The role of the weakest-link mechanism in controlling the plasticity of micropillars

We present a computational study on the effects of sample size on the strength and plastic flow characteristics of micropillars under compression loading. We conduct three-dimensional simulations using the parametric dislocation dynamics coupled with the boundary element method. Two different loading techniques are performed. The plastic flow characteristics as well as the stress-strain behavior of simulated micropillars are shown to be in general agreement with experimental observations. The flow strength versus the diameter of the micropillar follows a power law with an exponent equal to -0.69. A stronger correlation is observed between the flow strength and the average length of activated dislocation sources. This relationship is again a power law, with an exponent -0.85. Simulation results with and without the activation of cross-slip are compared. Discontinuous hardening is observed when cross-slip is included. Experimentally observed size effects on plastic flow and work-hardening are consistent with a “weakest-link activation mechanism”.     

三次标准加入光度法同时测定铁钴镍的研究

利用在乙酸缓冲溶液中铁、钴、镍与１－亚硝基－２－蔡酚－３,６－二磺酸钠（ＮＲＳ）生成有色配合物的反应,结合在两次标准加入法原理的基础上,提出了三组分同时测定的三次标准加入法,并应用于铁、钴、镍的同时测定。为消除组分间协同效应所引起的吸光度加合性的偏离,定义了三组分协同效应系数,并将其引入三组分同时测定方法,补偿吸光度对线性的偏离;补偿后铁、钴、镍的测定线性范围分别为０．０３～３．５０,０．０５～３     

Zn(Ⅱ)、Ni(Ⅱ)与5-氯水杨醛缩乙二胺Schiff碱单、双核配合物的合成及其对O2-的催化歧化作用

多核或异核配合物的研究是近年来很引人注目的领域,因为这类配合物在磁交换作用、催化活性、生物模拟方面有广阔的应用前景 ［1］。有关资料报道 Ｓｃｈｉｆｆ碱类配合物可作为螯合剂、稳定剂、催化剂等,尤其对Ｏ２－具有较强的抑制作用。本文合成了未见文献报道的五种Ｓｃｈｉｆｆ碱配合物,研究了它们的组成和结构,并采用ＮＢＴ（核黄素一蛋氨酸）光照法测定了这类配合物催化Ｏ２－的歧化反应活性。结果表明上述化合物具有高稳定性和惰性,其生理作用优于一般配合物。１实验部分１．１仪器及试剂 日本岛津一４３５型红外光谱仪,上海产…     

Simultaneous Determination of Nickel(II) and Copper(II) by Second‐Derivative Spectrophotometric Method in Micellar Media

A second‐derivative spectrophotometric method based on zero‐crossing over technique is developed in simultaneous determination of copper(II) and nickel(II) ions. Methylthymol blue (MTB) as a chromogenic reagent and cetyltrimethylammonium bromide as a surfactant were used, and measurements were carried out in buffered solution at pH 6 and at a temperature of 25 °C. The amplitude of derivative spectra was measured at wavelengths of 631.9 and 587.7 nm for the simultaneous determination of Ni²⁺ and Cu²⁺, respectively. Linearity was obtained in the range of 0.5–5.0 μg mL^?1 for both ions in the presence of 0.0–5.0 μg mL^?1 of the other ion as an interfering ion. IUPAC detection limits for Cu²⁺ and Ni²⁺ ions were obtained at 0.48 and 0.43 μg mL^?1, respectively. The proposed procedure has been applied successfully for the simultaneous determination of copper and nickel in synthetic binary mixtures and real samples.     

Ligand assembly and metal ion complexation: syntheses and X-ray structures of Ni(II) and Cu(II) benzoate and 4-tert-butylbenzoate complexes of cyclam

The syntheses and X-ray structures of trans-[Ni(O-benzoato)₂(cyclam)], trans-[Cu(H₂O)₂(cyclam)]-(benzoate)₂·2H₂O and trans-[Cu(H₂O)₂(cyclam)](4-t-butyl-benzoate)₂ (where cyclam is 1,4,8,11-tetraazacyclotetradecane) are described. The nickel complex has a tetragonally distorted octahedral coordination geometry with cyclam occupying the equatorial plane in a stable trans-III arrangement, with benzoate ligands filling the axial positions. The structure closely resembles the arrangement in the previously described hydrogen-bonded (metal-free) ligand assembly [(cyclamH₂)·(4-t-butyl benzoate)₂]·2(benzoic acid) if the latter benzoic acid moieties, which do not interact directly with the cyclam moiety, are ignored. The 2?:?1 fragment thus may be viewed as a ligand assembly “preorganized” for nickel ion complexation. In contrast to the nickel structure, the two trans-axial sites in both copper structures are occupied by aqua rather than O-carboxylate ligands. Although they do not form part of the inner coordination sphere in either complex, the two carboxylate anions remain hydrogen bound to the (coordinated) cyclam ligand, with the mode of packing being generally similar in each complex.     

Characterization and Molecular Structure of Bis(Isopropyl Xanthate) Bis(1,10-Phenanthroline) Nickel(II): [Ni(phen)2(CH3)2CHOCSS](CH3)2CHOCSS

The crystal and molecular structure of the title compound, [Ni(phen)₂(CH₃)₂CHOCSS](CH₃)₂CHOCSS has been determined by X-ray diffraction. The brown crystal is triclinic of space group Pi, with parameters a = 11.790(2), b = 12.410(3), c = 12.680(3) Å, α = 92.49(3), β = 96.54(3), γ = 117.43(3)° and Z = 2. The compound contains a six-coordinate cation and an isopropyl xanthate anion (CH₃)₂CHOCSS^?, the central Ni atom is chelated by four nitrogen atoms of two phenanthroline ligands and two sulfur atoms of an isopropyl xanthate ligand. The TG data indicate that it decomposed completely at 734°C.     

Humidity sensing properties of Ni(OH)2 nanoparticles synthesized via sonochemical method

This work focuses on humidity sensor based Ni(OH)₂ nanoparticles. The sonochemical method was employed to prepare nanoparticles and impedance analysis was used to characterize sensitivity, response, and recovery time of the prepared sensor. The Ni(OH)₂ sensor was found to have high sensitivity and fast response/recovery time to humidity, and its impedance changed approximately two orders of magnitude from about 2.01 MΩ in dry air 20% RH (relative humidity) to 0.0258 MΩ in 90% RH air. Our results demonstrate the potential application of Ni(OH)₂ nanoparticles for fabricating high performance humidity sensors.