This research details an investigation into processes employing laser technology to create design-led three-dimensional textiles. An analysis of historical and contemporary methods for making three-dimensional textiles categorises these as processes that construct a three-dimensional textile, processes that apply or remove material from an existing textile to generate three-dimensionality or processes that form an existing textile into a three-dimensional shape. Techniques used in these processes are a combination of joining, cutting, forming or embellishment. Laser processing is embedded in textile manufacturing for cutting and marking. This research develops three novel processes: laser-assisted template pleating which offers full design freedom and may be applied to both textile and non-textile materials. The language of origami is used to describe designs and inspire new design. laser pre-processing of cashmere cloth which facilitates surface patterning through laser interventions in the manufacturing cycle. laser sintering on textile substrates which applies additive manufacturing techniques to textiles for the generation of three-dimensional surface patterning and structures. A method is developed for determining optimum parameters for laser processing materials. It may be used by designers for parameter selection for processing new materials or parameter modification when working across systems.

The term nanoceramics is well known in the ceramic field for at least two decades. Even though there are many reports that nanoceramics are superior in terms of mechanical and other properties, no comprehensive and conclusive study on the grain size dependent variation in mechanical properties. So this study was an attempt to study the property variation with grain size and yttria content for a well known ceramic, yttria stabilised zirconia. High solids content but low viscosity YSZ nanosuspensions have been slip cast into -52% dense, very homogeneous green bodies in sizes up to 60 mm in diameter. Sintering cycles have been optimised using both hybrid and conventional two-step heating to yield densities >99.5% of theoretical whilst retaining a mean grain size of <100 nm. The sintered samples have been characterised for hardness, toughness, strength, wear resistance and hydrothermal ageing resistance. The results have been compared with that of a submicron zirconia ceramic prepared using a commercial powder. The strength of the nanoceramics has been found to be very similar to that of conventional submicron ceramics, viz. -10Pa, although the fracture mechanism was different. Two toughness measurement approaches have been used, indentation and surface crack in flexure. The results indicate that the nano 1.5YSZ ceramics may be best viewed as crack, or damage, initiation resistant rather than crack propagation resistant; indentation toughness measurements as high as 14.5 MPa m 112 were observed. Micro-Raman mapping was demonstrated to be a very effective technique to map the phase transformations in zirconia. The wear mechanism of nanozirconia has been observed to be different compared to that in conventional, submicron YSZ and the wear rates to be lower, particularly under wet conditions. In addition, and potentially most usefully, the nan03YSZ ceramics appear to be completely immune to hydrothermal ageing for up to 2 weeks at 245°C & 7 bar; conditions that see a conventional, commercial submicron ceramic disintegrate completely within 1 hour.

This research introduces a method to aid the design of products or parts to be made using Additive Manufacturing (AM), particularly the laser sintering (LS) system. The research began with a literature review that encompassed the subjects of design and AM and through this the need for an assistive design approach for AM was identified. Undertaking the literature review also confirmed that little has been done in the area of supporting the design of AM parts or products. Preliminary investigations were conducted to identify the design factors to consider for AM. Two preliminary investigations were conducted, the first investigation was conducted to identify the reasons for designing for AM, the need for a design support tool for AM and current challenges of student industrial designers designing parts or products for AM, and also to identify the type of design support they required. Further investigation were conducted to examine how AM products are developed by professional industrial designers and to understand their design processes and procedures. The study has identified specific AM enabled design features that the designers have been able to create within their case study products. Detailed observation of the case study products and parts reveals a number of features that are only economical or possible to produce with AM. A taxonomy of AM enabled design features was developed as a precursor for the development of a computer based design tool. The AM enabled design features was defined as a features that would be uneconomical or very expensive to be produced with conventional methods. The taxonomy has four top-level taxons based on four main reasons for using AM, namely user fit requirements, improved product functionality requirements, parts consolidation requirements and improvement of aesthetics or form requirements. Each of these requirements was expanded further into thirteen sub categories of applications that contained 106 examples of design features that are only possible to manufacture using AM technology. The collected and grouped design features were presented in a form of a database as a method to aid product design of parts or products for AM. A series of user trials were conducted that showed the database enabled industrial designers to visualise and gather design feature information that could be incorporated into their own design work. Finally, conclusions are drawn and suggestions for future work are listed. In summary, it can be concluded that this research project has been a success, having addressed all of the objectives that were identified at its outset. From the user trial results, it is clear to see that the proposed tool would be an effective tool to support product design for AM, particularly from an educational perspective. The tool was found to be beneficial to student designers to take advantage of the design freedom offered by AM in order to produce improved product design. As AM becomes more widely used, it is anticipated that new design features will emerge that could be included in future versions of the database so that it will remain a rich source of inspirational information for tomorrow s industrial designers.

This thesis is focused on achieving materials with non-equilibrium structures fabricated by high-energy laser sintering. The chosen precursor materials have rigid and inert structures like high-melting point ceramics or metals. It was necessary to use real-time monitoring of temperature and spectrum profiles for selecting the optimal laser parameters for the laser sintering process. This monitoring was done by an off-axial setup that also controls the surface morphologies during the laser irradiation process. The laser focal spot receives very high temperatures and subsequent extreme cooling rates within a short time period. New non-equilibrium structures will emerge ruled by kinetics, huge temperature gradients or stresses and freeze by quenching in solid state. These material structures were found to form at different length scales from nano- to macro-level, frequently by a hierarchical ordering. This opens a method to engineer materials with both hierarchical and non-equilibrium structures by a single operation in both metal and ceramics by laser sintering. In the Co-Cr-Mo alloy system, structures on three levels of lengths were observed, namely i) nano-level structures dominated by the grain boundary segregation; ii) micron-level structures characterized by the interlocked clusters of columns; and iii) macro-level structures defined by the selected laser scan patterns. The non-equilibrium structures of the Co-Cr-Mo alloy are related to mechanical, corrosion and bio-compatibility properties. In ZrO2 ceramics, the final product had a non-equilibrium nano- and micron-sized structure created by uneven absorption of laser energy and rupture. The structure inside the micron-sized grains is formed through ordered coalescence of nano-crystals. Properties of the laser sintered materials were established and related to the observed structures. The materials properties might be tailored by controlling the structures in different levels and potential applications of the new materials will be given. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 3: Accepted. Paper 4: Submitted. Paper 5: Manuscript.</p>

A potential route for converting different carbon sources (coal, natural gas and biomass) into synthetic fuels is the transformation of these raw materials into synthesis gas (CO and H2), followed by a catalytic step which converts this gas into the desired fuels. The present thesis has focused on two catalytic steps: Fischer-Tropsch synthesis (FTS) and methanation. The Fischer-Tropsch synthesis serves to convert synthesis gas into liquid hydrocarbon-based fuels. Methanation serves instead to produce synthetic natural gas (SNG). Cobalt catalysts have been used in FTS while nickel catalysts have been used in methanation.             The catalyst lifetime is a parameter of critical importance both in FTS and methanation. The aim of this thesis was to investigate the deactivation causes of the cobalt and nickel catalysts in their respective reactions.             The resistance to carbonyl-induced sintering of nickel catalysts supported on different carriers (γ-Al2O3, SiO2, TiO2 and α-Al2O3) was studied. TiO2-supported nickel catalysts exhibited lower sintering rates than the other catalysts. The effect of the catalyst pellet size was also evaluated on γ-Al2O3-supported nickel catalysts. The use of large catalyst pellets gave considerably lower sintering rates. The resistance to carbon formation on the above-mentioned supported nickel catalysts was also evaluated. Once again, TiO2-supported nickel catalysts exhibited the lowest carbon formation rates. Finally, the effect of operating conditions on carbon formation and deactivation was studied using Ni/TiO2 catalysts. The use of higher H2/CO ratios and higher pressures reduced the carbon formation rate. Increasing the temperature from 280 °C to 340 °C favored carbon deposition. The addition of steam also reduced the carbon formation rate but accelerated catalyst deactivation.             The decline in activity of cobalt catalysts with increasing sulfur concentration was also assessed by ex situ poisoning of a cobalt catalyst. A deactivation model was proposed to predict the decline in activity as function of the sulfur coverage and the sulfur-to-cobalt active site ratio. The results also indicate that sulfur decreases the selectivity to long-chain hydrocarbons and olefins. / <p>QC 20160817</p>

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.

Cette étude s'inscrit dans le cadre du développement de nouveaux matériaux pour la fabrication additive. Notre objectif est la fabrication de pièces comprenant un alliage métallique complexe (CMA) à l'aide d'un laser UV de stéréolithographie. L'alliage choisi est un alliage quasicristallin dominé par une phase icosaédrique du système AlCuFeB. Des poudres brutes d'atomisations ont été caractérisées par diffractions des rayons X et analyse thermique différentielle. Nous avons montré une bonne absorbance optique de la poudre dans le domaine UV-visible qui rend possible un début de frittage sous l'effet du laser correspondant à la formation de pontages entre les grains à une température d'environ 820°C. Concernant la fabrication à partir d'une suspension de poudres dans un liant, nous avons étudié les propriétés de mouillage des particules AlCuFeB et optimisé un mélange avec une résine époxy chargée par 20 % vol. de particules CMA. L'absorption optique de la suspension dans le domaine UV est suffisante pour fabriquer une pièce composite par stéréolithographie. La granulométrie utilisée est inférieure à 25 µm. Nous avons ainsi réussi à fabriquer des pièces de 14 mm de hauteur, en additionnant des couches de 50 µm. À partir des pièces réalisées, nous avons caractérisé la dureté et les propriétés tribologiques de ce nouveau matériau composite. La dureté des pièces ainsi fabriquées est supérieure à celle de la résine seule et atteint 88 Shore D. Nous avons également mis en évidence une amélioration de 30 % du coefficient de frottement et une diminution du volume d'usure de 40 % par rapport au matériau de la matrice époxy. Ces propriétés rendent attractif ce nouveau matériau composite pour la fabrication par stéréolithographie / This study aimed at developing new materials for additive manufacturing. We focused on producing parts containing complex metallic alloys (CMA) using a UV laser used for stereolithography. The selected intermetallic is a quasicrystalline alloy dominated by the icosahedral phase in the system AlCuFeB. The raw powders produced by gas atomization were characterized by X-ray diffraction and differential thermal analysis. The powders exhibit good optical absorption properties in the UV-visible range allowing direct laser sintering as evidenced by the formation of bridges between the grains at a temperature of about 820°C. In a second step, we have considered the manufacturing of parts made of a suspension of CMA powders in a binder. We have studied the wetting properties of the particles AlCuFeB and optimized a mixture consisting of an epoxy resin filled with 20 % vol. of CMA particles. The optical absorption of the suspension in the UV range was sufficient to produce composite parts by stereolithography. The particle size used was smaller than 25 micrometers. We have managed to make parts reaching 14 mm in height by adding layers with a thickness of 50 microns. Using test samples, we have characterized the hardness and the tribological properties of this new composite material. The hardness of the parts produced by stereolithography is larger than that of epoxy parts and reaches 88 Shore D. We have also shown a 30 % reduction of the friction coefficient as well as a 40 % reduction of wear losses compared to the epoxy matrix. These properties make attractive this new composite material for stereolithography applications

Wavy type Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) have been shown to be conducive to improving the effective electrochemical reaction area contributing to higher performance, compared with planar type SC-SOFCs of the same diameter. This study presents a fabrication process for wavy type SC-SOFCs with a single fabrication step via co-sintering of a triple-layer structure. The monitoring and observation of the curvature evolution of bi- and triple-layer structures during co-sintering has resulted in an improved process with reduced manufacturing time and effort, as regards the co-sintering process for multi-layer structures. Investigation using in-situ monitoring helps different shrinkage behaviours of each porous layer to minimise mismatched stresses along with avoidance of severe warping and cracking. In the co-sintering of the multi-layer structures, the induced in-plane stresses contribute to curvature evolution in the structure, which can be utilised in the design of a curved multi-layer structure via the co-sintering process. For intermediate temperature SOFCs, the materials used are NiO/CGO for anode; CGO for electrolyte; and LSCF for cathode. These materials are tape-casted with 20μm thickness and assembled for bi- and triple-layer structures by hot pressing. Sintering mismatch stresses have been analysed in bi-layer structures, consisting of NiO/CGO-CGO and CGO-LSCF. The maximum sintering mismatch stress was calculated at interface of bi-layer structure in the top layer. In order to achieve the desired wavy type triple-layer structure, flexible green layers of each component were stacked up and laid on alumina rods to support the curvature during the process. In-situ observation, to monitor the shrinkage of each material and the curvature evolution of the structures, was performed using a long focus microscope (Infinity K-2). With these values, the main factors such as viscosity, shrinkage rate of each material, and curvature rate are investigated to determine the sintering mismatch stresses. This enables the prediction of curvature for triple-layer structure and the prediction is validated by in-situ monitoring of the triple-layer structure co-sintering process. Zero-deflection condition is confirmed to maintain initial shape during co-sintering and helps to minimise the development of undesired curvature in the triple-layer structure. Performance testing of the wavy cell was carried out in a methane-air mixture (CH4:O2 =1:1). In comparison with a planar SC-SOFC, it showed higher OCV which might be attributed to not only macro deformation, but also microstructural distribution affecting the effective gas diffusion paths and electrochemical active sites.

[pt] O presente trabalho apresenta um estudo preliminar sobre a síntese de membranas macroporosas de óxido de magnésio, com uma faixa de porosidade estreita e homogênea, mediante uma técnica reprodutível e visando sua aplicação futura na separação de substâncias gasosas impossíveis de serem separadas por métodos convencionais. As membranas foram criadas a partir da sinterização das respetivas nanopartículas obtidas pelo método sol-gel/nano matriz, usando nitrato de magnésio como precursor principal e álcool polivinílico, PVA, como matriz das nanoestruturas. Foram avaliados diferentes parâmetros de pressão e temperatura de sinterização. As amostras obtidas foram analisadas por MEV, DRX, BET e Porosimetria por Intrusão de Mercúrio (PIM). Os resultados mostram que o material obtido apresenta tamanho de partículas uniforme, confirmando assim a sinterização. O tamanho de cristalito médio foi de 160nm, sendo que o tamanho médio de grãos foi de 450nm; os materiais que apresentaram melhores propriedades foram aqueles sinterizados a 1000 e 1100 graus Celsius com pressão de 173MPa, e a 1000 graus Celsius com 260MPa. A macroporosidade obtida se encontra numa faixa muito perto do limite com a mesoporosidade, sendo que quase 97 por cento dos macroporos estão entre 50 e 150nm de raio. Os resultados indicam que a técnica foi reprodutível e a faixa de poros é razoavelmente estreita, o que permitirá aplicar a membrana na separação de substâncias específicas. / [en] This work present a preliminary study on the synthesis of macroporous membranes of magnesium oxide with a homogeneous and a narrow range of porosity obtained by a reproducible technique, which aims their future application in the separation of gaseous substances impossible to separate by conventional techniques. The membranes were obtained by the sintering of the respective nanoparticles which were obtained by the sol-gel/nanotemplate technique, using a magnesium nitrate as the main precursor and polyvinyl alcohol, PVA, as a template of the nanostructures. Pressure and Temperature were the sintering parameters evaluated in the present research. The samples obtained were analyzed by SEM, XRD, BET, and Intrusion Mercury Porosimetry (IMP). The results show uniformity in the particles size of the material, confirming the sintering process. The average crystallite size was 160nm, and the average grain size was 450nm, the samples showing better properties were those sintered at 1000 and 1100 Celsius degrees at a pressure of 173MPa, and 1000 Celsius degrees at 260MPa. The range macroporosity obtained limit with the mesoporosity, nearly 97 per cent of the macropores is between 50 and 150nm radius. The results indicate that the technique is reproducible and the pores range is reasonably small, this will allow to apply the membrane in the separation of certain substances.

<p></p><p>Flexible electronics involve electronic circuits fabricated on flexible substrates. They have promising applications in wearable devices and flexible sensors etc. and have thus attracted much research interest in recent years. The working environment of flexible electronic devices may require them to go through repeating deformations, during which cracks may generate and grow in the metallic components of the devices, reducing service life of these devices. To address such challenges, it is desirable to investigate methods to improve the reliability of flexible electronics in these working conditions. </p> <p>This research reported here will focus on topics related to laser-based fabrication of carbon nanotube-metal composites on flexible substrates: </p> <p>Experimental studies were carried out to investigate the structures and properties of carbon nanotube – metal composites produced by a laser-based fabrication process on flexible substrates. Extensive characterizations and testes were carried out, including measurements of electrical resistivity of laser-sintered material, characterizations with SEM, TEM, EDS and XPS, and mechanical performance tests (bending fatigue test, static tensile test and adhesion test). The experimental study suggests that the laser-fabricated metal composites have promising potentials to help enhancing reliability and durability of metal components in flexible electronic devices. </p> <p>A molecular dynamics model was also developed to study the coalescence of metal nanoparticles (gold NPs in this study) around the end of a multi-walled carbon nanotube (MWCNT) and their interaction with the CNT at elevated temperatures. The MD model was first tested by comparing the MD-predicted NP melting points with experiment-deduced results from the literature. Then the coalescence of five 3-nm Au NPs around the end of a MWCNT and their interactions with the CNT were studied with MD simulations. The molecular system was studied under different elevated temperatures and for different carbon nanotube diameters, and the simulation results were analyzed and discussed. </p><br><p></p>