Features of the kinetics of chemical reactions in a nanostructured liquid

A review of the literature on the supramolecular structure of a liquid medium and the kinetics of formation of the structure has been presented. The models that relate the kinetics of chemical reactions to the liquid medium structure have been discussed. It has been shown that the results of the mathematical modeling of the kinetics of reactions in a nanostructured liquid medium taking into account the difference in the reactivity of molecules of the reagents and associates are consistent with the experimental data; in particular, they can be used to explain the cause of the observed kinetic anomalies.     

Electronic States of Nanostructured Systems: Titanium and Zirconia

The density functional method with pseudopotentials are used to study the electron states of nanoparticles and nanostructured systems: chains, films, and three-dimensional nanosystems of titanium and zirconia. It is shown that all studied titanium nanosystems have the density of electronic states (DES) of the metallic type, but zirconia nanosystem demonstrates a dielectric energy gap in the vicinity of the Fermi level. The density of states of nanostructured titanium is close in shape to DES of the single crystal but has a smoother shape due to disordering of the atomic arrangement. The forbidden band width of the nanostructured zirconia is smaller as compared to the corresponding width in crystalline ZrO₂, supposedly because of incomplete saturation of ionic bonds.     

两相钛合金再结晶退火组织与织构演变的蒙特卡罗模拟

蒙特卡罗(MC)方法被广泛应用于模拟金属材料在退火过程中的静态再结晶行为. 在已有两相材料晶粒长大MC模型基础上, 引入形核阶段, 综合考虑再结晶晶粒吞并形变晶粒和再结晶晶粒竞争长大两种情况, 建立了退火时两相合金再结晶MC模型.结合电子背散射衍射所测 初始晶粒形貌、相成分、晶体学取向及应变储能相对值, 该模型被应用于TC11钛合金退火过程中的微观组织及织构演变模拟.结果表明, 所建模型能够较好体现退火过程中两相晶粒的形核及晶粒长大行为. 与β相相比较, α相具有较低的再结晶速率和较高的晶粒长大速率, 前者主要归结于α相较低的初始应变储能, 后者则体现了该条件下初始组织形貌、分布及两相比例对晶粒长大具有重要影响; 由于非均匀形核的影响, 模拟得到的再结晶速率变化与 假设均匀形核的Johnson-Mehl-Avrami-Kolmogorov 再结晶方程存在明显差异.同时, 两相的基本织构特征在退火过程中无明显变化, 但织构强度增加. 关键词： 两相钛合金 再结晶 蒙特卡罗方法 织构     

Diagnostics of properties of capacitor foil with extended nanostructured surface

The results of the study of nanostructured titanium coating used for producing cathode foils of electrolytic capacitors with the best operating characteristics in the world are described. The coating is produced by titanium deposition on an aluminum substrate by electron-beam evaporation in a nitrogen atmosphere. The study was performed using scanning electron microscopy, atomic-force microscopy, X-ray photoelectron spectroscopy, and thermodesorption spectroscopy.     

Fabrication of superhydrophilic or superhydrophobic self-cleaning metal surfaces using picosecond laser pulses and chemical fluorination

Bioinspired superhydrophilic/phobic self-cleaning surfaces have recently drawn a lot of interest in both fundamental and applied research. A hybrid method to produce the self-cleaning property of micro/nanostructured surface using ultra-fast laser pulses followed by chemical fluorination is proposed. The typical micro/nanocomposite structures that form from microporous arrays and microgroove groups have been processed by picosecond laser on titanium alloy surface. The surface hydrophilic/phobic and self-cleaning properties of micro/nanostructures before and after fluorination with fluoroalkyl-silane were investigated using surface contact angle measurements. The results indicate that surface properties change from hydrophilic to hydrophobic after fluorination, and the micro/nanostructured surface with increased roughness contributes to the improvement of surface hydrophobicity. The micro/nanomodification can make the original hydrophilic titanium alloy surface more hydrophilic or superhydrophilic. It also can make an originally hydrophobic fluorinated titanium alloy surface more hydrophobic or superhydrophobic. The produced micro/nanostructured titanium alloy surfaces show excellent self-cleaning properties regardless of the fluorination treatment, although the fluorinated surfaces have slightly better self-cleaning properties. It is found that surface treatment using ultra-fast laser pulses and subsequent chemical fluorination is an effective way to manipulate surface wettability and obtain self-cleaning properties.     

Morphological transition from the Euclidean to the fractal shape of the Lüders band in the aluminum-magnesium alloy AMg6

The spatio-temporal structure of the Lüders band in artificially aged and recrystallized AMg6 alloys deformed under uniaxial tension at a constant stress rate = const has been investigated using high-speed video recording. A kinetic morphological transition has been revealed between the Euclidean and fractal shapes of the Lüders band due to a transformation of the initial microstructure of the alloy from the precipitation structure formed as a result of the artificial aging to the collective recrystallization structure. The mechanisms of formation of the dendrite-like fractal structure of the Lüders front have been discussed.     

Physicochemical Properties of TiN Powder Produced by Arc Discharge Technique

The physicochemical properties of ultrafine TiN powder produced by atomization of titanium in a low-pressure nitrogen-argon gas mixture are studied. It is shown that the TiN powder is composed of nanocrystalline particles with narrow particle-size distribution. The oxidation and recrystallization problems are discussed.     

Surface impurity diffusion-induced recrystallization of ultrafine-grained molybdenum

Methods of scanning and transmission electron microscopy are used to perform a comparative analysis of the structur evolution of ultrafine-grained molybdenum subjected to nickel-free annealing and to diffusion annealing accompanied by nickel penetration from the surface into the bulk of Mo(Ni) specimens. The kinetics of nickel diffusion-induced recrystallization of ultrafine-grained molybdenum in the temperature interval 1123–1223 K is investigated and the recrystallization activation energy is determined. Plausible reasons for a decrease in the nickel diffusion-induced recrystallization temperature of ultrafine-grained molybdenum as compared to its fine-grained cousin are discussed. The nickel diffusivity in ultrafine-grained molybdenum along grain boundaries is estimated on the basis of the results obtained. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 37–42, May, 2007.     

热加工过程中动态再结晶现象的多相场研究

金属热加工过程中的动态再结晶引起的组织演化难以通过实验实时观察, 本文基于Ginzburg-Landau动力学方程, 构造多相场法与位错密度计算相耦合的物理模型, 模拟了热加工过程中的动态再结晶现象.研究了不同温度和不同应变速率下的动态再结晶过程, 阐述了应力-应变曲线由单峰形式转变为多峰形式的原因.此外, 本文利用多相场法对多阶段变形过程进行了系统模拟, 研究了静态回复对动态再结晶过程的影响, 分析了不同的热加工参数对动态再结晶动力学的影响, 发现在变形间断过程中, 晶粒尺寸不断增大, 较高的变形温度和较低的应变速率可以加速动态再结晶过程.     

Supercube grains leading to a strong cube texture and a broad grain size distribution after recrystallization

This work revisits the classical subject of recrystallization of cold-rolled copper. Two characterization techniques are combined: three-dimensional X-ray diffraction using synchrotron X-rays, which is used to measure the growth kinetics of individual grains in situ, and electron backscatter diffraction, which is used for statistical analysis of the microstructural evolution. As the most striking result, the strong cube texture after recrystallization is found to be related to a few super large cube grains, which were named supercube grains. These few supercube grains become large due to higher growth rates. However, most other cube grains do not grow preferentially. Because of the few supercube grains, the grain size distribution after recrystallization is broad. Reasons for the higher growth rates of supercube grains are discussed, and are related to the local deformed microstructure.     

On the thermal stability of the cobalt nanostructure formed under severe plastic deformation

The results of the investigations of the temperature dependence of thermal expansion of nanostructured cobalt have been presented. It has been shown that deformation nanostructuring results in the nonlinear behavior of the cobalt thermal expansion curve, and the manifestation of a stepwise sample elongation in the phase transformation temperature range in this curve disappears. It has been found that the sample length at room temperature changes after cycles of heating to various temperatures. Based on the results obtained and X-ray diffraction data, it has been demonstrated that there is a correlation of these changes with recovery and recrystallization processes.     

Recrystallization inhibition assessed by splat cooling and optical recrystallometry

Levels of recrystallization have been measured by two distinct techniques; a splat cooling assay and a new device, an optical recrystallometer, which measures the change in light transmittance through a frozen sample. Both techniques indicate the presence of recrystallization inhibitors in a grass extract and in other samples. The advantages of each method of measuring recrystallization are discussed.     

Detection of recrystallized structure by means of automatic analysis of electron backscattered diffraction patterns

The possibility of applying the automatic analysis of electron backscattered diffraction (EBSD) patterns to reveal the recrystallized structure in the partially recrystallized material has been discussed. The analysis has been performed based on new experimental results. It has been shown that the EBSD method can be successfully used to investigate the recrystallization process.     

Effect of impact-induced melting on interface microstructure and bonding of cold-sprayed zinc coating

Zn particles are employed to create different impact conditions, including impact-induced interface melting in cold spraying. The influence of particle impact conditions on the interfacial microstructure evolution, microhardness and the bonding of particles in cold-sprayed Zn coatings are studied. An examination of coating surface morphology provides convincing evidence for melting at particle interfaces. The results reveal that the nanostructured phase was formed at the interface areas between deposited particles in coating resulting from the recrystallization of deformed grains. Melting at interfaces significantly enhances the bonding between the substrate and the coating and between the deposited Zn particles in the coating through the formation of a metallurgical bond. In addition, high driving gas temperature causes the decreasing hardness of deposited Zn coatings. The effects of particle conditions on the impact-induced melting and bonding mechanisms are discussed.     

Control of the shell structure of ZnO–ZnS core-shell structure

Nanostructured ZnO–ZnS core-shell powders were synthesized through a solution method using a thioacetamide (TAA) solution in deionized water. ZnO powder and TAA solution were employed to supply zinc and sulfur ions to form the ZnO–ZnS core-shell structures. The structure of the ZnS shell was strongly affected by the mole concentration of the TAA, and the structural properties were characterized by X-ray diffraction and high-resolution transmission electron microscopy. The optical properties of the nanostructured powders were also compared with those of pure ZnO powder. The ultraviolet (UV) emission was greatly enhanced compared to when pure ZnO powder was used in the nanostructured powder synthesized using the 0.5 M TAA solution, while the UV emission of that with the 0.05 M TAA solution was reduced. The green emission of the nanostructured powders was reduced compared to when the pure ZnO powder was used. The mechanism of the structural changes in the core-shell structures is proposed here and its effect on the luminescent properties is discussed.     

Possibility of Combining Nuclear Level Pumping in a Plasma with Lasing in a Solid

Nuclear isomers can be used for the storage and release of “clean” nuclear energy and several triggering schemes have been discussed. Here the possibility to utilize resonance between atomic and nuclear transitions in the form of a hybridization of atomic-nuclear excitation is considered. Several isotopes and specific nuclear levels are identified as candidates for triggering via atomic transitions. A variety of ionization states and atomic-shell configurations arises in a hot plasma generated by short high-power pulses of laser light. The non-radiative conversion of the ionization energy within an atom can be suppressed in the hot plasma surroundings. The time scales of different processes in nuclear, atomic and condensed-matter subsystems are compared and the fast ionization in a solid, X-ray radiance in a plasma, and sample melting and recrystallization may precede nuclear fluorescence. A time scale shorter than 0.1 ns makes this sequence promising for the collective excitation of short-lived modes in a nuclear subsystem. This revised version was published online in August 2006 with corrections to the Cover Date.     

Enhancement of Molar Heat Capacity of Nanostructured Al2O3

The nanosized alumina prepared by the hydrolysis method with an average particle size of 20 nm was characterized by X-ray diffraction. The heat capacity measurements of the prepared sample were carried out using an adiabatic calorimeter in the temperature range from 78 to 370 K. Enhancement of heat capacity was observed in the nanostructured materials as the heat capacity data were compared with those of the corresponding coarse-grained materials. The enhanced heat capacity was discussed on the basis of experiments. Differential scanning calorimetry and thermogravimetry were used to determine the thermal stability of the nanostructured alumina.     

A study of the mechanically milled h-BN-H system

Defective nanostructured h-BN, with different structural characteristics, can be prepared by mechanical milling under hydrogen and argon atmospheres. When h-BN was mechanically milled under a hydrogen atmosphere, hydrogen could be trapped by the B- and N-dangling bonds formed; the amount of which reached up to 2.6mass% after 80 h milling. The absorbed hydrogen can be released only as molecular hydrogen starting from about 570 K. As is clarified by a combination of TDS and IR measurements, the hydrogen detrapped from B–H and N–H bonds dominates the desorption at the lower and higher temperature ranges, respectively. After the nanostructured h-BN was heated to 1173 K, some of the hydrogen was still trapped by N–H bonds where, correspondingly, no recrystallization was detected. PACS 81.05.Tp; 61.46.+w; 81.20.Ev; 81.05.Zx