The project synthesizes phase pure Yttria particles using flame spray pyrolysis, and to experimentally determines the effect of various process parameters like residence time, adiabatic flame temperature and precursor droplet size on the phase of Yttria particles generated. Further, through experimentation and based on the understanding of the process, conditions that produce pure monoclinic Y2O3 particles were found. An ultrasonic atomization set-up was used to introduce precursor droplets (aqueous solution of yttrium nitrate hex hydrate) into the flame. A hydrogen-oxygen diffusion flame was used to realize the high temperature aerosol synthesis. The particles were collected on filters and analyzed using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Individual process parameters (flame temperature, residence time, precursor concentration, precursor droplet size) were varied in continuous trials, keeping the rest of the parameters constant. The effect of the varied parameter on the phase of the product Yttria particles was then analyzed. Pre-flame heating was undertaken using a nozzle heater at variable power. Precursor solution concentrations of 0.026 mol/L, 0.26 mol/L, and 0.65 mol/L were used. Residence time was varied by means of burner diameter (9.5 mm and 1.6 mm ID). Large precursor droplets were removed by means of an inertial impactor. The higher flame temperatures and precursor heating favor the formation of monoclinic yttrium oxide. The fraction of the cubic phase is closely related to the particle diameter. All particles larger than a critical size were of the cubic phase. Phase pure monoclinic yttrium oxide particles were successfully synthesized. The end conditions included a precursor concentration of 0.65 mol/L, a pure hydrogen-oxygen flame and a 1.6 mm burner. The precursor droplets entrained fuel gas was passed through a round jet impactor and preheated at full power (130 VA). The particles synthesized were in the size range of 0.350 to 1.7 µm.

The project synthesizes phase pure Yttria particles using flame spray pyrolysis, and to experimentally determines the effect of various process parameters like residence time, adiabatic flame temperature and precursor droplet size on the phase of Yttria particles generated. Further, through experimentation and based on the understanding of the process, conditions that produce pure monoclinic Y2O3 particles were found. An ultrasonic atomization set-up was used to introduce precursor droplets (aqueous solution of yttrium nitrate hex hydrate) into the flame. A hydrogen-oxygen diffusion flame was used to realize the high temperature aerosol synthesis. The particles were collected on filters and analyzed using X-Ray Diffraction (XRD) and Transmission Electron Microscopy (TEM). Individual process parameters (flame temperature, residence time, precursor concentration, precursor droplet size) were varied in continuous trials, keeping the rest of the parameters constant. The effect of the varied parameter on the phase of the product Yttria particles was then analyzed. Pre-flame heating was undertaken using a nozzle heater at variable power. Precursor solution concentrations of 0.026 mol/L, 0.26 mol/L, and 0.65 mol/L were used. Residence time was varied by means of burner diameter (9.5 mm and 1.6 mm ID). Large precursor droplets were removed by means of an inertial impactor. The higher flame temperatures and precursor heating favor the formation of monoclinic yttrium oxide. The fraction of the cubic phase is closely related to the particle diameter. All particles larger than a critical size were of the cubic phase. Phase pure monoclinic yttrium oxide particles were successfully synthesized. The end conditions included a precursor concentration of 0.65 mol/L, a pure hydrogen-oxygen flame and a 1.6 mm burner. The precursor droplets entrained fuel gas was passed through a round jet impactor and preheated at full power (130 VA). The particles synthesized were in the size range of 0.350 to 1.7 µm.

No description available.

Interfaces between graphene and dissimilar materials are needed for making devices, but those interfaces also modify the graphene properties due to charge transfer and/or symmetry breaking. In this dissertation we investigate the technology of preparing graphene on different substrates and how the substrate influences the electronic properties of graphene. Synthesizing large area graphene on late transition metals by chemical vapor deposition is a promising approach for many applications of graphene. Among the transition metals, nickel has advantages because the good lattice match and strong interaction between graphene/Ni(111) enables the synthesis of a single domain of graphene on Ni(111). However, the nickel substrate alters the electronic structure of graphene due to substrate induced symmetry breaking and chemical interaction of the metal d-band with graphene. Similar chemical interactions are observed for other transition metals with a d-band close to the Fermi-level. On the other hand, graphene mainly physisorbs on transition metals with a lower lying d-band center. In this thesis we investigate the growth of graphene on nickel by vacuum chemical vapor deposition (CVD). In particular, we present our studies of graphene synthesis on Ni(111) substrates. We demonstrate the self-limiting monolayer of single domain of graphene can be grown on single crystal Ni(111). Our studies also show that selective twisted bilayer graphene can be grown by carbon segregation on Ni(111)-films. To modify the interaction between graphene and the nickel substrate we investigated the intercalation of tin. In the case of graphene physisorbed on weakly interacting metals, some charge doping of graphene occurs due to work function differences between graphene and the metal. Using x-ray photoemission spectroscopy (XPS) we correlate the charge doping of graphene on different metals with the C-1s binding energy. This study demonstrate that XPS can be used to determine the Fermi-level in graphene. While metal intercalation can alter the interaction with the substrate it does not avoid overlap of electronics states at the Fermi-level. Therefore a band gap material should be inserted between the graphene and the metal growth substrate (in this case Pt(111)). This is accomplished by oxidation of intercalated iron at elevated oxygen pressure. We demonstrate that a 2D-FeO layer can be formed in between graphene and the Pt(111) surface. We discuss the role of the 2D-FeO moiré-structure on the nanoscale electronic properties of graphene. To date good quality graphene can only be grown by CVD on late transition metals. To obtain graphene on other substrates the graphene can be transferred mechanically from a growth substrate to various other materials. We demonstrate that this transfer can also be achieved to tungsten, an early transition metal that easily forms a carbide. In our studies to avoid oxidation of the tungsten substrate and reaction of the graphene with the tungsten substrate under thermal treatment, protection of the W(110) surface with sulfur has been explored. For the integration of graphene into device architectures, graphene has to be interfaced with high-κ dielectrics. However, because of the inert nature of graphene, most high-κ do not wet graphene and thus preventing formation of contiguous dielectric layers. Yttrium oxide (Y2O3) has been demonstrated to be an exception and we characterized the growth of Y2O3 on various metal supported graphene and graphene transferred to SiO2. We showed that such a Y2O3 layer can also act as seeding layer for the growth of alumina, which is the preferred dielectric material in many applications. Finally, we investigate the charge doping of graphene in a metal/graphene/dielectric stack and find that the charge doping of graphene is a function of both the work function of the metal as well as the covering dielectric. Thus the dielectric layer can modify the charge doping of graphene at a metal contact.

abstract: Nanoporous crystalline oxides with high porosity and large surface areas are promising in catalysis, clean energy technologies and environmental applications all which require efficient chemical reactions at solid-solid, solid-liquid, and/or solid-gas interfaces. Achieving the balance between open porosity and structural stability is an ongoing challenge when synthesizing such porous materials. Increasing porosity while maintaining an open porous network usually comes at the cost of fragility, as seen for example in ultra low density, highly random porous aerogels. It has become increasingly important to develop synthetic techniques that produce materials with these desired properties while utilizing low cost precursors and increasing their structural strength. Based on non-alkoxide sol-gel chemistry, two novel synthetic methods for nanoporous metal oxides have been developed. The first is a high temperature combustion method that utilizes biorenewable oil, affording gamma alumina (Al2O3) with a surface area over 300 cm3/g and porosity over 80% and controllable pore sizes (average pore width 8 to 20 nm). The calcined crystalline products exhibit an aerogel-like textural mesoporosity. To demonstrate the versatility of the new method, it was used to synthesize highly porous amorphous silica (SiO2) which exhibited increased mechanical robustness while achieving a surface area of 960 m2/g and porosity of 85%. The second method utilizes sequential gelation of inorganic and organic precursors forming an interpenetrating inorganic/organic gel network. The method affords yttria-stabilized zirconia with surface area over 90 cm3/g and porosity over 60% and controllable pore sizes (average pore width 6 to 12 nm). X-ray diffraction, gas sorption analysis, Raman spectroscopy, nuclear magnetic resonance spectroscopy and electron microscopy were all used to characterize the structure, morphology, and the chemical structure of the newly afforded materials. Both novel methods produce products that show superior pore properties and robustness compared to equivalent commercially available and currently reported materials. / Dissertation/Thesis / Ph.D. Chemistry 2012

>Magister Scientiae - MSc / Inorganic based membranes which have a symmetric/asymmetric structure have been produced using an immersion induced phase inversion and sintering method. An organic binder solution (dope) containing yttria-stabilised zirconium (YSZ) particles is spun through a triple orifice spinneret to form a hollow fibre precursor, which is then sintered at elevated temperatures to form a ceramic support. The phase inversion process for the formation of hollow fibre membranes was studied in order to produce the best morphological structure/support for palladium based membranes. The spinning parameters, particle size, non-solvent concentration, internal coagulant as well as the calcination temperature were investigated in order to determine the optimum values. Sintering temperature was also investigated, which would yield a sponge-like structure with an optimized permeability, while retaining a smooth outer surface. The supports produced by phase inversion were characterized in terms of dimension by mercury porosimetry, compressed air permeability, Surface Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The morphology of the produced ceramic support showed either dense or porous characteristics governed by the dynamics of the phase inversion process. The particle size of YSZ was examined in order to decrease the amount of agglomerates in the spinning suspension. Zetasizer tests indicated that at 15 minutes, the ultrasonic bath effectively homogenised the YSZ particles and prohibited soft agglomerates from reforming in the spinning suspension. In this study, an increase in air gap had no noticeable effect on the finger like voids but it had a considerable effect on both the inner diameter (ID) and outer diameter (OD) of the green fibres, while an increase in bore liquid flow rate and extrusion pressure promoted viscous fingering and significant effect on the ID and OD of the fibres, respectively. There was a decrease in porosity and permeability with increasing sintering temperature, addition of water concentration in the spinning suspension and varying N-methylpyrrolidone (NMP) aqueous solution of the internal coagulant. The amount of YSZ added to the starting suspension influenced the properties of the support structure. Viscous deformation was observed for dope with lower particle loading thus resulted in the formation of cracks and defects during sintering.

Electrical and thermal conductivities of the yttria-stabilised zirconia/alumina (YSZ/Al2O3) composites and the yttria-zirconia-ceria (YSZ-CeO2) solid solutions are studied in this thesis. The electrical conductivity of the YSZ/Al2O3 composites decreases with an increase in the volume fraction of Al2O3 and exhibits typical percolation behaviour. The electrical conductivity of the YSZ/Al2O3 interface is higher than that of the YSZ grain boundary, but lower than that of the YSZ grains. The thermal conductivity of the YSZ/Al2O3 composites increases with an increase in the Al2O3 volume fraction, and it can be fitted well to the Maxwell theoretical model, which indicates the absence of obvious interfacial thermal resistances in the composites. The low interfacial thermal resistance of the YSZ/Al2O3 interface is due to the 'clean' and coherent nature of the YSZ/Al2O3 interface, along with the small difference between the elastic properties of YSZ and Al2O3. The electrical conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions has a 'V-shape' variation as a function of the mole ratio of CeO2 (x). In the ZrO2-rich region (x < 0.5), CeO2 doping increases the concentration of defect associates which limits the mobility of the oxygen vacancies; in the CeO2-rich region (x > 0.5), the increase of x increases the lattice parameter, which enlarges the free channel for oxygen vacancy migration. A comparison of the YSZ-CeO2 solid solutions with the YSZ-HfO2 series indicates the ionic radius of the tetravalent dopant determines the composition dependence of the ionic conductivity of the solid solutions.The thermal conductivity of the [(ZrO2)1-x(CeO2)x]0.92(Y2O3)0.08 (0 ≤ x ≤ 1) solid solutions also has a 'V-shape' variation as a function of the mole ratio of CeO2 (x), which indicates an incorporation of Zr4+ and Ce4+ can effectively decrease the thermal conductivity of the end members YSZ and yttria-doped ceria (YDC). In the ZrO2-rich region (0 ≤ x ≤ 0.5), the thermal conductivity is almost temperature independent; in the CeO2-rich region (0.5 ≤ x ≤ 1), it decreases obviously with increasing temperature. By calculating the phonon scattering coefficients, it is concluded that the composition dependence of the thermal conductivity in the ternary solid solutions is dominated by the mass difference between Zr and Ce at the cation sites, whereas the temperature dependence is determined by the order/disorder of oxygen vacancies at the anion sites.

No description available.

Currently, industrial processes that produce silicon occur in batch units which are energy intensive, capital intensive, and emit harmful pollutants into the atmosphere. A new technology, solid oxide membrane (SOM) processing, seeks to produce silicon without direct emissions and with lower energy and capital costs. Previous studies have shown that this technology can produce silicon; however, the proof-of- concept cell was incapable of producing large volumes of silicon due to restrictions in the molten salt. Current research has engineered an oxyfluoride molten salt to be more efficient in four main ways: higher amount of silica in the molten salt, chemistry stable with the yttria-stabilized zirconia (YSZ) membrane, low volatility, and high electrical conductivity. The newly designed salt allows for up to 25 at% of silicon oxide to dissolve into the flux, removing mass transfer limitations. The mixture utilizes calcium oxide to stabilize the presence of silicon oxide, giving the flux a volatility of less than 0.1 µg/cm 2 *s. The presence of calcium oxide also increases the optical basicity of the system, allowing the flux to be compatible with the YSZ membrane showing no signs of corrosion. Lastly, the new flux composition has a conductivity of 2.87 and 4.38 S/cm, at 1050 °C and 1100 °C, respectively, which is above the desired value of 1 S/cm. vii Combining these improvements in the salt with pre-existing techniques, silicon crystals were produced in the new SOM cell. Two distinct SOM cell configurations were attempted, one with a liquid cathode (tin) and one with a solid cathode (molybdenum). Both cells were able to successfully make silicon metal. The tin cathode was able to produce high purity silicon crystals extracted via acid etching. The molybdenum cathode produced a plated layer of molybdenum disilicide. Samples were examined by using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS). An equivalent circuit model for the SOM process was developed to calculate polarization losses during the electrolysis process.

Le développement de couches minces dopées terres rares a suscité un regain d'intérêt au cours des dernières années. Dans ce mémoire nous présentons l'élaboration des couches minces d'yttria (Y2O3), d'alumine (Al2O3) et les couches mixtes Y2O3-Al2O3 dopées erbium. La technique utilisée est le procédé de dépôt chimique en phase vapeur à partir de précurseurs organométallique (MOCVD) assisté par aérosol. Un dispositif d'irradiation UV est appliqué afin d'assister le processus de réaction avec une modification de l'hygrométrie de l'air vecteur. Les meilleures propriétés sont obtenues pour les couches déposées sous une forte humidité de l'air vecteur et avec l'assistance UV. Dans ces conditions les couches d'yttria présentent une faible vitesse de croissance, une faible contamination organique et une bonne cristallinité dans la phase cubique de l'yttria. Plusieurs phénomènes d'Up-conversion ont été mis en évidence dans les spectres de fluorescence visible de l'erbium dans l'yttria. Une durée de vie du niveau 4I13/2 de l'erbium de 3.07 ms a été mesurée pour ce matériau après recuit à 800°C. Cette valeur est supérieure à celle obtenue pour l'échantillon déposé sous une faible humidité de l'air et sans l'assistance UV après recuit à 1000°C. Les couches d'alumine déposées dans les conditions optimales présentent des vitesses de croissance élevées et se caractérisent par une grande stabilité thermique, permettant l'élimination complète des impuretés tout en restant amorphe. Enfin, l'étude du système Y2O3-Al2O3 montre que les conditions de dépôt jouent un rôle important sur la composition et les propriétés physico-chimiques des dépôts. / The development of rare earth-doped thin film has gained interest over these last few years. In this report we present the elaboration of erbium-doped yttria (Y2O3), alumina (Al2O3) and yttria-alumina (Y2O3-Al2O3) films. The technique used is aerosol assisted chemical vapor deposition processes with metalorganic precursors (MOCVD). A UV-irradiation device is applied to assist the reaction process with a modification in the air humidity of the carrier gas. The best properties are obtained on thin films grown under high air humidity and with UV-assistance. Under such deposition conditions the yttria films present a low growth rate, low organic contamination and higher crystallisation degree in the yttria cubic structure. Several up-conversion phenomena are point out in the visible fluorescence spectra of the erbium ion in yttria. A lifetime of the 4I13/2 Er3+ level of 3.07 ms was found in this material after annealing at 800°C. This value is higher than that obtained for the sample deposited under low air humidity and without UV assistance after annealing at 1000°C. Alumina film deposited under optimal conditions show high growth rate and was a high thermal stability; allow the complete elimination of impurities while remaining amorphous. At last, the results of system Y2O3-Al2O3 indicates that deposition conditions play an important role on the composition and physicochemical properties of films.