A study of the growth of monocrystals of tellurium and selenium-tellurium alloys by the Czochralski method has been made, together with measurements of the photoconductivity in such materials. In tellurium, it was found that large temperature gradients occur within a growing ingot which cause an increase in the concentration of lattice defects. This concentration can be reduced by subsequent annealing. An etch pit orientation effect was observed enabling the growth direction of an ingot to be determined, arising from a correspondence between preferential growth and etching planes. Photoconductivity in tellurium at 77 K was found to be decreased by abrasive polishing of the samples and increased by annealing. Transient photoconductivity was found to be characterized approximately by two time constants, one of the order of microseconds and the other tens of microseconds. The largest D* detectivity measured on the samples was 1.3 x 10('11) cm Hz(' 1/2)w('-1) at 3.5 (mu)m. Crystals of Se(,x)Te(,1-x) were prepared by the Czochralski method for Te-rich and Se-rich compositions with 0.1 > x > 0.95. For intermediate compositions with 0.1 < x < 0.95 it was not possible to obtain Czochralski-ingots due to a meniscus rupture problem arising from excess selenium at the growing interface. In this case crystallographically aligned samples were obtained by a slow cooling method. Measurements on the Se(,x)Te(,1-x) alloys showed a continuous wavelength displacement of the photoconductivity maximum from 3.7 to about 0.8 (mu)m in going from tellurium to selenium. This was accompanied by an increase of some 5 orders of magnitude in the photoresponse, in the photoconductive decay time constants and in the electrical resistivity. From the results the estimated energy gaps were found to change continuously from tellurium to selenium with a possible change of slope starting near 40 at.% Se.

No description available.

Selenium (Se) is an essential element. Supplementation of Se as yeast-Se in animal and human diets has been proven to have beneficial health effects. The goal of this study was to add a maximum amount of Se in yeast metabolism in order to optimize its incorporation in amino acids. A bakery yeast strain of Saccharomyces cerevisiae (S. cerevisiae) was studied for its tolerance to Se when the latter was incorporated at different levels. Fermentations were run at 27°C for 8 h and 24 h. The maximum Se incorporation was achieved when 12.6 mmol of Se, as sodium selenite salt, was added to the culture medium and fermented for 24 h. A final Se concentration of 1550 +/- 35 mug/g yeast was obtained by this treatment. / Different yeast strains of S. cerevisiae were also studied for their capacity to incorporate Se. Five yeast strains of wine and four yeast strains of beer were fermented for 24 h and tested for their capacity to incorporate Se. The amount of 12.6 mmol Se was added in the growth medium. A maximum of 642.6 +/- 3.6 mug Se/g yeast was found to be incorporated in Uvaferm BC wine strain. Uvaferm windsor of beer strain was able to incorporate a maximum of 826.8 +/- 10.4 mug Se/g yeast. These yeast strains could be used as alternatives for Se supplementation. / Se speciation was carried out on the bakery yeast strain containing 1550 +/- 35 mug Se/g yeast, using Fast Phase Liquid Chromatography (FPLC) and amino acid analysis. Out of 1550 +/- 35 mug Se/g yeast, 57.5% Se was present as selenoaminoacids. The yeast extract contained 147 +/- 14 mug/g of SeCys, 248 +/- 13 mug/g of SeCyst and 295 +/- 17 mug/g of SeMet. Yeast cell walls contained 65 +/- 8 mug/g of SeMet; 69 +/- 5 mug/g of SeCyst and 67 +/- 9 mug/g of SeCys. These selenoaminoacids are known for their beneficial health effects. The produced Se-enriched bakery yeast could be used, after evaluated to be toxicologically safe, as an efficient dietary supplement.

The purpose of this study was to investigate whether the beneficial effects which the consumption of fish oil imparts on hemostatic function can be modified by the level of dietary selenium. Male Sprague Dawley rats were fed for eight weeks semipurified diets containing 7% corn oil (by weight) or 5.5% fish oil (MaxEPA) plus 1.5% corn oil with or without selenium supplementation. The indicators of selenium status (glutathione peroxidase activity and selenium level) were significantly lower in the rats given inadequate selenium, regardless of the type of fat fed. In the animals fed adequate selenium, these same indicators tended to be lower when fish oil was fed. Although feeding of fish oil increased hepatic and aortic malondialdehyde (MDA), selenium supplementation decreased its level in the liver. Selenium deficiency led to a decrease in the relative weight percent of 22:6 n-3 in aorta and plasma. Increases in the levels of 20:5 n-3, 22:5 n-3, 22:6 n-3, 20:3 n-6 and a decrease in the level of 20:4 n-6 were observed in plasma total lipids and aortic and hepatic phospholipids when fish oil was fed. The increased level of 20:3 n-6 suggests that delta 5-desaturase activity was decreased by fish oil feeding. The level of aortic 6-keto-prostaglandin F₁alpha (6- keto-PGF₁alpha) was highest in the rats fed diets that contained corn oil but no selenium supplementation; selenium supplementation, however, eliminated the difference in the level of 6-keto-PGF₁alpha between fish oil and corn oil fed groups. The levels of thromboxane B₂ (TXB₂) and ADP-induced platelet aggregation were decreased significantly by fish oil feeding and tended to be lower with selenium supplementation. Selenium supplementation did not increase bleeding time while fish oil feeding did. These data indicate that selenium supplementation may decrease fish oil induced lipid peroxidation in liver: this is reflected in the lower hepatic MDA levels in the fish oil fed animals with selenium supplementation and the increased 22:6 n-3 levels in aorta and plasma. Selenium deficiency led to an increase in the level of 6-keto-PGF₁alpha in the rats fed corn oil. Its effects on TXB₂ level and ADP-induced platelet aggregation are marginal. Overall the beneficial effect of selenium supplementation on hemostatic function appears weaker than that of fish oil feeding. / Graduation date: 1990

Graduation date: 1991

vii, 165 [14] leaves : ill. ; 26 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1973

The current work investigates the photocatalytic reduction of selenium (Se) ions, selenate Se(VI) and selenite Se(IV), from two perspectives: Se ion removal from water and wastewater and the formation of nano-Se compounds. Se ion pollution has become an environmental issue in recent years, and hence there is an urgent need for an efficient removal technique. In addition, there is increasing interest in the formation of nano-size semiconductors for niche applications. Since Se is a semiconductor, its formation onto the semiconductor TiO2 could lead to the discovery of new composite materials. The current study has successfully elucidated the mechanism of Se ions reduction by photocatalysis. Factors such as the simultaneous adsorption of the Se ions (the electron scavenger in this case) and a suitable organic compound (the hole scavenger), and the chemical properties of the hole scavenger were crucial for effective and efficient Se ions photoreduction. Optimum conditions in relation to pH, concentrations and types of hole scavenger were reported and discussed. It was also found that stoichiometric adsorption ratio of formate and selenate resulted to optimum photoreduction rate. A modified Langmuir-Hinshelwood kinetic model that considered the simultaneous adsorption of both solutes was derived. The current investigation has also seen the successful formation Se deposits of different morphologies onto the TiO2 particles. Discrete Se particles of various sizes in the nano-size range as well as a Se film were deposited onto the TiO2 particles under different initial experimental conditions. The Se-TiO2 composite semiconductor was explored for the removal of cadmium Cd2+ ions, which resulted in the formation of CdSe-TiO2 systems. The photoreduction of Se ions using silver-modified TiO2 showed the enhanced reduction of Se ions to Se2- in the form of H2Se gas. It is suggested that the H2Se gas generated from the current photoreduction process could be used as a safer and cheaper technique in the formation of Se-compounds such copper selenide, cadmium selenide and zinc selenide. All these compounds were widely used in optical and semiconducting devices.

The current work investigates the photocatalytic reduction of selenium (Se) ions, selenate Se(VI) and selenite Se(IV), from two perspectives: Se ion removal from water and wastewater and the formation of nano-Se compounds. Se ion pollution has become an environmental issue in recent years, and hence there is an urgent need for an efficient removal technique. In addition, there is increasing interest in the formation of nano-size semiconductors for niche applications. Since Se is a semiconductor, its formation onto the semiconductor TiO2 could lead to the discovery of new composite materials. The current study has successfully elucidated the mechanism of Se ions reduction by photocatalysis. Factors such as the simultaneous adsorption of the Se ions (the electron scavenger in this case) and a suitable organic compound (the hole scavenger), and the chemical properties of the hole scavenger were crucial for effective and efficient Se ions photoreduction. Optimum conditions in relation to pH, concentrations and types of hole scavenger were reported and discussed. It was also found that stoichiometric adsorption ratio of formate and selenate resulted to optimum photoreduction rate. A modified Langmuir-Hinshelwood kinetic model that considered the simultaneous adsorption of both solutes was derived. The current investigation has also seen the successful formation Se deposits of different morphologies onto the TiO2 particles. Discrete Se particles of various sizes in the nano-size range as well as a Se film were deposited onto the TiO2 particles under different initial experimental conditions. The Se-TiO2 composite semiconductor was explored for the removal of cadmium Cd2+ ions, which resulted in the formation of CdSe-TiO2 systems. The photoreduction of Se ions using silver-modified TiO2 showed the enhanced reduction of Se ions to Se2- in the form of H2Se gas. It is suggested that the H2Se gas generated from the current photoreduction process could be used as a safer and cheaper technique in the formation of Se-compounds such copper selenide, cadmium selenide and zinc selenide. All these compounds were widely used in optical and semiconducting devices.

Thesis (Ph. D.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 4, 2008) Vita. Includes bibliographical references.

Thesis (Ph.D.) -- University of Adelaide, Dept. of Physical and Inorganic Chemistry, 1973.