Selenium Particles Research Articles

The influences of dietary intakes and supplementation with selenium and vitamin E on reproduction diseases and reproductive efficiency in cattle and sheep.

Retained placenta, endometritis, cystic ovaries and low conception rates are often considered as interconnected conditions in cattle. Wide ranges in amounts of selenium and vitamin E supplements have been advised in late-pregnancy diets and, frequently, they can be synergistically beneficial. Animals at grass or with other green foods should be of adequate vitamin E status, but dietary selenium deficiencies are both more frequent and severe. Selenium status is important for super-ovulation in cattle and multiple births in ewes because of its importance in sperm transport and establishment of ova. However, the potential toxicity of selenium-enriched feed supplements restricts their use on a free-access basis. Giving sodium selenite or selenate by injection provides only a short-term response in the plasma. Barium selenate given in oil by injection provides a more durable response but has potential tissue residue problems. Compressed metallic selenium powder with iron powder in high-density reticulo-ruminal pellets gives sustained release, but uncertainties regarding possible surface coating and the variable effects of selenium particle size may require additional grinders to ensure prolonged release. Neither reticulo-ruminal pellets of such composition nor barium selenate by injection may be used worldwide because only sodium selenite and selenate have general regulatory approval. A sustained-release multi-trace element/vitamin rumen bolus system effective for several months has increased lambing percentages in ewes, and increased herd conception rates and reduced the spread of calving for herds of beef cattle.

The Formation of Nano-sized Selenium-titanium Dioxide Composite Semiconductors by Photocatalysis

Nano-sized selenium (Se) particles were deposited onto titanium dioxide (TiO2) by the photocatalytic reduction of selenate (Se(VI)) and selenite (Se(IV)) ions. Se particles deposition on TiO2 was only observed in the presence of formic acid, which acted as the organic hole scavenger. The Se particles formed were crystalline. Se particles of different size could be formed onto the TiO2 particles by manipulating experimental parameters such as pH and the Se precursor used. When Se(VI) ions were used as the precursor, the Se particles formed on TiO2 were found to be spherical in shape, up to 6 times bigger than the TiO2 particles (up to 145 nm) and discretely formed on the TiO2 particles. The growth and sphericity of the Se particles were explained in terms of electron transfer across the p–n junctions formed by the p-type Se and n-type TiO2 semiconductors under illumination and the adsorption of the Se(VI) ions. The size of the Se particles were found to be dependent on the amount of Se(VI) photoreduced. When Se(IV) ions were used as the precursor for Se particles formation, the particles formed were much smaller than that of TiO2 crystals (less than 25 nm) and also more evenly dispersed on the TiO2 particles.

Electrochemical Preparation of Cadmium Selenide Nanoparticles by the Use of Molecular Templates

We report the electrochemical preparation of cadmium selenide nanoparticles at gold electrodes modified with molecular templates. The molecular templates were obtained by properly arranging thiolated β-cyclodextrin self-assembled monolayers (SAMs) on gold electrodes. Selenium was first deposited on a SAM-modified gold electrode at an appropriate potential, followed by reduction to in a solution containing leading to the deposition of CdSe. The Cd codeposited at the time of CdSe deposition was removed by anodic dissolution at a potential where it was oxidized. Scanning electron microscopic pictures showed that and cadmium selenide particles of smaller than 60 and 150 nm diam, respectively, were deposited on the SAM-modified gold electrodes. Selenium particles of as small as 1-2 nm diam and ∼0.2 nm height were observed by in situ electrochemical scanning tunneling microscopy experiments during the early stages of electrochemical deposition. © 2001 The Electrochemical Society. All rights reserved.

Singular Diffusion as a Function of Nanoparticles Size in Antimony Film–Selenium Particles and Antimony Film–Tellurium Particles

A recently developed chemical synthesis method using the nanoparticle size as a parameter has been applied to Sb film–Se particle and Sb film–Te particle systems. In the Sb–Se system, the diffusion of Se atoms to the Sb film can be clearly seen for Se particle sizes less than 50 nm. Diffusion of Sb atoms predominantly took place in the case of the Sb–Te system. The uniqueness of the reaction consists in the diffusion direction of nanoparticles. Comparison with previous work (Kaito et al., 1998b) is made on the basis of the particle stability and electronegativity.

Reduction of Selenium Oxyanions by Enterobacter cloacae SLD1a-1: Isolation and Growth of the Bacterium and Its Expulsion of Selenium Particles

A facultative bacterium capable of removing the selenium (Se) oxyanions selenate (SeO(inf4)(sup2-)) and selenite (SeO(inf3)(sup2-)) from solution culture in flasks open to the atmosphere was isolated and studied with the goal of assessing its potential for use in bioremediation of seleniferous agricultural drainage water. Elemental Se (Se(sup0)) was confirmed as a product of the reaction. The organism, identified as Enterobacter cloacae and designated strain SLD1a-1 (ATCC 700258), removed from 61.5 to 94.5% of added SeO(inf4)(sup2-) (the primary species present in agricultural drainage water) at concentrations from 13 to 1,266 (mu)M. Equimolar amounts of nitrate (NO(inf3)(sup-)), which interferes with SeO(inf4)(sup2-) reduction in some organisms, did not influence the reaction in growth experiments but had a slight inhibitory effect in a washed-cell suspension. Washed-cell suspension experiments also showed that (i) SeO(inf3)(sup2-) is a transitory intermediate in reduction of SeO(inf4)(sup2-), being produced and rapidly reduced concomitantly; (ii) NO(inf3)(sup-) is also reduced concomitantly and at a much higher rate than SeO(inf4)(sup2-); and (iii) although enzymatic, reduction of either oxyanion does not appear to be an inducible process. Transmission electron microscopy revealed that precipitate particles are <0.1 (mu)m in diameter, and these particles were observed free in the medium. Evidence indicates that SLD1a-1 uses SeO(inf4)(sup2-) as an alternate electron acceptor and that the reaction occurs via a membrane-associated reductase(s) followed by rapid expulsion of the Se particles.

Optical transient induced absorption in ultrasmall particles of amorphous selenium

Nonlinear optical properties of ultrasmall particles of amorphous selenium were studied by pump-probe picosecond technique. The effect of induced absorption with maximum around 2.1 eV was observed. It relaxes completely according to a monoexponential law with decay time ∼ 550 ps. Several possible mechanisms for this effect are considered and absorption due to trapped electron-hole pairs is proposed to be the main mechanism responsible for the transient induced absorption.

Picosecond induced absorption in ultradisperse amorphous selenium particles

A study was made of the induced absorption in amorphous selenium particles (average radius ~20 nm) embedded in a polymer. A picosecond pump and probe technique was used. The change in the absorption was measured in the spectral range 550–750 nm when the pump radiation was in the form of pulses of 15 ps duration and 2.3 eV photon energy. The induced-absorption spectra were attributed to optical exciton—biexciton transitions. The exciton lifetime was estimated to be 424 ± 32 ps.

Selenium supplements for grazing sheep. 3. Development of an intra-ruminal pellet with an extended life

Factors affecting the longevity of intra-ruminal selenium pellets were examined in two factorial experiments, in which the release rate of biologically active selenium was deduced from changes in blood selenium concentration in grazing sheep. In Experiment 1, 150 sheep were given 10 g pellets which were either solid or hollow, contained 5% or 10% selenium present as either fine or coarse particles, and with 0% or 1% magnesium stearate added as a lubricant. The pellets were pressed at either high or low pressures, and blood selenium concentrations were monitored for 4.5 years. In experiment 2, 88 sheep were given pellets containing either 5, 10 or 15% selenium, 1, 3 or 5% magnesium stearate and elemental selenium of four particle sizes. Blood selenium concentrations were determined over 4 years. Pellets recovered at the end of both experiments were scored for encrustation and analysed for selenium. Pellet longevity, blood selenium concentrations and the proportion of sheep whose blood selenium concentration was increased by > 0.02 μg Se ml −1 were greater in pellets containing more selenium and in those pressed at higher pressures. Pellets pressed from coarser selenium particles, those containing 1% magnesium stearate and hollow pellets were generally superior but differences were not consistently observed. Interactions were generally small and differences in the release rate of selenium were large when a number of main effects were varied. Fewer solid pellets were recovered at the end of the Experiment 1 than hollow pellets and the missing pellets were assumed to have been regurgitated. Eleven percent of the solid pellets administered were not found in Border Leicester × Merino sheep at the end of Experiment I. while 1% were not found in Merino sheep at the end of Experiment 2. Pellets manufactured from 15% selenium were effective in meeting the selenium requirement of all supplemented sheep for at least 4 years, and possibly for the commercial life of the sheep; those containing 10% selenium were effective for 3 years.

The efficacy of intraruminal pellets composed of elemental selenium and iron in sheep

Commercial selenium pellets, manufactured after CSIRO workers drew attention to the significance of grain size on the rate of release of selenium, were tested in 27 sheep grazing a low-selenium New Zealand pasture. The pellets were shown by microscopy to contain mainly 10-20 pm particles of selenium, often agglomerated into larger lumps. There was a considerable variation in the length of time pellets maintained blood selenium levels above the deficiency level of 250 nmol/e (20 microg/l). Whereas four animals given pellets had blood levels below 250 nmol/l after only 343 days, two animals had levels of 375 and 400 nmol/l after 651 days when the level in control sheep was 125 +/- 32 nmol/l. The pellets were recovered from all but one animal and had varying degrees of surface coating which was assumed to be mainly calcium phosphate. Two pellets recovered from sheep at 386 and 484 days, when blood selenium levels were 175 and 1813 nmol/l respectively, were sectioned and examined by light and electron microscopy. Both pellets still contained unreacted selenium but differed in the degree of surface coating. The pellet recovered at 386 days had a solid and continuous coating whereas the coating on the pellet recovered at 484 days was not continuous and consisted of an open lattice of interlocking needles. It appears that it is the extent of this coating which limits the effective life of the pellet in sheep.

Influence of structure defects on the damage threshold of ZnSe crystals

Optical breakdown in the bulk of ZnSe subjected to τ ~ 100 nsec pulses of λ = 10.6 μ laser radiation resulted from thermoelastic damage of submicron gas–selenium particles containing radiation-absorbing associates of carbon with oxygen and hydrogen. The breakdown power density was governed not so much by the density of the particles as the nature of defects which they decorated. The proposed grading of the defect content of crystals should make it possible to estimate the bulk optical strength of zinc selenide without destructive testing.

Vacuum deposition of amorphous selenium on polymeric substrates Part I: Preliminary evaluation using a dynamic coating device

The interaction of vacuum-deposited selenium with a polymeric substrate is shown to be dependent on the temperature of the substrate. Selenium may be deposited either as large or small particles in the polymer bulk or as large or small particles or agglomerates on the surface. The size, shape and position of these selenium particles are in general agreement with the proposed deposition mechanism. The deposition of selenium on crystalline polymers is very difficult to control because of the rapid change of rheology with temperature. This suggests that the rheology of the substrate is a critical factor in the control of selenium particle size, shape and position.

Vacuum deposition of amorphous selenium on polymeric substrates II. Use of a temperature-gradient vacuum coating device

The vacuum deposition of amorphous selenium on polymeric substrates is an important process in the preparation of migration-imaging film. A temperature-gradient vacuum coating device has been constructed and used to relate substrate temperature, composition and rheology, deposition rate (selenium flux) and selenium re-evaporation rate from polymer or deposited selenium to the selenium particle size, shape, position and distribution on and within the polymeric substrate. Conditions are defined at which submicron selenium particles can be formed within the polymeric substrate contiguous to the coating surface.

Frequency-dependent electrical behavior of polycrystalline trigonal selenium and its relationship to xerographic performance of selenium particle contact photoreceptors

A detailed correlation between the xerographic performance of trigonal selenium binder layers and the dc and low-frequency ac dark conductivity of these photoreceptors and of polycrystalline compactions fabricated from identical starting materials has been established. Studies of the temperature dependence of the ac conductivity of compactions and of xerographic layers as functions of thermal history and ambient gas exposure indicate that heating (∼150 °C) the pigment in oxygen (but not argon or nitrogen) is required to achieve adequate xerographic sensitivity. This heat treatment also converts the original simply activated conductivity to a complicated function of temperature, characterized by a local conductivity maximum near room temperature. From this result a large decrease in xerographic sensitivity (a factor of 2–3) with increasing temperature from 20 to 40 °C was first predicted and subsequently observed. Evidence that these effects are not due to absorption and desorption of weakly bound gases is presented. The frequency and ambient gas dependence of the ac conductivity of compactions and layers indicate that their dc and low-frequency ac conductivity (and thus the layer xerographic properties) are primarily controlled by interparticle barriers and that the thermal history and ambient gas effects modulate these barriers. Key requisites of models constructed to explain this behavior are discussed.

Light-temperature interference governing the inverse/combined photoadsorption and photodeposition of a-selenium films

Study of parameters governing the kinetics of the photodeposition of selenium (Selor process) and thus, that of the underlying phenomena — inverse and combined photoadsorption from colloid sols, has revealed the “compensation temperature” T *. If the temperature of the process is less than T *, the illumination enhances the rate of adsorption of selenium particles, through lowering the potential barrier of adsorption. When T > T * an inverse effect should take place (due to a prevailing influence of a decrease of the “light susceptibility” of selenium which serves as a preexponential factor). By means of mathematical approximations of experimental data, a general kinetics equation has been elaborated, describing the dependencies of the growth rate on temperature, light intensity and wavelength. This contains seven constants calculated starting from the experimental data.

Photodeposition of amorphous selenium films by the “selor” process III: Interpretation of the structural and kinetics studies

Discussion of the structural observations and the kinetics studies descrived in the two previous parts of this work leads to the conclusion that the photodeposition of selenium films from colloid sols (a process labelled Selor) is based on the phenomena of inverse and of combined photoadsorption. Inverse photoadsorption is considered to occur because of photoexcitation of the adsorbing colloid particles; combined photoadsorption is considered as a superposition of inverse photo-adsorption and conventional photoadsorption. (In the latter only the substrate is photoactivated.) Interpretation of the experimental data is made on the assuption that the activated adsorption is the rate-controlling step. An interference equation is discussed which reflects the simultaneous influence of light and temperature. This is the photogeneration of charges which is assumed to be responsible for the selenium activation, the latter facilitating adsorption by lowering the potential barrier to adsorption (and to the merging of selenium particles on the substrate surface). The contribution of a liquid-like flow of adsorbed selenium particles in the overall process is discussed. A general explanation of experimental data relating to the Selor process is suggested.

Mechanism of selenium pink colouration in glass

The mechanism of pink colouration with selenium in glass has been studied. When selenium-containing glasses are melted under reducing conditions, loss of selenium from the melt is decreased but a dark brown colour results due to the iron-selenide-oxide complex formation. Even a small amount of CeO2 in the batch oxidizes selenium and bleaches the pink colour; large concentrations of arsenic oxide in the batch also have the same effect. Oxidizing conditions in the melt do not produce any larger selenium loss from the melt than that with “neutral” melting conditions. On electron microscope examination, pink glasses coloured with selenium revealed spherical particles. Mie's scattering curves due to spherical selenium particles of different average sizes and size distributions have been calculated and the experimental absorption bands of pink selenium glasses have been shown to be consistent with elemental selenium particles of average diameter 50 to 250 nm with large size distributions.

Cinétique de Coagulation et Stabilité Des Suspensions Colloidales Lyophobes De Sélénium

AbstractCoagulation kinetics of homodisperse hydrosols containing spherical particles of selenium have been studied.Two independant experimental methods were used. One is based on direct observation of the sols under the ultramicroscope, the particles contained in a given volume being counted.The second method is a spectrophotometric one, based on Mie's theory.It has been possible to reproduce and to interpret the abnormally low value of R/a (R being the distance between the centers and a, the radius of the particles) observed by Kruyt and van Arkel for the rapid coagulation of selenium hydrosols.The Schultze‐Hardy rule, interpreted theoretically by Verwey and Overbeek was confirmed quantitatively.The potential values calculated by Reerink and Overbeek's equations are far too low.Notwithstanding the use of spherical particles of identical size, there was a considerable dispersion of the Van der Waals constant (2.10−14 to 25.10−14 ergs) obtained under various conditions.