show that porous ceramics membranes can be produced by replica using yttria and rare earth concentrate containing yttria, using alkaline pH, anionic polyelectrolyte and a nylon-cotton cloth as replica matrix.

No description available.

Extensive attention has been paid to consolidate nanoparticles into nanocrystalline components that possess better properties than their coarse-grained counterparts. Nanocrystalline monolithic tungsten (W) has been envisaged to possess better properties than coarse-grained tungsten and to improve the performance of many military components. Commercially available nano-W powders were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and Brunauer, Emmett, and Teller (BET) measurement. While the bulk of nano-W powders consisted of bcc-W as confirmed by XRD and TEM, much of their surface consisted of WO3 with traces of WO2 and WC. Despite the irregular morphology and agglomerates greater than 1 m in size, the diameter of individual nano-W powders ranged from 30 to 100 nm with a surface area of 10.4 m2/g. To obtain green bodies of higher densities and more homogeneous microstructures after consolidation, W nanopowders were de-agglomerated in water and slip cast in plaster molds. De-agglomeration in water was conducted by repeated ultrasonication, washing, centrifuge and pH adjustment. The change in particle size and morphology was examined via SEM. After the initial surface oxide was removed by repeated washing, the reactivity of W nanoparticles to water was somewhat inhibited. Increasing the number of cycles for ultrasonication and washing increased the pH, the degree of de-agglomeration and the stability of W suspension. The zeta potential was more negative with increasing pH and most negative at pH values close to 5. Viscosity also decreased with increasing pH and reached a minimum at a pH 5. To obtain the highest solid loading with the lowest viscosity, the pH value of W suspension was adjusted to 5 using aqueous tetramethylammonium hydroxide solutions. The relative density of the slip cast increased with longer ultrasonic time, increasing slurry pH up to 5, and consequent increase in solids loading. Smaller particles were separated from larger ones by ultrasonication, washing with water and centrifugation. At a 27.8 vol.% solids loading, the size-separated fine W slurry was slip cast into pellets with relative green densities up to 41.3 % and approximate particle sizes of 100 nm. W powders were also ultrasonicated in aqueous poly (ethyleneimine) (PEI) solutions with various concentrations. SEM examinations of particle sizes showed that 1 wt.% PEI led to the optimum dispersion and ultrasonication for longer time with a low power resulted in better dispersion. 0.5 g of W powders were ultrasonicated in 10 ml aqueous poly (allylamine hydrochloride) (PAH) solutions with molar concentrations ranging from 0.01 to 0.05 M. W suspensions with 0.03 M and 0.04 M PAH after two washing cycles showed improved dispersion. Cold isostatic pressing can further increase the green density following slip casting. Sintered slip casts made from de-agglomerated nanoparticle W showed a lower density, more uniform microstructure, smaller grains and smaller pores than the sintered dry pressed pellets.

The manufacturing of UHTC materials has significantly advanced over recent years, allowing for the development of new microstructures, architectures, shapes, and geometries to explore new properties and applications for these materials beyond aerospace. One of the UHTCs, titanium diboride (TiB2) exhibits high electrical and thermal conductivity that could satisfy the needs of functional ceramic component applications, like battery cathodes, by tailoring its microstructure and architecture. This thesis represents one of the first detailed studies to understand how the processing-microstructure-properties relationship of TiB2 can be shifted to explore new applications. In order to do that, TiB2 has been manufactured with a processing technique never used before, with significant porosity, exploration of which has been very limited for this material. Additionally, this thesis also explores the synthesis and utilization of novel anisotropic particles to further explore this material relationship. In this work, aqueous tape casting of TiB2 has been investigated. Zeta potential measurements and suspension rheology were used to understand the role of dispersant, binder and plasticizer in the suspension and their interaction with the surface chemistry of the TiB2 particles to develop a stable, homogenous suspension, with minimum additive amounts (0-2 wt%). Homogeneous, flexible and strong TiB2 tapes were prepared using suspensions with 30 vol% solids and characterized to compare different compositions, mixing methods, and thicknesses. The characterization shows the tailoring of the properties as a function of the controlled suspension formulation with minimum amount of additives. Green tapes with 2 wt% dispersant, 1 wt% binder, and 2 wt% plasticizer had similar microstructure to those with half the plasticizer but quintuple the Young's modulus (1.96 GPa). The effect on other relevant properties is also discussed. Tape casting aligns anisotropic particles along the direction of casting, which can be taken advantage of for increasing fracture toughness directionally or producing aligned pore networks using sacrificial fillers. The relationship between alignment, porosity, and the mechanical properties of titanium diboride has not been studied. In this work, we characterize the porous sintered bodies produced through aqueous tape casting of non-spherical TiB2 particles of aspect ratio close to 1, as well as composites with an added high aspect ratio particle (2 wt% PCN-222). Synthesis of uniform, spherical ZrC is difficult and generally not cost-effective, as is the case for most ultra-high temperature ceramics. High aspect ratio particles for reinforcement of ceramic composites are even more difficult to synthesize. Metal organic frameworks (MOF) are crystalline coordination polymers composed of multidentate organic linkers bridging metal nodes to form porous structures. Thermal decomposition of MOFs presents a new and cost-effective route to synthesis of ZrC. In this study, heat treatment at 2000°C of MOF PCN-222 produces zirconium carbide (ZrC) within a highly anisotropic particle. The resulting rod-shaped, glass-like carbon matrix embedded with ZrC crystals is described. These rods have potential as reinforcements for iii high temperature applications and as a synthetic route for ultra-high temperature ceramics with unique morphologies. It is the first time that this type of transformation from a MOF into a UHTC has been reported. We have determined through analysis of SEM images that regardless of tape casting speed, about 57% of the TiB2 particles are aligned with the tape casting direction. The mechanical properties are dominated by the effects of the porosity (38%), but the alignment exhibited here could be further exploited for anisotropic behavior across the sintered tapes. Composites cast with high aspect ratio particles exhibited strong alignment in the casting direction. Further work is required to understand the interplay between alignment and porosity and their effects on material properties. / Doctor of Philosophy / Titanium diboride (TiB2) is an ultra-high temperature ceramic with a melting point of 3225°C. Many applications for this material require fully dense structural ceramics, such as cutting tools,1 armor,2 and high temperature structural supports.2,3 These applications rely mainly on the high mechanical strength of TiB2, which is maintained in extreme thermal and chemical environments. The field of knowledge surrounding TiB2 lacks information about the ways that porosity affects its otherwise well-known properties;4,5 to bridge this gap could open up applications for functional and porous ceramics such as lithium-air batteries,6 electrochemical components,7 semiconductors,8 and more. This work intends to provide a foundation for this endeavor by developing for the first time a colloidal suspension formulation that allows for the tape casting of TiB2 and characterizing the resulting porous ceramics. Among these new potential applications, many require thin ceramics less than 1 mm thick—a result which has been accomplished for other materials via tape casting.4,9 This is a wet route of producing ceramics that provides the ability to tailor the surface chemistry of the particles, giving greater control over the stability of the suspension (TiB2 particles suspended in water) and quality of the end product than is afforded by dry processing routes.10 This also allows for more complex shaping than simple pressing, which ultimately saves costs; by producing the near-net shape in the green body before firing, less machining must be done to the sintered body when it is removed from the high temperature furnace.11 In tape casting, the suspension is spread over a substrate by a doctor blade to the desired thickness. It is known that tape casting tends to align anisotropic particles along the direction of casting due to a nonuniform velocity imparted by the shear force of the doctor blade spreading the suspension, an advantage which can provide directional properties in the final ceramic.9 While this process is well known, it has never been applied to the material TiB2 prior to this work. In this work, a suspension is formulated to allow for the tape casting of TiB2 with minimum organic additive content, which is cost-effective and reduces potential for defects. Porosity and alignment in the tape cast specimens are characterized. For comparison, a highly anisotropic or rod-shaped particle (PCN-222, a metal organic framework material) was included in the TiB2 suspensions for tape casting. This metal organic framework (MOF) has been transformed into a high temperature material after thermal treatment at the sintering temperature of 2000°C, showing that the resulting particle is made of glass-like carbon embedded with zirconium carbide (ZrC) crystallites. This particle could be used as a reinforcement for ultra-high temperature ceramics, and in this work was shown to align strongly in the tape casting direction. At the level of porosity (38%) and alignment (57%) in the TiB2 specimens in this study, porosity dominates the mechanical properties. This relationship is shown to be more complicated than lowering the strength by the same proportion that the density is lowered, and various models for understanding the role of porosity on the elastic modulus are explored.

Polymer coatings are thin films of polymer deposited on different substrates for various applications. Such surface coatings can serve a functional purpose (adhesives, photographic films), protective purpose (anticorrosion), or decorative purpose (paint). Additionally, their composite coatings containing ceramic, or metal particles are often used to enhance durability, functionality, or aesthetics. Electrophoretic deposition (EPD) and dip coating are two promising methods for the fabrication of polymer and composite coatings due to the ease of fabrication, low cost, and high-volume production. EPD involves the electrophoresis of charged particles and their deposition on the electrode surface, which requires the colloidal particles to be charged in a stable suspension as a precursor solution for deposition. Many polymers cannot be deposited by EPD directly because of their charge neutrality and poor dispersion. Therefore, it is critical to develop efficient charging dispersants to modify electrically neutral polymers for their EPD. The approach was inspired by the strong solubilization power of bile acids in the human body. Two types of bile salts, cholic acid sodium salt and sodium chenodeoxycholate, and three types of biosurfactants, carbenoxolone sodium salt, glycyrrhizic acid, and 18β-glycyrrhetinic acid, which share similar structures with bile salts, were discovered for charging, dispersion, and EPD of different materials. The electrically neutral polymers (PTFE and PVDF), chemically inert materials (diamond, nanodiamond, graphene, carbon dots, carbon nanotubes and Zr-doped hydrotalcite (MHT)), and their composites can be well dispersed in suspension and deposited using these bio-surfactants as dispersants. It was found that the unique chemical structures of these biomolecules play vital roles in the surface modification and EPD of different materials. Moreover, the deposited polymer (PVDF, PTFE) and composite (PTFE-MHT) coatings can provide outstanding corrosion protection for stainless steel. The biomimetic and versatile strategy opens a way for the deposition of other electrically neutral materials through EPD. These findings also provide a promising strategy for selecting new dispersants for EPD. The deposition of high molecular weight (MW) polymers such as poly(ethyl methacrylate) (PEMA) at high concentrations in non-toxic solvents continues to be a challenge for dip coating. In this work, we firstly proposed using water-isopropanol as a co-solvent to dissolve high MW PEMA at high concentrations. It was found that water molecules can solvate carbonyl groups of PEMA and facilitate their dissolution. This method avoided the usage of toxic solvents and a long-time heating procedure for their removal. Moreover, it allows the fabrication of high-quality PEMA and composite coatings containing different flame retardant materials (FRMs), including double hydroxide LiAl2(OH)7.2H2O (LiAlDH), huntite, halloysite and hydrotalcite, through the dip coating method. A novel solid state synthesis method was proposed to fabricate LiAlDH, which is promising for the fabrication of other advanced DHs. Such composite coatings combined advanced properties of PEMA and functional properties of FRMs, such as corrosion inhibition and FR properties. / Thesis / Doctor of Engineering (DEng) / Polymer and composite coatings have been utilized for a wide range of applications due to their barrier properties, scratch and abrasion resistance, chemical resistance, and biocompatibility. Various techniques have been developed to fabricate polymer and composite coatings, such as electrophoretic deposition (EPD) and the dip coating method. However, limitations remain. EPD unitizes an electrical field to drive charged particles in a suspension toward conductive substrates to achieve film deposition. This process requires a stable suspension with charged particles, therefore, the electroneutral polymers present difficulties in their EPD. In addition, dissolving high molecular weight polymers at high concentrations in a non-toxic solvent is currently challenging, which is vital to utilize dip coating technique. The objective of this work was to develop advanced charging dispersants for EPD of electroneutral polymers and non-toxic solvents for dip coating of high molecular weight polymers. New biomimetic and versatile approaches have been developed for EPD of different electrically neutral polymers, chemically inert materials, and their composite coatings. A non-toxic co-solvent was proposed to dissolve high molecular weight polymer at high concentration for dip coating of the polymer and its composite coatings containing flame retardant materials. The results presented in this work showed the formation of high-quality films with multifunctionality and paved new strategies for further developments.

Nanostructured materials are the next generation of high-performance materials, harnessing the novel properties of their nanosized constituents. The controlled assembly of nanosized particles and the design of the optimal nanostructure require a detailed understanding of particle interactions and robust methods to tune them. This thesis describes innovative approaches to these challenges, relating to the determination of Hamaker constants for iron oxide nanoparticles, the packaging of nanopowders into redispersible granules, the tuning of the wetting behavior of nanocrystals and the simulation of collective magnetic properties in arrays of superparamagnetic nanoparticles. The non-retarded Hamaker constants for iron oxides have been calculated from their optical properties based on Lifshitz theory. The results show that the magnitude of vdW interactions in non-polar solvents has previously been overestimated up to 10 times. Our calculations support the experimental observations that oleate-capped nanoparticles smaller than 15 nm in diameter can indeed form colloidally-stable dispersions in hydrocarbons. In addition, a simple procedure has been devised to remove the oleate-capping on the iron oxide nanoparticles, enabling their use in fluorometric assays for water remediation, with a sensitivity more than 100 times below the critical micelle concentration for non-ionic surfactants. Nanosized particles are inherently more difficult to handle in the dry state than larger micron-sized powders, e.g. because of poor flowability, agglomeration and potential toxicity. The rheology of concentrated slurries of TiO2 powder was optimized by the addition of sodium polyacrylate, and spray-dried into fully redispersible micron-sized granules. The polymer was embedded into the granules, where it could serve as a re-dispersing aid. Monte Carlo (MC) simulations have been applied to the collective magnetic behavior of nanoparticle arrays of various thicknesses. The decrease in magnetic susceptibility with the thickness observed experimentally was reproduced by the simulations. Ferromagnetic couplings in the arrays are enhanced by the finite thickness, and decrease in strength with increasing thickness. The simulations indicate the formation of vortex states with increasing thickness, along with a change in their orientation, which becomes more and more isotropic as the thickness increases. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 2: Manuscript.</p>

Macroporous ceramic materials have found widespread technological application ranging from particulate filters in diesel engines, tissue engineering scaffolds, and as support materials in carbon capture processes. This thesis demonstrates how the pore space of macroporous alumina can be manipulated, analysed in three-dimensions (3D) using visualisation techniques, and functionalised with a CO2-adsorbing material. A novel method was developed to produce macroporous alumina materials: by combining sacrificial templating with thermally expandable polymeric microspheres and gel-casting of an alumina suspension. This method offers a versatile production of macroporous ceramics in which the level of porosity and the pore size distribution can easily be altered by varying the amount and type of spheres. The permeability to fluid flow could be regulated by controlling the connectivity of the pore space and the size of the smallest constrictions between the pores. Sacrificial templating with particle-coated expandable spheres significantly increased the fraction of isolated pore clusters and reduced both the sizes and the numbers of connections between neighbouring pores, compared to templating with un-coated spheres. The macroporous alumina materials were characterised with X-ray micro-computed tomography (μ-CT). The 3D data-sets obtained by X-ray μ-CT were used to calculate the spatial variation in porosity, the throat and pore size distributions and to calculate the permeability to fluid flow. The throat and pore size distributions were also able to be accurately quantified in only one extrusion and intrusion cycle with water-based porosimetry; a relatively novel and simple characterisation technique. The pore walls of the macroporous alumina materials were also coated with zeolite films by a colloidal processing technique. The CO2-uptake of the coated alumina materials and of hierarchically porous monoliths of zeolites was evaluated and compared. / As the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Accepted. Paper 5: Manuscript. Paper 6: Submitted.