Generation of Electrical Currents and Magnetic Fields by Grain Boundary Motion

The effect of an induced magnetic moment due to grain boundary motion in a magnetic field was studied theoretically in a microscopic and a mesoscopic approximation. It was found that the induced moment generates a drag force on the boundary, which depends on the orientation of the magnetic field with regard to the crystal axis, as observed experimentally. However, the magnitude of the theoretically predicted dependency is much smaller than experimentally observed and even opposite with regard to the orientation dependence. Therefore, the electromagnetic drag can be neglected in comparison with other driving forces for grain boundary motion, but the effect may play a role for fast moving dislocations in a magnetic field.     

Effect of hydrostatic pressure on the migration of tilt grain boundaries in Sn- and Al-bicrystals

Abstract

The use of hydrostatic pressure as an intensive parameter for investigation of grain boundaries (GBs) migration in bicrystals is potentially important in gaining additional information on the mechanism of GB migration. This is because an analysis of the pressure dependence of the GB mobility yields a new activation parameter of the migration process, namely the activation volume V* which quantitatively is the difference between the volumes of the system in the ground and activated states. Only a few experiments to study the pressure dependence of GB mobility are known [1,2]. These experiments were made on polycrystalline materials. They provide the average data for all GBs in polycrystal and do not permit the determination of the connection between GB structure and value of activation volume V* of GB migration. In studying the mobility of single boundaries of a given type, there is the possibility of connecting the activation volume with the GB structural peculiarities, in particular, of determining the misorientation dependence of the activation volume, that is, of determining V* for GBs having various degrees of ordering.     

The Shape of the Moving Grain Boundary in the Reversed-Capillary Technique Under Consideration of the Drag Effect

The shape of the curved part of the migrating grain boundary driven by capillary forces was studied for the reversed-capillary bicrystal technique. A comparison of experimentally observed and theoretically calculated shapes showed good agreement when the drag effect by mobile obstacles was taken into account. So far previous studies dealing with the reversed-capillary technique have not considered the drag effect. Consequently, they assume a scaling behavior of the shape of the moving grain boundary. In this study it is shown that this assumption generally is not possible for the reversed-capillary technique. Furthermore, it is shown that the geometry factor used for determination of the driving force is dependent on the displacement. Problems specific to the reversed-capillary technique due to the drag effect are discussed. The analysis of the boundary shape is presented as a tool to distinguish free and dragged motion.     

Effect of finite boundary junction mobility on the growth rate of grains in 3D polycrystals

With decreasing grain size, grain boundary junctions become increasingly important for microstructure evolution. We show that the effect of a limited mobility of triple junctions on the growth rate of polycrystals can be implemented in theories of three-dimensional (3D) grain growth. Respective analytical relations are derived on the basis of the average n-hedra approach introduced by Glicksman to describe the volume rate of change of 3D grains in a polycrystalline aggregate under the impact of a limited triple junction mobility. The theoretical predictions were compared to network-model computer simulations, and good agreement was obtained.     

Influence of interparticle interactions on the kinetics of self-assembly and mechanical strength of nanoparticulate aggregates

Computer simulations based on Discrete Element Method have been performed in order to investigate the influence of interparticle interactions on the kinetics of self-assembly and the mechanical strength of nanoparticle aggregates.Three different systems have been considered.In the first system the interaction between particles has been simulated using the JKR (Johnson,Kendall and Roberts) contact theory,while in the second and third systems the interaction between particles has been simulated using van der Waals and electrostatic forces respectively.In order to compare the mechanical behaviour of the three systems,the magnitude of the maximum attractive force between particles has been kept the same in all cases.However,the relationship between force and separation distance differs from case to case and thus,the range of the interparticle force.The results clearly indicate that as the range of the interparticle force increases,the self-assembly process is faster and the work required to produce the mechanical failure of the assemblies increases by more than one order of magnitude.     

The stability of triple junctions during the grain boundary diffusion process

The grain boundary diffusion in a system with triple junctions is considered in such a geometry, in which the flows of diffusing atoms meet at the triple line. The solutions of the diffusion equation is given in the frameworks of Fisher's model and under the assumption of quasi-stationary distribution of the diffusing atoms along the grain boundaries. The change of the mechanical equilibrium at the triple junction due to the increase of the concentration of solute atoms is considered. It is shown that under some circumstances the triple junction looses its stability with respect to migration in the direction to the diffusion source. The stability diagrams in the segregation-diffusivity parameter space are plotted.     

Use of o-hydroxyaminobenzoic acid for the preparation of heterocyclic compounds

Anthranilic acid and its derivatives are widely used for the synthesis of nitrogen-containing benzoheterocycles, while its analog o-hydroxyaminobenzoic acid has been used only to prepare unsubstituted 2,1-benzoisoxazolone ¦1¦.     

Features of migration of triple junctions of different configuration

The stationary motion of individual triple junctions of different crystal geometry has been experimentally investigated. It is shown that triple junctions are characterized by intrinsic finite mobilities and drag parameters. The difference in the temperature dependences of the drag parameters of triple junctions may lead to the formation of an inhomogeneous polycrystalline microstructure during isothermal annealings.