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101.
102.
热障涂层作为航空发动机的关键技术,一旦在使用过程中失效将导致严重的后果。然而,热障涂层在使用过程中不可避免地会接触到钙镁铝硅酸盐(CMAS),引发涂层剥落,使高温合金直接暴露在高温燃气中,带来巨大的危险。因此,热障涂层的CMAS侵蚀及防护问题近年来得到了广泛关注。本文在介绍传统氧化钇稳定氧化锆(YSZ)涂层受CMAS侵蚀现状的基础上,明确了CMAS侵蚀YSZ的化学作用过程,阐明了YSZ涂层的失效机制,比较了不同种类CMAS的侵蚀效果,总结了目前热障涂层抵抗CMAS侵蚀的主要方法,并阐述了基于自损型防护原理开展的新型热障涂层材料的CMAS侵蚀行为研究进展,以期为未来航空发动机用热障涂层陶瓷材料的选择和CMAS防护提供有益参考。 相似文献
103.
《Journal of the European Ceramic Society》2017,37(6):2491-2499
The key requirements for a successful thermal and environmental barrier coating (T/EBC) material include stability in high temperature water vapor, low Young's modulus, close thermal expansion coefficient (TEC) with mullite, low thermal conductivity and weak mechanical anisotropy. The current prime candidates for top coat are ytterbium silicates (Yb2SiO5 and Yb2Si2O7). A major weakness of these two silicates is the severe anisotropy in mechanical properties and thermal expansion that would lead to cracking of the coating. Thus, searching for new materials with weak mechanical and thermal anisotropy is of signification. In this work, the crystal structure, mechanical and thermal properties of a promising T/EBC candidate, Yb4Al2O9, are investigated theoretically and experimentally. Good ductility, low shear deformation resistance, low Young's modulus (151 GPa) and low thermal conductivity (0.78 W m−1 K−1) is underpinned by heterogeneous bonding characteristic and distortion of the structure. Close TEC (6.27 × 10−6 K−1) with mullite and weak mechanical anisotropy highlight the suitability of Yb4Al2O9 as a prospective T/EBC. 相似文献
104.
《Ceramics International》2017,43(12):8879-8885
The present paper focuses on near infrared (NIR) down-conversion photoluminescence (PL) properties by studying the energy transfer mechanism between Er3+ and Yb3+ in CaMoO4:Er3+, Yb3+ phosphors. We have successfully synthesized a series of Er3+ doped and Yb3+ codoped CaMoO4 phosphors by hydrothermal method. The down-conversion of Er3+-Yb3+ combination with CaMoO4 phosphor is designed to overcome the energy losses due to spectral mismatch when a high energy photon is incident on the Si-solar cell. The XRD, FESEM, EDX, PL, UV–Vis, Lifetime measurements were carried out to characterize the prepared down-converting phosphors. The crystallinity and surface morphology were studied by X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The down-conversion PL spectra have been studied using 380 nm excitation wavelength. The Er3+ doped phosphors exhibit hypersensitive emission at 555 nm in the visible region due to 4S3/2→4I15/2 transition. The addition of Yb3+ into Er3+ doped CaMoO4 attribute an emission at 980 nm due to 2F5/2→2F7/2 transition. The decrease in emission intensity in visible region and increase in NIR region reveals the energy transfer from Er3+ to Yb3+ through cross relaxation. The UV–Vis–NIR spectra shows the strong absorption peak around 1000 nm due to Yb3+ ion. The lifetime measurement also reveals the energy transfer from Er3+ to Yb3+ ions. The maximum value of energy transfer efficiency (ETE) and corresponding theoretical internal quantum efficiency are estimated as 74% and 174% respectively. 相似文献
105.
106.
《中国稀土学报(英文版)》2020,38(8):921-926
Amine elimination of Ln[N(SiMe_3)_2]_3(μ-Cl)Li(THF)_3 with aminophenol H[ON] {H[ON]=2-(CH_2 NC_5 H_(10))-4,6-~tBu_2-C_6 H_3OH} in 1:2 molar ratio in THF gave the monometallic rare-earth metal amide complexes[ON]_2 LnN(SiMe_3)_2(Ln=Yb(1),Y(2),Gd(3),Sm(4),Nd(5)) in 57%-73% isolated yields.All these complexes were characterized by elemental analysis.The molecular structures of complexes 1-4 were determined by single crystal X-ray diffraction.These complexes are highly active for L-Iactide polymerization to give high molecular weight polymers with unimodal molecular weight distributions.In addition,these complexes can also initiate rac-lactide polymerization with high activity to afford heterotactic-rich polylactides. 相似文献
107.
We have investigated the irradiation conditions of femtosecond laser pulses for quantitative atom probe analyses of rare-earth (RE) doped ceria. The influence of laser wavelength, power, pulse frequency, as well as specimen temperature on mass resolution and background noise of atom probe mass spectra were investigated. Furthermore, quantitative atom probe analysis of yttrium distribution in Y-doped ceria was carried out with the optimized evaporation conditions. The distribution of yttrium was found to be uniform within the grains, but they were confirmed to be segregated at grain boundaries. 相似文献
108.
Rare-earth-based permanent magnets are one of the most important magnets in both scientific and industrial fields. With the development of technology, nanostructured rare-earth-based permanent magnets with high energy products are highly required. In this article, we will review the progress in chemical synthetic strategies of nanostructured rare-earth-based permanent magnets. 相似文献
109.
Yapei Peng Xinqiang Yuan Long Zhang Peiguang Yan Wenfei Zhang Shuangchen Ruan 《中国稀土学报(英文版)》2019,37(5):487-491
Mid-infrared laser materials with low phonon energy have significant applications. However, the development of available glass systems for high-power laser gain medium have posed a great challenge.Therefore, we investigated the 2.7 μm spectroscopic properties of Er~(3+)/Yb~(3+) -codoped oxyfluoride glass containing gallium, which were prepared by typically melting and quenching methods. The 2.7 μm luminescence properties of the Er~(3+)/Yb~(3+)-codoped oxyfluoride glass containing gallium were recorded by a 980 nm laser diode. The Judde Ofelt parameters, decay curves, emission cross section, energy transfer efficiency and quantum efficiency were calculated. The maximum emission cross section of YbFGa-0.5 is 1.63 × 10~(-20) cm~2 by 980 nm excitation. The energy transfer efficiency is calculated to be77.8% for the YbFGa-0.5 glass around 2700 nm. The quantum efficiency at 1530 nm is 65.6%. The result reveals that the best doping concentration ratio of Er~(3+):Yb~(3+) ions is 1:0.5, and suggests an effective energy transfer from Yb~(3+) to Er~(3+) ions. 相似文献
110.
《Journal of the European Ceramic Society》2020,40(15):5740-5748
A study on the influence of the silicate composition on the self-healing ability of a promising environmental barrier coating (EBC) material is reported. The EBC material consists of silicon carbide particles dispersed in a ytterbium silicate matrix. The composition of the silicate was varied from pure monosilicate to pure disilicate including a mixture of 50 vol-% of both phases. Pre-cracked specimens were mechanically tested before and after thermal annealing in air at 1400 °C accompanied by microstructural investigations. It is shown, that the self-healing mechanism is based on the application of compressive surface stresses due to graded oxidation of the SiC particles. With increasing amount of disilicate strength and self-healing ability increase. 相似文献