Oxidation Of ZnS Research Articles

Fabrication and Characterizations of ZnO and ZnO:Mn Nanocrystalline Thin Films

AbstractThis paper provides a brief summary of the structural and optical study of ZnO and ZnO:Mn materials fabricated from simple process: oxidation of ZnS and ZnS:Mn thin films grown by LPMOCVD. Both structural analysis and optical characterization have confirmed the good quality ZnO material formation. XRD results suggest that the fabricated ZnO film is composed of ∼30 nm ZnO nanocrystals with a hexagonal wurtzite structure. Raman spectra show a strong resonant multiphonon effect. In all cases, a UV emission is observed at ∼ 380 nm. A green emission is also observed in the ZnO nanocrystalline film. On the other hand, it is demonstrated that the Mn doping in ZnS film can dramatically affect the luminescence properties of end products: nanocrystalline ZnO thin films. The photoluminescence spectra of the films with an optimized Mn doping concentration only showed the ultraviolet emission, while the green emission was fully quenched. It is argued that the presence of the Mn can effectively passivate the electron and hole trapping sites at the surface and interface of the ZnO nanocrystals.

Tower-like structure of ZnO nanocolumns.

The tower-like structure of ZnO nanocolumns grows normal to alumina substrates via pyrolysis and oxidation of ZnS, and is formed by stacking of ZnO nanocrystals layer upon layer.

Characterisation of zinc in slags originated from a contaminated sediment by coupling μ-PIXE, μ-RBS, μ-EXAFS and powder EXAFS spectroscopy

Depositing dredged sediments on soils is usual but it is a hazardous practice for the local environment when these sediments are polluted by heavy metals. This chemical hazard can be assessed by determining the speciation of metals. In this study, slags highly polluted with Zn and originated from a contaminated dredged sediment were investigated. Zn speciation was studied by laterally resolved techniques such as μ-particle induced X-ray emission (μ-PIXE), μ-Rutherford backscattering spectrometry (μ-RBS), μ-extended X-ray absorption fine structure (μ-EXAFS), and bulk analyses such as powder EXAFS spectroscopy. μ-PIXE and μ-RBS results showed that high concentrations of Zn were associated with S in localised areas at the surface of the slags while moderate amounts of Zn were mainly associated with Fe in the matrix. EXAFS results allowed to identify ZnS and Zn sorbed on ferrihydrite (5Fe 2O 3·9H 2O), proxy for iron oxy-hydroxides, as the main Zn-bearing phases. The occurrence of this Zn–iron oxy-hydroxide is interpreted as a mobilisation of Zn released from ZnS oxidation.

Degradation proof modification of ZnS-based phosphors with ZnO nanoparticles

ZnS:Ag,Cl phosphor particles were coated discretely by ZnO nanoparticles to prevent degradation by electron bombardment at 7kV. The degradation of ZnS:Ag,Cl modified with ZnO nanosize particles was reduced by 40% after 9h exposure to 7kV electron beams, in comparison with that without ZnO nanosize particles. The predominant mechanism of degradation prevention is to suppress surface oxidation of ZnS by residual oxygen during cathodoluminescence (CL) experiment. Increased electric conduction and associated protection from local heating are the main reasons for degradation suppression, as confirmed by experimental measurement of degradation for the insulating ZnS:Ag,Cl phosphor.

High temperature growth of ZnS films on bare Si and transformation of ZnS to ZnO by thermal oxidation

ZnS films were grown on Si (100) at high temperatures by pulsed laser deposition using a KrF excimer laser. The growth temperature was varied from 200 to 700 °C and all films were found to have a specific preferential orientation. With increasing Ts, growth rate decreased but the quality of the film improved. The highest quality ZnS film was obtained at 700 °C. The presence of ZnS+ ions among the ablation products of a ZnS target was verified by laser desorption time of flight mass spectroscopy measurements. ZnO was formed by thermal oxidation of ZnS and the films showed strong near band-edge emission at 3.26 eV.

Change of Antibacterial Activity with Oxidation of ZnS Powder.

The antibacterial activities of samples prepared from oxidation of ZnS powder were studied by measuring the change in electrical conductivity with the growth of Escherichia coli. Oxidation of ZnS occurred at above 550°C in air and then the amount of ZnO increased with increasing the oxidizing temperature. The obtained crystal structure of ZnO was a zinc-blende type. From results of antibacterial tests on ZnS powder samples before and after oxidation, the antibacterial activity was found to increase with increasing the oxidizing temperature. However, no activity of ZnS was observed, irrespective of the powder concentration. The pH value after dispersing the powder samples in physical saline solution was in the range between 5.5 and 8.0, increasing with the formation of ZnO.

The oxidation kinetics of zinc sulphide with Thiobacillus ferrooxidans

The kinetics and rate limiting sub-processes in the bacterial oxidation of zinc sulphide with Thiobacillus ferrooxidans were examined. The oxidation rate of synthetic ZnS in the presence and absence of bacteria at equal ferrous and ferric iron concentration and pH, was measured in parallel batch experiments. Bacteria oxidize Fe 2+ produced in the chemical oxidation of ZnS with Fe 3+. In the fermenter without bacteria hydrogen peroxide was added to regenerate ferric iron and maintain the Fe 2+ concentration equal to that in the fermenter with bacteria. No significant differences in the oxidation rates of zinc sulphide were found between the slurry with and without bacteria at equal Fe 2+ and Fe 3+ concentrations. Consequently, an indirect mechanism (i.e. chemical oxidation of ZnS with Fe 3+ to Zn 2+, S 0 and Fe 2+, and bacterial oxidation of S 0 to SO 4 2− and Fe 2+ to Fe 3+) determines the oxidation rate of ZnS in the bacterial oxidation process. From the experiments it was shown that T. ferrooxidans prefers S 0 as a substrate and the regeneration of Fe 3+ can even become terminated. From the experimental data several suggestions for improved process design and experimental research are given.

97/03159 Capacity comparisons and operating experience of reciprocating chillers with R407C and R22

Zinc oxide-based materials are commonly used for the final desulfurization of synthesis gas in IGCC and Fischer–Tropsch based XTL processes. The formation of large amount of solid waste is the major issue of this process. In-situ oxidative regeneration is a promising way to reduce this waste formation and enhance desulfurization process efficiency and economics. However, previous studies showed that one of the major drawbacks of oxidative regeneration of sulfided oxides relies in the high operating temperature range required to overcome the formation of inhibitory sulfate phases. A preliminary work of the authors focused on single oxides identified that regeneration temperature of zinc oxide-based sorbent could be reduced through the addition of molybdenum oxide. Two composites oxides – a single oxides mixture (ZnO and MoO3) and a mixed oxide (ZnMoO4) – were synthesized and characterized. Their sulfidation and oxidative regeneration properties were investigated through thermogravimetry and in-situ characterizations. Sulfidation of the single oxides mixture was shown to be similar to the combination of the sulfidation of both independent single oxides. Mixed oxide sulfidation leads to ZnMoO4 phase demixing into ZnS, MoS2 and ZnMoO3. The oxidative regenerations of the sulfided single oxide mixtures and mixed oxide are initiated, respectively, at 350 °C and 300 °C. These temperatures are 250 °C and 300 °C lower than the regeneration temperature of a pure ZnS. For the sulfided mixed oxide regeneration is even complete at 500 °C under isothermal conditions. Regeneration of sulfided oxides mixture and mixed oxide was thus shown to exhibit synergetic effects, resulting from exothermic oxidative reactions of molybdenum phases. Heat energy released during these reactions is assumed to enhance ZnS oxidation kinetics at a temperature lower than the previously measured one.

97/03157 Air conditioning technology. Shell and tube water chillers

Zinc oxide-based materials are commonly used for the final desulfurization of synthesis gas in IGCC and Fischer–Tropsch based XTL processes. The formation of large amount of solid waste is the major issue of this process. In-situ oxidative regeneration is a promising way to reduce this waste formation and enhance desulfurization process efficiency and economics. However, previous studies showed that one of the major drawbacks of oxidative regeneration of sulfided oxides relies in the high operating temperature range required to overcome the formation of inhibitory sulfate phases. A preliminary work of the authors focused on single oxides identified that regeneration temperature of zinc oxide-based sorbent could be reduced through the addition of molybdenum oxide. Two composites oxides – a single oxides mixture (ZnO and MoO3) and a mixed oxide (ZnMoO4) – were synthesized and characterized. Their sulfidation and oxidative regeneration properties were investigated through thermogravimetry and in-situ characterizations. Sulfidation of the single oxides mixture was shown to be similar to the combination of the sulfidation of both independent single oxides. Mixed oxide sulfidation leads to ZnMoO4 phase demixing into ZnS, MoS2 and ZnMoO3. The oxidative regenerations of the sulfided single oxide mixtures and mixed oxide are initiated, respectively, at 350 °C and 300 °C. These temperatures are 250 °C and 300 °C lower than the regeneration temperature of a pure ZnS. For the sulfided mixed oxide regeneration is even complete at 500 °C under isothermal conditions. Regeneration of sulfided oxides mixture and mixed oxide was thus shown to exhibit synergetic effects, resulting from exothermic oxidative reactions of molybdenum phases. Heat energy released during these reactions is assumed to enhance ZnS oxidation kinetics at a temperature lower than the previously measured one.

Phenomenon of sinter network formation of ZnO in high-temperature environments

The process of sintering oxidation of zinc and lead sulfide concentrates is discussed. The process product is Zn−Pb sinter, the main metal-bearing ingredient for the ISP shaft furnace. Zn−Pb concentrates contain three principal metal sulfides: ZnS, PbS and FeS2, of which ZnS plays the main role in forming the Zn−Pb sinter structure. It was decided to investigate the formation of ZnO crystallites. Zn−Pb sinters obtained on a D-L sinter belt (operating temperature 1250–1350°C) were subjected to SEM observations with simultaneous micro-X-ray analysis of sites chosen in the field under observation; ZnO crystallites formed as a result of the oxidation of ZnS have a typical dendrite structure leading to the formation of ‘sinter networks’; their structure is illustrated by SEM microphotographs.

Oxidation of zinc sulfide by means of zinc sulfate

The problems dealt with in this study concern the oxidation of metal sulfides, in particular attention to the reactions between MSO 4 and MS. The paper contains some experimental results obtained in analyzing the interaction between ZnSO 4 and ZnS by means of thermogravimetric analysis, radiomarking using the isotope 35S, X-ray phase analysis and chemical analysis. It was found that irrespective to the molar ratio of ZnSO 4 to ZnS, the process has two stages. In the first stage, the following equation may be applied: 11ZnSO 4(α) + ZnS = 4(ZnO · 2ZnSO 4) + 48O 2 The second stage may be described by the expression 3(ZnO · 2ZnSO 4) + 2ZnS = 11ZnO + 88O 2 In addition, the effect of the molar ratio of ZnSO 4 to ZnS and of the process temperature on the oxidation rate of ZnS mixed with ZnSO 4, was determined. The results were compared with those obtained for the oxidation of ZnS in air. The activation energies in both stages of the process were also determined.

Surface free energy components of monodisperse zinc sulfide

Apolar, Lifshitz-van der Waals ( γ LW ) and polar, acid-base (Lewis) ( γ AB ) surface free energy components, of monosized, spherical ZnS colloidal particles were experimentally determined using the thin-layer wicking technique. The results were compared with those obtained on a pure, commercial sample of zinc sulfide. The fact that the synthetized sample showed a very high electron-donor ( γ s −) component suggested that some species, related in principle to surface oxidation of ZnS during the synthesis reaction, could be formed on the surface of the particles. To check for this possibility, the surface free energy components of pure and oxidized ZnS, and of zinc oxide and sulfate, were determined by both the contact angle and thin-layer wicking methods. The similarity between γ s components obtained with both methods for pure ZnS lead to the conclusion that both techniques give reliable results. The high γ s − value determined for synthetic ZnS particles cannot be explained simply by surface oxidation of the colloidal particles, since partially oxidized ZnS, or even zinc oxide or sulfate, gave very similar γ s −, always lower than that found for synthetic spherical ZnS. The fact that the Lifshitz-van der Waals ( γ s LW ) component of the surface free energy is somewhat higher for the latter material is believed to be related to elemental sulfur present on the surface of the particles. The general compatibility of the results obtained by both methods suggests that the thin-layer wicking technique is useful to further characterize these or other systems, particularly if the examined material is sufficiently monodisperse.

PROPAGATION OF REACTION FRONTS IN NONCATALYTIC NONISOTHERMAL GAS-SOLID FIXED BED REACTORS

This paper is devoted to the analysis of reaction fronts, in a noncatalytic nonisothermal gas-solid fixed bed reactor. A novel technique to obtain analytical approximate solutions by means of simple functions is presented. These analytical approximate solutions can be used to investigate the effect of various parameters in the reactor performance without resorting to numerical analysis. In addition, for adiabatic conditions and/or fast kinetics, the relationship between dependent variables can be investigated analytically. The technique is illustrated by analyzing the oxidation of ZnS in a fixed-bed reactor.

Electron-beam-enhanced oxidation processes in II-VI compound semiconductors observed by high-resolution electron microscopy

Enhanced oxidation of ZnS and ZnSe semiconductor surfaces has been observed in situ during electron irradiation in a high-resolution electron microscope. The phase present at the surface region has been identified as ZnO by optical diffractogram and selected area electron diffraction techniques. For ZnS oxidation, both hexagonal ZnO having a random orientation and cubic ZnO in perfect epitaxial relationship with the bulk ZnS were observed. Enhanced oxidation of ZnSe to ZnO has also been observed under electron beam irradiation. However, only the hexagonal form was observed. The oxidation rates for both ZnS and ZnSe depended on electron flux but was independent of orientation. A model in which the oxidation process is limited by diffusion through the oxide film is proposed. By electron irradiation the diffusion rate is enhanced presumably by a nonthermal process.

Mechanism of zinc sulphide oxidation

Investigations have been carried out on the thermodynamics, kinetics and mechanism of oxidation of ZnS. The following methods were used: thermodynamic, DT, TG, chemical, phase chemical, gaseous and X-ray (structural, phase, micro-) analyses, scanning electronic microscopy, stereomicroscopy, electronography, analysis of kinetic data, etc. Chemical potential diagrams (log p so 2 -log p o 2 ) have been constructed at various temperatures and the regions of stability of the separate compounds were defined. A multi-strata, strongly porous, finely grained oxide product has been obtained. The layers have a thickness of 5–20 μm and are marked off by cracks up to 1–2 μm wide. This determines the evolution of the oxidation process of particles of the floatation concentrate in a fluidized bed at the high temperature of roasting zinc concentrates under a kinetic regime. A mechanism is suggested for oxidation of a separate particle of ZnS, reporting both the evolution of the chemical process itself and the evolution of heat, heat and mass changes, and changes in the structure and porosity of the solid reagent and product. Structural models are suggested in oxidizing lamellae and spherical particles of ZnS.

ZnS湿式酸化の二，三の実験

ZnS湿式酸化の二，三の実験

酸性溶液中のZnSの湿式酸化に関する速度論的研究

酸性溶液中のZnSの湿式酸化に関する速度論的研究