透明多晶尖晶石的制备研究

本文报道了采用高纯、超细的尖晶石粉末作为起始原料,用真空烧结法结合热等静压后处理技术制备透明多晶尖晶石材料,合成的原料纯度较高、粒度小、粒径分布窄.测试了尖晶石的透过率、抗弯强度、硬度、热膨胀系数等主要物理性能.制备的多晶尖晶石材料从紫外、可见光到近红外波段的透过率在75;以上.     

沸石分子筛单晶体弹塑性双线性本构关系的实验研究与有限元确定

为研究两种沸石分子筛方钠石SOD和镁碱沸石FER的力学性能,采用纳米压痕技术,测得随载荷连续变化的位移,得到载荷-位移曲线图.根据Olive算法,利用接触刚度连续测量技术,得到这两种沸石分子筛的硬度及弹性模量.基于弹塑性双线性本构关系假定,用ANSYS有限元程序模拟纳米压痕实验过程,利用搜索法得到沸石大单晶SOD和FER的双线性本构关系.     

高压下ReB2的结构特性及弹性性质

本文采用密度泛函理论中的赝势平面波法计算了ReB₂的P6₃/mmc晶体结构(即hP6-ReB₂)的结构特性及弹性性质。在计算了hP6-ReB₂的平衡结构参数后,从热力学、动力学及机械力学三方面验证了其结构稳定性。研究发现,hP6-ReB₂在高压下的弹性系数、各个弹性模量均随压强的增加而增大。泊松比显示hP6-ReB₂表现为脆性。三种类型的弹性波随压强的变化趋势显示hP6-ReB₂为弹性各向异性晶体。经估算,hP6-ReB₂结构的维氏硬度约为38.2 GPa。电子态密度揭示了hP6-ReB₂的Re—B和B—B之间存在着强共价键,并且随着压强的增加共价键逐渐增强。     

Ab initio study of electronic structure of strained

Micro-hardness and scratch adhesion testing are the most commonly used techniques for assessing the mechanical properties of thin films. Both of these testing methods utilize single-point contact and induce plastic deformation in the substrate and film. However, the influence of adhesion on the measured hardness has been seldom reported so far. In our experiments, diamond-like carbon (DLC) and silicon carbide (SiC) films deposited on silicon and nickel-based alloy substrates by pulsed laser ablation were indented and scratched by a Vickers micro-hardness tester and a diamond-cutter, respectively. It was found that the composite hardness decreased more rapidly for poor adhesion when increasing the indentation load. The result was explained by the elastic-plastic deformation mode of indentation and helped us to understand the physical meaning of one parameter commonly introduced in the models used to separate film hardness from the composite hardness. Received 30 June 1998     

Effect of Various Impurities on the Hardness of NaCl Crystals

The hardness of NaCl crystal in the presence of mono, divalent and polyvalent ions were measured. Measurements were made in the indentation load range from 5 x 10^‐3 to 20 x 10^‐3 N. The measured data showed that there is an indentation size effect. Classical Meyer's law was used for the characterization of crystal hardness f NaCl. The Meyer index was found to be smaller than 2 indicating brittle material characteristic. The PRS model was also used for the determination of the load‐independent microhardness value. It was found that the crystal hardness of NaCl is chancing depending on the type of impurity and the concentration.     

Polynomial time approximation of dense weighted instances of MAX‐CUT

We give the first polynomial time approximability characterization of denseweighted instances of MAX‐CUT, and some other dense weighted 𝒩𝒫‐hard problems in terms of their empirical weight distributions. This also gives the first almost sharp characterization of inapproximability of unweighted 0, 1 MAX‐BISECTION instances in terms of their density parameter. © 2000 John Wiley & Sons, Inc. Random Struct. Alg., 16: 314–332, 2000     

Nanomechanical and optical studies on polymeric membranes

The nanomechanical properties of poly(ethylene terephthalate) (PET) membranes, were examined in light of nanoindentation experiments under conditions of maximum contact load in the range of 0.5-12 m?. Spectroscopic Ellipsometry (SE) from 1.5 to 6.5 ev (Vis-FUV range) was also applied to probe the dielectric function (ϵ(ω) of the industrially supplied membranes, as well as their geometrical structure. Mechanical stretching (uniaxial or biaxial) procedures are usually applied for the elongation of the polymeric membranes, their thickness reduction and enhancement of their mechanical and optical performance, causing a preferable orientation of the macromolecules close to the surface. Nanoindentation and se testing have revealed the existence of a two-layer geometrical structure of the pet membranes, consisting of a thick amorphous pet layer and a thin crystalline-like pet overlayer, with increased hardness (elastic modulus). The analyses of the experimental dataprovides quantitative information on the formed overlayer, which is ascribed to the processing history of the membrane.     

Metal cations toxicity: An inorganic interpretation

Chemical hardness is one of the useful parameters giving information about the toxic nature of the structures. In the present work, absolute chemical hardness imparted to the science by Pearson, the hydration enthalpies, the element's electronegativity, as calculated by Batsanov (using the force constants of the bonds), the calculated electrostatic charge on the hydrated cations, the absolute radii for the metals and the effective nuclear charges, were correlated with available toxicology data for a series of metal cations (namely Hg²⁺, Cd²⁺, Cu²⁺ and K⁺) in order to obtain, from a physicochemical point of view, a better understanding of the deleterious actions of metal cations on living organisms. A series of linear curves and empirical equations were obtained, providing a convincing picture of the correlation toxicity-physical inorganic chemistry.     

Inference of Mechanical Properties from Instrumented Depth Sensing Indentation at Tiny Loads and Indentation Depths

Different hardness measures as Vickers, Brinell and Meyer hardness are discussed with respect to their physical interpretation. Meyer hardness is found to be best suited as a measure of plastic properties. The outline of a depth sensing nanoindentation experiment is described, and particular emphasis is given to the correct deduction of the contact area from indenter penetration data. Experimental complications, as phase transformations, finite machine compliance, thermal and pieco drift, and sample creep are detailed with, and their impact on the calculation of hardness and elastic modulus is shown. Furthermore the onset of yielding in dependence on critical load, indenter curvature and yield strength is discussed.