High Oxygen Flow Rate Research Articles

Growth of superconducting Bi 2Sr 2CaCu 2O 8+ δ whiskers by a modified annealing process

Growth of long whiskers of superconducting Bi 2Sr 2CaCu 2O 8+ δ by a modified annealing process has been reported. A twofold increase in the growth rate of whiskers has been achieved by a stepwise cooling during annealing. A relatively higher oxygen flow rate (200–300 ml/min) and step-cooled annealing process enable the continuous whisker growth by eliminating the latent heat generated during crystallization. Whiskers of maximum length 10 mm have been grown by the combined effect of step-cooled annealing and continuous supply of atomic species at the growth site. The whiskers possess clean surface without the stacked layer and laminar structure. EDX analysis confirmed the compositional uniformity of the whiskers. The grown whiskers show a superconducting transition at 76 K, which implies that the whiskers are over-doped.

Effect of oxygen flow rate on the structural and electrochemical properties of lithium nickel oxides synthesized by the sol–gel method

The structural and electrochemical properties of LiNiO2 powders were investigated as a function of the oxygen flow rate employed in the preparation of lithium nickel oxide. It was found that oxygen played an important role in the synthesis of highly crystallized LiNiO2(R3¯m). In the crystallization process of LiNiO2, a deficiency of oxygen in the calcination reactor induced the formation of impurities and cubic rock-salt structure (Fm3m) in LiNiO2 powders. For LiNiO2 prepared at higher oxygen flow rates, the electrode delivered high discharge capacities with relatively good retention rates. But very low electrode capacity was obtained from LiNiO2 prepared at lower oxygen flow rates.

Characterization of Niobium Oxide Films Prepared by Reactive DC Magnetron Sputtering

Niobium oxide films have been prepared on glass and Si(100) substrates by reactive dc magnetron sputtering of a metallic Nb target in an argon-oxygen atmosphere. The properties of the films as a function of oxygen partial pressure have been studied systematically by Rutherford backscattering spectroscopy, X-ray diffraction, X-ray reflectometry and optical spectroscopy. Rutherford backscattering studies show that the films are substoichiometric at lower oxygen flow while stoichiometric films can be formed above 7.5 sccm O2 flow. Grazing incidence X-ray diffraction studies show that the films are amorphous. X-ray reflectometry was used to determine the sputter rate, density and surface roughness of the films. The films prepared at lower oxygen flow rates had a higher density than those prepared at higher oxygen flow rates. For appropriate oxygen flow rates fully transparent niobium oxide films can be grown with rates up to 0.5 nm/s for a constant cathode current of 900 mA. From optical spectroscopy measurements of reflectance and transmittance we have determined the optical constants such as the refractive index (n), extinction coefficient (k) and band gap (Eg) as well as the film thickness. For the fully transparent films prepared above 7.5 sccm O2 flow rate a band gap of 3.5 to 3.6 eV is obtained. Optical spectroscopy measurements show that the refractive index of the films decreases upon increasing oxygen flow rate and this finding is related to a decrease of density upon increasing oxygen flow.

Refining of metallurgical-grade silicon by inductive plasma

A new process combining inductive plasma torch and electromagnetic stirring of molten silicon in a cold crucible has been developed to refine upgraded metallurgical silicon. The addition of reactive gases to the plasma leads to volatilisation of impurities at the liquid silicon surface. The concentration of boron impurities decreased from 15 ppmw in the raw material to less than 2 ppmw after the plasma treatment. The most volatile form of boron was BOH, which was obtained by simultaneous treatment with oxygen and hydrogen. The limitation in boron volatilisation is due to the formation, at high oxygen flow rate, of a silica layer at the surface of the molten silicon, which results in a dramatic drop of the volatilisation rate. In contrast to boron, the concentration of phosphorus was reduced by only a factor of two, although the remainder seems to be electrically neutral. Thermodynamic studies suggest that phosphorus could be trapped as phosphate in combination with metallic impurities. Cells made of material produced using this technique exhibited a conversion efficiency of 12.4%.

Flame Made Titania/Silica Epoxidation Catalysts

Flame aerosol technology has been used to prepare titania/silica mixed oxide nanoparticles. A stream of argon containing evaporated hexamethyldisiloxane and titanium-tetraisopropoxide was brought into a methane–oxygen diffusion flame. Upon condensation, nanoparticles of titania/silica with high titania dispersion were formed. The powders were characterized using transmission electron microscopy, nitrogen adsorption, pore size analysis, laser-assisted ion-coupled plasma mass spectroscopy, UV–VIS spectroscopy, and diffuse reflectance IR spectroscopy. The powders consisted of agglomerates of primary particles from 10 to 20 nm in diameter at high oxygen-to-methane ratios in the flame. The morphology changed to larger, spherical particles when low oxygen-to-methane ratios were used. The catalytic materials were tested for the epoxidation of 2-cyclohexenol by tert.-butylhydroperoxide at 90°C. The activity and selectivity were investigated as a function of flame parameters used for catalyst preparation. The flame made catalysts showed better selectivity for the epoxidation than corresponding aerogels, but at lower activity. Epoxidation selectivity referred to TBHP reached 93%, whereas olefin selectivity was 83% at 80% conversion. The best catalytic performance was obtained with nanoparticles containing 1 to 3.2 wt% titania. The rate and selectivity achieved with the flame made catalysts were independent of the oxygen-to-methane ratio in the flame at high oxygen flow rate, whereas at low oxygen flow rate the activity and selectivity decreased considerably.

Room-temperature epitaxial growth of CeO2(001) thin films on Si(001) substrates by electron beam evaporation

Epitaxial growth of CeO2(001) thin films on Si(001) substrates was achieved by electron beam evaporation. Reflection high-energy electron diffraction and cross-sectional high-resolution transmission electron microscopy established the formation of an epitaxial CeO2(001)/Si(001) structure with a cube-on-cube configuration. The epitaxial structure had to be formed at a temperature below 200 °C with a Si(001)-2×1, 1×2 reconstructed surface, and it could be formed even at room temperature. In order to improve the crystallinity, homoepitaxial growth conditions at a higher temperature with a high oxygen flow rate were also investigated. Homoepitaxy of ceria grown on a 5-nm-thick initial layer was demonstrated by θ/2θ-scan and φ-scan of x-ray diffraction.

Influence of oxygen flow rate on the structural and mechanical properties of reactively magnetron sputter-deposited Zr–B–O coatings

Zr–B–O coatings were deposited on both construction steel and stainless steel substrates by magnetron sputtering of ZrB 2 targets in reactive Ar–O 2 gaseous mixtures. In this paper, the deposition rate and the structural and mechanical properties of Zr–B–O films will be investigated as a function of the inlet oxygen flow rate. We will show that two domains are available owing to the sputtering phenomena. In the former, the coating enrichment is quite proportional to the oxygen flow rate. Even for a weak oxygen enrichment, amorphization of the Zr–B–O films is observed which also decreases both their intrinsic internal stress and microhardness, thus improving the physical quality of the coatings. As the oxygen flow rate increases, the amorphous coatings, initially composed of a single-phase ZrB 2− x O x solid solution, present an increasing fraction of amorphous ZrO 2, and then, of amorphous B 2O 3 simultaneously with the disappearance of the metallic solid solution. Higher oxygen flow rates allow the synthesis of optically transparent amorphous oxide mixture films, the composition and mechanical properties of which become independent of the inlet oxygen flow rate.

Fire hazards and CO2 laser resurfacing.

The purpose of this study was to investigate the fire risk of laser resurfacing in the presence of supplemental oxygen. This study aims at defining safety parameters of variables such as laser energy level, oxygen flow rate, and "oxygen to laser target distance" when oxygen is delivered through a nasal cannula or nasopharyngeal tube. The typical operating room environment was simulated in the laboratory using the Yucatan minipig animal model. The energy source was a Coherent Ultrapulse CO2 laser. It was found that combustion did not occur at laser settings of 500 mJ, 50 W, 100 kHz, and a density of 5, used in conjunction with an oxygen flow rate of 6 liter/minute with the target area as close as 0.5 cm to the oxygen delivery. A total of 400 computer pattern generator treatments were delivered using this energy setting without observation of any combustion (p < 0.001). This provides evidence that while using even somewhat high laser settings and oxygen flow rate, laser induced fires can be avoided. We conclude that use of the laser in the presence of oxygen is safe, provided the target area is free of combustible fuels. Despite this assurance, laser mishaps are serious because they lead to both morbidity and mortality. It is our recommendation that close attention be constantly paid to all details, thus reducing the hazard potential of laser energy on local factors in an oxygen-rich environment.

Characterization of a low temperature, low pressure plasma enhanced chemical vapor deposition tetraethylorthosilicate oxide deposition process

A low temperature (180 °C) and pressure (⩽750 mTorr) tetraethylorthosilicate (TEOS) oxide deposition process was developed and characterized in a commercially available plasma enhanced chemical vapor deposition reactor. The reactor uses a dual frequency, capacitively coupled, parallel plate electrode design, which employs multistation sequential deposition to enhance throughput and uniformity. Deposition rate, within wafer film thickness uniformity, and film stress were characterized as a function of process pressure, gas composition, rf power, and temperature. Production quality oxide films were deposited using low TEOS flow rate (45 sccm), high oxygen flow rate (4000 sccm), and low pressure (500 mTorr). Deposition rate increased linearly with TEOS flow rate and decreases with oxygen flow rate. Deposition rate was weakly dependent on high frequency power and independent of pressure in this low pressure regime. Film thickness uniformity across a 200 mm wafer improved with decreasing TEOS flow rate and pressure. Uniformity was a weak function of oxygen flow rate and high frequency power. Film stress became more compressive with decreasing TEOS flow rate and was a weak function of oxygen flow rate, high and low frequency power, and pressure. A high quality TEOS oxide was deposited in this new processing regime, suitable for integrated circuit applications.

Hydrogen incorporation in dual-mode PECVD amorphous silicon oxide thin films

Hydrogen incorporation in amorphous silicon oxide thin films a-SiO x :H (0.5< x<2.0) was studied quantitatively by combining nuclear analysis (Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA)) and IR absorption spectroscopy. The films were obtained at low temperatures (40250 °C) and high growth rates ( R d) up to 55 Å s −1 using a dualplasma-enhanced chemical vapour deposition (dual-PECVD) reactor. Hydrogen atoms were bonded to Si in Si-rich films, whereas in nearly stoichiometric films H atoms were only bonded to oxygen in Si-OH and H 2O configurations. The intensity of the OH broad absorption band increased for films produced at low temperatures and high oxygen flow rates (high deposition rates). No modification of the spectrum was observed after thermal annealing at 250 °C, even for thin films deposited at 70 °C, indicating good stability of the bonded H. Quantitative analysis of the stoichiometry of the films was undertaken, and the proportionality constants between the atomic concentration and the integrated absorbance for Si O Si, Si O H and H O H stretching modes and the H O H bending mode are given.

Reactive Ion Etching of the fluorinated polyimide film

AbstractThe etch conditions affecting the etching of the fluorinated polyimide films in RF plasma using oxygen or fluorine-containing oxygen has been investigated. The effect of power, oxygen gas flow rate, and gas composition on the etch rate of fluorinated polyimide have been determined. The etch rate of the fluorinated polyimide increases linearly with the power and oxygen gas flow. The saturation at high oxygen flow rate indicates a saturation or steady state achieved at the polyimide-oxygen reaction interface. However, the etch rate increases when CF4 is added to oxygen, up to about 10% CF4 in O2, and then decreases to a smaller and CF4 concentration independent value. The etch selectivity of hard mask against fluorinated polyimide has been determined. The PECVD silicon nitride and PETEOS are found to be excellent hard mask for pattering these polyimides. The trench profile of the polyimide film also has been examined by patterning and etching the different trench sizes in fluorinated polyimide. It is concluded that this fluorinated polyimide can be etched with oxygen or fluorine containing oxygen plasma.

Comparison of nasal prongs and nasopharyngeal catheter for the delivery of oxygen in children with hypoxemia because of a lower respiratory tract infection

Objective: To determine the best method of oxygen delivery for children in developing countries who have hypoxemia caused by acute lower respiratory tract infection. Methods: One hundred eighteen children between 7 days and 5 years of age with a lower respiratory tract infection and arterial hemoglobin oxygen saturation (Sa O 2) less than 90% were randomly selected to receive oxygen by nasopharyngeal (NP) catheter (n = 56) or nasal prongs (n = 62). A crossover study to determine the flow rate necessary to achieve an Sa O 2 of 95% was performed in 60 children. Results: One hundred twelve children could be oxygenated by the allocated method; in six oxygenation was poor with either method. The mean duration of therapy was 87.5 hours for the prongs and 94.9 hours for the NP catheter (not significant). The median oxygen consumption was 2142 L for prongs and 1692 L for the NP catheter (not significant). In the crossover study the prongs needed, on average, 26% higher oxygen flow rates than the NP catheter to obtain an Sa O 2 of 95% ( p = 0.003). Complete nasal obstruction was observed in 24 of the children (44%) in the NP catheter group and in 8 (13%) in the prongs group ( p <0.001). Eighteen children died, 11 with NP catheter and 7 with prongs (not significant). Conclusions: Because nasal prongs are less prone to complications, and oxygenation in children is equally effective, they are a more appropriate method than the NP catheter for oxygen delivery to children in developing countries with acute lower respiratory tract infections. (J P EDIATR 1995;127:378-83)

Ethanol production from glucose by free and agar-entrapped batch cultures ofSaccharomyces cerevisiae at different oxygenation levels

The influence of the oxygenation level on glucose alcoholic fermentation by free- and immobilized-cell batch cultures ofSaccharomyces cerevisiae (CBS 1200) was investigated. Ethanol production by suspended cultures was stimulated by moderate oxygen flow rates (OFRs) but inhibited by higher OFRs (1.25 mol O2 h−1 dm−3). On the contrary, agar-entrapped yeasts displayed the best fermentation performance under strict anaerobiosis and were less affected than free cultures by high OFRs. These results are dicussed by referring to the substrate mass transfer limitations inherent in immobilized-cell systems.

The origin of the inhomogeneity of electrical resistivity in magnetron-sputtered indium tin oxide thin films

The intensity distribution of the ion flux on a substrate surface has been measured to examine the origin of the inhomogeneity of resistivity in magnetron-sputtered indium tin oxide (ITO) thin films. Ion flux intensity was determined as the product of ion saturation current Ii and floating potential Vf which were measured by a cylindrical Langmuir probe placed near a glass substrate. IiVf varied depending on the substrate position and showed a maximum near the upper position of the target erosion line. The resistivity of the ITO films showed a minimum at a certain oxygen flow rate. The oxygen flow rate where resistivity showed a minimum decreased as IiVf increased. Carrier mobility increased as IiVf increased under low oxygen flow rate conditions. Carrier concentration decreased as IiVf increased under high oxygen flow rate conditions. The film microstructure and composition were related to the electrical properties.

Clinical Experience and Physiologic Results with an Implantable Intratracheal Oxygen Catheter

Ten patients with chronic lung disease received an implanted ITOC. Seven patients continue to use their catheters after a mean period of 14.75 months. Four catheters were removed, 2 at 1 month, 1 after 10 months and 1 after 13 months. One patient requested a second catheter. Three patients experienced mucus plug formation; this was transient in two patients, but led to removal of the catheter in the third. To determine the degree of oxygen-saving afforded by the ITOC, SaO2 was measured at rest and during exercise for eight of the ten subjects using a double-blind technique. The calculated oxygen savings were around 40 percent both at rest and during exercise. The ITOCs were well received by the majority of our patients and were shown to produce a useful saving of oxygen which is of benefit to patients using portable systems and those who require high oxygen flow rates.

Photosensitized oxidation of bromide to bromine with phthalic acid derivatives in aqueous solutions

The photosensitized oxidation of oxygenated aqueous acidic solutions of potassium bromide was studied, testing the effects of various organic sensitizers. Very effective sensitization was found with aluminum tetrasulfo phthalocyanine tetrasodium salt (AISP c), copper tetrasulfo phthalocyanine tetrasodium salt (CuSP c), cobalt tetrasulfo phthalocyanine tetrasodium salt (CoSP c), phthalic acid and 4-sulfo-phthalic acid. The photo-oxidation of bromide in the presence of AISP c increased both with rising acid concentration and with higher oxygen flow rate, and was not affected by addition of the singlet oxygen quencher 1,4-diazabicyclo-(2.2.2)octane (DABCO). For AISP c, CoSP c and CuSP c, the photoactivity for bromide oxidation continued even after the dyes had become bleached, indicating that the actual sensitizer must be a stable photolysis product of the tetrasulfonated phthalocyanines. In the absence of added bromide, with CuSP c in 2.0M HCl, the photo-oxidation of chloride to chlorine occurred, but at a much smaller rate than that of bromide.

The Effect of Arterial Filtration on Reduction of Gaseous Microemboli in the Middle Cerebral Artery During Cardiopulmonary Bypass

Noninvasive in vivo detection of gaseous microemboli in the middle cerebral artery, by transcranial Doppler ultrasound, was used to determine the effect of filtration in the arterial catheter using 25- and 40-μm filters and bubble oxygenators in patients undergoing cardiopulmonary bypass surgery. Eighteen patients undergoing coronary artery bypass surgery were studied using a closed cardiac (unvented heart) model. Group 1 patients (no filters) had the highest incidence of gaseous microemboli, as indicated by the ultrasound microemboli index, at both high and low oxygen flow rates. Group 2 patients (40-μm filters) had a significantly lower microemboli index, particularly at low oxygen flow rates ( t = 4.9, p < 0.001). The 25-μm group patients had the lowest values of all. No microemboli were detected at low oxygen flow rates, and microemboli were detected in only 0.1% of the samples at high oxygen flow rates. Additionally, observations on vented hearts in 3 patients undergoing cardiac valve surgery indicate that the origin of gaseous microemboli may be air trapped inside the heart.

Dependence of Magnetic Properties of Metal Evaporated Tape on O2 Gas Flow Rate

Co-Ni films were evaporated on PET substrates with oxygen gas introduced into the chamber at various flow rates (0 ~ 300 ml), and its effects on the magnetic properties of the films were studied with its flow rate as a parameter. From the angular distribution of the film coercivity, two switching mechanisms seemed to exist in the film. They are 1) coherent rotation of the magnetization, and 2) domain wall motion. At higher O 2 flow rates the former region tended to broaden, suggesting a finer columnar grain structure. The dependence of coercivities on temperature grew more marked at higher oxygen flow rates.

The role of oxygen in oblique-deposited CoNi thin films

Some effects due to the introduction of oxygen during oblique deposition of CoNi films on both the magnetic properties and the columnar structure of the deposited film are described. A double-peak variation of the in-plane coercivity with the oxygen flow rate is proposed to be due to competing contributions from (i) a shape transition in the columnar structure, and (ii) the segregation of oxygen and formation of oxides in and around the polycrystalline columns influencing both the nucleation and pinning of reverse domains and domain walls. Typically, films deposited at a low-oxygen flow rate have a curved-columnar structure, whereas above a critical, high-oxygen flow rate, the films have a straight canted-columnar morphology.

Fixed Performance Oxygen Masks

Fixed performance oxygen masks operate by supplying mixtures of oxygen and air at rates exceeding the inspiratory flow rate of the patient. In this study the oxygen concentration delivered by three fixed performance oxygen masks was determined non-invasively at various inspiratory flow rates. At low inspiratory flow rates all the masks studied acted as fixed performance devices. When the peak inspiratory rate increased the performance of all the masks showed some variability. The change from fixed to variable performance depended on the relation between inspiratory flow rate and the total gas flow delivered by the mask and was independent of the volume of the mask. Hence the use of low volume masks and high oxygen flow rates should produce more consistent results than high volume masks and lower flow rates.