Diffusion Constant Of Oxygen Research Articles

Diffusivity and Solubility of Oxygen in Solvents for Metal/Oxygen Batteries: A Combined Theoretical and Experimental Study

The solubility and the diffusion constant of oxygen in the electrolyte are crucial parameters in the kinetics of metal/oxygen batteries since they govern the discharge current that can be achieved. However, both parameters are often unknown or scatter widely in literature. Evaluating these parameters in typical solvents and electrolytes is therefore essential toward better quantitative understanding and improvement of metal/oxygen batteries. Using oxygen uptake experiments and molecular dynamics simulations, we compare theoretical and experimental approaches to determine oxygen diffusion coefficients in several molecular solvents that are commonly used. We report diffusion coefficients and Henry's law constants of oxygen for a series of glymes with different chain length and perfluorinated solvents, and discuss the benefit of using both experiment and simulation to determine these parameters. In all nine investigated solvents, the difference between simulated and measured diffusion coefficients is small in comparison to the magnitude of the coefficients. The methodology and the reported values for oxygen solubility and diffusivity form a solid starting point for further investigations into more complex electrolyte solutions. Ultimately, they might help to propel research on metal/oxygen batteries even further.

Radial oxygen precipitation of a 12” CZ silicon crystal studied in-situ with high energy X-ray diffraction

The radial oxygen nucleation and precipitation in Czochralski-grown silicon crystals is observed in real time via the local evolution of the X-ray Bragg intensity. Using a high X-ray energy and a divergent beam setup, it becomes possible to examine the impact of the local as-grown point defect configuration on the formation of bulk micro defects in a crystal of macroscopic dimensions. As a salient feature the transition from vacancy- to interstitial-dominated regions in a 12” crystal can be identified, and its influence on the precipitation kinetics is quantified through effective oxygen diffusion constant. It appears enhanced by up to a factor of six in vacancy-rich regions as compared to crystal volumes which are identified as point-defect free where it agrees well with the literature value.

Molecular Dynamics Simulation of Thermodynamic Properties in Uranium Dioxide

In the present study, we investigated the thermodynamic properties of uranium dioxide (UO2) by molecular dynamics (MD) simulations. As for solid UO2, the lattice parameter, density, and enthalpy obtained by MD simulations were in good agreement with existing experimental data and previous theoretical predictions. The calculated thermal conductivities matched the experiment results at the midtemperature range but were underestimated at very low and very high temperatures. The calculation results of mean square displacement represented the stability of uranium at all temperatures and the high mobility of oxygen toward 3000 K. By fitting the diffusivity constant of oxygen with the Vogel-Fulcher-Tamman law, we noticed a secondary phase transition near 2006.4 K, which can be identified as a “strong” to “fragile” supercooled liquid or glass phase transition in UO2. By fitting the oxygen diffusion constant with the Arrhenius equation, activation energies of 2.0 and 2.7 eV that we obtained were fairly close to the recommended values of 2.3 to 2.6 eV.

Modulation of enzyme catalytic properties and biosensor calibration parameters with chlorides: Studies with glucose oxidase

We studied the modulation of calibration parameters of biosensors, in which glucose oxidase was used for bio-recognition, in the presence of different chlorides by following the transient phase dynamics of oxygen concentration with an oxygen optrode. The mechanism of modulation was characterized with the changes of the glucose oxidase catalytic constant and oxygen diffusion constant. The modulation of two biosensor calibration parameters were studied: the maximum calculated signal change was amplified for about 20% in the presence of sodium and magnesium chlorides; the value of the kinetic parameter decreased along with the addition of salts and increased only at sodium chloride concentrations over 0.5mM. Besides glucose bioassay, the amplification of calibration parameters was also studied in cascaded two-enzyme lactose biosensor, where the initial step of lactose bio-recognition, the β-galactosidase – catalyzed lactose hydrolysis, was additionally accelerated by magnesium ions.

Lateral oxygen diffusion dominated extrinsic degradation of small molecular organic solar cells

Organic solar cells (OSCs) generally degrade seriously due to the rapid intake of oxygen and water if exposed to the air. In this paper, we investigated the extrinsic degradation of OSCs by showing the remarkable acceleration effect of fluorescent lamps. We attributed this effect to the accelerated lateral diffusion of oxygen in the fullerene layer under light. We simulated the dynamics of this process using a finite-element method. The simulation suggests that the diffusion constant of oxygen in cells increases approximately sevenfold under fluorescent lamps. We finally reported a recovering phenomenon of an unencapsulated OSC in dark, which demands more investigations.

Modeling of Oxygen Transport and Cell Killing in Type‐II Photodynamic Therapy

Photodynamic therapy (PDT) provides an effective option for treatment of tumors and other diseases in superficial tissues and attracts attention for in vitro study with cells. In this study, we present a significantly improved model of in vitro cell killing through Type-II PDT for simulation of the molecular interactions and cell killing in time domain in the presence of oxygen transport within a spherical cell. The self-consistency of the approach is examined by determination of conditions for obtaining positive definitive solutions of molecular concentrations. Decay constants of photosensitizers and unoxidized receptors are extracted as the key indices of molecular kinetics with different oxygen diffusion constants and permeability at the cell membrane. By coupling the molecular kinetics to cell killing, we develop a modeling method of PDT cytotoxicity caused by singlet oxygen and obtain the cell survival ratio as a function of light fluence or initial photosensitizer concentration with different photon density or irradiance of incident light and other parameters of oxygen transport. The results show that the present model of Type-II PDT yields a powerful tool to quantitate various events underlying PDT at the molecular and cellular levels and to interpret experimental results of in vitro cell studies.

Tuning of oxidation states in the LaNiO3−δ perovskite around the insulator-metal transition

The LaNiO3−δ perovskite has been studied during its reoxygenation process at the reversible insulator-metal transition by spectroscopic ellipsometry for different pressures and temperatures conditions. First, it was demonstrated that the reoxygenation dynamics increases with both increasing pressure and temperature. Considering the temperature dependent experiments, two regimes of kinetics have been identified: a slow reoxygenation dynamics at low temperature (below 523 K) and fast dynamics above 623 K. Second, contrary to our expectations, the reoxygenation process of a preliminary reduced sample is completed after a sufficient time delay even for the smallest investigated temperature of 473 K or oxygen pressure of 0.03 μbar, respectively. Modeling the change in extinction coefficient as a function of time during the reoxygenation, it was found that the oxygen diffusion coefficient varies from 4.2×10−14 to 1.1×10−13 cm2/s depending on the temperature (473 to 523 K). This oxygen diffusion constant is similar in magnitude order to those observed in the YBCO superconductor. At the light of these investigations, a pulsed oxygen injection was used, allowing a control of the injected oxygen quantity and by consequence, it was possible to precisely tune the oxidation state for a LaNiO3−δ film between the reversible reduced sample and the stoichiometric compound. In situ ellipsometry measurements are simultaneously performed to follow changes in optical constants.

A Simulation Study of Self-Extinguishing Cigarettes

Abstract In some parts of the USA and in Canada smouldering cigarettes are required to extinguish if placed on a certain number of layers of filter paper. This is usually achieved by the use of bands on the cigarette paper, which reduce oxygen diffusion into the cigarette. From a smoker's perspective, however, it is desirable that a cigarette does not extinguish if left to smoulder, for example, in an ash tray. To facilitate the design of papers for such cigarettes the influence of various cigarette parameters on self-extinguishment is investigated by numerical simulation of a one-dimensional cigarette model, which describes the main thermodynamic behaviour of smouldering cigarettes. The tobacco density, the tobacco heat capacity, the width of the bands on the cigarette paper and the heat released during combustion are chosen as parameters whose influence on the required oxygen diffusion constant of the bands on the cigarette paper is investigated. As these parameters are subject to a certain variation, it is assumed that the parameters are independently normally distributed. Based on this assumption the probability that a cigarette with given mean parameter values will extinguish, is calculated numerically. The results show that the admissible range of diffusion constants for the bands on the cigarette paper is in general quite small and it is reduced even further if statistical variations of the cigarette parameters are considered. The results provide guidelines for the appropriate choice of the diffusion constant of the bands on the cigarette paper such that the cigarettes comply with legal requirements and do not extinguish during normal smoking.

Partial Analytical Solution of a Model Used for Measuring Oxygen Diffusion Coefficients of Polymer Films by Luminescence Quenching

Many aspects of optical chemical sensor design would benefit from a better knowledge of the diffusion properties of the analyte in the polymer host. The response times of such sensors to a step change of analyte concentration are of vital interest for many applications of fast-responding sensors. Further, the diffusion properties govern their quenching behavior and their sensitivity. A method for determination of the diffusion constant of oxygen in polymers has been developed and used by several groups in the past. The underlying mathematical model for luminescence quenching by molecules of a gas in a single sensing layer on an impermeable support has not yet been completely derived in an analytical form and still uses tedious numerical methods. We present a partial analytical solution to the problem of modeling the time dependence of luminescence generated by in- or out-diffusion of a gaseous quencher in a polymer film in which a luminophor is immobilized and offer a suitable method to predict sensor response times.

Diffusion constant of oxygen in Si melt

Diffusion constant of oxygen in Si melt

Oxygen diffusion in silicon oxide films produced by different methods

Thin films of silicon oxide were prepared on copper substrates using several techniques, such as DC sputtering, sol-gel and microwave decomposition of gases (SiH 4 and O 2). The sol-gel films were made using a conventional mixture of tetraethoxysilane (TEOS), water and ethanol, with various TEOS/water ratios. The oxygen diffusion coefficient is found from the thickness of the copper oxide layer formed at the copper–SiO 2 interface, which was estimated from reflectivity and Auger spectroscopy measurements. Thermal treatments at various temperatures allowed us to determine the temperature dependence of the diffusion coefficient. It is found that the diffusion coefficient depends on the method of preparation of the SiO 2 layer, which could be related to differences in the structure of the oxide layer. This conclusion is confirmed by the dielectric breakdown measurements. It follows from the results obtained that the oxygen diffusion constants and the dielectric breakdown field could be the indicators of the structural quality of silica.

Oxygen diffusion in silica glass prepared by the sol–gel method

The oxygen diffusion constants for SiO 2 coatings, prepared by the sol–gel method, were determined from Auger depth profile and Raman measurements. To do that, the coatings were deposited on copper substrates, and isothermally treated at various temperatures in air. The oxygen diffusion through the glass coating formed an oxide layer at the copper/SiO 2 interface. The treatment times, at a given temperature were maintained until the minimum thickness of the copper oxide layer formed at the copper/SiO 2 interface was detectable by Raman spectroscopy. This oxide layer thickness was determined from Auger depth profile measurements. The room temperature values for the diffusion constant and the activation energy were, 2.2×10 −15 cm 2/s and 0.5 eV, respectively.

Molecular dynamics simulation of oxygen in silicon melt

Molecular dynamic simulation of an oxygen atom in silicon crystal and the melt was carried out to obtain the diffusion constants of oxygen in the melt. The simulation using mixed potential in the melt, in which an oxygen atom and 216 silicon atoms were taken into account has been carried out. Vibration frequencies of oxygen and vacancy–oxygen (V–O) pair in the crystal have been calculated. Calculated frequency of oxygen and V–O pair were 1000 and 820 cm −1, respectively, while the experimental results which were obtained from Fourier transform spectra of infrared absorption (FTIR) are 1100 and 830 cm −1, respectively. Oxygen diffusion constant was obtained in an elevated temperature of 1700 K. Calculated diffusion constant of oxygen in the melt was 1×10 −4 cm 2/s.

Segregation of Oxygen at a Solid/Liquid Interface in Silicon

The incorporation of oxygen into silicon single crystals from the melt is examined in terms of an experiment and a model on a transient solidification. A transient analysis offered an effective segregation coefficient of oxygen in silicon and a diffusion constant of oxygen in the melt almost independently. The analysis estimated these values of effective segregation coefficient of oxygen in silicon and diffusion constant of oxygen in the melt.

Imaging hypoxia and blood flow in normal tissues.

Oxygen deficiencies in normal tissue are assumed to be rare. This assumption is based upon detailed and time-tested mathematical and physiological models (for reviews see Oxygen Transport to Tissue Series). The input parameters to such models require detailed estimates of various circulatory and tissue properties: blood flow, distribution, oxygenation and pH; tissue cellularity, respiration rate and oxygen diffusion constant. Many of these parameters are only available in a global sense; thus there have been many experimental approaches to the assessment of tissue oxygenation. These include measurements by invasive devices such as microelectrodes. More recently, non-invasive techniques have been introduced, such as phosphorescence decay of blood-born dyes activated by short light pulses (Rumsey et al., 1988; Lo et al., 1996) and EPR of carbon particles (Vahidi et al., 1994). The former technique, introduced by Dr David Wilson, has the dual advantages of accurate temporal and spatial resolution (see reports this conference). One indirect method of tissue oxygen assessment utilizes the known oxygen-dependence of cellular radiation response - cells with oxygen tensions below about 20mm of Hg become progressively more radiation resistant. By measuring the radiation response of stem cells in the skin, investigators have concluded that some degree of hypoxia exists in this tissue (Douglas et al, 1975).

Gas permeation properties of organosilicon-containing polystyrenes

para-Substituted polystyrenes that possess one to four Si atoms in each substituent were prepared using our original synthetic methods. The gas permeation properties of these polymer membranes were investigated in detail. With an increasing Si content in the polymer membrane, it was determined that the solubility of oxygen increased. The para-substituted polystyrenes with a branched substituent at the α-position showed higher permeability than those of the non-branched ones. With a higher glass transition temperature ( T g) of the membrane, a higher diffusion constant of oxygen was obtained. Consequently, p poly[4-{bis(trimethylsilyl)methyl}styrene] which had the highest T g among the membranes investigated in this study, showed the highest oxygen permeation coefficient (37–45 Barrer). The activation energy of the oxygen permeation in this membrane was 3.0 kcal/mol.

Diffusion limited oxygen precipitation in silicon: Precipitate growth kinetics and phase formation

Published experimental data on silicon oxide precipitate growth kinetics are interpreted in the framework of the theory of Ham for diffusion limited precipitation. A growth law for plate-like, octahedral and spherical precipitates is derived showing a size dependence which varies as the square root of time. Using well accepted data for the solubility and the diffusion constant of oxygen in silicon, the calculations suggest that the precipitated phase is closer to SiO than to SiO2.

Effect of an Oxygen-Binding Reaction at the Cobalt Porphyrin Site Fixed in a Polymer Membrane on Facilitated Oxygen Transport

Abstract Oxygen transport was facilitated in polymer membranes bonded with new derivatives of [meso-α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrinato]cobalt (CoPs). The oxygen-binding reactivity of fixed CoPs strongly influenced the facilitated oxygen transport. CoP having a larger cavity structure showed a more rapid reactivity and achieved a higher oxygen permeability in the membrane. There existed correlations of the oxygen-binding and -dissociation rate constants with the diffusion constant of oxygen via CoPs fixed in the membrane.

Oxygenation and aging processes in melt textured YBa 2Cu 3O 7-δ

Melt textured bulk YBa 2Cu 3O 7−Y 2BaCuO 5 composites have been prepared by using a modified Bridgman method in order to improve its current carrying capacity. In this work we show that the final performances of these materials at high fields depend drastically on the oxygenation process. Due to the large anisotropy of the oxygen diffusion constants the final oxygen distribution depends on the precise microstructure and an accurate annealing process is required in order to avoid the appearance of oxygen-deficient zones due to insufficient oxygenation.

Cobalt porphyrin-Mediated Oxygen Transport in a Polymer Membrane: Effect of the Cobalt porphyrin Structure on the Oxygen-Binding Reaction, Oxygen-Diffusion Constants, and Oxygen-Transport Efficiency

New derivatives of (meso-[alpha],[alpha],[alpha],[alpha]-tetrakis(o-pivalamidophenyl)porphinato)cobalt (CoPs) were characterized by oxygen-binding equilibrium and rate constants of the cobalt centered in the porphyrins. They depended on the structure of the porphyrin; for example, the rate constants of oxygen binding and dissociation (k[sub on] and k[sub off]) for [alpha][sup 3][beta]-CoP[sub 4]P were 3 and 20 times as large as those for [alpha][sup 4]-CoB[sub 4]P, respectively. Oxygen transport through the polymer membranes containing CoPs as the fixed oxygen carriers was facilitated and was affected by the oxygen-binding character or the structure of CoPs. The logarithmically linear correlation of the oxygen-dissociation rate constant of CoPs (k[sub off] = (3-66) x 10[sup 3] S[sup [minus]1]) with the diffusion constant of oxygen via CoPs fixed in the membranes (D[sub cc] = (3-140) x 10[sup [minus]9] cm[sup 2] s[sup [minus]1]) was given for those six CoP derivatives. 26 refs., 5 figs., 2 tabs.