共查询到20条相似文献,搜索用时 31 毫秒
1.
《Ceramics International》2016,42(9):11239-11247
In this study, Cu and Mo ions were doped in Ca3Co4O9−δ to improve the electrical conductivity and electrochemical behavior of Ca3Co4O9−δ ceramic and the performance of a solid oxide fuel cell (SOFC) single cell based on NiO-SDC/SDC/doped Ca3Co4O9−δ-SDC were examined. Cu substitution in the monoclinic Ca3Co4O9−δ ceramic effectively enhanced the densification, slightly increased the grain size, and triggered the formation of some Ca3Co2O6; however, no second phase was found in porous Mo-doped Ca3Co4O9−δ ceramics even when the sintering temperature reached 1050 °C. Substitution of Cu ions caused slight increase in the Co3+ and Co4+ contents and decrease in the Co2+ content; however, doping with Mo ions showed the opposite trend. Doping the Ca3Co4O9−δ ceramic with a small amount of Cu or Mo increased its electrical conductivity. The maximum electrical conductivity measured was 218.8 S cm−1 for the Ca3Co3.9Cu0.1O9−δ ceramic at 800 °C. The Ca3Co3.9Cu0.1O9−δ ceramic with a coefficient of thermal expansion coefficient of 12.1×10−6 K−1 was chosen as the cathode to build SOFC single cells consisting of a 20 μm SDC electrolyte layer. Without optimizing the microstructure of the cathode or hermetically sealing the cell against the gas, a power density of 0.367 Wcm−2 at 750 °C was achieved, demonstrating that Cu-doped Ca3Co4O9−δ can be used as a potential cathode material for IT-SOFCs. 相似文献
2.
《Journal of the European Ceramic Society》2017,37(13):3909-3915
Highly porous Ca3Co4O9 thermoelectric oxide ceramics for high-temperature application were fabricated by sol–gel synthesis and subsequent conventional sintering. Growth mechanism of misfit-layered Ca3Co4O9 phase, from sol–gel synthesis educts and upcoming intermediates, was characterized by in-situ X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations. The Ca3Co4O9 ceramic exhibits a relative density of 67.7%. Thermoelectric properties were measured from 373 K to 1073 K. At 1073 K a power factor of 2.46 μW cm−1 K−2, a very low heat conductivity of 0.63 W m−1 K−1 and entropy conductivity of 0.61 mW m−1 K−2 were achieved. The maintained figure of merit ZT of 0.4 from sol–gel synthesized Ca3Co4O9 is the highest obtained from conventional, non-doped Ca3Co4O9. The high porosity and consequently reduced thermal conductivity leads to a high ZT value. 相似文献
3.
Yi-Cheng Liou Zong-Sian Tsai Kuan-Zong Fung Chi-Yang Liu 《Ceramics International》2010,36(6):1887-1892
Fabrication of Ni4Nb2O9 ceramics via a reaction-sintering process was investigated. A mixture of raw materials was sintered into ceramics by bypassing calcination and subsequent pulverization stages. Ni4Nb2O9 phase appeared at 1300 °C and increased with increasing soak time. Ni4Nb2O9 content was found >96% in 1350 °C/2 h sintering pellets. A density of 5.71 g/cm3 was obtained for pellets sintered at 1350 °C for 2 h. This reaches 96.5% of the theoretical density. As the sintering temperature increased to 1350 °C, an abnormal grain growth occurred and grains >100 μm could be found. ?r of 15.4–16.9 are found in pellets sintered at 1200–1300 °C. Q × f increased from 9380 GHz in pellets sintered at 1200 °C to 14,650 GHz in pellets sintered at 1250 °C. 相似文献
4.
《Ceramics International》2016,42(6):7315-7327
Single-phase Ca3Co4O9 with a high porosity, having a ZT of 0.09 at 627 °C, was successfully prepared by a simple solid-state reaction using fine powders of CaCO3 and Co3O4 after a calcination at 760 °C for 12 hours. It was excellent either for the preparation of the starting powder for the processing of the Ca3Co4O9 ceramics or for direct processing. The influence of already-reported processing methods (classic sintering, hot pressing, free-edge spark-plasma sintering (SPS) of a sintered pellet) and new methods, such as free-edge SPS of a pellet from just-compacted powder, cold pressing of a sintered pellet without post annealing, and free-edge cold pressing of a sintered pellet with post-annealing, on the preparation of Ca3Co4O9 ceramics was studied. The results showed how the density, the grain morphology and the microstructural anisotropy can all influence the thermoelectric characteristics of Ca3Co4O9 ceramics measured in directions parallel and perpendicular to the applied pressure. While the fully dense (99%) and perfectly textured ceramics prepared by the free-edge SPS of a pellet from just-compacted powder had a ZT of 0.17, the highest ZT of 0.31 was obtained for the free-edge cold-pressed and annealed ceramics with modest texturing and low density (65%), having a very low κ of 0.47 W/mK. The results also showed that thin and irregular-shaped plate-like grains with sharp edges are preferred, while their thickening accompanied by rounding of their shape resulted in a reduced thermoelectric performance. The study revealed both the possibilities and the limitations for enhancing the TE characteristics of Ca3Co4O9 ceramics just through microstructure optimisation. 相似文献
5.
《Ceramics International》2017,43(18):16159-16166
Small-sized Ca2.8-xBixDy0.2Co4O9+δ (0 ≤ x ≤ 0.1) powders with a plate-like morphology were synthesized via the citric acid-assisted sol-gel method. The structural and thermoelectric properties of Ca2.8-xBixDy0.2Co4O9 samples were studied with an emphasis placed on the Bi content and the fabrication process. The as-sintered Ca2.8-xBixDy0.2Co4O9 samples exhibited a single Ca3Co4O9+δ phase and a plate-like morphology. With increased Bi content, the grain size of the sintered Ca2.8-xBixDy0.2Co4O9 samples decreased, whereas the density of the sintered Ca2.8-xBixDy0.2Co4O9 samples increased. The incorporation of Bi up to x = 0.075 yielded high electrical conductivity. Meanwhile, the Seebeck coefficient decreased with increases in Bi content. The largest power factor (2.18 × 10−4 W m−1 K−2 at 800 °C) was obtained for the twice-sintered Ca2.725Bi0.075Dy0.2Co4O9. The partial substitution of Bi for Ca and the twice sintering were a highly effective route for improving the thermoelectric properties of Ca2.8Dy0.2Co4O9. 相似文献
6.
《Journal of the European Ceramic Society》2006,26(13):2845-2849
Low temperature sintering of iron deficient hexagonal Co2Z type ferrites is attempted to prepare a chip inductor for ultra high frequency uses. It should be attained below the melting point of silver (960 °C) used as the electrode material of the chip inductor. The best result is obtained for the sample with the composition 2.15Co0.6Cu0.4O·3Ba0.79Sr0.16Bi0.05O·9.725Fe2O3 sintered at 925 °C containing 0.5 wt.% of lithium bismuth oxide as a sintering additive. Its density and permeability reaches 5.0 g/cm3 and 7, respectively. As a result, the impedance of the chip inductor also reaches 390 ohm at 2 GHz using this material. 相似文献
7.
《Journal of the European Ceramic Society》2014,34(15):3715-3722
The properties of sputtering targets have recently been found to affect the performances of sputtered films and the sputtering process. To develop high-quality GZO ceramic targets, the influences of Ga2O3 content and sintering temperature on the sintering behavior, microstructure, and electrical properties of GZO ceramic targets were studied.The results showed that the increase in Ga2O3 content from 3 wt% (GZO-3Ga) and 5 wt% (GZO-5Ga) not only inhibited the densification but retarded grain growth. During sintering, ZnGa2O4 phase formed before 800 °C, and Zn9Ga2O12 phase was found after sintering at 1000 °C. Moreover, after sintering at 1200 °C, the number of Zn9Ga2O12 precipitates increased at the expense of ZnGa2O4 and ZnGa2O4 disappearing completely. The relative density, grain size, and resistivity of GZO-3Ga sintered at 1400 °C in air were 99.3%, 3.3 μm, and 2.8 × 10−3 Ω cm, respectively. These properties of GZO ceramics are comparable to properties reported in the literature for AZO sintered in air. 相似文献
8.
Thomas Schulz Timmy Reimann Arne Bochmann Andre Vogel Beate Capraro Björn Mieller Steffen Teichert Jörg Töpfer 《Journal of the European Ceramic Society》2018,38(4):1600-1607
The sintering behavior and the thermoelectric performance of Ca3Co4O9 multilayer laminates were studied, and a multilayer thermoelectric generator was fabricated. Compacts and multilayer samples with anisotropic microstructure and residual porosity were obtained after conventional sintering at 920 °C, whereas dense and isotropic multilayer samples were prepared by firing at 1200 °C and reoxidation at 900 °C. A hot-pressed sample has a dense and anisotropic microstructure. Samples sintered at 920 °C exhibit low electrical conductivity due to the low density, whereas the Seebeck coefficient is not sensitive to preparation conditions. However, thermal conductivity of multilayers is very low, and, hence acceptable ZT values are obtained. A transversal multilayer thermoelectric generator (TMLTEG) was fabricated by stacking layers of Ca3Co4O9 green tapes, AgPd conductor printing, and co-firing at 920 °C. The TMLTEG has a power output of 3 mW at ΔT = 200 K in the temperature interval of 25 °C to 300 °C. 相似文献
9.
《Journal of the European Ceramic Society》2005,25(7):1057-1065
The high sintering temperature required for aluminum nitride (AlN) at typically 1800 °C, is an impediment to its development as an engineering material. Spark plasma sintering (SPS) of AlN is carried out with samarium oxide (Sm2O3) as sintering additive at a sintering temperature as low as 1500–1600 °C. The effect of sintering temperature and SPS cycle on the microstructure and performance of AlN is studied. There appears to be a direct correlation between SPS temperature and number of repeated SPS sintering cycle per sample with the density of the final sintered sample. The addition of Sm2O3 as a sintering aid (1 and 3 wt.%) improves the properties and density of AlN noticeably. Thermal conductivity of AlN samples improves with increase in number of SPS cycle (maximum of 2) and sintering temperature (up to 1600 °C). Thermal conductivity is found to be greatly improved with the presence of Sm2O3 as sintering additive, with a thermal conductivity value about 118 W m−1 K−1) for the 3 wt.% Sm2O3-doped AlN sample SPS at 1500 °C for 3 min. Dielectric constant of the sintered AlN samples is dependent on the relative density of the samples. The number of repeated SPS cycle and sintering aid do not, however, cause significant elevation of the dielectric constant of the final sintered samples. Microstructures of the AlN samples show that, densification of AlN sample is effectively enhanced through increase in the operating SPS temperature and the employment of multiple SPS cycles. Addition of Sm2O3 greatly improves the densification of AlN sample while maintaining a fine grain structure. The Sm2O3 dopant modifies the microstructures to decidedly faceted AlN grains, resulting in the flattening of AlN–AlN grain contacts. 相似文献
10.
New morphological Ba0.5Sr0.5Co0.8Fe0.2O3−α hollow fibre membranes with high oxygen permeation fluxes
Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3?α (BSCF) hollow fibre membranes were fabricated by a combined phase inversion and sintering technique. The membranes were characterised by XRD, SEM and tested for air separation. The membrane possesses a novel morphology consisting of one dense layer and one porous layer. Oxygen permeation fluxes through the obtained hollow fibre membranes were measured in the temperature range 650–950 °C using helium sweep gas rates from 50 to 200 mL min?1. Experimental results indicated the oxygen permeation flux through the BSCF hollow fibre membrane sintered at 1050 °C was approximately 11.46 mL min?1 cm?2 at 950 °C when the helium sweep rate was kept at 200 mL min?1. The BSCF hollow fibre membrane showed a stable oxygen permeation flux of 8.60 mL min?1 cm?2 over the investigated period of 120 h at 900 °C. 相似文献
11.
Hiroyuki Miyazaki Kiyoshi Hirao Yu-ichi Yoshizawa 《Journal of the European Ceramic Society》2012,32(12):3297-3301
1 mol% of MgO was added together with 7 mol% of Yb2O3 as sintering additives to silicon nitride powder to fabricate advanced silicon nitride ceramics with both high thermal conductivity and low dielectric loss at 2 GHz. The mixed powder was CIPed at a pressure of 120 MPa and was gas-pressure sintered at 1900 °C to >98% of theoretical density. The sintered Si3N4 sample exhibited a high thermal conductivity of ~100 W m?1 K?1 and a loss tangent (tan δ) of ~4 × 10?4, concurrently. The tan δ was further reduced by half after the heat treatment at 1300 °C for 24 h. The improvement in tan δ due to the annealing was explained from the point of crystallization of the intergranular glassy phase. 相似文献
12.
M.A. Madre F.M. Costa N.M. Ferreira A. Sotelo M.A. Torres G. Constantinescu Sh. Rasekh J.C. Diez 《Journal of the European Ceramic Society》2013,33(10):1747-1754
High-performance Ca3Co4O9 thermoelectric ceramic has been prepared from a Ca1?xCoxO/CayCo1?yO divorced eutectic structure produced by a directional melt-grown using the laser floating zone technique. This material has been grown at very high solidification rate in order to produce a very fine microstructure to reduce the necessary annealing time to recover the Ca3Co4O9 thermoelectric phase as the major one. As-grown and annealed samples were microstructurally characterized to determine the phases and estimate the extent of Ca3Co4O9 formation with time and related with their thermoelectric performances. The optimum annealing time, 72 h, has been determined by the maximum power factor value (about 0.42 mW K?2m?1), which is around the best values reported in textured materials (~0.40 mW K?2m?1). This high power factor outcome from the high Ca3Co4O9 phase content, apparent density and Co3+/Co4+ relationship determinations performed in the present work. 相似文献
13.
《Ceramics International》2016,42(8):9482-9487
In this study, hybrid microwave sintering of Ca3Co4O9 thermoelectric materials was implemented for the first time. Thermoelectric properties of samples sintered in different conditions and in conventional electrical furnace, using the same temperatures and dwell times, were assessed and compared. Microwave processing was found to promote densification and grain texturing in Ca3Co4O9 bulk ceramics, leading to a significant increase of the electrical conductivity. Seebeck coefficient and thermal conductivity were essentially unaffected by the microstructural changes. Prolonged exposure to microwave radiation at 800 °C led to partial phase decomposition and consequent formation of Ca3Co2O6 and Co3O4 impurities, with minor effect on the charge transport. Still, the significant presence of residual porosity suggests the need for further optimization of powder and microwave processing conditions. 相似文献
14.
Darja Lisjak 《Journal of the European Ceramic Society》2012,32(12):3351-3360
The sintering of the M-type hexaferrites, AFe12O19 (A = Ba, Sr), was studied. The effects of the A cation type, the partial CuO substitution for Fe2O3 and the Fe deficiency on the sintering were examined. Samples with nominal compositions of Ba1?zSrzCuxFey?xO19?δ (z = 0 or 0.5, x = 0–1.0 and y = 11–12) were prepared with a solid-state reaction at 1000 °C. The CuO addition enhanced significantly the sintering rate of the hexaferrites at temperatures below 1100 °C, while a moderate effect on the sintering was caused by a partial substitution of Sr for Ba. The diffusion studies showed that the CuO addition enabled the reactive liquid-phase sintering of hexaferrites at 1000 °C. The relative sintered densities of the Cu-containing hexaferrite ceramics sintered at 1000 °C for 3 h were around 90%. The addition of CuO had a strong effect on the coercivity, but only a moderate effect on the magnetization of the studied ceramics. 相似文献
15.
Yike Zeng Fei Yao Guangzu Zhang Sisi Liu Shenglin Jiang Yan Yu Jungang He Ling Zhang Jinqiao Yi 《Ceramics International》2013,39(4):3709-3714
Pb(Zr0.9Ti0.1)O3 pyroelectric thick films adding various amounts of the sintering aids Bi2O3–Li2CO3 have been deposited on the substrates Al2O3 by the screen-printing process, and the dependence of microstructure, dielectric and pyroelectric properties on the content of sintering aids has been studied. When the amount of Bi2O3–Li2CO3 increases from 0 wt% to 5.4 wt%, the sintering temperature of the thick films decreases from 1100 °C to 900 °C, and the grain size and the lattice constant decrease either, but the density and the dielectric constant increase. The Pb(Zr0.9Ti0.1)O3 thick film with 5.4 wt% of Bi2O3–Li2CO3 sintered at 900 °C has the maximum pyroelectric coefficient 10.51×10?8 C/cm?2 K?1 and the highest figure-of-merit 10.58×10?5 Pa?0.5. 相似文献
16.
《Ceramics International》2017,43(18):16048-16054
Samples of SiC+10 vol%(Al2O3+Dy2O3) and SiC+10 vol%(Al2O3+Yb2O3) mixtures were obtained by cold isostatic pressing and sintered for one hour in a dilatometer at 1800 °C and 1900 °C, applying heating rates of 10, 20 and 30 °C/min. The results of the complete sintering cycle indicated that the heating rates do not significantly influence the shrinkage, but that temperature and total sintering time may be relevant factors. The compacts sintered at 1900 °C shrank on average 9% more than those sintered at 1800 °C, and it was found that the sintering time can be reduced by 40–50% at faster heating rates. The maximum shrinkage rates occurred at temperatures lower than those of the sintering thresholds for the two mixtures, two temperatures and three heating rates. It was also found that after formation of the liquid, the mechanisms of particle rearrangement and solution-precipitation were not as fast as reported in the literature, even at high heating rates, for example 30 °C/min, but they are responsible for much of the shrinkage occurring throughout the sintering cycle. 相似文献
17.
《Ceramics International》2017,43(12):9153-9157
Si3N4 based composites were successfully sintered by spark plasma sintering using low cost BaCO3, SiO2 and Al2O3 as additives. Powder mixtures were sintered at 1600–1800 °C for 5 and 10 min. Displacement-temperature-time (DTT) diagrams were used to evaluate the sintering behavior. Shrinkage curve revealed that densification was performed between 1100 and 1700 °C. The specimen sintered at 1700 °C showed the maximum relative density (99.8±0.1%), flexural strength (352±16 MPa), Vickers harness (11±0.1 GPa) and toughness (5.6±0.05 MPa m1/2). 相似文献
18.
《Ceramics International》2022,48(1):455-462
The calcium cobaltite Ca3-xLaxCo4-yCuyO9+δ with x and y = 0 and 0.1 were synthesized and the electrical, thermal, and catalytic behaviors for the oxygen reduction reaction (ORR) for use as air electrodes in intermediate-temperature solid oxide fuel cells (IT-SOFCs) were evaluated. X?ray diffraction confirms the Ca3-xLaxCo4-yCuyO9+δ samples were crystallized in a monoclinic structure and scanning electron microscopic image shows lamella-like grain formation. Introduction of dopants decreases slightly the loss of lattice oxygen and thermal expansion co-efficient. The Ca3-xLaxCo4-yCuyO9+δ samples exhibit good phase stability for long-term operation, thermal expansion, and chemical compatibility with the Ce0.8Gd0.2O2-δ electrolyte. Among the studied samples, Ca2.9La0.1Co4O9+δ shows a maximum conductivity of 176 Scm?1 at 800 °C. Although the doped samples exhibit a higher total electrical conductivity, an improved symmetrical cell performance is displayed by the undoped sample. Comparing the sintering temperatures, the composite cathode Ca3Co4O9+δ + Ce0.8Gd0.2O2-δ sintered at 800 °C exhibit the lowest area specific resistance of 0.154 Ω cm2 at 800 °C in air. In the Ca3-xLaxCo4-yCuyO9+δ + GDC composite cathodes, the charge-transfer process at high frequencies presents a major rate limiting step for the oxygen reduction reaction. 相似文献
19.
《Ceramics International》2017,43(18):16403-16407
In this paper, we have reported the signature of multiferroicity and pyroelectricity in BaFe12O19 hexaferrite close to room temperature. The BaFe12O19 hexaferrite samples are synthesized by co-precipitation method at different sintering temperature ranging from 800 to 1200 °C and study their structural, ferroelectric, magnetic, magnetoelectric and pyroelectric properties. X-ray Diffraction patterns show the pure phase formation for all samples. Morphological changes are examined through the scanning electron microscope. The maximum ferroelectric polarization (0.66 μC/cm2) is observed for the sample sintered at 1200 °C, however maximum magnetic polarization 74 emu/g is observed for sample sintered at 1000 °C. Magneto-electric coupling measurements are also performed through dynamic method and average magneto-electric coupling coefficient (~ 7.05 × 10−7 mV/cm Oe2) is observed at room temperature for the sample sintered at 1200 °C. Furthermore, maximum pyroelectric constant (147 × 10−13C/cm2 °C) is observed at 75 °C for BaFe12O19 samples sintered at 1200 °C. The observation of both multiferroicity and pyroelectricity close to room temperature in BaFe12O19 hexaferrite is interesting and useful for multifunctional devices. 相似文献
20.
José M. Porras-Vázquez Lucía dos Santos-Gómez Isabel Santacruz Miguel A.G. Aranda David Marrero-López Enrique R. Losilla 《Ceramics International》2012,38(4):3327-3335
Apatite-type silicates are considered as promising electrolytes for solid oxide fuel cells (SOFC). However more studies on the chemical compatibility of these materials with common SOFC electrodes are required. Here, we report the synthesis of single phase La9Sr1Si6O26.5 composition by reactive sintering at 1650 °C for 10 h. Fully dense pellets showed very high oxide-anion conductivity, 25 mS cm?1 at 700 °C. Furthermore, the chemical compatibility of La9Sr1Si6O26.5 with some selected cathode materials has also been investigated. The lowest reaction temperatures were determined to be 1100 °C, 1000 °C and 900 °C for La0.8Sr0.2MnO3?δ, La2Ni0.8Cu0.2O4 and La0.6Sr0.4Co0.8Fe0.2O3, respectively. The segregation of minor amounts of SiO2 seems to be a key limiting factor that must be overcome. Finally, these cathode materials were deposited over dense oxy-apatite pellets and the area specific resistances in symmetrical cells were determined. These values, at 700 °C, were 14.4 and 2.6 Ω cm2 for La0.8Sr0.2MnO3?δ and La0.6Sr0.4Co0.8Fe0.2O3?δ, respectively. Furthermore, the area specific resistances are notably improved 0.6 Ω cm2 when a 50 wt.% composite of La0.6Sr0.4Co0.8Fe0.2O3?δ and Ce0.8Gd0.2O1.9 is used. 相似文献