Papers by Keyword: Selenium

Abstract: Hainan soil pH continues to decrease, and the reduced soil selenium availability of stagnic anthrosols caused by soil acidification influence the selenium absorption in selenium-rich areas. Taking stagnic anthrosols in selenium-rich areas as the object, the soil total selenium concentration and sequential fractionations of surface layer were analyzed, which are Exchangeable (EX), Carbonate-bound (AC), Fe & Mn oxided-bound (OX), Organic-bound (OC) and Residual (RES). The results show that selenium in soil is unevenly distributed among various fractionations, with the RES and OC accounting for the highest proportion. The sum of the selenium content of these two forms is 89.84%. The AC is easily absorbed and utilized by crops. The selenium content in EX and AC are only 1.64% and 2.17%. Soil pH has the most significant impact on the content of EX. Soil acidification will significantly reduce the proportion of this part of selenium, resulting in a decrease in the bioavailability of soil selenium. Especially when the soil pH is higher than 5.5, the proportion of EX in the soil increases with the the pH dropped significantly.

Abstract: As_xSe_1-x glasses with x from 0,05 to 0,55 were prepared at two melting temperatures, 700 and 850 °C. Batch materials from several suppliers were used for glass synthesis. Density and IR transmittance of glasses were measured. It was found that data for density of glasses prepared at 700 °C have sufficient scatter, so dependence of molar volume on composition is not smooth. Data for glasses synthesized at 850 °C are in good agreement with reference ones. According to data of IR spectroscopy the main impurity in glasses is oxygen in several molecular forms. Oxygen gets in glass together with arsenic. Its content can be noticeably decreased by the heat treatment of As at from 300 to 350 °C and Se at 310 °C before weighting and by the heat treatment of batch at 200 °C before the sealing of silica ampoule. Optical quality of glass samples is good enough for the use them as IR transparent material for lens manufacturing.

Abstract: The application of selenium and mercury and the raw materials for extracting selenium and mercury were introduced. The current separation and extraction processes of selenium and mercury were described in detail, including pyrometallurgy and hydrometallurgy process, in addition to oxygen pressure leaching method and complex acid leaching method.

Abstract: The present work concerns studies aiming at determination of optimal parameters of obtaining selenium coatings on a copper substrate through the cathodic reduction from sulphate and citrate solutions. The voltammetric analysis was performed in selected solutions to define electrode reactions within the examined range of potentials as well as an influence of pH on their kinetics. The range of potentials in which selenium is reduced to Se⁰, and then to Se^2- was determined. The next stage was performing several electrolysis, where the working electrode was copper. It was to define an influence of citric acid, sodium sulphate, electrolyte pH and the electrolysis potential on the quality of the obtained coatings. The coatings were analysed with the use of X-ray spectrofluorimetry, X-ray diffraction and scanning electron microscopy.

Abstract: Surface states have hindered and degraded many semiconductor devices since the Bardeen era. Surface states originate from dangling bonds on the surface. This paper discusses a generic solution to surface states, i.e. valence-mending passivation. For the Si (100) surface, a single atomic layer of valence-mending sulfur, selenium or tellurium can terminate ~99% of the dangling bonds, while group VII fluorine or chlorine can terminate the remaining 1%. Valence-mending passivation of Si (100) has been demonstrated using CVD, MBE and solution passivation. The keys to valence-mending passivation include an atomically-clean Si (100) surface for passivation and precisely one monolayer of valence-mending atoms on the surface. The passivated surface exhibits unprecedented properties. Electronically the Schottky barrier height between various metals and valence-mended Si (100) now follows more closely the Mott-Schottky theory. With metals of extreme workfunctions, new records for low and high Schottky barriers are created on Si (100). The highest barrier so far is 1.14 eV, i.e. a larger-than-bandgap barrier, and the lowest barrier is below 0.08 eV and potentially negative. Chemically silicidation between metal and valence-mended Si (100) is suppressed up to 500 °C, and the thermally-stable record Schottky barriers enable their applications in nanoelectronic, optoelectronic and photovoltaic devices. Another application is transition metal dichalcogenides. Valence-mended Si (100) is an ideal starting surface for growth of dichalcogenides, as it provides only van der Waals bonding to the dichalcogenide.

Abstract: The oxidative-reductive carbonylation of dimethyamine and aromatic nitro-compound catalyzed by selenium to yield herbicides has been studied. The selectivity of herbicide is above 99%. In the reaction there is a phase-transfer process.The catalyst can also be separated from the product by simple phase separation.

Abstract: Selenium is a rare element in nature. It is used in the food, pharmaceutical, and glass industries. In commercial glasses, selenium is the element responsible for most of the pink or light red color, but its effect is primarily dependent on the oxidation state of the element in the glassy matrix. Besides, selenium is highly volatile, and as high as 80 wt% may be lost in the furnace during the industrial glass elaboration. The sol–gel method yields synthesized materials of high purity and homogeneity, and uses low processing temperatures. Samples of silica gels were obtained by sol-gel method, incorporating precursors of selenium, with the main objective of reducing selenium losses during its heating. The results of optical absorption, XRD and thermal analysis (TGA, DSC) of the gels are presented and discussed.

Abstract: Aiming to apply in removal of selenium from contaminated waste water, we have studied the immobilization of Se (IV) and Se (VI) into the hydrate of calcium alumino-zincate (14CaO.5Al₂O₃.6ZnO, shown as C₁₄A₅Z₆). By adding 2 g of C₁₄A₅Z₆ to 1 L of 5 mg/L Se (VI) solution, the concentration of Se (VI) was decreased to less than 0.01 mg/L within 60 minutes. In the case of using 1 g of calcium hydroxide with 2 g of C₁₄A₅Z₆, the Se (VI) concentration reached to 0.01 mg/L within 30 minutes. On the other hand, the concentration of Se (IV) was decreased from 5 mg/L to 0.16 mg/L in 60 minutes whilst it reached to 0.041 mg/L by adding calcium hydroxide in the same reaction period. The immobilization capacity of selenium were 222 and 127 mg/g for Se (IV) and Se (VI), respectively. By adding calcium hydroxide, the immobilization capacity of C₁₄A₅Z₆ was increased to 240 and 200 mg/g for Se (IV) and Se (VI), respectively.

Abstract: 0.2000g mogroside sample is digested by 7.0ml nitric acid and 3.0ml hydrogen peroxide, and generated by coprecipitation enrichment hydride - atomic fluorescence spectrometry determines trace selenium in it. Under optimum experiment conditions, a standard curve was produced using selenium standard solution, the linear equation is I_se=2890.6c+0.0012,compared wish the linear relaticnship is not by coprecipitation direct determination of standard series I_se=82.56c+0.0018 Selenium detection sensitivity was increased by 35.01 times,the correlation coefficient of obtained linear regression equation is 0.9996, the detection limit is 0.0012μg/L and the relative standard deviation is 0.76% (n=5). Containing 0.1808μg.g-1 Se Luo Han Shen samples. Based on mogroside sample, add a certain of standard solution to do recovery experiment, the obtained recovery rate is in 95.8%~103.6% and the result is satisfactory.

Abstract: The content of selenium in Shiitake was determined by hydride-atomic fluorescence spectrometry and the sources of uncertainty were evaluated. Each parameter in mathematic model was analyzed to evaluate the type A and type B uncertainties in the method. To obtain the uncertainty evaluation , each uncertainty component was synthesized and extended by the current international method . The evaluation results showed that the major source of the uncertainty in the method was the sample solution volume and the standard curve.