Oxygen-deficient Atmosphere Research Articles

Influences of sintering atmosphere on the formation and photocatalytic property of BaFe 2O 4

Spinel compounds (BaFe 2O 4) were synthesized through different routes. X-ray powder diffraction (XRD) and Fourier transition infrared spectroscopy (FTIR) proved that the formation of the spinel structure was influenced by the sintering atmosphere and the spinel structure could not be obtained in an oxygen-deficient atmosphere. An excellent photocatalytic property of synthesized BaFe 2O 4 was found. Photocatalytic experiments were carried out on the degradation of methyl orange and the absorbencies of samples were determined by UV–vis spectrophotometer.

Electronic properties of thermally formed thin iron oxide films

The oxide layer, present between an organic coating and the substrate, guarantees adhesion of the coating and plays a determinating role in the delamination rate of the organic coating. The purpose of this study is to compare the resistive and semiconducting properties of thermal oxides formed on steel in two different atmospheres at 250 °C: an oxygen rich atmosphere, air, and an oxygen deficient atmosphere, N 2. In N 2, a magnetite layer grows while in air a duplex oxide film forms composed by an inner magnetite layer and a thin outer hematite scale. The heat treatment for different amounts of time at high temperature was used as method to sample the thickness variation and change in electronic and semiconducting properties of the thermal oxide layers. Firstly, linear voltammetric measurements were performed to have a first insight in the electrochemical behavior of the thermal oxides in a borate buffer solution. Electrochemical impedance spectroscopy in the same buffer combined with the Mott–Schottky analysis were used to determine the semiconducting properties of the thermal oxides. By spectroscopic ellipsometry (SE) and atomic force microscopy (AFM), respectively, the thickness and roughness of the oxide layers were determined supporting the physical interpretation of the voltammetric and EIS data. These measurements clearly showed that oxide layers with different constitution, oxide resistance, flatband potential and doping concentration can be grown by changing the atmosphere.

Computational Fluid Dynamics Simulation and Validation of H2S Removal from Fan-Ventilated Confined-Space Manure Storages

Confined-space manure storage entry is a major safety concern in the agricultural industry. An oxygen-deficient atmosphere as well as toxic and/or explosive gases (i.e., NH3, H2S, CH4, and CO2) often results from fermentation of the stored manure and accumulation in confined areas. These gases may create very hazardous conditions for farm workers who may need to enter these confined-space manure storages to work or perform maintenance. Hydrogen sulfide (H2S) was used as an indicator gas to investigate the effectiveness of forced-ventilation strategies for eliminating the toxic and oxygen-deficient atmospheres in confined-space manure storages. The overall goal of this research was to develop and validate computational fluid dynamics (CFD) modeling protocols to simulate H2S removal from fan-ventilated confined-space manure storages. The CFD model was used to identify the time taken to reach the OSHA permissible exposure limit of H2S (Tpel). This article presents the CFD model simulations of evacuating H2S during forced ventilation for the best ventilation strategies identified in previous research for a typical rectangular on-farm manure tank with three cover types (i.e., solid, fully slotted, and partially slotted) and the validation of the CFD modeling protocols based on comparisons between simulated and measured H2S evacuation times. Simulated and measured evacuation times within the confined-space manure storages evaluated agreed within 10% at all measuring locations except those immediately adjacent to the ventilation fan jet for all three cover types for both high (5 AC min-1) and low (3 AC min-1) air exchange (AC) rates. Corresponding evacuation times agreed within 15% for all cover types and air exchange rates in the high-velocity gradient region of the ventilation fan jet.

Growth and characterization of reduced and unreduced Rh doped potassium niobate single crystals

Rh doped potassium niobate single crystals are grown by the high-temperature solution growth (HTSG) method with a melt doping level of 1500 mg/g. The crystals are reduced to different levels by subjecting them to an in situ high-temperature reduction under an oxygen-deficient atmosphere followed by fast cooling. The characterization results indicate a segregation coefficient of slightly less than 1% for rhodium. The high-resolution X-ray diffraction studies reveal only a slight broadening for reduced crystals, indicating that the reduction process does not deteriorate strongly the crystalline perfection. Loss of an oxygen atom by formation of an oxygen vacancy accompanied by releasing two electrons is identified as the most likely defect mechanism for the reduction, which results in a lower valence of Rh in the lattice and appears a strong change in the absorption spectrum. The reduction is also accompanied by a loss of hydrogen that leads to a decrease of the infrared (IR) vibrational bonds associated to the OH complex. Two-wave mixing measurements show that majority charge carriers for highly reduced crystals change from holes in unreduced crystals to electrons in reduced crystals at longer wavelength (>580 nm).

Electrical conductivity mechanisms in zinc oxide thin films deposited by pulsed laser deposition using different growth environments

The mechanisms of electrical conduction in zinc oxide thin films, grown by pulsed laser deposition, have been investigated as a function of preparation conditions. The films were deposited on glass and silicon nitride coated silicon, using oxygen rich, oxygen deficient, or nitrogen atmospheres. The substrates were held at 473 K during deposition, and subsequently cooled down to room temperature in oxygen rich atmosphere of 4 Pa, or oxygen deficient atmosphere of 2×10−3 Pa. Films deposited and cooled in an oxygen deficient atmosphere exhibited very high donor concentration, originated in intrinsic defects, and an impurity band related mechanism of conduction. Films deposited under relatively high oxygen pressure were highly resistive and showed, upon ultraviolet light irradiation, grain boundary controlled electrical transport. An enhancement of the conductivity was observed when using a nitrogen atmosphere during the deposition, and oxygen atmosphere during cooling. In this case, the dependence of the conductivity with temperature followed Motts' Law of variable range hopping, characteristic of a material with localized states randomly located in space. Since the density of hopping centers appears to be much larger than the density of nitrogen incorporated in this sample, it is suggested that the nitrogen induces defects in the zinc oxide lattice that behave as localized hopping centers, as well as carrier suppliers, giving rise to the observed conductivity.

227 還元加熱法によるPOPs汚染土壌処理(安定化・無害化処理,資源循環・廃棄物処理技術)

A reductive heating treatment test using pilot scale equipment was carried out to develop an on-site decontamination process for POPs in polluted soil at lower temperatures. The pilot-scale test confirmed the reduction of BHCs from 2,354 μg/kg to 0.31 μg/kg for contaminated soil, namely removal rate of 99.99% at 550℃ for one hour under an oxygen deficient atmosphere. The content of Dioxins in treated water and gas from the reductive heating equipment also met the Japanese regulations.

Argon protects hypoxia-, cisplatin- and gentamycin-exposed hair cells in the newborn rat’s organ of Corti

During the last few years, an important protective effect of the noble gas xenon against neuronal hypoxic damage was observed. However, argon (Ar), a gas from the same chemical group, but less expensive and without anesthetic effect at normobaric pressure, has not been studied in terms of possible biological effects on cell protection. Ar was tested for its ability to protect organotypic cultures of the organ of Corti from 3–5 day old rats against hypoxia, cisplatin, and gentamycin toxicity. Cultures were exposed to nitrogen hypoxia (5% CO 2, 95% N 2), Ar hypoxia (5% CO 2, 95% Ar) or normoxia for 30 h. Ar protected the hair cells from hypoxia-induced damage by about 25%. Ar–oxygen (O 2) mixtures (21% O 2, 5% CO 2, 74% Ar) had no effect on the hair cell survival. Cisplatin (7.5–25 μM) and gentamycin (5–40 μM) exposed in medium under air damaged the hair cells in a dose-dependent manner. The exposure of cisplatin- and gentamycin-treated cultures to the Ar–O 2 atmosphere significantly reduced the hair cell damage by up to 25%. This protective effect of Ar might provide a new protective approach against ototoxic processes.

Structure and electrical properties of CdIn2O4 thin films sputtered at elevated substrate temperatures

A Hall mobility as high as 39.4 cm2 V−1 s−1 was obtained for cadmium indate (CdIn2O4) thin films deposited by rf reactive sputtering from a Cd–In alloy target. The structural and electrical properties for both as-sputtered and after-annealed thin films were studied as a function of the substrate temperatures. The results revealed that elevated substrate temperatures favour the formation of CdIn2O4 thin films with spinel phase. The electrical properties can be understood by a combination of the occupancy of In cations on the tetrahedral vacancies in the spinel unit cell at the elevated substrate temperatures and the formation of oxygen vacancies originating from off-stoichiometry. It can be inferred that the presence of secondary phases in the CdIn2O4 thin films deposited in an oxygen-deficient atmosphere is responsible for their electrical properties. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Dehalogenation potential of municipal waste incineration fly ash. I. General principles.

It is well known that the fly ash from filters of municipal waste incinerators (MWI-FA) shows dehalogenation properties after heating it to 240-450 degrees C. However, this property is not general, and fly ash samples do not possess dehalogenation ability at all in many cases. Fly ash has a very variable composition, and the state of the fly ash matter therefore plays the decisive role. In the present paper, the function of important components responsible for the dehalogenation activity of MWI-FA is analysed and compared with the model fly ash. With the aim of accounting for the dehalogenation activity of MWI-FA, the following studies of hexachlorobenzene (HCB) dechlorination were performed: The role of copper in dehalogenation experiments was evaluated for five types of metallic copper. The gasification of carbon in MWI-FA was studied in the 250-350 degrees C temperature range. Five different kinds of carbon were used, combined with conventional Cu(o) and activated nanosize copper powder. The dechlorination experiments were also carried out with Cu(II) compounds such as CuO, Cu(OH)2, CuCl2 and CuSO4. The results were discussed from the standpoint of thermodynamics of potential reactions. Based on these results, the model of fly ash was proposed, containing silica gel, metallic copper and carbon. The dechlorination ability of MWI-FA and the model fly ash are compared under oxygen-deficient atmosphere. The results show that, under given experimental conditions, copper acts in the dechlorination as a stoichiometric agent rather than as a catalyst. The increased surface activity of copper enhances its dechlorination activity. It was found further that the presence of copper leads to a decrease in the temperature of carbon gasification. The cyclic valence change from Cu(o) to Cu+ or Cu2+ is a prerequisite for the dehalogenation to take place. Thermodynamic analysis of the dechlorination effect, as well as the comparison of dechlorination pathways on MWI-FA and model fly ash, can provide a deeper understanding of the studied reaction.

Field-Effect Transistors Based on Single Semiconducting Oxide Nanobelts

We have fabricated field-effect transistors (FETs) based on single SnO2 and ZnO nanobelts of thicknesses between 10 and 30 nm. Switching ratios as large as 6 orders of magnitude and conductivities as high as 15 (Ω cm)-1 are observed. Annealing SnO2 nanobelt FETs in an oxygen-deficient atmosphere produces a negative shift in gate threshold voltage, indicating doping by the generation of surface oxygen vacancies. This treatment provides an effective way of tuning the electrical performance of the nanobelt devices. The ability of SnO2 FETs to act as gas sensors is also demonstrated. SnO2 FETs with lengths of about 500 nm or less show an anomalous behavior where the conductance cannot be modulated by the gate. ZnO nanobelt FETs are sensitive to ultraviolet light. Both photogeneration of electron−hole pairs and doping by UV induced surface desorption contribute to the conductivity.

Natural nuclear fission reactors: time constraints for occurrence, and their relation to uranium and manganese deposits and to the evolution of the atmosphere

Abstract Knowledge of the formation conditions of Francevillian uranium and manganese ore deposits as well as natural fission reactors sheds light on the early evolution of the atmosphere between 1950 and 2150 Ma ago. The model explaining the formation of the Oklo uranium deposits suggests that at the time of sediment deposition in the Franceville basin 2150 million years ago, the oxygen deficient atmosphere would have inhibited uranium dissolution. Dissolution of uranium was only possible during later diagenesis, approximately 1950 Ma. Reduction reactions in the presence of hydrocarbons allowed precipitation of dissolved uranium to U4+, forming deposits with high enough uranium contents to trigger subsequent nuclear fission reactions. Such a model is in agreement with earlier suggestions that oxygen contents in atmosphere increased during a ‘transition phase’ some 2450–2100 Ma ago. The manganese deposits were formed before the uranium deposits, during the deposition of the black shales and very early diagenesis, and thus at a time when oxygen content in atmosphere was very low. Carbon isotopes data of organic matter show decrease of δ13C upward in the Francevillian series (−20 to −46% PDB) reflecting the high CH4 and low O2 contents in the atmosphere during sediment deposition. This favoured anoxic conditions during deposition of the basinal FB black shales and likewise the migration of Mn over long distances. The manganese precipitated first as Mn-oxides at the shallow edges of the Franceville basin, in photic zones, where photosynthetic organisms flourished. Mn-oxides were then reduced in the black shales forming Mn-carbonates when conditions became more reducing during transgression episodes and/or the first stages of burial. In the black shales, reducing conditions prevailed until recent weathering, allowing the good preservation of organic matter and the Mn deposits. The present-day alteration is responsible for the dissolution of Mn-carbonates and precipitation of Mn-oxides at the water table to form the high grade Mn ore (45–50% Mn). Development of photosynthesizing organisms, a volcanic source of the Mn, and favourable palaeogeography of the Francevillian basins are all important parameters for the formation of the Mn deposits. For the occurrence of the natural nuclear reactors, the age of 2.0 Ga is the main parameter that controls the abundance of fissile 235U and the critical mass. Before 2.0 Ga the 235U/238U ratio was sufficiently high for fission reactions to occur but conditions favourable for forming high grade uranium ores were not achieved. Then, after 2.0 Ga the increase of oxygen in the atmosphere commonly led to the formation of high grade uranium ores in which the 235U/238U ratio was too low to support criticality.

Leachate treatment by the reverse osmosis system

The DT-Module system for landfill leachate treatment installed at Yachiyo Town in the Kanto District of Japan was put into service in April 1999. The system, which is equipped with a disc-tube type reverse osmosis (RO) membrane module called the DT-Module, has been operating satisfactorily for more than two and a half years, producing very-high-quality product water, after treating very-high-salinity water with high-scaling ions. On the other hand, in Japan, the dioxin problem has become increasingly severe, and development work for dioxin removal incorporated in leachate treatment has also been requested. The DT-Module system showed excellent performance in removing dioxins from leachate. For dioxins in sludge from the settling basin and dried salt from the concentrate of the RO system, successful destruction data were obtained by furnace system heating in an oxygen-deficient atmosphere. The removal rate of dioxins by the DT-Module system and the destruction rate by the furnace were both higher than 99.9%. By applying the DT-Module system together with the furnace system, an excellent leachate treatment and a complete dioxin removal and destruction system have become available for leachate from landfills depositing incineration residue-containing dioxins.

Effect of reaction time on PCDD and PCDF formation by de novo synthetic reactions under oxygen deficient and rich atmosphere.

The effect of reaction time on formation of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) was studied under laboratory conditions in the system containing municipal waste incineration fly ash, activated carbon and copper chloride dihydrate at 300 degrees C in 99.999% N2 and N2 + 10% O2 atmosphere. The concentrations of tetra- to octa-chlorinated isomers as well as I-TEQ concentrations of toxic congeners are reported. The mechanism of PCDD and PCDF formation from chlorophenols and chlorinated biphenyls is discussed in the light of the time changes of PCDD/PCDF ratios.

Protection of Striatal Neurons by Joint Blockade of D1 and D2 Receptor Subtypes in an in Vitro Model of Cerebral Hypoxia

Massive increases in extracellular dopamine have been reported in the ischemic rodent striatum, implicating this neurotransmitter in toxic events. We have examined whether dopamine receptor antagonists are protective against hypoxic insult, using brain slices containing the rostral striatum obtained from adult male C57/BLIcrfat mice. Slices were subjected in vitro to 20 min nitrogen hypoxia, with or without addition of: (i) 50 μM haloperidol (D2 receptor antagonist and sigma ligand), (ii) 10 μM SCH23390 (selective D1 receptor antagonist), (iii) 10 μM eticlopride (selective D2 receptor antagonist), (iv) 10 μM SCH23390 and 10 μM eticlopride in combination, and (v) 10 μM MK-801 (noncompetitive NMDA receptor antagonist). Subsequently, slices were reoxygenated, fixed 2 h postinsult, and processed for light microscopy. Damage was assessed by calculating pyknotic profiles as a percentage of total neuronal profiles present. No pyknotic profiles were detected in normoxic control tissue, but this phenotype predominated in most slices subject to hypoxia alone (60.1 ± 30.6% pyknotic profiles). Marked protection was produced by haloperidol (7.1 ± 7.6%, P = 0.002), MK-801 (8.6 ± 6.9%, P = 0.007), and the combined application of SCH23390 and eticlopride (5.9 ± 9.4%, P = 0.001). No protection was demonstrated for SCH23390 or eticlopride when applied separately. These data suggest that hypoxic damage in the rostral mouse striatum is mediated via NMDA, D1, and D2 receptors. Protection against hypoxic damage by dopamine receptor antagonists requires the combined blockade of both classes of dopamine receptor.

Safe design and operation of a cryogenic air separation unit

AbstractCryogenic Air Separation Units (ASUs) frequently supply oxygen and nitrogen to chemical, petroleum and manufacturing customers. Typically, the ASU is located remotely from the use point, and the products are supplied via a pipeline. This paper provides the basic design and operating methods to safely operate an ASU. The four primary hazards associated with these units are: (1) the potential for rapid oxidation, (2) interfaces between the ASU and the downstream systems, (3) pre s s u re excursions due to vaporizing liquids, and (4) oxygen enriched or deficient atmospheres. Requirements for safely handling oxygen within the air separation facility and at the product use point are also discussed in this paper.

Growth behavior and defects in conductive SrRuO3 thin films grown on a Si(100) substrate by sputtering

The microstructural characteristics of ion-beam-sputtered conductive SrRuO3 films, such as interfacial reactions, which govern growth behavior, defects, and thermal stability, were investigated using transmission electron microscopy. On a Si substrate, two binary constituents of SrRuO3, i.e., SrO and RuO2 were shown to have quite different reaction behaviors. The reduction of the RuO2 constituent to elemental Ru by Si led to an unstable contact of SrRuO3 on the Si substrate. Possible reaction thermodynamics are suggested, which are based on the formation energies of the corresponding reactions. In the case of films grown in an oxygen-deficient atmosphere, stacking faults were observed. The stacking faults originated from twinning on the {111}pc plane to accommodate the oxygen deficiency in the growth atmosphere by changing the arrangement of RuO6 octahedra from corner to one of face sharing.

Porous TiO2: Electron Transport and Application to Dye Sensitized Injection Solar Cells

Porous TiO2 (anatase, rutile) belongs to the class of materials with very low drift mobility of electrons (10—4–10—7 cm/Vs). The drift mobility is limited by traps being responsible for the slow interparticle charge transfer. The deep traps are generated at the TiO2 surface in oxygen deficient atmosphere and should be avoided in dye sensitized injection solar cells since they increase the saturation current. Another group of defects is related to disorder in the bulk TiO2. The disorder is much stronger for anatase than for rutile. The respective optical bandgap of the undisturbed anatase is 3.45 eV. The disorder related defects do not limit the efficiency of the dye sensitized injection solar cell. The current dependent barrier height has been shown to be important as a limiting factor for the energy conversion efficiency in dye sensitized injection solar cells at moderate light intensity.

Structural properties of superconducting PrBa 2Cu 3O 7−δ single crystals

The influence of high-temperature reduction/oxidation treatment on the structural properties of superconducting PrBa 2Cu 3O 7−δ (PrBCO) single crystals was examined. The scanning electron microscopy (SEM) analysis has shown that even the short-lasting exposure to the oxygen-deficient atmosphere leads to creation of regular-shaped crystallites of PrBaO 3 and BaCuO 2 phases with the size of 0.5 ÷ 2.0 μm on the smooth and flat crystal surface. The energy dispersive x-ray (EDX) investigations performed on the cross-sections of the superconducting crystals have indicated that the post-growth thermal treatment reduces the amount of Pr on the Ba-sites. Our results strongly support all the concepts attributing the suppression of superconductivity in this system to the excess of Pr in the crystal structure of samples synthesised by the standard methods.

Study on PbWO 4 doped with Y, Sb

A series of PbWO 4(PWO) powders, undoped and doped with Y and or Sb, were prepared in air and studied by cathodoluminescence, photoluminescence excitation and emission spectra, and compared with that of undoped and Sb doped PWO single crystals grown by the Bridgman method. The luminescence of PWO prepared in air at high temperature (900° C) is mainly in a broad green band, and its intensity of emission is stronger than that of doped PWO. However the luminescence of PWO:Sb prepared in an oxygen deficient atmosphere is better than undoped PWO.

Medical evaluation for respirator use

The purpose of a respirator is to prevent the inhalation of harmful airborne substances or to provide a source of respirable air when breathing in oxygen-deficient atmospheres. For a physician to recommend the use of respirator, general background information on respiratory-protective devices is required. The first part of this clinical practice review describes the general aspects of industrial hygiene, respirators and a respirator-certification program. The second part addresses matters related to medical certification for respirator use. Medical certification for respirators is an important part of the activities of the occupational physician. To determine whether a worker is able to tolerate the added strain of a respiratory protective device is a complex process in which factors such as fitness for work, health of the individual, characteristics of the work itself, and the properties, type, and requirements of the respiratory protective device, have to be considered. Medical certification is of utmost importance for respirator use, and it should be viewed as an element in a comprehensive respiratory protection program. A comprehensive program is the key element in affording the workers' effective respiratory protection once the initial steps of the hierarchy of methods of hazard control have proved insufficient or infeasible. As a result, the need for the industrial hygiene/safety officer, the worker, the employer and the medical professional to work as a team is much more than in any other field of occupational medicine--a necessary requirement for making the right decision.