Effect Of Oxygen Addition Research Articles

Oxygen consumption by anaerobic Saccharomyces cerevisiae under enological conditions: effect on fermentation kinetics.

The anaerobic growth of the yeast Saccharomyces cerevisiae normally requires the addition of molecular oxygen, which is used to synthesize sterols and unsaturated fatty acids (UFAs). A single oxygen pulse can stimulate enological fermentation, but the biochemical pathways involved in this phenomenon remain to be elucidated. We showed that the addition of oxygen (0.3 to 1.5 mg/g [dry mass] of yeast) to a lipid-depleted medium mainly resulted in the synthesis of the sterols and UFAs required for cell growth. However, the addition of oxygen during the stationary phase in a medium containing excess ergosterol and oleic acid increased the specific fermentation rate, increased cell viability, and shortened the fermentation period. Neither the respiratory chain nor de novo protein synthesis was required for these medium- and long-term effects. As de novo lipid synthesis may be involved in ethanol tolerance, we studied the effect of oxygen addition on sterol and UFA auxotrophs (erg1 and ole1 mutants, respectively). Both mutants exhibited normal anaerobic fermentation kinetics. However, only the ole1 mutant strain responded to the oxygen pulse during the stationary phase, suggesting that de novo sterol synthesis is required for the oxygen-induced increase of the specific fermentation rate. In conclusion, the sterol pathway appears to contribute significantly to the oxygen consumption capacities of cells under anaerobic conditions. Nevertheless, we demonstrated the existence of alternative oxygen consumption pathways that are neither linked to the respiratory chain nor linked to heme, sterol, or UFA synthesis. These pathways dissipate the oxygen added during the stationary phase, without affecting the fermentation kinetics.

Thermal stability and flammability studies of coated polymer powders using a plasma fluidized bed process

In this work, the thermal stability of organosilicon coatings, polyamide-6 powders and polyamide-6 clay nanocomposite powders coated with organosilicon are studied. The coatings were obtained from polymerization of 1.1.3.3-tetramethyldisiloxane (TMDS) monomer doped with oxygen using a cold remote nitrogen plasma (CRNP) process. A fluidized bed reactor using CRNP assisted polymerization was used to coat the polymer powders. The effect of oxygen addition to TMDS on the thermal stability was investigated. Oxygen addition to TMDS promotes the formation of more thermally stable coated polymers. In the case of the polyamide-6 clay nanocomposite, the Limiting Oxygen Index values were much improved. This shows that the deposits are effective fire retardant coatings.

Hydrogen plasma treatment on catalytic layer and effect of oxygen additions on plasma enhanced chemical vapor deposition of carbon nanotube

Multi-wall carbon nanotubes have been synthesized by plasma enhanced chemical vapor deposition (CVD) on Co-coated silicon substrates. Prior to the deposition of carbon nanotubes, dense and uniform nanosized catalytic seeds were formed by hydrogen plasma treatment on Co thin film. The size and morphology of Co catalytic seeds varied with hydrogen plasma treatment time. In the carbon nanotube growing process, a mixture of CH 4 and H 2 was used as gas source. Small O 2 additions to the CH 4–H 2 gas mixture (0∼12% of mixture gas) improved the purity of carbon nanotubes and surprisingly led to high quality even at low growth temperature (610°C) as observed in high-resolution transmission electron microscopy (HRTEM). In order to understand the growth process by CH 4–H 2–O 2 plasma CVD in detail, optical emission spectroscopy (OES) was introduced. The results of OES analysis showed that, with the increase of oxygen amount, the intensity of C 2 decreased gradually, but the intensity of the OH radical increased sharply. It probably leads to increasing the etching effect on defective structure by affluent OH radical and suppressing super-saturation of carbon molecules at growing edges.

Effect of oxygen addition on boron incorporation on semiconductive diamond CVD

The suppression effect of oxygen on elemental incorporation in homoepitaxial diamond films grown by microwave assisted CVD is investigated by secondary ion mass spectrometry. In the H2–CH4–B2H6–O2 gas system, boron incorporation into CVD diamond decreases with increasing oxygen addition, and boron concentration can be controlled by oxygen addition. In the H2–CH4–B2H6 gas system, a linear relationship between diborane in the gas and boron incorporation is observed. The growth rate of diamond is reduced by small amount of diborane.

Characterization of Ti(N xO y) coatings produced by the arc ion plating method

The effect of oxygen addition to TiN was investigated by producing oxynitride films with the arc ion plating method. These titanium oxynitride films were identified to be NaCl(B1) structure by XRD measurements with θ-20 and glancing angle methods. By increasing the content of oxygen in the deposited films, the preferential orientation of the films changed from the <111> direction to the <200> direction, and the existence of titanium ions with a higher valence, such as Ti 3+ and Ti 4+ as well as divalent titanium, in the deposited films was indicated by the change of Ti 2p photoelectron spectra. From the result on Vickers hardness, it was also indicated that suitable addition of oxygen to TiN is preferable to improve the hardness of the TiN films.

Effect of growth-rate ratio on surface morphology of homoepitaxial diamond (100) and (111)

Homoepitaxial diamond (100) and (111) films were grown side by side in a hot filament reactor at 875 °C with and without oxygen. The growth rates and surface morphologies were monitored by in situ Fizeau interferometry and atomic force microscopy, respectively. Penetration twins were observed on the (100) surface at a low (100)-to-(111) growth-rate ratio but not at a high value, as expected. Surprisingly, penetration twins were not observed on the (111) surfaces, which were dominated by contact twins in both cases. Implications of these results for microstructural control of diamond films and the effect of oxygen additions are discussed.

Highly selective etching for polysilicon and etch-induced damage to gate oxide with halogen-bearing electron-cyclotron-resonance plasma

The investigations of polysilicon etching with three halogen-bearing plasmas (SF6, Cl2, and HBr) in an electron-cyclotron-resonance reactor have been made. We examine the etching characteristics which include etching rate, anisotropy, and selectivity based on the discussions of the chemical and electrical properties of the F, Cl, and Br radicals. It was found that the degree of anisotropy strongly depends on the deposition of a silicon halide film on sidewall and on the spontaneous etching properties of three halogen plasma mixtures. The selectivity to oxide is related to the amount of silicon halides that are produced during etching poly-Si and the electrically polarized level of these products when they adsorb on the oxide surface. We find that the selectivity on oxide is approximately infinite for the HBr system and over 90 for the Cl2 system. In addition, the effects of oxygen addition, microwave power, and rf power are also investigated. It was found that the maximum etching rate and selectivity of SF6, Cl2, and HBr plasmas occurred at concentrations of added oxygen at about 7.5%, 5%, and 3% total flow rates, respectively. The suitable range for the microwave power applied is from 250 to 300 W and the most respectable value of applied rf power is about 35 W. Concurrently, the local surface charging causing damage to the gate oxide during the overetching period is studied. It is observed that low device yield, large flatband voltage Vfb shift, and high interface-state density Dit are correlated with longer overetch and high antenna ratio structure of the device. A more obvious degradation is observed in the SF6 gaseous system than in Cl2 and HBr ones. Finally, the influence of magnetic coil current on device damage is also addressed.

Effect of Pressure on the Nucleation of Diamond with Addition of Oxygen in the Microwave Plasma Chemical Vapor Deposition System

Effect of oxygen addition on diamond film deposition at higher pressure was studied. It was found that addition of oxygen suppressed diamond nucleation, and the effect of suppression increased with increasing pressure, and at certain pressure level diamond deposition was completely prohibited. Etching effect due to oxygen addition dominated at the very early stage (nucleation stage), therefore it is still possible to take the advantage of oxygen addition on quality improvement of diamond films by introducing oxygen after the nucleation stage.

Coronary arteriography with an oxygenated contrast medium: Cardiac effects in dogs with and without acute ischemic heart failure

We investigated the possible cardiac effects of oxygen addition to contrast media (CM) during coronary arteriography in dogs that did and did not have ischemic heart failure. Acute ischemic heart failure was induced by injecting small plastic microspheres into the left coronary artery of 18 dogs. Hemodynamic and electrophysiologic measurements were performed during a single injection before and during heart failure and during a single injection and five rapidly repeated CM injections during heart failure. Iohexol supplemented with electrolytes (iohexol + electrolytes = IPE), oxygenated IPE (IPE+O), Ringer acetate, and oxygenated Ringer acetate were injected into the left coronary artery. Single injections of IPE and IPE+O induced small hemodynamic and electrophysiologic effects. However, repeated injections of IPE and IPE+O increased left ventricular inotropy (maximum value of the first derivative of the left ventricular pressure) by 36% and 39%, reduced heart rate by 7% (for both), and lengthened QTc time (corrected QT interval) by 39 and 38 msec, respectively. A comparison of IPE and IPE+O revealed no statistically significant differences. Although electrolyte addition to nonionic CM may reduce the risk of cardiac complications during coronary arteriography, oxygenation does not seem to significantly further reduce this risk.

An X-ray photoelectron spectroscopic investigation into the chemical structure of deposits formed from hexamethyldisiloxane/ oxygen plasmas

The effect of oxygen addition to microwave-sustained plasmas of hexamethyldisiloxane (HMDSO) has been investigated. Attention was directed to the solid products formed on aluminium substrates (plasma deposits). To enable a quantitative analysis of these, X-ray photoelectron spectroscopy (XPS) of standard silicon-containing materials was carried out. When suitable charge correction is applied to the XP spectra of HMDSO/O2 plasma deposits, a number of very clear trends emerge. From changes in elemental composition, core line binding energies (Si2p, C 1s, and O 1s) and widths, we show how oxygen addition to the plasma affects the chemical nature of the plasma deposit. The data reported also provide (some limited) information on the reactions taking place in the plasma.

Neutron-scattering determination of the structural parameters versus oxygen content of YBa 2Cu 3O 6+ x single crystals

The crystal structure of high-quality single crystals of YBa 2Cu 3O 6 + x grown in zirconia curcibles was studied systematically versus oxygen concentration by four-circle neutron diffraction at room temperature. The oxygen contents ranged from x = 0.18 (insulating, tetragonal phase) to x = 0.96 (superconducting, orthorhombic phase). In the orthorhombic phase, both twinned and detwinned samples were measured. A detailed discussion is presented of the systematic changes taking place in the atomic positions and Debye-Waller factors as the oxygen content is varied. Some qualitative highlights are that one can identify two distinct regions within the unit cell: the characteristics of the atoms near the CuO x basal plane are essentially driven by the effect of oxygen addition, whereas near the CuO 2 bilayer, the trends are more subtle and presumably dominated by charge transfer and bond-distance effects. Also, there is neither an abrupt change of the apical-oxygen position at the orthorhombic to tetragonal transition, nor is there any indication of depletion of the atomic sites except for the chain-site oxygen. The superconducting critical temperatures or Néel temperatures, as well as the existence of oxygen-ordered superstructures are reported.

Reduction of Nitric Oxide over Magnesium Oxide and Dolomite at Fluidized Bed Conditions

The reduction of nitric oxide over lime and char at fluidized bed conditions has been studied by many authors, but less attention has been paid to other surfaces existing in the boiler. This investigation concerns the reduction of nitric oxide by carbon monoxide, with or without oxygen present, and also the effect of small amounts of water. The reactions were studied in a fixed-bed quartz reactor with quartz, magnesium oxide, magnesium hydroxide, and dolomite as bed materials in the temperature interval 600-950 °C. The residence time and the concentrations of nitric oxide, carbon monoxide, and oxygen were varied. Magnesium oxide formed from heated magnesium hydroxide and calcined dolomite were more active than magnesium oxide of analytical grade, which indicates that the origin of the surface is important for the reaction. The reaction between nitric oxide and carbon monoxide is very sensitive to the presence of oxygen. When oxygen was present the reduction of NO almost ceased. However, if the gases were thoroughly dried, the effect of oxygen addition was not that severe.

Effect of oxygen addition to an argon glow-discharge plasma source in atomic emission spectrometry

Small amounts of oxygen gas greatly change the characteristics of the argon plasma light source in glow-discharge emission spectrometry. The influence of oxygen addition on the sputtering rate and the excitation of the analytes in the argon plasma was investigated by employing argon-oxygen binary mixed gases having well-defined compositions. Strong quenching by oxygen was observed from the intensity of the emission lines originating from the analyte element as well as the gas species. The negative effect caused by oxygen gas in analytical applications with the glow-discharge lamp should be noted.

The effects of oxygen on diamond synthesis by hot-filament chemical vapor deposition

The effects of oxygen addition on the synthesis of diamond are extensively studied by using the hot-filament chemical vapor deposition (HFCVD) method, in which it is simple and easy to control the deposition parameters independently. Diamond films are deposited on silicon wafers under the conditions of substrate temperature 530–950 ‡C; total reaction pressure 700–8000 Pa; and methane concentration 0.4–2.4% in both CH4–H2 and CH4–H2–O2 systems. At deposition conditions of low substrate temperature, high CH4 concentration or high total pressure, soot-like carbon and/or graphite are deposited without oxygen addition. When even a small amount of oxygen (about 0.6%) is added, well-faceted diamond films are observed in scanning electron microscopy micrographs and a sharp diamond peak in the Raman spectra appears. The range of deposition parameters for high-quality diamond syntheses are extended by oxygen addition (low substrate temperature, high methane concentration and high reaction pressure).

Influence of oxygen on the deposition of diamond coatings by microwave plasma CVD

The effect of oxygen addition in the plasma composition and diamond structure has been investigated during diamond film growth by microwave-assisted chemical vapour deposition (MWCVD) from CH 4+ H 2 gas mixtures. Optical emission spectroscopy (OES) and mass spectrometry have been used for detection of chemical species present in the plasma. The results for the gas mixtures with and without O 2 show noticeable changes in the plasma composition, as detected by the presence of oxygenated species (mainly CO and OH), produced by the oxygen addition to the discharge. We have related the diamond content in the films with the CO mole fraction present in the discharge. The etching of the non-diamond compounds seems to be due to OH radicals as well as to atomic oxygen present in the discharge which are able to etch carbon at higher rates.

Effects of Oxygen Addition on Growth of Diamond Film by Arc Discharge Plasma Jet Chemical Vapor Deposition

Effects of oxygen addition on growth and crystallinity of diamond films are discussed. The etch rate of graphite by Ar-O2 plasma jet is 130 times larger than that by Ar-H2 plasma jet. Nucleation density of diamonds decreases with oxygen addition. The growth rate of diamond decreases with increase in the amount of added oxygen. Surface unevenness and porosity also decrease with increase in the amount of added oxygen, and it was found that the optimum oxygen concentration is about 33%. A diamond film of 1.2 mm thickness was fabricated under these conditions in 20 h. Surface unevenness of the diamond film was reduced to about 100 µm. The growth rates of the {111} planes and {100} planes become isotropic with 33% oxygen content. Therefore the diamond film surface is only slightly uneven and the film shows good crystallinity.

Effects of Oxygen Addition in the CCl4 Reactive Ion Etching of a-SiC:H Films

We have studied the effects of oxygen addition in the CCl4 reactive ion etching of hydrogenated amorphous silicon carbide (a-SiC:H) films. The effects of oxygen on the etching profile of a-SiC:H films, the etch rates of a-SiC:H and oxide, and the etching selectivity of a-SiC:H/oxide are examined. It is observed that the addition of oxygen into CCl4 plasma greatly increases the etch rate of a-SiC:H and the etching selectivity of a-SiC:H/oxide, while gradually changes the etching process from being anisotropic to isotropic. Experimental data are interpreted with the examining of the plasma phase chemistry and ion bombardment energy. An etch mechanism is proposed for explaining the observed effects.

Effect of oxygen addition on mechanical properties of TiAl at 293–1273 K

Mechanical properties of Ti−50, −53, and −56 at.% Al alloys doped with 0, 0.1, 0.2 and 0.3 mass% oxygen have been studied in compression tests at temperatures from 293 K to 1273 K in a vacuum. The yield stress in Ti−50 at.% Al alloy increased by about 1.5 times owing to the addition of 0.3 mass% oxygen at all testing temperatures. In Ti−53 and −56 at.% Al alloys the increases of yield stress due to the addition of oxygen were not as pronounced as those in Ti−50 at.% Al alloys. The work hardening coefficients increased at 293–873 K but they decreased at 1073–1273 K with increasing oxygen and aluminum content. Insoluble particles extracted isolated by a mixed acid from TiAl alloys were α-Al2O3 phase and the amount of α-Al2O3 phase increased with increasing aluminum and oxygen content. The increase of yield stress at all testing temperatures occurred owing to the solid solution hardening of oxygen in Ti−50 at.% Al alloy and the dispersion strengthening of α-Al2O3 in Ti−53 and Ti−56 at.% Al alloys.

Effects of oxygen and pressure on diamond synthesis in a magnetoactive microwave discharge

The effects of oxygen addition and total pressure on the synthesis of diamond have been studied in a magnetically enhanced microwave discharge. Diamond films were deposited on silicon substrates at substrate temperatures from 540 to 650 °C and total pressures from 2 to 20 Torr, and were characterized by microprobe and macrochamber Raman spectroscopy and scanning electron microscopy. Without oxygen, Raman spectra of these films display only graphitic peaks. As oxygen is added, faceted crystalline diamond is observed in scanning electron microscope micrographs and a sharp diamond peak in the Raman spectrum appears. With 2% oxygen, diamond films exhibiting a pure diamond Raman peak at ∼1334 cm−1 with very small nondiamond carbon peaks were grown at relatively low temperature (∼600 °C) and low pressure (5–10 Torr).

Effect of Oxygen Addition to a Near-Sooting Ethene Inverse Diffusion Flame

Abstract The pyrolysis zone of a near-sooting ethene inverse diffusion flame (IDF, with oxidizer in the central stream) has been probed for temperature and species concentrations. Oxidation processes can play an indirect but significant role on the observed intermediate hydrocarbon species profiles, and therefore on soot formation. Intermediate hydrocarbons can be formed near the main oxidation zone, and diffuse back into the colder fuel-rich region. Acetylene, C4 species (1,3 butadiene, vinylacetylene and diacetylene) and benzene are indicative of ethene pyrolysis and are observed to build up slowly with height. Methane, ethane and C4 species (allene, propyne and propene) are more indicative of ethene oxidation, and form rapidly low in the flame. The addition of a trace amount of oxygen to the fuel decreased the concentrations of the pyrolytic species and indicates that fuel pyrolysis rates were not enhanced by oxygen addition to the fuel in the present non-sooting flame. However, oxygen addition increased the concentrations of the species associated with oxidation. The relative importance of oxidation and pyrolysis cannot be separated in diffusion flames for fuels which yield similar product distributions from pyrolysis and oxidation experiments.