Attenuated total reflection spectroscopy under conditions of weak absorption: Further development of a new method for determination of integrated intensities

Development of a new method for the determination of the integrated intensities in isotropic condensed media is suggested. In a previous publication, with the use of analytical calculations, it is shown that, for the ATR spectra measured under conditions of weak absorption, the area under the absorbance curve of an isolated Lorentzian band is directly proportional to the integrated intensity of this band. It is also shown that the proportionality coefficient between these two parameters contains only one unknown parameter: the real part of the complex dielectric constant for the studied medium at the maximum of the studied band. In order to determine the numerical value of this parameter and, at the same time, to find the integrated intensity value, it is suggested to carry out two experiments; in these experiments, the same band is studied while the most important parameters are varied, such as the IRE refractive index, the angle of incidence, and the polarization. The main random and systematic errors of the suggested method are considered: ways to minimize these errors are discussed. The approach developed in this work is compared with other methods for determination of the integrated intensities.     

TC6钛合金动态压缩变形中“应力塌陷”的形成原因

采用分离式Hopkinson Bar技术和一种新型的中断动态试验方法对TC6钛合金进行了动态压缩试验,通过光学显微镜、扫描电子显微镜分析了TC6钛合金变形到不同应变量时所产生绝热剪切带的微观形貌,通过与宏观力学响应相对应,研究了TC6钛合金在动态压缩变形中,绝热剪切带的形成过程及造成应力快速下降的原因。结果表明:在高应变率下,材料绝热剪切带的形成是一个由萌生、扩展、完全发展组成的过程;在应变率为2.5×10~3s~(-1)的动态压缩过程中,"应力塌陷"现象是由于材料内产生了大于一定尺寸的微裂纹所致。     

Evolution of the Temperature Field and Macrolocalization of Strain under Intermittent Yield

Results of a study of special features of macrolocalization of strain under intermittent yield obtained with the help of thermal imaging and analysis of thermograms are presented. The stage of initiation of strain bands is discovered and detected. It is shown that the beginning of intermittent yield may be preceded by macroscopic nonuniformity of strain, which does not disturb the stability but activates the beginning of band formation. Static loading in the elastoplastic range is shown to be accompanied by a decrease in the temperature. Specific features of the evolution of temperature fields are determined for different serration patterns. It is shown that local heating due to the formation of one strain band can activate the formation of the next band. It is inferred that the method of thermal imaging is very effective for studying special features of plastic strain.     

Cyclic UV-Vis spectrovoltammetry of polyaniline

Polyaniline films deposited on indium-tin oxide (ITO) glass sheet electrodes were investigated by UV-Vis spectroelectrochemistry. A hysteresis in absorbance versus electrode potential profiles was found during cyclic potential sweeps for three characteristic absorbance bands of polyaniline. The hysteresis was shown to depend on the potential scan rate. Linear correlations were found between the electrode potential of absorbance half-intensity and the potential scan rate. From these relationships it is concluded that the growth rate of the absorbance of the main band in the red region of the spectrum during the anodic potential sweep is more sensitive to the potential scan rate than the decrease of the absorbance in the reverse cathodic scan. Thus, the coloration of polyaniline film proceeds slower during its anodic oxidation than its bleaching during the reverse cathodic reduction.     

TC6钛合金绝热剪切带不同发展阶段的精细结构

采用分离式Hopkinson Bar技术对TC6钛合金进行动态剪切试验,通过光学显微镜、扫描电镜及透射电镜研究Tc6钛合金绝热剪切带不同发展阶段的精细结构及其形成机制.结果表明:在高应变率下,材料绝热剪切带的形成是一个由萌生、扩展、完全发展组成的过程,Tc6钛合金绝热剪切带在不同发展阶段的精细结构有很大的不同,从萌生到完全发展,塑性变形剧烈程度逐渐增大,位错在TC6钛合金绝热剪切带的形成中起到非常重要的作用.     

MICROSTRUCTURE AND MACROSEGREGATION OF Al-7%Si ALLOY SOLIDIFIED UNDER COMPLEX EFFECTS OF ELECTROMAGNETIC AND CENTRIFUGAL FORCES

1.IntroductionElectromagneticcentrifugalcasting(EMCC)isanewtechnologydevelopedfromcentrifUgalcastingandelectromagneticstirringprocessing.WithaseeofEMFgeneratingdeyicemountedonacentrifugalcastingmachine,liquidmetalssolidifyunderthecomplexeffectsofEMFandcentrifugalforce.ThequalityofthecastingsiscontrolledbymodifyingtheparametersofEMFandcentrifugalcasting.Thistechnologyprovedveryeffective...inimprovingthemacrostructureandpropertiesofthecastings['].WiththeeffectoftheEMF,thereisalwaysaconve…     

Dynamic fragmentation induced by network-like shear bands in a Zr-based bulk metallic glass

Dynamic fragmentation induced by network-like shear bands is observed in a Zr-based bulk metallic glass subjected to impact loading, which is different from shear failure via one dominant shear band under quasi-static compression. Further, the influence of elastic strain energy on the evolution of shear bands is investigated. It is shown that the shear-band pattern occurring in one dominated mode or in multiple modes strongly depends on the loading rates. Dynamic fragmentation is due to the competition between the elastic strain energy driving a shear band and the dissipated energy along the shear band.     

Gradient viscoplastic modelling of material instabilities in metals

A gradient viscoplasticity model has been used to analyse stationary and propagative instabilities. It is demonstrated that the use of viscous regularisation is effective for both quasistatic and dynamic problems. Due to the influence of the length scales that are introduced in the model, the numerical simulation gives mesh-objective results with a finite width and unique orientation of the shear band. The numerical simulation of shear banding and propagative Portevin-Le Chatelier bands will be discussed. A 3D analysis of shear banding is shown to give significantly differentresults than the 2D plane strain analysis under similar conditions. Very fine meshes are needed to obtain accurate solutions for the shear band. The Arbitrary Lagrangian Eulerian remeshing method will be used to relocate elements from outside to inside the shear band to minimise computer costs.     

Protonation and charge transfer in polyaniline: an optical absorption study of the mixed solutions

Interaction of polyaniline (PANI) with a protonating dopant, dodecylbenzenesulfonic acid (DBSA), and an organic electron acceptor, pentadecyltetracyanoquinodimethane (C₁₅TCNQ), is studied in DMSO solutions, using optical absorption spectroscopy. Each of the two agents alone induces an absorption band at 417 nm, attributable to cation-radicals of PANI. Free carrier absorbance in the near-infrared is absent in the case of C₁₅TCNQ. Moreover, the charge-transfer interaction between PANI and C₁₅TCNQ suppresses a transition to the conductive state. When PANI/C₁₅TCNQ mixtures are aged, a new band near 500 nm appears that can be attributed to an adduct of PANI and C₁₅TCNQ.     

Microstructural, optical and quantum confinement effect study of mechanically synthesized ZnTe quantum dots

ZnTe quantum dots (QD) have been synthesized in a quick single-step process by mechanically alloying a stoichiometric mixture of elemental Zn and Te powders at room temperature under Ar with 1 h of milling. The detailed microstructure of these powdered QD has been characterized by both Rietveld analysis of X-ray powder diffraction data and high resolution transmission electron microscopy. The results reveal that almost monodispersed spherical QD of ∼5 nm size were synthesized after 15 h of milling. These QD all belong to the cubic (Zn blende) phase and contain different kinds of stacking faults but with low lattice strain. The UV-vis absorbance spectra of ZnTe QD depict a significant blue shift with decreasing size of QD and the band gap estimated taken from the sharp absorbance peak position is greater than that of the bulk counterpart. The band gap increases with increasing milling time up to 15 h with a continuous decrease in the size of these QD and, therefore, their optical properties can be fine tuned by varying the milling time.     

TC6钛合金不同组织绝热剪切带的形成机理

采用分离式Hopkinson Bar技术对TC6钛合金等轴组织及网篮组织试样进行了动态剪切试验,通过光学显微镜、扫描电镜及透射电镜研究了TC6钛合金2种组织绝热剪切带的形成机理.结果表明:由于组织状态不同,其绝热剪切带的形成机理也不同;等轴组织绝热剪切带的形成是位错增殖、运动及塞积的结果,而网篮组织绝热剪切带的形成则是动态再结晶的结果.     

带极堆焊带极电流磁控技术的试验研究

利用模拟带极堆焊状态下带极电流对控制磁场存在与否及强度、位置变化的反应,应用电工学原理分析带极堆焊磁控技术。结果表明,在相同的电流、电压参数条件下,磁控装置的磁极所处位置、磁场强度会直接影响带极电流的分布,造成电流在带极宽度方向上的改变。由此推断堆焊时电磁控制是磁场对电流分布状态的控制,进而控制电弧在带极宽度方向上的均匀性和稳定性,保证宽带极的稳定堆焊。     

Ti-15Mo-3Al-2.7Nb-0.2Si钛合金绝热剪切带的微观结构演化

采用分离式Hopkinson压杆技术对Ti-15Mo-3Al-2.7Nb-0.2Si钛合金的帽形试样进行了强迫剪切试验,通过扫描电镜(SEM)及透射电镜(TEM)研究了Ti-15Mo-3Al-2.7Nb-0.2Si钛合金在动态加载下绝热剪切带的微观结构演化.结果表明:Ti-15Mo-3Al-2.7Nb-0.2Si钛合金由于其组织以bee晶格的a相为主,具有较好的变形能力,因此其绝热剪切带的形成是位错运动的结果;剪切带的微观结构演化过程为:晶粒在外加切应力作用下拉长变形一拉长晶粒的破碎-形成呈一定方向排列的细小等轴晶:带内形成的细小等轴晶尺寸为O.2～0.4ìm.     

高应变速率下45钢绝热剪切变形特征

基于退火、正火、调质三种不同热处理状态的45钢的帽型试样强迫剪切实验,在Hopkinson压杆的不同速率加载条件下,利用金相显微镜和扫描电镜测试方法研究了材料绝热剪切的变形特征和敏感性,分析了组织因素对绝热剪切的影响规律。结果表明,材料的组织不同,其绝热剪切变形的特征也不同。45钢正火态、调质态中均出现转变带,其余为形变带。随着加载速率和材料强度的提高,绝热剪切带由形变带变为转变带,剪切带宽度越窄,绝热剪切越敏感。     

Special features of warping of cast and welded parts at elevated temperatures under the action of residual temperatures

The regular features in warping of cast and welded parts produced from various alloys at elevated temperatures under the action of residual stresses are studied. The warping process under the action of residual stresses is directly reproduced on special cast and welded specimens. The temperature dependence of the warping is shown to behave similarly for various alloys and has an extremum at a specific temperature. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 3, pp. 34–35, March, 1999.     

Electrochemical and photoelectrochemical study of gallium arsenide–polybithiophene composite

Bithiophene (BiTh) was galvanostatically polymerized in the presence of gallium arsenide (GaAs) particles at different concentration. The properties of the composite layers were studied by electrochemical method (cyclic voltammetry), UV–vis spectroscopy and photocurrent measurements. From UV–vis spectroscopy studies, the absorbance of the composites is larger than the polybithiophene absorbance in the UV region. The p-type semiconducting behaviour of the reduced polybithiophene was studied by photocurrent measurements. It was observed that the photocurrents of the composites was higher than that of the PBiTh without GaAs, and increased with GaAs concentration.     

Superconductivity of the quasi-one-dimensional semiconductor — polyacene

Superconductivity in polyacene with zero or small band gap is studied within the mean field approximation. It turns out that the BCS gap and the transition temperature are not exponential but proportional to the square of the interaction constant. Even if a band gap exists, superconductivity persists as long as the band gap is small. Interchain transfers reduce the BCS gap and the transition temperature.     

电子晶体学图像处理及其在材料科学中的应用

本文指出，借助高分辨电子显微镜观察到的显微像并不总直观地反映晶 体结构，对于在特定离焦条件下拍摄到的结构像，其分辨率还要受显微镜分辨本领的限制，只有超高压高分辨电子显微镜才能直接给出原子分辨率的结构像。文章介绍了衍射晶体学与高分辨电子显微学相结合起来的优越性，和据此发展的电子晶体学图像处理技术，用此技术可以实现“从头”测定晶体结构，并能把中等电压电子显微镜得到的结构像分辨率约提高1倍，达到原子分辨率。文中举例介绍了此技术在测定晶体结构和缺陷中的应用。     

基于分光光度法的冷轧带钢表面残油量检测与分析

利用石油醚提取带钢表面轧制油,采用紫外分光光度法测定带钢表面含油量.利用CCl4提取带钢表面油脂,用红外分光测油仪测出油类物质在2 930,2 960,3 030 cm-1谱带处的吸光度,根据三个吸光度计算得出带钢表面总的含油量.结果表明,红外分光光度法和紫外分光光度法均能测定冷轧带钢表面的含油量,两种方法简单、快速,...     

Comparative analysis of the phosphorescence characteristics of copper(II), platinum(II), and osmium(II) porphyrinates in polystyrene matrix at temperatures of 77 and 298 K

Comparative analysis of phosphorescence spectra of 15-crown-5-substituted copper(II) (Cu(II)TCP), platinum(II) (Pt(II)TCP), and osmium (II) (Os(II)TCP) posphyrinates in a polystyrene film, as well as of phosphorescence quenching curves, at the temperatures of 298 and 77 K is carried out. It is found that the halfwidth of emission bands decreases under cooling due to a decrease in the population of the vibration satellites of electron transitions and a shift of the emission band maximums into the blue spectral range is observed. The curves of phosphorescence quenching of metal porphyrinates at 298 and 77 K are analyzed. It is shown that copper(II) porphyrinate Cu(II)TCP can be of interest as a low-temperature sensor due to the considerable change in the phosphorescence lifetime at a decrease in temperature.