共查询到20条相似文献,搜索用时 15 毫秒
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Boron carbide is a ceramic material possessing unique properties, and hence, high technological applications. The wetting behavior of ceramics by liquid alloys, which is of crucial importance in a variety of materials processing technologies, is determined by interfacial chemical interactions. In the present paper, the interfacial interactions of B4C with a series of Ni-Cr-Si alloys with Ni/Cr = 3.4 have been studied. For this purpose, a thermodynamic method was developed to predict the interactions. In addition, the interfacial structure and chemical composition were examined using SEM-EDS technique. Good agreement was found between the theoretical calculations and experimental data. It was revealed that the amount of Si content in the alloys plays a major role on the interfacial reactions as well as the interface microstructure. 相似文献
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The transport properties of the molecular-scale B2C and BC3 electronic devices are investigated with an ab initio method combined with a nonequilibrium Green function technique. The effects of different BC graphenes and ribbon lengths on the transport properties of the devices are significant. The results show that the devices with different BC graphenes and sizes have unusual transmission coefficients, which leads to special current transport mechanisms for the devices. Notably, the current strength of the device with the shortest ribbon length is the largest in three B2C devices, but the current strength of the device with the shortest ribbon length is the smallest for BC3 device. 相似文献
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Electronic structure of deformed carbon nanotubes varies widely depending on their chirality and deformation mode. We present a framework to analyze these variations by quantifying the dispersion relation and density of states. The theory is based on the Huckel tight-binding model and confirmed by four orbital tight-binding simulations of nanotubes under stretching, compression, torsion, and bending. It unriddles and unifies previous band gap studies and predicts the shifting, merging, and splitting of Van Hove singularities in the density of state, and the zigzag pattern of band gap change with strains. Possible applications to nanotube devices and spectroscopy research are also presented. 相似文献
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Liang Shi Yunle GuLuyang Chen Yitai Qian Zeheng YangJianhua Ma 《Solid State Communications》2003,128(1):5-7
B4C ultrafine powders were successfully synthesized at 450 °C through a new co-reduction route. The synthesis was carried out in an autoclave by using BBr3 and CCl4 as the reactants and metallic Na as the co-reductant. The X-ray powder diffraction pattern and Raman spectra indicate the formation of B4C. An atomic ratio of B to C of 4.09:1.0 was determined from X-ray photoelectron spectra. Transmission electron microscopy images shows that typical B4C crystallites are composed of uniform ultrafine spherical and rod-like particles. 相似文献
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V.V Ivanovskaya A.N EnyashinA.A Sofronov Yu.N MakurinN.I Medvedeva A.L Ivanovskii 《Solid State Communications》2003,126(9):489-493
Atomistic models of quasi-one-dimensional vanadium pentoxide nanostructures—single-walled nanotubes formed by rolling (010) layers of V2O5 are constructed and their electronic properties and bond indices are studied using the tight-binding band method. We show that all zigzag (n,0)- and armchair (n,n)-like nanotubes are uniformly semiconducting, and the band gap trends to vanish as the tube diameters decrease. The V-O covalent bonds were found to be the strongest interactions in V2O5 tubes, whereas V-V bonds proved to be much weaker. 相似文献
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为了实现7 nm波段Mo/B4C多层膜反射镜元件的制备,研究了不同退火方式对Mo/B4C多层膜应力和热稳定性的影响。首先,采用直流磁控溅射方法分别基于石英和硅基板制作Mo/B4C多层膜样品,设计周期为3.58 nm、周期数为60,Mo膜层厚度与周期的比值为0.4。其次,采用不同的退火方式对所制作的样品进行退火实验,最高退火温度500 ℃。最后,分别采用X射线掠入射反射、X射线散射和光学干涉仪的方法对退火前后的Mo/B4C多层膜的周期、界面粗糙度和应力进行测试。测试结果表明采用真空退火方式能够有效降低Mo/B4C多层膜的应力,且退火前后Mo/B4C多层膜的周期和界面粗糙度无明显变化,证明Mo/B4C多层膜在500 ℃以内具有很好的热稳定性。 相似文献
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Compared to experiment, the adsorption energies, bonding properties, and electronic structure of two different Al2O3/B4C bridge sites with seven different Al2O3 surfaces are investigated by ab initio periodic density functional theory. The Al2O3/B4C ceramic sintered in Ar is synthesized and measured by XRD and TEM. The calculated results reveal that the densification of O_bridge site of Al2O3/B4C surface is better than that of Al_bridge. The Al2O3 (1 1 3)/B4C with O_bridge is the most favorable and stable. The electronic structure shows that the electron hybridization exists between Al, O atoms and C, B atoms. The results indicate that the calculated results are in good agreement with the experiment. 相似文献
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H. Wang F.J. Yang Q. Mo J. Zhang H.B. Wang Y. Wang 《Journal of magnetism and magnetic materials》2009,321(17):2627-2629
FePt multilayer composite films with and without B4C interlayer have been prepared by magnetron sputtering, respectively, and subsequent annealing in vacuum. It was found that the B4C layers effectively serve as spacers to separate the FePt layers, enhancing (0 0 1) orientation of FePt alloy. Our results show that highly (0 0 1) oriented FePt/B4C films have significant potential as perpendicular recording media. 相似文献
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H. Hoshizuki S. Mitsudo T. Saji K. Matsuura T. Idehara M. Glyavin A. Eremeev T. Honda Y. Iwai H. Nishi A. Kitano J. Ishibashi 《International Journal of Infrared and Millimeter Waves》2005,26(11):1531-1541
Boron carbide (B4C) is one of advanced materials and is being used in a wide rage of applications. The unique feature of this material is its
large neutron-absorbing cross-section. Some of its most prominent applications are controlling rods in nuclear reactors and
radiation protection. 24 GHz microwave processing for B4C ceramics were performed under flowing argon gas using the sintering system. Sintering at the high temperature (up to 2200°C)
was achieved using thermal insulation system consists of fiber-board, boron nitride powder, and boron nitride case. The sintered
samples were achieved 90 % of theoretical. 相似文献
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In this paper, a simple theoretical model combining Monte Carlo simulation with the enthalpy method is provided to simulate the damage resistance of B4C/Si-sub mirror under X-ray free-electron laser irradiation. Two different damage mechanisms are found, dependent on the photon energy. The optimum B4C film thickness is determined by studying the dependence of the damage resistance on the film thickness. Based on the optimized film thickness, the damage thresholds are simula... 相似文献
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Peng WangChang-Ge Piao Rui-Ying MengYan Cheng Guang-Fu Ji 《Physica B: Condensed Matter》2012,407(2):227-231
The elastic and electronic structure properties of YNi2B2C under pressure are investigated by performing the generalized gradient approximation (GGA) and local density approximation (LDA) correction scheme in the frame of density functional theory (DFT). The pressure dependences of the normalized lattice parameters a/a0 and c/c0, the ratio c/a, and the normalized primitive volume V/V0 of YNi2B2C are also obtained. The lattice constants and bulk modulus obtained are in agreement with the available experimental and other theoretical data. We have also studied the pressure dependences of elastic properties. It is found that, as pressure increases, the elastic constants C11, C33, C66, C12, and C13 increase, the variation of elastic constant C44 is not obvious. Moreover, our compressional and shear wave velocities VL=6.99 km/s and VS=3.67 km/s as well as the Debye temperature Θ=549.7 K at 0 GPa compare favorably with the available experimental data. The pressure dependences of band structures, energy gap and density of states are also investigated. 相似文献
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Using the -band tight-binding (TB) model and the quantum box boundary
condition, we have discussed how both of the applied strain and
finite-length affect the energy bands of metallic carbon nanotubes (CNTs).
It is found that, for finite-length CNTs, energy gap for the armchair tube
under uniaxial strain and metallic zigzag tube under torsional strain will
oscillate with increasing strain, which do not exist in the case of
infinite-length CNTs, and will be able to be observed by experiments in
future. 相似文献
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采用蒙特卡罗方法, 利用MCNP程序计算了在中子能量为0.5–20 MeV, 235U核热中子裂变源条件下, 厚度为3–9 cm、碳化硼含量5%–15%的铝基碳化硼复合材料在空气、水、200–1400 ppm (1 ppm=10-6) 硼酸溶液介质中的中子透射系数. 结果表明: B4C/Al复合材料的透射系数随碳化硼含量和材料厚度的增加而减少, 随中子能量的升高而增大, 而硼酸浓度的改变对中子透射系数影响不大. B4C/Al复合材料在水中比硼酸中更能发挥其屏蔽效果, 在空气中屏蔽特性显现出“反转”现象, 中子能量高于5 MeV时透射系数几乎没有变化. 在裂变源条件下的B4C/Al复合材料中子透射系数均比稳定源20 MeV 低. 介质的中子屏蔽效果是硼酸溶液>水> 空气, 水介质的中子透射系数与介质厚度呈指数下降关系, 裂变源和稳定源条件下分别近似为e-0.71x和e-0.669x, x为厚度(cm).
关键词:
蒙特卡罗
乏燃料设备
中子吸收材料
4C/Al')" href="#">B4C/Al 相似文献
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Y.Y. Sun I. Rusakova R.L. Meng Y. Cao P. Gautier-Picard C.W. Chu 《Physica C: Superconductivity and its Applications》1994,230(3-4):435-442
We have carried out a systematic structural, electric, and magnetic study on Y---Pd---B---C samples with different compositions with emphasis on the as-cast and annealed YPd5B3C0.3 which was first reported to superconduct at 23 K by Cava et al. We found that the tetragonal body-centered YPd2B2C with lattice parameters a=3.71 Å and c=10.81 Å is the phase responsible for the 23 K superconductivity and that YPd2B2C is metastable, which is consistent with the suggestion made by Cava et al. [1]: it is not stable at high temperatures nor stabilizable by Ni doping, although its isostructural compound, YNi2B2C, exists. Two new phases with Y:Pd ratios of 1:7 and 2:3, respectively, have also bee detected. 相似文献
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In this work, the specific heat of NdNi2B2C was computed with the three sets of crystal-field parameters proposed by previous authors. All curves of the heat capacity plotted with the calculated results exhibit sharp peaks around the magnetic transition temperature TN as experimentally observed. To understand the mechanism of its magnetic ordering, we also calculated the magnetization of the material in low temperature region with the ground crystal-field (CF) level, the two lowest CF levels, and the full CF levels of J=9/2 multiplet respectively for comparison. Using the two eigenstates of the ground CF level, we derived a formula for 〈Jx〉 with mean-field approach for theoretical analysis. Both our numeric and theoretical results suggest that the two lowest CF levels play dominant roles in the magnetic process of the material below TN. It is also very interesting to notice that the ground CF level itself results in a larger TN, but the inclusion of the first excited CF doublet in calculations instead hinders the magnetic ordering, leading to a weakly reduced transition temperature. 相似文献
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We examine the electronic and magnetic structures of iron telluride KFe2Te2 using first-principle calculations. We demonstrate that the ground state of this compound is in bicollinear antiferromagnetic order with Fe local moments (~ 2.6 μB) that are ferromagnetically aligned along a diagonal direction and antiferromagnetically aligned along the other diagonal in the Fe-Fe square lattice, similar to the alignment discovered in the parent compound of superconductor α-FeTe. This bicollinear antiferromagnetic order results from the interplay among the nearest, next-nearest, and next-nextnearest neighbor exchange interactions, which are mediated by Te 5p orbitals. This finding may aid our understanding of the interplay between magnetism and superconductivity in the family of iron-based materials. 相似文献