Journal of Alloys and Compounds
As hydrogen, deuterium and tritium storage materials, a series of investigations of mechanical and thermal properties of titanium hydrides, deuterides and tritides have been performed, however, very limited theoretical studies of thermodynamic properties for them can be found. Based on density-functional theory (DFT) and density-functional perturbation theory (DFPT) we have discussed systematically the hydrogen isotope effects on the thermodynamic properties of TiX2 (X = H, D, and T) system. Our calculations indicate that for evaluating accurately their physical properties at absolute zero temperature, such as the equilibrium lattice constants, bulk modulus, and heat of formation, the zero-point energy correction must be taken into account. By performing the phonon calculation within quasiharmonic approximation (QHA), we obtain their vibrational free energies, vibrational entropies, and temperature dependence of specific heat, thermal expansion, and bulk modulus. Those results demonstrate that comparing with TiH2, TiT2 and TiD2 are more stable and the zero-point effects play an important role in their thermal expansion. The increase in the force constant between Ti and H causes the higher value of specific heat of TiH2 during the phase transition from FCC to FCT. In addition, comparing with available experimental values, we can conclude that QHA is feasible for describing the thermal properties of TiX2. (C) 2006 Elsevier B.V. All rights reserved.
关键词:
isotope effects;thermodynamic properties;density-functional;perturbation theory;quasiharmonic approximation;functional perturbation-theory;neutron spectroscopy;thermal-properties;titanium;hydrogen;dependence;expansion;constants;palladium;hydrides
Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
张昕
,
周鑫
,
张红
原子核物理评论
采用4GyX射线辐照人乳腺癌细胞MCF-7,分别在照射后0,2,4,8,16,24,48,72和144h时间点收集细胞,提取DNA并以聚合酶链式反应进行扩增,再以BsaXI限制性内切酶对扩增产物进行消化,消化产物以琼脂糖凝胶电泳进行分离.结果表明,4GyX射线辐照可引起D310片段突变,且该突变在经辐照之后144h检测水平明显超过野生型.
关键词:
X射线辐照
,
线粒体DNA损伤
,
D310片段突变
,
聚合酶链式反应
朱杰武
,
柳永宁
,
许雁
,
冯耀荣
机械工程材料
doi:10.3969/j.issn.1000-3738.2005.06.007
在不同温度下测试了X70管线钢动态断裂韧度K1d、J1d和止裂韧度K1a以及夏氏V型缺口冲击韧度Ak,对三者的关系进行了分析.结果表明:温度和加载速率都对断裂韧度产生影响;加载速率变化引起的韧-脆断裂转变具有热激活特征,在热激活分析基础上,在应力强度因子速率K=15 MPa·m1/2s-1条件下,得出断裂韧度、止裂韧度和冲击韧度三者的关系:Ak=4.84×106T-2.8K1d(或K1a).可以用小试样Ak数据计算得到K1d和K1a.
关键词:
管线钢
,
断裂韧度
,
止裂韧度
,
韧-脆断裂转变
陈永亮
,
崔雅静
,
杨烨
,
王磊
,
李仪成
,
张勇
,
赵勇
低温物理学报
通过在SmFeAsO中Fe位上掺入5d过渡金属Ir,得到了一种新的铁基超导体SmFe_(1-x)Ir_xAsO,当x=0.05时,样品表现出超导电性,超导转变温度为8K,当x=0. 15时,超导转变温度达到最大值17. 3K X射线衍射结果表明所有样品均属四方ZrCuSiAs-type结构,SEM结果表明SmFe_(1-x)Ir_xAsO样品具有片层状形貌特征,随着Ir掺杂量的增大,晶格参数a增大而c减小,结合EDX数据,表明Ir掺人了SmFeAsO晶格当中.
关键词:
铁基超导体
,
ZrCuSiAs结构
魏恺文
,
王泽敏
,
曾晓雁
金属学报
doi:10.11900/0412.1961.2015.00212
利用OM, SEM, EDS, XRF和XRD等方法研究了AZ91D镁合金在激光选区熔化中的元素烧损机制以及烧损对成形试样化学成分、显微组织及力学性能的影响. 结果表明, 成形试样中Mg的相对含量(86.61%~88.68%)低于粉末原料中Mg的相对含量(90.63%), 而其Al的相对含量(10.40%~12.56%)则高于后者(8.97%). 该结果与基于Langmuir模型的计算结果相符, 表明在激光作用下主要是Mg发生了烧损. 成形试样的Mg与Al质量比η随激光体能量密度EV的增加呈现先上升后下降并最终趋于稳定的演变规律. 采用55.6 J/mm3的EV所成形试样(试样No.8)的η值最接近粉末原料. 使用回归分析法建立了η与EV的解析关系, 其拟合度指标系数R2为0.858. 成分变化最为显著之一的成形试样No.1 (采用166.7 J/mm3的EV所成形)与压铸态AZ91D 的组织特征相似, 均为β-Mg17Al12相呈网状分布于α-Mg基体间的典型凝固组织. 但成形试样No.1的β-Mg17Al12相含量及其α-Mg基体中Al的固溶量明显高于压铸态AZ91D. 成分变化导致成形试样No.1的拉伸强度及显微硬度得到提升, 但使其延伸率有所下降.
关键词:
激光选区熔化
,
AZ91D镁合金
,
元素烧损
,
化学成分
,
显微组织
,
力学性能
Journal of Physics-Condensed Matter
By the use of a first principles density functional theory, two kinds of models, namely the Rice-Wang thermodynamics model and the Seah quasi-chemical model, are employed to evaluate the embrittling tendency of a grain boundary (GB) due to the 3d element segregation. The first principles method based on those two models is appropriate for calculating the chemical and structural relaxation contributions to the changes of GB cohesion with the 3d segregants. The effects of the 3d transition elements, such as Ti, V, Cr and Mn, on a stable fcc Fe Sigma 11 [1 (1) over bar0]/(11 (3) over bar) GB are studied and the difference between these two models is interpreted. When the chemical and the structural relaxation effects are taken into account, the calculated results for these two models are coincident for most of the elements studied, except for chromium. After analysing their chemical bonding in detail, we find that this discrepancy may be attributable to a lower susceptibility of the Seah model to the bonding anisotropy caused by Cr in the GB. It is proposed that the Seah model should be prudently used for some elements, especially those lying in the middle of a transition period.
关键词:
phosphorus;adsorption;interstitials;decohesion;magnetism;systems;cluster;metals;boron
Physical Review B
In the investigation of the optical and magnetic properties of the semiconductors containing transition-metal ions, the one-electron orbital cannot be treated with a pure d orbital because of a strong covalence. This paper presents the energy matrix of the d*(8) and d*(2) (d* means a modified d function) system, in which the covalence is described by two covalent factors. The differences between the matrix diagonal elements of the t(2)(m)e(n) term of the d*(8) system and the t(2)(6-m)e(4-n) term of the d*(2) system vary with m and n. The d(N) electron system can be explained with the d(10-N) hole system because the difference between the energy matrix of the d(N) and d(10-N) systems has a fixed value. However, this kind of simple relation does not exist for the d*(N) and d*(10-N) systems when the covalence is considered. A numerical calculation shows that the variation of the energy levels with the covalence for Ni2+ in the d*(8) electron system is larger than that in the d*(2) hole system. The calculated energy levels obtained from the d*(8) matrix are in good agreement with the experimental data of the Ni2+ ion for ZnS:Ni and ZnSe:Ni. This suggests that the d*(8) electron system instead of the d*(2) hole system should be used in the investigation of optical and magnetic properties of semiconductor containing Ni2+ ions.
关键词:
zns-ni;absorption;vanadium;impurities;spectra;ions
