Helium Oxygen Research Articles

Oxidative dehydrogenation of propane on V 2O 5/TiO 2 catalysts under transient conditions

Oxidehydrogenation of propane was studied on two catalysts containing an equivalent of five theoretical monolayers of V 2O 5 prepared by impregnation of anatase TiO 2 with ammonium metavanadate, drying and calcination. One of the catalysts was doped with potassium (K/V=0.1). Transient kinetic experiments have been performed using concentration steps of active gases (propane and oxygen) in helium. Absence of significant mass and heat transfer effects has been verified. The experimental partial pressure curves of products have been satisfactorily simulated using a mechanism based on a proposition of Oyama. The potassium-doped catalyst could be treated within this model on the assumption that its surface was composed of modified and non-modified regions.

Headspace oxygen in sample vials affects volatiles production of meat during the automated purge-and-Trap/GC analyses.

Headspace oxygen in sample vial for the purge-and-trap dynamic headspace/gas chromatography method oxidizes meat if held hours before purging, influences volatile profiles, and misrepresents the true composition of volatiles. Helium flush and helium flush plus oxygen absorber were used to eliminate residual oxygen and minimize oxidative changes in meat during sample holding time. Both helium flush and helium flush plus oxygen absorber treatments were effective in preventing an increase in 2-thiobarbituric acid reactive substances (TBARSs) and volatiles production in raw meat for up to 640 min of sample holding. With helium flush plus oxygen absorber, only 1-octen-3-ol increased during the 1280-min sample holding time. However, the hexanal peak in raw meat was interfered by 2,6-dimethyl heptane when oxygen absorber was added. Therefore, use of oxygen absorber was not appropriate for raw meat. Helium flush reduced oxidative changes in cooked meat during sample holding time but was not able to stop oxidative changes in meat after 160 min sample holding. A combination of helium flush and oxygen absorber was effective in preventing volatiles production in cooked meat for over 20 h of sample holding at 4 degrees C.

The thermoregulatory limits of an Australian Passerine, the Silvereye ( Zosterops lateralis)

(1) The thermal capabilities of Australian silvereyes ( Zosterops lateralis, 11 g) were investigated both at low and high ambient temperatures ( T a) during the photophase and scotophase. (2). The peak metabolic rate (PMR) induced by helium–oxygen (79:21 %, He–O 2) exposure during the photophase was 15.64±1.55 mL O 2 g −1 h −1 at an effective lower survival limit T a ( T pmr) of −39.7±6.1°C. (3). Above the thermoneutral zone (TNZ), metabolic rate, body temperature ( T b), and thermal conductance increased steeply, but they were able to withstand a T a of 39°C. (4). Our study shows that silvereyes are able to tolerate an impressive range of T a from about −42°C to at least +39°C and are able to produce enough heat to maintain a thermal difference between T b and T a of up to 80°C.

Ion/molecule reactions of protonated diglycine: an electrospray ionization flow tube reactor experiment

Reactions of protonated diglycine, GLY 2H +, with methanol, ammonia, and a series of methylamines were studied under thermal conditions with a combination of an electrospray ion source and a flow tube reactor. The major primary reaction product in all of the systems studied is the complex formed between the ionic and neutral reagents in a ternary association reaction involving the helium carrier gas and oxygen or nitrogen molecules as collisionally stabilizing species. Effective binary rate constants were determined experimentally and compared with calculated ion dipole collision rate constants. Proton transfer was observed from GLY 2H + to trimethylamine but not to any of the other reagents studied. Secondary products observed include formation of protonated mixed trimers of GLY 2 with two amine molecules. In the case of methanol, a secondary product is the protonated mixed dimer of GLY 2 and dimethylether. The results will be discussed in the light of the mechanisms of hydrogen-deuterium (H-D) exchange of GLY 2H + with deuterated isotopomers of methanol and ammonia studied previously by various groups.

Oxygen uptake during peritoneal ventilation in a porcine model of hypoxemia.

Peritoneal ventilation (PV) can greatly increase PaO2 in hypoxemic rabbits. We tested the hypothesis that the peritoneum can provide a gas exchange surface for oxygen uptake in larger animals that, like humans, have a smaller relative peritoneal surface area and corresponding blood flow. Prospective, randomized, controlled animal study. University research laboratory. In six anesthetized pigs, a modified endotracheal tube (9.0-inner diameter) was inserted into the peritoneal cavity, and the peritoneal cavity was ventilated with oxygen in helium in gas phase. Measurements of peritoneal oxygen uptake and mixed venous oxygen saturation were made over 30 mins of: a) baseline FiO2 0.20, no PV; b) FiO2 0.20, PV; c) FiO2 0.20, PV, dopamine 5 microg/kg/min; d) baseline FiO2 0.15, no PV; e) FiO2 0.15, PV; and f) FiO2 0.15, PV, dopamine 5 microg/kg/min. Mixed venous oxygen saturation was 61% at the baseline FiO2 of 0.20 and 33% at an FiO2 of 0.15 and did not increase significantly from baseline with PV or with dopamine at either FiO2. Peritoneal oxygen uptake, measured with a waterseal spirometer, was 9.1+/-3.1 (SD) and 11.9+/-3.0 mL/min when lung FiO2 was 0.20 and 0.15, respectively, and 9.7+/-2.8 and 12.2+/-2.7 mL/min when FiO2 was 0.20 and 0.15 and dopamine was infused, respectively. Peritoneal ventilation does not result in clinically significant oxygen uptake or alter mixed venous oxygen saturation in a porcine model of hypoxemia.

Pyrolysis of polypropylene in the presence of oxygen

The polypropylene (PP) was coated on porous α-alumina particles and then pyrolyzed in a flow of helium or a mixture of helium–oxygen at atmospheric pressure. The mass release from PP was dramatically enhanced in the presence of oxygen at temperatures in the range of 200–300°C. The temperature for the 50% mass release was ca. 250°C at an oxygen partial pressure ( P O 2 ) of 16.7 kPa and was lowered by 190°C as compared with a system which contained no oxygen. When P O 2 was higher than 4.2 kPa, the mass release rate obeyed first-order kinetics with respect to P O 2 , and the activation energy was calculated and found to be 65–75 kJ/mol. The activation energy was considerably lower than that for pyrolysis in the absence of oxygen (230 kJ/mol) and agreed well with the value for formation of peroxides on tertiary carbons. When the pyrolysis was conducted at 250°C under P O 2 =16.7 kPa, the carbon-based yield of volatiles exceeded 90%, and the yields of CS 2-soluble oil and wax were 76% and 6.0%, respectively. The carbon-based yields of other products were: Acetone, 2.5%; methanol, 1.5%; CO, 3.0%; CO 2, 2.2% and solid residue; 10%. Proton NMR (nuclear magnetic resonance) analysis showed that the CS 2-soluble oil possessed an elemental composition of C 100H 187O 11. The average number of carbon atoms per molecule of the oil was approximately 10, and –CH 2–OH, –C(CH 3)CO and CH 2 were typical end groups. Their formation is explained by the decomposition of peroxides formed on tertiary carbons.

Regional Deposition of Inhaled Evans Blue Dye in Mechanically Ventilated Rabbits with Air or Helium Oxygen Mixture

An animal model has been used and further developed to examine and evaluate differences in regional deposition patterns of an Evans Blue dye (EB) tracer aerosol. This was done by using different carrier gas composition of either He-O2 (80% helium, 20% oxygen) or air (79% nitrogen, 21% oxygen) in histamine-provoked and nonprovoked rabbits. The ratio of peripheral deposition to total deposition (central + peripheral), in relation to percentage increase in intratracheal pressure (ITPΔ%), was used as an evaluation tool. The animals were tracheostomized, cannulated, and ventilated in a volume-controlled mode until they were stable. Saline or histamine was then administrated for 2 min before the tracer aerosol EB was given. The percentage increase in intratracheal pressure before and after provocation was calculated (7TPA%) and was, on average, 51 ± 20% for air and 51 ± 20% for He-O2. EB was extracted from lung tissues and measured with a spectrophotometer. The absorbance in different lung regions was used as a measure of the distribution of aerosol. Bronchial provocation gave a central deposition 0.55 ± 0.11 (mean ± SD, ratio = peripheral deposition/central + peripheral deposition) compared to 0.80 ± 0.09 in the control group. He-O2-ventilated rabbits showed significantly higher peripheral deposition ratio (0.67 ± 0.12) compared with air-ventilated rabbits (0.55 ± 0.11). The latter finding may be due to the difference in the degree of turbulent flow. There were significant correlations between intratracheal peak pressure and peripheral deposition, r = -.60 and r = -.71 for air and He-O2, respectively. This study demonstrates the possibility of using a rabbit model and different carrier gases for evaluation of effects of bronchial provocation.

ANXIETY, SENSORIMOTOR AND COGNITIVE PERFORMANCE DURING A HYDROGEN–OXYGEN DIVE AND LONG-TERM CONFINEMENT IN A PRESSURE CHAMBER

Occupational deep diving is an extreme situation that is characterized by both social and physical stressor agents such as long-term confinement and high-pressure exposure. High pressure is known to be a basic aetiological factor underlying central nervous system changes that include psychosensorimotor disorders. The authors report anxiety, sensorimotor, and cognitive responses in commercial divers participating in a hydrogen–oxygen experimental dive to 300 metres depth with long-term confinement in a pressure chamber. Anxiety data confirm that living and working in a high pressure of inert gases is not inherently stressful and further support the view that the main factor involved in the development of diving anxiety is the social environment rather than the physical environment. Alternatively, the cognitive and behavioural data suggest that the future of hydrogen as a diving gas could be limited, at least for depths greater than 200 metres, to an additional role to the basic helium–oxygen mixture.

The effect of He?O2 exposure on metabolic rate, thermoregulation and thermal conductance during normothermia and daily torpor

Recently it was proposed that the low metabolic rate during torpor may be better explained by the reduction of thermal conductance than the drop of body temperature or metabolic inhibition. We tested this hypothesis by simultaneously measuring body temperature and metabolic rate as a function of ambient temperature in both torpid and normothermic stripe-faced dunnarts, Sminthopsis macroura (Marsupialia; approx. 25 g body mass), exposed to either air or He−O2 (21% oxygen in helium) atmospheres. He−O2 exposure increases the thermal conductance of homeothermic mammals by about twofold in comparison to an air atmosphere without apparent side-effects. Normothermic S. macroura exposed to He−O2 increased resting metabolic rate by about twofold in comparison to that in air because of the twofold increase in apparent thermal conductance. Torpid S. macroura exposed to He−O2 at ambient temperatures above the set-point for body temperature showed a completely different metabolic response. In contrast to normothermic individuals, torpid individuals significantly decreased or maintained a similar metabolic rate as those in air although the apparent thermal conductance in He−O2 was slightly raised. Moreover, the metabolic rate during torpor was only a fraction of that of normothermic individuals although the apparent thermal conductance differed only marginally between normothermia and torpor. Our study shows that a low thermal conductance is not the reason for the low metabolic rates during torpor. It suggests that interrelations between metabolic rate and body temperature of torpid endotherms above the set-point for body temperature differ fundamentally from those of normothermic and homeothermic endotherms.

Lithium wall conditioning for fuel and impurity control

Small-scale laboratory experiments on wall conditioning by thin lithium layer deposition are carried out. Suppression of carbon impurities by lithium deposition onto graphite walls are clearly demonstrated by a glow discharge in 1% oxygen in helium. Strong gettering effects of clean lithium surfaces on oxygen and hydrogen atoms are found, supporting recent findings in fusion devices. The maximum number of H atoms pumped by the lithium layer at room temperature is approximately equal to the number of Li atoms in the vessel. Thus, the effective solubility of hydrogen in lithium is as high as H (Li + H) ≈ 50% which is orders of magnitude larger than the values in the thermal equilibrium state. Furthermore, most of the hydrogens pumped by the lithium layer are desorbed as H 2 molecules at relatively low temperatures such as 200 °C. This thermal desorption study suggests a very slow formation of lithium hydride whose thermal decomposition takes place at ≈ 700 °C.

A free molecule aerodynamic investigation using multiple satellite analysis

The inaccuracies of numerical satellite positioning in Low Earth Orbit are predominantly due to the errors in calculating the aerodynamic forces. This is due to the unknown interactions of the rarefied atmosphere on the satellite surface, and the errors of the atmospheric density models. To improve knowledge of the gas-surface interactions, the effects of aerodynamic forces upon the orbits of satellites can be isolated, using precise orbital analysis (POA). When examining the orbit of a single satellite, the solution is restricted by the limited observational data, atmospheric model errors and the inevitable correlations between the atmospheric and aerodynamic models. To address these, three satellite orbits are examined simultaneously. The satellite orbits analysed are those of ERS1, a remote sensing satellite, and the geodetic satellite's STARLETTE and STELLA. They orbit at 800 to 1000 km where helium and atomic oxygen are dominant. The collisional energies of helium and atomic oxygen upon the spacecraft surface are 1.25 and 5 eV, respectively. This preliminary analysis suggests that the re-emission of these particles are at lower speeds and lower emitted angles than those measured in laboratory molecular beam experiments. The analysis suggests that the bulk speed of the emitted particles is about 2 km s −1, and in a direction approximately half way between the specular direction and the surface normal. This emission produces a drag coefficient on an aluminium sphere of 2.52.

Kinetics of PdO combustion catalysis

The kinetics of the catalytic combustion of methane by supported palladium oxide catalysts (2 wt.-% Pd/La 2O 3·11A1 2O 3 and 5 wt.-%Pd/ γ-A1 20 3 were examined for several oxygen partial pressure levels over the temperature range from 40–900°C using temperature-programmed reaction and slow ramp and hold temperature-time transient techniques. Combustion rates were measured by differential reaction in a fixed bed of powdered catalyst at lower temperatures (200–500°C). Also, by preparing the catalysts as thin (ca. 10 μm) coatings on an alumina tube and conducting the experiments with very high flows of dilute methane and oxygen in helium, the rate measurements were extended up to 900°C without significant contribution from gas phase reactions. The specific combustion activity of supported PdO shows a persistent hysteresis between 450 and 750°C, i.e., the rate of combustion between these temperature limits depends strongly on whether the catalyst is cooling from above 750°C or heating from below 450°C. This region is also notable for negative apparent activation energy in the rate of methane oxidation, i.e., the rate increases with decreasing temperature during reoxidation of the Pd metal and decreases with increasing temperature (especially with low oxygen partial pressure) prior to decomposition of the bulk oxide. Detailed time-temperature transient kinetic analyses were performed for supported PdO catalysts within the 450–750°C temperature range. The hysteresis in methane combustion rate is caused by a higher activation energy for reduction of oxygen chemisorbed on metallic Pd and by suppressed reoxidation of Pd metal relative to PdO decomposition.

OXIDATIVE COUPLING OF METHANE ON SUPERCONDUCTOR-TYPE CATALYTIC MATERIALS

Oxidative coupling of methane to higher hydrocarbons was investigated using alkali and rare earth cuprates such as YBa2Cu3O7−x, La1.8Ba0.2CuO and La2CuO4. Oxygen and methane in helium were fed to the reactor in a cofeed mode. Approximately, 5 g of catalyst in powder form was placed in a quartz flow reactor in all experiments. Oxygen partial pressure was changed as a parameter (P0 = 0.5 to 9.1 kPa) while keeping methane partial pressure and temperature constant at 18kPa and 1023 K respectively. Investigation of catalytic activity in terms of overall methane conversion and C2 + (C2H4+C2H6) product selectivity indicated that higher conversions and lower selectivities were obtained as O2 partial pressure was increased at a constant methane partial pressure of 8kPa. In comparing the performance of the two catalysts, La1.8Ba0.2CuO and La2CuO4; the selectivity results indicated a positive influence of incorporation of Ba into La2CuO4 structure. Similarly, selectivity values substantially increased teaching 86.3%...

Mid‐latitude incoherent scatter observations of helium and hydrogen ions

We have successfully employed a constrained non‐linear least squares analysis of incoherent scatter data from the topside ionosphere over Arecibo, Puerto Rico to simultaneously deduce concentrations of helium ions, protons, and oxygen ions as well as ion and electron temperatures. The constraint encourages smooth temperature profiles, and its use avoids unrealistic parameter values in regions where light ions are more than 80% of the total. Here we report proton concentrations that remain higher than helium ion concentrations, even though the latter reach 30% of the total and exceed the oxygen ion densities at altitudes as low as 700 km at night and 1500 km in the day‐time. Before local sunrise the effects of conjugate‐point photoelectrons are clearly seen, while after sunrise the transition height between oxygen and helium rises much more rapidly than does the transition from oxygen to hydrogen.

Determination of Intraparticle Diffusivities Using a Single Pellet String Fixed Bed and a Shallow-Bed Diffusion Cell

Two experimental techniques and the corresponding theoretical models were used for determining gas adsorption equilibria and intraparticle mass transport parameters. These methods include a diffusion cell adapted to be used with small particles (shallow-bed diffusion cell) and the chromatographic method using a single pellet string fixed bed. The experimental systems used were oxygen, nitrogen, and argon in helium over the Rhone Poulenc 4A and 5A zeolite and LaRoche alumina at various temperatures. The conditions where other mass transport resistances can be neglected (film diffusion in the chromatographic method) or independently obtained (bulk diffusion in the cell and axial dispersion in the fixed bed) are discussed. Also, a sensitivity analysis is used which shows that it is not possible to estimate the microparticle diffusivities in 5A zeolite and LaRoche alumina and also the macropore diffusivities in 4A zeolite. In the last case we assume that the macropore diffusivities are the same as in 5A because both zeolites come from the same manufacturer and so possibly only differ in the type and number of cations. The temperature dependency of the microparticle diffusivities follows an Arrhenius-like equation. The consistency of the results obtained by both methods confirms that the experimental techniques and the corresponding models are reliable. Also, the shallow-bed diffusion cell presents some advantages over the chromatographic method, such as simplicity, easy temperature control, no need for evaluation of flow patterns, and smaller amounts of materials

Variation of local charge states and the local electrostatic potential during oxygen adsorption on a caesiated Si(001) surface probed with helium metastables and oxygen molecules

We have investigated the initial stage of the oxygen uptake process at a Cs/Si(001) surface by metastable de-excitation spectroscopy (MDS) and by observing the electron emission induced by the incidence of oxygen molecules. MDS revealed that the amount of oxygen adsorbed at the topmost layer increases in parallel with the decrease of Cs 6s̃ intensity. However, the work function minimum occurred midway in this initial, monotonous, oxygen-uptake stage. The low-energy cutoff in electron spectra induced by oxygen molecules from the gas phase exhibited a variation in the local electrostatic potential (near the positions where a non-adiabatic process occurred for the incident oxygen molecules) different from the usual behavior of the work function. The mechanism of oxygen uptake is discussed in connection with the local structures of the electronic states and the electrostatic potential.

Variation of local charge states and the local electrostatic potential during oxygen adsorption on a caesiated Si(001) surface probed with helium metastables and oxygen molecules

We have investigated the initial stage of the oxygen uptake process at a Cs/Si(001) surface by metastable de-excitation spectroscopy (MDS) and by observing the electron emission induced by the incidence of oxygen molecules. MDS revealed that the amount of oxygen adsorbed at the topmost layer increases in parallel with the decrease of Cs 6s̄ intensity. However, the work function minimum occurred midway in this initial, monotonous, oxygen-uptake stage. The low-energy cutoff in electron spectra induced by oxygen molecules from the gas phase exhibited a variation in the local electrostatic potential (near the positions where a non-adiabatic process occurred for the incident oxygen molecules) different from the usual behavior of the work function. The mechanism of oxygen uptake is discussed in connection with the local structures of the electronic states and the electrostatic potential.

An improved method of preserving and extracting mineral matter from coal by very low-temperature ashing (VLTA)

Low-temperature ashing (LTA) has been used to extract mineral matter from coal. The problem has been that the ashing temperature could not be measured and consequently the ashing processes could not be controlled. The ashing temperature in this study was measured by thermographs, which indicate the highest temperature reached during ashing. Some of the disadvantages of LTA were shown to be due to the ashing temperature being too high (150–300 °C). It was also confirmed that the mineral matter, especially sulphide, usually oxidizes and some is lost as SO 2. To solve these problems, a new method was developed, very low-temperature ashing (VLTA), to preserve and extract mineral matter from coal without loss or damage of the original phases. It was shown that to obtain an ‘in situ’ ash, the ashing temperature should not exceed 60–70 °C, regardless of the rank of the coal. To decrease the ashing temperature, the oxygen was diluted with helium to decrease the reaction rate. To achieve this very low temperature, the ashing atmosphere ( oxygen helium ratio) must be adjusted for coal rank and sulphur content.

Experimental Evaluation of the Consequences of Uranium Bed Air-Ingress Accidents

To help resolve unknowns regarding consequences of air-ingress accidents in uranium beds, a series of experiments was conducted at Ontario Hydro Research Division with the participation of Princeton Plasma Physics Laboratory and the Idaho National Engineering Laboratory. These experiments involved exposure of uranium beds of various sizes to air, oxygen in helium, argon and Nitrogen. Beds of 5-gram to 3-kg uranium capacity were tested. Starting temperatures ranged from 294 K to 824 K. Results of these experiments showed that in every test the reaction was restrained with modest temperature excursions. Either surface films or gas blanketing may be responsible for quenching the reaction with air. In these tests the reaction appears to be stopped by a diffusive barrier film of reaction products that grows on the surface of the uranium grains. The only tritium emissions appeared to be due to thermal oscillation-driven gas expansion. Our conclusion is that the hazard associated with an air-ingress accident involving a uranium bed is smaller than we thought initially. With proper bed design, the energy release will be modest and should not result in damage to the bed structure. Tritium release can be minimized or prevented by keeping the bed only partially loaded.

Reactions of aromatic ethers with atomic oxygen O( 3P) in the gas phase

In the slow combustion of aromatic hydrocarbons partially oxidized hydrocarbons are intermediate products. Therefore aromatic ethers may be of interest in combustion processes in fuel rich flames. Only a few data are available for their reactions, especially at high temperatures. Here we report measurements for the reaction of ethylphenylether, diphenylether, anisole and phenol with O atoms. A continuous flow reactor with molecular beam sampling and mass spectrometric detection was used. Oxygen atoms were produced by a chopped microwave discharge in a mixture of the carrier gas helium and molecular oxygen. The concentration of O atoms was 50–650 times higher than the hydrocarbon concentration so that we obtained pseudo first order kinetics. The reactor is made of quartz. The temperature range from 298 K to 870 K was investigated. The obtained data can be represented as a straight line in the Arrhenius plot. The rate constants (k(T) in units of cm3* mol−1* s−1) are: k ( diphenylether ) = ( 0.87 ± 0.17 ) ∗ 10 13 exp ⁡ ( − 1656 ± 166 T ) k ( ethylphenylether ) = ( 1.35 ± 0.27 ) ∗ 10 13 exp ⁡ ( − 1576 ± 158 T ) k ( anisole ) = ( 1.67 ± 0.34 ) ∗ 10 13 exp ⁡ ( − 1479 ± 148 T ) k ( phenol ) = ( 1.70 ± 0.34 ) ∗ 10 13 exp ⁡ ( − 1540 ± 157 T ) We found that the data fit very well in a plot of activation energy vs adiabatic ionization potential and also in the Hammett plot for the reaction of oxygen atoms with aromatic compounds. The slope of both plots and thermochemical calculations support the assumption of an electrophilic addition of O(3P) atoms to the aromatic system.