Ceria based materials have attracted a great deal of interest particularly in area of UV shielding, oxide ion conductivity, solid state electrolyte for fuel cells, automotive exhaust catalysis, water gas shift (WGS) reaction catalysis and also in thermo-chemical water splitting cycles to generate hydrogen. Therefore great deal of efforts was devoted to synthesize nanocrystalline ceria and related materials with different shape and sizes. For example, hierarchically mesostructured doped CeO2 showed potential photvoltic response for solar cell applications. Substitution of lower valent metal ions (Ca2+, Gd3+, Tb3+, Sm3+) in CeO2 enhances oxide ion conductivity for solid oxide fuel cell applications. Eventhough ZrO2 is a nonreducible oxide, CeO2-ZrO2 solid solution has attracted a lot of attention in exhaust catalysis because it exhibited high oxygen storage capacity (OSC). Noble metal ion (M = Pt4+/2+, Au3+, Rh3+, Pd2+ and Ag+) substituted CeO2 (Ce1-xMxO2-δ and Ti1-xMxO2-δ, x = 0.01-0.03) prepared by solution combustion method have shown much higher three-way catalytic property compared same amount of noble metal impregnated to CeO2. Ionically substituted Pt and Au in CeO2 also showed high WGS activity. CeO2-MOx (M= Mn, Fe, Cu, Ni) mixed oxides have shown high activity for hydrogen generation by thermal splitting of water. In chapter 1, we have discussed recent developments on various synthesis strategies of ceria based materials for specific catalytic application. In this thesis, we have explored new route to synthesize Ce1-xMxO2-δ and Ti1-xMxO2-δ (M = transition metal, noble metal) nanocrystallites. Specifically we have addressed the effect of reducible metal ion substitution on the OSC of CeO2 for auto exhaust treatment, hydrogen generation and electro-chemical applications. Controlled synthesis of CeO2 and Ce1-xMxO2-δ (M = Zr, Ti, Y, Pr and Fe) nanocrystallites by hydrothermal method is presented in Chapter 2. The method is based on complexation of metal ion by diethylenetriamine (DETA) or melamine and the simultaneous hydrolysis of metal ion complexes in hydrothermal condition. Size of the crystallites can be controlled by varying the time and temperature of the reaction. 15% Fe3+ ion substituted CeO2 (Ce0.85Fe0.15O2-δ) nanocrystallites have shown higher oxygen storage capacity than Ce0.5Zr0.5O2 at lower temperature. A brief description of material characterization techniques such as powder X-ray diffraction (XRD) and Rietveld refinement of structure, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) is presented. The home-built hydrogen uptake measurement system for OSC study and temperature programmed catalytic reaction system with a quadrupole mass spectrometer and an on-line gas-chromatograph for gas analysis is also described in this chapter. In chapter 3, hydrothermal synthesis of Ce1-xCrxO2+δ (0≤x≤1/3) nanocrystallites is presented. Up to 33% Cr ion substitution in CeO2 could be achieved only by the complexation of Ce(NH4)2(NO3)6 and CrO3 with DETA and simultaneous hydrolysis of the complexes in hydrothermal condition at 200 oC. Powder XRD, XPS and TEM studies confirm that the compound crystallizes in cubic fluorite structure where Ce exist in +4 oxidation state and Cr exist in 4+ and +6 (mixed valance) oxidation states in the ratio of 2: 1. Composition x = 0.33 (Ce2/3Cr1/3O2+δ) showed higher OSC (0.33 mol of [O]) than the maximum OSC observed for CeO2-ZrO2 solid solutions. Formation and higher OSC of Ce2/3Cr1/3O2+δ is attributed to interaction of Ce4+/3+ and Cr3+/4+/6+ redox couples in fluorite structure. The material shows oxygen evolution at ~400 oC in air and hence it is a true oxygen storage material. Oxygen evolution property of Ce0.67Cr0.33O2.11 and subsequent generation of hydrogen by thermal splitting of water is presented in chapter 4. Among the ceria based oxides, Ce0.67Cr0.33O2.11 being the only compound like UO2+δ to have excess oxygen possessing fluorite structure, it releases a large proportion of its lattice oxygen (0.167 M [O]/mole of compound) by heating the material under N2 flow at relatively low temperature (465 oC) directly and almost stoichiometric amount of H2 (0.152 M/Mol of compound) is generated at much lower temperature (65 oC) by thermosplitting of water. The reversible nature of oxygen release and intake of this material is attributed to its fluorite structure and internal coupling between the Ce4+/Ce3+ and Cr4+/6+/Cr3+ redox couples. In chapter 5, we present the hydrothermal synthesis and three-way catalytic activity of Ce1-xRuxO2-δ (0≤x≤0.1) nanocrystallites. Powder XRD, Rietveld refinement, TEM and XPS reveals that the compounds crystallized in fluorite structure where Ru exist in +4 state and Ce in mixed valent (+3, +4) state. Substitution of Ru4+ ion in CeO2 activated the lattice oxygen and Ce0.9Ru0.1O2-δ can reversibly releases 0.42[O]/mol of compound, which is higher than maximum OSC of 0.22 [O]/mol of compound observed for Ce0.50Zr0.50O2. Utilization of higher OSC of Ce1-xRuxO2-δ (x = 0.05 and 0.10) is also shown by low temperature CO oxidation with these catalysts, both in presence/absence of feed oxygen. Ru4+ ion act as active centre for reducing molecules (CO, hydrocarbon ‘HC’) and oxide ion vacancy acts as an active centre for O2 and NOx in this compound. Ce1-xRuxO2-δ not only act as a high oxygen storage material but it also shows high activity towards CO, hydrocarbon ‘HC’ oxidation and NO reduction by CO at low temperature with high N2 selectivity for 3-way catalysis. Study of water gas shift reaction over Ce0.95Ru0.05O2-δ catalyst is presented in chapter 6. The catalyst showed very high WGS activity in terms of high conversion rate (20.5 μmol.g-1.s-1 at 275 oC) and low activation energy (~50.6 kcal/mol). The reason for this seems to be high adsorption propensity of CO on Ru4+ ion and easy extraction of oxygen from lattice to form CO2. This step creates oxide ion vacancy in the catalyst lattice and H2O can adsorb on lattice sites oxygen vacancy and regenerate the lattice by releasing H2. Even in presence of externally fed CO2 and H2, complete conversion of CO to CO2 was observed with 100 % H2 selectivity with Ce0.95Ru0.05O2-δcatalyst in the temperature range of 305-385 oC and no trace of methane formation was observed in this temperature range. Catalyst does not deactivate in long duration on/off WGS reaction cycle because sintering of noble metal or active sites is avoided in this catalyst as Ru4+ ion is substituted in CeO2 lattice. Due to highly acidic nature of Ru4+ ion, surface carbonated formation is prohibited. In chapter 7, synthesis of Ce1-xFexO2-δ (0≤x≤0.45) and Ce0.65Fe0.33Pd0.02O2-δnanocrystallites is presented by sonochemical method. Powder XRD, XPS and TEM studies confirm that the compounds of ~4 nm sizes is crystallized in fluorite structure where Fe is in +3, Ce is in +4 and Pd is in +2 oxidation state. Due to substitution of smaller Fe3+ ion in CeO2, lattice oxygen is activated and Ce0.67Fe0.33O1.835 reversibly releases 0.31[O] up to 600 oC which is higher or comparable to the maximum OSC observed for CeO2-ZrO2 based solid solutions. Due to internal interaction of Pd2+/0(0.89 V), Fe3+/2+ (0.77 V) with Ce4+/3+ (1.61 V) redox couples, Pd ion accelerates the electron transfer from Fe2+ to Ce4+ in Ce0.65Fe0.33Pd0.02O1.815, making it a high oxygen storage material as well as highly active catalyst for CO oxidation and WGS reaction. Activation energy for CO oxidation with O2 over Ce0.65Fe0.33Pd0.02O1.815 is found as low as 38 kJ/mol. CO conversion to CO2 is 100% H2 specific in WGS reaction with these catalysts. Conversion rate was found as high 27.2 μmol.g-1.s-1 and activation energy was found 46.4 kJ/mol for Ce0.65Fe0.33Pd0.02O1.815. Only 1-3% Pt, Pd ion can be substituted in CeO2 is by the solution combustion method. We show that even up to 10% of Pt and Pd ion can be substituted in CeO2 by sonication method. In chapter 8, we present the sonochemical synthesis redox property and methanol electro-oxidation activity of hierarchical Ce1-xMxO2-δ (M = Pt and Pd, 0≤x≤0.1) nanocrystallites. Powder XRD, TEM, SEM and XPS study confirms that hierarchical structure compound crystallize in fluorite structure. Pt exists in +4 state and Ce in mixed valent (+3, +4) state in Ce1-xPtxO2-δ and Pd exist in +2 state and Ce in mixed valent (+3, +4) state in Ce1-xPdxO2-δ. Substitution of Pt and Pd ion in CeO2 activated the lattice oxygen. Hydrogen absorption study show higher H/Pt ratio ~8.1 and H/Pd ratio ~4.2 in respective oxides. Reversible nature of higher oxygen storage capacity or higher H/P, H/Pd ratio is due to interaction of redox couples of Pt4+/2+(0.91V), Pt2+/0(1.18V), Pd2+/0(0.92V) and Ce4+/3+(1.61V). Due to participation of lattice oxygen, Ce0.95Pt0.05O1.95 and Ce0.95Pd0.05O1.90 have shown higher electro-oxidation of methanol compared to same moles of Pt in 5%Pt/C. In chapter 9, we present sonochemical synthesis of Ti1-xPtxO2 (0≤x≤0.1) nanocrystallites: a new high capacity anode material for rechargeable Li ion battery. Continuing our interest in synthesis of nanomaterials, we thought if we can extend the same sonochemical method to synthesize metal ion doped TiO2. Doping of TiO2 with a suitable metal ion where dopant redox potential couples with that of titanium (Ti4+) and act as catalyst for additional reduction of Ti4+ to Ti2+ (Ti4+ →Ti3+→Ti2+) is envisaged here to enhance lithium storage even higher than one Li/TiO2. 10 atom % Pt ion substituted TiO2, Ti0.9Pt0.1O2 nanocrystallites of ~4 nm size was synthesized by sonochemical method using diethylenetriamine (DETA) as complexing agent. Powder XRD, Rietveld refinement, TEM and XPS studies reveal that Ti0.9Pt0.1O2 nanocrystallites crystallize in anatase structure and both Ti and Pt are in 4+ oxidation state. Due to Pt4+ ion substitution in TiO2, reducibility of TiO2 was enhanced and Ti4+ was reduced up to Ti2+ state via coupling of Pt states (Pt4+/Pt2+/Pt0) with Ti states (Ti4+/Ti3+/Ti2+). Galvanostatic cycling of Ti0.9Pt0.1O2 against lithium showed very high capacity of 430 mAhg-1 or exchange of ~1.5Li/Ti0.9Pt0.1O2 which is much higher than the highest capacity of 305 mAhg-1 or insertion of ~0.9Li/TiO2 achieved for TiO2(B) nanowires. In chapter 10, we present the conclusions and critical review on the study of transition metal and noble metal ion substituted CeO2 and TiO2.

<p>Applications of Aluminum (Al) alloys in harsh environments involving high stress and high temperatures are often hindered because of their inherently low strength and poor performance at high temperatures. The strongest commercial Al alloys reported up to date have a maximum strength less than 700 MPa. Although ultrafine grained Al alloys prepared by severe plastic deformation have higher strength, they encounter grain growth at moderate temperatures. </p> <p>This thesis focuses on adopting transition metal solutes and non-equilibrium approach to fabricate high-strength, thermally stable nanotwinned Al alloys. To understand the underlying deformation mechanisms of nanotwinned Al alloys, <i>in-situ</i> micromechanical tests, high resolution and analytical transmission microscopy and atomistic simulations were used. Our studies show that nanotwinned supersaturated Al-Fe alloys have a maximum hardness and flow stress of ~ 5.5 GPa and 1.6 GPa, respectively. The apparent directionality of the vertical incoherent twin boundaries renders plastic anisotropy and compression-tension asymmetry in the nanotwinned Al-Fe alloys, revealed by systematic <i>in-situ</i> tensile and compressive micromechanical experiments conducted from both in-plane and out-of-plane directions. Moreover, the nanotwinned Al-Fe alloys experience no apparent softening when tested at 200 °C. When selectively incorporating with one additional solute as stabilizer, the ternary nanotwinned Al alloys can preserve an exceptionally high flow stress, exceeding 2 GPa, prior to precipitous softening at an annealing temperature of > 400 °C. The thesis offers a new perspective to the design of future strong, deformable and thermally stable nanostructured Al alloys. </p>

This thesis deals with an introduction to the theory of switching power supplies and with properties of magnetic materials. Special attention is paid to nanocrystalline materials. It also discusses the issues of simulating the behavior of ferromagnets. The properties of commonly used ferrite material and nanocrystalline materials was measured. Using the created program for the design of forward converter is designed a switching power supply to verify its proposal. Design optimization is based on using a nanocrystalline core, which allows to reduce the operating frequency.

Nanocrystalline diamond (NCD) films possess great mechanical properties (low friction coefficient, high hardness etc.), chemical properties (e.g. low corrosivity or chemical inertness) and good biocompatibility. This makes them perspective materials for protective coatings of medical implants and devices. As bacteria biofilms are often very resistant to antibacterial treatment, materials with anti-bacterial or at least anti-adhesive properties are needed. The interaction of NCD films with bacteria has not been properly examined yet. The aim of this thesis was to introduce and optimize the methods for routine bacterial biofilm cultivation and analysis, use them to investigate the ability of NCD films to inhibit the attachment and biofilm formation of Escherichia coli and correlate it with the NCD surface hydrophobicity. The materials used for the study were hydrogenated NCD (hydrophobic), oxidized NCD (hydrophilic) and uncoated glass. For bacterial biofilm growth, cultivation in six-well plates and continuous cultivation in CDC Bioreactor was used. Several methods were tested for quantitative biofilm detachment and analysis. The putative anti-bacterial properties of NCD material were not confirmed in this work. Higher bacterial attachment to NCD films in comparison to the uncoated glass was...

Im quaternären System Erdalkalimetall-Silicium-Chlor-Wasserstoff bildet sich bei der Umsetzung des Metalls mit einer SiCl4-H2-Atmosphäre eine quaternäre Phase. Diese metastabile Phase zerfällt beim Abkühlen in das Metallchlorid und Silicium in nanokristalliner Form. Die vorliegende Arbeit hat sich mit der tiefergehenden Charakterisierung der quaternären Phase beschäftigt. Dazu wurden die Eigenschaften des quaternären Systems aus den Eigenschaften der sechs binären und vier ternären Systemen abgeleitet. Die Oberfläche wurde erstmals mit Photoelektronenspektroskopie charakterisiert. Zusätzlich gelang erstmalig die Verfolgung der Bildungsreaktion durch Messung des Spannungsabfalls über das Reaktionssystem. Erste Ansätze zur Aufklärung des Bildungsmechanismus ausgehend von den Ergebnissen der Charakterisierung wurden zusätzlich aufgezeigt.

Damage to the central nervous system (CNS) leads to the generation of an immune response which culminates with the encapsulation of the damaged area. The encapsulation, known as a glial scar, essentially breaks neural signal pathways and blocks signal transmissions to and from the CNS. The effect is the loss of motor and sensory control for the damaged individual. One method that has been used successfully to treat this problem is the use of a brain-machine interface (BMI) which can intercept signals from the brain and use these signals to control a machine. Although there are many types of BMI devices, implantable devices show the greatest promise with the ability to target specific areas of the CNS, with reduced noise levels and faster signal interception, and the fact that they can also be used to send signals to neurons. The largest problem that has plagued this type of BMI device is that the materials that have been used for their construction are not chemically resilient, elicit a negative biological response, or have difficulty functioning for extended periods of time in the harsh body environment. Many of these implantable devices experience catastrophic failure within weeks to months because of these negative factors. New materials must be examined to advance the future utilization of BMI devices to assist people with CNS damage or disease. We have proposed that two semiconductor materials, cubic silicon carbide (3C-SiC) and nanocrystalline diamond (NCD), which should provide solutions to the material biocompatibility problems experienced by implantable BMI devices. We have shown in this study that these two materials show chemical resilience to neuronal cellular processes, and we show evidence which indicates that these materials possess good biocompatibility with neural cell lines that, in the worst case, is comparable to celltreated polystyrene and, in most cases, even surpasses polystyrene. We have utilized 3C-SiC within an electrode device and activated the action potential of differentiated PC12 cells. This work details our initial efforts to modify the surfaces of these materials in order to improve cellular interaction and biocompatibility, and we examine our current and future work on improving our implantable BMI devices.

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<p>This research study has been devoted to the study of magnetic properties and magnetic transport of nanocrystalline Ni and Ni-15% Fe alloys consisting of randomly oriented grains with an average size of 23 and 12 (nm), respectively. The structures of the deposits were confirmed by the XRD analysis using Rietveld refinement technique. The as-deposited Ni and Ni-15%Fe sample was comprised exclusively of the γ phase with lattice parameter of 3.5270 (nm) and 3.5424 (nm), respectively. The small increase in lattice parameter was attributed to the replacement of iron solutes in the Ni sites in lattice. Texture analysis of nanocrystalline Ni and Ni-15%Fe revealed that textures components of both materials is qualitatively the same and vary in terms of volume fraction. Both material showed strong <100> fibre texture with some contribution of the <111> component. The calculated volume fraction of the <100> and <111> components were respectively 17.157% and 3.201% for Ni and, 22.032% and 6.160% for Ni-15%Fe and the rest being confined to the random texture.</p> <p>Magnetic measurements show that all samples exhibit low loss hysteresis loops with high permeabilities. The presence of 15%Fe in Ni leads to enhancement of the saturation magnetization (M_s) regardless of the direction of the applied field. M_s shows an increase from 60.169 (emu/gr) in nanocrystalline Ni to 93.67 (emu/gr) in Ni-15%Fe sample at T=2K. No strong temperature–dependence of the magnetization was observed for samples, but the magnetization of the Ni-15%Fe samples at T=2K were slightly higher than that of T=298K. The coercivity values of nanocrystalline Ni-15%Fe were in all cases smaller than that of nanocrystalline Ni samples. Good agreement between random anisotropy model (RAM) theory and experiment for nanocrystalline Ni and Ni-15%Fe samples was observed. The ferromagnetic exchange length (L_ex) was larger than the average grain size (D) for samples at all times. The effective magnetic anisotropy constants (K_eff) of the nanocrystalline Ni and Ni-15%Fe alloys were measured using the law of approach to saturation. At T=2K, the K_eff of Ni-15%Fe samples were measured to be 1.7037´10⁵ (erg/cm³) and 2.71996 ´10⁵ (erg/cm³) at field parallel and perpendicular, respectively. These values were almost half of the values obtained for nanocrystalline Ni samples 4.66091´10⁵ (erg/cm³) and 4.19703´10⁵ (erg/cm³). Temperature dependence measurements showed that K_eff constants decrease with increasing temperature. The angular dependence MR studies on nanocrystalline Ni and Ni-15%Fe resulted in a twofold, and a fourfold symmetric behaviour, respectively. The field dependence MR measured at various sample tilt with respect to the applied field, showed various trends from pure positive MR to pure negative MR, which partially could be explained by magnetocrystalline anisotropy of the samples.</p> / Master of Applied Science (MASc)