STUDY OF THE STRUCTURE AND PROPERTIES OF LEAD-FREE RAPIDLY SOLIDIFIED ZINC-BASED ALLOYS DURING A HEAT TREATMENT

Представлены результаты исследований влияния сверхвысоких скоростей охлаждения расплава, равных не менее 10К/с, на свойства быстрозатвердевших сплавов системы Zn - Sn. Верхняя область фольги, контактирующая с кристаллизатором в процессе затвердевания, имела дисперсные частицы второй фазы, и по мере удаления от верхних слоёв размеры частиц укрупнялись. При комнатной температуре протекает распад пересыщенного твёрдого раствора с выделением дисперсных частиц. Дополнительная термическая обработка приводит к укрупнению частиц второй фазы, и способствует снижению микротвёрдости. Быстрозатвердевшие фольги с максимальной концентрацией цинка характеризуются наличием текстуры (0001), которая по мере увеличения содержания олова в цинке ослабляется, и при легировании выше 20 мас. % Sn происходит перестройка на текстуру (101̅0). Термическая обработка до 160 °С не приводит к изменению текстуры. The results of studies of the effect of ultrahigh melt cooling rates, equal to at least 10 K/s, on the properties of rapidly solidified alloys of the Zn - Sn system are presented. The upper region of the foil, in contact with the crystallizer during solidification, had more dispersed particles of the second phase, and as the distance from the upper layers increased, the particle sizes increased. At room temperature, the decomposition of a supersaturated solid solution proceeds with the release of dispersed particles. Additional heat treatment leads to the coarsening of the particles of the second phase, and helps to reduce the microhardness. Rapidly solidified foils with a maximum zinc concentration are characterized by the presence of a (0001) texture, which weakens as the tin content in zinc increases, and upon alloying up to 30 wt. % Sn is rearranged to (101̅0) texture. Heat treatment up to 160 °C does not change the texture.

Dynamic processes in transient phases during self-assembly of organic semiconductor thin films

Crystallization of organic semiconductor small molecules from solution proceeds in multiple steps. This study describes how asymmetric molecules lead to long-lived transient phases and their impact on carrier mobility for electronic devices.

Aqueous Flow Hydroxycarbonylation of Aryl Halides Catalyzed by an Amphiphilic Polymer-Supported Palladium–Diphenylphosphine Catalyst

An aqueous continuous-flow reaction system is developed for the palladium-catalyzed hydroxycarbonylation of aryl halides. Flow hydroxycarbonylation of aryl halides in aqueous solution proceeds efficiently in a flow reactor containing a palladium–diphenylphosphine complex immobilized on an amphiphilic polystyrene–poly(ethylene glycol) resin to give the corresponding benzoic acids in excellent yields.

The mechanism of electrochemical reduction of hydrogen peroxide on silver nanoparticles

Reduction of hydrogen peroxide on silver nanoparticle modified electrodes in the neutral solution proceeds through a CE mechanism.

Partial Decoupling of the Matrix Method for Planar Mechanisms Inverse Dynamics

This paper presents a partial decoupling method for the well-known matrix method commonly in use for the linear inverse dynamics problem of planar mechanisms. Any mechanism with a dyad of binary links can benefit from the proposed method, which involves extracting submatrices by looking for sufficient columns of zeros such that a reduced problem may first be solved with an equal number of scalar equations and unknowns. Then some equal-and-opposite internal joint forces are transferred to the remaining FBDs and the solution proceeds until the input link is solved in a decoupled manner. The method leads to significant reductions in computational cost for common planar mechanisms. The kinematics & dynamics textbooks have overlooked this partial decoupling in their presentations of the matrix method for inverse dynamics.

Determination of an effect of 3-chlorophenol on hydroxyl radical generation during ozonation through kinetic study in the power law type

Ozone decomposition in aqueous solution proceeds through a radical type chain mechanism. These reactions involve the very reactive and catalytic intermediates hydroxyl (OH) radical, O2− radical, HO2 radical, OH−, H2O2, etc. OH radical is proposed as an important factor in the ozonation of water. In the previous study, generation of OH radical in the ozonation of water containing 3-chlorophenol was mathematically evaluated. In this study, we estimated the kinetic equation for the effect of 3-chlorophenol on OH radical generation during ozonation using the power law equation, in order to analyze it more correctly. The OH radical was trapped with a 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as a stable adduct, DMPO-OH. The relationship between the ozone concentration, 3-chlorophenol content, and the initial velocity (ν0) of DMPO-OH generation was analyzed mathematically, and the following equation was obtained: ν0 (10−6 M/s)=(1.58×10−5)×[3-chlorophenol (10−6 M)]×[ozone (10−6 M)]2.40+(3.09×10−5)×[ozone (10−6 M)]1.72. The equation fitted very well with the experimental results, and square of the correlation coefficient was larger than 0.9.

A kinetic study of enhancing effect by phenolic compounds on the hydroxyl radical generation during ozonation

Ozone decomposition in aqueous solution proceeds through a radical type chain mechanism. These reactions involve the very reactive and catalytic intermediates O2- radical, OH radical, HO2 radical, OH-, H2O2, etc. OH radical is proposed as an important factor in the ozonation of water among them. In the present study, the enhancing effects of several phenolic compounds; phenol, 2-, 3-, 4-monochloro, 2,4-dichloro, 2,4,6-trichlorophenol on OH radical generation were mathematically evaluated using the electron spin resonance (ESR)/spin-trapping technique. OH radical was trapped with a 5,5-dimethyl-1-pyrroline-Noxide (DMPO) as a stable adduct, DMPO-OH. The initial velocities of DMPO-OH generation in ozonated water containing phenolic compounds were quantitatively measured using a combined system of ESR spectroscopy with stopped-flow apparatus, which was controlled by homemade software. The initial velocities of DMPO-OH generation increased as a function of the ozone concentration. The relation among ozone concentration, amount of phenolic compounds and the initial velocity (ν0) of DMPO-OH generation was mathematically analyzed and the following equation was obtained, ν0 (10-6 M/s) = (A′ × [PhOHs (10-9M)] + 0.0005) exp (60 × [ozone (10-9 M)]). The equation fitted very well with the experimental results, and the correlation coefficient was larger than 0.98.

Radiation-induced dissolution of chromium oxide in aqueous solutions

Gamma irradiation of suspensions of a commercial sample of α-Cr2O3 in the presence of KBrO3 in the concentration range 0.1 ≤ [BrO3−] ≤ 0.4 mol dm−3, at pH 4 and 25 °C brings about oxidative dissolution. Release of Cr(VI) to the solution proceeds at a constant rate that increases with bromate concentration, even in conditions of quantitative eaq− scavenging. A mechanism of reactions is proposed in which OH and BrO2 radicals oxidize surface Cr(III) to Cr(IV), and ionic release is achieved by oxidation of surface Cr(IV) by bromate. The corresponding set of equations was solved by a rigid method for the integration of ordinary differential equations, using these two heterogeneous rate constants as adjustable parameters. The calculated profiles are in close agreement with the experimental data. Key words: chromium oxides, radiation-induced dissolution, oxidation dissolution.

Analysis of Unsteady Compressible Viscous Layers

The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy–Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low-frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.

Analysis of Unsteady Compressible Viscous Layers

The development of an analysis to predict the unsteady compressible flows in blade boundary layers and wakes is presented. The equations that govern the flows in these regions are transformed using an unsteady turbulent generalization of the Levy-Lees transformation. The transformed equations are solved using a finite difference technique in which the solution proceeds by marching in time and in the streamwise direction. Both laminar and turbulent flows are studied, the latter using algebraic turbulence and transition models. Laminar solutions for a flat plate are shown to approach classical asymptotic results for both high and low frequency unsteady motions. Turbulent flat-plate results are in qualitative agreement with previous predictions and measurements. Finally, the numerical technique is also applied to the stator and rotor of a low-speed turbine stage to determine unsteady effects on surface heating. The results compare reasonably well with measured heat transfer data and indicate that nonlinear effects have minimal impact on the mean and unsteady components of the flow.