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1.
Anode substrate has a great effect on screen-printing fabrication of yttria-stabilized zirconia (YSZ) electrolyte film and cell performance. In this work, NiO+YSZ anode substrate was prepared by a conventional ceramic sintering method, on which dense YSZ electrolyte film was successfully fabricated by screen-printing method. Microstructure of the anode substrate and cell performance were investigated. The optimal amount of addition of starch to the anode substrate was 20 wt%. The optimal temperature for pre-sintering of NiO powder was 800 °C. A single cell with the NiO powder pre-sintered at 800 °C exhibited the highest power density of 0.95 W cm−2 at 700 °C.  相似文献   

2.
The combined influence of a two-step sintering (TSS) process and addition of V2O5 on the microstructure and magnetic properties of NiZn ferrite was investigated. As comparison, samples prepared by the conventional single-step sintering (SSS) procedure were also studied. It was found that with 0.3 wt% V2O5 additive, the sample sintered by the two-step sintering process at a high temperature of 1250 °C for 30 min and a lower temperature of 1180 °C for 3 h exhibited more homogeneous microstructure and higher permeability with a high Q-factor. The results showed that the TSS method with suitable additive brought positive improvement of the microstructure and magnetic properties of NiZn ferrite.  相似文献   

3.
The magnetic properties of 1.5 at% Fe-doped NiO bulk samples were investigated. The samples were prepared by sintering the corresponding precursor in air at temperatures between 400 and 800 °C for 6 h. The synthesis was by a chemical co-precipitation and post-thermal decomposition method. In order to allow a comparison, a NiO/0.76 at% NiFe2O4 mixture was also prepared. The X-ray diffraction pattern shows that the samples that were sintered at 400 and 600 °C remain single phase. As the sintering temperature increased to 800 °C, however, the sample becomes a mixture of NiO and NiFe2O4 ferrite phases. The samples were investigated by measuring their magnetization as a function of magnetic field. The samples sintered between 400 and 800 °C and the one mixed directly with NiFe2O4 nanoparticles show a coercivity value of Hc≈200, 325, 350 and 110 Oe, respectively. The magnetic properties of the samples depend strongly on the sintering temperature. Simultaneously, the field-cooling hysteresis loop shift also observed after cooling the sample sintered at 600 °C to low temperature suggests the possibility of the existence of a ferromagnetic/antiferromagnetic exchange coupling.  相似文献   

4.
We have studied sub-stoichiometric Ni-Cu-Zn ferrites with iron deficiency (i.e., <50mol% Fe2O3) of composition Ni0.20Cu0.20Zn0.60+zFe2−zO4−(z/2) with 0≤z≤0.06. The temperature of maximum shrinkage rate is shifted from T=1000 °C for z=0 towards lower temperatures down to T=900 °C for a sub-stoichiometric ferrite with z=0.02. Dense samples are obtained after firing at 900 °C for z>0 only. Sub-stoichiometric compositions (z>0) do not form single-phase spinel ferrites after sintering at 900 °C, but rather represent mixtures of CuO and a stoichiometric ferrite with slightly modified composition. The formation of small amounts of CuO at grain boundaries is demonstrated by XRD and SEM. The permeability is increased from μ=80 for stoichiometric ferrites (z=0) to μ=660 for z=0.02. The formation of CuO during sintering of sub-stoichiometric ferrites supports densification and is a prerequisite for low temperature firing of multilayer inductors. Addition of 1 wt% Bi2O3 as liquid phase sintering aid is required to provide sufficient densification of the stoichiometric ferrite (z=0) at 900 °C. Addition of 0.37 wt% Bi2O3 to a sub-stoichiometric ferrite (z=0.02) results in dense samples after firing at 900 °C; however, the microstructure formation is dominated by heterogeneous grain growth.  相似文献   

5.
The preparation, microstructure development and dielectric properties of Bi1.5ZnNb1.5O7 pyrochlore ceramics by metallo-organic decomposition (MOD) route are reported. Homogeneous precalcined ceramic powders of 13-36 nm crystallite size were obtained at temperatures ranging from 500 to 700 °C. The thermal decomposition/oxidation of the gelled precursor solution was chemically analyzed, TG/DTA, XRD, and SEM, led to the formation of a pure cubic pyrochlore phase with a stoichiometry close to Bi1.5ZnNb1.5O7 which begins to form at 500 °C. The metallo-organic precursor synthesis method, where Bi, Zn and Nb ions are chelated to form metal complexes, allows the control of Bi/Zn/Nb stoichiometric ratio on a molecular scale leading to the rapid formation of bismuth zinc niobate (Bi1.5ZnNb1.5O7) ceramic fine powders with pure pyrochlore structure. The powders were pressed into pellets and can be sintered at temperatures as low as 800-1000 °C. Fine crystalline ceramics with the grain size in the range of 200-500 nm have been obtained at the sintering temperature of 800 °C. The dielectric properties in high frequency to microwave range were measured and discussed.  相似文献   

6.
The effects of sintering temperature and Bi2O3 content on the microstructure and magnetic properties of lithium–zinc (LiZn) ferrites prepared by a conventional ceramic method were investigated. The results show that the densification behavior and grain growth rate were greatly improved by the addition of Bi2O3, because a liquid phase sintering occurred during the sintering process at high temperature due to the low-melting point of Bi2O3 (825 °C). X-ray diffraction (XRD) patterns of the slightly doped samples did not reveal the appearance of any phase other than spinel LiZn ferrite. However, the secondary phase of perovskite BiFeO3 was detected for Bi2O3 content of more than 0.25 wt%. The studies further show that Bi oxide was present at grain boundary, and promoted the grain growth as reaction center at lower temperature. A high saturation magnetization, squareness ratio, minimum ferromagnetic resonance linewidth and low coercive force were obtained for the sample with 1.00 wt% Bi2O additive at lower sintering temperature (1100 °C).  相似文献   

7.
We report a new synthesis route for preparation of single-domain barium hexaferrite (BaFe12O19) particles with high saturation magnetization. Nitric acid, known as a good oxidizer, is used as a mixing medium during the synthesis. It is shown that formation of BaFe12O19 phase starts at 800 °C, which is considerably lower than the typical ceramic process and develops with increasing temperature. Both magnetization measurements and scanning electron microscope micrographs reveal that the particles are single domain up to 1000 °C at which the highest coercive field of 3.6 kOe was obtained. The best saturation magnetization of ≈60 emu/g at 1.5 T was achieved by sintering for 2 h at 1200 °C. Annealing at temperatures higher than 1000 °C increased the saturation magnetization, on the other hand, decreased the coercive field which was due to the formation of multi-domain particles with larger grain sizes. It is shown that the best sintering to obtain fine particles of BaFe12O19 occurs at temperatures 900-1000 °C. Finally, magnetic interactions between the hard BaFe12O19 phase and impurity phases were investigated using the Stoner-Wohlfarth model.  相似文献   

8.
In3+ was used as dopant for BaZrO3 proton conductor and 30 at%-doped BaZrO3 samples (BaZr0.7In0.3O3-δ, BZI) were prepared as electrolyte materials for proton-conducting solid oxide fuel cells (SOFCs). The BZI material showed a much improved sinteractivity compared with the conventional Y-doped BaZrO3. The BZI pellets reached almost full density after sintering at 1600 °C for 10 h, whereas the Y-doped BaZrO3 samples still remained porous under the same sintering conditions. The conductivity measurements indicated that BZI pellets showed smaller bulk but improved grain boundary proton conductivity, when compared with Y-doped BaZrO3 samples. A total proton conductivity of 1.7 × 10−3 S cm−1 was obtained for the BZI sample at 700 °C in wet 10% H2 atmosphere. The BZI electrolyte material also showed adequate chemical stability against CO2 and H2O, which is promising for application in fuel cells.  相似文献   

9.
In order to estimate the phase stability and homogeneous range of BaZrO3, which is expected as a candidate electrolyte material for intermediate temperature solid oxide fuel cell, the phase relation in the BaO-ZrO2-YO1.5 systems has been examined at a typical processing temperature of 1600 °C. The stable existence of two cubic phases of BaZrO3, termed as BZ(I) and BZ(II), with different dopant concentration is observed above 1400 °C in the present study. The latter is of long-range ordered supercell with a wide range of solid solution between Ba3Zr2YO8.5 and Ba9Zr4Y8O29. Also observed is the presence of liquid phase at higher BaO concentration region above the ternary eutectic temperature that is estimated to be around 1300 °C, giving enormous effects to sintering process when Y3+ is overdoped beyond the solubility limit. From the present results, the pseudo-ternary phase diagram of BaO-ZrO2-YO1.5 of the isothermal section at 1600 °C is proposed.  相似文献   

10.
A direct carbon fuel cell offers a high efficiency alternative to traditional coal fired electrical power plants. In this paper, the electrochemical performance of electrolyte supported button cells with Gd2O3-doped CeO2 (CGO) electrolyte is reported over the temperature range 600 to 800 °C with solid carbon as a fuel and He/CO2 as the purge gases in the fuel chamber. The electrochemical characterisation of the cells was carried out by the Galvanostatic Current Interruption (GCI) technique and measuring V-I and P-I curves. Power densities over 50 mWcm-2 have been demonstrated using carbon black as the fuel. Results indicate that at low temperatures around 600 °C, the direct electrochemical oxidation of carbon takes place. However, at higher temperatures (800 °C) both direct electrochemical oxidation and the reverse Boudouard reaction take place leading to some loss in fuel cell thermodynamic efficiency and reduced fuel utilisation due to the in-situ production of CO. In order to avoid reverse Boudouard reaction whilst maximising performance, an operating temperature of around 700 °C appears optimal. Further, the electrochemical performance of fuel cells has been compared for graphite and carbon black fuels. It was found that graphitic carbon fuel is electrochemically less reactive than relatively amorphous carbon black fuel in the DCFC when tested under similar conditions.  相似文献   

11.
The effect of post sintering annealing on the dielectric response of (Pb1−xBax)(Yb0.5Ta0.5)O3 ceramics in the diffuse phase transition range (x=0.2) has been investigated. The samples are prepared by conventional solid-state reaction method. The samples are sintered at 1300 °C for 2 h and annealed at different temperatures (800, 900 and 1000 °C) for 8 h and at 800 °C for different time durations (8, 12 and 24 h). A significant change in the dielectric response has been observed in all the samples. The dielectric constant increases remarkably and the dielectric loss tangent decreases. The dielectric peaks of the annealed samples are observed to be more diffused with noticeable frequency dispersion compared to the as sintered sample.  相似文献   

12.
Mixed manganese-zinc and nickel-zinc ferrites of composition Mn0.2Ni0.8−xZnxFe2O4 where x=0.4x=0.4, 0.5 and 0.6 have been synthesized by the citrate precursor technique. Decomposition of the precursor at temperatures as low as 500 °C gives the ferrite powder. The ferrites have been investigated for their electrical and magnetic properties such as saturation magnetization, initial permeability, Curie temperature, AC-resistivity and dielectric constant as a function of sintering temperature and zinc content. Structural properties such as lattice parameter, grain size and density are also studied. The mixed compositions exhibited higher saturation magnetizations at sintering temperatures as low as 1200 °C. While the Curie temperature decreased with zinc content, the permeability was found to increase. The AC-resistivity ranged from 105–107 Ω cm and decreased with zinc content and sintering temperature. The dielectric constants were lower than those normally reported for the Mn–Zn ferrites. Samples sintered at 1400 °C densified to about 94% of the theoretical density and the grain size was of the order of about 1.5 μm for the samples sintered at 1200 °C and increased subsequently with sintering temperature.  相似文献   

13.
CoFe2O4/Fe3O4 nano-composite ceramics were synthesized by Spark Plasma Sintering. The X-ray diffraction patterns show that all samples are composed of CoFe2O4 and Fe3O4 phases when the sintering temperature is below 900 °C. It is found that the magnetic properties strongly depend on the sintering temperature. The two-step hysteresis loops for samples sintered below 500 °C are observed, but when sintering temperature reaches 500 °C, the step disappears, which indicates that the CoFe2O4 and Fe3O4 are well exchange coupled. As the sintering temperature increases from 500 to 800 °C, the results of X-ray diffractometer indicate the constriction of crystalline regions due to the ion diffusion at the interfaces of CoFe2O4/Fe3O4 phases, which have great impact on the magnetic properties.  相似文献   

14.
Room-temperature ferromagnetism (RTFM) is investigated in the polycrystalline bulk (ZnO)0.98(MnO2)0.02 samples prepared by a modified solid-state sintering route. Successive sintering of a sample was carried out in air at different temperatures in the range of 400-1000 °C. The study of magnetization and phase-investigation in the sample was carried out after each sintering step. The progressive suppression of impurities and the consequent reduction in RTFM is clearly observed in the samples with increase in the sintering temperature up to 800 °C. The subsequent successive sintering of the (ZnO)0.98(MnO2)0.02 sample up to 1000 °C yields fully paramagnetic sample exhibiting wurtzite structure. The studies support the conjecture (Kundaliya et al., Nat. Mater. 3 (2004) 709 [18]) that RTFM in this system has an origin related to a randomly distributed impurity phase produced by local dissolution of ZnO and MnO2.  相似文献   

15.
A series of iron- and/or aluminium-doped apatite-type lanthanum silicates (ATLS) La9.83Si6 ‐ x ‐ yAlxFeyO26 ± δ (x = 0, 0.25, 0.75, and 1.5, y = 0, 0.25, 0.75, and 1.5) were synthesized using the mechanochemical activation (MA), solid state reaction (SSR), Pechini (Pe) and sol-gel (SG) methods. The total conductivity of the prepared materials was measured under air in the temperature range 600-850 °C using 4-probe AC impedance spectroscopy. Its dependence on composition, synthesis method, sintering conditions and powder particle size was investigated. It was found that for electrolytes of the same composition, those prepared via mechanochemical activation exhibited the highest total specific conductivity, which was improved with increasing Al- and decreasing Fe-content. The highest conductivity value at 700 °C, equal to 2.04 × 10− 2 S cm− 1, was observed for the La9.83Si5Al0.75Fe0.25O26 ± δ electrolyte. La9.83Si4.5Fe1.5O26 ± δ electrolyte samples synthesized using the Pechini method exhibited higher conductivity when sintered conventionally than when spark-plasma sintering (SPS) was used.  相似文献   

16.
The effect of ZnO on phase emergence and microstructure properties of glass and glass-ceramics with composition 25SiO2-50CaO-15P2O5-(10 − x)Fe2O3-xZnO (where x = 0, 2, 5, 7 mol%) has been studied. They have been characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Surface modifications of these glass-ceramics in simulated body fluid have been studied using Fourier transform infrared reflection spectroscopy (FTIR), XPS and SEM. Results have shown a decrease in the fraction of non-bridging oxygen with increase in zinc oxide content. Emergence of crystalline phases in glass-ceramics at different heat treatment temperatures was studied using XRD. When glass is heat treated at 800 °C calcium phosphate, hematite and magnetite are developed as major phases in the glass-ceramics samples with ZnO up to 5 mol%. In addition to these, calcium silicate (Ca3Si2O7) phase is also observed when glass is heat treated at 1000 °C. The microstructure of the glass-ceramics heat treated at 800 °C exhibits the formation of nano-size (40-50 nm) grains. On heat treatment at 1000 °C crystallites grow to above 50 nm size and more than one phase are observed in the microstructure. The formation of thin flake-like structure with coarse particles is observed at high zinc oxide concentration (x = 7 mol%). In vitro studies have shown the surface modifications and formation of Ca-P-rich layer on the glass-ceramics when immersed in simulated body fluids (SBF) for different durations. The bioactive response was found to depend on ZnO content.  相似文献   

17.
Spherical-shaped Li4Ti5O12 anode powders with a mean size of 1.5 μm were prepared by spray pyrolysis. The precursor powders obtained by spray pyrolysis had no peaks of crystal structure of Li4Ti5O12. The powders post-treated at temperatures of 800 and 900 °C had the single phase of spinel Li4Ti5O12. The powders post-treated at a temperature of 1000 °C had main peaks of the Li4Ti5O12 phase and small impurity peaks of Li2Ti3O7. The spherical shape of the precursor powders was maintained after post-treatment at temperatures below 800 °C. The Brunauer-Emmett-Teller (BET) surface areas of the Li4Ti5O12 anode powders post-treated at temperatures of 700, 800 and 900 °C were 4.9, 1.6 and 1.5 m2/g, respectively. The initial discharge capacities of Li4Ti5O12 powders were changed from 108 to 175 mAh/g when the post-treatment temperatures were changed from 700 to 1000 °C. The maximum initial discharge capacity of the Li4Ti5O12 powders was obtained at a post-treatment temperature of 800 °C, which had good cycle properties below current densities of 0.7 C.  相似文献   

18.
YSr2Fe3O8 − δ was prepared by traditional solid state reaction method and characterized by X-ray diffraction, ac impedance, dc conductivity, dilatometry and thermogravimetric analysis for possible use in solid oxide fuel cells (SOFCs). YSr2Fe3O8 − δ crystallizes with tetragonal symmetry in the space group P4/mmm and found to be stable at high temperatures under H2 and air. Four probe dc electrical conductivity measurements show that the conductivity increases up to 745 K and then decreases with temperature; the highest conductivity σ745K = 43.5 S cm− 1. The n-type conductivity at low oxygen partial pressure (pO2) changes to p-type at high pO2. Polarization behavior was investigated measuring the ac impedance response in symmetrical cell arrangements in air with YSZ and GDC electrolytes. Cathodic area specific resistance (ASR) varies with firing temperature. The lowest area specific resistance was observed with a GDC electrolyte fired at 1000 °C. In case of YSZ, ASR increases and in case of GDC, ASR decreases in air when electrode firing temperature decreases. At 800 °C ASRs are 0.20 Ω cm2 and 0.65 Ω cm2 with GDC and YSZ electrolytes, respectively, in air. Fuel cell measurements with symmetrical electrodes were performed using a thin YSZ electrolyte under H2 at anode and air at cathode, show that the power density is about 0.035 W/cm2 at 900 °C.  相似文献   

19.
Preparation of LaNi1 − xFexO3, which is one of the candidate materials of solid oxide fuel cell cathode, current collecting layer and interconnect coating was examined with Pechini method and solid state reaction method. Single phase LaNi1 − xFexO3 with large Ni content has successfully been prepared by low temperature sintering as 750 °C with Pechini method, whereas large amount of raw materials has remained with solid state reaction method by sintering at the same temperature. It can be ascribed to more homogenous cation distribution in raw powder material prior to sintering with Pechini method. It has also been revealed that LaNi1 − xFexO3 with x lower than 0.3 is thermodynamically unstable in air above 1000 °C. LaNi0.6Fe0.4O3 showed superior property as cathode material with high electrical conductivity, thermodynamic stability and appropriate sintering property.  相似文献   

20.
The preparation of nano-sized BaCeO3 powder using starch as a polymerization agent is described herein. Phase evolution during the decomposition process of a (BaCe)-gel was monitored by XRD. A phase-pure nano-sized BaCeO3 powder was obtained after calcining of the (BaCe)-gel at 920 °C. The resulting powder has a specific surface area of 15.4 m2/g. TEM investigations reveal particles mainly in the size range of 30 to 65 nm. The shrinkage and sintering behavior of resulting powder compacts were studied in comparison to a coarse-grained mixed-oxide BaCeO3 powder (SBET = 2.1 m2/g). Dilatometric measurements show that the beginning of shrinkage of compacts from the nano-sized powder is downshifted by 300 °C compared to mixed-oxide powder. Compacts from the nano-sized powder reach a relative density of 91% after sintering at 1450 °C for 10 h.  相似文献   

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