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<p>  </p> <p>Silicon carbide (SiC) is a ceramic material of interest for many applications due to its mechanical properties, oxidation resistance, and high thermal conductivity. However, one limitation of SiC is its low fracture toughness. There is evidence that SiC with crystallographic texture and an anisotropic microstructure of aligned plate-shaped grains has improved fracture toughness without sacrificing strength. Previous techniques to create these materials have made use of either pressure during densification or a strong magnetic field, but these processes limit possible geometries that can be created. In this dissertation, the additive manufacturing technique direct ink writing (DIW) and pressureless templated grain growth (TGG) are proposed as a route to complex-shaped textured SiC. </p> <p><br></p> <p>DIW is a colloidal processing technique where ceramic suspensions are extruded through a nozzle along a path, building up a part layer-by-layer. High aspect ratio particles can be aligned via the forces in the print nozzle. In this work, single crystal SiC platelet seed particles were added to a SiC suspension and aligned with DIW. After densification, samples were annealed above the sintering temperature. During annealing, TGG occurs where the platelet seed particles grow at the expense of the finer matrix particles, and this results in crystallographic texture. </p> <p><br></p> <p>First, work on the development of the DIW process for the creation of textured SiC is shown. Aqueous SiC suspensions were developed with a high solids loading (> 50 vol%) and low polymer content (< 5 vol%) to maximize the density achieved during sintering, which is ideal for TGG. Four rheological parameters (viscosity of the suspension at 5 s­-1, zero shear viscosity, oscillatory yield stress, and equilibrium storage modulus) were related to the amount of viscosity modifying polymer (polyvinylpyrrolidone) and observed quality of prints. The best prints were made from suspensions that had a viscosity of 30-35 Pa s, ZSV of 5000-7000 Pa s, and yield stress 100-150 Pa. The best suspension for printing was identified to be 53 vol% solids with 0.2 vol% PVP due to its high particle loading and ability to create consistent prints. The addition of 5 vol% platelet particles to the suspension did not impact the rheology or printability significantly.</p> <p><br></p> <p>Next, textured SiC ceramics over 95% theoretical density were created via pressureless sintering and annealing. Samples were fabricated with and without 5 vol% platelet seeds, and with and without annealing at 2050 ºC and 2150 ºC. The effects of DIW, seed particles, and annealing temperature on the microstructure and crystallographic texture are presented. Annealing lead to the development of large, high aspect ratio plate-shaped grains among a matrix of many finer, low aspect ratio grains. Higher annealing temperatures and addition of platelet seeds both increased the size of the large grains. Samples were found to be textured regardless of having platelet seeds. Via x-ray diffraction and electron backscatter diffraction, unseeded SiC was found to have texture where the crystallographic direction [0001] had a preferred orientation perpendicular to the normal direction. This occurred for both DIW and cast SiC, so the texture development must have occurred during sintering, though the mechanism is unknown. For seeded SiC, platelet seeds aligned in DIW successfully seeded the grain growth to develop crystallographic texture. The texture was mainly influenced by the alignment of platelet seed particles via shear stresses in the print nozzle, causing a one-dimensional texture where [0001] is perpendicular to the printing direction. However, it was found that the texture was not the expected one-dimensional, concentric alignment of platelet particles in DIW, so the shear stresses in the nozzle are not solely responsible for the texture developed.</p> <p><br></p> <p>Finally, the mechanical behavior of these materials was explored via 4-point flexural strength testing and Weibull analysis. The effect of texture, print orientation, and printing defects on the mechanical and fracture behavior of these materials is discussed. Mechanical tests were conducted both parallel and perpendicular to the printing direction. DIW samples were found to have a variety of defects after densification, including visible print lines, air bubbles, and porosity. Unseeded SiC annealed at 2050 ºC tested parallel to the print direction was found to have the best combination of mechanical properties among all annealed SiC, with evidence of toughening on the fracture surface, flexural strength 405 ± 16 MPa, and Weibull modulus of 15.4. Seeded SiC annealed at 2050 ºC had a high degree of transgranular fracture among large plate-shaped grains, but still had a flexural strength 339 ± 41 MPa. However, improved alignment of grains in future work may increase the incidence of intergranular fracture. At both annealing temperatures, textured SiC created with aligned platelet seed particles was found to have comparable mechanical strength to those fabricated without seed particles despite having a coarser microstructure, suggesting texture may influence the mechanical properties. </p>

<p> Ink-jet printing onto flat paper is a widely established process. In this thesis, we make extensions to printing on target surfaces such as metals and glass, using a 5-axis orientable head. Original artwork is created using CAD, and is sampled to create the ink jet point cloud. The target surface location is registered using a standard Coordinate Measuring Machine (CMM) 5-axis touch trigger probe. The probe is then replaced with the ink jet head and the printing process is carried out. Demonstration of the system is illustrated using flat metal and glass samples, as well as rapid prototyped 3-D plastic shapes.</p> / Thesis / Master of Applied Science (MASc)

<p dir="ltr">A new class of bioplastics polymer materials synthesized from hemp-derived cannabinoids are demonstrated through a lifecycle approach. The poly(cannabinoid) material platform is utilized to develop application-specific polymers for the fabrication of electrocardiogram electrodes and on-skin heaters. A rigid homopolymer pCBD-adipate is synthesized to formulate conductive composite inks and a CBD/CBG block copolymer is developed as an adhesive. Inks are printed using the DIW process allowing for versatile and rapid prototyping of devices. ECG performance assessments yield comparable performance to conventional wet gel electrodes in ambient conditions, and improved performance in submerged testing. Heating devices are demonstrated for conformality by application to a joint, as well as self-regulating capabilities by controller-free joule heating. Following device applications, pCBD-adipate homopolymer conductive composite is used to demonstrate disposal routes of poly(cannabinoid)s through mechanical and chemical recycling. Mechanical recycling exhibits high conductivity over multiple cycles but notably diminishes. Chemical recycling achieved through base-catalyzed hydrolysis of the ester bonds is successfully shown to yield cannabidiol monomer after filtration, thereby paving the path towards full circularity of poly(cannabinoid)s.</p>

No / In this study, we have shown how particles in carbon black tattoo ink accumulate in the human skin dermis using fine-resolution atomic force microscopy, with which a single ink particle in the collagenous network can be imaged. This information further demonstrates that tattoo inks are nano-particles. Further, we have deposited a commercially available tattoo ink on a glass slide and calculated a range of volumes for single ink particles.

This Master's project deals with implementation of uC/OS-II real-time operating system on FITkit 3 platform, its testing and proving its functionality with simple examples. Describes an example of uC/OS-II application for displaying images on a E-ink display and application of ECCA method for increasing fault tolerance of the system.

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Low profile, conformal antennas have considerable advantages for Aerospace and Military platforms where conventional antenna system add weight and drag. Direct Write (DW) technology has been earmarked as a potential method for fabricating low profile antennas directly onto structural components. This thesis determines the key design rules and requirements for DW fabrication of planar antennas. From this, three key areas were investigated: the characterisation of DW ink materials for functionality and durability in harsh environments, localised processing of DW inks and the optimisation of DW conductive ink material properties for antenna fabrication. This study mainly focused on established DW technologies such as micro-nozzle and inkjet printing due to their ability to print on conformal surfaces. From initial characterisation studies it was found that silver based micro-nozzle PTF inks had greater adhesion then silver nano-particle inkjet inks but had lower conductivity (2% bulk conductivity of silver as opposed to 8% bulk conductivity). At higher curing temperatures (>300??C) inkjet inks were able to achieve conductivities of 33% bulk conductivity of silver. However, these temperatures were not suitable for processing on temperature sensitive surfaces such as carbon fibre. Durability tests showed that silver PTF inks were able to withstand standard aerospace environments apart from Skydrol immersion. It was found that DW inks should achieve a minimum conductivity of 30% bulk silver to reduce antenna and transmission line losses. Using a localised electroplating process (known as brush plating) it was shown that a copper layer could be deposited onto silver inkjet inks and thermoplastic PTF inks with a copper layer exhibiting a bulk conductivity of 66% bulk copper and 57% bulk copper respectively. This was an improvement on previous electroless plating techniques which reported bulk copper conductivities of 50% whilst also enabling DW inks to be plated without the need for a chemical bath. One of the limitations of many DW ink materials is they require curing or sintering before they become functional. Conventional heat treatment is performed using an oven which is not suitable when processing DW materials onto large structural component. Previous literature has investigated laser curing as means of overcoming this problem. However, lasers are monochromatic and can therefore be inefficient when curing materials that have absorption bands that differ from the laser wavelength. To investigate this, a laser diode system was compared to a broadband spot curing system. In the curing trials it was found that silver inks could be cured with much lower energy density (by a factor of 10) using the broadband white light source. Spectroscopy also revealed that broadband curing could be more advantageous when curing DW dielectric ink materials as these inks absorb at multiple wavelengths but have low heat conductivity. Themodynamical modelling of the curing process with the broadband heat source was also performed. Using this model it was shown that the parameters required to cure the ink with the broadband heat source only caused heat penetration by a few hundred micro-metres into the top surface of the substrate at very short exposure times (~1s). This suggested that this curing method could be used to process the DW inks on temperature sensitive materials without causing any significant damage. Using a combination of the developments made in this thesis the RF properties of the DW inks were measured after broadband curing and copper plating. It was found that the copper plated DW ink tracks gave an equivalent transmission line loss to a copper etched line. To test this further a number of GPS patch antennas were fabricated out of the DW ink materials. Again the copper plated antenna gave similar properties to the copper etched antenna. To demonstrate the printing capabilities of the micro-nozzle system a mock wireless telecommunications antenna was fabricated on to a GRP UAV wing. In this demonstrator a dielectric and conductive antenna pattern was fabricated on to the leading edge of the wing component using a combination of convection curing and laser curing (using an 808nm diode laser).