Effect of dopant valence on the oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ （M -Ni,Al and Zr） mixed-conducting oxides

The effect of dopant valence on oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ （M = Ni, Al and Zr） mixed-conducting oxides were investigated in detail by O2-TPD and oxygen permeation measurement. The SrCo0.4Fe0.5M0.1O3-δ for M = Fe, Ni, Al and Zr were denoted as SCF, SCFN, SCFA and SCFZ, respectively. O2-TPD analysis revealed that the amount of α oxygen desorption decreased with increasing the valance of doped metal elements （SCFN 〉 SCFA SCF 〉 SCFZ）. The oxygen permeation flux at the temperature ≈igher than 1148 K decreased in the order of SCFN 〉 SCF 〉 SCFZ 〉 SCFA. Single activation for oxygen permeation was observed for SCFZ oxide and the activation energies of SCF and SCFA change at around 1073 K, while the change temoerature of SCFN was about 1173 K.     

Study of the oxygen permeability of ceramic membranes based on nonstoichiometric perovskites SrCo0.8–x Fe0.2W x O3–δ

The effect of the substitution of highly charged cations W⁶⁺ for Co³⁺/Co⁴⁺ cations in the SrCo_0.8Fe_0.2O_3–δ structure on the transport properties of new membrane materials has been studied.     

Effect of Transition Metals (Cu, Co and Fe) on the Autothermal Reforming of Methane over Ni/Ce0.2Zr0.1Al0.7Oδ Catalyst

The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1 Al0.7Oδcatalyst. The effects of transition metals on the catalytic properties of Ni/Ce0.2Zr0.1 Al0.7Oδautothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature, and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδwas found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1-xO2 solid solution were formed in the preparation process of catalysts. Strong interaction was found to exist between NiO and CexZr1-xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ.     

Remarkable dependence of electrochemical performance of SrCo0.8Fe0.2O(3-δ) on A-site nonstoichiometry

SrCo(0.8)Fe(0.2)O(3-δ) is a controversial material whether it is used as an oxygen permeable membrane or as a cathode of solid oxide fuel cells. In this paper, carefully synthesized powders of perovskite-type Sr(x)Co(0.8)Fe(0.2)O(3-δ) (x = 0.80-1.20) oxides are utilized to investigate the effect of A-site nonstoichiometry on their electrochemical performance. The electrical conductivity, sintering property and stability in ambient air of Sr(x)Co(0.8)Fe(0.2)O(3-δ) are critically dependent on the A-site nonstoichiometry. Sr(1.00)Co(0.8)Fe(0.2)O(3-δ) has a single-phase cubic perovskite structure, but a cobalt-iron oxide impurity appears in A-site cation deficient samples and Sr(3)(Co, Fe)(2)O(7-δ) appears when there is an A-site cation excess. It was found that the presence of the cobalt-iron oxide improves the electrochemical performance. However, Sr(3)(Co, Fe)(2)O(7-δ) has a significant negative influence on the electrochemical activity for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The peak power densities with a single-layer Sr(1.00)Co(0.8)Fe(0.2)O(3-δ) cathode are 275, 475, 749 and 962 mW cm(-2) at 550, 600, 650 and 700 °C, respectively, values which are slightly lower than those for Sr(0.95)Co(0.8)Fe(0.2)O(3-δ) (e.g. 1025 mW cm(-2) at 700 °C) but much higher than those for Sr(1.05)Co(0.8)Fe(0.2)O(3-δ) (e.g. only 371 mW cm(-2) at 700 °C). This remarkable dependence of electrochemical performance of the Sr(x)Co(0.8)Fe(0.2)O(3-δ) cathode on the A-site nonstoichiometry reveals that lower values of electrochemical activity reported in the literature may be induced by an A-site cation excess. Therefore, to obtain a high performance of Sr(x)Co(0.8)Fe(0.2)O(3-δ) cathode for IT-SOFCs, an A-site cation excess must be avoided.     

Effect of synthesis method on oxygen adsorption/desorption properties of La–Sr–Co–Fe–O perovskite-type oxide

There has been a growing interest in utilizing La–Sr–Co–Fe–O perovskite-type oxide for efficient high temperature oxygen adsorption applications and oxygen removal process. In this paper, we focus our attention on the analysis of the determinants of the synthesis methods of La_0.6Sr_0.4Co_0.2Fe_0.8O_3?δ (LSCF) powders for the oxygen adsorption/desorption applications. To this aim, LSCF powders were successfully synthesized by different synthesis routes using polymerized complex and citrate methods. The effects of synthesis methods on the structure, particle size, specific surface area, oxygen adsorption/desorption kinetics, and oxygen uptake capacities of LSCF perovskite-type oxides were investigated. The oxygen adsorption/desorption capacities and kinetics of the LSCF oxides increase with increasing (1) the temperature from 700 to 900 °C and (2) the surface area observed at a given temperature. Collectively, the experimental observations suggest that particle sizes may play an important role in oxygen uptake capacities and adsorption/desorption kinetics.     

Effect of hydrogen reduction temperature on the microstructure and magnetic properties of Fe–Ni powders

The effect of hydrogen reduction temperature on the properties of Fe–Ni powders was described. The mixed powders of Fe-oxide and NiO were prepared by chemical solution mixing of nitrates powders and calcination at 350 °C for 2 h in air. The calcined powders formed small agglomeration with an average particle size of 100 nm. The microstructure and magnetic properties were investigated by using X-ray diffractometry, thermogravimetry, differential thermal analyzer, and vibrating sample magnetometer. Microstructure and thermal analysis revealed that the Fe-oxide and NiO phase were changed to FeNi₃ phase in the temperature range of 245–310 °C, and by heat-up to 690 °C the FeNi₃ phase was transformed to γ-FeNi phase. The reduced powder at 350 °C showed saturation magnetization of 76.3 emu/g and coercivity of 205.5 Oe, while the reduced powders at 690 °C exhibited saturation magnetization of 84.0 emu/g and coercivity of 14.0 Oe. The change of magnetic properties was discussed by the observed microstructural features.

     

Sm0.5Sr0.5Co0.4M0.6O3 (M=Co,Mn, Fe)作为IT-SOFCs阴极的结构与性能

通过X射线衍射(XRD)、热重、热膨胀、电导率以及交流阻抗等测试方法, 研究了Sm0.5Sr0.5Co0.4M0.6O3(M=Co, Mn, Fe; 分别简写为SSCC, SSCM, SSCF)作为中低温固体氧化物燃料电池(IT-SOFCs)阴极的结构与性能. 研究表明, 固相法合成的Sm0.5Sr0.5Co0.4M0.6O3均为正交钙钛矿型结构, 材料的结构参数和性能都与M元素半径及M—O的键能有关. 晶胞参数随着Co、Mn、Fe的顺序增大.材料的氧空位浓度、热膨胀系数、电导率、电极催化活性随着Co、Fe、Mn的顺序降低. 同时由于SSCM较低的氧空位浓度, 使得电极反应受到氧在电极内的扩散过程控制, 具有较差的电极催化性能, 而SSCC和SSCF较高的氧空位浓度, 电极反应同时受到电极表面氧还原反应和氧离子在电极中的扩散过程混合控制. 由于SSCF具有较高的氧扩散系数, 使得700 ℃以上SSCF电极表面氧还原电阻(ASR)也低于SSCC的, 因而出现了SSCF的总电极催化活性高于SSCC的现象.     

Effect of nano-Al2O3 particles and of the Co concentration on the corrosion behavior of electrodeposited Ni–Co alloys

Incorporation of nano-Al₂O₃ particles into a Ni–Co alloy by electrodeposition influences the corrosion properties, morphology, and structure of the layers. The resistance against corrosion of Ni–Co/Al₂O₃ composite films deposited on stainless steel was investigated in a 0.1-M NaCl solution by potentiodynamic polarization. The presence of nanoparticles improves the corrosion resistance of Ni–Co/nano-Al₂O₃ deposits when compared to pure Ni–Co alloy. Moreover, by increasing the pH of the electrodeposition bath and the content of Co in the alloy, the resistance against corrosion is furthermore improved. The morphology of the deposits before and after their corrosion was analyzed by scanning electron microscopy. The presence of the embedded alumina particles in the Ni–Co alloys was one of the key factors that limited further propagation of corrosion on the metallic surface. Preferential corrosion attack, in the form of a pitting corrosion, was located mainly at the grain boundaries.     

BaCe0.5Zr0.4Y0.1O3-δ粉体的溶胶-凝胶法和高温固相法制备及性能表征

分别通过溶胶-凝胶法和高温固相反应法制备了BaCe0.5Zr0.4Y0.1O3-δ粉体.采用热重-差热分析(TG-DTA),粉末X射线衍射(XRD),扫描电子显微镜(SEM),傅立叶红外衍射(FT-IR),N2吸附-脱附等方法对所制备的粉体进行了表征.结果表明:用溶胶-凝胶法在1200 ℃×10 h可以合成纯的BaCe0.5Zr0.4Y0.1O3-δ粉体,合成温度比传统的高温固相反应法降低400 ℃左右;溶胶-凝胶法合成粉体具有多孔结构特征,与固相法合成粉体相比具有较高的比表面积.但致密化试验表明:溶胶-凝胶法合成粉体与固相法合成粉体相比具有较低的烧结活性.溶胶-凝胶法合成粉体颗粒表面残余的有机基团和颗粒内部的大量微孔将在致密化过程中产生空间位阻,从而影响高温下原子的迁移,阻碍材料的致密化过程.     

Preparation and Characterization of Single-Phase Perovskite La0.6Sr0.4Co0.8Fe0.2O3-δ

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℃.     

Effect of γ-irradiation and doping with MoO3 and V2O5 on surface and catalytic properties of manganese oxides

The effects of γ-irradiation (0.2–1.6 MGy), thermal treatment and doping with MoO₃ and V₂O₅ (0.25–4 mol%) on the surface and catalytic properties of manganese oxides prepared by thermal decomposition of manganese carbonate at 400°C and 600°C have been investigated. The techniques employed were X-ray diffraction, nitrogen adsorption at −196°C, oxidation of CO by O₂ at 120–220°C and decomposition of H₂O₂ at 20–50°C. The results revealed that γ-irradiation decreased the particle size of manganese oxides, increased their specific surface areas, decreased the amount of surface excess oxygen and decreased their catalytic activities. The doping with MoO₃ and V₂O₅ conducted at 600°C brought about a measurable decrease in the BET-surface area and catalytic activities of the treated solids. These results were discussed in terms of splitting of manganese oxide particles and removal of chemisorbed oxygen by treating with γ-irradiation and formation of manganese molybdate and vanadates by treating with the used dopant oxides.     

Effect of cobalt on the activity of dual phase “(Gd0.6Sr0.4)0.99Fe1-xCoxO3-δ” SOFC cathodes

Journal of Solid State Electrochemistry - The effect of the amount of cobalt in (Gd0.6Sr0.4)0.99Fe1-xCoxO3-δ solid oxide fuel cell (SOFC) cathodes (x = 0.00, 0.05, 0.10, 0.15, 0.20...     

Redox chemistry and magnetism of LaSrM(0.5)Ru(0.5)O(4±δ) (M = Co, Ni and Zn) Ruddlesden-Popper phases

The n = 1 Ruddlesden-Popper (RP) phases LaSrM(0.5)Ru(0.5)O(4±δ) (M = Co, Ni and Zn) have been prepared by solid state reactions and structurally characterized by powder X-ray and electron diffraction. All the samples adopt the tetragonal I4/mmm space group with random M and Ru cation occupation on the B-sites. The potential causes of no cation ordering are discussed. A combined analysis of the tolerance factors, the distortion of the octahedral coordination of M and Ru cations and the magnetic interactions between M and Ru cations provide a better understanding for forming a phase with 3D cation ordering on the B-sites in the n = 1 RP phases. The investigation of XPS spectra suggests that the transition element species exist as mixed ion pairs, Ru((4-δ)+)-Ru(4+)? Co(2+)-Co(3+) in LaSrCo(0.5)Ru(0.5)O(4), and Ru(4+)-Ru((4+δ)+)? Ni(+)-Ni(2+) in LaSrNi(0.5)Ru(0.5)O(4), which is consistent with cation disorder over the B sites. LaSrCo(0.5)Ru(0.5)O(4) shows a weakly ferromagnetic behaviour below 50 K; LaSrNi(0.5)Ru(0.5)O(4) is evidenced by the presence of long-range magnetic ordering at a Néel temperature of 125 K, and LaSrZn(0.5)Ru(0.5)O(4) exhibits a paramagnetic behaviour down to 5 K. Due to atomic disorder, Ru4d, O2p covalent coupling is weakened, strengthening the intraatomic spin-spin coupling among the π* electrons. Charge transfer between Ru and Co or Ru and Ni, as well as the increasing overlap of both nearest-neighbour and next-nearest-neighbour Ru 4d electrons due to atomic disorder, favour the formation of ferromagnetic interactions. Although antiferromagnetism is dominant, particularly in LaSrNi(0.5)Ru(0.5)O(4), ferromagnetic interactions are stronger in the title compounds than in the related La(2)MRuO(6) (M = Co, Ni) double perovskites where the B-site cations are ordered.     

Assessment of prospective cathodes based on (1-x)Ca3Co4O9+δ-xBaCe0.5Zr0.3Y0.1Yb0.1O3-δ composites for protonic ceramic electrochemical cells

Journal of Solid State Electrochemistry - This work presents investigation of novel composite electrodes comprising misfit layered oxide Ca3Co4O9+δ and protonic conductor...     

Influence of current collecting and functional layer thickness on the performance stability of La0.6Sr0.4Co0.2Fe0.8O3-δ-Ce0.8Sm0.2O1.9 composite cathode

Journal of Solid State Electrochemistry - The effect of current collecting layer (CCL) and cathode functional layer (CFL) thicknesses on the catalytic activity of the...     

Effect of oxygen deficit on the state of iron atoms and57Fe Mössbauer spectral parameters in YBa2(Cu1−xFex)3O6.0 by the results ofX α -DV calculations

The electronic structure of the clusters [Fe^mO_n]^m–2n, which model local structure defects arising in doping the tetragonal phase of yttrium-barium ceramics with iron atoms, has been calculated using the X-discrete variation (DV) method. According to the results of calculations of the hyperfine magnetic field and the quadrupole splitting of⁵⁷Fe Mössbauer spectra in YBa₂(Cu_1-xFe_x)₃O_6.0, the gamma resonance (GR) doublet with quadrupole splitting ||2 mm/s is most likely attributable to the Fe atoms localized in the Cu(1) position and having the valence 2+ and a dumbbell configuration of the nearest environment cluster.Institute of Solid State Chemistry, Ural Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 4, pp. 71–76, July–August, 1993.Translated by A. Sergeeva     

Effect of Substitution of Cobalt for Iron in Sr4Fe6O13-δon the Catalytic Activity for Methane Combustion

A series of mixed oxides Sr₄Fe_6?xCo_xO_13?δ (x=0, 1, 2, 3, or 4) were prepared by sol‐gel method and used for catalytic combustion of methane. The structural properties of oxides were characterized by XRD, TGA, and XPS. The layered intergrowth perovskite‐like oxide Sr₄Fe₅CoO_13?δ exhibits the highest catalytic activity for methane combustion under the experimental conditions. The enhanced catalytic activity of Sr₄Fe₅CoO_13?δ for methane combustion could be attributed to the increased amount of oxygen vacancy caused by the partial substitution of cobalt for iron in the Sr₄Fe₆O₁₃, which was confirmed by TGA and XPS.     

Effect of Fe2O3 as an accelerator on the reaction mechanism of Al–TiO2 nanothermite system

Thermite reactions between aluminum and metal oxides could lead to the formation of intermetallic matrix composites used in high-temperature industrial applications. Thermite reaction in Al–TiO₂ system needs a considerable amount of energy to take place by mechanochemical or by the combustion synthesis (CS) method due to the low amount of reaction enthalpy in Al–TiO₂ system. In this study, Fe₂O₃ was chosen as a accelerator for this system, to generate a high amount of heat which could be released between Fe₂O₃ and Al, leading to a more convenient reaction between Al and TiO₂ in the CS process. The results of XRD, SEM, and DSC analyses indicated that both the mechanical activation of Al–TiO₂ system in a high-energy ball mill and the Fe₂O₃ addition led to considerable effects of reduction in the reaction temperature and increase in the reaction intensity in Al–TiO₂ nanothermite system. Finally, it was shown that Fe₃Al intermetallic compounds as well as γ-AlTi and alumina phases in the final products were formed after the CS of the milled powders.