共查询到20条相似文献,搜索用时 0 毫秒
1.
Chuangang Fan Wei Liu Zengqiang Deng Yanbo Zuo Chusheng Chen Dongsik Bae 《Journal of membrane science》2007,290(1-2):73-77
In this article, the phase compositions, thermal, mechanical and transport properties of both the SrCo0.8Fe0.2O3−δ (SCF) and the SrCo0.8Fe0.1Sn0.1O3−δ (SSCF) ceramic membranes were investigated systematically. As compared with the SCF membrane, the SSCF one had a more promoted thermal shock resistance, which related to its small thermal expansion coefficient between them and an enhanced composite structure for it. For the SCF membrane, a permeation rate of 1.9 × 10−6 mol cm−2 s−1 was obtained at 1000 °C and under the oxygen partial pressure gradient of PO2 (h)/PO2 (l) = 0.209 atm/0.012 atm; however, the permeation rate was 2.5 × 10−6 mol cm−2 s−1 for the SSCF one in the same measuring condition. In addition, both peak values of total electrical conductivity (σe) for SSCF sample appeared with increasing temperature. The second peak value of σe for SSCF one was regarded as the contribution from its minor phase, which appeared with the mixed conducting behavior resulting from partly Co-dissolving into its lattice. 相似文献
2.
Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) hollow fibers were fabricated using a phase inversion/sintering method. As oxygen permeation of BSCF hollow fibers is controlled by the rate surface exchange kinetics, catalytic Ag particles were coated on both inner and outer surfaces using chemical deposition method, as verified by SEM and EDX. The Ag coated BSCF membranes showed up to 100% increase in oxygen permeation at 700 °C, and improvements lower than 10% were measured at 950 °C as compared with unmodified membranes. It was found that Ag catalyst surface loading was non-homogenous and concentrated on the perovskite grain boundaries. As a result, lighter Ag surface loading delivered improved oxygen flux while oxygen flux reached a maximum even though in the presence of excess catalyst loading. The catalytic activity of Ag was beneficial in enhancing surface reaction kinetics up to 850 °C attributed to the spillover effect. Above this temperature, the increase in oxygen permeation rate was marginally diminished due to the reduction of the spillover effect. 相似文献
3.
A phase-inversion/sintering technique has been employed in the production of La0.6Sr0.4Co0.2Fe0.8O3−α (LSCF) hollow fibre membranes, a bundle of which has then been placed in a high-temperature furnace for production of high purity oxygen from air at temperatures between 980 °C and 1060 °C. By applying a vacuum in the hollow fibre lumens, a product stream containing oxygen purity of 97.15% has been obtained. The downstream vacuum degree higher than 99 kPa shows negligible effect on the oxygen production rate. Studies on long-term operation suggest that the LSCF hollow fibre membranes are less stable for the oxygen production due to the segregation of the constituent membrane elements and the formation of new phases on the outer membrane surfaces. The effect of the operating cycle on the retrogression of membrane performance is much larger than that of duration used in a single cycle. 相似文献
4.
Dense tubular Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCFO) membranes were successfully prepared by the plastic extrusion method. The oxygen permeation flux was determined at different oxygen partial pressures in the shell side and different temperatures between 700 and 900 °C. The oxygen vacancy diffusion coefficients (Dv) at different temperatures were calculated from the dependence of oxygen permeation flux on the oxygen partial pressure term based on the surface current exchange model. No unsteady-state of oxygen permeation flux was observed at the initial stage in our experiments. The reason is the equilibrium time is too short (less than 10 min) to observe the unsteady-state in time. The increase of the helium flow rate can increase the oxygen permeation flux, which is due to the decrease of the oxygen partial pressure in the tube side with increasing of the helium flow rate. The oxygen permeation flux can also be affected by the air flow rate in the shell side when the air flow rate is lower than 150 ml/min. But the oxygen permeation flux is insensitive to the air flow rate when the air flow is higher than 150 ml/min. The membrane tube was operated steadily for 150 h with oxygen permeation flux of 1.12 ml/(cm2 min) at 875 °C. X-ray diffraction (XRD) and energy dispersive spectroscopy (EDS) analysis showed that both the surface exposed to air and the surface exposed to helium of the BSCFO membrane tube after permeation for 150 h are similar to the fresh membrane tube in composition and structure. These results indicated that the membrane tube exhibits high structure stability. 相似文献
5.
Jung-Min Kim Gab-Jin Hwang Sang-Ho Lee Chu-Sik Park Jong-Won Kim Young-Ho Kim 《Journal of membrane science》2005,250(1-2):11-16
The oxygen separation membrane having perovskite structure for the partial oxidation of methane to synthesis gas was prepared. La0.7Sr0.3Ga0.6Fe0.4O3−δ (LSGF) perovskite membrane coated with La0.6Sr0.4CoO3−δ (LSC) (M1), and the one side of M1 membrane coated with NiO (M2) was prepared to examine the partial oxidation of methane. The single oxygen permeations of the LSC + LSGF (M1) membrane and NiO coated membrane (M2) were measured. The oxygen permeation flux in M1 membrane was higher than that of M1 membrane at 850 °C.
The partial oxidation experiment of methane using the prepared membranes was examined at 850 °C. The value of CH4 conversion and CO selectivity of M2 membrane was higher than that of M1 membrane.
NiO/NiAl2O4 catalyst was used to improve the methane conversion, and the partial oxidation experiment of methane with M1 membrane was examined at 850 °C. The CH4 conversion was 88%, and CO selectivity was 100%. 相似文献
6.
Jianxin Yi Yanbo Zuo Wei Liu Louis Winnubst Chusheng Chen 《Journal of membrane science》2006,280(1-2):849-855
A composite of oxygen ion conducting oxide Ce0.8Sm0.2O2−δ (60 vol.%) and electron conducting oxide La0.8Sr0.2CrO3−δ was prepared by sintering a powder compact at a temperature of 1550 °C. No significant reaction between the two constituent oxides was observed under preparation and oxygen permeation conditions. Appreciable oxygen permeation fluxes through the composite membrane were measured at elevated temperatures with one side of it exposed to the ambient air and the other side to a flowing helium gas stream. The oxygen flux initially increased with time, and took a long time to reach a steady value. A steady oxygen permeation flux as high as 1.4 × 10−7 mol cm−2 s−1 was obtained with a 0.3 mm thick membrane at 950 °C under a relatively small oxygen partial pressure difference of 0.21 bar/0.0092 bar. It was revealed that the overall oxygen permeation process was mainly limited by the transport in the bulk of the membrane in the range of the membrane thickness greater than 1.0 mm, and the limitation by the surface oxygen exchange came into play at reduced thickness of 0.6 mm. 相似文献
7.
A synthetic route for advanced perovskites is elucidated that consists of a combined EDTA/citrate complexing of metal cations and the subsequent drying and firing at moderate temperatures. A fine-scale intermixing of cations is maintained during all the processing steps. The perovskite-type oxide is formed already in an intermediate step at 700 °C by the reaction of an ultra-finely dispersed powder consisting of a mixed barium–strontium carbonate, a zinc–iron spinel, and zinc oxide. The process yields powders of good sinterability and finally dense ceramics composed of stoichiometric perovskite grains of the type (Ba,Sr)(Zn,Fe)O3−δ. 相似文献
8.
The phase diagram of the SrCo0.8Fe0.2O3−δ compound has been determined at high temperatures (823?T?1223 K) and in the oxygen partial pressure range (10−5?pO2?1 atm) by thermogravimetric measurements of the equilibrium pO2, high temperature X-ray diffraction and electrical conductivity measurements. The cubic perovskite phase SrCo0.8Fe0.2O3−δ is stable in a broad range of oxygen content, while the orthorhombic brownmillerite phase SrCo0.8Fe0.2O2.5 stabilizes within a small range around 3−δ=2.5 at temperatures below 1073 K. Equilibrium pO2 measurements under isothermal conditions show chemical hysteresis at the perovskite to brownmillerite transition. The hysteresis loop decreases its amplitude in pO2 with decreasing temperature. This behavior is discussed considering the evolution from coherent intergrowth interfaces with elastic strain energy to incoherent interfaces without elastic strain energy as T decreases. The thermodynamic quantities hO2oxide and sO2oxide for the perovskite phase decrease when increasing the oxygen defects concentration. The electrical conductivity (σ) of the cubic phase exhibits a thermally activated behavior at high temperature. The variation of σ with the oxygen content is non-linear and the activation energy varies from 0.4 to 0.28 eV as the oxygen content increases from 2.4 to 2.6. These results are interpreted in the frame of the small polaron model. 相似文献
9.
V. Tikhonovich E. Naumovich D. Logvinovich V. Kharton A. Vecher 《Journal of Solid State Electrochemistry》2003,7(2):77-82
Oxygen-deficient phases based on perovskite-like strontium cobaltites-ferrites are promising mixed conductors for high-temperature
electrochemical applications. The p(O2)-T-δ diagrams for the oxide systems SrCo1–
x
–
y
Fe
x
Cr
y
O3–
δ (x=0.10–0.40; y=0–0.05) were studied at 500–1000 °C in the oxygen pressure range from 10–5 to 0.21 atm using the coulometric titration technique and thermogravimetric analysis. Stability limits of the cubic perovskite
phases having a high oxygen ionic conductivity were evaluated as functions of temperature, oxygen partial pressure and oxygen
nonstoichiometry. It was found that doping with chromium and increasing the iron content in SrCo(Fe,Cr)O3–
δ both lead to a considerable enlargement of the cubic perovskite phase existence domain towards lower temperatures and reduced
oxygen pressures.
Electronic Publication 相似文献
10.
Mingya Cai Song Liu Konstantin Efimov Jürgen Caro Armin Feldhoff Haihui Wang 《Journal of membrane science》2009,343(1-2):90-96
A mixed proton–electron conducting perovskite made of BaCe0.95Nd0.05O3−δ (BCN) was prepared by EDTA/citric acid complexing method. The precursor was characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction (XRD). In order to learn the perovskite formation process during the calcination, the intermediate, i.e. the sample calcined at 750 °C for 5 h, was investigated by scanning (STEM), energy-filtered (EFTEM), and high-resolution transmission electron microscopy (HRTEM) as well as electron energy-loss spectroscopy (EELS). The results revealed that the perovskite structure was formed via a solid-state reaction between barium–cerium mixed carbonate and cerium–neodymium mixed oxide particles. Dense mixed proton–electron conducting BCN membranes were made by pressing BCN powder followed by sintering. The microstructure of the sintered membranes was investigated by scanning electron microscopy (SEM). Hydrogen permeation through the BCN membrane was studied using a high-temperature permeator. The hydrogen permeation fluxes under wet conditions are higher than those under dry conditions, which is due to increased proton concentrations in the H+ hopping via OH groups. The hydrogen permeation increased with increasing hydrogen and steam concentrations in the feed. For a steam concentration of 15 vol.%, the hydrogen permeation flux reaches 0.026 ml/min cm2. 相似文献
11.
12.
Francesco Bozza Riccardo Polini Enrico Traversa 《Electrochemistry communications》2009,11(8):1680-1683
Remarkable power density was obtained for anode-supported solid oxide fuel cells (SOFCs) based on La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte films, fabricated following an original procedure that allowed avoiding undesired reactions between LSGM and electrode materials, especially Ni. Electrophoretic deposition (EPD) was used for the fabrication of 30 μm-thick electrolyte films. Anode supports were made of La0.4Ce0.6O2−x (LDC). The LSGM powder was deposited by EPD on an LDC green tape-cast membrane added with carbon powder, both as pore former and substrate conductivity booster. A subsequent co-firing step at 1490 °C produced dense electrolyte films on porous LDC skeletons. Then, a La0.8Sr0.2Fe0.8Co0.2O3−δ (LSFC) cathode was applied by slurry-coating and calcined at 1100 °C. Finally, the porous LDC layer was impregnated with molten Ni nitrate to obtain, after calcination at 900 °C, a composite NiO–LDC anode. Maximum power densities of 780, 450, 275, 175, and 100 mW/cm2 at 700, 650, 600, 550, and 500 °C, respectively, were obtained using H2 as fuel and air as oxidant, demonstrating the success of the processing strategy. As a comparison, electrolyte-supported SOFCs made of the same materials were tested, showing a maximum power density of 150 mW/cm2 at 700 °C, more than 5 times smaller than the anode-supported counterpart. 相似文献
13.
采用溶胶-凝胶法制备了La0.7Sr0.3Co0.8Fe0.2O3钙钛矿催化剂,考察了还原剂种类(CO,C3H6,H2)对催化剂在氮氧化物储存还原(NSR)循环前后的氮氧化物储存量(NSC)和NO-to-NO2转化率的影响.O2程序升温脱附(O2-TPD)实验结果表明,CO还原后的钙钛矿催化剂上形成了较多的氧空位,而氧空位则是一种有效的NOx储存活性中心.活性测试和傅里叶红外变换(FTIR)光谱表征结果显示:在NSR循环中,以CO为还原剂时催化剂显示了最佳的氮氧化物(NOx)储存效果.进一步的研究结果显示,当采用CO作为还原剂时,经过三次NSR循环后,催化剂中出现了Sr3Fe2O7新物相,而该物相可能具有比La0.7Sr0.3Co0.8Fe0.2O3钙钛矿更佳的NOx储存性能.综上所述,CO作为还原剂时可能使钙钛矿催化剂产生更多的氧空位以及更易于储存NOx的Sr3Fe2O7物相,这些原因使其NOx储存性能得到了大幅度改善. 相似文献
14.
The growth of REBa2Cu3O7−δ (REBCO = rare earth elements) high-temperature superconducting thick films by liquid phase epitaxy is reviewed, which are most promising for electronic device and coated conductor applications. The paper focused on thermodynamic relations, chemical reactions and physical phenomena in the liquid phase epitaxy process, which are closely related to the control of the microstructures and properties of materials. Recent progresses achieved and the problems to be solved have been reviewed in above sections. 相似文献
15.
La0.8Sr0.2Fe1-xScxO3-δ催化剂的制备、表征及甲烷催化燃烧性能 总被引:1,自引:0,他引:1
采用甘氨酸-硝酸盐溶液燃烧法制备了钙钛矿型氧化物催化剂La0.8Sr0.2Fe1-xScxO3-δ (LSFS, x=0, 0.3,0.4, 0.5, 0.6, 0.8, 1), 利用X射线衍射(XRD)、H2程序升温还原(H2-TPR)、扫描电子显微镜(SEM)和比表面积测试等手段对催化剂进行了系统表征, 并在常压微型固定床反应器上考察了催化剂对甲烷燃烧的催化性能. 结果表明, 经空气气氛下900 °C煅烧5 h制备的LSFS均具有单一的钙钛矿结构, 在La0.8Sr0.2FeO3-δ (LSF)中掺杂Sc有助于改善催化剂的抗烧结性能, 提高催化剂的比表面积. 当LSF 中的Sc 掺杂量为0.4-0.6 时, 所形成的LSFS表现出良好的甲烷催化燃烧活性, 其中Sc 掺杂量为0.5 时, 其起燃温度(T10)和完全转化温度(T90)分别为406和563 °C, 与La0.8Sr0.2FeO3-δ和La0.8Sr0.2ScO3-δ相比, T10分别降低了14和87 °C; T90分别降低了59和95 °C. 相似文献
16.
Wenhui Yuan Xiaofang Hu Li Li College of Chemical Engineering Energy South China University of Technology Guangdong Key Laboratory of Green Chemicals Guangzhou China 《天然气化学杂志》2006,15(1):58-62
Single-phase perovskite La0.6Sr0.4Co0.8Fe0.2O3-δ has been successfully prepared by using citrate-EDTA complexation method at relatively low calcination temperature. The structure and thermal decomposition process of the complex precursor have been investigated by means of differential scanning calorimetry-thermal gravimetric analysis (DSC/TGA), X-ray diffraction (XRD), and Fourier transform infrared spectroscopic (FT-IR) measurements. The precursor decomposed completely and started to form perovskite-type oxide above 420℃ according to the differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) results. Single-phase perovskite La0.6Sr0.4Co0.8Fe0.2O3-δ obtained has been confirmed from the XRD pattern, and no peak of SrCO3 was found by XR.D of the oxides synthesized at a relatively low temperature of 800 ℃. The reducibility of La0.6Sr0.4Co0.8Fe0.2O3-δ was also characterized by the temperature programmed reduction (TPR) technique. Disk shaped dense La0.6Sr0.4Co0.8Fe0.2O3-δ membrane was prepared by the isostatical pressing method. The oxygen flux rate of dense La0.6Sr0.4Co0.8Fe0.2O3-δ membrane was (2.8-18)×10-8 mol/(cm2·s) in the temperature range of 800-1 000℃. 相似文献
17.
Yegang Lu Sannian Song Zhitang Song Wanchun Ren Cheng Peng Yan Cheng Bo Liu 《Solid State Sciences》2011,13(11):1943-1947
The phase change characteristics of HfO2 doping on GeTe thin films were investigated by X-ray photoelectron spectroscopy, X-ray diffraction patterns, scanning electron microscope, atom force microscopy, and in situ resistance-temperature measurements. It is shown that the crystallization of amorphous GeTe film could be suppressed by the incorporation of HfO2, which had a favorable effect on the archival life stability. The activation energy for crystallization increased from 2.36 to 4.69 eV, and the temperature for 10 years data retention increased from 108 to 187 °C with the increasing concentration of HfO2 form 0 to 12 mol%. Meanwhile, the grain size and surface roughness decreased. Phase change memory based on GeTe–HfO2 film was fabricated and characterized. A reversible phase change could be trigged by the pulse with at least 100 ns width which was shorter than that of Ge2Sb2Te5 (500 ns). The resistance ratio between amorphous and crystalline states achieved 500 times. The minimum energy necessary for RESET operation of GeTe–HfO2 based test cell was much smaller than that of Ge2Sb2Te5-based one. 相似文献
18.
The magnetic and electric transport properties of La1−xBaxCoO3 (0<x≤0.50) have been studied systematically. Two effects of substitution divalent ions on the spin-state transition of Co3+ have been differentiated for the substitution of Ba2+ for La3+ in La1−xBaxCoO3. The first is the transition from low-spin state to high-spin state due to lattice expansion, and the second is the transition from low-spin state to intermediate-spin state caused by the strong hybridization between ligand (oxygen) 2p and Co 3d orbital with introduction of holes in the oxygen 2p orbital. Based on the two different spin-state transition mechanisms and experimental results, a phase separation model has been developed and a very detailed magnetic and electric phase diagram of La1−xBaxCoO3 has been constructed. 相似文献
19.
The bulk superconducting YCa2Cu3O7−δ compounds are prepared at an ordinary pressure of oxygen by conventional solid-state reaction method. The formation of sample is tested by means of XRD and is studied for their ac susceptibility below room temperature up to 77.5 K. The samples are found single-phase orthorhombic structure and found superconducting at 83.5 K. It is shown that the analysis is consistent with published data on YBa2Cu3O7−δ oxide superconductor. 相似文献
20.
A sub-solidus phase evolution study was done in CeO2-Sc2O3 and CeO2-Lu2O3 systems under slow-cooled conditions from 1400 °C. Long-range order probing of X-ray diffraction technique is utilized in conjunction with the ability of Raman spectroscopy to detect the changes in local co-ordination. Lu2O3 showed solubility of 30 mol% in CeO2, thus forming an anion deficient fluorite-type (F-type) solid solution, whereas Sc2O3 did not show any discernible solubility. A biphasic region (F+C) was unequivocally detected by Raman spectroscopy in Ce1−xLuxO2−x/2 (0.4?x?0.9) and in Ce1−xScxO2−x/2 (0.1?x?0.9) systems. Raman spectroscopy was valuable in studying these systems since oxygen vacancies are created on doping RE2O3 into ceria and Raman spectroscopy is very much sensitive to oxygen polarizability and local coordination. Back scattered images collected on representative compositions support the above-mentioned results. 相似文献