Changes In Oxygen Partial Pressure Research Articles

The clinical effect of pulmonary infection control window for sequence ventilation on treatment of severe pneumonia with respiratory failure

Objective To explore the clinical effect of pulmonary infection control window for sequence ven-tilation on treatment of severe pneumonia with respiratory failure, and to observe and analyze the prognosis. Methods 102 severe pneumonia patients complicated with respiratory failure were selected. They were divided into the observation group and the control group by the random number table method. The patients of the observation group were treated with pulmonary infection control window for sequence ventilation treatment, the control group were treated with conven-tional sequence ventilation treatment. The change of blood oxygen partial pressure(PaO2), carbon dioxide partial pres-sure(PaCO2) and blood oxygen saturation(SaO2)before and after ventilation, and the treatment time and symptoms improve time and the complications such as ventilator associated pneumonia(VAP)of the two groups were observed. Results PaO2 and SaO2 of the observation group after the ventilation were(75.60±2.89)mmHg and(0.78±0.09), which were higher than control group after the ventilation(70.48±3.16)mmHg and(0.71±0.11),and data of two groups after ventilation were higher than those before the treatment, differences were statistically significant(t＝11.30,10.92,13.26,14.08,all P＜0.05).PaCO2 of the observation group after the ventilation was 49.21±3.22 mmHg, which was lower than that of control group after the ventilation of 54.35±3.82 mmHg, and data of two groups after treatment was lower than before treatment, the differences were statistically significant(t＝12.44,11.85,14.16,13.42,all P＜0.05). The total mechanical ventilation time of the observation group, respiratory difficulty relief time, lung then disappear time and hospital stay time were(5.24±1.83)d,(38.13±2.91)h,(6.72±0.40)d and (15.33±3.18)d, which were lower than those of control group, the differences were statistically significant(t＝9.87,10.21,10.46,11.08,all P＜0.05). The general adverse reaction and the death rate of the observation group was 9.80%(5／51), which was lower than 19.61% of the control group(χ2＝9.85,P＜0.05). Conclusion There was effect of pulmonary infection control window for sequence ventilation treatment of severe pneumonia with respirato-ry failure, and it could improve effectively lung function and the prognosis and reduce the incidence of complications. Key words: Pneumonia; Respiratory Insufficiency; Time Factors; Ventilators, Mechanical

Experimental investigation of the effect of polymer matrices on polymer fibre optic oxygen sensors and their time response characteristics using a vacuum testing chamber and a liquid flow apparatus

Very fast sensors that are able to track rapid changes in oxygen partial pressure (PO2) in the gas and liquid phases are increasingly required in scientific research – particularly in the life sciences. Recent interest in monitoring very fast changes in the PO2 of arterial blood in some respiratory failure conditions is one such example. Previous attempts to design fast intravascular electrochemical oxygen sensors for use in physiology and medicine have failed to meet the criteria that are now required in modern investigations. However, miniature photonic devices are capable of meeting this need. In this article, we present an inexpensive polymer type fibre-optic, oxygen sensor that is two orders of magnitude faster than conventional electrochemical oxygen sensors. It is constructed with biologically inert polymer materials and is both sufficiently small and robust for direct insertion in to a human artery. The sensors were tested and evaluated in both a gas testing chamber and in a flowing liquid test system. The results showed a very fast T90 response time, typically circa 20ms when tested in the gas phase, and circa 100ms in flowing liquid.

Hybrid co-deposition of mixed-valent molybdenum–germanium oxides (MoxGeyOz): A route to tunable optical transmission

Mixed-valent oxides of molybdenum and germanium were deposited simultaneously using reactive magnetron co-deposition within an oxygen–argon environment. The films' stoichiometry, optical, and physical properties were varied through changes in oxygen partial pressure induced by systematic variation of the potential applied to the molybdenum cathode. The oxygen partial pressure was determined from the drop in pressure as measured by a capacitance manometer, assuming constant argon partial pressure. To facilitate deposition, a constant power of 100W DC was applied to the germanium cathode, while power was applied to the molybdenum target using a modulated pulse power supply. Modulated pulse power magnetron sputtering was used due to its ability to generate high target power densities, allowing for rapid reduction of oxygen on the surface of the “oxygen poisoned” molybdenum cathode, as well as for its highly metallic plasma resulting in increased oxygen-gettering capability. Changes in the modulated pulse power supply's capacitor bank voltage load, stepped from settings of 300 to 380V, resulted in films ranging from mixtures of transparent GeO2 (Ge4+) and MoO3 (Mo6+) to the introduction of various absorptive ionic species including Mo5+, Mo4+, Ge2+ and Ge0, as determined from X-ray photoelectron spectroscopy. The presence of each of the aforementioned ions results in characteristic changes in the films' band energies and optical absorption. As deposited MoxGeyOz thin films grown using this method have been shown to have optical gap energies that are able to be tailored between 3.57eV and 0.18eV, spanning useful ranges for devices operating in the visible and near-infrared.

Changes in Oxygen Partial Pressure in the Vitreous Body and Arterial Blood of Rabbits Depending on Oxygen Concentration in Inspired Mixture.

We demonstrated that the vitreous body of one-month-old rabbits becomes a "reservoir" for storage and accumulation of oxygen after exposure to additional oxygenation of the organism (O2 concentrations in inspired gas mixture were 40, 60, 85, and 99%). The higher was O2 concentration in inspired mixture, the higher was oxygen saturation of the blood and vitreous body. O2 concentration of 40% was relatively safe for eye tissues. O2 concentration >60% induced oxygen accumulation in the vitreous body, which can be a provoking factor for the development of oxygen-induced pathologies.

Intraoperative volume restriction in esophageal cancer surgery: an exploratory randomized clinical trial.

AimTo investigate whether the fluid volume administered during esophageal cancer surgery affects pulmonary gas exchange and tissue perfusion.MethodsAn exploratory single-center randomized clinical trial was performed. Patients with esophageal cancer who underwent Lewis-Tanner procedure between June 2011 and August 2012 at the Department of Thoracic surgery “Jordanovac”, Zagreb were analyzed. Patients were randomized (1:1) to receive a restrictive volume of intraoperative fluid (≤8 mL/kg/h) or a liberal volume (>8 mL/kg/h). Changes in oxygen partial pressure (Pao2), inspired oxygen fraction (FiO2), creatinine, and lactate were measured during and after surgery.ResultsOverall 16 patients were randomized and they all were analyzed (restrictive group n = 8, liberal group n = 8). The baseline value Pao2/FiO2 ratio (restrictive) was 345.01 ± 35.31 and the value six hours after extubation was 315.51 ± 32.91; the baseline Pao2/FiO2 ratio (liberal) was 330.11 ± 34.71 and the value six hours after extubation was 307.11 ± 30.31. The baseline creatinine value (restrictive) was 91.91 ± 12.67 and the value six hours after extubation was 100.88 ± 18.33; the baseline creatinine value (liberal) was 90.88 ± 14.99 and the value six hours after extubation was 93.51 ± 16.37. The baseline lactate value (restrictive) was 3.93 ± 1.33 and the value six hours after extubation was 2.69 ± 0.91. The baseline lactate value (liberal) was 3.26 ± 1.25 and the value six hours after extubation was 2.40 ± 1.08. The two groups showed no significant differences in Pao2/FiO2 ratio (P = 0.410), creatinine (P = 0.410), or lactate (P = 0.574).ConclusionsRestriction of intraoperative applied volume does not significantly affect pulmonary exchange function or tissue perfusion in patients undergoing surgical treatment for esophageal cancer.Trial registration number: Clinical Trials NCT 02033213.

Exploring the Kinetics and Thermodynamics of Voltage Fade

Layered-layered, lithium-, manganese-rich, nickel-manganese-cobalt (LMR-NMC) oxides are commonly used as cathode materials for lithium-ion batteries. They can be thought of as composite materials consisting of (monoclinic) Li2MnO3 and (layered) Li(Ni1-a-bMnaCob)O2 (a>0; b<1) and written as xLi2MnO3▪(1-x) Li(Ni1-a-bMnaCob)O2. With a desirable combination of low-cost and high energy density, they have attracted much attention for transportation applications. During cycling, these materials display voltage fade; i.e., the voltage vs. normalized capacity curve tends to droop. Voltage fade reduces the energy density of the material during its lifetime and, consequently, a significant research effort is being devoted to prevent it altogether. In an alternative approach, it may be possible to retard the voltage fade process to the point where it has only a minor impact on battery performance. However, this approach requires detailed understanding of the kinetics and thermodynamic driving force of voltage fade, of which there is scant information in the literature. In order to bridge this gap, we explore the effects of cycling temperature and oxygen availability during synthesis on voltage fade. We cycled half-cells containing 0.5Li2MnO3•0.5LiNi0.375Mn0.375Co0.25O2 (or Li1.50Ni0.1875Co0.125Mn0.6875O2.50) cathodes at 25, 35, 45 and 55°C at a 20 mA/g rate. Analysis of the change in open-circuit voltage values from t=0 for each temperature showed that these data can be fit to a kinetic rate law containing t 1/2 and t terms. Indeed, the dependence of the coefficients of these terms with temperature suggests two competing chemical processes. We explored the response of LMR-NMC oxides using Li1.50Ni0.15Co0.167Mn0.683O2.50 (HL) and Li1.30Ni0.15Co0.167Mn0.683O2.30 (LL) to changes in oxygen partial pressure during synthesis. The oxygen partial pressures were 1.0, 2.0 × 10-1, 2.0 × 10-2, and 2.0 × 10-3 atm. There were several partial-pressure-dependent trends in the data. For example, examining the dependence of the deviation from nominal lithium stoichiometry on pO2 shows that it decreases with increasing pO2 for both the HL and LL material. These and other trends will be discussed. This work was performed under the auspices of the DOE Office of Vehicle Technologies, Hybrid and Electric Systems, under Contract No. DE-AC02-06CH11357. The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory ("Argonne"). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.

Confirmation of the Dominant Defect Mechanism in Amorphous In–Zn–O Through the Application of In Situ Brouwer Analysis

The dominant point defect mechanism of amorphous (a‐) indium zinc oxide (IZO) was probed through in situ electrical characterization of sputtered a‐IZO thin films in response to changes in oxygen partial pressure (pO) at 300C. The results yielded a power law dependence of conductivity (σ) versus pO of ∼−1/6. This experimental method, known as Brouwer analysis, confirms doubly‐charged oxygen vacancies as the dominant defect species in a‐IZO. The success of this study suggests that Brouwer analysis is a viable method for studying the defect mechanisms of amorphous oxides.

Application of improved double-oxygen-pipe structure for patients after operation of esophageal carcinoma

Objective To analyze the effect of improved double-oxygen-pipe structure for postoperative esophageal cancer patients. Methods We chose 60 cases of esophageal cancer patients and randomly divided them into observation group and control group, 30 cases in each group. The observation group were treated by improved double-oxygen-pipe absorption, and the control group underwent traditional single-oxygen-pipe. The change of arterial blood oxygen partial pressure (PaO2), carbon dioxide partial pressure (PaCO2) and SpO2 were observed in the two groups of patients after the operation and compared the comfort level of the oxygen absorption. Results Two groups of patients with PaO2 and SpO2 improved to (95.04±4.63)% and (96.93±4.60)mmHg after 1 day operation, compared with (91.26±7.27)%, (90.37±2.88)mmHg in the control group with statistical differences between two groups (t=2.213, 4.371; P<0.05). There were 25 cases (83.33%) of patients in the observation group with comfort, that was significantly higher than 12 cases (40%) of patients in the control group, and the differences were statistically significant (χ2=8.992, 11.365; P<0.05). The observation group had only 1 case (3.33%) self extubation which was less than that of the control group (17 cases) occupied 56.57% (Z/χ2=8.992, 11.365; P<0.05). Conclusions Improved double-oxygen-pipe structure can improve the recovery of PaO2 and SpO2 in postoperative patients and improve the comfort and compliance of oxygen absorption. This method is worthy to popularized in clinical. Key words: Esophageal carcinoma; Oxygen absorption; Comfort

Interpreting equilibrium-conductivity and conductivity-relaxation measurements to establish thermodynamic and transport properties for multiple charged defect conducting ceramics.

A model-based interpretation of measured equilibrium conductivity and conductivity relaxation is developed to establish thermodynamic, transport, and kinetics parameters for multiple charged defect conducting (MCDC) ceramic materials. The present study focuses on 10% yttrium-doped barium zirconate (BZY10). In principle, using the Nernst-Einstein relationship, equilibrium conductivity measurements are sufficient to establish thermodynamic and transport properties. However, in practice it is difficult to establish unique sets of properties using equilibrium conductivity alone. Combining equilibrium and conductivity-relaxation measurements serves to significantly improve the quantitative fidelity of the derived material properties. The models are developed using a Nernst-Planck-Poisson (NPP) formulation, which enables the quantitative representation of conductivity relaxations caused by very large changes in oxygen partial pressure.

Spin-Labeled Uni-Lamellar Vesicles as an Oxygen Sensitive Analyte for Measurement of Cellular Respiration using Rat Dopaminergic Neuronal Cells

Small uni-lamellar vesicles were prepared from 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) with 1% spin label of 1-palmitoyl-2-(16-doxylstearoyl)phosphatidylcholine (16-PC). POPC membranes are in the fluid phase in the physiological temperature range, which ensures high solubility of oxygen in the membrane center where the 16-PC nitroxide moiety is located. The nitroxide moiety is isolated from cellular reductants and paramagnetic ions that might interfere with spin-label oximetry measurements. This analyte is stable in cell suspensions and can be used in studies as long as 400 min. The saturation recovery EPR approach, possibly for the first time, was used to study cellular respiration of rat dopaminergic neuronal cells. It is widely accepted that this approach is the most direct way to carry out oximetric studies. The preliminary experiments were carried out at X-band for closed chamber geometry. Oximetric measurements were performed for cell concentrations from 750 to 5000 cells in one µL of culture media. Results confirmed that the oxygen consumption rate was linearly proportional to the number of cells. Furthermore at the lower cell concentration, we found a breaking point in the rate which is not due to diffusion limitation but is due to the change in cell metabolism because there is not enough oxygen, consistent with Michaelis-Menten kinetics. In the developed analyte, the same hydrocarbon environment, which dissolves oxygen very well, always surrounds nitroxide moieties of spin-label molecules. Therefore, the partial pressure of oxygen influence the EPR spectrum of spin-labels in the analyte. Such microscopic analytes are readily and uniformly distributed within the sample, thus giving a rapid response to changes in oxygen partial pressure. The improved oximetry methodology developed here presents a high impact opportunity for non-invasive assessment of disease mechanisms and response to therapeutic intervention.

Prediction of the molecular response to pertubations from single cell measurements

The response of protein signalization networks to perturbations is analysed from single cell measurements. This experimental approach allows characterizing the fluctuations in protein expression levels from cell to cell. The analysis is based on an information theoretic approach grounded in thermodynamics leading to a quantitative version of Le Chatelier principle which allows to predict the molecular response. Two systems are investigated: human macrophages subjected to lipopolysaccharide challenge, analogous to the immune response against Gram-negative bacteria and the response of the proteins involved in the mTOR signalizing network of GBM cancer cells to changes in partial oxygen pressure.

Does Urinary Trypsin Inhibitor Have a Role in Acute Lung Injury Induced by Pulmonary Contusion

We evaluate the efficacy of urinary trypsin inhibitor (UTI) on inflammation, oxidative stress, hypoxemia, and diseased lesion in a rat model of acute lung injury induced by blunt trauma. Rats were allocated to 4 groups. One group served as normal control. The other 3 groups had a moderate pulmonary contusion. Except for 1 sham group administrated saline, 1 group was administrated low-dose UTI (20,000 U/kg), and another group was administrated high-dose UTI (50,000 U/kg). Twelve hours after contusion, neutrophil counting in bronchoalveolar lavage fluid (BALF) was performed and tumor necrosis factor α level and albumin level in BALF was tested. Lung tissue malondialdehyde levels, superoxide dismutase, and catalase activity was investigated, and blood gas analysis and contusion volume quantification using 3-dimensional computed tomography were performed. High-dose UTI significantly decreased neutrophil count and tumor necrosis factor α level in BALF (P<0.05) and decreased albumin level in BALF but without significance. Lung tissue malondialdehyde levels was significantly reduced, whereas superoxide dismutase and catalase activity were elevated by UTI with significance (P<0.05) especially high-dose UTI. No statistical significance was seen in the change in arterial oxygen partial pressure (PaO2) and contusion volume by UTI (P>0.05). UTI has a dose-dependent trend to ameliorate inflammatory and oxygen stress in pulmonary contusion-induced acute lung injury. However, the effect on hypoxemia and contusion lesion and the best administration regime should be investigated in future study.

Oxygen sensor nanoparticles for monitoring bacterial growth and characterization of dose–response functions in microfluidic screenings

We are presenting a microfluidic droplet-based system for non-invasive, simultaneous optical monitoring of oxygen during bacterial cultivation in nL-sized droplets using ~350 nm nanobeads made from polystyrene and doped with the NIR-emitting oxygen probe platinum (II) 5, 10, 15, 20-meso-tetraphenyltetrabenzoporphyrin (PtTPTBP). Data were readout by a two-channel micro flow-through fluorimeter and a two-channel micro flow-through photometer. The time-resolved miniaturized optical multi endpoint detection was applied to simultaneously sense dissolved oxygen, cellular autofluorescence, and cell density in nL-sized segments. Two bacterial strains were studied that are resistant to heavy metal ions, viz. Streptomyces acidiscabies E13 and Psychrobacillus psychrodurans UrPLO1. The study has two main features in that it demonstrates (a) the possibility to monitor the changes in oxygen partial pressure during metabolic activity of different bacterial cultures inside droplets, and (b) the efficiency of droplet-based microfluidic techniques along with multi-parameter optical sensing for highly resolved microtoxicological screenings in aquatic systems.

Preparation of a porous ceria coating for a resistive oxygen sensor

Oxygen sensors play important roles in areas such as determining the oxygen content in exhaust gas and optimizing combustion. Resistive oxygen sensors made of an n-type semiconductor, doped ceria (CeO2), have recently received much attention due to their relatively compact and simple structures. In the present study, alumina substrate was first coated with electrodes by screen printing. Porous ceria films were then coated on the electrodes using different mixtures of two undoped ceria powders synthesized by spray-pyrolysis and precipitation, respectively. The ratios of the two powders were varied to produce differences in the heat-treated porosity of the ceria films. The resistive oxygen sensors exhibited a 3-D interconnected pore structure that could be optimized by varying the powder ratio for sensing properties. The dynamic response to the change in oxygen partial pressure of the optimized porous structure at 1073 and 1123K was >1.8 times faster than those of non-optimized structures. Details on the processing, optimization of compositions, and responses to variation in oxygen partial pressure are provided. The mechanisms for the formations of the powders and the porous coatings are also described.

Measurement of hydrogen and oxygen chemical potential in yttria doped barium cerate (BCY) electrolyte of anode-supported protonic ceramic fuel cells

Yttria doped barium cerate (BCY) electrolyte, Ni + BCY anode supported protonic ceramic fuel cells were fabricated with Pt reference electrodes embedded in a thin (∼40 microns) electrolyte layer. The embedded electrodes function as selective probes exchanging only electrons with the BCY so that the voltage measurements (ΔV) using the embedded probes through the electrolyte correspond to a change in the reduced negative electrochemical potential of electrons (Δφ). Using this method, the corresponding change in hydrogen and oxygen chemical potential (ΔμH2, ΔμO2) or partial pressure of hydrogen and oxygen (ΔpH2, ΔpO2) were determined on the basis of the local equilibrium assumption, allowing us to investigate ionic and electronic transport properties through the BCY electrolyte. The results indicate that the pH2 and pO2 change mainly occurs across the middle electrolyte region while the electrolyte regions close to the anode and the cathode showed very small variation. The present work revealed that the BCY electrolyte consists of three major parts with different transport properties; 1) mixed ionic-electronic conduction in the electrolyte close to the anode side (reducing atmosphere), 2) predominantly ionic conduction in the middle region, 3) mixed ionic-hole conduction in the electrolyte close to the cathode side (oxidizing atmosphere).

(Invited) Impact of Size Scale on Electro-Chemo-Mechanical Coupling Properties in MIECs: Bulk and Thin Film (Pr,Ce)O2-δ

Many oxides exhibit advantageous properties in energy conversion and storage applications, such as solid oxide fuel cells (SOFCs), heterogeneous catalysis, photoelectrochemical cells, and batteries, due in part to their high temperature stability, corrosion resistance, and dopant cation solubility, respectively. In particular, mixed ionic and electronic conducting oxides have been demonstrated to aid in increasing reaction kinetics at electrodes in SOFCs due to the simultaneous presence of electrons and oxygen vacancies. With changes in oxygen partial pressure and temperature during normal operation operation, the defect concentration and hence transport characteristics of MIEC oxides inevitably change. In addition, defects are often coupled to a significant lattice dilation, known as chemical expansion, which under some circumstances leads to mechanical failure. Furthermore, as length scales are reduced, the energetics for electron and vacancy formation have been shown to be modified. In this presentation, recent work examining the the interplay of electro-chemo-mechanical properties of bulk ceramic to thin film size scales will be discussed. This work was facilitated by using the model material system, (Pr,Ce)O2-δ (PCO), which, due to the ease of reduction of Pr from 4+ to 3+ valence, exhibits significant MIEC behavior at relatively high oxygen pressures (e.g. air). Impedance spectroscopy was used to study both the oxygen exchange resistance and oxygen content (via chemical capacitance) of cells consisting of PCO thin films deposited on yttria stabilized zirconia substrates. When compared to defect formation energies derived from a detailed thermogravimetric and conductivity model for bulk PCO, films were found to exhibit enhanced reducibility. This phenomenon was further verified using an in situ optical transmission measurement of films, coupled with chemical capacitance, which correlated the amount of absorbing Pr4+ centers to oxygen vacancy concentration. Additionally, oxygen exchange probed by optical transmission relaxation measurements on “bare” films exhibited slower kinetics as compared to corresponding electrochemical measurements. The role of metal electrodes as well as impurities in modifying oxygen exchange rate will be discussed, as well as new means to improve oxygen exchange of the aged “bare” film surface. Lastly, thermo-chemical expansion measurements of bulk and thin film PCO samples will be presented with discussion related to the atomistic role of individual point defects and defect association.

Porous Thick Film Low Temperature Lanthanum Strontium Ferrite Oxygen Surface Exchange Coefficient Measurements By Curvature Relaxation

Introduction Mixed ionic electronic conducting (MIEC) materials, such as Lanthanum Strontium Ferrite (LSF), are widely used in solid oxide fuel cell cathodes, catalytic converters, and other applications. Changes in temperature or oxygen partial pressure (pO2) give rise to simultaneous changes in oxygen nonstoichiometry, cation oxidation state, and lattice strain in these materials.(1) This interplay between the mechanical and chemical behaviors of these materials allows the oxygen chemical surface exchange coefficient (k) of a mechano-chemically active film bonded to an inert substrate to be measured via the curvature relaxation (κR) technique.(2) Upon instantaneous small step changes in pO2, the k of a porous film can be determined using Equation [1], where κ, κ0 , and κ∞ are the instantaneous, initial, and new-pO2-equilibrated curvature, respectively, ki is the surface exchange coefficient for a portion of the film with faction of surface area, Ai , t is time, VV is the volume fraction porosity, and SV is the volume specific surface area.(3-6) This κR technique provides an in-situ, electrode-free method to measure porous film k’s, and also allows the film stress to be evaluated from the bilayer curvature via Stoney’s Equation. Experimental Methods 5-µm-thick porous La0.6Sr0.4FeO3-δ (LSF64) films were spray deposited onto single crystal (Y2O3)0.13(ZrO2)0.87 (YSZ) substrates. The curvature relaxation of the bilayers was measured at different pO2’s and temperatures using an in-situ Multi-beam Optical Stress Sensor (MOSS) apparatus, as described in Yang et al.(2) Results and Discussion Figure 1 shows the κR of LSF64|YSZ bilayers subjected to multiple pO2 cycles at two different temperatures. Reproducible relaxation kinetics was observed, and equilibrium curvature levels were consistent with the thermal expansion mismatch at these temperatures.As shown in Figure 2, a normalized curvature relaxation can be fitted to a single surface exchange coefficient. As shown in Figure 3, the k’s of LSF64 were measured down to 250oC for the first time in this study and agreed well with the low temperature extrapolation of the bulk sample k’s measured by ten Elshof et al.(7) A similar activation energy (EA=1.3 eV) is also observed. The stress in the film is smaller than that of previously measured sputtered thin films. The k and EA’s are different than those measured for pulsed laser deposited thin films, possibly caused by difference stress levels in the film, the presence/absence of electrodes, or other effects. The errors of both kand stress measurements are smaller than the symbols. Conclusions Surface exchange coefficients and stresses of porous thick film LSF64 were measured for the first time using a curvature relaxation technique. The film had relatively low stress and similar k and EA’s compared to low temperature extrapolations of bulk LSF64 measurements in the literature. Acknowledgements This work was funded by a Michigan State University faculty startup grant.

Diffusion of Oxygen in Ceria at Elevated Temperatures and Its Application to H2O/CO2 Splitting Thermochemical Redox Cycles

Determination of reaction and oxygen diffusion rates at elevated temperatures is essential for modeling, design, and optimization of high-temperature solar thermochemical fuel production processes, but such data for state-of-the-art redox materials, such as ceria, is sparse. Here, we investigate the solid-state reduction and oxidation of sintered nonstoichiometric ceria at elevated temperatures relevant to solar thermochemical redox cycles for splitting H2O and CO2 (1673 K ≤ T ≤ 1823 K, 3 × 10–4 atm ≤ pO2 ≤ 2.5 × 10–3 atm). Relaxation experiments are performed by subjecting the sintered ceria to rapid oxygen partial pressure changes and measuring the time required to achieve thermodynamic equilibrium state. From such data, we elucidate information regarding ambipolar oxygen diffusion coefficients through comparison of experimental data to a numerical approximation of Fick’s second law based on finite difference methods. In contrast to typically applied analytical approaches, where diffusion coefficients a...

Simulation of oxygen diffusion process on electrical conductivity relaxation

Abstract Finite element method (FEM) simulations were carried out for modeling the electrical conductivity relaxation (ECR) process of a mixed ionic electronic conductor upon abrupt change of oxygen partial pressure. Oxygen diffusion pathway was simulated considering enhanced surface exchange rate on the current and voltage terminals formed on the specimen. The results suggested that the vacancy diffusion coefficient, DV, ECR, obtained from ECR method appears to be dependent on vacancy concentration, δ, even though the true DV is constant. The effects of the following parameters were investigated; degree of catalytic effect, surface reaction rate constant and sample dimension. Change in the sample dimension in a realistic range did not effectively suppress the modification of diffusion paths, and the change of apparent chemical diffusion coefficient, Dchem, app, was inevitable when surface reaction rate constant, kchem, and Dchem are in the same range. The results of the FEM simulation were confirmed by ECR experiments with catalytic active (Pt) and inactive (Au) electrodes.

Partial Conductivities and Chemical Diffusivities of Multi-Ion Transporting BaZrxCe0.85-xY0.15O3-δ (x = 0, 0.2, 0.4 and 0.6)

BaZrxCe0.85-xY0.15O3-δ (BZCY); x = 0–0.6, were synthesized by a solid state reaction method. The phase composition of calcined powders was analyzed by powder X-Ray diffraction (XRD), which showed an orthorhombic lattice for BaCeY0.15O3-δ (BZCY0), BaZr0.2Ce0.65Y0.15O3-δ (BZCY20) and BaZr0.4Ce0.45Y0.15O3-δ (BZCY40), and a cubic lattice for BaZr0.6Ce0.25Y0.15O3-δ (BZCY60), indicating a transition from orthorhombic to cubic lattice with increasing Zr content. The defect chemical analysis of BZCY system was performed in order to analyze their charge and mass transport properties and the solutions of analytical defect equations were obtained in terms of various defect concentrations to calculate the partial conductivities and transport numbers of various charge carriers. The electrical conductivity was monitored by 4-probe dc-conductivity measurement with respect to the changes in oxygen partial pressure (pO2) and water vapor pressure (pH2O) at different temperatures. The electrical conductivity relaxation (ECR) during oxidation/reduction in −2.4<log(pO2/atm)<−0.6 range at a fixed pH2O, and during hydration/dehydration in air in −3.3<log(pH2O/atm)<−2.3 range was recorded, and the surface exchange coefficients and chemical diffusivities of oxygen and hydrogen were calculated from Fick's second law by nonlinear least squares fitting of the conductivity data.