沈海军
材料科学与工程学报
分析了螺旋状碳纳米管沿其轴向的热传导特性.给出了螺旋碳纳米管轴向热传导系数ks的经验表达式.为验证Ks公式的有效性,还将螺旋碳纳米管ks的理论解和相应的有限元结果进行了比较.结果发现,螺旋碳纳米管的ks理论解和有限元结果较为接近.本文螺旋碳纳米管的轴向热传导系数ks表达式对人们进一步研究螺旋碳纳米管的热学特性具有重要的参考意义.
关键词:
螺旋碳纳米管
,
碳纳米管
,
热传导
李秋义
,
王志伟
,
李云霞
,
田砾
材料科学与工艺
doi:10.3969/j.issn.1005-0299.2008.04.026
通过正交试验,研究了水泥用量、粉煤灰用量、体积砂率等因素对高强高性能轻集料混凝土的强度、密度和工作性的影响规律.给出了利用700级海泥陶粒制备高强高性能轻集料混凝土的适宜配合比:水泥用量为385ks/m3-450ks/m3,Ⅱ级粉煤灰用量为125ks/m3-150ks/m3,体积砂率为35%,外加剂为胶凝材料的1.5%,水约150ks/m3-160ks/m3.该混凝土的密度等级为1800级,28d强度可达45 Mpa～50MPa,快速冻融循环可超过300次,RCM法测得的氯离子扩散系数仅为8.95×10-12m2/s～7.73×10-12m2/s,且工作性较好,基本克服了陶粒的上浮问题.
关键词:
海泥陶粒
,
轻集料混凝土
,
配合比
,
工作性
Journal of Magnetism and Magnetic Materials
First-principles full-potential linearized augmented plane-wave method is used to investigate the electronic structure and magnetic properties of hypothetical zinc-blende and rocksalt LiS, NaS and KS. We find that all the compounds except rocksalt LiS exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 mu(B) per formula unit. The ferromagnetism results from the spin-polarization of p states of anion S. Total energies calculations indicate the rocksalt phase is lower in energy than the zinc-blende one. The total energy differences are about 0.38, 0.36 and 0.32 eV per formula unit for LiS, NaS and KS, respectively. Meanwhile, it is shown that rocksalt NaS and KS have the half-metallic gaps of 0.22 and 0.41 eV, respectively, and the half-metallic gaps are 0.03, 0.46 and 0.65 eV for zinc-blende LiS, NaS and KS, respectively. We also find the half-metallicity is robust against the lattice contraction up to 7% and 13% for rocksalt NaS and KS, respectively. Although rocksalt LiS is nonmagnetic and metallic at the equilibrium lattice constant, it shows half-metallic ferromagnetism when the lattice constant is larger than 5.40 angstrom. (C) 2011 Elsevier B.V. All rights reserved.
关键词:
Half-metallicity;Density of state;First-principles calculation;molecular-beam epitaxy
Physical Review B
An elastic Ising model for CoMnO(6) chain is proposed to explain the ferroelectricity induced by collinear magnetic order in Ca(3)CoMnO(6), and then a mean-field theory with interchain spin interactions based on this model is developed. With inclusion of the dynamics of polarization domains at finite temperature, we address the rationality of our theory by the good agreement of the calculated electric polarization and dielectric susceptibility with the reported data on Ca(3)Co(2-x)Mn(x)O(6) (x approximate to 0.96) [Y. J. Choi, H. T. Yi, S. Lee, Q. Huang, V. Kiryukhin, and S.-W. Cheong, Phys. Rev. Lett. 100, 047601 (2008)], a typical diatomic Ising spin chain system, while the predicted magnetic susceptibility shows some difference from experiment, the reason of which is discussed.
关键词:
calcium compounds;cobalt compounds;dielectric polarisation;ferroelectricity;Ising model;magnetic susceptibility;multiferroics;optical susceptibility;one-dimensional oxides;magnetic-properties;multiferroics;ca3co1+xmn1-xo6
International Journal of Modern Physics B
The pore characteristics and pore size distribution of porous near-equiatomic NiTi shape memory alloy fabricated by self-propagating high-temperature synthesis (SHS) are described in detail. The effects of different heat treatments on the transformation of porous NiTi alloy were investigated by differential scanning calorimetry (DSC), x-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that heat treatment had strong influences on the transformation temperatures and latent heats of transformation. When the porous alloy was annealed at 648K and 748K for 3.6ks, two steps transformation including R transformation occurred during cooling and heating and the R transformation temperatures are lower than B2 <-> B19' transformation temperatures. However, no transformation was detected within the experimental temperature range if the porous alloy was solution treated at 1133K for 2.4ks. This novel phenomenon was the results of extensive Ti2Ni intermetallic compound precipitation. The transformation temperatures of porous NiTi alloy after annealing at 1323K for 3.6ks were much lower than those of the untreated alloy.
关键词:
Porous nickel titanium shape memory alloy;Martensite transformation;Self-propagation high-temperature synthesis;martensitic-transformation;phase;mechanism;temperature
