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1.
The electronic conductivity of the nonstoichiometric potassium ferrite phase (with the β-alumina structure) has been measured as a function of temperature and potassium ion concentration. The latter was varied by coulometric titration using the cell: K 11q/K-β-alumina/K 1+xFe 11O 17. At 523°K the conductivity increased nearly linearly as x was increased from 0.09 to 0.65 while the activation energy for conduction decreased from 0.1 to 0.07 eV. The cell emf was completely reversible. The results are consistent with the view that the excess potassium ions are charge compensated by reduction of Fe 3+ to Fe 2+, and a comparison with results in the literature for some ironcontaining spinels suggests that a similar small polaron electron hopping mechanism operates. 相似文献
2.
We explore the new concept for a ceramics membrane reactor including the investigation of the nickel-based catalysts for methane conversion into synthesis gas and the exploitation of an oxide ionic and electronic mixed conductor. When Ca 0.8Sr 0.2Ti 1−xFe xO 3−α exhibiting the ionic and electronic mixed conduction was used as a support material of Ni based catalyst, coke formation over the catalyst under the methane conversion with air or carbon dioxide was strongly depended on the iron (III) ion contents, x. From the relationship between the amount of carbon deposited on the catalyst and the mixed conduction in support oxide materials, it was suggested that the self-migration of lattice oxygen inside the support regulated by the balance between the oxide ionic and electronic conductivities played an important role to prevent from accumulating the deposited carbon over the catalysts. In addition, we demonstrated the methane conversion into synthesis gas at 1173 K with one component ceramics membrane reactor constructed with the same type of perovskite-type oxide for both the catalyst supported and mixed conductor. 相似文献
3.
K-promoted hematite catalysts for ethylbenzene dehydrogenation were studied by thermal analysis (TG/DTG) and high-temperature
XRD. The formation of potassium ferrite (K 2Fe 2O 4), considered to be a catalytically active phase, was observed during calcination of the Ce-promoted catalysts. A linear correlation
of the catalytic activity and the temperature of potassium ferrites formation was found.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
4.
通过高温固相合成法首次合成了La 2Mo 1.8Ga 0.2O 9陶瓷样品. 粉末XRD结果表明, 该样品为单一立方相La 2Mo 2O 9结构. 以陶瓷样品为固体电解质、多孔性铂为电极, 采用交流阻抗谱、气体浓差电池、氧泵等方法研究了样品在600~1000 ℃下各种气氛中的离子导电特性. 结果表明, 氧浓差电池电动势的实测值与理论值吻合得很好, 氧离子迁移数为1, 表明该陶瓷样品在该温度下氧气气氛中为一纯氧离子导体; 氧泵(氧的电化学透过)实验结果进一步证实了该样品在氧气气氛中为一纯氧离子导体; 在氧分压 p(O 2)=10 -5~10 5 Pa的高氧分压气氛中, 电导率与氧分压变化基本无关, 表明在该氧分压范围内样品为纯离子导体, 这与氧浓差电池电动势测定结果相吻合; 在低氧分压为10 -5~10 -15 Pa范围内, 总电导率随氧分压降低而稍有升高, 表明在该氧分压范围样品为氧离子与电子的混合导体; 在600~1000 ℃下氧离子电导率>10 -2 S•cm -1, 显著高于母体La 2Mo 2O 9的氧离子电导率, 1000 ℃时的氧离子电导率为0.07 S•cm -1. 相似文献
5.
大洋锰结核又称铁锰结核、多金属结核,常见于4 000~6 000 m的海底沉积物表层,在世界各大洋底均有分布,预计总储量超过3×1012 t[1].天然锰结核含有Mn和Fe,以及Cu、Co、Ni、铂族和稀土等60多种金属元素,其中锰占20%~30%,铁约占3~20%[2].从化学成分而言,大洋锰结核与Mn-铁氧体(铁酸锰)十分接近.以锰结核为原料合成Mn-铁氧体可以为这种天然资源的开发利用提供新思路. 相似文献
6.
Zinc ferrite nanocomposite was synthesized via thermal decomposition of zinc acetate and iron nitrate at three different temperatures (350, 450, and 550 °C). The influence of the thermal decomposition of precursors on the formation zinc ferrites was studied by differential thermal gravimetry and thermogravimetry (TG). The TG curve shows two steps for the thermal decomposition with mass loss of 17.3 % at 78 °C and 63.3 % at 315 °C. The prepared zinc ferrites nanocomposite was characterized by X-ray diffraction and scanning electron microscopy. The X-ray diffractograms of ZnFe 2O 4 shows that a crystalline phase, spinel system is formed. SEM micrograph of the zinc ferrite nanocomposite indicates the formation of uniformly spherical 48-nm nanograins. The properties of the zinc ferrite phase were strongly dependent on their calcinations temperature and molar ratio of precursors. 相似文献
7.
高温固相反应合成了固体电解质Li9-nxM^n+xN2Cl3(M=Na、Mg、Al)。利用粉末X射线衍射测定样品结构,测定了离子电导率,分解电压和电子电导。得出掺杂可以提高快离子快离子导体材料Li9N2Cl3中的Li^+离子可以很大程度的提高其电导率。 相似文献
8.
In this work, the magneto-phase transitions in pure lithium (Li0.5Fe2.5O4), lithium–zinc (Li0.4Fe2.4Zn0.2O4) and lithium–titanium (Li0.6Fe2.2Ti0.2O4) ferrites were studied by the thermogravimetric analysis in magnetic field, which is known as the thermomagnetometry method. The ferrites were prepared by the solid-state synthesis from oxides and carbonates. The Curie point of magnetic phase in ferrites and their composite mixtures was determined from the derivative thermogravimetric curve in the region of ferrite mass change associated with the ferrimagnet–paramagnet transition in the magnetic phase. The method based on the analysis of ferrite mass change at Curie temperature was developed to estimate the ferrite phase concentrations in composite magnetic materials. 相似文献
9.
An enhancement of the electrical conductivity has been found in nano-grain sized Ce 0.9Gd 0.1O 2−δ ceramics when measured in N 2 ( pO2=3.5×10 −6 atm) in comparison with the most commonly accepted values of bulk ionic conductivity. We first present the synthesis and characterisation of the nanoparticles later used for the preparation of dense nanoceramics of Gd-doped CeO 2. The nanoparticles were characterised by X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The good sintering properties of these nanopowders allowed us to obtain very dense ceramics (>90% theoretical density) while keeping the grain size close to 100 nm. The microstructure of these nanoceramics was analysed by AFM and scanning electron microscopy (SEM) while the electrical characterisation was performed by the 4-point dc technique between 500 and 950 °C in air or N 2 and ac impedance between 150 and 400 °C in air and or argon. We briefly discuss the possibilities of electron vs. oxygen ion conduction and grain boundary vs. bulk conductivity. The features exhibited by these ceramics represent an increased potential to process solid electroceramics materials with specific levels of electronic and/or ionic conductivities for a variety of electrochemical devices. 相似文献
10.
Bi 2Al 4O 9 ceramics are difficult to sinter to greater than 80% theoretical density due to peritectic decomposition at 1,070 °C. A novel processing method is discussed where a high-bismuth oxide-based liquid is used as a sintering aid. After sintering, the high bismuth oxide phase is removed by leaching with 40% acetic acid. The resulting samples are phase pure and ∼91% dense. The grain size varies in a wide range with the average grain size of ∼1 μm. The electrical properties of these ceramics were measured as functions of temperature (550–850 °C) and oxygen partial pressure (6×10 −6–1 atm). The total conductivity was separated into electronic and ionic contributions. The low ionic conductivity indicates that the material is not an ‘intrinsically defective fast ion conductor’. The ionic conductivity is due almost exclusively to compensating oxygen vacancies related to impurities. With increasing temperature and decreasing oxygen partial pressure, the electronic conduction dominates over the ionic conduction. 相似文献
11.
Copper ferrite is a promising material for hydrogen production through thermochemical water splitting. In this work, the cation
distribution of copper ferrite and the corresponding oxygen-deficient compound of spinel structure was analyzed based on the
crystal structural chemistry theory. The mechanism of oxygen releasing of CuO, Fe 2O 3, CuFe 2O 4 and metal (M=Ni, Mn or Zn) doped copper ferrite in the process of temperature rising was investigated by differential thermal
analysis-thermogravimetry (DTA-TG). By combining the theoretical analysis with experimental results, the mechanism of oxygen
releasing of copper ferrite is proposed, which is different from that of other ferrites. For copper ferrite, the oxygen releasing
caused by Cu(II)→Cu(I) plays a predominant role, while for other ferrites, the oxygen releasing resulting from Fe(III)·Fe(II)
is dominant.
Supported by the National Defense Fundamental Research Fund (Grant No. A1420080145) 相似文献
12.
The synthesis of the Ni 0.5-xZn 0.5-xCu 2xFe 2O 4 (x = 0; 0.10 and 0.15) ferrite with the differential of pilot-scale production by the combustion reaction method was investigated for RAM application purposes. Combustion temperatures ranging from 682 °C to 738 °C were observed. All ferrites were sintered at 1200 °C for 1 h. A comprehensive study of the influence of substitution with Cu 2+ in a partial and proportional way to the Ni 2+ and Zn 2+ ions, doping mode little reported in the literature, and also of the sintering process over the structural, textural, morphological, magnetic and electromagnetic properties of NiZnCu ferrites was performed. The XRD patterns of the ferrites as synthesized revealed the formation of the cubic structure of the inverse spinel as majoritary phase, and traces of hematite and zinc oxide as segregated phases. After sintering, it was proven the single-phase formation of cubic spinel ferrite structure. The introduction of Cu led to a reduction in the lattice parameter, whose values ranged from 8.337 to 8.385 Å. The EDX results confirm the composition of oxides. The textural and morphological analyses confirmed the densest characteristic, with increase of particle size and reducing of surface area and pore volume after Cu-doping. All ferrites showed characteristics of soft ferrimagnetic material, where the increase in Cu content contributed to a slight reduction in saturation magnetization, whose values were of ~22–29 emu/g for the as synthesized ferrites and ~71–85 emu/g for the sintered ones. The best result of electromagnetic absorption in X-band was presented by the sintered ferrite with 0.3 mol of Cu, reaching an attenuation of 99.8% at 11.5 GHz frequency, thus confirming the efficiency of the pilot-scale combustion synthesis in obtaining a ferrite with great potential for RAM application. 相似文献
13.
The transport effect by means of HCl in the case of spinels Me 3O 4 and ferrites MeFe 2O 4 (equations see “Inhaltsübersicht”) between T 2 = 1000°C and T 1 = 800°C was experimentally investigated under so-called “standard conditions”. Transported crystals and residues were characterized by chemical analysis and the magnetic moment. For nickel ferrite, the effect of transport was calculated by the model of diffusion in dependence on total pressure and compared with experimental values. In the case of nickel and magnesium ferrite, transport starting from the basic oxides was also achieved. By measurements of the line width of ferromagnetic resonance the quality of the transported crystals of the last two ferrites has been checked. 相似文献
14.
The ionic conductivity of solid solution Cd 0.77Sr 0.23F 2 is 1.6 × 10 −4 S/cm at 500 K. The conduction mechanism changes from a vacancy mechanism to an interstitial one at 523–553 K. In solid solutions Cd 0.9R 0.1F 2.1 (R = La-Lu, Y), the activation enthalpy of conduction decreases from 0.9 to 0.8 eV with decreasing ionic radius of R 3+, raising the 500-K conductivity from 6 ×10 −6 S/cm for La 3+to 6 × 10 −5 S/cm for Lu 3+. For crystalline Cd 0.95In 0.05F 2.05, ionic and electronic conductivities at 313 K equal 5 × 10 −4 and 5 − 10 −6 S/cm.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 627–632.Original Russian Text Copyright © 2005 by Sorokin, Buchinskaya, Sul’yanova, Sobolev. 相似文献
15.
采用高温固相反应法制备了非化学计量组成的Ba1.03Ce0.8 Ho0.2O3-α 固体电解质,用XRD和SEM对其相组成和表面及断面形貌进行了表征。用气体浓差电池方法测定了材料在600~1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中的离子迁移数;用交流阻抗谱技术测定了它们在各实验气氛中的电导率。研究了材料的离子导电特性,并与BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α 的性能进行了比较。结果表明:该材料为单相钙钛矿型斜方晶结构。在600~1000 ℃温度范围内、干燥空气中,是氧离子与电子空穴的混合导体,氧离子迁移数为0.10~0.36;在湿润空气中,是质子、氧离子与电子空穴的混合导体,质子迁移数为0.11~0.01,氧离子迁移数为0.34~0.30;在湿润氢气气氛中,是纯质子导体,质子迁移数为1。在600~1000 ℃温度范围内,干燥空气、湿润空气和湿润氢气气氛中,非化学计量组成材料(x = 1.03,0.97)的电导率高于化学计量组成材料(x = 1)的电导率,其中,Ba1.03Ce0.8 Ho0.2O3-α的电导率最高 (1000 ℃时、在干燥空气气氛中:3.92×10-2 S·cm-1;在湿润空气气氛中:3.46×10-2 S·cm-1;在湿润氢气气氛中:2.10×10-2 S·cm-1)。Ba1.03Ce0.8 Ho0.2O3-α材料的离子导电性优于BaCe0.8Ho0.2O3-α 和Ba0.97Ce0.8Ho0.2O3-α。 相似文献
16.
The method of electrostatic spray pyrolysis was designed to apply protective coatings based on Mn-Co spinel to ferrite stainless steels (Crofer22APU and 08Kh18T1). The comparative thermogravimetric (TG) studies of ferrite stainless steels with and without protective coatings were carried out. The electrochemical characteristics of protective coatings exposed to long current loading were studied. The formation processes of Cr 2O 3 oxide films were studied at the contact of ferrite stainless steel with La 0.8Sr 0.2MnO 3 ionic and electronic conductor. The coatings of Mn-Co spinel were shown not preventing formation of continuous oxide film on the stainless steel surface. 相似文献
17.
Polymeric solid electrolytes which show bi-or single-ionic tunneling were prepared, and their unique ion conduction was applied for the design of some devices. Poly [(oligooxyethylene) methacrylatel] /MX hybrids and poly [(oligooxyethylene) methacrylate- co-methacrylic acid alkali metal salts] were prepared as typical models of those tunneling systems. These showed ionic conductivities above 10 ?5 and 10 ?7 S/cm at room temperature, respectively. An all-solid-state electrochromic display and a dry battery were prepared with these polymeric solid electrolytes. The all-solid-state electrochromic display showed excellent coloring and bleaching response by 1–3 V. The all-solid-state battery showed V oc = 3.1 V stability for over 2 weeks. Their characteristics as well as their mechanism are also reported. 相似文献
18.
Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10 −8 S cm −1) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li−Li symmetric cells with 30 times longer cycling life and Li−LiCoO 2 full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li−LiCoO 2 ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm −2. The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity. 相似文献
19.
The electrical conductivity of nominally pure K 2FeCl 5·H 2O and anhydrous K 2AlF 5 has been studied from 300 to 690°K. K 2FeCl 5·H 2O exhibits mixed ionic and electronic conduction, whereas K 2AlF 5 is a pure ionic conductor. The mass and charge transport processes in K 2FeCl 5·H 2O seem to be governed by deviations from both molecularity and stoichiometry. At elevated temperatures both potassium and chloride ions are mobile in K 2FeCl 5·H 2O. 相似文献
20.
Conditions were established and individual and mixed ferrites with the general formula Cu xZn 1?xFe 2O 4 ( x=0; 0.1; 0.2; 0.3; 0.4; 0.5; 0.6; 0.7; 0.8; 1.0) were synthesized from the CuO?ZnO?Fe 2O 3 system. X-ray phase analysis, Mössbauer spectroscopy and microscopic examinations revealed that the obtained ferrites are monophase samples. A magnetic device was attached to the Q-Derivatograph (MOM, Hungary) and successfully used for sample investigation in a magnetic field, and in particular for Curie (Neel) temperature determination. The ferrite composition and the thermal treatment conditions were shown to correlate with the Neel temperature of the synthesized ferrites. 相似文献
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