Crystallization Of Selenium Research Articles

Fabrication and development of biogenic selenium nanoparticles incorporated alginate hydrogel wound care material: a pre-clinical study

ABSTRACT In this study, we attempted to make a nanocomposite wound dressing that was both interactive and bioactive. In order to characterize the biogenic selenium nanoparticles, characterization techniques such as SEM, EDX, DLS, Zetasizer, FTIR, and XRD were utilized. The XRD results showed that the peaks located at around 2θ = 23.9°, 30.1°, 41.6°, 44.1°, and 52.9° that are corresponded to the (100), (101), (110), (102), and (201) reflections of the pure hexagonal phase of selenium crystals. The results of zeta potential measurement showed that the biosynthesized SeNPs have a zeta potential of around −27.5 mV. Studies conducted on animals using a full-thickness wound model of the rat’s skin showed that the wound dressing was able to speed up the natural process of wound healing. Based on the findings, it was determined that the wound dressing has the potential to serve as an effective wound dressing and healing material.

Spin transport and thermoelectric properties in chiral selenium crystals

Spin transport and thermoelectric properties in chiral selenium crystals

Early crystallization of amorphous selenium under high pressure studied by synchrotron XRD method

The amorphous selenium (a-Se) was studied via x-ray diffraction (XRD) under pressures ranging from ambient pressure up to 30 GPa at room temperature to study its high-pressure behavior. Two compressional experiments on a-Se samples, with and without heat treatment, respectively, were conducted. Contrary to the previous reports that a-Se crystallized abruptly at around 12 GPa, in this work we report an early partially crystallized state at 4.9 GPa before completing the crystallization at around 9.5 GPa based on in-situ high pressure XRD measurements on the a-Se with 70 °C heat treatment. In comparison, crystallization pressure on another a-Se sample without thermal treatment history was observed to be 12.7 GPa, consistent with the previously reported crystallization pressure. Thus, it is proposed in this work that prior heat treatment of a-Se can result in an earlier crystallization under high pressure, which helps to understand the possible mechanism caused by the previous controversial reports on pressure induced crystallization behavior in a-Se.

Effect of ultrasonic-induced selenium crystallization behavior during selenium reduction

In this work, the crystallization process of selenium was accelerated by ultrasonic wave. The effects of ultrasonic waves and conventional conditions of selenium crystallization were compared to understand the effects of different conditions on crystallization, including ultrasonic time, ultrasonic power, reduction temperature, and H2SeO3 concentration. The mechanism of ultrasound affecting selenium crystallization was also investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results showed that ultrasonic time, ultrasonic power, and reduction temperature significantly influenced the crystallization process and morphology of selenium. Ultrasonic time had a large effect on the completeness (all products have been crystallized) and integrity of the crystallization of the products. Meanwhile, ultrasonic power and reduction temperature had no effect on the completeness of crystallization. However, it had a significant effect on the morphology and integrity of the crystallized products, and different morphologies of the nano-selenium materials could be obtained by changing the ultrasonic parameters. Both primary and secondary nucleation are important in the process of ultrasound-accelerated selenium crystallization. The cavitation effect and mechanical fluctuant effects generated by ultrasound could reduce the crystallization induction time and accelerate the primary nucleation rate. The high-speed micro-jet formed in the rupture of the cavitation bubble generated is the most important reason to influence the secondary nucleation of the system.

Surface mobility in amorphous selenium and comparison with organic molecular glasses.

Surface diffusion is important for a broad range of chemical and physical processes that take place at the surfaces of amorphous solids, including surface crystallization. In this work, the temporal evolution of nanoholes is monitored with atomic force microscopy to quantify the surface dynamics of amorphous selenium. In molecular glasses, the surface diffusion coefficient has been shown to scale with the surface crystal growth rate (us) according to the power relation us ≈ Ds 0.87. In this study, we observe that the same power law applies to surface crystallization of amorphous selenium, a representative inorganic polymer glass. Our study shows that the surface diffusion coefficient can be used to quantitatively predict surface crystallization rates in a chemically diverse range of materials.

Doping and biaxial deformation engineering the thermoelectric transport properties in selenium crystal

The electronic structure and thermoelectric transport properties of elemental selenium which has a chiral chain structure are investigated using first principle calculations and Boltzmann transport theory. Results show that selenium can achieve high zT value along the chain under p-type doping. Biaxial deformation is found to be capable of influencing the band structure and the effective mass and further manipulating the thermoelectric transport properties. The −2% biaxial compressive strain can realize the heavy and light band converged to improve both the Seebeck coefficient and the electrical conductivity. These results pave the way towards opportunities for developing inter-chain van der Waals bonded chiral-based polychalcogenide thermoelectric materials.

Biosynthesis of selenium nanoparticles mediated by fungus Mariannaea sp. HJ and their characterization

The biosynthesis of selenium nanoparticles (SeNPs) by Mariannaea sp. HJ was reported for the first time. Different cultural conditions, including SeO2 concentrations and pH were studied, 2 mM SeO2 and pH 10 were favorable for the removal of Se(IV), and extracellular SeNPs were observed at alkaline pH values. UV–vis spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were used to characterize SeNPs. The results showed that removal of Se(IV) ions occurred during the late exponential phase of strain HJ. TEM and SEM images revealed that spherical nanoparticles were deposited on the cell wall and in the cytoplasmic region of strain HJ with a uniform size distribution. XRD pattern suggested the standard hexagonal phase of selenium crystals. FTIR, XPS and selective passivation experiments implicated that lipid and amide groups were involved in the formation process and Se(-I) or Se(-II) species were demonstrated to be functioned in this process. Based on the SDS-PAGE analysis, the up-regulated proteins of MW ∼91.6 and ∼37.4–57.2 kDa might promote SeNP formation, and a number of proteins adsorbed on the surface of nanoparticles, which may act as a natural stabilizing agent.

Investigation of the processes of softening and crystallization of glassy selenium by dynamic mechanical analysis method

Purpose. The purpose of this work was the investigation of mechanical characteristics of glassy and polycrystalline selenium in glasstransition and crystallization regions by dynamic mechanical analysis method and also the determination of relaxation parameters and establishing the mechanism of dissipative processes in selenium above its softening temperature . Methods. It was measured the mechanical loss tangent and dynamic modulus of elasticity as functions of tem perature. Measurement of these parameters were performed in the mode of forced bending oscillations at a frequency of 0.5 Hz using the Q400 TMA device at a temperature range 220 K - 450 K. Results. In glassy selenium in softening temperature region the a-process of mechanical relaxation with a relative decrease of the elastic module ∆E/E = 0.73 was found. Rapid increase in the elastic modulus due to the crystallization processes of glassy selenium in the interval 353 K - 378 K was observed. Cooling of selenium sample from 450 K to 220 K did not reveal of glassforming effects on the temperature dependences of the elastic modulus and the mechanical loss tangent: a sample of selenium was polycrystalline. Maxima are observed in the temperature dependences of the tangent of the angle of mechanical losses at the α-process of relaxation and crystallization of glassy selenium. Conclusions. In the temperature dependence of the elastic module of glassy selenium a high elasticity plateau was found. The presence of a highly elastic state in glassy selenium in the temperature range 325 K-350 K and crystallization process in the range of 353 K-378 K are shown. In polycrystalline selenium there are no dissipative processes that are characteristic of the glasslike state.

Compressibility, Electrical Conductivity, and Crystallization of Glassy Selenium at a High Pressure

The volume and the electrical resistivity of glassy selenium (g-Se) are precisely measured at a high hydrostatic pressure up to 9 GPa. The bulk modulus at normal pressure (B = 9.05 ± 0.15 GPa) and its baric derivative ( $$B_{P}^{'}$$ = 6.4 ± 0.2) fall on the general concentration dependence of the properties of Se–Ge glasses. The bulk modulus is found to behave substantially nonlinearly in the pressure range P < 3 GPa, and this behavior is not related to glass density relaxation (which is absent in this pressure range). The electrical resistivity of g-Se decreases almost exponentially with increasing pressure and reaches 20 Ω cm at 8.75 GPa. The inelastic behavior and weak volume relaxation in g-Se begin at a pressure above 3.5 GPa. Both the volume and the logarithm of electrical resistivity exhibit noticeable (logarithmic in time) relaxation at above 8 GPa. The detected volume hysteresis (1%) and significant (two orders of magnitude) electrical resistivity hysteresis are associated with the pressure-induced structural changes in the glass. They cannot be explained by partial glass crystallization, since no crystalline phase impurity was detected right after experiments. A noticeable (about 1.5%) crystalline phase impurity appears in a sample only after long-term (1 day) storage at a pressure above 8 GPa. Moreover, the crystallization kinetics of g-Se is studied under normal conditions after the action of a high pressure.

Lattice Symmetry of Nanothin Crystals, Direct and Reciprocal Space Isomorphism, and the Curie Symmetry Principle

The symmetry of direct and reciprocal lattices and the symmetry of bend contours present in the electron microscopy images of nanothin crystals with elastic rotational distortion of the lattice are examined using the example of nanothin selenium crystals.

Pressure effect on thermal-induced crystallization of amorphous selenium up to 5.5 GPa

Thermal stability of bulk melt-quenched amorphous selenium (a-Se) has been investigated with a multi-anvil apparatus in a pressure range of 0.5–5.5GPa. An anomalous pressure effect on thermal-induced crystallization of a-Se is observed through in situ temperature measurements. In the lower-pressure range (0.5–2.0GPa), the onset crystallization temperature (Tx) increases largely with increasing pressure. However, in the higher-pressure range of 2.0–5.5GPa, Tx does not increase but remains almost constant when pressure is applied. The results are briefly discussed with regard to the various pressure effects on amorphous solids and may be explained by considering that two different crystallization mechanisms are probably involved in the two pressure regions.

Native selenium as a byproduct of microbial oxidation of distorted pyrite crystals: the first occurrence in the Carpathians

Abstract Acicular crystals of native selenium up to 30 μm long occur together with barite on the surface of goethite partial pseudomorphs after millimeter-sized pseudotetragonal-prismatic pyrite crystals in calcite veins that cross-cut Senonian sandstones of the Silesian Nappe in the western Polish Outer Carpathians. Native selenium originated from selenium apparently released during bacteria-induced oxidation of pyrite at neutral or near-neutral pH conditions. Oxidizing bacteria preferentially colonized {100} faces of pyrite relative {111} faces.

Biosynthesis and structural characterization of selenium nanoparticles mediated by Zooglea ramigera

Abstract In the present study, biosynthesis of selenium nanoparticles with non-pathogenic, ecofriendly, easily available bacterium Zooglea ramigera was reported. The bacterium Z. ramigera was grown aerobically with selenium oxyanions (as the electron acceptor). It was formed extracellular, stable, uniform, nanospherical structure of monoclinic crystalline selenium. The biosynthesized selenium nanoparticles were spherical (by TEM) in shape with the size range of 30 nm to 150 nm. The formation of selenium nanorods (trigonal) was also observed. XRD and SAED analyses revealed that synthesized selenium nanoparticles were selenium crystal of the pure hexagonal phase. A hypothetical mechanism for biological synthesis of selenium nanoparticles was also proposed.

Investigation of the solid state reactions by time-resolved X-ray diffraction while crystallizing kesterite Cu2ZnSnSe4 thin films

The pentanary chalcogenide Cu2ZnSn(S,Se)4 (CZTSSe) compound is attracting considerable attention as a low-cost and high-efficient solar cell. The band gap can be tuned by adding Se to pure kesterite Cu2ZnSnS4, which influences the crystallization kinetics. The investigation of the crystallization of the pure selenium (Se) compound Cu2ZnSnSe4 can be helpful in understanding the reaction path between the elements of CZTSSe. Sputtered Cu-poor intermetallic Cu–Zn–Sn precursors were deposited on Mo-coated polyimide foil and sequentially capped by a thermally evaporated Se layer. Two different amounts of Se were deposited: amount that exactly matches the composition of Cu2ZnSnSe4; and that corresponding to twofold excess of the compound's element ratio. These two compositions were chosen to investigate influences of the amount of Se on the reaction path and kinetics. Also, the reaction of pure metallic Sn with Se was studied by stacking Sn layers on Mo-coated foils for observing a Sn-loss phenomenon. It was also deposited with two different amounts of Se matching approximately the compositions of SnSe and SnSe2. Time-resolved X-ray diffraction was employed to measure the solid state reactions while increasing the sample temperature up to 550°C at a rate of 0.5K/s in an evacuated reaction chamber. After the experiment, sample is analyzed by Raman spectroscopy to distinguish the CZTSe from secondary phases.

Evolution of formation of interblock boundaries in nanothin selenium crystals

Evolution of formation of interblock boundaries in nanothin selenium crystals

Evolution of the shape of nanothin selenium crystals during their growth in amorphous films

Evolution of the shape of nanothin selenium crystals during their growth in amorphous films

The selenium based chalcogenide glasses with low content of As and Sb: DSC, StepScan DSC and Raman spectroscopy study

Thermal properties and structure of As x Se 100− x and Sb x Se 100− x glass-forming systems ( x = 0, 1, 2, 4, 8 and 16) were studied by conventional and StepScan DSCs and Raman spectroscopy. Compositional dependence of the glass transition temperature, T g, was determined from reversible part of StepScan DSC records and discussed. The attention was also focused on the crystallization of undercooled melts of these systems. It was found that only selenium crystallizes from undercooled melts of As–Se system and its tendency to crystallize decreases markedly with increasing As content, for arsenic content higher than 4 at.% no crystallization was observed. In the case of Sb–Se system Sb 2Se 3 crystallizes in the first step followed by trigonal selenium crystallization from non-stoichiometric undercooled melt. Sb 2Se 3 crystallizes from incongruent melt with crystallization enthalpy Δ H c(Sb 2Se 3) = −52 ± 2 J/(g of Sb 2Se 3), Johnson–Mehl–Avrami kinetics of crystallization and kinetic exponent close to 3 was found. Raman spectra were measured to obtain basic information on the structure of both glassy systems.

Measurements of DSC isothermal crystallization kinetics in amorphous selenium bulk samples

In this research, the activation energies of crystallization of amorphous selenium (Se) were studied under isothermal conditions using a differential scanning calorimetric (DSC) technique. The activation energy for crystallization was determined to be 77 ± 6 kJ mol −1. The Avrami exponent was found to be about 2 for an annealing temperature of T ≤ 361 K, indicating two-dimensional growth. As the annealing temperature increases beyond 365 K, the Avrami exponent mostly gives values more than 2.5, indicating three-dimensional growth. The effects of annealing were revealed by studying the morphology of the samples with a scanning electron microscope (SEM).

Pressure-induced crystallization and phase transformation of amorphous selenium: Ramanspectroscopy and x-ray diffraction studies

High-pressure Raman spectroscopy studies have been carried out on amorphous Se (a-Se)at room temperature in a diamond anvil cell with an 830 nm exciting line. Raman evidencefor the pressure-induced crystallization of a-Se and the coexistence of the unknownhigh-pressure phase with the hexagonal phase is presented for the first time. Furtherexperimental proof of high-pressure angle-dispersive x-ray diffraction studies for a-Seindicates that the unknown high-pressure phase is also a mixture phase of the tetragonalI41/acd and Se IV structure. Our Raman and x-ray diffraction results suggest that hexagonal Se Iundergoes a direct transition to triclinic Se III at about 19 GPa, which is in good agreementwith the theoretical prediction.

Lattice geometry change of nanothin selenium crystals with the growth in amorphous films

Lattice geometry change of nanothin selenium crystals with the growth in amorphous films