Phosphate is one of the essential minerals for all living organisms. It has to be supplied to the soil in order for plant growth. In Turkey, most of the soils lack phosphate mineral. Although this can be overcome by the use of phosphate fertilizers, in Turkey there are no phosphate mines being utilized / and this brings about the need to import phosphate rock and phosphate fertilizers. The estimated phosphate rock reserve of Turkey is around 300 million tons, but it cannot be utilized since no economical method of upgrading has been proved to work yet. The aim of this study has been two-fold / to determine the effects of several parameters on the cell flotation of Mardin-Mazidagi phosphate rock and to increase the grade of the product above 30% P2O5 content with a reasonable recovery rate, so that it could be used commercially. Phosphate rock upgrading was made by using flotation in a cell. There are many factors affecting the recovery and grade of the product such as, particle size, pulp pH, collector volume, acid and collector conditioning times and temperature. Phosphate rock samples used contained 14% P2O5, 43% CaCO3 and 1% SiO2 with a CaO/P2O5 ratio of 3.1. Due to the low silica content, one-stage flotation was made. In the experiments, effects of the important parameters were tested at constant pulp density (10% solids by weight). Particle sizes were between 53 m and 150 m, while the pH values were kept between 5,0 - 6,5 using amounts of acid within the range of 6 - 19 kg H3PO4/ton of rock. The collector (mixture of kerosene and oleic acid in 1:3 volumetric ratio) was used in the range of 0,6 ml (0,96 kg collector/ton rock) and 5,4 ml (8,64 kg collector/ton rock). Acid and collector conditioning times were changed between 10-110 s and 10-80 s, respectively. The temperature range was between 15-35 &deg / C. At the end of the parametric studies a grade of 36% P2O5 with a recovery of 93% could be obtained.

No description available.

Cell adhesion to proteins adsorbed onto implanted surfaces is particularly important to host responses in biomedical and tissue engineering applications. Biomaterial surface properties influence the type, quantity and functional presentation (activity) of proteins adsorbed upon contact with physiological fluids, and modulate subsequent cell response. Cell adhesion to extracellular matrix proteins (e.g. fibronectin) is primarily mediated by the integrin family of cell-surface receptors. Integrins not only anchor cells, supporting cell spreading and migration, but also trigger signals that regulate survival, proliferation and differentiation. A fundamental understanding of the adhesive interactions at the biomaterial interface is critical to the rational design of biomaterial surfaces. Using model surfaces of self-assembled monolayers of alkanethiols on gold presenting well-defined surface chemistries (CH3, OH, COOH, NH2), we investigated the effects of surface chemistry on osteoblastic differentiation. We report that surface chemistry effectively modulates fibronectin adsorption, integrin binding, focal adhesion assembly and signaling to direct the osteoblast cellular functions of adhesion strength, gene expression and matrix mineralization. Specifically, surfaces presenting OH and NH2 functionalities provide enhanced functional presentation of adsorbed fibronectin, promoting specificity of integrin binding as well as elevating focal adhesion assembly and signaling. Furthermore, the OH and NH2 surfaces supported elevated levels of osteoblast differentiation as evidenced by osteoblast-specific gene expression and matrix mineralization. These results contribute to the development of design principles for the engineering of surfaces that direct cell adhesion for biomedical and tissue engineering applications. In particular, the understanding provided by this analysis may be useful in the engineering of surface properties for bone tissue repair and regeneration.

The discovery of MCM-41 materials have attracted substantial research attention due to the remarkable features of these materials including a narrow pore size distribution, high surface area, high pore volume, and high thermal and hydrothermal stability, as well as, parallel hexagonal arrangement of uniform cylindrical pores without pore channel intersection. These well-defined structural characteristics make them ideal media to study the adsorption, catalysis, ion exchange, and separation. MCM-41 sample used in this study was synthesized in (Chemical Engineering Department, Gazi University). The MCM-41 was synthesized by using sodium silicate (0.0705 mol, 27% Silica) as a source of silica and surfactant cetyltrimethylammoniumbromides (CTMABr) (0.036 mol) as template. A characteristic feature of this direct hydothermal synthesis was relatively long synthesis time (96 hour at 120&deg / C). MCM-41 was characterized by using XRD, and nitrogen physisorption analysis techniques. The characteristic peak in the low-angle region corresponding to 2&amp / #952 / = 2.406&deg / was obtained for MCM-41 sample indicating high structural ordering of the MCM-41sample. The BET, surface area was found as (492.2 m /g), with an average pore diameter (25 &Aring / ). In this study the sorption equilibrium of C aromatics (p-xylene, m-xylene, o-xylene, and ethylbenzene ) on MCM-41 at different temperatures (30&deg / C, 50&deg / C, 65&deg / C, 80&deg / C) was investigated by using an automated gravimetric electrobalance system. It was found that the amounts of each sorbate (p-xylene, m-xylene, o-xylene, and ethylbenzene) adsorbed at a given relative pressure on MCM-41 decreased when the temperature of the adsorption isotherms increases. The adsorption isotherms were type V, according to IUPAC isotherm classification due to the mesoporous nature of the MCM-41 sample. The hysteresis are associated with condensation-evaporation within a narrow distribution of mesopores with each adsorption isotherms. It was shown that as the temperature for the adsorption isotherms increases the size of hysteresis decreases for each sorbate. The volume of sorbates (V ) were obtained from the mass uptake at maximum relative pressure by taking the normal liquid density at the adsorption temperature for all sorbates. These values are significantly lower than that obtained from low-temperature nitrogen isotherm. The reason of this difference is that the density of the adsorbed phase is unlikely to be exactly the same as that of the liquid adsorptive and curvature of some isotherms at high relative pressure leads to uncertainty in the location of the upper limit for pore filling.

The room temperature photocatalytic oxidation of carbon monoxide in excess air was examined over silica/titania and 0.1%palladium/silica/titania catalysts under UV irradiation. The experiments were conducted in batch re-circulated reactor with the initial 1000 ppm carbon monoxide in air and 0.5 g catalyst charge and the conversion of carbon monoxide to carbon dioxide was followed by FT-IR spectro-photometer. The change in gas composition in dark and under 36 Watts of UV irradiation exposed to a catalyst area of 12.4 centimeter square indicated both adsorption of carbon monoxide and conversion of carbon monoxide to carbon dioxide over the catalyst samples. The effect of catalyst composition (silica/titania) ratio and the presence of palladium oxide were investigated. The catalyst samples were synthesized by sol-gel technique and all samples were hydrothermally treated before calcination in air. The catalyst samples were characterized by XRD and nitrogen adsorption techniques. XRD results indicated that titania is comprised of pure anatase phase and palladium oxide preferantially dispersed over titania. BET surface area of the samples were observed to increase with silica loading and the BJH results showed isotherms of Type V v with H2 hysteresis loops. The highest carbon monoxide adsorption rate constant was achieved with pure silica with the highest surface area. Photocatalytic activity measurements indicated that carbon monoxide in excess air can be successfully oxidized at room temperature over the titania photocatalyts. Higher physisorption was observed over higher silica containing samples and higher oxidation activity was observed with increasing titania/silica ratio. The optimum titania/silica ratio was determined by the titania content and surface area of catalyst. The activity tests were also indicated that the addition of palladium oxide phase synergistically increased the adsorption and oxidation activity of the catalysts.

Thesis (Ph. D.)--University of Chicago, Dept. of Chemistry, June 2001. / Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Florida, 2000. / Title from first page of PDF file. Document formatted into pages; contains ix, 242 p.; also contains graphics. Vita. Includes bibliographical references (p. 232-241).

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 154-161).

Thesis (Ph. D.)--University of Oregon, 2002. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 187-198). Also available for download via the World Wide Web; free to University of Oregon users.

Semiconductor nanowires are one-dimensional nanoscale systems that exhibit many unique properties. Their nanoscale size can lead to defect densities and impurity populations different than bulk materials, resulting in altered diffusion behavior and mechanical properties. Synthetic methods now support the large-scale production of semiconductor nanowires, enabling a new class of materials and devices that use macroscopic quantities of nanowires. These advances have created an opportunity to fabricate bulk structures which exhibit the unique physical properties of semiconductor nanowires, bridging the properties of a nanoscale system with macroscopic materials. High aspect ratio germanium nanowires were synthesized in supercritical organic solvents using colloidal gold nanocrystal seeds. The nanowires were chemically passivated inside the reactor system using in situ thermal hydrogermylation and thiolation. The chemical stability of the passivated nanowires was studied by exposure to highly corrosive and oxidative environments. Chemical surface functionalization of germanium nanowires was investigated by covalently tethering carboxylic acid groups to the surface, as a general platform for the further functionalization of nanowire surfaces with molecules such as polyethylene glycol. Surface functionalization with dopant-containing molecules was also explored as a potential route for doping nanowires. In addition, static charging was exploited in the development of an electrostatic deposition method for semiconductor nanowires. In situ transmission electron microscopy experiments were conducted on gold-seeded germanium nanowires encapsulated within a volume-restricting carbon shell. A depressed eutectic melting temperature was observed, along with strong capillary effects, and the solid-state diffusion of gold into the crystalline stem of the germanium nanowire, occurring at rates orders of magnitude slower than in the bulk. Copper, nickel, and gold diffusion in silicon nanowires were also investigated. The rate of gold diffusion was found to be a strong function of the amount of gold available to the system. Finally, germanium nanowires were found to exhibit exceptional mechanical properties, with bending strengths approaching that of an ideal, defect-free, perfect crystal, and strength-to-weight ratios greater than either Kevlar or carbon fiber. Macroscopic quantities of nanowires were used to fabricate large sheets of free-standing semiconductor nanowire fabric, and the physical, morphological, and optical properties of the material were investigated. / text