Oxygen Permeation Experiments Research Articles

Perovskite‐related ZrO2‐doped SrCo0.4 Fe0.6O3‐δ membrane for oxygen permeation

AbstractA typical perovskite La0.2Sr0.8Co0.2Fe0.8O3‐δ (LSCF) membrane and a novel perovskite‐related ZrO2‐doped SrCo0.4Fe0.6O3‐δ (SCFZ) membrane were successfully prepared. The sintered membranes were characterized by an in‐situ high‐temperature X‐ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Oxygen permeabilities of the two dense membranes were measured in the temperature range of 923 to 1,173 K under a fixed oxygen partial pressure gradient. The results of the oxygen permeation experiment and high‐temperature X‐ray diffraction in argon atmosphere indicate that the perovskite‐related SCFZ membrane has higher oxygen fluxes and is stable than that of the LSCF membrane at elevated temperatures and reduced oxygen partial pressures.

Oxygen Permeation Properties of Dense Bi1.5Er0.5 O 3 ‐ Ag Cermet Membranes

Oxygen permeation experiments were performed on dense mixed‐conducting ceramic‐metal composite membranes (thickness 0.2 to 2 mm) with 10.0, 27.8, and 40.0 volume percent (v/o) silver, respectively, in the temperature range 873 to 993 K and oxygen partial pressure range to 1 bar . The oxygen fluxes increased with increasing silver content. In the cermets with a nonpercolative silver phase (10.0 and 27.8 v/o), the increased oxygen flux relative to that of pure was attributed to faster kinetics of surface oxygen exchange in the presence of silver. Percolativity of the silver phase in the 40 v/o Ag composition enhances the ambipolar diffusion of oxygen ions and electrons. High oxygen fluxes ( at 873 K) were observed with the latter composition, which were shown to be fully limited by the surface exchange kinetics. The activation energy for oxygen permeation in the temperature range 848 to 1003 K is about 85 to 95 kJ/mol for the compositions without percolativity of silver and 115 kJ/mol for the composite with 40 v/o Ag, which reflects a change of the rate‐limiting step upon passing the percolation threshold. Results from both permeation and isotopic exchange measurements on the composition with Ag percolativity indicated the kinetic order of the surface process in oxygen to be 1/4, indicating a process fundamentally different from that on pure .

Ceramic Membranes by Electrochemical Vapor Deposition of Zirconia‐Yttria‐Terbia Layers on Porous Substrates

By means of electrochemical vapor deposition (EVD), it is possible to grow thin, dense layers of zirconia/yttria/terbia solid solution (ZYT) on porous ceramic substrates. These layers can be used as ceramic membranes for oxygen separation. The kinetics of the EVD process, the morphology of the grown layers and their oxygen permeation properties are investigated. At a deposition temperature of 800°C, the EVD layer growth is limited by bulk electrochemical transport. At 1000°C the layer growth is limited by pore diffusion of the oxygen source reactant. The EVD‐grown ZYT layers show columnar structures with prismatic grains on top; the size of the grains (1 to 2 μm) increases slightly with temperature and deposition time. ZYT is deposited mainly in the cubic doped zirconia phase. Oxygen permeation experiments show that the oxygen permeation flux through the ZYT layers is limited by an electrochemical process. Permeation values in the order of 10−8 mol/cm2 s have been observed (900–1000°C, air vs. ).

The radiation resistance of thermoset plastics—III. Oxygen permeation experiments

For the interpretation of the results of long term irradiation experiments in the presence of air it is necessary to know about the penetration of oxygen into the plastic material in the course of time. Therefore the oxygen permeability of two thermoset plastics (made from two unsaturated polyester resin thermosetting moulding compounds) was measured in the temperature range 20–60°C. For the Typ 802, the following data were generated at 23°C: permeability coefficient P=3.08 × 10 -15cm 3·cm⧸cm 2·s·Pa, diffusion coefficient D=1.03×10 -8cm 2⧸s, solubility coefficient S=3.00×10 -7cm 3⧸cm 3·Pa. The permeability of two thermoset phenol-formaldehyde plastics and one melamine-formaldehyde plastic was found to be immeasurably small, i.e. P<3×10 -17cm 3·cm⧸ cm 2· s·,Pa at 60°C. For discs of 4mm thickness made from the polyester plastics, oxygen concentration profiles were calculated which are built up in the course of time during storage in air at 23°C. For both other materials the profiles were estimated by assuming P=3×10 -17 at 60°C and the activation energy and the solubility being the same as in the case of polyester plastics.

Oxygen semipermeable solid oxide membrane composites prepared by electrochemical vapor deposition

Ceramic membrane composites consisting of a coarse porous α-alumina or two-layer porous alumina membrane support and an oxygen semipermeable gas tight thin (0.2–5 μm) yttria stabilized zirconia (YSZ) film are prepared by the electrochemical vapor deposition (EVD) method. The minimum gas-tight thickness of the YSZ films depends strongly on the average pore size of the support on which the films are deposited by the EVD process. The oxygen permeation fluxes through such gas tight YSZ membrane composites, measured in situ on the EVD apparatus, are in the range of 3 × 10 −9 to 6 × 10 −8 mol/cm 2-sec with an oxygen partial pressures of P′ O 2 (high) ≈ 3 × 10 −2 atm and P″ O 2 (low) ≈ 10 −5 atm, much larger than the literature data for thicker YSZ pellets. During the oxygen permeation experiments the rate-limiting step is found to be the bulk electrochemical transport in the grown YSZ films with a thickness smaller than 10 μm.

Photoaddition of maleic anhydride to unsaturated polymers in homogeneous solution, solid polymer–solution, and solid polymer–vapor systems

AbstractPhotoreactions of maleic anhydride (MAH) with unsaturated olefinic polymers such as 1,2‐polybutadiene, 1,4‐polybutadiene, block copolymer of styrene and butadiene, polystyrene, poly(styrene‐co‐isoprene), and poly(styrene‐alt‐methyl methacrylate) were investigated in air. When the polymers have olefinic unsaturation, the addition of MAH to the polymers in homogeneous solutions proceeded efficiently by a chain mechanism, and the quantum yield of the photoaddition of MAH was greater than unity under irradiation at λ &gt; 310 nm. From the effects of solvent and photosensitizer, a radical chain mechanism involving crosslinking of the polymers by MAH molecules was suggested. Together with the spectroscopic results, the reaction mechanism was discussed. The photoaddition reaction was then applied to the surface photomodification of polymer films. Photoreactions were conducted at the interphase between solid polymer and acetone solution of MAH and also at the interphase between solid polymer and gaseous MAH. Irradiation by a 300‐W high‐pressure mercury lamp could bring about considerable modification of the surface properties of the polymers, which then show improved wettability and dyeability. From the oxygen permeation experiments, the present interfacial phototreatment was shown to provide a double‐layered polymer film in which one side of the film is polar and hydrophilic while the other side is nonpolar and hydrophobic.