Oxygen permeability of teflon–PFA tubing

The permeability coefficient for oxygen diffusing through a sample of Teflon-PFA tubing was determined experimentally. The source of the diffusing oxygen was ambient temperature air surrounding a coiled length of the PFA tubing. High pressure nitrogen was directed through the center of the PFA tubing. Oxygen permeating from the low pressure ambient air source, through the PFA tubing, and into the flowing high pressure nitrogen was observed in the effluent gases as they passed through a trace oxygen analyzer. By this means, oxygen concentrations in the effluent nitrogen were determined as a function of varying nitrogen flow rates, at nitrogen gas pressures of 4.4 and 7.8 atm (absolute), within the tubing bore. All measurements were also carried out at ambient temperatures of 21 ± 1°C. In addition, a theoretically related graphical method of evaluating the experimental data was developed and subsequently employed to actually determine the oxygen permeability coefficient for this system.     

Gas permeation resistance of a perfluoroalkoxy‐tetrafluoroethylene copolymer

The permeation resistance of perfluoroalkoxy (PFA), a polytetrafluoroethylene (PTFE) copolymer, to various gases was explored. The diffusion and permeability coefficients for hydrogen, oxygen, nitrogen, and air were measured with extruded films using standard manometric techniques. For thicker films, transport properties were independent of film thickness. For the thinnest films, the diffusivity and permeability coefficients were slightly higher because of reduced crystallinity. The solubility of these apolar permeants in PFA was quite low and behaved ideally. Therefore, the permeation characteristics of air could be calculated from those of nitrogen and oxygen. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2122–2125, 2006     

Surface modification of tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) by plasmas for copper metallization

Tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) sheet surfaces were modified with argon, helium, oxygen, and hydrogen plasmas. How the four plasmas modified the PFA sheet surfaces was investigated. All plasmas modified the PFA surfaces and at the same time initiated degradation of the PFA polymer chains. The balance between modification and degradation was strongly influenced by the magnitude of the discharge current in the plasmas. Efficiency of the plasmas in modification was hydrogen plasma > oxygen plasma > argon plasma > helium plasma. The modification involved defluorination of CF₂ carbons into CHF and CH₂ carbons and oxidation into O? CH₂, O? CHF, and O? CF₂ groups. The surface‐modification technique (a combination of hydrogen plasma treatment and silane coupling treatment) proposed in this study was applied for copper metallization of the PFA surface. The utility of the technique was confirmed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1087–1097, 2002     

The diffusion coefficients of helium,hydrogen, oxygen and nitrogen in water determined from the permeability of a stagnant liquid layer in the quasi-s

At temperatures between 10 and 60°C the diffusion coefficients of helium, hydrogen, oxygen and nitrogen in water have been determined from the permeability of a stagnant liquid layer in the quasi-steady state (SLL method). With this method we actually measure the difference in diffusive flow between two gases through a horizontal stagnant liquid layer between gas-permeable membranes. If oxygen is one of the gases, we are able to determine the diffusion coefficient of oxygen with a maximum experimental error of 3.5% and that of the other gases within 5%. Results are given and compared with experimental values stated in the literature.     

Sintering Alumina: Effect of Atmospheres

Two effects of atmosphere on the sintering of alumina powder compacts were investigated. Changing the oxidizing conditions during early-stage sintering measurements showed that, within the range −70°F dew point oxygen to −70°F hydrogen equilibrated with alumina, there was no observable effect on sintering rate. The effect of trapped atmosphere on closure of pores was determined from apparent density limits obtained at high sintering temperatures and long sintering times. The complete elimination of porosity during sintering of alumina was possible if discontinuous grain growth was controlled and if the ambient atmosphere was hydrogen, oxygen, or vacuum. Porosity could not be completely eliminated when the ambient atmosphere was helium, argon, or nitrogen (or therefore air).     

Correlation between gas transport properties and the morphology/dynamics of crystalline fluorinated copolymer membranes

The crystalline structure, dynamics, and gas transport properties (i.e., the gas permeability, gas diffusion coefficient, and gas solubility coefficient) of poly(tetrafluoroethylene‐co‐perfluoroethylvinylether) (PFA) membranes were systematically investigated via differential scanning calorimetry, wide/small/ultra‐small‐angle X‐ray scattering, and quasielastic neutron scattering measurements. We evaluated the gas transport properties using a constant‐volume/variable‐pressure method. The gas permeability and the gas diffusion coefficient decreased with increasing crystallinity of the PFA membranes at crystallinities below 32%. However, in membranes with a crystallinity of 32% or greater, these parameters depended on the characteristics of the gas molecules, such as their kinetic diameter. The so‐called long spacing period and the thickness of the crystalline/amorphous regions increased with crystallinity according to the small/ultra‐small‐angle X‐ray scattering results. Furthermore, the quasielastic neutron scattering measurements indicated that the scattering law was well fitted to a sum of narrow and broad Lorentzian components. In particular, the narrow components, that is, the local motion of amorphous components and side chains, increased with crystallinity. These results suggest that large gas molecules could pass through the PFA membranes, assisted by the motion in the amorphous region. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45665.     

Permeability coefficient of proton-irradiated poly(ethylene terephthalate) thin films

The principle of operation of an apparatus developed to study gas permeation through thin films is described, and the measurement method is discussed. Use is made of diffusion theory to obtain an expression for the permeability coefficient as a function of the rate of increase of the pressure in the receiving volume. The activation energy for permeation of helium through PET is determined. The permeability coefficient for helium is found to increase significantly with the range of the implanted protons although the incident charge has been kept constant. The hypothesis of structural modifications of the proton implanted PET seems to be confirmed by small-angle X-ray scattering experiments on the irradiated samples.     

Preparation and oxygen permeation of U‐shaped perovskite hollow‐fiber membranes

The oxygen permeation of dense U‐shaped perovskite hollow‐fiber membranes based on Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3?δ prepared by a phase inversion spinning process is reported. The perovskite hollow fibers with totally dense wall were obtained with the outer diameter of 1.147 mm and the inner diameter of 0.691 mm. The dependences of the oxygen permeation on the air flow rate on the shell side, the helium flow rate on the core side, the oxygen partial pressures, and the operating temperatures were experimentally investigated. According to the Wagner theory, it follows that the oxygen transport through the U‐shaped hollow‐fiber membrane is controlled by both surface reaction and bulk diffusion at the temperature ranges of 750–950°C. High oxygen permeation flux of 3.0 ml/(min cm²) was kept for about 250 h at 950°C under the conditions of the air feed flow rate of 150 ml/min and the helium flow rate of 50 ml/min. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

The Effect of Ambient Conditions on the Burning Rate of Gel Fuel Droplets

An experimental study was conducted to determine the dependence of the burning rate coefficient of gel fuel droplets on the pressure at different ambient oxygen nitrogen mixtures. Experiments were conducted using a pressure chamber, in which the droplet was suspended and the combustion process was video‐photographed by a high‐speed digital video camera. The tests were conducted at pressures between 0.1–4 MPa at different ambient oxygen nitrogen compositions (air, 40 % O₂ – 60 % N₂, and 60 % O₂ – 40 % N₂). The fuel was a compound of 95 % kerosene and 5 % gellant. At sub‐critical pressure conditions, the burning rate coefficient was found to increase with increasing ambient oxygen mass fraction. At supercritical conditions, no dependence of the burning rate coefficient on the ambient mixture was found. The results indicate that the burning rate coefficient depends on the oxygen partial pressure, at least at low pressures.     

Effect of water on the oxygen barrier properties of poly(ethylene terephthalate) and polylactide films

The aim of this work was to study the variations in the oxygen diffusion, solubility, and permeability coefficients of polylactide (PLA) films at different temperatures (5, 23, and 40°C) and water activities (0–0.9). The results were compared with the oxygen diffusion, solubility, and permeability coefficients obtained for poly(ethylene terephthalate) (PET) films under the same experimental conditions. The water sorption isotherm for PLA films was also determined. Diffusion coefficients were determined with the half‐sorption time method. Also, a consistency test for continuous‐flow permeability experimental data was run to obtain the diffusion coefficient with the lowest experimental error and to confirm that oxygen underwent Fickian diffusion in the PLA films. The permeability coefficients were obtained from steady‐state permeability experiments. The results indicated that the PLA films absorbed very low amounts of water, and no significant variation of the absorbed water with the temperature was found. The oxygen permeability coefficients obtained for PLA films (2–12 × 10^?18 kg m/m² s Pa) were higher than those obtained for PET films (1–6 × 10^?19 kg m/m² s Pa) at different temperatures and water activities. Moreover, the permeability coefficients for PLA and PET films did not change significantly with changes in the water activity at temperatures lower than 23°C. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1790–1803, 2004     

Permeability of oxygen and nitrogen gases in ethyl cellulose solid films retaining cholesteric liquid crystalline order

Ethyl cellulose (EC) films that retain lyotropic and thermotropic cholesteric liquid crystalline order, and an amorphous EC film were prepared. The liquid crystalline order was identified by optical measurements. The comparative permeability of oxygen and nitrogen gases for three kinds of EC film was determined, and the applicability of the EC films that retained cholesteric liquid crystalline order to oxygen enrichment are discussed. The permeability of oxygen or nitrogen gas for the liquid crystalline films was lower than that for the amorphous ones. The activation energy for the permeability coefficient of oxygen gas was ca. 3.5 kcal/mol. The ratio of permeability coefficient for oxygen gas to that for nitrogen gas was less than 4. Interestingly, the permselectivity of oxygen and nitrogen gases for the liquid crystalline films was greater than that for the amorphous ones. © 1996 John Wiley & Sons, Inc.     

Theoretical Analysis,Calculation, and Prediction of the Air Permeability of Textiles

Scientific principles were developed for predicting the air permeability of textiles based on current concepts concerning the air permeability of textiles and the assumptions of gas and hydrodynamics. Based on the physical concepts concerning flow of gases through porous systems, a theoretical model was elaborated to describe the dependence of the rate of passage of air through fabric on external ambient factors and the characteristics of their structure. The through porosity, thickness, and hydraulic diameter of the pores were determined with the most important characteristics of the structure of the fabrics in the complex index of their structure, with which their air permeability is closely correlated. The possibility of using the model for predicting the air permeability of fabrics was demonstrated. The differences in the results of determining the through porosity of fabrics obtained in using different methods were established during experimental testing of the theoretical model. Because of the very high reliability of the results, the estimation method was approved for use in research. A complex index for their structure which takes into account the effect of the most important structural characteristics — surface density, thickness, average density, filling of the material by the fibre — was proposed based on an analysis of the results of the study of the effect of the structural characteristics of nonwoven materials (NM) on their air permeability. The high degree of correlation of air permeability with this index allows using the dependences obtained with it for predicting the air permeability of NM. __________ Translated from Khimicheskie Volokna, No. 5, pp. 47–54, September–October, 2005.     

Model Development and Parameter Estimation for the Oxidation of Pyrrhotite‐Containing Rock Surfaces

A novel experimental method was developed for the evaluation of the biotic oxidation rate of waste rock containing sulphide minerals. Sized waste rock samples were inoculated with an Acidithiobacillus ferrooxidans suspension and sparged with discontinuing humidified air to yield the oxygen consumption rate. A kinetic/mass transport model was proposed based on oxidation of pyrrhotite. Bayesian statistical analysis using the Metropolis‐Hastings algorithm showed that at ambient oxygen concentration the mean (i.e., estimated) values of the initial oxygen flux, the reaction order, the oxygen diffusion coefficient through the oxidation product layer, and the surface reaction rate constant were 1.3×10^?7 mol/m².s, 0.55, 2.91×10^?13 m²/s and 3.23×10^?7 mol^0.45/m^0.35.s, respectively.     

Synthesis of silicalite-poly(furfuryl alcohol) composite membranes for oxygen enrichment from air

ABSTRACT: Silicalite-poly(furfuryl alcohol) [PFA] composite membranes were prepared by solution casting of silicalite-furfuryl alcohol [FA] suspension on a porous polysulfone substrate and subsequent in situ polymerization of FA. X-ray diffraction, nitrogen sorption, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize silicalite nanocrystals and silicalite-PFA composite membranes. The silicalite-PFA composite membrane with 20 wt.% silicalite loading exhibits good oxygen/nitrogen selectivity (4.15) and high oxygen permeability (1,132.6 Barrers) at 50°C. Silicalite-PFA composite membranes are promising for the production of oxygen-enriched air for various applications.     

Interactions of Cold Radiofrequency Plasma with Solid Wood I. Nitrogen Permeability along the Grain

Exposure of 1.5 cm diameter × 1.2 cm long white fir and Douglas-fir heart-and sapwood samples to the action of cold radiofrequency oxygen, nitrogen, and helium plasmas strongly increased wood permeability to nitrogen flow along the grain. Oxygen was most effective, followed by nitrogen and helium. While an increase in radiofrequency energy level increased the effect, the opposite was true for an increase in reactant gas flow rate. With white fir the rate of permeability increase was higher at the beginning of the plasma treatment. This was attributed to differing ablation rates of cellulose, hemicelluloses, and lignin. No significant time difference in the rate of permeability increase was observed with Douglas-fir. Extractives suppressed the plasmainduced permeability increase; thus extraction with water and ethanol, followed by oxygen plasma treatment increased permeability of Douglas-fir heartwood 32 times, while plasma treatment of the unextracted Douglas-fir increased permeability only 8 times. The permeability of extracted and oxygen plasma-treated wood did not vary much across the grain, but did decrease with distance from the ends of the samples due to incomplete removal of extractives from the center.     

Investigation of oxygen diffusion into contact lenses using electron spin resonance spectroscopy

Oxygen permeability is the most important parameter of contact lenses, as lack of oxygen causes corneal edema and threatens the vision of the patient. This study was unique in that it used an electron spin resonance (ESR) technique to determine the oxygen diffusion coefficient (D) of contact lenses. Although there are many methods and techniques for investigating oxygen diffusion into contact lenses, ESR was used for the first time in this study. The ESR technique is based on the scavenging of radicals produced in lenses by oxygen. As a contact lens is not a paramagnetic substance, it cannot give an ESR spectrum. But it does produce an ESR spectrum after γ irradiation. When a vacuum‐irradiated contact lens is exposed to air, the radicals trapped in the lens are transformed into peroxide radicals by the addition of molecular oxygen to the free radicals, and the ESR spectrum begins to change with time. This effect can be used as a tool to measure oxygen uptake in irradiated contact lenses. The oxygen diffusion coefficient of a contact lens was determined from changes in ESR signal intensity varying with time. The diffusion coefficients of oxygen for a contact lens were determined for rapid decay [(1.5 + 0.4) × 10^?8 cm²/s] and slow decay [(1.3 + 0.3) × 10^?9 cm²/s] in this study. These values are in agreement with the D values given in the literature for polymeric materials used for contact lenses. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2937–2941, 2006     

Effect of crystallization on barrier properties of formulated polylactide

Polylactide (PLA), a biodegradable polymer obtained from biomass, was formulated with a nucleating agent, talc, and a plasticizer, acetyl tributyl citrate, and cold crystallized in α and α′ form. The barrier properties of crystallized PLA were investigated as a function of the formulation and the crystalline form, thanks to three molecules with increasing polymer interactions, i.e. helium, oxygen and ethyl acetate (EA). Contrary to expectation, the oxygen diffusion coefficient in neat and formulated PLA did not decrease with crystallization. Even an increase of the diffusion coefficient was noticed for the most interacting probe, EA, in formulated PLA. Conditioning of neat and formulated PLA in an atmosphere containing EA vapour caused a modification of the material structure by plasticization and induced crystallization even at small EA activities. The plasticizing effect caused the glass transition temperature T_g to shift to below ambient temperature. In the case of neat PLA induced crystallization in solely the α form was obtained, and in the case of formulated PLA a blend of α and α′ forms was observed. Copyright © 2011 Society of Chemical Industry     

Oxygen enrichment from air through multilayer thin low‐density polyethylene films

Several multilayer thin low‐density polyethylene (LDPE) films were fabricated by blown thin film having a thickness of 7 μm and an area of 130 cm². They were characterized for their oxygen‐enrichment performance from air by a constant pressure–variable volume method in a round permeate cell with an effective area of 73.9 cm². The relationship between oxygen‐enrichment properties, including oxygen‐enriched air (OEA) flux, oxygen concentration, permeability coefficients of OEA, oxygen, nitrogen, as well as separation factor through the multilayer LDPE films, and operating parameters, including transfilm pressure difference, retentate/permeate flux ratio, temperature, as well as layer number, are all discussed in detail. It is found that all of the preceding oxygen‐enrichment parameters increase continuously with an increase of transfilm pressure difference from 0.1 to 0.65 MPa, especially for the trilayer and tetralayer LDPE films. The oxygen concentration and separation factor appear to rapidly increase within the retentate/permeate flux ratio below 200, and then become unchangeable beyond that, whereas the OEA flux and the permeability coefficients of OEA, oxygen, and nitrogen seem to remain nearly constant within the whole retentate/permeate flux ratio investigated, especially for the monolayer and bilayer LDPE films. The selectivity becomes inferior, whereas the permeability becomes superior, as the operating temperature increases from 23 to 31°C. The highest oxygen concentration was found to be 44.8% for monolayer LDPE film in a single step with air containing oxygen of 20.9% as a feed gas and operating pressure of 0.5 MPa at a retentate/permeate flux ratio of 340 and 23°C. The results demonstrate a possibility to prepare an oxygen‐enriching membrane directly from air, based on the easily obtained thin LDPE films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3013–3021, 2002; DOI 10.1002/app.2331     

Effective diffusivity and optimum apparent density of vanadia catalysts for sulfur dioxide oxidation

The effective diffusivities of air and SO₂ in four industrial vanadium pentoxide catalysts were measured at steady-state using helium as the counter diffusing gas. An improved catalyst mounting technique and diffusion cell were employed. The nonsurface component of diffusion was successfully correlated using Bruggeman's model for tortuosity. and ¯a based on pore size distribution data or calculated from specific pore volume and surface. However, it was necessary to use flow porosity in place of open porosity. Since the same pore model can be used for the catalytic oxidation So₂, non-reacting flow measurements can be employed to predict effective diffusivities under reaction conditions in this case.With models for the effective diffusivity and the kinetics of the catalytic oxidation of SO₂, an optimum apparent density of the catalyst may be determined which gives the maximum rate of reaction per unit volume of catalyst. Calculations are given for the SVD catalyst.     

The mechanism of air/oxygen/helium atmospheric plasma action on PVA

The effect of the air/oxygen/helium atmospheric plasma treatment on desizing polyvinyl alcohol (PVA) on cotton fabric was discussed as compared with the conventional H2O2 desizing. The possible change mechanism of PVA during atmospheric plasma exposure was induced through a combination of weight loss of PVA after plasma, PVA dissolving rate in water at room temperature, X‐ray photoelectron spectroscopy, and Fourier Transform infrared spectroscopy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006