Two direct consolidation methods usually used for advanced ceramics have been combined in this project in order to develop a novel fabrication route for traditional ceramics. Specifically the method used is based on the Additive Manufacturing extrusion process using direct writing of high solid loading ceramic pastes and then freeze-casting to solidify the deposited material. This novel fabrication method, for which a patent has been granted, has been christened “Direct Writing Freeze-Casting” (DWFC). Although the DWFC process is the subject of investigation by other researchers for a range of different applications, including the production of medical implants with alumina, the research presented in this thesis focuses on its use in the manufacture of white wares, giftware, and applied arts and crafts in general. This new system will provide designers, potters, artists, craft makers and manufacturers with a flexible and automated way of manufacturing porcelain objects. One of the major challenges to be overcome to exploit the DWFC process is the development of suitable slurry material formulations. Initial trials demonstrated that it is not possible to use conventional clay based porcelain materials with a platelet shaped microstructure which inhibits freeze casting. In this thesis the development and characterisation of non plastic porcelain slurry, based on substitution of kaolin (clay) with a calcined clay material (molochite), which can be processed using this new method is presented. The new non plastic porcelain formulation, which has a high solid load of 75.47% wt., has been subjected to detailed analysis to assess its suitability at each stage of the process; extrusion, freeze-casting (solidification) and firing.

Every year, accidents, falls, sport injuries and other incidents cause thousands of people to suffer spinal cord injury (SCI). In the United States alone, it is estimated that the number of Americans that live with SCI is around 259,000, with 12,000 new cases that happen annually (1). These injuries lead to spinal cord damages expressed by massive nerve tract degeneration followed by neurological loss, paralysis and disabilities. Therapy of SCI patients with non-steroidal anti-inflammatory drugs (NSAIDs) help in diminishing secondary injury and lessen pain and swelling. However these drugs do not promote tissue repair. Therefore there is an unmet clinical need to develop technologies and therapeutic strategies that compensate loss of neuronal tissue, support and facilitate reestablishment of nerve tracks connectivity in the injured spinal cord. Recent progress in nerve regeneration indicates that a tissue engineering approach using soft tissue scaffolds, stem cells and neurotrophins, can lead to a partial therapy in animal models of SCI. Bioengineered scaffolds prepared by freeze casting technology provide an experimental tool for guidance of regenerating neuronal tracts and/or axons and therefore are useful for regeneration of injured spinal cord. In this engineering approach for scaffold preparation, temperature controlled directional solidification of an aqueous polymer(s) solution creates channels of different diameters that can direct axonal outgrowth of neurons populating the scaffold. In a previous study from our laboratory, such scaffolds promoted differentiation of neurons, a process facilitated by co-population of the scaffold’s channels with endothelial cells. “Green” plant proteins, such as soybean proteins, are becoming an attractive alternative source of natural polymers for a variety of biomedical applications including scaffold fabrication for neuronal tissue regeneration. In the present study, we developed a second generation of improved, microchanneled composite scaffolds from gelatin and soy protein isolate cross-linked with genipin (2 w/v %, 0.5 w/v %, 1 w/v %, respectively). The fabrication of these scaffolds by a controlled freeze drying technique, their mechanical properties (stiffness, ~3-4 kPa) as well as their uniform longitudinal channels of a diameter of ~30-55 µm is described. Preliminary biocompatibility experiments in 2D and 3D using the above mentioned scaffolds populated with either undifferentiated PC12 cells or nerve growth factor differentiated PC12 cells indicated partial biocompatibility of the scaffolds for neuronal growth. Improving the biocompatibility of these composite scaffolds is under investigation in our laboratory. / Bioengineering

Porous silica-based nanocomposites are promising ceramics, as they exhibit high specific surface area, highly porous network, and a surface that can be easily functionalized. This dissertation describes the results of a study on the formation and properties of porous silica nanoparticle-based composites, using techniques of freeze casting and sintering. Kaolinite platelets and silica nanorods were added into the nanoparticle system, and their effects on modifying the porous microstructures and physical properties were investigated. During freeze casting, homogeneous microstructures with highly interconnected porosity are fabricated. Kaolinite addition results in large and more interconnected pores, while added silica nanorods cause a pore morphology evolution from circular to elongated spherical pores with increasing aspect ratio. The specific surface areas (area/mass) of the particles are conserved during freeze casting and values for the resulting composites can be accurately predicted using the area and mass of the components assuming conservation of area. Both kaolinite platelets and silica nanorods effectively improved the strength of the freeze cast green composites as they distribute any applied stress over a larger portion of the sample. Upon sintering, added kaolinite is found to modify the sintering behavior of the silica nanoparticles and a transitioning interfacial phase is identified when sintering temperature is above 1250 °C. This new phase contributes to the further enhancement of strength and this strengthening effect depends on composition and initial solids loading. After sintering at 1250 °C for 1 h, a ceramic containing 10 vol% kaolinite and 8 vol% silica has a maximum strength while maintaining a ~69% porosity. The kaolinite-silica composites with lower solids loading exhibit faster sintering (e.g. larger shrinkage, more extensive thickening of the pore walls), which, in turn, results in a rapid increase in mechanical strength. Based on the understanding of the composite properties and the underlying principles, a novel method for creating nanocomposites with precisely controllable specific surface area is developed. With repeated nanoparticle suspension infiltration, freeze drying, and sintering, the specific surface area can be varied from less than one to well over 100 m2/g, demonstrating potential application as liquid membranes. / Ph. D.

The design and fabrication of porous ceramic materials with anisotropic properties has, in recent years, gained popularity due to their potential application in various areas that include medical, energy, defense, space, and aerospace. Freeze-casting is an effective, low-cost, and safe method as a wet shaping technique to create these structures. To control the morphology of these materials, many critical factors were found to play an important role. In this dissertation, the processing parameters of the magnetic field-assisted freeze-casting method were optimized with a focus on comparing the structure obtained using vertical and horizontal magnetic fields and understanding the mechanisms that occur under different freezing modes. More specifically, this processing method was used to produce Al2O3 and B4C porous ceramics materials with unidirectionally-aligned pore channels. The effect of the vertical and horizontal magnetic field strength and direction, concentration of magnetic material (Fe3O4), cooling rate, and freezing time were examined. The resulting ceramics with highly aligned pore channels were infiltrated with molten metal to create metal matrix composites. The mechanical properties of these structures were measured and were subsequently correlated to their morphology and composition.

Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2017-12-12T13:03:18Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Eduardo Pagano.pdf: 5564139 bytes, checksum: 41a00843092c58a3dcd62662b42000f1 (MD5) / Made available in DSpace on 2017-12-12T13:03:18Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Eduardo Pagano.pdf: 5564139 bytes, checksum: 41a00843092c58a3dcd62662b42000f1 (MD5) Previous issue date: 2017-08-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Neste estudo foi realizado a obtenção e caracterização de materiais cerâmicos de alumina com gradiente funcional de porosidade. Foram utilizados como os métodos de processamento a rota de freeze casting em água e a fase de sacrifício utilizando o amido. Os materiais utilizados para a produção das amostras foram a alumina e o amido de milho de pureza analítica. Foram investigadas as características de porosidade quanto a morfologia de poros, distribuição dos poros pela matriz e interferência do processamento na formação destes. Para o estudo da porosidade, os métodos de porosimetria via método de Arquimedes em água e penetração de mercúrio foram aplicados na analise desta porosidade obtida. As propriedades mecânicas, bem como o modo de fratura obtido, também foram investigadas em ensaio de compressão uniaxial em uma máquina de ensaios universal. As imagens obtidas por microscopia eletrônica de varredura auxiliaram a correlacionar os dados obtidos nos ensaios de porosimetrias com a resposta mecânica obtida do material. Os resultados obtidos entre os métodos, quanto à porosidade, revelam diferenças consideráveis na distribuição e quantidade de poros ao se comparar o freeze casting com a fase de sacrifício com amido. Porém quanto a tamanho, os valores se mantiveram bem próximos. A resistência mecânica em compressão é maior nas amostras com amido, porém estas amostras falham de forma catastrófica. As amostras de freeze casting, por sua vez, possuem menor resistência mecânica e tiveram suas fraturas influenciadas por vários fatores durante o processamento. A morfologia de poros e microestrutura apresentada pelos dois métodos aplicados são consequência direta da rota de processamento utilizada. Nas amostras por freeze casting, foram observados canais de poros. Já as amostras com amido como fase de sacrifício, os poros são arredondados e não conectados / In this study, preparation and characterization of alumina ceramic materials with functional porosity gradients were performed. Freeze casting of alumina slurries, using water as the chosen solvent, and sacrificial phase method using corn starch as sacrificial phase, were implemented. The materials used to produce the samples were alumina and analytical purity corn starch. Porosity characteristics were investigated concerning pore morphology, pore distribution in the ceramic matrix and processing route interference in pore formation. The evaluation of porosity was made utilizing porosity determination methods as mercury intrusion and Archimedes method with water as immersion liquid. The mechanical properties, as well as the fracture mode, were investigated during uniaxial compressive test in a universal testing machine. Using the images obtained by scanning electron microscopy (SEM), it was possible to correlate the data obtained in the porosimetry analysis with the mechanical response obtained from the material. In terms of porosity, the results between the processing routes reveal considerable differences in pore distribution and quantity of pores. However, the pore sizes obtained for both methods were pretty close to each other. The mechanical strength during compressive stress was higher in the samples produced via sacrificial phase method, but those samples failed catastrophically. Freeze casting samples, on the other hand, had lower mechanical resistance and their fractures were directly influenced by several factors during their assembly processing. The pore and microstructure morphology presented by both methods were direct consequence of the processing route used. In the samples produced by freeze casting, pore channels were observed. The samples produced via sacrificial phased method using corn starch presented unconnected rounded pores.

MAX-phase ceramics are a class of ductile ceramic material group with the general molecular formula Mn+1AXn (n = 1, 2, 3….), where M is an early transition element, A is an element from the ‘A’ group of the periodic table and X is either nitride or carbide. One advantage of these materials is that they maintain their strength at high temperatures. In addition these ceramic materials possess the best properties of both ceramics and metals. Some of their important characteristics are low density, high stiffness, machinability, excellent thermal and electrical conductivity and they even exhibit some plasticity at elevated temperature. These amazing combinations of properties have made researchers foresee the technological importance of these materials as a structural ceramic for high temperature application. Since this ceramic is relatively new to the market, only a handful of work has been undertaken on this material and its applications are limited to heating elements. In addition, analysis of the thermodynamic data on this material is incomplete. This PhD work addresses this issue and conducts a complete thermodynamic analysis involved in the formation mechanism of the ternary titanium carbide MAX-phase Ti2AlC ceramic, using Self-propagating High temperature Synthesis (SHS) form of combustion synthesis process, based on the following exothermic reaction: (2+x) Ti + (y) Al + C → Ti2AlC + (x) Ti + (y) Al (i) Where x and y = 0.1. 0.2, 0.3… A thermodynamic model has been formulated to predict the temperature evolution during the reaction (i), for the formation of Ti2AlC using SHS process. In addition the effect of particle size in the elemental reaction has been studied on the formation mechanism of Ti2AlC and methods to control the porosity by fine tuning the particle size has been recognized. Manufacturing processes such as Self-propagating High temperature Synthesis (SHS), foam replication and freeze casting have been developed in this thesis to produce micro and macro porous Ti2AlC ceramic mainly for electrode applications. A systematic material development technique to produce macro porous Ti2AlC ceramic, using a foam replication technique has been established in this research work. The material fabricated by this technique has a uniform pore size (up to 5mm), with open interconnected pores and is ideal for a flow battery application which requires a multifunctional electrode material which is highly porous to allow the flow of electrolyte through it, is corrosion resistant and at the same time being electrically conductive. The mechanical properties of the ceramic produced by this method has been characterised and steps to mitigate the cracks and defects formed during the fabrication process to obtain structurally stable macro porous Ti2AlC ceramic has been reported in this work. This research demonstrates that one of the applications of macro porous Ti2AlC ceramic formed using foam replication technique is as an electrode material in a photo-Microbial Fuel Cell (p-MFC). Graded porosity micro porous Ti2AlC ceramics have also been fabricated using a freeze casting technique, with camphene as the freezing vehicle. A systematic material development process has been tailored for this particular material. A ceramic material with gradient pore size ranging from 27-305µm has been fabricated using this technique. This type of ceramic is a good candidate as an electrode material in micro-redox battery and for sensing applications. A variety of processing parameters such as solid loading (amount of ceramic content in the material), freezing temperature and mould material which affect the pore formation and pore size have been studied in this PhD and the range of porosities achieved by controlling these parameters have been reported.

CO2 adsorption is considered as a promising strategy to decrease the amount of CO2 in the atmosphere and stop global warming. The goal of this project is to prepare a cellulose-based CO2 adsorbent with a good mass transfer. Monolithic adsorbent based on cellulose nanofibrils (CNF) was fabricated via freeze-casting. 0.1g or 0.5g cellulose acetate (CA) or 0.1g acetylated CNC (aCNC) was dipped into the crosslinked aerogel to increase its CO2 capacity. Acetylation of CNC was confirmed by Fourier transformed infrared spectroscopy (FT-IR) and the degree of substitution was determined to be 1.6 through titration. Scanning electron microscopy (SEM) images showed that monolithic structure was formed through freeze-casting and the structure was maintained after dipping. Compression test suggested that the mechanical properties of the aerogel increased with the increasing amount of dipped CA, while the CO2 capacity of the adsorbent decreased. Furthermore, the outstanding reinforcing effect of aCNC was noticed in the compression test, and the aerogel dipped with aCNC has the highest CO2 capacity with a value of 1.49 mmol/g.

Magnetic field-assisted freeze-casting was used to create porous B4C ceramic preforms. An optimum slurry consisted of a mixture of B4C powders with 6 wt.% Er2O3 powder in an H2O-PVA solution and was cooled at a rate of 1 °C/min from room temperature to -30 °C resulting in porous green state ceramic preform with vertical channels. The Er2O3 powder was added to improve the magnetic response of the slurry. The preform was then sublimated to remove H2O and then sintered. The sintered ceramic preform was then infiltrated in the most vertically aligned channel direction with molten Al (A356) metal through a vacuum-assisted pump to create the metal matrix composite (MMC). Finite element analysis simulations were used to analyze and predict the anisotropic effect of B4C channel alignment on mechanical properties. The mechanical properties of the composite were then experimentally found via compression testing, which was compared with rule-of-mixtures and finite element modeling simulations, to analyze the effect of anisotropy due to magnetic field-assisted freeze-casting. This study reinforces the viability of cost-effective magnetic field-assisted freeze-casting as a method to create highly directional ceramic preforms, which can be subsequently metal infiltrated to produce MMCs with highly anisotropic toughness.

Freeze casting is a colloidal processing technique that shows great promise for development of nanostructured materials. A ceramic nanopowder is dispersed with a polymer in water, under carefully controlled pH. The suspension is cast into a suitable mold and frozen, then de-molded and exposed to a vacuum to sublimate and remove the water. Polymer adsorption and rheology were studied to optimize and characterize a colloidal suspension of a 38 nm Al2O3 powder. The dispersant, dispersant amount, pH and solids loading were examined to determine the best conditions for freeze casting. Based on adsorption and viscosity data, optimal conditions for freeze casting were found with Poly(acrylic acid) (PAA) dispersant, at 2.00 wt% (of Al2O3), pH of 9.5, and a solids loading of 40 vol%. Carbon nanotubes (CNTs) were added to that suspension in increments of 0.14, 0.28, 0.53, 1.30 and 2.60 vol%. The viscosity increased dramatically upon addition of 1.30 vol% CNTs. The colloidal CNT-Al2O3 suspension was successfully freeze cast and the microstructure showed a very smooth fracture surface. It was determined that upon resting, the suspension undergoes a physical change which must be completed to obtain advantageous microstructure. Freeze cast Al2O3 discs with and without CNTs were measured using a concentric ring test, with strengths on the order of one MPa. The freeze cast sample was successfully debinded, but the heating profile attempted was not effective in obtaining full density. / Master of Science

Submitted by Angela Maria de Oliveira (amolivei@uepg.br) on 2019-02-27T11:49:16Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Gustavo Antoniacomi de Carvalho.pdf: 6310308 bytes, checksum: 8e1efd9d86bc5a1adf80b45bba2a3985 (MD5) / Made available in DSpace on 2019-02-27T11:49:16Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) Gustavo Antoniacomi de Carvalho.pdf: 6310308 bytes, checksum: 8e1efd9d86bc5a1adf80b45bba2a3985 (MD5) Previous issue date: 2018-01-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Cerâmicas porosas vêm ganhando visibilidade devido a algumas aplicações tecnológicas interessantes, tais como a utilização em eletrólitos sólidos, ânodos de células a combustível, filtros cerâmicos e reposição óssea e dental. Dentre elas, há especial atenção ao estudo de materiais porosos com porosidade graduada, nos quais a quantidade de poros e a morfologia dos mesmos se alteram pelo volume do material. Nesse trabalho foi realizado o processamento e caracterização de materiais cerâmicos de alumina com porosidade graduada a partir das técnicas de freeze casting e colagem de barbotina, utilizando hidróxido de alumínio e amido de arroz como fases de sacrifício. Após a conformação das amostras por esses métodos, a porosidade foi caracterizada por microscopia eletrônica de varredura, pelas medidas de porosidade aparente feita pelo Princípio de Arquimedes e pela distribuição de tamanho de poros feita pela técnica de porosimetria de mercúrio. Foi avaliada também a resistência mecânica das amostras a partir de ensaio de compressão. Foi confirmada a relação entre as amostras processados isoladamente e suas respectivas camadas nas amostras graduadas. Foi observada também uma boa interação interfacial entre cada uma das camadas das amostras graduadas. A porosidade das amostras com porosidade graduada se manteve próxima do esperado, o valor esperado foi determinado a partir da média das amostras processadas isoladamente em relação às camadas do material com porosidade graduada. O ensaio mecânico demonstrou que não houve influência das interfaces dos materiais graduados na sua resistência à compressão. / Porous ceramics have been gaining visibility due to some interesting technological applications, such as its use as solid electrolytes, fuel cell anodes, ceramic filters and bone and dental reposition. Among them, there is special care in studying graded porosity materials, where the quantity of pores and pore morphology changes through the material volume. In this work the processing and characterization of alumina ceramic materials with functionally graded porosity by freeze casting and slip casting techniques using aluminum hydroxide and rice starch as sacrificial template was performed. After conformation, the porosity was characterized through electron scanning microscopy, apparent porosity through Archimedes method and median pore size through mercury porosimetry. The mechanical resistance was also obtained by compression testing. The analysis allowed to confirm the relation between each of the isolated samples’ microstructure and its respective layer in each of the graded materials, also, the graded materials shown good interfacial interaction between each of the layers. The porosity in graded materials kept close to the expected value, which was determined by the medium value of the porosities of the isolated samples respective to the graded material. Mechanical testing shown that there was no influence of the graded material interfaces in its compressive strength.