O2 Stream Research Articles

YBa2Cu3O6+δ as an Oxygen Separation Membrane

Appreciable oxygen permeability at elevated temperatures (650–850°C) allows the well-known high-temperature superconductor YBa2Cu3O6+δ to be used as an oxygen separation membrane. Permeation of air through a YBa2Cu3O6+δ disk 1.2 mm thick gave an O2 stream in which N2 was barely detectable by gas chromatography. This technology may have potential applications in high-temperature oxygen-based industrial processes.

Lead dioxide electrodes for high potential anodic processes

Doping of PbO2 by cations (Fe3+, Co2+ and Ni2+), by F- and by cations and F- simultaneously is discussed as a way of improving the stability and electrochemical activity in processes occurring at high potentials. Doping allows the control of the amount of structural water in an oxide. Radiotracer experiments showed that high electrodeposition current densities favour the segregation of incorporated tritium (protons) at the surface. On the other hand, fluorine doping results in a marked decrease in the amount of surface oxygen species. The influence of doping with metal cations strongly depends on the nature of the metal. Iron behaves like fluorine, while nickel causes an accumulation of surface oxygen species. Doped PbO2 electrodes have quite good activities for the electrogeneration of ozone. In particular, Fe and Co doped PbO2 showed a current efficiency of 15-20%for this process. This result is relevant to our recent studies on ?cathodic oxidation?, i.e., an ozone mediated electrochemical method in which an O2 stream is used to sweep theO2/O3 gas mixture produced at a PbO2 anode into the cathodic compartment of the same electrochemical cell containing polluting species.

Crystal Structure of Partially Pd2+-Exchanged Zeolite X Dehydrated in Oxygen at 400 °C. Formation of Linear Pd2O3 Clusters Proposed To Be HO−PdIV−O−PdIV−OH in (Pd2+)14(HOPdOPdOH4+)8(Na+)32−Si100Al92O384

The crystal structure of partially Pd2+-exchanged zeolite X, dehydrated at 400 °C in a flowing O2 stream (a = 24.982(4) Å), has been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3̄ at 21(1) °C. The crystal was first Pd2+-exchanged in a flowing stream of 0.05 M aqueous Pd(NH3)4Cl2 for 3 days. After dehydration at 400 °C in flowing oxygen, the crystal was evacuated at 21(1) °C and 2 × 10-6 Torr for 2 h. The structure was refined to the final error indices R1 = 0.070 and R2 = 0.051 for the 196 reflections for which I > 2σ(I). In this structure, Pd2+ ions are found at four crystallographic sites: Na+ ions fill just one, and nonframework oxygens are found at two. Eight Pd2+ ions and eight O2- ions fill the 16 double six-oxygen ring (D6R) centers (site I) per unit cell; this interpretation of the electron density at site I behaves well in least-squares refinement. Each of these Pd2+ ions is octahedrally coordinated by framework oxygens. Sixteen Pd4+ ions at site I‘ (Pd−O = 2.103(13) Å) lie in six-ring planes. With the eight oxide ions at site I at central positions and 16 more teriminal, they form eight linear O−Pd−O−Pd−O clusters along 3-fold axes per unit cell. Each passes through the center of a D6R and extends into its two adjacent sodalite cavities. Considering bond lengths and charge balance, it is proposed that they are [HO−PdIV−O−PdIV−OH]4+ clusters with O−Pd−O−Pd−O linear. Thirty-two Na+ ions fill site II and are recessed 1.03(1) Å into the supercage from the single six-ring plane (Na−O = 2.258(11) Å). About two Pd2+ ions at another site I‘ (Pd−O = 2.371(11) Å) are displaced 1.11 Å from six-ring plane into sodalite cages. About four Pd2+ ions lie at site III‘ in the supercage (Pd−O = 2.16(5) Å).

Heat production from reaction of inhalation anesthetics with dry soda lime

There are some case reports about excessive heat production in the absorbent canister when sevoflurane or enflurane are washed into a circle containing dried soda lime. This observation was often made in the DRAGER ISO 8 circle system with the gas inlet upstream of the soda lime canister with the gas-flow from bottom to top. The temperature in the center of an absorbent canister was measured 3.0 cm and 7.5 cm above the bottom. Soda lime (DRAGERSORB 800) was dried in an O2 stream for 2-3 days until there was no further loss in weight. 5 Vol% of desflurane, enflurane, isoflurane and sevoflurane in 2 1/min O2 or 4 Vol% of halothane in 2.5 I/min O2 were continuously fed into the canister. The concentration of the respective inhalational agents were measured after the soda lime canister using a DATEX Capnomac. Experiments were performed at ambient temperatures of 20-22 degrees C. A considerable temperature increase was achieved with all anaesthetics. The highest temperatures were measured at the upper sensor with 56-58 degrees C for desflurane, 76-80 degrees C for enflurane and isoflurane, 84-88 degrees C for halothane and 126-130 degrees C for sevoflurane. IR-detection for some agents was considerably delayed or the time course indicated that other compounds might have formed which absorb at the wavelength monitored. The high temperatures indicate the degradation rather than absorption of the volatile anaesthetics. CO is known to be degradation product of all currently used volatile anaesthetics except sevoflurane. Sevoflurane, however, produced the highest temperatures passing through dried soda lime. There are no reports about new specific breakdown products for sevoflurane on dried soda lime.

Membrane-Based Integrated Absorption−Oxidation Reactor for Destroying VOCs in Air

This proof-of-concept research describes a novel membrane-based, integrated absorber−reactor operat ing at ambient temperature and atmospheric pressure. It degrades volatile organic compounds (VOCs) in a gaseous stream by ozonation in an inert stagnant fluorocarbon (FC) phase having a high ozone solubility. This FC phase acts as a reaction medium and a liquid membrane. The reactor has two sets of nonporous silicone capillaries. The VOC-containing gas flows through one set and supplies the VOC to the FC phase. The O3−O2 stream flowing through the other supplies O3 to the FC phase. There is also a set of mi- croporous Teflon tubules through which water flows removing oxidation products partitioning from the FC phase. With trichloroethylene (TCE), 60% conversion was obtained for 50 000 ppmv TCE in N2 flowing at 30 cm3/min and 40% for 18 000 ppmv flowing at 50 cm3/min. For 220 ppmv TCE feed, 90% conversion was obtained at 20 cm3/min flow rate and 60% at 60 cm3/min. A conversion in excess of 97% was achieved for a toluene feed of 205 ppmv present in N2 flowing at 11 cm3/min. No FC phase regeneration is required; it is constantly cleaned by the ozonation reactions. The materials of construction were found to hold up well under repeated experimentation.

Ferric Leghemoglobin in Plant-Attached Leguminous Nodules.

Leghemoglobin (Lb) is essential for nitrogen fixation by intact leguminous nodules. To determine whether ferric Lb (Lb3+) was detectable in nodules under normal or stressed conditions, we monitored the status of Lb in intact nodules attached to sweet clover (Melilotus officinalis) and soybean (Glycine max [L.] Merr.) roots exposed to various conditions. The effects of N2 and O2 streams and elevated nicotinate levels on root-attached nodules were tested to determine whether the spectrophotometric technique was showing the predicted responses of Lb. The soybean and sweet clover nodules' Lb spectra indicated predominantly ferrous Lb and LbO2 in young (34 d) plants. As the nodule aged beyond 45 d, it was possible to induce Lb3+ with a 100% O2 stream (15 min). At 65 d without inducement, the nodule Lb status indicated the presence of some Lb3+ along with ferrous Lb and oxyferrous Lb. Nicotinate and fluoride were used as ligands to identify Lb3+. Computer-calculated difference spectra were used to demonstrate the changes in Lb spectra under different conditions. Some conditions that increased absorbance in the 626 nm region (indicating Lb3+ accumulation) were root-fed ascorbate and dehydroascorbate, plant exposure to darkness, and nodule water immersion.

The Oxidation Behavior of a Si-Ti-C-O Fiber with a Low Oxygen Content

The Si-Ti-C-O fiber (STC (6)) with a low oxygen content of 6mass% was oxidized at temperatures in the range of 1273 to 1773K in order to measure its oxidation rate and thereby to elucidate its oxidation behavior. These results were compared to those of the commercial fibers having 18 and 13mass% O (STC (18) and STC (13)). The kinetic data of STC (6) were expressed by the contracting-cylinder formula. The activation energies were calculated to be 72 and 430kJ/mol at the low-temperature (T 1473K) regions, respectively. On the other hand, STC (18) and STC (13) had activation energies of oxidation of E=72kJ/mol and E=70kJ/mol within the whole temperature range, respectively. Oxidation of STC (6) with a low oxygen content is considered to be similar in kinetic behavior to that of pure SiC.The oxide film consisted of SiO2 and TiO2; and the former was amorphous during the low-temperature oxidation process tending to be crystallized into cristobalite at higher temperatures. The average size of crystallized β-SiC particles of the interface between the oxide film and unoxidized core fiber was larger than that of core of the fiber. This is because the progress of the crystallization in O2 stream is considered to have been suppressed when the fiber was completely covered with the oxide film. When the fiber was oxidized at 1773K, the interface between the oxide film and the unoxidized core fiber contained many microcracks; moreover, the core fiber lost 75% of its original strength at room temperature. It is quite possible that these defects were produced by a contraction due to transformation of cristobalite (α-β) during cooling from the oxidation temperatures.

Catalytic and Thermal Behavior of Cerium Oxide Supported onSiO2 and Al2O3 for Methane Combustion

Abstract CeO2/SiO2 and CeO2/Al2O3 catalysts oxidized at 1173 K in O2 stream were employed to investigate the catalytic activity for methane combustion and the behavior of CeO2 on supports by the oxidation at 1173 K. CeO2/SiO2 catalyst gave a poor catalytic activity by comparison with that of CeO2/Al2O3 catalyst. The crystallite size of CeO2 of the silica catalyst was found to be 1.5 times larger. In addition, Auger Electron Spectroscopy (AES) analysis after the oxidation at 1173 K proved that cerium species existed on and within the silica support. We conclude that the low surface density of CeO2 might contribute to the poor activity of CeO2/SiO2 catalyst for methane combustion.

Ｂｉ‐２２２３相におけるＰｂ化合物の析出・再固溶におよぼす雰囲気の影響

Thermal behavior of the Bi-2223 phase in the Bi, Pb-Sr-Ca-Cu-O system, especially segregation and dissolution reaction of the phase which was identified as Sr2.5Bi0.5Pb3Ca2CuO2, has been studied by XRD, SQUID and resistivity measurements. On annealing below 830°C in air, the phase precipitated from the 2223 crystals. When the 2223 phase was annealed at 750°C in O2stream, the precipitation of the 3321 phase increased. On annealing at 750°C in Ar stream, however, no precipitation of the phase was detected. By reheateing at 850°C even for 1min, the phase was almost dissolved into the mother 2223 crystals. When the 2223 phase was reheated at 750°C in Ar stream after annealing at 750°C in air, the 3321 phase disappeared. On the contrary, the phase was stable on reheating at 870°C in O2 stream. Therefore, it seems that the and the 2223 phase coexist in epuilibrium in a high oxygen partial pressure.

Numerical Simulation of Supersonic Flow CO Chemical Laser Solving Navier-Stokes Equations.

The flow field of a supersonic flow CO chemical laser is simulated solving two-dimensional Navier-Stokes equations, and the effects of viscosity, shock waves and the mixing process on the small signal gain coefficients are studied. The calculated flow pattern agrees very well with the chemiluminescence from the laser cavity which was observed previously. Both the calculation and the experiment show that the O2 streams and the dissociated CS2 streams collide with each other at the nozzle exits, generating oblique shock waves. It is also shown that mixing of the O2 streams and the dissociated CS2 streams is significantly slow, and the temperature and gain distributions in the mixing layer are strongly influenced by the shock waves and expansion waves. The calculated distributions of the small signal gain coefficients along the flow agree fairly well with the measured values in the region near the nozzle exits where the three-dimensional effects are relatively weak.

Suppression of Pyrolysis of Si-C-O Fiber with Oxide Film

The pyrolysis of Si-C-O fiber (Nicalon) coated with an oxide film has been investigated. Nicalon fiber was heated in an O2 stream, and was subsequently heated in an Ar stream at temperatures from 1573 to 1773K. The mass change of the fiber was determined with a thermobalance. The reaction products were examined by X-ray diffraction, SEM and TEM observations. During formation of the oxide film, the amorphous fiber core grew to the microcrystalline β-SiC. The mass of Nicalon coated with the oxide film did not change, when heated in an Ar stream, indicating the suppression of the pyrolysis of the fiber core. Because of the suppression, the high temperature strength of the core was appreciably retained. The oxide film was smooth, and crystallized from amorphous silica to cristobalite only partially during the heat treatment in Ar. Hence, it is considered that the SiO2 layer retards the pyrolysis of the fiber core by restricting the outward transport of the gaseous products, SiO and CO.

Heterogeneous Nucleation of Superparamagnetic Phases in “Fe-Bearing Cordierite-Glasses

ABSTRACTGlasses of stoichiometric cordierite composition Mg2(Al1−xFex)4Si5O18, containing very low iron contents (x=0.015 and 0.005) have been investigated by 57Fe Mössbauer spectroscopy. At higher Fe concentrations spinel exsolution has been observed in X-ray powder patterns. To allow Mössbauer spectroscopy at very low Fe-concentrations (<0.8 weight* Fe2O), starting materials were doped with 100% 57Fe. Glasses prepared in air at 1560°C were also oxidized In water saturated O2 stream. Glasses were crystallized to cordierite by heating In air at 1100 to 1400°C. 57Fe-Mössbauer spectra of all samples are governed by a doublet typical for Fe2+ in octahedral coordination (IS: 1.09–1.15, QS: 2.00–2.31 in MM/s relative to metallic iron). X-ray powder patterns exhibit no additional phases. But, the 295 K and 5 K Mössbauer spectra of treated and untreated glasses and of cordierltes exhibit broad lines, which have been fitted by applying internal magnetic hyperfine fields H of ca. 500 kG. These lines are attributed to heterogeneously nucleated, superparamagnetic (MgFe) (AlFe)2O4 spinels of complex compositions. From the calculated subspec-tra one may conclude that 35 to 65% of the total iron, depending on preparation conditions, is incorporated in the spinels.

Photochemical Reaction of Perillaldehyde under Various Conditions

(-)-PeriIlaldehyde (1) was photoirradiated by a 400 W high-pressure mercury lamp under various conditions. In MeOH, 1 was degraded to give two new MeOH adducts (2 and 3) and a new methyl ether (4) under an N2 stream, while 1 was converted to a dimethyl acetal (5) and oxidation product (6) in addition to 2 and 3 under an 02 stream. In EtOAc, 1 disappeared to afford two new dimers (7 and 8) under an N2 stream, while 1 was changed to two oxygenated products (9 and 10) including a new compound under an O2 stream. In the presence of rose bengal (RB), 1 was converted to 5 by visible light in MeOH under an N2 stream. Photosensitization of RB was observed under an O2 stream, and two new oxygenated products (11 and 12) were formed. Perillaldehyde was relatively stable in n-hexane under an N2 stream or in the presence of RB under an O2 stream.

Effect of Oxygen on Pyrolysis of SiC Fiber Synthesized from Polycarbosilane

The fibers containing 5% O (fiber-A) and 17% O (fiber-B) were prepared from polycarbosilane by the oxidation at 453K and 503K in O2 stream and by the heat treatment at 1473K in Ar stream, and the effect of oxygen on the mechanism of the pyrolysis of SiC fibers was studied. The rate of pyrolysis of the SiC fiber was measured with a thermo-balance in an atmosphere of Ar from 1673K to 1973K. The pyrolysis products were examined by X-ray diffraction, SEM and TEM observations. The core of the original fiber-A crystallized slightly, though its surface was amorphous. The pyrolysis proceeded rapidly in the early stage of reaction, but it was remarkably sluggish in the late stage. The SiC crystallite in the fiber coarsened only at the surface. The surface layer with high concentrations of oxygen decomposed rapidly, but the core with low concentrations of oxygen was difficult to decompose. The fiber-B, which was amorphous in the original state, decomposed to β-SiC rapidly. SiC crystallite grew and coarsened throughout the whole region of the fiber. The rate of pyrolysis was described by an Avrami-Erofeev equation. The rate-determining step changed from the crystal growth controlled by diffusion to that controlled by chemical reaction with rising pyrolysic temperature.

ＣＶＤ‐ＳｉＣコーティング・ニカロンの酸化機構

The oxidation mechanism of Nicalon coated with CVD⋅SiC layer was studied. Using CH3SiCl3-H2 gas mixture, CVD⋅SiC was deposited on Nicalon fiber heated at 1473K. The rate of oxidation was measured with a thermobalance in O2 stream at temperatures from 1473 to 1773K. The reaction products were examined by X-ray diffraction and SEM observation.The oxidation film was formed at the skin. of CVD⋅SiC layer. Neither oxidation nor pyrolysis proceeded in Nicalon coated with CVD⋅SiC. The oxidation rate of CVD⋅SiC was slower than that of Nicalon. The oxidation rate of CVD⋅SiC followed the parabolic rate law. The activation energy was 186kJ/mol. It is considered that the oxidation rate is controlled by the gaseous diffusion through the micro-pores in the oxide film.

Ignition and combustion of aluminum in carbon dioxide streams

With the prospect of using Al as fuel in a CO2 breathing engine in Mars atmosphere containing no oxygen, an experimental study on the ignition and combustion of Al was performed by using the stagnation region of impinging pure CO2 streams over a wide range of pressure and velocity of the streams. Al could ignite spontaneously in the CO2 streams, and the critical ignition temperature decreased with decreasing pressure and velocity of the streams. In the ignition process whether surface reactions proceeded initially to form a protective Al2O3 film on the Al surface or not was found to play a crucial role. When the surface was not covered with the film, ignition occurred in the gas phase leading to development of a luminous flame. During combustion, the Al surface remained clean, and AlO was produced in the gas phase due to the reaction of Al vapor with CO2. The AlO had a peak concentration in the gas phase away from the surface, and Al2O3 was condensed there. The burning rates of Al in the CO2 streams were estimated to be much lower than those of Mg in a CO2 stream and B in a O2 stream. The combustion mechanism for the Al-CO2 system has been postulated, including the surface and gas phase reactions producing Al vapor, AlO, Al2O, CO and condensed Al2O3. The ignition mechanism is discussed, and the role of CO2 diffusion from the upstream to the surface, controlled by a non-dimensional ejection parameter, is clarified.

Low-temperature oxidation of YBa2Cu3O6.0 with nitrogen dioxide

Nitrogen dioxide was used to oxidize nonsuperconducting, powdered YBa2Cu3O6.0 to form a material that exhibits the Meissner effect at liquid nitrogen temperature. Nitrogen dioxide treatment at 200 °C for 70 h results in a mixed-phase material containing superconducting YBa2Cu3O6.9 that exhibits onset of superconductivity at 91.5 K and a midpoint at 88 K. During a 70-h exposure of YBa2Cu3O6 to NO2 at 200 °C, a mixture of oxidation and degradation products is formed, including YBa2Cu3O6.9 (61% by weight) and Ba(NO3)2 (23% by weight). Heating the NO2-treated product to 900 °C results in the evolution of NO, NO2, and O2; cooling the sample and annealing at 400 °C in an O2 stream generates the superconducting oxide.

ChemInform Abstract: High Frequency Capacitance‐Voltage Characteristics of Thermally Grown SiO2 Films on β‐SiC.

AbstractSiO2 films on β‐SiC are thermally grown either under dry (O2 stream, 1000 °C) or wet (argon stream loaded with H2O vapor, 1150 °C) conditions and studied by C‐V measurements.

ChemInform Abstract: Metal Oxide Bound Rhodium Dioxygen and Ozone Complexes.

AbstractTreatment of (I) with a stream of dry O2 (140 °C, 500 h) or with dry ozone (1% in O2, 25 °C, 5 h) gives (II) or (III).

Measurements of Small Signal Gain Coefficients of a Supersonic Flow CO Chemical Laser

Small signal gain coefficients of a supersonic flow CO chemical laser are measured using a shock tunnel facility. A high temperature mixture of CS2, CS, S2, S and Ar is produced in a shock tube, where the thermal dissociation of CS, diluted in Ar is accomplished by a reflected shock wave. The shock-heated mixture is exhausted through two-dimensional supersonic nozzles mounted at the end of the tube and mixed with the supersonic streams of O2. Then, the vibrationally excited Co molecules are produced in the mixed streams. In the present paper, the dependence of the small signal gain coefficients on the downstream distance from the nozzle, the plenum conditions and the transition branch is studied. The data obtained in the present experiments are available to examine the propriety of the theoretical model which was developed previously.