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基于密度泛函理论(DFT)第一性原理方法,研究了Si、Ni、Mn、Cr、Mo在fcc-Fe/NbX (X=C, N)界面的偏析行为,并分析了合金元素偏析对界面体系的影响。结果表明,fcc-Fe/NbN界面结合强度相较于fcc-Fe/NbC界面结合强度略有提升;Si稳定存在于Fe基体中,Ni、Mn在界面有轻微偏析倾向,Cr、Mo在界面和NbX (X=C,N)内均存在偏析,其中,Mo向界面偏析倾向更大;Cr、Mo偏析在fcc-Fe/NbC界面一定程度上降低了界面的结合能力,但体系稳定性有所提升,Cr、Mo偏析在fcc-Fe/NbN界面一定程度上提高了界面的结合能力,但Mo使得体系稳定性下降。  相似文献   
3.
《Ceramics International》2022,48(20):29862-29872
Thermal shock parameters (R, R''', R'''' and Rst) of MgAlON–MgO composites obtained with additions of spent MgO–C brick were calculated using measured mechanical properties and thermal expansion coefficient, determining their resistance to fracture initiation and crack propagation. The cyclic thermal shock experiments of MgAlON–MgO composites performed from 1398 K to ambient temperature indicate that as number of thermal shock cycle increases, retained strength ratio of MgAlON and MgAlON–4.2 wt%MgO sharply decrease and then keep constant, while that of MgAlON–10.5 wt%MgO and MgAlON–15.7 wt%MgO slowly decrease. The reason for the difference is that MgAlON and MgAlON–4.2 wt%MgO show low value of R''' and R'''', and high value of R and Rst. Moreover, precipitation of impurity containing Fe may play a positive role in improvement of thermal shock resistance of MgAlON–MgO composites. MgAlON?4.2 wt%MgO has the maximum retained strength (55 MPa) even after 5 thermal shock cycles, which is expected to be used in the metallurgical industry.  相似文献   
4.
The influences of the SiC infiltration and coating on the compressive mechanical behaviours of 2D C/SiC composites were determined up to 1600 °C at 0.001 and 1000/s strain rates in argon and air. In addition, the failure mechanisms responsible for the compressive mechanical behaviours were elucidated through in-situ observation and micro-analysis-based methods. The 2D C/SiC composite compressive strength was highly sensitive to temperature, loading rate, and oxidation, and was enhanced by the change in the thermal residual stress and decreased by oxidation. In argon, because of the extra infiltrated SiC matrix, SiC treated 2D C/SiC specimens exhibited higher compressive strengths and lower strain rate sensitivity factors than SiC untreated 2D C/SiC specimens. The SiC coating effectively improved the oxidation resistance of the 2D C/SiC composites in air, regardless of the temperature, strain rate, and oxidative damage-which depends on SiC coating, strain rate, and temperature.  相似文献   
5.
This study deals with the manufacturing of catalyst-coated membranes (CCMs) for newcomers in the field of coating. Although there are many studies on electrode ink composition for improving the performance of proton-exchange membrane fuel cells (PEMFCs), there are few papers dealing with electrode coating itself. Usually, it is a know-how that often remains secret and constitutes the added value of scientific teams or the business of industrialists. In this paper, we identify and clarify the role of key parameters to improve coating quality and also to correlate coating quality with fuel cell performance via polarization curves and electrochemical active surface area measurements. We found that the coating configurations can affect the performance of lab-made CCMs in PEMFCs. After the repeatability of the performance obtained by our coating method has been proved, we show that: (i) edge effects, due to mask shadowing - cannot be neglected when the active surface area is low, (ii) a heterogeneous thickness electrode produces performance lower than a homogeneous thickness electrode, and (iii) the origin and storage of platinum on carbon powders are a very important source of variability in the obtained results.  相似文献   
6.
介绍了中国石油石油化工研究院自主开发的新型碳三馏分加氢催化剂PEC-31在中国石油兰州石化公司24万t/a乙烯装置稳定运行超过200 d的首次工业应用情况。结果表明:在加氢反应器入口碳三馏分物料中的甲基乙炔(MA)和丙二烯(PD)混合物(MAPD)体积分数为 2.0%~3.5%,氢气与丙炔&丙二烯的摩尔比为1.00~1.50,反应器入口温度为32 ℃,碳三馏分物料的液相体积空速为40~45 h-1的工况下,PEC-31催化剂作用下的MAPD转化率、丙烯选择性相应均值分别为98.50%,80.10%。  相似文献   
7.
通过试验得出了C105混凝土100 mm×100 mm×100 mm立方体非标准试件抗压强度换算系数以及C105混凝土的标准方差和强度变异系数。采用理论计算,得到了棱柱体抗压强度与立方体抗压强度的比值αc1,并与试验实测平均值进行了比较,验证了理论计算方法的可行性。此外,通过对比分析,探讨了直接外延法和引用公式法两种C105混凝土设计参数计算方法的正确性,研究结果可为C105管桩混凝土的设计和应用提供参考。  相似文献   
8.
Mixed-matrix membranes (MMMs), judiciously combining processability of polymer and remarkable separation performance of nanofillers, have been extensive pursuits for molecular separation process. Permeability matching between filler and polymer is one of the necessary requisites to desirable mixed-matrix effect. Considering the superior molecular sieving effect of UTSA-280 metal-organic frameworks on C2H4 and C2H6, here, we report two types of UTSA-280/6FDA-polyimide MMMs toward C2H4/C2H6 separation. The molecular sieving effect of UTSA-280 endowed 6FDA-DAM:DABA(3:2) membrane with simultaneous improvements in C2H4 permeability and C2H4/C2H6 selectivity. Optimally, when the filler reached 21.80 wt%, C2H4 permeability and C2H4/C2H6 selectivity was increased to 6.49 Barrer (by 15%) and 4.94 (by 32%), respectively. On the contrary, UTSA-280/6FDA-DAM MMMs showed undesirable mixed-matrix effect that C2H4 permeability decreased meanwhile C2H4/C2H6 selectivity nearly kept at polymeric pristine membrane level. It was found that permeability matching between two phases was responsible to these opposite mixed-matrix effects. More specifically, UTSA-280 had a relatively low gas permeability so that it required a less permeable polymeric matrix like 6FDA-DAM:DABA(3:2) to exert its molecular sieving effect. Furthermore, the optimal-matching 6FDA-matrix in permeability with UTSA-280 fillers was predicted by theoretical model. This work not only reports improving C2H4/C2H6 separation performance via mixed-matrix formulation, but also emphasizes the importance of permeability matching between polymer and filler to realize the mixed-matrix effect.  相似文献   
9.
Ta-Hf-C ternary ceramics are good candidates for structural components used in extreme thermal environment. However, intrinsic brittleness greatly restricts their applications in reality. Here, we report a novel TaHfC2-based composite with superior strength and toughness by employing Ta foil as interlayers to generate a multi-scale laminated structure together with the in situ formed Ta2C MXene during sintering. Owing to the unique composition and microstructure, the tensile strength, shear strength, fracture toughness (KIC), and work of fracture of Ta/TaHfC2 have reached 233 ± 12 MPa, 64 ± 6 MPa, 13.16 ± 0.03 MPa·m1/2, and 1726 ± 448 J/m2 simultaneously, and all showed substantial increments when compared with TaHfC2 monolithic ceramic and related Ta-Hf-C materials as showed in literatures. This study significantly improved the toughness of TaHfC2, and it provides a new high-performance thermal structural material for the aerospace industry as well as a new idea for toughening ultra-high temperature ceramics (UHTCs) of transition metal carbides.  相似文献   
10.
A chromium carbide (Cr-C) coating in-situ formed on the C/C substrate is successfully prepared by a novel reactive wetting strategy. The interfacial microstructure and oxidation resistance of coated C/C composites are investigated in detail. The as-prepared coating mainly consists of Cr23C6 and Cr7C3, forming a tight joining with the C/C substrate. Compared to uncoated samples, the oxidation weight loss of coated C/C composites is substantially reduced at high temperatures. Furthermore, the hardness of coated C/C composites is significantly increased, enhancing their ability to resist external damage. This reactive wetting strategy can also be used to prepare uniform coatings on C/C composites with complex grooved structure or large size. Surprisingly, coated C/C composites possess a low weight gain of 3.7% due to thin coating (< 10 µm), which can maintain their advantage of low density.  相似文献   
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