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61.
Bum-Jin Chung Jeong-Hwan Heo Min-Hwan Kim Gyeong-Uk Kang 《International Journal of Heat and Mass Transfer》2011,54(1-3):135-141
Natural convection experiments inside a vertical cylindrical cavity were performed for Rayleigh numbers of 1.08 × 1010–2.11 × 1013 and for four different geometrical arrangements: both-open (pipe-shape), bottom-closed (cup-shape), top-closed (cap), and both-closed (cavity) cylinders. A copper electroplating system was employed for the measurements of heat transfer rates using analogy concept. The lids used to close top or bottom were adiabatic; i.e. inactive surfaces in the electrodeposition experiments. The bottom-closed cavity showed the highest heat transfer rates and then followed both-closed, both-open, top-closed ones in both laminar and turbulent flows. The results were in satisfactory agreements with the existing correlations developed for similar geometrical configurations and the empirical correlations were derived. The numerical simulations were carried out using the FLUENT 6.2 to explain the measured results. The analysis of the streamline and the local Nusselt number gave explanations for the observation. 相似文献
62.
In an effort to improve the performance of SUS 430 alloy as a metallic interconnect material, a low cost and Cr-free spinel coating of NiMn2O4 is prepared on SUS 430 alloy substrate by the sol-gel method and evaluated in terms of the microstructure, oxidation resistance and electrical conductivity. A oxide scale of 3-4 μm thick is formed during cyclic oxidation at 750 °C in air for 1000 h, consisting of an inner layer of doped Cr2O3 and an outer layer of doped NiMn2O4 and Mn2O3; and the growth of Cr2O3 and formation of MnCr2O4 are depressed. The oxidation kinetics obeys the parabolic law with a rate constant as low as 4.59 × 10−15 g2 cm−4 s−1. The area specific resistance at temperatures between 600 and 800 °C is in the range of 6 and 17 mΩ cm2. The above results indicate that NiMn2O4 is a promising coating material for metallic interconnects of the intermediate temperature solid oxide fuel cells. 相似文献
63.
Xiang XuFangzhong Wang Yihui LiuJian Pu Bo Chi Li Jian 《Journal of power sources》2011,196(22):9365-9368
Solution impregnated La0.8Sr0.2Co0.8Ni0.2O3 + Gd-doped CeO2 (LSCN + GDC) cathodes for intermediate temperature solid oxide fuel cells (IT-SOFC) are prepared and their electrochemical properties are evaluated and compared with the conventional LSCN cathodes. The results indicate that the cathode performance can be enhanced by the presence of the nanosized microstructure produced with the solution impregnation method. It is determined that the amount of LSCN loading in the LSCN + GDC composite cathode needs to be higher than 35 wt% in order to achieve a performance superior to that of the conventional LSCN cathode. The optimum amount of LSCN loading is in the range of 45-55 wt% with an activation energy near 1.32 eV for oxygen reduction. At temperatures between 600 and 750 °C, the polarization resistance of the 55 wt% LSCN loaded LSCN + GDC cathode is in the range of 1.07 and 0.08 Ω cm2, which is only about one half of that for the conventional cathode. 相似文献
64.
《Ceramics International》2022,48(21):31381-31388
Lead-free bulk ceramics for advanced pulse power capacitors possess low recoverable energy storage density (Wrec) under low electric field. Sodium bismuth titanate (Bi0.5Na0.5TiO3, BNT)-based ferroelectrics have attracted great attention due to their large maximum polarization (Pm) and high power density. The BNT-ST: xAlN ceramics are designed and fabricated to get high Wrec and large Pm under low electric field simultaneously. An excellent large Pm (49.04 μC/cm2) and Wrec (2.07 J/cm3) under low electric field (160 kV/cm) are acquired in BNT-ST: 0.1 wt% AlN. The domain structure evolution and polarization switching are investigated systematically using piezoresponse force microscopy (PFM). The introduction of AlN promotes the formation of thermal conductive network and the crystallization of ceramics, thus improving thermal stability and increasing Pm significantly. The higher density of domain walls and the larger negative built-in voltage may be beneficial to increase breakdown field strength (Eb), while the more 180° domains induce by electric field and the better domain switching behavior contribute to a significant increase in Pm. The enhanced Eb and super high Pm are favorable for obtaining high Wrec under low electric field which will boost the application of BNT-based ferroelectrics in advanced pulse power capacitors. 相似文献
65.
《Ceramics International》2022,48(20):30224-30228
High densification and fine grain size are the key to achieve excellent mechanical properties of ceramic materials. Pressure-assisted sintering is an effective approach to achieve this goal. However, the pressure at different sintering stages has different effects on the densification behavior of nano-ceramics. In this work, it is found that adjusting the pressure applying regime during Spark Plasma Sintering of nano-alumina ceramics can effectively increase the densification rate and balance the relationship between the densification behaviors of particle coarsening, grain growth and vapor migration. When the pressure is applied at the beginning of the second sintering stage, the high densification and fine grain size microstructures can be both obtained at lower temperatures, leading to the best mechanical properties. This result is of great significance for the preparation of nano-ceramics with excellent mechanical properties. 相似文献
67.
《Ceramics International》2022,48(5):6266-6276
Porous diatomite ceramics with hierarchical pores and high apparent porosity (50.29–56%) were successfully fabricated via direct stereolithography. The pre-ball-milling time, dispersant type and dispersant concentration were systematically investigated to prepare diatomite pastes with high solid loading, low viscosity and a self-supporting effect. The results showed that a pre-ball-milling time of 24 h was more suitable to prepare diatomite pastes with high solid loading, and Span80 at 2 wt% was the optimal dispersant to obtain 40 vol% diatomite paste with a low viscosity and a self-supporting effect. To restrain the formation of defects, a heating rate as low as 0.2 °C/min was allowed to control the pyrolysis rate in the multistage debinding process. At sintering temperatures ranging from 900 °C to 1000 °C, porous diatomite ceramics exhibited a typical bimodal porosity, high apparent porosity and great flexural strength. 相似文献
68.
《Ceramics International》2022,48(22):33580-33587
To improve the dimensional accuracy, surface quality, and mechanical properties of binder jet additive manufactured ceramic parts, in this work, nanozirconia dispersion and binder were used to prepare a jet solution to investigate the effect of nanozirconia content of the jet solution on the properties of zirconia ceramic green and sintered bodies. When the nanozirconia content of the jet solution increased from 0 to 20 wt%, the forming precision of the zirconia ceramic green bodies improved, the surface roughness decreased, and the density increased. After sintering at 1400 °C for 2 h, linear shrinkage along the height, width, and length of the zirconia ceramics decreased by 6.27%, 10.20%, and 5.45%, respectively, while the surface roughness decreased by 42.87%, and the bending strength increased by 145.60%. With increasing nanozirconia content of the jet solution, the spreading and infiltration distance of the jetted solution in the powder layer decreased, the thickness of the deposition layer of nanozirconia on the surface of the zirconia particles in the powder layer increased, and the pore size of the powder layer decreased significantly. This increased the density of the green bodies; thus, improving the sintering properties of the zirconia ceramics. 相似文献
69.
《Journal of the European Ceramic Society》2022,42(13):5698-5704
A cold sintering process is adopted to pre-densify CaF2 ceramics from 85.7% at 300 MPa to 91.7% at 750 MPa. Subsequent post-annealings at 1000–1150 °C lead to further improvements in densification, where great enhancements of grain size and crystallinity are also observed from the scanning and transmission electron micrographs. Significant advances in Qf values are achieved in the post-annealed CaF2 ceramics. The optimum Qf value (80,522 GHz) is achieved after cold sintering at 750 MPa and post-annealing at 1000 °C, which is three times higher than the conventional sintered one at 1000 °C (26,448 GHz). Moreover, the obtained low-εr (5.9–6.5) of CaF2 ceramics suggests broad application prospects in the high-band microwave communications. A microstrip patch antenna is fabricated using the CaF2 ceramics as the substrate, which operates at 7.89 GHz in the C-band, with an S11 of ?13.4 dB, simulated high gain and efficiency of 6.41 dBi and ?0.56 dB, respectively. 相似文献
70.
Tong Wei Bo Liu Lichao Jia Renhong Li 《International Journal of Hydrogen Energy》2021,46(48):24441-24460
SOFC (solid oxide fuel cell, SOFC) is recognized to be efficient green energy technology in the 21st century. However, when hydrocarbons are directly used as fuel, carbon deposition is easy to occur in Ni-based anode, thus losing electrochemical catalytic activity. Fuel pre-reforming is also called on-cell reforming of hydrocarbons, which has been a promising solution for alleviating the carbon deposition problem in cermet anodes to varying degrees. And the key factor is to find an efficient and stable fuel reforming catalyst. Perovskite oxides have stable structure, highly catalytic activity and adjustable thermal expansion coefficient for using on the cells, showing great potentials of application for fuel reforming. In this paper, we summarize the application of perovskite catalyst in CH4 fuel reforming based on the research of our group and other scholars, and puts forward the corresponding views and perspective, especially in perovskite catalyst with Ni exsolution. 相似文献