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101.
Ning Liao Yawei Li Jiangbo Shan Tianbin Zhu Shaobai Sang Dechang Jia 《Ceramics International》2018,44(3):3319-3325
Expanded graphite with nano SiC and amorphous SiCxOy coating was successfully prepared through pyrolysing silane coupling agent (SCA), where the grafting of SCA dominated the final products. The results show that mainly amorphous SiCxOy coating covers expanded graphite at 1000 °C, regardless of the SCA concentration. In comparison, nano SiC coating can be synthesized at 1200 °C depending on the good dispersion of SCA (with a SCA concentration of 50 vol%). The formed SiC coating contributes to much higher peak oxidation temperature (812.1 °C) than 678.0 °C of the pure expanded graphite. Meanwhile, the oxidation activation energies of expanded graphite are remarkably improved from 149.15 kJ/mol to 176.16 kJ/mol (based on Kissinger method), attributing to the derived nano SiC and SiCxOy coating. 相似文献
102.
Zhi-Jia Xu Song Yang Guang-Hua Hu Qing-Hui Wang Jing-Rong Li 《International Journal of Hydrogen Energy》2018,43(9):4355-4370
A macroscopic numerical method is proposed to study the flow distribution uniformity of a novel porous copper fiber sintered felt (PCFSF), which has gradient porosities and was developed as the methanol steam reforming micro-reactor catalyst support for hydrogen production for fuel cell applications. The macroscopic porous media developed by the ANSYS/FLUENT software is used to represent the PCFSF. Our results indicate that the gradient porosity can reshape the flow distribution of PCFSFs greatly, thus producing significant influence on their performance. It is further revealed that, for a PCFSF with a determined gradient porosity configuration but different reactant feed directions, the velocity uniformity can be used as a quantitative criterion to evaluate the performance of hydrogen production. Furthermore, new gradient PCFSFs are produced according to the flow distribution of original gradient PCFSFs. The preliminary experimental results of the new gradient PCFSFs of 0.8-0.9-0.7 and 0.7-0.9-0.8 exhibit better methanol conversion and H2 flow rate. This indicates that the numerical method can be used for the optimization of PCFSFs' gradient porosity configuration, which consists of the shape and position of the interfaces between different porosity portions, the number of interfaces and the porosity distribution in different portions. 相似文献
103.
Chi-Yeong Ahn Wonchan Hwang Hyunjoon Lee Sungjun Kim Ji Eun Park Ok-Hee Kim Min Her Yong-Hun Cho Yung-Eun Sung 《International Journal of Hydrogen Energy》2018,43(21):10070-10081
An ideal oxygen reduction catalyst for use in fuel cells should exhibit both long-term durability and high activity. In this study, to increase the durability of highly loaded platinum- and platinum-nickel alloy catalysts possessing different types of carbon supports, a nitrogen-doped carbon shell was introduced on the catalyst surface through dopamine coating. As the catalyst surfaces were altered following shell formation, the ionomer contents of the catalyst inks were adjusted to optimise the three-phase boundary formation. Single cell tests were then conducted on these inks by applying them in a membrane electrolyte assembly. Furthermore, to confirm the durability of the catalysts under accelerated conditions, the operation was continued for 200 h at 70 °C and at a relative humidity of 100%. Transmission electron microscopy and electrochemical analysis were conducted before and after the durability tests, and the observed phenomena were discussed for catalysts bearing different types of carbon supports. 相似文献
104.
Anton Salomon Lilit Amirkhanyan Christiane Ullrich Mykhaylo Motylenko Olga Fabrichnaya Jens Kortus David Rafaja 《Journal of the European Ceramic Society》2018,38(16):5590-5600
Rutile coatings deposited on corundum substrates are considered as promising functional elements improving the efficiency of the filtration of oxide inclusions out of aluminium melts. This contribution describes the reactions between rutile and two kinds of the aluminium melts and discusses the consequences of these reactions for the filtration process. It was found that the contact of rutile coatings with molten aluminium leads to the formation of a corundum layer at the solid/liquid interface. The exposure of the rutile coatings to molten AlSi7Mg0.6 alloy produces an interface layer of MgTiO3. The interface layers possess defined orientation relationship to rutile which is characteristic for locally heteroepitaxial growth. The density functional theory calculations revealed that the TiO2/α-Al2O3 and TiO2/MgTiO3 interfaces with the orientation relationships observed experimentally have low interface energies. The mechanisms of the interface layer formation and the impact of these layers on the degradation of the rutile coatings are discussed. 相似文献
105.
In-situ SiC nanowire (SiCnw)/pyrolytic carbon (PyC) core-shell structures were introduced to mainly improve the thermal shock performance of chemical vapor deposition (CVD)-SiC coating on carbon/carbon (C/C) composites. The microstructure, phase composition, and mechanical properties of the CVD-SiC coating toughened by SiCnw/PyC core-shell structures were studied as well. The results show that the introduction of SiCnw/PyC core-shell structures can effectively alleviate the mismatch of coefficient of thermal expansion (CTE) between SiC coating and C/C substrate, thus enhancing the thermal shock resistance of the coating. Furthermore, the increased numbers of interfaces in the SiC coating owing to the addition of core-shell structures are beneficial to the mechanical properties of the coating after thermal shock test. 相似文献
106.
Jinshuang Wang Junbin Sun Qiangshan Jing Bing Liu Hao Zhang Jieyan Yuan Shujuan Dong Xin Zhou Xueqiang Cao 《Journal of the European Ceramic Society》2018,38(7):2841-2850
The properties of ZrO2 co-stabilized by CeO2 and TiO2 ceramic bulks were investigated for potential thermal barrier coating (TBC) applications. Results showed that the (Ce0.15Tix)Zr0.85-xO7 (x?=?0.05, 0.10, 0.15) compositions with single tetragonal phase were more stable than the traditional 8YSZ at 1573?K. These compositions also showed a large thermal expansion coefficient (TEC) and a high fracture toughness, which were comparable to those of YSZ. However, the phase stability, fracture toughness and sintering resistance of the CeO2-TiO2-ZrO2 system showed a decline tendency with the increase of TiO2 content. The TEC of the ceramic bulks decreased with increase of TiO2 content as well because the crystal energy was enhanced with increasing substitution of Zr4+ by smaller Ti4+. The (Ce0.15Ti0.05)Zr0.8O2 had the best comprehensive properties among the (Ce0.15Tix)Zr0.85-xO2 compositions as well as a low thermal conductivity. Therefore, it can be explored as a TBC candidate material for high-temperature applications. 相似文献
107.
Laura R. Turcer Amanda R. Krause Hector F. Garces Lin Zhang Nitin P. Padture 《Journal of the European Ceramic Society》2018,38(11):3905-3913
The high-temperature (1500?°C) interactions of two promising dense, polycrystalline EBC ceramics, YAlO3 (YAP) and γ-Y2Si2O7, with a calcia-magnesia-aluminosilicate (CMAS) glass have been explored as part of a model study. Despite the fact that the optical basicities of both the EBC ceramics and the CMAS are similar, they both react with the CMAS. In the case of the Si-free YAlO3, the reaction zone is small and it comprises three regions of reaction-crystallization products, including Y-Ca-Si apatite solid-solution (ss) and Y3Al5O12 (YAG)(ss). In contrast, only Y-Ca-Si apatite(ss) forms in the case of Si-containing γ-Y2Si2O7, and the reaction zone is an order-of-magnitude thicker. These CMAS interactions are analyzed in detail, and are found to be strikingly different than those observed in Y-free EBC ceramics (β-Yb2Si2O7 and β-Sc2Si2O7) in the accompanying Part II paper. This is attributed to the presence of the Y in the YAlO3 and γ-Y2Si2O7 EBC ceramics. 相似文献
108.
A simple interface fracture test for ceramic environmental barrier coatings (EBCs) on ceramic matrix composites (CMCs) was developed. A variation on the asymmetric double cantilever beam (ADCB) test was proposed so that the interface toughness could be measured in a small specimen of simple shape without applying interlaminar loading to the CMC substrate. The proposed test was applied to an EBC consisting of a mullite layer and Si bond coat on a monolithic SiC substrate. A pre-crack was introduced by pop-in cracking, and then a notch overlapping the pre-crack was machined. The pre-crack was opened by inserting a wedge into the notch. From the critical notch opening displacement the crack starts to propagate, interface toughness is calculated. The measured interface toughness was 4.1?J/m2. Finally, the application range of the test was discussed and suggestions were made for introduction of the notch and pre-crack. 相似文献
109.
110.