Amorphous As2S3 Research Articles

Electric field induced second harmonic generation in arsenic sulfide deposited by thermal evaporation.

Electric field induced second harmonic (EFISH) measurements are performed on thin films of arsenic sulfide deposited on chromium coated fused silica substrates by thermal evaporation of amorphous As2S3 bulk material. EFISH allows to widely tune the second-order optical susceptibility (χ(2)). An observed shift of the minimum of the second harmonic generation (SHG) intensity away from 0 V reveals a non-EFISH bulk χ(2), which is unexpected for amorphous materials. Additional SHG measurements on as-deposited films for investigation of the non-EFISH bulk χ(2) show Maker fringe patterns. Analyzing them and calibrating the SHG response against beta barium borate (BBO) crystal allows us to extract the components of the χ(2) tensor. The main component of this non-EFISH bulk χ(2) has a value of ∼0.22 pm/V. By increasing the χ(2) by applying the dc electric field a maximum value of 3.8 pm/V was achieved in EFISH measurements. This value is comparable to the χ(2) of traditional nonlinear crystals, e.g., BBO, which makes arsenic sulfide an interesting candidate for nonlinear hybrid structures.

Photo-induced bending of amorphous As2S3 bulk and fiber driven by optical torque

Photo-induced bending of amorphous As2S3 bulk and fiber driven by optical torque

Four-Layer Surface Plasmon Resonance Structures with Amorphous As2S3 Chalcogenide Films: A Review.

The paper is a review of surface plasmon resonance (SPR) structures containing amorphous chalcogenide (ChG) films as plasmonic waveguides. The calculation method and specific characteristics obtained for four-layer SPR structures containing films made of amorphous As2S3 and As2Se3 are presented. The paper is mainly based on our previously obtained and published scattered results, to which a generalized point of view was applied. In our analysis, we demonstrate that, through proper choice of the SPR structure layer parameters, we can control the resonance angle, the sharpness of the SPR resonance curve, the penetration depth, and the sensitivity to changes in the refractive index of the analyte. These results are obtained by operating with the thickness of the ChG film and the parameters of the coupling prism. Aspects regarding the realization of the coupling prism are discussed. Two distinct cases are analyzed: first, when the prism is made of material with a refractive index higher than that of the waveguide material; second, when the prism is made of material with a lower refractive index. We demonstrated experimentally that the change in reflectance self-induced by the modification in As2S3 refractive index exhibits a hysteresis loop. We present specific results regarding the identification of alcohols, hydrocarbons, and the marker of E. coli bacteria.

Treatment and recycling of arsenic slag by hydrothermal reduction of As2S3 to As(0)

Arsenic existed concomitantly with minerals containing precious or non-ferrous metals, in which arsenic-containing wastewater (ACW) is inevitably generated during the process of smelting. In the treatment of ACW, the precipitation method using sulphide is widely used, but the resulting arsenic sulphide slag poses a risk of secondary pollution. In this work, a reduction strategy was developed to transform arsenic sulphide slag into elementary arsenic under hydrothermal conditions by using sodium formate as the reductant, with the aim to treat the slag and recycle As. The experimental results show that As(0) can be obtained by one-step hydrothermal reduction by sodium formate at temperature of 200 ℃ and pH 4, and the purity of elementary arsenic produced under the optimum conditions is higher than 90%. Mechanism analyses reveal that the reduction process of As2S3 to As(0) experiences two steps, where amorphous As2S3 primary particles first transform and crystallize into partially reductive AsS in a bulk size, and then AsS is further reduced into As(0) through a collapse process to form small particles. This work provides a recycling strategy for the efficient conversion of arsenic sulphide slag to As(0) for potential applications.

Treatment of Acidic Solutions Containing As(III) and As(V) by Sulfide Precipitation: Comparison of Precipitates and Sulfurization Process

Sulfide precipitation has been widely applied to remove arsenic from acidic wastewater containing As(III) and As(V), due to its simple process and high efficiency. However, the characteristics and composition of the precipitates are also of importance for its further treatment and disposal. To explore the characteristics of elemental S formed by reduction and the combined form of the generated S and As2S3, the characteristics of precipitates sulfurized from As(III) and As(V) and the effects of temperature, the S(-II) to As ratio (S/As), Cl− concentration (cCl−), and the volume fraction of H2SO4 (φH2SO4(v)) on the sulfurization of As(III) and As(V) were investigated in detail. The results showed that the contents of As and S were 60.37% and 39.73% in precipitate-As(III), while they accounted for 47.46% and 52.64% in precipitate-As(V); both precipitate-As(III) and precipitate-As(V) were mainly composed of amorphous As2S3, while the latter contained elemental S. Temperature and S(-II)/As(III) slightly affected the sulfurization process of As(III), while for As(V), as the temperature increased, the content of As2S3 in precipitate-As(V) increased significantly. Additionally, with the S(-II)/As(V) increasing, the content of A2S3 increased continuously. This study provides a further clarification of the specific composition and structure of the complex precipitates of arsenic sulfide, which will benefit the efficient stabilization of the arsenic sulfide sludge.

Mechanism of Photoinduced Gyrotropic Phenomena in Amorphous As2S3

Little is known why illumination of linearly polarized continuous‐wave laser light can induce gyrotropy (optical rotatory power) and macroscopic circular/screwing deformations in amorphous As2S3. Gyrotropy appears through scattering and deflection of the incident light in combination with negative photoinduced birefringence. The gyrotropy could also trigger atomic motions under photoinduced fluidity, which produces macroscopic deformations.

Amorphous As2S3 Doped with Transition Metals: An Ab Initio Study of Electronic Structure and Magnetic Properties.

Crystalline transition-metal chalcogenides are the focus of solid state research. At the same time, very little is known about amorphous chalcogenides doped with transition metals. To close this gap, we have studied, using first principle simulations, the effect of doping the typical chalcogenide glass As2S3 with transition metals (Mo, W and V). While the undoped glass is a semiconductor with a density functional theory gap of about 1 eV, doping results in the formation of a finite density of states (semiconductor-to-metal transformation) at the Fermi level accompanied by an appearance of magnetic properties, the magnetic character depending on the nature of the dopant. Whilst the magnetic response is mainly associated with d-orbitals of the transition metal dopants, partial densities of spin-up and spin-down states associated with arsenic and sulphur also become slightly asymmetric. Our results demonstrate that chalcogenide glasses doped with transition metals may become a technologically important material.

Ermakovite (NH4)(As2O3)2Br, a new exhalative arsenite bromide mineral from the Fan-Yagnob coal deposit, Tajikistan

AbstractIn terrestrial rocks, Br minerals are extremely rare with only nine minerals known where Br is a dominant component. A new arsenite bromide mineral ermakovite, (NH4)(As2O3)2Br, was discovered at the tract of Kukhi-Malik, Fan-Yagnob coal deposit, ca. 75 km N of Dushanbe, Tajikistan. Ermakovite is a fumarolic mineral formed directly from gas from a natural underground coal fire. Associated minerals are sulfur, realgar, amorphous As-sulfides, salammoniac, alacránite, bonazziite and thermessaite-(NH4). In addition, there are amorphous As2S3 intergrowths associated with ermakovite. The mineral typically occurs as tabular or prismatic hexagonal crystals up to 200 μm with the following forms: c (001), m (010) and p (014). Spherulites and multi-twinned intergrowths are very common. The mineral is optically uniaxial (–), ω = 1.960 (5) and ɛ = 1.716(3) (589 nm). The measured density is 3.64(2) g/cm3. The mineral is insoluble in water, HCl, HNO3 and organic solvents. The empirical formula calculated on the basis of (As+Sb) = 4 atoms per formula unit is [(NH4)0.92Na0.01]0.93(As3.94Sb0.06)4.00O6.02(Br0.97Cl0.08I0.01)1.06. The strongest lines in the powder X-ray diffraction pattern are [d, Å (I, %) (hkl)]: 9.160 (80)(001); 4.560(90)(002); 3.228(100) (102); 2.629(80)(110); and 2.522(60)(103). Ermakovite is hexagonal, P6/mmm, a = 5.271(3), c = 9.157(6) Å, V = 220.3(3) Å3 and Z = 1. The sandwich-type structure of ermakovite is based on three types of layers: (1) a honeycomb [As2O3] arsenite layer; (2) an NH4+ layer; and (3) a Br layer. The layer stacking sequence is ⋅⋅⋅NH4–As2O3–Br–As2O3–NH4⋅⋅⋅. Ermakovite has a synthetic analogue. Infrared and Raman spectra are also reported.An overview of the processes that give rise to high concentrations of Br, leading to the formation of exotic Br minerals, is given.

Pulsed light effects in amorphous As2S3: review

Pulsed light effects in amorphous As2S3: review

Transient photodarkening induced by a nanosecond pulsed laser in amorphous and liquid As2Se3: fractal characteristics in relaxation dynamics

Transient photodarkening induced by a nanosecond pulsed laser in amorphous and liquid As2Se3: fractal characteristics in relaxation dynamics

The arsenic species in the sulfidic environments: Determination, transformation, and geochemical implications

The species and fate of arsenic (As) are closely related to sulfide (S−II) in the anaerobic and sulfidic environment. In this work, the mechanisms and kinetics of arsenate (AsV) reduction by S−II at different pHs, S−II/AsV molar ratios, and initial AsV concentrations in the absence (or presence) of Al-hydroxide were studied, where the concentrations of various kinds of As species, namely AsV, arsenite (AsIII), and thioarsenics (ThioAs) were qualitatively and quantitatively determined by liquid chromatography with atomic fluorescence spectrophotometry. The results showed that under acidic or neutral conditions, ThioAs may act as intermediate(s), where amorphous As2S3 precipitate was observed at pH 5 in high S−II condition. By comparison, at pH 9, AsV was probably directly reduced to AsIII with polysulfide as the byproduct. The reaction rate was faster at mildly acidic pH than that of neutral or alkaline pH, as well as in the presence of Al-hydroxide. The findings may give further insights about the role of ThioAs in the biogeochemical cycle of As.

Находка бонацциита и алакранита в возгонах природного подземного угольного пожара в урочище Кухи-Малик, Таджикистан

бонацциит, алакранит, ральгар, сульфиды мышьяка, псевдофумаролы, угольный пожар, возгоны, Таджикистан, Фан-Ягнобское месторождение, Кухи-Малик Two rare minerals were found in the sublimates of a natural coal fire at the Fan-Yagnob coal deposit (Tajikistan) – bonazzite As4S4 and alacranite As8S9. Bonazzite occurs as orange, orange-red rhombic tapered crystals, both skeletal, block, and full-faceted, from 0.1 to 1.5 mm in size. Bonazziite grows on realgar crystals or on a matrix, composed of amorphous As2S3. The association contains sal-ammoniac and ermakovite (NH4)(As2O3)2Br; crystals of the latter also grows on bonazziite. In transmitted light in thin sections, bonazzite is yellowish-brown, biaxial (+). Dispersion is strong, v > r. 2Vmeas. = + 60(5)°. Refractive indices are significantly higher than n = 2.05. In reflected light, it is gray with intense internal reflections ranging from yellow-green to red. Digests in 5M KOH, producing brown colored spots. The unit cell parameters from X-ray powder data are as follows: a9.972(5), b 9.435(3), c 8.870(6) Å, β 102.25(4) º, V 815(1) Å3. The X-ray ratio b : c= 1.063, morphological ratio (if to assign the symbol {111} to the most developed face) from the results of goniometric measurements from 0.817 to 0.870. Indicing of this facet, applying X-ray cell parameters leads to irrational symbols.Bonazziite crystals are assumed to be paramorphoses on a related phase with some different cell parameters. Measured density (g/cm3) 3.57(1), calculated 3.52. Chemical analysis by electron microprobe using EDS (12 points), As 69.01, S 29.86, Se 0.47, total 99.34 wt.%. The empirical formula is As4.01S3.96Se0.02. Adjacent realgar does not contain Se at the sensitivity level of the microprobe analysis. Powdery yellow As-sulfide sometimes develops on realgar, it also grows as rhombic brittle crystals, similar to those of bonazzite. X-ray powder data shows, it is close to alacranite with cell parameters a 9.90(5), b 9.58(5), c 9.11(5) Å, β 101.6(6) º, V 847(5) Å3.The growth of bonazzite could have been originated by a local increase in temperature (but no more than up to 320 °C – the upper temperature limit of stability of the realgar) and/or Se occurence in the gas precipitates, which played the role of a stabilizing impurity that caused the growth of bonazzite on the realgar. A local change in the thermal regime probably led to the appearance of related alacranite.

Mass transport in amorphous As2S3 films due to directional light scattering under illumination by an oblique tightly focused beam

Photoinduced deformation of an amorphous As2S3 film surface under illumination by sub-bandgap (638 nm) and above-bandgap (532 nm) polarized laser light at oblique incidence are studied by atomic force microscopy performed directly after the film exposure to the laser beam. Photoinduced expansion as well as directional mass transport from the laser spot are observed. The photodeformation character under sub-bandgap and above-bandgap illumination are discussed in view of the optical forces (gradient force and scattering force) due to the interaction of light with the amorphous As2S3 film .

Hydrocarbons detection using surface plasmon resonance with As2S3 thin film waveguide

Surface plasmon resonance containing amorphous As2S3 film is proposed as a chemical sensor to highlight several liquid hydrocarbons. Method is label-free and is based on detection of small changes in the refractive index. As2S3 operates as plasmonic waveguide which confines the probing beam to the interface with liquid hydrocarbons. The method can easily distinguish hydrocarbons with very close refractive indices. The film thicknesses were optimized to obtain the best sensitivity and resolving power. Minimum reflectance of SPR less than 1 % was found for optimal calculated film thicknesses, the sensitivity to the refractive index changes being 2·10-5 .

Speciation characterization of arsenic-bearing phase in arsenic sulfide sludge and the sequential leaching mechanisms

Arsenic sulfide sludge (ASS) is a kind of deleterious waste which contains various valuable metallic elements, such as Re and Pb, which are always associated with arsenic-bearing phases in ASS. The leaching speed and efficiency of valuable elements may depend on the phase constitution. Here, we proposed a sequential leaching method to thoroughly understand the constitution of arsenic-bearing phase and the distribution of valuable elements in ASS. The results show that five major arsenic-bearing phases exist in ASS: amorphous As2S3, crystalline As4S4, As2O3, and As atoms dissolved into the lattice of PbS and PbSO4 phases. Re is mainly distributed in As2S3 and As4S4 phases. During the leaching process, the dissolution of As2O3 particles and As2O3 layers on the surface of As2S3/As4S4 particles occurs first. Then, the reaction between As2S3/As4S4 particles and copper sulfate happens. The order of leaching sequence is As2O3, amorphous As2S3 and crystalline As4S4. The majority of Re element exists in the solution while almost all Pb element remains in the solid residues, which is beneficial for the separation and purification valuable elements individually. This work not only detailed determines the arsenic-bearing species, but also provides significant theoretical bases for extracting valuable elements from ASS.

Optical properties of amorphous [formula omitted] doped with lanthanum oxide and erbium oxide

The photoluminescence (PL) spectra of amorphous As2S3 samples are investigated in a wide temperature interval by using the optical and ellipsometric methods. PL spectra under radiation with excitation energy smaller than Tauc’s edge energy allows us to determine all defect states in the forbidden band of amorphous As2S3. The ellipsometric investigation of a−As2S3 on reflection indicates precise anomaly of real and imaginary parts of the dielectric function around the transition edge corresponding to the inter-band transition, determined from photoluminescence measurements. PL investigation of La2O3, Er2O3 and As2S3:(La2O3)(Er2O3) compounds from nearest ultra-violate up to infra-red (IR) energy interval shows a coincidence of many absorption lines of La2O3 and Er2O3, furthermore surviving of these lines in As2S3:(La2O3)(Er2O3). These facts allow us to conclude that S atoms in As2S3:(La2O3)(Er2O3) replace O atoms, and that the discrete PL lines observed as in La2O3, Er2O3 as well as in As2S3:(La2O3)(Er2O3) belong to La and Er atoms. Comparison of PL spectra lines of La2Os and As2S3:(La2O3)5% with those of Er2O3 and As2S3:(Er2O3)5% shows that the intensity of the former lines is 2–3 order stronger than those of the latter samples’ lines. Nevertheless this picture is reversed for amorphous As2S3 samples simultaneously doped with La2O3 and Er2O3, which confirms that a cross relaxation from excited states of La to Er takes place. It is worthy to note that the PL spectra in IR-region were firstly measured in this work in order to get a complete information on the localized states density in the forbidden band of a−As2S3.

Kinetics and mechanisms of arsenic and sulfur release from crystalline orpiment

Arsenic trisulfide (As2S3), in both amorphous and crystalline form, is a significant arsenic-containing compound naturally occurring in mine waste rock or generated as metallurgical waste. It is typically unstable in the enviroment, especially under alkaline and oxidizing conditions, which is a significant barrier to fixation of arsenic present in metallurgical waste streams in the form of arsenic trisulfide. Our previous study has shown the effect of different factors on the kinetics and mechanisms of arsenic and sulfur release from amorphous As2S3. To assess the effect of crystallinity on the stability of arsenic trisulfide, a series of laboratory leaching tests were performed with crystalline orpiment under fully controlled conditions. The experimental results showed that the release of arsenic and sulfur increased with pH, dissolved oxygen concentration, and temperature, but the release rates were much slower than those of amorphous arsenic trisulfude. The speciation analyses indicated that arsenic was present in the leachates as arsenite, which was subsequently oxidized to arsenate to different extents; thiosulfate was the main soluble sulfur species, which was converted to sulfate via oxidation and disproportionation pathways. The kinetic modeling suggested that the arsenic release process is a mixed-control reaction, in which the surface chemical reaction and the diffusion of dissolved oxygen through a product layer control the arsenic release rate. The solid surface characterization supported the presence of an arsenic-deficient phase enriched in elemental sulfur on the solid surfaces. The product layer acted as a barrier to the diffusion of reagents, as evidenced by the leaching being sensitive to the removal of elemental sulfur.

Transformation behavior of the morphology, structure and toxicity of amorphous As2S3 during hydrothermal process

Arsenic sulfide sludge (ASS) is a typical hazardous waste in the non-ferrous smelting industry. In our previous study, ASS was effectively stabilized by hydrothermal treatment. However, the mechanism of hydrothermal stabilization is still unclear. Amorphous As2S3 is the main component of ASS. Therefore, in this work, the hydrothermal transformation behavior of amorphous As2S3 precipitated with NaAsO2 and Na2S·9H2O under acidic aqueous was investigated for a better understanding of hydrothermal stabilization process of ASS. It was found that under the conditions of 210 °C, initial pH 2 and solid-to-liquid (S/L) ratio 1:5, amorphous As2S3 floc gradually transformed to spherulitic particles and showed aggregation behavior with the extension of hydrothermal duration. The spherulitic particles were identified as orpiment, which was the crystalline arsenic mineral in the nature. Moreover, the As leaching concentration of hydrothermal products decreased remarkably with the transformation from amorphous As2S3 to orpiment. Under certain hydrothermal conditions, the As leaching concentration of amorphous As2S3 can be reduced from 139.4 mg/L to less than 5 mg/L. Hence, the mineralization from amorphous As2S3 to orpiment was the significant reason for the stabilization of arsenic sulfide during hydrothermal treatment. This paper provided a theoretical support for the hydrothermal stabilization of ASS.

The density, nanohardness and some optical properties of As-S and As-Se chalcogenide bulk glasses and thin films.

Amorphous As2S3, As2Se3 and As1Se99 bulk glasses and thin films were prepared by the melt quenching technique and vacuum thermal evaporation, respectively, on different substrates. The density (ρ) – determined by the simple and cheap method of precise weighting, refractive index (n), structural arrangement – inferred from Raman spectroscopy, and nanohardness (Hind) were determined for all the studied materials in both bulk and thin film states. It is found that regardless of the chemical composition, the bulk glass density, refractive index and nanohardness are higher in comparison with those of the corresponding virgin and by annealing relaxed thin films, and the observed differences are discussed. The almost negligible influence of the substrate on the thin films density, structural arrangement and nanohardness, was observed.

Removal of arsenic from acid wastewater via sulfide precipitation and its hydrothermal mineralization stabilization

Abstract To achieve a safe treatment of arsenic-containing acid wastewater, a new process was proposed, including arsenic removal via sulfide precipitation and hydrothermal mineralization stabilization. Under optimal conditions of sulfide precipitation, 99.65% of arsenic from wastewater was precipitated in the form of amorphous As2S3. The As leaching concentration of amorphous As2S3 in TCLP (toxicity characteristic leaching procedure) test was up to 212.97 mg/L, therefore, hydrothermal mineralization was adopted to improve the stability of amorphous As2S3. The results showed that the As leaching concentration of mineralized As2S3 was only 4.82 mg/L. Furthermore, the amorphous As2S3 could be transformed into crystallized As2S3 (orpiment) in the presence of mineralizer Na2SO4. Simultaneously, the As leaching concentration of crystallized As2S3 was further reduced to 3.86 mg/L. Hydrothermal mineralization was an effective method for the stabilization of As2S3. Therefore, this process has a greater application in the treatment of arsenic-containing wastewater.