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排序方式: 共有1293条查询结果,搜索用时 15 毫秒
1.
Wei Zhou Rui-ming Yin Lan Long Heng Luo Wei-da Hu Yan-hong Ding Yang Li 《Ceramics International》2018,44(11):12301-12307
Si3N4 ceramics modified with SiC nanofibers were prepared by gel casting aiming to enhance the dielectric and microwave absorption properties at temperatures ranging from 25?°C to 800?°C within X-band (8.2–12.4?GHz). The results indicate that the complex permittivity and dielectric loss are significantly increased with increased weight fraction of SiC nanofibers in the Si3N4 ceramics. Meanwhile, both complex permittivity and dielectric loss of SiC nanofibers modified Si3N4 ceramics are obviously temperature-dependent, and increase with the higher test temperatures. Increased charges mobility along conducting paths made of self-interconnected SiC nanofibers together with multi-scale net-shaped structure composed of SiC nanofibers, Si3N4 grains and micro-pores are the main reason for these enhancements in dielectric properties. Moreover, the calculated microwave absorption demonstrates that much enhanced microwave attenuation abilities can be achieved in the SiC nanofibers modified Si3N4 ceramics, and temperature has positive effects on the microwave absorption performance. The SiC nanofibers modified Si3N4 ceramics will be promising candidates as microwave absorbing materials for high-temperature applications. 相似文献
2.
针对光伏以低惯量、弱阻尼的特征大规模接入电网,给电网稳定性带来不利影响的问题,基于功频下垂控制的光伏并网发电系统,借鉴经典电气转矩分析法,从物理机制层面上分析影响系统惯量、阻尼以及同步能力的作用规律。研究结果表明对于控制参数的影响规律而言,惯量特性主要受功率环的比例系数Kp影响,且随Kp的增大而增强;阻尼特性受频率下垂系数Dp影响比较明显,且随Dp的增大而减弱;同步特性只受功率环的比例积分系数Ki影响,且随Ki的增大而增强。通过仿真验证了理论分析的正确性。 相似文献
3.
《Carbon》2015
Fabrication of graphitized carbon materials (e.g. carbon nanotubes and graphene) normally entails the assistance of transition metal catalyst. In this paper, a nitrogen doped carbon foam (NCF) with both graphitized and porous carbon structure was fabricated by direct pyrolysis of melamine foam (MF) without using any transition metal catalyst. The graphitized carbon structure was possibly attributed to the triazine moieties in the MF precursor. The introduction of oxygen groups in the oxidation step resulted in the formation of large amount of micro- and mesopores and therefore high specific surface area. The NCF exhibited a three-dimensional cellular network consisting of carbon microfiber with abundant micro- and mesopores and giving rise to a specific surface area over 980 m2 g−1. Due to such graphitized porous structure, the NCF was demonstrated to have superior resilience, excellent electrocatalytic activity and good durability for oxygen reduction. 相似文献
4.
《Calphad》2015
The total energies of Laves phases in the Cr–Nb and Zr–Cr systems have been calculated by the pseudo-potential VASP code with a full relaxation of all structural parameters. The special quasirandom structures (SQSs) have been constructed and their total energies have been calculated by the VASP code to predict the enthalpies of mixing for bcc and hcp solid solution phases. The phonon calculations for the C14 and C15 Laves phases have been performed to analyze the phase stability at elevated temperatures. The experimental study on the Zr–Cr system has been carried out at different temperatures to determine the phase boundaries. Based on these results, thermodynamic models of Cr–Nb and Zr–Cr with extension to the ternary Zr–Nb–Cr systems have been developed in this work by using the CALPHAD approach. 相似文献
6.
《Calphad》2015
A numerical technique for constructing thermodynamic databases has been proposed. This technique offers accurate calculations of solidification temperature, phase fractions, and solute concentrations of specific alloys in quaternary systems. The thermodynamic data is extracted by calling the TQ-interface (Thermodynamic Calculation Interface) from Thermo-Calc software, and modeled through efficient computational approaches such as polynomial regression and interpolation. This method is described in three parts. First, the applicability of regression functions is demonstrated on the Al–Si binary phase diagram. Second, the way of combining polynomial regression and interpolation is applied to model the Al–Si–Mg ternary system. Finally, the A356 alloy, which belongs to the Al–Si–Mg–Fe system, is modeled by a series of sub-ternary systems using regression and interpolation. The valid accuracy of the method is demonstrated by comparing the present results with those calculated using Thermo-Calc software. The application of the TQ-interface to solidification processes in Scheil and lever-rule models is also included. The results indicate that this method can offer accurate thermodynamic parameters for the A356 alloy in Al–Si–Mg–Fe system and reduce CPU time significantly when applied to solidification simulation. Several problems and the corresponding strategies for high order functions, unsmooth variations of thermodynamic information and partition coefficients are discussed to improve this method. This technique can also be applied to other specific alloys with small variations of thermodynamic variables in quaternary systems. 相似文献
7.
8.
Thermally sprayed carbide-based coatings are nowadays extensively considered as an alternative to electrolytic hard chrome (EHC) coatings to reduce the environmental impact and the overall cost associated with EHC process. In this investigation, high-velocity oxy-fuel (HVOF) spray process was employed to prepare coatings using the traditional carbide powders namely the WC-10Co4Cr, the Cr3C2-25NiCr and a new type of mixed carbide powder WC-40Cr3C2-25NiCr. The Powder deposition rate, basic mechanical properties, abrasive wear, slurry erosion and corrosion resistance of the three coatings were then compared with the EHC coating. The results show that WC-10Co4Cr coating exhibited the highest hardness, abrasive wear and slurry erosion resistance followed by WC-40Cr3C2-25NiCr, EHC, and Cr3C2-25NiCr coating. The deposition efficiency of the powders as per hierarchy was found to be WC-40Cr3C2-25NiCr > WC-10Co4Cr > Cr3C2-25NiCr and all the HVOF sprayed coatings exhibited higher corrosion resistance than EHC coating. The highest powder deposition efficiency coupled with low density, acceptable tribo-corrosion performance, as well as low post processing cost makes the HVOF sprayed WC-40Cr3C2-25NiCr coating a potential candidate to replace the EHC coating. 相似文献
9.
10.
《Journal of the European Ceramic Society》2022,42(8):3415-3426
Herein, a reliable diffusion bonding of Ti3Si(Al)C2 ceramic is achieved by applying Au foil as an interlayer at 650 °C for 30 min with an axial pressure of 20 MPa. This novel method significantly decreases the bonding temperature, which is about 150 °C lower than the lowest bonding temperature from current research to the best of our knowledge. Maximum shear strength of 58 MPa is achieved at 650 °C among the bonding temperature range of 600 °C~800 °C. The microstructure evolution mechanism and the relationship between microstructure and mechanical property are discussed. The facile mutual diffusion of Au with de-intercalated Al and Si from Ti3Si(Al)C2 is considered critical in achieving sound interfacial bonding. 相似文献