Diffusion Constant Of Oxygen Research Articles

High-temperature resistivity and oxygen diffusion in Bi 2Sr 2CaCu 2O x

We have investigated high temperature electrical resistivity and oxygen diffusion in single crystal Bi 2Sr 2CaCu 2O x . Above ∼400° C, oxygen is readily exchanged with the sample environment which strongly influences the functional form of the resistivity. By changing the partial pressure of oxygen in the sample environment and by continuously monitoring the sample resistance at fixed temperature, we determine oxygen diffusion constants at selected temperatures. In-diffusion is found to be significantly faster than out-diffusion. The in-diffusion data suggest an activated from with a diffusion constant given by D = D 0 exp (− E/ k B T) with D 0 = 11.7 cm 2/ s and E = 1.16 eV.

Oxygen dissolution and transport in cobaltporphyrin‐bound organophosphazene membranes

AbstractRubbery poly(organophosphazene)s were synthesized, and were combined with cobaltporphyrin (CoP) which binds molecular oxygen rapidly and reversibly. The apparent oxygen‐binding equilibrium constant (Kapp) is in proportion to the physical solubility coefficient of oxygen in the polymer, although the reduced equilibrium and thermodynamic parameters are not dependent on the polymer matrix species. Diffusivity of oxygen via the fixed CoP(DC) is enhanced for poly(organophosphazene) membranes with a larger oxygen diffusion constant. Poly(organophosphazene) membranes with both a large Kapp and DC yield high oxygen permeability.

The influence of polymorphic form on oxygen and water vapor transmission through lipid films

AbstractFully‐hydrogenated soybean and rapeseed oil was blended 2:1, layered on a filter paper support, adjusted to the desired polymorphic form and tested for resistance to transmission to oxygen and water vapor. Resistance to oxygen transport decreased upon conversion from α to the β′ form and then increased substantially upon conversion to the β polymorph. This was attributed to the greater solid‐state density of the β form, which likely affects resistance to gas flux by lowering the oxygen diffusion constant through the film. Resistance to water vapor transmission also decreased following the α to β′ transition and then increased somewhat upon conversion to the β form. However, resistance of the β form did not exceed that of the α form at any of the temperatures tested. Moisture sorption characteristics of the various polymorphic forms apparently caused relative resistance values for water vapor flux to differ, somewhat from those for oxygen flux.

On the kinetics of superconducting phase formation in Y 1Ba 2Cu 3O y

The high-temperature superconductor Y 1Ba 2Cu 3O y was investigated by in situ X-ray diffraction experiments at high temperatures and by differential scanning calorimetry under various partial pressures of oxygen, by thermogravimetrical analysis, and by resistivity measurements. As-prepared and oxygen-deficient samples were annealed under various oxygen atmospheres at constant oxygen partial pressures and/or constant temperatures below 800 °C. The smallest oxygen partial pressure necessary for orthorhombic phase formation was measured at various temperatures and the kinetics of the tetragonal-to-orthorhombic transition was studied. A diffusion constant of oxygen in the “123” compound at 400 °C of about 1 × 10 − 11 cm 2s − 1 and an activation energy of diffusion of about 1.6 eV was determined.

Oxygen diffusion to the bulk and crystallite boundaries in PbTe films

Thermal oxygen diffusion to the bulk and at crystallite boundaries (CB) in PbTe films have been experimentally investigated. Ions O + implanted in subsurface layer of films served as source of diffusion to the bulk; this diffusion process was provided by annealing in vacuum. Diffusion along CB was stimulated by air annealing of the films. It was proved that changes of properties during diffusion in n-type PbTe films mainly occured owing to localization of oxygen at CB. For investigated films oxygen diffusion constant and activation energy of the process have been obtained.

Diffusion of oxygen in water and hydrocarbons using an electron spin resonance spin-label technique

The Smoluchowski equation for the bimolecular collision rate of dissolved oxygen molecules with spin labels yielded values for the diffusion constant of oxygen in water that are in agreement with the Stokes-Einstein equation (D infinity T/eta, where eta is the macroscopic viscosity) and with published values obtained by conventional methods. Heisenberg exchange at an interaction distance of 4.5 A occurs with a probability close to one for each encounter. In mixed hydrocarbons (olive oil, paraffin oils) and sec-butyl benzene, D infinity (T/eta)rho, where rho lies between 0.5 and 1. Oxygen diffuses in the hydrocarbons between 10 and 100 times more rapidly than predicted from the macroscopic viscosity. Similar results would be expected for diffusion of oxygen in model and biological membranes. Parallel measurements of rotational diffusion of the spin labels show little correlation with measurements of translational diffusion of oxygen. Dipolar interactions between spin labels and oxygen appear negligible except in the limit of highest viscosities.

A novel technique for measuring TH diffusion constant of oxygen in polymer films

A simple technique has been developed facilitating measurement of the diffusion constant for O 2 in polymeric glasses. The method used is such that measurements can be made over a wide range of temperatures. Measured values for the diffusion constant for O 2 in poly(styrene) and poly(methyl methacrylate) are reported.

アルミニウムはんだ付部の耐食性について(第1報)

The external cathodic polarization curves of each cast alloy such as Al-Sn, Al-Zn and Zn-Sn systems, which were dipped in 3% NaCl aqueous solution, were investigated by a potentiostatic method to determine the corrosion behavior of soft-soldered joint in aluminum. The profiles of the polarization curves were conventionally divided into two categories: straight line and curved line type. The former was seen in Al-Sn system only and this phenomenon was presumed as the cathode reaction of Eyring's protrotopic process, because the value of transfer coefficient calculated by using the measured value in this type was about 0.33 and was nearly equal to that of tin having a cathode control of activation process. The latter was seen in all of metals used as alloying elements and the remainder among the alloys tested here and this phenomenon was considered as the concentration polarization, where a cathode reaction is controlled by a diffusion process of dissolved oxygen. To do this consideration, iL, a limiting current density, was approximately calculated by the following equation introduced by using Fick's-Law.iL=2⋅F⋅D01/2[O2]⋅t-1/2/√πWhere F is Faraday constant, D0 is the diffusion constant of oxygen, [O2] is the concentration of disolved oxygen, t is the dipping time of sample. While the measured value for iL was decided by appling an overvoltage intercept method to the external cathodic polarization curve.From the electrochemical measurements mentioned above, it has been concluded that the natural electrode potentials of soldered joints in aluminum were not necessarily the important factor governing the corrosion rate between the aluminum, the various phases in the solder and the layer that forms at the aluminum and solder interface.

POLYSTYRENE MEMBRANES FOR COVERING OXYGEN ELECTRODES FOR USE IN TISSUE.

BARE electrodes for measuring tissue oxygen tension polarographically have several disadvantages. The electrode current depends not only on the oxygen tension at the cathode surface but also on the diffusion constant of oxygen and the blood flow pattern in the tissue in that region. In addition, the electrode current slowly falls when the bare cathode is exposed to tissue or blood. Clark1 overcame this latter difficulty by using electrodes covered with a membrane for measurements in blood. The remaining difficulties in tissue can be overcome by using a membrane-covered electrode together with a pulsed voltage2. In this way the region around the cathode surface which is depleted of oxygen, due to the oxygen reduction process, is limited to the membrane and the thin saline layer behind it and does not extend into the tissue, where there is an unknown diffusion constant and blood flow pattern. The membrane-covered electrode, in contrast with the bare electrode, may be calibrated in vitro before use and the calibration will be valid for conditions in vivo. A number of membrane materials have been tried, for example collodion, rubber, polyethylene, polytetrafluoroethylene and ‘Cellophane’. In the past we have found the most suitable membranes to be latex rubber sheaths. A disadvantage is that the electrodes must be mounted in the sheaths shortly before use, which can be a very lengthy operation. Furthermore, the rubber can move relative to the cathode and cause a change in calibration. Bartels et al.3,4 reported that electrodes for use in blood samples can be covered with polystyrene and used with a continuously applied voltage. We have found that if our electrodes are coated with polystyrene and are used with a pulsed voltage, the more exacting requirements for measurements in tissue are met, and the disadvantages associated with rubber membranes are avoided. Such polystyrene-covered electrodes are independent of stirring effects outside the membrane, have a time response of a few seconds, are not poisoned by tissue and are easy to prepare. Further advantages are that there is no need for a membrane holder in the electrode assembly and the electrode tip can be made small and streamlined. Electrodes with an overall diameter of only 0.3 mm have been made and used satisfactorily in tissue.

The High-Temperature Oxidation Kinetics of Zirconium

An investigation of the parabolic-linear oxidation of zirconium at 800° and 850°C is reported. It was found that irrespective of the oxygen concentration in the metal substrate, parabolic kinetics represent the growth of the initial compact oxide scale while linear kinetics represent the later stage s of growth. Metallographic observations indicated a transition from a compact to compact plus porous oxide scale. Accompanying hardness measurements demonstrated that oxygen penetrated into the metal via a steady concentration profile during linear oxidation. An exponential solution of the diffusion equation fitted to the concentration profile gave evaluations of the oxygen diffusion constant in the metal which are in good agreement with such evaluations from diffusion experiments. Several features of the oxidation kinetics of zirconium and titanium were correlated as further elucidation of the properties of metals in Periodic Subgroup IVB.

The High-Temperature Oxidation Kinetics of Zirconium

AbstractAn investigation of the parabolic-linear oxidation of zirconium at 800° and 850°C is reported. It was found that irrespective of the oxygen concentration in the metal substrate, parabolic kinetics represent the growth of the initial compact oxide scale while linear kinetics represent the later stage s of growth. Metallographic observations indicated a transition from a compact to compact plus porous oxide scale. Accompanying hardness measurements demonstrated that oxygen penetrated into the metal via a steady concentration profile during linear oxidation. An exponential solution of the diffusion equation fitted to the concentration profile gave evaluations of the oxygen diffusion constant in the metal which are in good agreement with such evaluations from diffusion experiments. Several features of the oxidation kinetics of zirconium and titanium were correlated as further elucidation of the properties of metals in Periodic Subgroup IVB.