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The formation and accumulation of ice on surfaces causes failures of industrial devices and facilities as well as domestic appliances. Solving these problems often requires energy-intensive and environmentally unfriendly de-icing methods. In order to eliminate the need for de-icing, passive hydrophobic/icephobic surfaces have been developed in recent years. Icephobic surfaces could be described as surfaces with low ice adhesion, enabling naturally present forces such as gravity or aerodynamic drag to remove the ice layer. Furthermore, a good icephobic surface should minimize ice accretion on the surface as well. Unfortunately, the reliability and durability of currently available icephobic surfaces are extremely limited since our understanding of the physics of icing is incomplete. Designing durable icephobic surfaces remains highly challenging and is currently unresolved. Besides, the complex phase change phenomena occurring at the water-substrate interface during freezing are still not clear, mainly due to a lack of characterization techniques to investigate an optically non-accessible interface: as an example, the mechanism for crack initiation and propagation, which is underpinning ice release from a surface, is poorly understood. As such, novel strategies should be developed that allow to better understand the mechanisms controlling the icing processes and provide new insights into the ice-surface interface. This Master Thesis introduces freezing X-ray Computed Tomography (XCT) as a novel characterization technique. The addition of an in-situ cooling stage, which was developed in-house, paves the way to explore an uncharted territory of icephobicity. While XCT has already been used to study the wettability of, for example, textiles and polymers, without the need for peripheral equipment within the system. Performing XCT in a temperature-controlled environment below 0°C is, however, still very uncommon. In most studies, the focus has only been on the ice entity itself, but, the ice-surface interface has not been thoroughly considered. Freezing XCT can drastically improve the way interfaces between supposedly icephobic surfaces and ice are characterized. Using freezing XCT on a surface with a frozen droplet, information on the three-dimensional shape, interface and internal structure (porosity) can be obtained, both qualitatively and quantitatively. The preliminary results illustrate that ice porosity is surface dependent. Currently, however, there is a gap in the state-of-the-art of anti- and de-icing techniques with regards to ice porosity. This is likely due to the lack of a technique that allows 3D quantitative analysis of porosity and the added complexity of taking porosity into account while modelling. In recent years, the interest in ice porosity and its effects is gradually increasing, indicating that porosity could be of great interest for various applications. Currently, it is shown that porosity influences the mechanical, optical, aerodynamic, and thermal properties of ice and could potentially be used to restore the Cassie-Baxter state, hence the importance of characterizing porosity to obtain a better understanding of the underlying mechanisms controlling ice adhesion. It will not only lead to a more comprehensive and fundamental view on icing but also to the development of novel ways to engineer icephobic coatings. XCT is expected to play a key role by characterizing the internal microstructure of ice droplets.

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This thesis aimed to lay the groundwork of a modeling framework to investigate the influence of the cooling rate on the solid-state nucleation and growth for the β→α transition in pure Ti using the phase-field method. In this work, homogeneous nucleation of α precipitates in a monocrystalline β matrix under a constant cooling rate was studied. Two models are presented: a small-scale nucleation and growth model that is able to study the growth behavior of critically sized nuclei on the nanometer scale, and a large-scale model that is able to study the microstructural evolution during the phase transformation on the micrometer scale. An expression for the α/β interface mobility in pure Ti is obtained based on the Turnbull estimation, and an approach is presented to consider the effect of the size of an α nucleus on the α/β interfacial energy. To account for the high driving forces in the nucleation model, a scaling factor is determined that results in a stable growth of a precipitate in the large-scale phase-field model. The kinetics of the β→α phase transformation according to the developed models is analyzed by means of the JMAK equation and shows good correspondence. The results of the large-scale model regarding the starting temperature of the homogeneous phase transformation in function of the cooling rate show a very good agreement with experimental results for highly pure Ti, and based on these results, the α/β interfacial energy during nucleation can be estimated to be equal to 0.03 J/m². In addition, the model showed that by increasing the cooling rate, the average grain size decreased, which is in good qualitative agreement with results from experimental observations, further indicating the usefulness of the developed model.

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This thesis investigated the manufacturing of calcium phosphate-based bone grafts through binder jetting. Three starting materials (HA, β-TCP, and BAG) were received or synthesized in-house. Prior to printing, spray drying was used to produce spherical spray dried agglomerate powders with enhanced flowability and morphology for layer depositioning. After printing, sintering was performed to consolidate and strengthen the scaffolds. Various characterizations on starting powders and spray dried mixtures were performed. The starting HA powder was phase pure. XRD results show that the as-synthesized β-TCP was actually a mixture of HA (39 wt%) and β-TCP (61 wt%). The BAG starting powder was P2O5-based (65.20 wt%). After spray drying, the particle size distribution was modified. All spray dried mixtures had a particle size distribution between 1-45 μm, except for the spray dried HA which had a wider distribution (1-100 μm). Moreover, spray dried mixtures have a large amount of agglomerates with round shape, which contributes to a better flowability compared to the starting materials. 3 M H3PO4 binder solution was selected because of its high wetting ratio, as determined by wettability testing. However, binder jetting of the spray dried powders using 3 M H3PO4 resulted in poorly bonded structures, due to a too low powder packing density and concomitant less efficient and effective binder deposition. Thermal analysis, including TMA and dilatometry, revealed that the optimum sintering temperature is 1100-1200 ℃ for porous HA and β-TCP containing materials, and 600 ℃ for BAG containing materials. The phase transformation of HA, HA+10 wt% β-TCP, and HA+ 20 wt% β-TCP scaffolds after sintering at 1100℃ for 2 h was analyzed by X-ray diffraction, showing that HA and CaHPO4 phases were present due to the setting reaction between HA and the H3PO4 binder. Key words: Calcium phosphates, Spray drying, Binder jetting, Sintering, Scaffolds

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Cemented carbide products are used in cutting, mining, oil drilling and tunnel boring due to their abrasion resistance, compressive strength, high elastic modulus, thermal shock resistance and wear resistance. Cemented carbides consist of a hard ceramic carbide phase and a soft metal binder. The hard carbide particles provide hardness and wear resistance to the material, while the soft metallic binder provides the toughness needed for the application. The composition of the cemented carbide can be optimised to satisfy all kinds of industrial applications. In this thesis, Niobium carbide, nickel, molybdenum and vanadium carbide powders were mixed in certain ratios and conventional pressureless sintered in the 1300°C-1480°C temperature range. Differential thermal analysis was performed to get the optimal sintering temperature. The microstructure and composition of the sintered cermets were examined by scanning electron microscopy and X-ray diffraction. Electron backscattered diffraction was used to analyze the grain orientation in both phases. Mechanical properties such as hardness, toughness and flexural strength were measured. Finally, the elastic modulus and damping of NbC cermets were measured as a function of temperature and the oxidation behavior of the NbC cermets was investigated. The density of the NbC cermets increased with increasing Ni content and the relative density of the cermets was strongly influenced by the sintering temperature. Fully densified cermets were obtained with a sintering temperature over 1340°C. After liquid phase sintering, both molybdenum and vanadium were more uniformly distributed in the microstructure. The hardness of the NbC cermets decreased with increasing Ni content, whereas the toughness and flexural strength increased. With longer oxidation time, the thickness of the oxide layer on the surface of the NbC cermets increased. The oxide layer thickness of NbC16Ni4Mo4VC changed linearly with oxidation time, whereas the oxide layer thickness of NbC8Ni4Mo4VC parabolically evolved with oxidation time. The Young’s modulus decreased with increasing temperature while the change in the damping curve as function of temperature revealed the onset of plastic deformation of the cermet materials.

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Nowadays, energy shortage has been an important issue in the world. Thermoelectric (TE) materials which can transfer temperature difference to electricity or vice versa have been addressed a lot of attention because of its potential for sustainability. The application of TE materials can also alleviate the demand for fossils. Bi2Te3 is one of the most commercial TE materials. Bi2Te3 with 3wt% excess Te is n-type and can switch to p-type by laser-induced Te evaporation via 3D Selective Laser Sintering (SLS) printing which is a technology of additive manufacturing (AM) and can minimize the waste. In this research, a printable film was prepared via blade coating with precise control of thickness, since green material thickness also has an impact on Seebeck coefficient. We found that TE performances are strong related to the laser power. With stronger power, samples have the trend to become more p-type. Through post treatments, including pre-sintering, cold pressing and post sintering, TE performances were further enhanced. The samples were also encapsulated with PDMS layer to achieve the flexibility. Young’s modulus of PDMS with different mixing ratio were obtained by tensile test.