Oxygen Permeation Properties Research Articles

Gelation, Oxygen Permeability, and Mechanical Properties of Mammalian and Fish Gelatin Films

The objective of this study was to evaluate the gelation, thermal, mechanical, and oxygen permeability properties of different mammalian, warm- and cold-water fish gelatin solutions and films. Mammalian gelatin solutions had the highest gel set temperatures, followed by warm-water fish and then cold-water fish gelatin solutions. These differences were related to concentrations of imino acids present in each gelatin, with mammalian gelatin having the highest and cold-water fish gelatin having the lowest concentrations. Mammalian and warm-water fish gelatin films contained helical structures, whereas cold-water fish gelatin films were amorphous. This was due to the films being dried at room temperature (23 °C), which was below or near the gelation temperatures of mammalian and warm-water fish gelatin solutions and well above the gelation temperature of cold-water fish gelatin solutions. Tensile strength, percent elongation, and puncture deformation were highest in mammalian gelatin films, followed by warm-water fish gelatin film and then by cold-water fish gelatin films. Oxygen permeability values of cold-water fish gelatin films were significantly lower than those for mammalian gelatin films. These differences were most likely due to higher moisture sorption in mammalian gelatin films, leading to higher oxygen diffusivity.

Mixed Conductivity, Nonstoichiometric Oxygen, and Oxygen Permeation Properties in Co-Doped Sr3Ti2O7−δ

Electrical conductivity and oxygen permeation rates in Co-doped Sr(3)Ti(2)O(7-δ) with Ruddesden-Popper type structures were investigated. The effects of metal dopants (M) in the Ti site of Sr(3)Ti(2)(M)O(7-δ) on the mixed conductivity were also studied. Doping of Sr(3)Ti(2)O(7-δ) with Co was found to be effective for improving the electrical conductivity as well as the oxygen permeation rate, which could be assigned to the increased oxygen vacancy concentration by doping Co(3+) into Ti(4+) sites. The nonstoichiometric oxygen of these oxides was measured by using a thermal gravimetric method. The creation of oxygen vacancies, which is compensated with Co(3+) doping, leads to higher oxide ion conductivity. The oxygen permeation rate monotonously increased with increasing amounts of Co in the Ti site. Sr(3)Ti(0.8)Co(1.2)O(7-δ) exhibited high oxide ion conductivity and a large oxygen permeation rate. The highest oxygen permeation rate achieved a value of 2.02 cc min(-1) cm(-2) at 1273 K for Sr(3)Ti(0.8)Co(1.2)O(7-δ). Neutron diffraction analysis and redox titration suggests that the oxygen diffusion occurs through oxygen vacancies in the perovskite block, but not through excess oxygen in the rock salt block.

Zirconium stabilized Ba 0.5Sr 0.5(Co 0.8− xZr x)Fe 0.2O 3− α perovskite hollow fibre membranes for oxygen separation

Ba 0.5Sr 0.5(Co 0.8− x Zr x )Fe 0.2O 3− α ( x = 0.0–0.3) (BSCZxF) ceramic powders were synthesized via an improved EDTA-citric acid complexing method. The BSCZxF ( x = 0.05, 0.1, 0.2) perovskite hollow fibre membranes were fabricated from the powders through a phase-version/sintering technique. The oxygen permeation properties of the hollow fibre membranes were measured under air/He gradients at 700–950 °C. Experimental results have shown that the composites with x = 0.05–0.20 Zr-doping content exhibit pure cubic perovskite structure but the BSCZ 0.30F oxide contains impurity phases. Due to the substitution of zirconium in Co sites, the phase stability, the mechanical strength and the densification properties of the BSCZxF hollow fibre membranes are improved noticeably. However, the oxygen permeation flux of the BSCZxF membranes decreases with increased activation energy as the Zr-doping content is increased from 0.05 to 0.20. The suitable Zr-doping content should be around x = 0.1 in order to obtain both high permeation fluxes and high permeation stability.

Synthesis and oxygen permeation properties of a Ce 0.8Sm 0.2O 2− δ–LaBaCo 2O 5+ δ dual-phase composite membrane

Ce 0.8Sm 0.2O 2− δ (SDC) and LaBaCo 2O 5+ δ (LBCO) powders with nanograins were prepared by the cationic surfactant CTAB (cetyltrimethylammonium bromide) assisting method from the inorganic precursor. XRD results reveal the good phase compatibility between fluorite (SDC) and double-perovskite (LBCO) even after sintering and operating at high temperature. The electron-conducting phase LBCO can form a percolative network in SDC–LBCO membrane when its content excesses the threshold value of 40 vol.%, as a consequence, a high electrical conductivity can be achieved with further LBCO addition. The oxygen permeation process is mainly limited by the bulk diffusion of oxygen ions in SDC–LBCO membrane when the membrane thickness is higher than 0.8 mm. The oxygen permeation flux increases with increasing temperature and decreasing membrane thickness. The maximum oxygen flux can achieve ca. 4.59 × 10 −7 mol cm −2 s −1 at 950 °C for 0.6-mm-thick composite membrane, making them be promising candidates for practical oxygen permeable devices.

First Principles Calculations of Oxygen Vacancy Formation and Migration in Ba1−xSrxCo1−yFeyO3−δ Perovskites

Based on first principles DFT calculations, we analyze oxygen vacancy formation and migration energies as a function of chemical composition in complex multicomponent (Ba,Sr)(Co,Fe)O3−δ perovskites which are candidate materials for SOFC cathodes and permeation membranes. The atomic relaxation, electronic charge redistribution and energies of the transition states of oxygen migration are compared for several perovskites to elucidate the atomistic reason for the exceptionally low migration barrier in Ba0.5Sr0.5Co0.8Fe0.2O3−δ that was previously determined experimentally. The critical comparison of Ba1−xSrxCo1−yFeyO3−δ perovskites with different cation compositions and arrangements shows that in addition to the geometric constraints the electronic structure plays a considerable role for the height of the oxygen migration barrier in these materials. These findings help understand advantages and limitations of the fast oxygen permeation and exchange properties of Ba0.5Sr0.5Co0.8Fe0.2O3−δ.

Effect of Co doping on oxygen permeation in Sr 3Ti 2O 7 with Ruddlesden-Popper structure

Effects of transition metal dopant to Ti site in Sr 3Ti 2-xM xO 7 (M = Fe, Ga, Co) on the electrical conductivity and the oxygen permeation property were investigated. Among the examined dopants, it was found that doping Co is the most effective for improving the electrical conductivity and the oxygen permeation rate. With increasing Co amount, electrical conductivity and oxygen permeation rate monotonically increased and the highest oxygen permeation rate is achieved at Sr 3Ti 0.8Co 1.2O 7 among the Co doped sample. On this composition, the oxygen permeation rate from air to He is achieved a value of 2.02 cc/min.cm 2 at 1273 K.

Effect of Sintering Temperature on the Behavior of Oxygen Permeation for La<sub>0.6</sub>Sr<sub>0.4</sub>Co<sub>0.2</sub>Fe<sub>0.8</sub>O<sub>3-δ</sub> Tubular Membranes

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) tubular membranes with relative density more than 95% were prepared using plastic extrusion method, and their oxygen permeation properties were characterized in steady state. It was found that the permeation properties were influenced apparently by the sintering temperature for the resulting LSCF membranes. The as prepared LSCF membrane sintered at 1300oC had a permeation rate by 5~6 times higher than that sintered at 1250oC. The XRD results showed that the as prepared LSCF membrane sintered at 1250oC had the content of impurity more than that sintered at 1300oC. Namely the reasonable elevation of sintering temperature can reduce the impurity in LSCF membranes, which was produced during green process, and the effect of impurity reduction can improve the transport capability of LSCF membranes made by plastic extrusion.

Preparation of Asymmetric Tubular Oxygen Separation Membrane with Oxygen Permeable Pr2Ni0.75Cu0.25Ga0.05O4+δ

The electrical conductivities and oxygen permeation properties of Pr2Ni0.75Cu0.25Ga0.05O4+δ were measured by conventional DC four-probe method with Pt electrode and gas chromatography. The total conductivities increased with an apparent slope of 1/6, satisfied by the charge neutrality condition at the p-type regime of . A tubular-type, asymmetric, mixed-conducting oxygen separation membrane was fabricated by drain casting method. A microporous, ceramic support was prepared by slurry processing, because the use of a slurry technique and a suspension of dispersed particles provides a lower final porosity and a more homogeneous particle packing than dry-pressing does. The 30 cm long, tubular, porous alumina with a soft surface was successfully prepared by drain casting. The surface SEM images revealed a structure with reasonable porosity and well-necked particles. A mixed-conducting layer of Pr2Ni0.75Cu0.25Ga0.05O4+δ was applied inside of the support tube by drain casting. A dense separation layer was successfully fabricated inside the porous alumina tube by sintering at 1473 K for 8 h in air.

Oxygen permeation, mechanical and structural properties of multilayer diffusion barrier coatings on polypropylene

To improve temperature durability for autoclaving of SiOx diffusion barrier coatings on polypropylene, plasma polymerized hexamethyldisiloxane (pp-HMDSO) is applied by plasma enhanced chemical vapour deposition as interlayer material and compared with results obtained with amorphous hydrogenated carbon–nitrogen (a-C : N : H) and a-Si : C : O : N : H interlayers. The influence of the O2/HMDSO ratio on the chemical structure and related mechanical and oxygen barrier properties is investigated by fragmentation tests, dilatometry, oxygen transmission rate, internal stress and mass density measurements as well as Fourier transform infrared and x-ray photoelectron spectroscopy. Carbon-rich, polymer-like coatings with low density, low internal stress and excellent adhesive and cohesive properties are found for pp-HMDSO at the expense of barrier performance. In the SiOx/pp-HMDSO coating a broad transition in chemical composition was observed, explaining improved mechanical properties responsible for good barrier performance after thermal cycling or autoclaving.

Effects of rock-salt layer on electronic and oxide ionic mixed conductivity in strontium titanate, SrO(SrTiO 3) n ( n = 1, 2, ∞)

Electronic conductivity and oxygen permeation properties of analogous compounds of SrO(SrTiO 3) n ( n = 1, 2) and SrTiO 3 were investigated. Electronic conductivity and oxide ion conductivity decrease with increasing n, and SrTiO 3 shows much higher conductivity. The effects of Co doping on oxide ion conductivity and electronic conductivity were also examined and it is observed that it is effective for increasing electrical conductivity and the oxygen permeation rate. Hall effect measurements suggests that the low electron-hole conductivity in Co-doped SrO(SrTiO 3) n ( n = 1, 2) can be assigned to a low mobility, which may result from the low electron and atomic density in the Sr–O rock-salt layer. Quantum mechanical calculations of the electron density also indicate low electron density in the rock-salt layer. This study reveals that the rock-salt layer consisting of Sr–O disturbs electron transfer in SrTiO X oxide and that the perovskite layer has much higher electronic and oxide ionic conductivity.

Structure effect on the oxygen permeation properties of barium bismuth iron oxide membranes

In this work, we investigated the oxygen permeation properties of barium bismuth iron oxide within the family of [Ba 2−3 x Bi 3 x−1 ][Fe 2 x Bi 1−2 x ]O 2+3 x/2 for x = 0.17–0.60. The structure changed progressively from cubic to tetragonal and then to hexagonal as function of x in accordance with the different relative amounts of bismuth on A-site and B-site of ABO 3− δ perovskite lattices. We found that the oxygen flux and electrical conductivity correlated strongly, and it was prevalent for the cubic structure ( x = 0.33–0.40) which conferred the highest oxygen flux of 0.59 ml min −1 cm −2 at 950 °C for a disk membrane x = 0.33 with a thickness of 1.2 mm. By reducing the thickness of the disk membrane to 0.8 mm, the oxygen flux increased to 0.77 ml min −1 cm −2, suggesting both surface kinetics and ion diffusion controlled oxygen flux, though the former was more prominent at higher temperatures. For disk membranes x = 0.45–0.60, the perovskite structure changed to tetragonal and hexagonal, and the oxygen flux was insignificant below 900 °C, clearly indicating electron conduction properties only. However, for two compositions with relatively high bismuth content, e.g. x = 0.55 and 0.60, there was a sudden and significant rise of oxygen permeability above 900 °C, by more than one order of magnitude. These materials changed conduction behavior from metallic to semiconductor at around 900 °C. These results suggest the advent of mixed ionic electronic conducting properties caused by the structure transition as bismuth ions changed their valence states to compensate for the oxygen vacancies formed within the perovskite lattices.

Oxygen Permeation Property in Nd Deficient Nd[sub 2]NiO[sub 4] Mixed Oxide Doped with Cu and Ga

Oxygen permeation property in Nd deficient Nd 2 NiO 4 was studied. The oxygen permeation rate increases with increasing Ga. Nd deficiency in Nd 2 NiO 4 is also useful for increasing the oxygen permeation rate. The improved oxygen permeation rate could be assigned to the increased amount of excess oxygen and stabilizing a tetragonal structure at a low temperature. The oxygen permeation rate of Nd 1.9 (Ni 0.75 Cu 0.25 ) 0.95 Ga 0.05 O 4 achieved a value of 3.6 cm 3 /min cm 2 from air to He at 1273 K with 0.5 mm thickness and this value belongs to the highest class in the reported oxygen permeation rate.

Nd:YAG Laser Perforation of Plastic Films for Enhanced Breathability

This study focused on investigating the Nd:YAG laser perforation process of several common plastic films including biaxially-oriented polypropylene (BOPP), biaxially-oriented polyethylene terephthalate (BOPET) and low density polyethylene (LDPE) films. Films were perforated under various pulse energies of 50, 150 and 250 mJ and with pulse duration of ~10 ns and pulse repetition of 1 Hz. It was found that, BOPP, BOPET and LDPE films could be perforated using our developed Nd:YAG laser perforating system. Perforation width or diameters of all films increased with increasing pulse energies. Observed perforations were different among the three film types. For instance, at the pulse energy of 150 mJ, average microperforation diameters of BOPP, BOPET, and LDPE were 51.9, 57.5, and 31.0 microns, respectively. Overall results clearly demonstrated that a Nd:YAG laser perforation process used in this study was effective in developing breathable packaging films with tailored oxygen permeation property. Commercial BOPP films containing 200-1,400 micro-perforations/m2 (average perforation diameter of  50 µm) showed a significant improvement in oxygen transmission rates (OTR) of 25-700% over that of the regular BOPP. Very high OTR films of 16,000 cc/m2.day could be effectively produced for the micro-perforated BOPP, where OTR values of close to 20,000 cc/m2.day was obtainable in the case of BOPET films.

Electrical conductivity and oxygen permeation properties of SrCoFeO x membranes

The total conductivity and oxygen permeation properties of dense SrCoFeO x membranes synthesized from the solid state method were studied in the temperature range of 700–900 °C. The SrCoFeO x membranes consist of an intergrowth (Sr 4Fe 6 − x Co x O 13 ± δ ), perovskite (SrFe 1 − x Co x O 3 − δ ), and spinel (Co 3 − x Fe x O 4) phase. SrCoFeO x exhibits n-type and p-type conduction at low and high oxygen partial pressures, respectively, and has a total conductivity of 16.5 S/cm at 900 °C in air. The oxygen permeation fluxes for SrCoFeO x and SrFeCo 0.5O x membranes were measured with either an inert or carbon monoxide sweep gas. The oxygen permeation fluxes were higher through SrCoFeO x membranes than SrFeCo 0.5O x membranes and can be attributed to a difference in the amount and makeup of the perovskite phase present in each composition. The oxygen permeation fluxes with a carbon monoxide sweep gas were approximately two orders of magnitude larger than the fluxes measured with an inert sweep gas for both compositions. The large oxygen permeation fluxes observed with a carbon monoxide sweep are due to a higher driving force for oxygen transport and a reaction on the sweep side of the membrane that maintains a low oxygen partial pressure.

Optimization of Ba xSr 1− xCo 0.9Nb 0.1O 3−δ perovskite as oxygen semi-permeable membranes by compositional tailoring

Mixed conducting SrCo 0.9Nb 0.1O 3−δ perovskite is a newly developed promising ceramic membrane material for air separation. In this work, SrCo 0.9Nb 0.1O 3−δ was further optimized by the introduction of Ba to partially replace Sr in the A-site of the perovskite structure. The phase structure, phase stability, carbonate formation rate under carbon dioxide atmosphere, electrical conductivity, oxygen desorption properties, and oxygen permeation properties of Ba x Sr 1− x Co 0.9Nb 0.1O 3−δ (BSCNx) with varying Ba 2+ doping level were systematically investigated. Pure phase cubic perovskite was formed at x = 0.0–0.8. BSCNx ( x = 0.0–0.8) can be stably operated in atmospheres with oxygen partial pressure varying from at least 1 atm to as low as 10 −5 atm (Ar atmosphere). The barium doping concentration had a significant effect on electrical conductivity and oxygen permeability of the membranes. BSCN0.6 had the highest oxygen permeation flux of 2.67 × 10 −6 mol cm −2 s −1 for 0.87 mm thickness at 900 °C and the highest oxygen ionic conductivity of 1.38 S cm −1 at 900 °C.

Mixed Oxide Ion and Hole Conductivity in Pr2 − αNi0.76 − xCu0.24GaxO4 + δ Membrane

The mixed conductivity and oxygen permeation properties of Pr-deficient were investigated. Among the dopants studied, the Ga-doped membrane was a superior mixed conductor, and it exhibited a high oxygen permeation rate compared with that of the other compositions. Examinations of membranes with different Ga concentrations revealed that the A-site cation-deficient composition, , had the highest permeability of (ca. ) from air to He at 1273 K in a 0.5 mm thick membrane. The oxygen permeation rate of decreased with thickness, indicating that the limiting factor is oxygen diffusivity in bulk. The Seebeck coefficient and oxygen permeation measurements suggest that the Ga dopant and Pr deficiency decreased the charge carrier density and improved the oxide ion conductivity. The estimated oxide ion conductivity in this material is a few times higher than that of the conventional mixed conductors such as Co-based perovskite.

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.

High Temperature Crystal Chemistry and Oxygen Permeation Properties of the Mixed Ionic–Electronic Conductors LnBaCo2O5 + δ ( Ln = Lanthanide )

The high temperature crystal chemistry and oxygen permeation properties of the cation-ordered perovskite oxides [lanthanide , Nd, and Sm] have been investigated in comparison with the cation-disordered perovskite. The (, Nd, and Sm) oxides exhibit a metal-insulator transition at , as evidenced by total conductivity measurements and high temperature X-ray diffraction data and an oxygen vacancy order–disorder transition at in air, as evidenced by an orthorhombic to tetragonal transition. At a given temperature, the oxygen permeation flux decreases from to Nd to Sm due to the changes in crystal symmetry and lattice strain. The oxygen permeation mechanism in the is bulk-diffusion-limited rather than surface-exchange-limited for membrane thickness .

An oxygen permeable membrane La 0.8Sr 0.2(Ga 0.8Mg 0.2) 1 − xCr xO 3 − δ for a reduced atmosphere

Mixed electron hole and oxide ion conducting perovskite-type oxides, La 0.8Sr 0.2(Ga 0.8Mg 0.2) 1 − x Cr x O 3 − δ (0 ≤ x ≤ 1.0) , were prepared by solid state reaction. The phase stability and the oxygen permeation properties of the oxides were examined as a function of the content of Cr. La 0.8Sr 0.2(Ga 0.8Mg 0.2) 1 − x Cr x O 3 − δ has a perovskite related tetragonal phase with x = 0.1 to 0.8. The total electrical conductivity of La 0.8Sr 0.2(Ga 0.8Mg 0.2) 1 − x Cr x O 3 − δ increases with increasing x. The oxygen permeation flux across the La 0.8Sr 0.2(Ga 0.8Mg 0.2) 1 − x Cr x O 3 − δ membranes at higher temperatures increases with x up to x = 04. The maximum oxygen permeation flux of 1.6 × 10 − 7 mol − 1 cm − 2 at 1100 °C in a oxygen activity gradient of air/10 − 2 Pa is observed in La 0.8Sr 0.2(Ga 0.8Mg 0.2) 0.6Cr 0.4O 3 − δ . This perovskite-type oxide is stable under an oxygen partial pressure of 7 × 10 − 10 Pa at 1000 °C.

SrCo 0.9Sc 0.1O 3− δ perovskite hollow fibre membranes for air separation at intermediate temperatures

SrCo 0.9Sc 0.1O 3 (SCSc) perovskite powders with sub-micron particle size were synthesized by a modified Pechini method combined with a post-treatment of sintering and ball-milling. From the prepared powders, the SCSc hollow fibre membranes with asymmetric structure and gas-tight property were fabricated by spinning a polymer solution containing 58.4 wt% SCSc followed by sintering at 1200 °C for 5 h. The oxygen permeation properties of the obtained SCSc fibres were measured under air/He gradients at 500–800 °C. This showed the oxygen flux of 1 mL cm −2 min −1 at 750 °C and 4.41 mL cm −2 min −1 at 900 °C. Modeling analysis reveals that the oxygen permeation process is predominated by oxygen surface exchange kinetics with an activation energy of 95.0 kJ mol −1. The SCSc membranes showed excellent oxygen permeation performance while exhibiting high structural and permeating stability at intermediate temperatures (500–800 °C).