摘要: Molecular dynamics are applied to simulate molecular motions in an aqueous solution of two soluble derivatives of a 100-ring polythiophene chain – one with sidechains terminating in a SO3– group, the other in NMe3+. Each chain is in a helical conformation defining a water-containing central channel along whose axis the dynamics of ions from the solution to the channel’s axial electrostatic potential is simulated. The profiles of these potentials distinguish the tendencies of the two channel species to occlude water molecules on their surfaces. Invoking the conductive polymer characteristics of polythiophene that can accomplish the transfer of electrons between the aromatic rings and redox reagents in the solution, the effect of this transfer on the axial potential and migration is followed. The electrostatic potential monitors differences in the association of the solvent molecules with the two species of helical polymer and shows that while Na+ and Cl– ions do not enter the channel in the absence of the redox changes, an ion with a selected charge does so spontaneously when appropriate electric charge is transferred to the channel. This enables the selected ion to travel about 10 – 20Å in the channel without the application of an external electric field.
摘要: This work provides an overview of organosilane metal pretreatments with a focus on water-based systems. Furthermore, this work aims to point out the key notes for organosilane technology to be fully transferred to industry.
摘要: In recent years, improvement of metals mechanical properties becomes one of the main challenges in materials and particularly in metallurgical industry. Mostly, an alloying process is typically applied to reach metals enhanced performance. This work, however, describes a different methodology, where WC and TiC nanoparticles used as a modifiers and then gas-dynamic treatment (GDT) are applied. These processes were investigated on a hypoeutectic casting aluminum A356 alloy. Microstructural evaluation illustrated that a coarse Al grains were refined as well as eutectic Si particles were formed. Subsequent mechanical properties tests revealed that aluminum elongation enhanced while strength remained unchanged. Addition of WC and TiC enhanced the elongation by 20-60%, depends on the mold area. A combined treatment, using GDT with addition of TiCN nanoparticles showed even improvement in both, elongation and strength by 18 and 19%, respectively. Moreover, based on the electron microscopy studies, this behavior was attributed to a grain-size strengthening mechanism, where a high concentration of grain boundaries serves as dislocation movement blockers
摘要: In this Chapter, we review knowledge about diffusion in quasi-crystalline alloys (quasicrystals). In Section 1 we first remind the reader of some major aspects of the quasi-crystalline state and in Section 2 we introduce phase diagrams with quasi-crystalline phases, for which detailed diffusion studies are available. We mention in Section 3 the more common experimental methods for diffusion studies. The diffusive motion of atoms in quasi-crystalline alloys can be studied by the same techniques used for crystalline metallic alloys and intermetallics – measurements of radiotracer diffusion and diffusion of stable isotopes and solute atoms by SIMS profiling. The best-studied quasi-crystalline alloys are icosahedral AlPdMn, icosahedral ZnMgRE (RE = rare earth metal), and decagonal AlNiCo. The major diffusion results for these quasicrystals are reviewed in Sections 4, 5, and 6. Section 7 is devoted to the pressure dependence of diffusion in quasicrystals and to a comparison of the activation volumes with those of crystalline metals. Positron annihilation studies are also mentioned, which together with activation volumes for diffusion strongly favour a vacancy mechanism in quasicrystals. The major results and conclusions are summarized in Section 8.
摘要: In this study, mass transport properties of liquid Cu-Ag alloys are investigated over wide temperature and composition ranges. The calculations are performed within the framework of the Green-Kubo (GK) formalism by using equilibrium molecular dynamics (MD) simulations along with one of the most reliable embedded-atom method potentials for this system developed by [P. Williams et al.: Modell. Simul. Mater. Sci. Eng. vol. 14 (2006), p. 817]. The approach employed allows for evaluation of the components’ self-diffusion coefficients as well as the phenomenological coefficient for mass transport Lcc. The results obtained in this study can be used to predict the kinetics of solidification of real liquid Cu-Ag alloys.
摘要: Molecular dynamics simulations were performed to analyze the curvature-driven shrinkage of individual cylindrical grains with geometrically different boundaries in Al. Grains with <100> tilt and mixed tilt-twist boundaries with the misorientations 5.5°, 16.3°, and 22.6° were simulated. The results revealed that the shrinking grains with tilt boundaries concurrently rotate increasing the misorientation angles, whereas grains with the mixed boundaries did not rotate during their shrinkage. Apparently, the grain boundary geometry/structure has a crucial impact on the observed rotational behavior of the computed grains. The grains with tilt boundaries rotate due to the lack of effectively operating mechanisms for annihilation of edge dislocations, which compose such boundaries. In contrast, for the mixed boundaries composed of edge-screw dislocations the sufficiently fast operating mechanisms of dislocation elimination are available, which facilitates grain shrinkage without rotation.
摘要: Supersaturated titanium-aluminum nitride (Ti1-xAlxN) is a very attractive material for a wide range of applications due to its high oxidation and wear resistance accompanied by high strength, hardness, thermal conductivity and thermal shock resistance. Currently, its applications are limited to coatings obtained by physical or chemical deposition. Bulk materials based on Ti1-xAlxN may be fabricated by powder metallurgy approach using powders synthesized by high-energy ball milling (HEBM), which composition corresponds to supersaturated Ti1-xAlxN solid solution. In the present study, thermal stability of the supersaturated Ti1-xAlxN solid solution was investigated. According to the quasi-binary TiN-AlN phase diagram, constructed using density functional theory (DFT) analysis, the concentration ranges, where decomposition takes place through spinodal decomposition or through nucleation and growth, were determined. Experimental study on thermal stability of solid Ti1-xAlxN solution powder was conducted by means of differential scanning calorimetry (DSC), Brunauer-Emmited-Teller (BET) and XRD. The results indicated that spinodal decomposition of Ti1-xAlxN starts at 800°C, while at temperature higher than 1300°C regular decomposition (nucleation and growth) is occur.
摘要: This study investigated the ambient blooming behavior of additives and mechanical properties of vulcanized natural rubber (VNR) loaded with non-ionic surfactants coco diethanolamide (CDEA) and glycerol monostearate (GMS). Taguchi method and analysis of variance (ANOVA) were used to determine the significant main effects of additives on bloom rates and mechanical properties of VNR. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) spectra of VNR surface confirm the presence of chemical functional groups of stearic acid, paraffin wax, used oil, CDEA, and GMS. The amount of bloom (MB) versus square root of time (t1/2) plot yields two linear regions corresponding to distinct bloom rates which suggest that the blooming behavior of additives follows a non-Fickian mechanism. High loadings of stearic acid, used oil, and paraffin wax increase the bloom rates due to migration of excess unreacted additives to the surface of VNR. Also, additives easily diffuse out of the VNR due to softening of the rubber matrix. High loadings of sulfur and CDEA consistently decrease the bloom rates because of the increase in crosslink density and increase in filler dispersion, making it difficult for additives to bloom out of rubber matrix. High loading of sulfur significantly improves the tensile and compression moduli of VNR. Meanwhile, high loadings of ZnO and used oil significantly decrease the tensile and compression moduli of VNR. Sulfur as a crosslinking agent increases the crosslink density which resulted to increase mechanical properties. Excess used oil and zinc stearate, reaction product of ZnO and stearic acid, on the VNR matrix resulted to rubber matrix softening and decrease in mechanical properties.
摘要: Sulfidation of undoped and aluminum doped zinc oxide materials has been performed by TGA under a H2S atmosphere in order to evaluate the impact of the doping element on sulfidation reaction kinetics and mechanism. The presence of aluminum seems to slow-down the reaction kinetics. This phenomenon might be explained by a modification of the solid state diffusion processes involved in ZnO sulfidation reaction and the related ZnS outward growth, assuming the presence of aluminum atoms inside ZnO and ZnS phases. In order to determine solid state diffusion mechanisms controlling the reaction kinetics, molecular dynamics simulations were performed using a Coulomb-Buckingham potential. Firstly, the diffusion of the different elements (Zn, O, S) was simulated for both the oxide and sulfide phases considering a vacancy mechanism. Secondly, simulations of the oxide phase doped by a trivalent cation were also performed. The results obtained in this preliminary work are presented and compared to the literature.