Oxygen-permeable Materials Research Articles

A promising cathode for intermediate temperature protonic ceramic fuel cells: BaCo0.4Fe0.4Zr0.2O3−δ

In this study, BaCo0.4Fe0.4Zr0.2O3−δ (BCFZ), which has been previously investigated as a stable oxygen permeable membrane material, is confirmed to be a promising cathode for intermediate temperature protonic ceramic fuel cells (IT-PCFCs). BCFZ shows lower electrode polarization resistances, longer performance stability, and better compatibility with the state of the art protonic ceramic electrolyte BaCe0.7Zr0.1Y0.1Yb0.1O3−δ (BCZYYb) than the prevailing cathode La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF). The oxygen reduction reaction (ORR) mechanism and the reaction kinetics are also investigated in detail. A single cell constructed from the BCFZ cathode with a BCZYYb electrolyte and BCZYYb-Ni anode demonstrates a power density of 225 mW cm−2 at 600 °C, which is ∼20 times greater than a single cell constructed from an LSCF cathode with the same electrolyte and anode under the same operating conditions.

High Ethylene Production through Oxidative Dehydrogenation of Ethane Membrane Reactors Based on Fast Oxygen‐Ion Conductors

AbstractHigh ethylene productivity through the oxidative dehydrogenation of ethane has been achieved in a catalytic membrane reactor based on a highly solid‐state oxygen permeable material (Ba0.5Sr0.5Co0.8Fe0.2O3−δ). Ethylene is selectively produced by avoiding the direct contact of molecular oxygen and hydrocarbons, thereby minimizing the oxygen concentration in the reaction side. Another key aspect in the process is the dilution of ethane in the feed to achieve high ethylene yields. There exists a specific combination of the ethane concentration and feed flow that maximizes ethylene productivity, whereas the diluting gas nature has a direct impact on the formation of higher olefins and coking issues. Indeed, the use of methane as an almost‐inert dilutant allows the reduction of oligomerization and aromatization of the formed ethylene and therefore improves the reactor stability even at operating temperatures from 800 to 900 °C. This behavior is attributed to the competitive adsorption of methane and ethane/ethylene, the modification of the radical‐driven homogeneous reaction, and the change of partially reducible membrane surface. The productivity values achieved at 850 °C were 383 mL min−1 cm−2 for Ar and 353 mL min−1 cm−2 for CH4, with a selectivity of 80 and 90 %, respectively.

Superior oxygen and glucose supply in perfusion cell cultures compared to static cell cultures demonstrated by simulations using the finite element method

Oxygen and glucose supply is one of the important factors for the growth and viability of the cells in cultivation of tissues, e.g., spheroid, multilayered cells, and three-dimensional tissue construct. In this study, we used finite element methods to simulate the flow profile as well as oxygen and glucose supply to the multilayered cells in a microwell array chip for static and perfusion cultures. The simulation results indicated that oxygen supply is more crucial than glucose supply in both static and perfusion cultures, and that the oxygen supply through the wall of the perfusion culture chip is important in perfusion cultures. Glucose concentrations decline with time in static cultures, whereas they can be maintained at a constant level over time in perfusion cultures. The simulation of perfusion cultures indicated that the important parameters for glucose supply are the flow rate of the perfusion medium and the length of the cell culture chamber. In a perfusion culture chip made of oxygen-permeable materials, e.g., polydimethylsiloxane, oxygen is hardly supplied via the perfusion medium, but mainly supplied through the walls of the perfusion culture chip. The simulation of perfusion cultures indicated that the important parameters for oxygen supply are the thickness of the flow channel and the oxygen permeability of the walls of the channel, i.e., the type of material and the thickness of the wall.

Oxygen-permeable membranes based on partially B-site substituted BaFe 1− yMyO 3− δ ( M=Cu or Ni)

We carried out the partial substitution of the B-site in BaFeO 3− δ perovskite with divalent cations to develop novel oxygen-permeable materials. We demonstrated that the partial substitution of Cu or Ni by more than 10% resulted in the stabilization of the cubic perovskite structure even at room temperature in a highly oxygen-permeable phase, as revealed by the X-ray diffraction (XRD) analysis. The Cu substitution was more effective for the stabilization, because the introduction of Cu in the lattice more effectively made the Goldschmidt tolerance factor ( t) close to 1.0. Ni- and Cu-substituted BaFeO 3− δ membranes showed higher oxygen permeabilities than their parent BaFeO 3− δ membranes particularly at lower temperatures around 600–700 °C owing to the stabilization of the cubic phase. Among the fabricated membranes, a BaFe 0.85Cu 0.15O 3− δ membrane (1.0 mm thickness) showed the highest oxygen permeation flux (1.8 cm 3 min −1 cm −2 at 930 °C) under an air/He gradient. The results indicated that Cu-substituted BaFeO 3–δ is promising as a material for Co-free membranes with high oxygen permeabilities.

Window on a Microworld: Simple Microfluidic Systems for Studying Microbial Transport in Porous Media

Microbial growth and transport in porous media have important implications for the quality of groundwater and surface water, the recycling of nutrients in the environment, as well as directly for the transmission of pathogens to drinking water supplies. Natural porous media is composed of an intricate physical topology, varied surface chemistries, dynamic gradients of nutrients and electron acceptors, and a patchy distribution of microbes. These features vary substantially over a length scale of microns, making the results of macro-scale investigations of microbial transport difficult to interpret, and the validation of mechanistic models challenging. Here we demonstrate how simple microfluidic devices can be used to visualize microbial interactions with micro-structured habitats, to identify key processes influencing the observed phenomena, and to systematically validate predictive models. Simple, easy-to-use flow cells were constructed out of the transparent, biocompatible and oxygen-permeable material poly(dimethyl siloxane). Standard methods of photolithography were used to make micro-structured masters, and replica molding was used to cast micro-structured flow cells from the masters. The physical design of the flow cell chamber is adaptable to the experimental requirements: microchannels can vary from simple linear connections to complex topologies with feature sizes as small as 2 microm. Our modular EcoChip flow cell array features dozens of identical chambers and flow control by a gravity-driven flow module. We demonstrate that through use of EcoChip devices, physical structures and pressure heads can be held constant or varied systematically while the influence of surface chemistry, fluid properties, or the characteristics of the microbial population is investigated. Through transport experiments using a non-pathogenic, green fluorescent protein-expressing Vibrio bacterial strain, we illustrate the importance of habitat structure, flow conditions, and inoculums size on fundamental transport phenomena, and with real-time particle-scale observations, demonstrate that microfluidics offer a compelling view of a hidden world.

Window on a Microworld: Simple Microfluidic Systems for Studying Microbial Transport in Porous Media

Microbial growth and transport in porous media have important implications for the quality of groundwater and surface water, the recycling of nutrients in the environment, as well as directly for the transmission of pathogens to drinking water supplies. Natural porous media is composed of an intricate physical topology, varied surface chemistries, dynamic gradients of nutrients and electron acceptors, and a patchy distribution of microbes. These features vary substantially over a length scale of microns, making the results of macro-scale investigations of microbial transport difficult to interpret, and the validation of mechanistic models challenging. Here we demonstrate how simple microfluidic devices can be used to visualize microbial interactions with micro-structured habitats, to identify key processes influencing the observed phenomena, and to systematically validate predictive models. Simple, easy-to-use flow cells were constructed out of the transparent, biocompatible and oxygen-permeable material poly(dimethyl siloxane). Standard methods of photolithography were used to make micro-structured masters, and replica molding was used to cast micro-structured flow cells from the masters. The physical design of the flow cell chamber is adaptable to the experimental requirements: microchannels can vary from simple linear connections to complex topologies with feature sizes as small as 2 μm. Our modular EcoChip flow cell array features dozens of identical chambers and flow control by a gravity-driven flow module. We demonstrate that through use of EcoChip devices, physical structures and pressure heads can be held constant or varied systematically while the influence of surface chemistry, fluid properties, or the characteristics of the microbial population is investigated. Through transport experiments using a non-pathogenic, green fluorescent protein-expressing Vibrio bacterial strain, we illustrate the importance of habitat structure, flow conditions, and inoculums size on fundamental transport phenomena, and with real-time particle-scale observations, demonstrate that microfluidics offer a compelling view of a hidden world.

Organometallic osmium and iridium complexes as phosphorescent dye in barometric sensitive coatings

Abstract Pressure sensitive paints (PSP) that measure changes in barometric pressure through oxygen quenching are an important analytical tool in wind tunnel and other research. PSPs are often used during the development phase of new aircraft, cars, and trucks where the performance of the proposed vehicle is researched. Previously, many PSPs have been based upon charged phosphorescent metal complex salts that may have poor solubility in the oxygen permeable host material. Charge neutral phosphorescent dyes should have better solubility, and to demonstrate this, neutral osmium and iridium complexes are presented in this report. X-ray structures are measured and DFT calculations are used to explain many of their properties. The complexes are dissolved into poly(1,1,1,3,3,3-hexafluoroisopropylmethacrylate-co-1H,1H-dihydroperfluorobutyl-methacrylate) (FIB), an oxygen permeable host polymer. The complexes exhibit good solubility and compatibility with the FIB polymer. The photo-degradation, temperature sensitivity, and Stern–Volmer curves of PSPs based on these complexes are presented. The complexes show great promise for use in PSPs.

Oxygen Permeation Properties of Partially A-Site Substituted BaFeO3 − δ Perovskites

To explore oxygen permeable materials, oxygen permeation properties of partially A-site substituted perovskites were investigated. Ba sites in were substituted with cations such as Na, Rb, Ca, Y, and La by 5%. The partial substitution with Ca, Y, and La, whose ionic radii are smaller than that of Ba, succeeded in stabilizing a cubic perovskite structure that is a highly oxygen permeable phase, as revealed by X-ray diffraction analysis. This can be explained in terms of a decrease in the tolerance factor . Among the (M = Na, Rb, Ca, Y, and La) membranes tested, showed the highest oxygen permeability at 600–930°C, owing to the stabilization of the cubic phase without the formation of impurity phases. From chemical analysis, the oxygen permeability of membranes was correlated with the amount of oxygen defects (δ) in the lattice. The oxygen permeation flux of membrane was significantly increased by reducing its thickness. Furthermore, a membrane exhibited good phase stability under He flow at elevated temperatures. The obtained results indicate the promising properties of membranes as a cobalt-free material that has a high oxygen permeability, good phase stability, and low cost.

Hydrogen amplification of coke oven gas by reforming of methane in a ceramic membrane reactor

To maximize hydrogen production from coke oven gas (COG), partial oxidation of methane in COG was studied thermodynamically and experimentally. Thermodynamic analysis indicates that an optimal hydrogen yield of 1.04–1.10 mole per mole of the consumed COG can be achieved when the initial ratio of O 2 and CH 4 is 0.57–0.46 in a temperature range of 800–900 °C, and the corresponding amplification of original hydrogen in COG reaches 1.8–1.9 times. The amplification of original hydrogen was carried out in a BaCo 0.7Fe 0.2Nb 0.1O 3−δ (BCFNO) membrane reactor, and the hydrogen yield in the lab scale was about 80% more than that of original H 2 in model COG. In a large hydrogen content in COG, the ceramic membrane reactors made from perovskite mixed-conducting oxygen-permeable materials must have higher stability to withstand the harsh reduction condition.

Optimization of a Prominent Oxygen-Permeable Device for Pancreatic Islets

Background We have demonstrated a culture bag system that is useful for pancreatic islet transplantation. To improve and simplify islet transplantation procedures from culture to transplantation, we developed a novel device specific for both islet culture and transplantation (TUBERO Device [TD]) using an oxygen-permeable material. Materials and Methods Porcine islets with 30 minutes warm ischemia time were cultured for 24 hours at 37°C in 5% CO 2 and humidified air under three different procedures: (1) ordinary culture flask, (2) culture bag suitable for platelets, and (3) TD. Loss of islets during culture, glucose-stimulated insulin release as an islet functional test, and ADP/ATP ratio as an index of islet viability tests were evaluated to compare the devices. TD was further applied in two clinical islet transplantations using non–heart-beating donors in Japan. Results The loss of islets during culture was considerably lower in the TD group. The stimulation index upon glucose challenge tests was significantly higher in the TD group than the others. The ADP/ATP ratio in TD group was significantly lower than that in the ordinary flask group, suggesting that the apoptotic islets were relatively lower among TD. Most importantly, TD was successfully applied both in the clinical islet cultures and in transplantation, resulting in excellent graft function. Conclusions We propose that the TD, a novel product, not only simplifies islet transplantation procedures, but also maintain the quality of isolated islets.

Hyper Oxygen-Permeable Rigid Contact Lenses as an Alternative for the Treatment of Pediatric Aphakia

To establish the safety and efficacy of a hyper oxygen-permeable rigid contact lens material, Menicon Z, for the fitting of aphakic infant eyes. A prospective study was performed on 16 eyes of 10 newly aphakic infants. Aphakic fittings were performed postoperatively with the Dyna Z intralimbal design of lenses, made exclusively from Menicon Z material for this study. Examinations were performed at 1 day, 1 week, 1 month, 3 months, and 6 months, during which the lenses were used on a 1-week extended-wear basis. The following outcome measures were evaluated at each visit: Fit Characteristics, Ocular Integrity, Usability, and Contact Lens Integrity. When used for the treatment of pediatric aphakia, the Menicon Z material provided excellent Fit Characteristics, was not damaging to the ocular structures, was relatively easy to manipulate for caregivers, and maintained its integrity well throughout the course of the study. Because there were no observable increases in the rate of microbial infection during the course of the study, the hyper oxygen-permeable nature of the Menicon Z material seems to provide adequate corneal oxygenation for aphakic children when used on a 1-week extended-wear basis. The Menicon Z contact lens material provides a safe and effective alternative for the treatment of infants and children requiring aphakic correction. This hyper oxygen-permeable material offers sufficient corneal oxygenation at the lens powers and thicknesses demanded by newly aphakic eyes combined with a low risk for associated complications.

Structural instability of cubic perovskite Ba xSr 1 − xCo 1 − yFe yO 3 − δ

Cubic perovskites Ba x Sr 1 − x Co 0.8Fe 0.2O 3 − δ (BSCF) are among the most promising oxygen permeable membrane materials and high-performance cathode materials for intermediate temperature solid oxide fuel cells. Here, we show that cubic BSCF becomes unstable in air at intermediate temperatures and gradually transforms to a hexagonal perovskite on cooling. Cubic and hexagonal BSCF polymorphs were observed to coexist below 850–900 °C, and the amount of the hexagonal polymorph was shown to increase at the expense of the cubic polymorph with decreasing temperature. Different chemical composition of the two coexisting phases was inferred, but a complete transformation to the hexagonal polymorph was hindered by slow cation diffusion. Due to the sluggish kinetics, usual cooling rates lead to the meta-stable cubic BSCF, but over time the transition to the stable hexagonal polymorph may be detrimental to applications incorporating BSCF. We show that the transformation of the cubic to hexagonal polymorph of BSCF can be rationalized by the Goldschmidt tolerance factor and accordingly suppressed by appropriate substitutions.

Stable immobilization of rat hepatocytes as hemispheroids onto collagen‐conjugated poly‐dimethylsiloxane (PDMS) surfaces: Importance of direct oxygenation through PDMS for both formation and function

The highly oxygen-permeable material, poly-dimethylsiloxane (PDMS), has the potential to be applied to cell culture microdevices, but cell detachment from PDMS has been a major problem. In this study, we demonstrate that a combination of collagen covalently immobilized PDMS and an adequate oxygen supply enables the establishment of a stable, attached spheroid (hemispheroid) culture of rat hepatocytes. The bottom PDMS surfaces were first treated with oxygen plasma, then coupled with aminosilane followed by a photoreactive crosslinker, and they were finally reacted with a collagen solution. X-ray photoelectron spectroscopy (XPS) and contact angle measurements showed that the covalent immobilization of collagen on the surface occurred only where the crosslinker had been introduced. On the collagen-conjugated PDMS surface, rat hepatocytes organized themselves into hemispheroids and maintained the viability and a remarkably high albumin production at least for 2 weeks of culture. In contrast, hepatocytes on the other types of PDMS surfaces formed suspended spheroids that had low albumin production. In addition, we showed that blocking the oxygen supply through the bottom PDMS surface inhibited the formation of hemispheroids and the augmentation of hepatocellular function. These results show that appropriate surface modification of PDMS is a promising approach towards the development of liver tissue microdevices.

A novel combustion route for the preparation of perovskite-type oxygen permeable materials

Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ perovskite-type oxygen permeable materials were prepared by a novel complexation/combustion (CC) method, where oxygen/air was introduced externally to assist combustion instead of adding an extra oxidant into a precursor solution. This method offers the advantages of facilitating the crystallization of perovskite phase and easy sample treatment. Compared with various self-propagating combustion systems, such as glycerol/nitrates (GlN), glycine nitrates (GN) and EDTA/citrate nitrates (ECN) routes, the CC method yields perovskite products with minimum phase contamination and the highest crystallinity. Additionally, the oxygen permeation tests and SEM studies revealed that the disc-shape membrane made from the CC powder exhibit less structure defects and higher oxygen permeation flux. The complexation/combustion method developed here is an attractive technique for synthesizing perovskite-type oxygen permeable materials.

Novel hollow fibre membrane reactor for the partial oxidation of methane

In recent years perovskite-type membranes (ABO 3) have been studied intensively as oxygen permeable materials. These perovskite ceramics very often have a disc or tube geometry. In this paper the first data of a membrane reactor for POM with hollow fibres as membrane are reported. The hollow fibres were spun from BCFZ (Ba(Co,Fe,Zr)O 3− δ ) powder. Diluted methane as well as methane with steam were investigated as reaction gases. The spent catalyst was investigated by high-resolution transmission electron microscopy (HR-TEM) after the reaction. Membrane failures were evaluated by field-emission scanning electron microscopy (FE-SEM).

Infectious Keratitis After Overnight Orthokeratology in Canada

To report 3 cases of infectious keratitis related to overnight orthokeratology use. Retrospective case observation. All 3 patients were using overnight orthokeratology lenses when they presented with unilateral corneal ulcers. The organisms isolated were Acanthamoeba, Pseudomonas aeruginosa, and Serratia marcescens. The clinical presentation and treatment of each case is presented. Overnight orthokeratology use may be associated with infectious keratitis despite the use of more oxygen-permeable materials and improved lens design. Patient education with informed consent, appropriate lens care, and meticulous follow-up is important. Because this complication is potentially sight threatening, orthokeratology requires further analysis and evaluation to establish its safety. The cases here are the first few reported cases in North America.

The Current State of Corneal Reshaping

The application of contact lenses to alter the shape of the cornea and temporarily reduce or eliminate myopia is known as orthokeratology, corneal refractive therapy, or corneal reshaping. It was first introduced in the 1960s, but high oxygen permeable materials and more sophisticated designs allow patients to wear contact lenses only during sleep, while dramatically improving the predictability and rate of myopia reduction. Many studies have shown that most corneal reshaping patients achieve uncorrected visual acuity of 20/25 or better that lasts all day long in one to two weeks of nighttime wear. Treatment is primarily effective through central epithelial thinning and midperipheral epithelial and stromal thickening. Much remains to be learned about corneal reshaping contact lenses and their effects on the cornea. The authors reviewed existing knowledge and determined what needs to be learned in order to provide patients with appropriate informed consent prior to corneal reshaping contact lens wear. While corneal reshaping contact lenses are effective at temporarily reducing or eliminating myopia, claims about the progress of myopia being controlled with corneal reshaping contact lenses should not be made until further studies are published in peer-reviewed literature. The incidence and prevalence of microbial keratitis related to corneal reshaping contact lens wear is not known. Any overnight wear of contact lenses increases the risk of infection, but it is not known whether the risks of microbial keratitis are greater for corneal reshaping overnight contact lens wearers than other form of overnight contact lens wear. It is also not known whether the risk of microbial keratitis is greater for children than adults, but we must determine if children are at greater risk than adults because many children are wearing corneal reshaping contact lenses. Finally, it is recommended that ongoing education be provided to practitioners and staff regarding safety, informed consent, and prevention of potential problems, with special emphasis on the critical need to properly and thoroughly disinfect lenses that will be worn overnight.

Fe/Mn-based Perovskite-Type Oxides with Excellent Oxygen Permeability and Reduction Tolerance

ABSTRACTA family of Co-free, Fe/Mn-based perovskite-type oxides, (Sr, A')(Fe, Mn)O3-δ (A'=La, Ba, Ca), was synthesized, and their oxygen permeability and phase stability in reducing atmosphere were investigated. The substitution of Mn at B site caused the decrease in oxygen permeability. As for the effect of A-site substitution, prominent promotion was observed by the substitution of Ba for 30% of Sr, and Ba0.3Sr0.7FeO3-δ was found to be one of most excellent oxygen permeable materials with the permeation flux of 3.0 cm3(STP) cm−2 min−1 at 900 °C. Reduction tolerance was evaluated by TG measurements in a 5%H2/N2 stream up to 1000 °C. After the TG measurements, crystal structures of La-Sr-Co-Fe-O and Sr-Fe-(Mn)-O perovskites were decomposed or transformed into low oxygen permeable phases, but the perovskite-type structure of Ba-Sr-Fe-(Mn)-O survived. The Fe/Mn-based perovskites with high oxygen permeability and exceeding reduction tolerance could be used as stable membrane materials for membrane reactors catalyzing NO-CH4 reaction and the partial oxidation of CH4 into synthesis gas.

Preparation and characterization of oxygen permeable membrane of SrFeCu0.2Ox

Abstract Dense ceramic mixed-conducting oxygen-permeable membrane materials have the potential to be incorporated into a variety of technological systems, including selective oxygen permeable membranes, gas sensors, membrane reactors and solid oxide fuel cells (SOFC). So the oxygen-permeable membranes are getting more attention. In previous works, most attention was paid to materials that have perovskite structure (for example, La-Sr-Co-Fe-O system). In the present work, a Sr-Fe-Cu-O system has been investigated. And SrFeCu 0.2 O x was successfully synthesized by solid-state reaction. The factors that influenced the syntheses were discussed. The structure of SrFeCu 0.2 O x was determined by XRD. It's found that SrFeCu 0.2 O x has a main cubic phase together with a small quantity of remaining CuO, and lattice constant a 0 =0.3846 nm. Oxygen permeation flux was measured by the GC method. The oxygen permeation flux is 1.70×10 −6 mol/cm 2 ·s (STP) at 825°C, showing that SrFeCu 0.2 O x is a promising oxygen permeable material.

Scleral contact lenses for overnight wear in the management of ocular surface disorders

To describe the use of overnight wear scleral contact lenses (Scl CLs). The authors describe 7 patients using this modality of contact lens wear. Most of the lenses were made from highly gas-permeable materials, but a long-standing case is also reported when the lenses were made from PMMA, which is impermeable to gases. There is a range of therapeutic indications for the use of Scl CLs. The development of rigid gas-permeable (RGP) materials has widened this range. Seven case reports are presented which describe patients in whom severe ocular surface disease has been managed with overnight-wear Scl CLs. The indications were: corneal exposure, post-radiotherapy complications, Stevens Johnson disease, recurrent erosion and congenital or post-surgical lid defects. Scl CLs provide a therapeutic option for a range of complicated corneal and ocular surface conditions for which the treatment by other methods is either unsuitable or less effective. They have several advantages over silicone rubber and hydrogel lenses. The relative ease of handling for some patients allows removal for cleaning, their rigidity gives stability and a high degree of protection to the ocular surface, and the presence of a pre-corneal fluid reservoir optically neutralises an irregular corneal surface. Highly oxygen-permeable materials enable consideration of overnight wear in appropriate circumstances.