abstract: Nanostructured zeolites, in particular nanocrystalline zeolites, are of great interest due to their efficient use in conventional catalysis, separations, and emerging applications. Despite the recent advances, fewer than 20 zeolite framework types have been synthesized in the form of nanocrystallites and their scalable synthesis has yet to be developed and understood. Geopolymers, claimed to be “amorphous cousins of zeolites”, are a class of ceramic-like aluminosilicate materials with prominent application in construction due to their unique chemical and mechanical properties. Despite the monolith form, geopolymers are fundamentally nanostructured materials and contain zeolite nanocrystallites. Herein, a new cost-effective and scalable synthesis of various types of nanocrystalline zeolites based on geopolymer chemistry is presented. The study includes the synthesis of highly crystalline discrete nanorods of a CAN zeolite framework structure that had not been achieved hitherto, the exploration of the Na−Al−Si−H2O kinetic phase diagram of hydrogels that gives SOD, CAN and FAU nanocrystalline zeolites, and the discovery of a unique formation mechanism of highly crystalline nanostructured FAU zeolite with intermediate gel products that possess an unprecedented uniform distribution of elements. This study demonstrated the possibility of using high-concentration hydrogels for the synthesis of nanocrystalline zeolites of additional framework structures. Moreover, a comprehensive study on nanostructured FAU zeolites ion-exchanged with Ag+, Zn2+, Cu2+ and Fe2+ for antibacterial applications is presented, which comprises metal ion release kinetics, antibacterial properties, and cytotoxicity. For the first time, superior metal ion release performance was confirmed for the nanostructured zeolites compared to their micron-sized counterparts. The metal ion-exchanged FAU nanostructured zeolites were established as new effective antibacterial materials featuring their unique physiochemical, antibacterial, and cytotoxic properties. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2019

Nanodiamond is currently one of the most researched materials in the field of regenerative medicine in the study of treatment of neurodegenerative diseases. Due to direct interaction of this material with nerve tissue, it needs to be biocompatible with primary neurons. Furthemore, it is desirable for the used material to induce cell adhesion and stimulate the adherent cells to regeneration. This work evaluates the biocompatibility of porous boron-doped diamond layers with the culture of primary neurons. We compared the effect of diamond surface treatment by poly- D-lysine (PDL) coating on the adhesion and prosperity of the primary neuronal culture. We found that the tested nanodiamond layers are biocompatible with the primary neuronal culture. We further conclude that the PDL coating slightly increases the rate of cell adhesion to the surface but on the other hand induces greater adhesion of glial cells than the surface without PDL coating. Key words: nanodiamond, biocompatibility, adhesion, neurons

MCrAlY coatings are commonly applied as the bond coat in TBCs used in modern gas turbines. Cold spray (or CS), characterized by low process temperature and high particle impact velocity, has been demonstrated as a promising alternative to thermal spray processes, such as air plasma spray (APS) and high velocity oxygen fuel (HVOF), for manufacturing MCrAlY coatings. The general objective of the thesis research is to characterize CS deposition on a single-crystal nickel-base superalloy and to develop low-cost/high-performance NiCoCrAlTaY coatings using the CS technique. Several individual studies were carried out with each having a specific focus towards achieving the general research objective. CS deposition of NiCoCrAlTaY coatings using nitrogen was first examined to verify the feasibility of replacing the expensive helium gas typically used as the CS process gas. Several materials were used as the substrates, and the effects of substrate materials and surface preparation on coating microstructure and properties were investigated. Recycling of non-deposited powder particles was then explored to reduce the costs associated with the feedstock powder. A cost model that includes the economics of powder recycling was developed for the CS process, showing that the use of nitrogen and powder recycling could potentially be cost-effective for CS deposition of MCrAlY coatings. A CS process that can produce in-situ nanocrystalline NiCoCrAlTaY coatings was proposed to develop coatings with enhanced oxidation performance. This CS approach utilizes conventional commercial powders instead of pre-milled nanocrystalline powders. Detailed characterization using the scanning electron microscope (SEM), scanning transmission electron microscope (STEM), and X-ray diffraction (XRD) was carried out to investigate the microstructure of the resulting CS NiCoCrAlTaY coatings, single-crystal substrate, and their interface. Isothermal oxidation performance of the CS NiCoCrAlTaY coatings was evaluated at 1100°C for 1h to 500h. Results revealed that the nanostructure promoted the α-Al2O3 scale formation and sustained α-Al2O3 scale growth, suggesting good isothermal oxidation performance. Finally, the effects of different processing sequences on CS NiCoCrAlTaY coating characteristics and short-term isothermal oxidation performance were investigated. Specifically, CS deposition of NiCoCrAlTaY coatings was carried out on single-crystal superalloy substrates that underwent various degrees of full heat treatments prior to being coated. The remaining superalloy heat treatments required were then performed on the coated samples after the CS deposition. The microstructures of the superalloy substrates and CS NiCoCrAlTaY coatings were characterized after each heat treatment. Isothermal oxidation performance of the coated samples following different sequences was evaluated at 1100°C for 2 hours. The results suggested a promising processing sequence that could potentially further improve the oxidation performance of CS NiCoCrAlTaY coatings.

<p>  </p> <p>Materials performance under extreme conditions is pivotal to the design of advanced nuclear reactor materials. Nanocrystalline metals possess improved radiation resistance and superior mechanical properties. However, it remains a major challenge to stabilize the fine grains in nanocrystalline materials at elevated temperatures. The response of abundant interfaces and triple junctions to thermal annealing, plastic straining and radiation damage profoundly influence the overall performance of nanocrystalline metals. The objective of this thesis is to illustrate a new alloy design strategy via engineering the interfaces and triple junctions of triphase nanocomposites to enhance the thermal stability, mechanical strength and radiation tolerance of nanocrystalline metallic materials simultaneously. </p> <p>In triphase nanocomposites where each phase is nearly immiscible to the others, the triple junctions and phase boundaries form a 3D interlocking network that could significantly increase the thermal and radiation stability. In this thesis, two distinct triphase architectures were explored: nanolaminate and nanocrystalline Cu-Ag-Fe composites fabricated by magnetron sputtering. The effectiveness of Cu-Ag-Fe triphase triple junctions in mitigating thermal grooving was evaluated by considering grooving kinetics. Additionally, micropillar compression tests on Cu-Ag-Fe nanolaminate composites demonstrated substantial enhancement of strength and strain hardening capability comparing to Cu/Fe multilayers. The nanocrystalline Cu-Ag-Fe composites exhibited a distinct texture evolution and greatly enhanced resistance to grain coarsening. In situ sequential dual beam (He + Kr) irradiation studies show nanocrystalline Cu-Ag-Fe composites have a remarkable bubble swelling resistance, suggesting the strong He storage and defect annihilation capability of the triphase nanocomposites. The results obtained from this thesis provide innovative perspectives on the design of high strength nanostructured metals with enhanced thermal stability and radiation tolerance.</p>

Titania (Titanium dioxide, TiO2) has been researched as a promising biomaterial due to its excellent biocompatibility. However, the main limitation of titania is its poor mechanical properties which limit its use in many load-bearing applications. In this thesis report, the properties of titania were improved by doping with small quantities of MgO, ZnO and SiO2 as sintering additives. Nanocrystalline powder was selected, as it possesses outstanding properties over conventional coarse-grained powders due to reduced grain size. Nanocrystalline anatase powder of size 5-15 nm was synthesized via a simple sol-gel technique. Small quantities of dopants were introduced into pure titania powder, through homogeneous mixing. The doped powder compositions were compacted uniaxially and sintered at 1300°C and 1500°C, separately, in air. The effects of sintering cycle and temperature on the microstructure, densification and mechanical properties of the sintered structures were studied. Mg doped structures recorded maximum sintered density of 3.87 g.cm-3. Phase analysis was carried out using powder XRD technique using Cu K[alpha] radiation. Microstructural analysis was performed using Scanning electron microscopy. The mechanical properties were assessed by evaluating hardness and biaxial flexural strength (ASTM F-394) of the structures. Results showed 12% increase in hardness and 18% increase in biaxial flexural strength in structures doped with ZnO and SiO2, respectively. Further, simulated body fluid maintained at 36.5°C was used to study the bioactivity and degradation behavior of the structures. The second part of the work aimed in the processing of porous titania scaffolds using polyethylene glycol as the pore-former. The green structures were sintered at 1400°C and 1500°C, separately in air and their properties have been studied. Microstructural analysis was carried out using Scanning electron microscope (SEM). Porosity was evaluated using the immersion technique. Vickers hardness and biaxial flexural tests were used to carry out the mechanical characterization. Further, the biomechanical/biodegradation behavior of the structures was assessed in simulated body fluid (SBF). Biodegradation and change in biomechanical properties as a function of time were studied in terms of weight change, change in Vickers hardness and biaxial flexural strength. The mechanical properties of porous titania scaffolds doped separately with MgO and ZnO have also been studied to investigate the influence of these additives on the properties of porous structures. The Vickers hardness and biaxial flexural strength were seen to improve with the addition of these sintering additives.

Yes / Heat-treatment is a frequently used technique for modifying the physical and chemical properties of materials. In this study, the effect of heat-treatment on the mechanical properties, thermal stability and surface morphology of two types of electrodeposited coatings (pure-Ni and Ni/Al2O3) were investigated. The XRD analyses showed that the crystal structure of the as-deposited coating changes from slightly amorphous to crystalline as the heat-treatment temperature increases. The heat-treatment of both the pure-Ni and the Ni/Al2O3 coating caused an increase of the grain size within the coatings. However, the unreinforced Ni coating experienced a faster growth rate than the Ni/Al2O3 coating, which resulted in a larger average grain size. The temperature-driven changes to the microstructure of the coatings caused a reduction in the hardness and wear resistance of the coatings. The presence of nanoparticles within the Ni/Al2O3 coating can successfully extend the operational temperature range of the coating to 473 K by pinning grain boundaries.

Yes / High-dose API powders which are to be tableted by direct compression should have high compactibility and compressibility. This note reports on a novel approach to the manufacture of crystalline powders intended for direct compaction with improved compactibility and compressibility properties. The poorly compactable API, chlorothiazide, was spray dried from a water/acetone solvent mix producing additive-free nanocrystalline microparticles (NCMPs) of median particle size 3.5 μm. Tablets compacted from NCMPs had tensile strengths ranging from 0.5 to 4.6 MPa (compared to 0.6–0.9 MPa for tablets of micronised CTZ) at compression forces ranging from 6 kN to 13 kN. NCMP tablets also had high porosities (34–20%) and large specific surface areas (4.4–4.8 m2/g). The time taken for tablets made of NCMPs to erode was not statistically longer (p > 0.05) than for tablets made of micronised CTZ. Fragmentation of NCMPs on compression was observed. The volume fraction of particles below 1 μm present in the suspension recovered after erosion of NCMP tablets was 34.8 ± 3.43%, while no nanosized particles were detected in the slurry after erosion of compacted micronised CTZ. / Solid State Pharmaceutical Cluster (SSPC), supported by Science Foundation Ireland under grant number 07/SRC/B1158.

In this thesis, novel bulk Al-based alloys with high content of Al have been produced by powder metallurgy methods from amorphous and partially amorphous materials. Different processing routes, i.e. mechanical alloying of elemental powder mixtures, controlled pulverization of melt-spun glassy ribbons and gas atomization, have been employed for the production of the Al-based powders. Among the different processing routes, gas atomization is the best choice for the production of Al-based amorphous and partially amorphous powders as precursors for the subsequent consolidation step because it allows the production of large quantities of powders with homogeneous properties (e.g. structure and thermal stability) along with a uniform size distribution of particles. Amorphous and nanocrystalline powders have to be consolidated to achieve dense bulk specimens. However, consolidation of these phases is not an easy task and special care has to be taken with respect to accurate control of the consolidation parameters in order to achieve dense bulk specimens without inducing undesirable microstructural transformations (e.g. crystallization and grain coarsening) or insufficient particle bonding. Consequently, the effect of temperature on viscosity as well as on phase formation has been studied in detail in order to select the proper consolidation parameters. Following their characterization, the Al-based powders have been consolidated into bulk specimens by hot pressing (HP), hot extrusion and spark plasma sintering (SPS) and their microstructure and mechanical properties have been extensively investigated. Consolidation into highly-dense bulk samples cannot be achieved without extended crystallization of the glassy precursors. Nevertheless, partial or full crystallization during consolidation leads to remarkable mechanical properties. For example, HP Al84Gd6Ni7Co3 samples display a remarkably high strength of about 1500 MPa, which is three times larger than the conventional high-strength Al-based alloys, along with a limited but distinct plastic deformability (3.5 – 4%). Lower strength (930 MPa) but remarkably larger plastic strain exceeding 25 % has been achieved for the Al87Ni8La5 gas-atomized powders consolidated by SPS above their crystallization temperature. Similarly, HP Al90.4Y4.4Ni4.3Co0.9 bulk samples display high compression strength ranging between 820 and 925 MPa combined with plastic strain in the range 14 – 30%. Finally, preliminary tensile tests for the Al90.4Y4.3Ni4.4Co0.9 alloy reveal promising tensile properties comparable to commercial high-strength Al-based alloys. The mechanical behavior of the consolidated specimens is strictly linked with their microstructure. High strength and reduced plasticity are observed when a residual amorphous phase is present. On the other hand, reduced strength but enhanced plastic deformation is a result of the complete crystallization of the glass and of the formation of a partially or fully interconnected network of deformable fcc Al. These results indicate that the combined devitrification and consolidation of glassy precursors is a particularly suitable method for the production of Al-based materials characterized by high strength combined with considerable plastic strain. Through this method, the mechanical properties of the consolidated samples can be varied within a wide range of strength and ductility depending on the microstructure and the consolidation techniques used. This might open a new route for the development of innovative high-performance Al-based materials for transport applications.

The main objective of this thesis is to obtain critical insight on the role of crystalline incompatibilities in strain and curvature, induced in presence of line defects i.e. dislocations and disclinations, on the energy and geometry of specific features of the local microstructure, and on the bulk mechanical response of nanocrystalline/ultra-fine grained materials. To that end, studies are performed at the (1) inter-atomic and fine scale, and (2) at the mesoscale. The modelling approach is based on the field dislocation and disclination mechanics theory of continuously representated dislocations and disclinations. New, thermodynamically rigorous, multi-scale elastic constitutive laws based on the couple stress theory are developed to capture the effect of strain and curvature incompatibilities on the Cauchy and couple stresses. A new meso-scale elasto-viscoplastic constitutive model of defect incompatibilities based on a fast Fourier transform technique is developed. The desired scale transitioning is achieved via novel phenomenological defect density transport equations and the newly developed elastic constitutive laws. At the fine scale, the model is applied to study energetic interactions between strain and curvature incompatibilities associated with grain boundaries and their influence on triple line energies. Results reveal that incompatible lattice strains have the most significant contribution to the energy. Incompatible lattice curvatures have negligible energetic contributions but are necessary to characterize the geometry of grain boundaries. Finally, both incompatible lattice strains and curvatures are necessary to capture the structure sensitive mechanical behavior of grain boundaries. At the mesoscale, deformation of nanocrystalline aggregates characterized by residual curvatures is studied to identify the impact of the latter's presence on the local and bulk mechanical response of the aggregate. Relaxation of local stresses generated from residual curvatures reproduces the effect of GB dislocation emission. Uniaxial tensile loading of nanocrystalline microstructures containing residual curvatures reveals a softening in the yield stress which could explain the breakdown in Hall-Petch law in the nanocrystalline regime. Next, the possibility of characterizing incompatibilities using X-ray or neutron diffraction techniques is tested. Results reveal that only strains and their gradients contribute to the broadening of diffraction peaks; curvatures and their gradients have no contribution. This study leads to the development of a new multi-scale averaged strain based Fourier technique for generating virtual diffraction peaks.

A better understanding of how the nanoscale environment affects the mechanical properties of materials, in particular metallic nanoparticles and nanocrystalline metals is vital to the development of next generation materials. Of special interest is obtaining a fundamental understanding of the inverse Hall-Petch Effect in nanocrystalline metals, and nanoindentation in individual nanoparticles. Understanding these subjects is critical to understanding how the mechanical properties of materials are fundamentally affected by nanoscale dimensions. These topics have been addressed by a combination of theoretical modeling and in-situ nanoindentation transmission electron microscopy (TEM) analysis. Specifically, the study of the inverse Hall-Petch effect in nanocrystalline metals will be investigated by a thorough review of the literature followed by a proposed novel theoretical model that better explains the experimentally observed behavior of nanocrystalline metals. On the other hand, the nanoindentation of individual nanoparticles is a very new research topic that has yet to aggregate a large body of experimental data. In this context, in-situ TEM nanoindentation experiments on silver nanoparticles will be first performed to determine the mechanisms of deformation in these nanostructures. A theoretical explanation for the observed deformation mechanisms will be then developed and its implications will be discussed. In addition to nanoparticles, this study will also provide unique and valuable insight into the deformation mechanisms of nanopillars, a growing area of research despite much controversy and speculation about their actual mechanisms of deformation. After studying the novel behavior of both nanocrystalline metals and nanoparticles, useful applications of both classes of materials will be explored. The discussion of applications will focus on utilizing the interesting behaviors explored in the dissertation. Of particular interest will be applications of nanoparticles and nanocrystalline materials to coatings, radiation resistance and super-plastic materials. / text