Thesis (M.S.)--University of Delaware, 2005. / Principal faculty advisor: Donald L. Sparks, Dept. of Plant & Soil Sciences. Includes bibliographical references.

Esta tese teve como objetivo desenvolver e caracterizar peças cerâmicas obtidas a partir de pós de alumina nas cores rosa e azul, produzidos por processo experimental. O desenvolvimento deste novo processo de produção gerou a necessidade de proteção realizada por meio de pedido de depósito de patente. Os pós produzidos foram caracterizados quanto à distribuição granulométrica e conformados por prensagem uniaxial em discos com 12 (±0,2)mm de diâmetro e 1,2 (±0,2)mm de espessura e os protocolos de sinterização foram definidos em função da cor e da concentração do aditivo utilizado. O feldspato foi escolhido como aditivo de sinterização para que a mesma ocorresse via fase líquida. Ele foi adicionado nas concentrações de 10, 15 e 20% tanto para os grupos de cor rosa (grupos R10, R15 e R20) quanto para os de cor azul (grupos A10, A15 e A20). Após a sinterização as peças foram analisadas quanto ao módulo de elasticidade, microdureza Vickers, rugosidade de superfície e tenacidade à fratura. O módulo de elasticidade variou de 183,2 a 157 GPa, nos grupos de cor rosa, e nos grupos de cor azul os valores variaram de 101,1 a 176,6 GPa. A rugosidade apresentou valores entre 0, 43 e 0,72 μm para os grupos de cor rosa e 0,39 e 0,6 μm para os grupos de cor azul. A dureza Vickers variou de 418,7 a 623,1 para a cor rosa e de 366,9 a 632 para cor azul. A tenacidade média para os grupos de cor rosa variou de 0,72 a 1,97 MPa.m1/2 e de 0,82 a 1,9 MPa.m1/2 para os grupos de cor azul. O grupo R10 apresentou valores médios de rugosidade significativamente maiores tanto em relação ao grupo R20 quanto ao grupo A10. As demais concentrações não apresentaram diferença significativa em relação às cores. A média dos valores de dureza do grupo A10 foi significativamente maior em relação às demais concentrações na mesma cor, no entanto não houve diferença quando comparado ao grupo R10. Os valores médios do módulo de elasticidade foram significativamente maiores nos grupos de cor rosa em relação aos grupos de cor azul para as mesmas concentrações com exceção do grupo R20 que apresentou valores menores, porém sem significância estatística. A tenacidade à fratura apresentou diferença estatística significativa apenas na comparação entre os grupos R10 e R20. Os valores de tenacidade mais próximos ao relatado pela literatura foram apresentados pelos grupos R20 e A20, porém há diferenças nos métodos de análise da tenacidade entre os estudos. As peças de cor azul com 10% de feldspato apresentaram os resultados mais favoráveis tanto em comparação com as diferentes concentrações na mesma cor quanto entre as diferentes cores. / The aim of this thesis was to develop and characterize ceramic pieces obtained from alumina powders in pink and blue colors produced by experimental procedure. The development of this new production process led to the need for protection of the knowledge generated thus an application for patent was done. The powders produced were characterized for particle size distribution and uniaxial pressed into discs with 12 (± 0.2) mm in diameter and 1.2 (± 0.2) mm thick. The sintering protocols were defined according to the color and concentration of the additive used. For sintering to happen into liquid fase the feldspar was chosen as a sintering additive. It was added at concentrations of 10, 15 and 20% for both pink (R10, R15 e R20) and blue (A10, A15 e A20) groups. After the sintering process an analysis of the elastic modulus, the Vickers hardness, surface roughness and fracture toughness of the samples were performed. The elastic modulus values ranged from 183.2 to 157 GPa in pink groups and 101.1 to 176.6 GPa in blue groups. The roughness mean varied between 0,43 and 0,72 μm in pink groups and between 0.39 and 0.6 μm in blue groups. The Vickers hardness number ranged from 418.7 to 623.1 in pink groups and from 366,9 a 632 in blue groups. The fracture toughness mean to pink groups ranged from 0.72 a 1.97 MPa.m1/2 and from 0.82 a 1.9 MPa.m1/2 to blue groups. The R10 group had significantly higher roughness mean values when compared to the groups R20 and A10. No significant difference was found on the others groups. The hardness average values of the A10 group were significantly higher when compared to other concentrations on the same color, however there was no difference when compared to the R10 group. The average values of the elastic modulus were significantly higher in pink groups when compared to blue groups for the same concentrations except the R20 group that showed lower values, but without statistical significance. The fracture toughness results showed a statistically significant difference when R10 and R20 groups were compared. The toughness values closer to those reported in the literature were presented by R20 and A20 groups, but there are differences in the methods of analysis of toughness between studies. The blue pieces with 10% of feldspar showed the most favorable results compared both between different concentrations of the same color as between different colors at the same concentration.

Esta tese teve como objetivo desenvolver e caracterizar peças cerâmicas obtidas a partir de pós de alumina nas cores rosa e azul, produzidos por processo experimental. O desenvolvimento deste novo processo de produção gerou a necessidade de proteção realizada por meio de pedido de depósito de patente. Os pós produzidos foram caracterizados quanto à distribuição granulométrica e conformados por prensagem uniaxial em discos com 12 (±0,2)mm de diâmetro e 1,2 (±0,2)mm de espessura e os protocolos de sinterização foram definidos em função da cor e da concentração do aditivo utilizado. O feldspato foi escolhido como aditivo de sinterização para que a mesma ocorresse via fase líquida. Ele foi adicionado nas concentrações de 10, 15 e 20% tanto para os grupos de cor rosa (grupos R10, R15 e R20) quanto para os de cor azul (grupos A10, A15 e A20). Após a sinterização as peças foram analisadas quanto ao módulo de elasticidade, microdureza Vickers, rugosidade de superfície e tenacidade à fratura. O módulo de elasticidade variou de 183,2 a 157 GPa, nos grupos de cor rosa, e nos grupos de cor azul os valores variaram de 101,1 a 176,6 GPa. A rugosidade apresentou valores entre 0, 43 e 0,72 μm para os grupos de cor rosa e 0,39 e 0,6 μm para os grupos de cor azul. A dureza Vickers variou de 418,7 a 623,1 para a cor rosa e de 366,9 a 632 para cor azul. A tenacidade média para os grupos de cor rosa variou de 0,72 a 1,97 MPa.m1/2 e de 0,82 a 1,9 MPa.m1/2 para os grupos de cor azul. O grupo R10 apresentou valores médios de rugosidade significativamente maiores tanto em relação ao grupo R20 quanto ao grupo A10. As demais concentrações não apresentaram diferença significativa em relação às cores. A média dos valores de dureza do grupo A10 foi significativamente maior em relação às demais concentrações na mesma cor, no entanto não houve diferença quando comparado ao grupo R10. Os valores médios do módulo de elasticidade foram significativamente maiores nos grupos de cor rosa em relação aos grupos de cor azul para as mesmas concentrações com exceção do grupo R20 que apresentou valores menores, porém sem significância estatística. A tenacidade à fratura apresentou diferença estatística significativa apenas na comparação entre os grupos R10 e R20. Os valores de tenacidade mais próximos ao relatado pela literatura foram apresentados pelos grupos R20 e A20, porém há diferenças nos métodos de análise da tenacidade entre os estudos. As peças de cor azul com 10% de feldspato apresentaram os resultados mais favoráveis tanto em comparação com as diferentes concentrações na mesma cor quanto entre as diferentes cores. / The aim of this thesis was to develop and characterize ceramic pieces obtained from alumina powders in pink and blue colors produced by experimental procedure. The development of this new production process led to the need for protection of the knowledge generated thus an application for patent was done. The powders produced were characterized for particle size distribution and uniaxial pressed into discs with 12 (± 0.2) mm in diameter and 1.2 (± 0.2) mm thick. The sintering protocols were defined according to the color and concentration of the additive used. For sintering to happen into liquid fase the feldspar was chosen as a sintering additive. It was added at concentrations of 10, 15 and 20% for both pink (R10, R15 e R20) and blue (A10, A15 e A20) groups. After the sintering process an analysis of the elastic modulus, the Vickers hardness, surface roughness and fracture toughness of the samples were performed. The elastic modulus values ranged from 183.2 to 157 GPa in pink groups and 101.1 to 176.6 GPa in blue groups. The roughness mean varied between 0,43 and 0,72 μm in pink groups and between 0.39 and 0.6 μm in blue groups. The Vickers hardness number ranged from 418.7 to 623.1 in pink groups and from 366,9 a 632 in blue groups. The fracture toughness mean to pink groups ranged from 0.72 a 1.97 MPa.m1/2 and from 0.82 a 1.9 MPa.m1/2 to blue groups. The R10 group had significantly higher roughness mean values when compared to the groups R20 and A10. No significant difference was found on the others groups. The hardness average values of the A10 group were significantly higher when compared to other concentrations on the same color, however there was no difference when compared to the R10 group. The average values of the elastic modulus were significantly higher in pink groups when compared to blue groups for the same concentrations except the R20 group that showed lower values, but without statistical significance. The fracture toughness results showed a statistically significant difference when R10 and R20 groups were compared. The toughness values closer to those reported in the literature were presented by R20 and A20 groups, but there are differences in the methods of analysis of toughness between studies. The blue pieces with 10% of feldspar showed the most favorable results compared both between different concentrations of the same color as between different colors at the same concentration.

Esta tese teve como objetivo desenvolver e caracterizar peças cerâmicas obtidas a partir de pós de alumina nas cores rosa e azul, produzidos por processo experimental. O desenvolvimento deste novo processo de produção gerou a necessidade de proteção realizada por meio de pedido de depósito de patente. Os pós produzidos foram caracterizados quanto à distribuição granulométrica e conformados por prensagem uniaxial em discos com 12 (±0,2)mm de diâmetro e 1,2 (±0,2)mm de espessura e os protocolos de sinterização foram definidos em função da cor e da concentração do aditivo utilizado. O feldspato foi escolhido como aditivo de sinterização para que a mesma ocorresse via fase líquida. Ele foi adicionado nas concentrações de 10, 15 e 20% tanto para os grupos de cor rosa (grupos R10, R15 e R20) quanto para os de cor azul (grupos A10, A15 e A20). Após a sinterização as peças foram analisadas quanto ao módulo de elasticidade, microdureza Vickers, rugosidade de superfície e tenacidade à fratura. O módulo de elasticidade variou de 183,2 a 157 GPa, nos grupos de cor rosa, e nos grupos de cor azul os valores variaram de 101,1 a 176,6 GPa. A rugosidade apresentou valores entre 0, 43 e 0,72 μm para os grupos de cor rosa e 0,39 e 0,6 μm para os grupos de cor azul. A dureza Vickers variou de 418,7 a 623,1 para a cor rosa e de 366,9 a 632 para cor azul. A tenacidade média para os grupos de cor rosa variou de 0,72 a 1,97 MPa.m1/2 e de 0,82 a 1,9 MPa.m1/2 para os grupos de cor azul. O grupo R10 apresentou valores médios de rugosidade significativamente maiores tanto em relação ao grupo R20 quanto ao grupo A10. As demais concentrações não apresentaram diferença significativa em relação às cores. A média dos valores de dureza do grupo A10 foi significativamente maior em relação às demais concentrações na mesma cor, no entanto não houve diferença quando comparado ao grupo R10. Os valores médios do módulo de elasticidade foram significativamente maiores nos grupos de cor rosa em relação aos grupos de cor azul para as mesmas concentrações com exceção do grupo R20 que apresentou valores menores, porém sem significância estatística. A tenacidade à fratura apresentou diferença estatística significativa apenas na comparação entre os grupos R10 e R20. Os valores de tenacidade mais próximos ao relatado pela literatura foram apresentados pelos grupos R20 e A20, porém há diferenças nos métodos de análise da tenacidade entre os estudos. As peças de cor azul com 10% de feldspato apresentaram os resultados mais favoráveis tanto em comparação com as diferentes concentrações na mesma cor quanto entre as diferentes cores. / The aim of this thesis was to develop and characterize ceramic pieces obtained from alumina powders in pink and blue colors produced by experimental procedure. The development of this new production process led to the need for protection of the knowledge generated thus an application for patent was done. The powders produced were characterized for particle size distribution and uniaxial pressed into discs with 12 (± 0.2) mm in diameter and 1.2 (± 0.2) mm thick. The sintering protocols were defined according to the color and concentration of the additive used. For sintering to happen into liquid fase the feldspar was chosen as a sintering additive. It was added at concentrations of 10, 15 and 20% for both pink (R10, R15 e R20) and blue (A10, A15 e A20) groups. After the sintering process an analysis of the elastic modulus, the Vickers hardness, surface roughness and fracture toughness of the samples were performed. The elastic modulus values ranged from 183.2 to 157 GPa in pink groups and 101.1 to 176.6 GPa in blue groups. The roughness mean varied between 0,43 and 0,72 μm in pink groups and between 0.39 and 0.6 μm in blue groups. The Vickers hardness number ranged from 418.7 to 623.1 in pink groups and from 366,9 a 632 in blue groups. The fracture toughness mean to pink groups ranged from 0.72 a 1.97 MPa.m1/2 and from 0.82 a 1.9 MPa.m1/2 to blue groups. The R10 group had significantly higher roughness mean values when compared to the groups R20 and A10. No significant difference was found on the others groups. The hardness average values of the A10 group were significantly higher when compared to other concentrations on the same color, however there was no difference when compared to the R10 group. The average values of the elastic modulus were significantly higher in pink groups when compared to blue groups for the same concentrations except the R20 group that showed lower values, but without statistical significance. The fracture toughness results showed a statistically significant difference when R10 and R20 groups were compared. The toughness values closer to those reported in the literature were presented by R20 and A20 groups, but there are differences in the methods of analysis of toughness between studies. The blue pieces with 10% of feldspar showed the most favorable results compared both between different concentrations of the same color as between different colors at the same concentration.

The structural and electrical properties of sublimed GaAs films, the dielectric properties of anodic A1₂O₃ films and the electrical properties of A1₂O₃/GaAs interfaces are of interest from the viewpoint of using GaAs and A1₂O₃ films in thin-film integrated circuits. A new method, the close-spaced sublimation (CSS) method, was developed and used to deposit GaAs films on sapphire. The effects of growth conditions on the structural properties of the films were investigated using optical and electron microscopy, an electron microprobe and X-ray diffraction techniques. Crystallites increased in size with increasing substrate temperature, from about 0.7μ to 20μ for substrate temperatures from 480 to 670°C. The degree of preferred orientation of crystallites in the films increased with increasing substrate temperature. The films exhibited <111> textures when substrate temperatures were above about 600°C. Single-crystal diffraction patterns were obtained from films deposited on substrates held at 630 to 640°C. Electron microprobe analysis indicated that the ratio of Ga to As in the films was stoichiometric to less than 2 wt %. The as-grown heteroepitaxial films were p-type with room-temperature hole Hall mobility up to 42 cm²/V-sec. The room-temperature resistivity ranged from 0.6Ω -cm to 1.6 x 10⁵Ω-cm. The resistivity of higher resistivity films was more temperature dependent than that of lower resistivity films. The electrical properties of the films are discussed in terms of the effects of space charge regions in the grains, potential barrier at the grain boundaries, deviation from stoichiometry, and compensation of impurities. Conductivity-type conversion of the as-grown films to n-type was done by postdeposition dopant diffusion. A room-temperature electron Hall mobility of 77 cm²/V-sec was obtained. While transistor action and rectification characteristics were observed in thin-film insulated-gate field-effect transistors and Au-Schottky barrier diodes made with GaAs films, better films are required before devices with characteristics competitive with bulk devices can be fabricated. An n-type homoepitaxial film was deposited by using the CSS method. The film's electron Hall mobility varied with temperature as T³ˡ², which is the form predicted by the Brooks-Herring formula for ionized impurity scattering. The room-temperature electron Hall mobility was 219 cm²/V-sec. A.c. bridge and step response methods were used to study the dielectric properties of anodic A1₂O₃ films. Metal/ A1₂O₃/Al capacitors were made using evaporated Al films on glass which-had been anodized in ammonium penta-borate dissolved in ethylene glycol. The dielectric constant and loss tangent of anodic A1₂O₃ decreased with increasing frequency over the range from 0.5 to 100 kHz. Step response currents followed a t⁻ⁿ law. For linear dielectric response, this corresponded to є”(ω) varying as ωⁿ⁻¹. Electrical properties of A1₂O₃/GaAs interfaces were studied using the metal-insulator-semiconductor (MIS) capacitance technique. Theoretical curves relating the capacitance of metal/ A1₂O₃/GaAs capacitor to the d.c. voltage applied across the capacitor were calculated and plotted. These capacitance-voltage (C-V) curves then served as a basis for the interpretation of experimental C-V curves. "Fast" surface state densities greater than 10¹²/cm²-eV were obtained. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The direct determination by Differential Pulse Anodic Stripping Voltammetry (DPASV) on a Mercury Thin Film Electrode of thallous ions in solution, in a slurry of 0.010 M aqueous NaF and gamma-A1203 , is reported at 25•C. An adsorption capacity of 72.8 Mg of Tl (I) per gram of gamma-A1203 was determined by continuous addition experiments with sixty minutes equilibration time. However, continuous addition experiments using 0.010 M aqueous NaC104 , as background electrolyte, showed no adsorption of Tl (I) onto gamma-A1203 . This is attributed to the affinity of Tl (I) for perchlorate over hydroxyl anions. The results obtained for the concentration of Tl (I) in solution in batches of 0. 010 M aqueous NaF with gamma-A1203 , in the range of pH from 7.5 to 10.5, determined by DPASV and Graphite Furnace Atomic Absorption Spectroscopy, agree with a 95% confidence level, given by the regression line analysis. A strong dependence on pH is observed for the adsorption of Tl (I) onto gamma-A1203 , in 0.010 M aqueous NaF. A change from low adsorption values at pH 8, to high adsorption at pH 10 was observed.

The alumina-catalyzed Cope rearrangements of meso- and dl-3,4-diphenylhexa-1,5-diene were examined in detail, following up a preliminary observation by H. Berg at Portland State University. Commercial column-chromatography grade alumina was employed, and was further activated before use.by heating at 650-700° for four hours. Using a ratio of 20 mg of dl-3,4-diphenylhex-l,5-diene to 1 g of alumina in heptane, the Cope rearrangement was complete within 15 minutes at room temperature to give exclusively trans,trans-1,6-diphenylhexa-1,5-diene. This was identified.by melting point, infrared spectroscopy and vapor phase chromatography The catalyzed rearrangement of meso-3,4-diphenylhexa-l,5-diene was run using the same diene to alumina ratio. It was found that 31% of the meso-diene was converted to cis,trans- and trans,trans-l,6-diphenylhexa-1,5-diene at room temperature in four hours. Product iso-merization appeared to take place; the initial ratio of cis,trans-diene to trans,trans-diene was estimated to be 73:27. Another run was carried out at 60°, where the problem of isomerization of cis,trans-diene to trans,trans-diene was more pronounced. The rearrangement gave cis, trans-diene and trans,trans-diene in a ratio of 58:42, as estimated by extrapolation of the product ratio to zero time. Approximately 95% of meso-diene had reacted in one hour at this temperature. The extent of conversion of mes-diene was calculated by quantitative infrared spectroscopy, and the isomeric distribution of products was determined by vapor phase chromatography. The product distribution in the alumina-catalyzed rearrangements parallels that of the thermal Cope rearrangement, where dl-diene gives exclusively trans,trans-diene at 80° with a half-life of eight hours and meso-diene gives 63% cis,trans-diene and 27% trans,trans-diene at 120° with a half-life of 15 hours.

Ultrasonic humidifier use is a potential source of human exposure to inhalable particulates. This paper focused on the behavior of insoluble iron oxides particles, and aluminum oxide particles in ultrasonic humidifiers. 10 mg/L Fe oxide particles and 5 mg/L Al oxide suspension solutions were added into tap water, as fill water for ultrasonic humidifiers operated for 14 hours. Denser, heavier particles of approximate 1.5 um diameter of iron or aluminum oxides accumulated in the humidifier reservoir. Smaller, suspended metal oxide particles of 0.22-0.57 um diameter were emitted as aerosols from humidifiers. Soluble anions and cations in tap water were present in the aerosols emitted from humidifiers. The results indicate that if suspended particles and dissolved minerals are present in source water, they will be transported in aerosolized waters. / M. S. / Ultrasonic humidifiers are used widely globally. However, they may cause adverse human health effects, such as respiratory damage, and even deaths. Previous work focused on the effect of soluble constituents in the fill water on the emissions of aerosols. This paper demonstrated the fate and transport of insoluble mineral particles in the ultrasonic humidifiers. The particles used were iron oxides particles powder (micro iron oxide, and nano iron oxide), and aluminum oxide particles in suspension (nano size), which have different mean particle sizes. Results showed only very small portion of iron oxides particles transported into the aerosols, and a relatively much bigger portion of aluminum oxide particles transported into the aerosols, which may be contributed by their differences in density and form. In conclusion, denser and heavier particles settled to the bottom of the humidifiers, while smaller and suspended particles were emitted in the aerosols.

The reaction between nitrogen-containing organic compounds (pyridines and amines) and alumina was studied through the use of chromatographic titrations and elemental analysis. The aluminum-nitrogen bond was the basis for the preparation of a series of new chromatographic adsorbents. A series of amines and pyridine homologs were bound to alumina and evaluated as chromatographic stationary phases. The surface coverage was determined using elemental analysis. The adsorption properties of the stationary phases were investigated by determining differential enthalpies, entropies, and free energies of adsorption for a selected group of organic moieties. Rate theory was used to examine further the interaction between the molecular probes and the tailored supports. Relative peak broadening was measured both as a function of flow rate and temperature to provide a chromatographic evaluation of molecular probe-adsorbent interaction occurring during the chromatographic process. Results indicated that the single-molecule moieties used as tailoring agents served as excellent deactivating agents but produced no significant changes in the selectivity of the adsorbents. Pellicular beads were synthesized by using 4-vinylpyridine as a linking agent between the alumina substrate and a series of polymers. The polymers used in this study were polystyrene, polymethylmethacrylate, and polyacrylonitrile. Each type of polymer-coated bead was prepared at different loading levels. Scanning electron microscopy was used to examine the gross change in the surface and elemental analysis used to determine the polymer loading. The adsorption properties of the polymeric pellicular supports were studied by determining the aforementioned thermodynamic quantities and by rate theory. The relative peak broadening was mentioned as a function of polymer type, loading, flow rate, and temperature. The chromatographic behavior of the selected molecular probes on the pellicular supports was sensitive to polymer type and loading. It was established that alumina can be modified with amines and pyridines and that a molecule possessing a nitrogen atom and a polymerization site can be used as an adhesive interface to chemically link polymeric phases to alumina. Currently, there are no commercially available modified aluminas. It has been demonstrated here that the preparation of such supports is feasible and can lead to chromatographically useful products.

Thin films of alumina were deposited on ferrite (NiₓZn₍₁₋ₓ₎Fe₂O₄), glass, single crystal silicon and graphite substrates by RF sputtering. Though standard, amorphous Al₂O₃ films are readily soluble in hot phosphoric acid, these sputtered films exhibited only reluctant etchability by the acid. Experiments were initially performed to understand the parameters in the sputtering process which were influential in the formation of unetchable films. The results showed that a high concentration of water vapor or oxygen molecules in the sputtering chamber during deposition was the most significant variable controlling the growth of unetchable films. The films were categorized according to their degree of solubility in H₃PO₄ and were examined using various microanalytical characterization techniques. TEM analysis directly showed the existence of crystalline γ-Al₂O₃ in the film at the film-substrate interface. The γ-Al₂O₃ phase grew with a preferred orientation coincident with the substrate orientation--as in heteroepitaxial growth. The occurrence of this film phase was related to the oxygen partial pressure, the substrate material, and the substrate temperature and was believed to be the cause of the film's incomplete etching behavior.