Proton segregation on a growing ice interface

Hydronium segregates to the surface of H₂O (D₂O) ice films grown on Pt(1 1 1) above 151 K (158 K). This is observed via the voltage that develops across the films, utilizing work function measurements. The dependence of this voltage on the film’s thickness is explained by a simple equilibrium model: as the film grows, most of the surface ions migrate so as to remain at the ice–vacuum interface, while a fixed percentage (0.05%) take the thermodynamically–unfavored route, to become incorporated into the growing bulk ice. This model implies a ΔG of about +0.1 eV for the movement of ions from the ice surface into the bulk ice.     

Resistivity distribution of silicon single crystals using codoping

Numerous studies including continuous Czochralski method and double crucible technique have been reported on the control of macroscopic axial resistivity distribution in bulk crystal growth. The simple codoping method for improving the productivity of silicon single-crystal growth by controlling axial specific resistivity distribution was proposed by Wang [Jpn. J. Appl. Phys. 43 (2004) 4079]. Wang [J. Crystal Growth 275 (2005) e73] demonstrated using numerical analysis and by experimental results that the axial specific resistivity distribution can be modified in melt growth of silicon crystals and relatively uniform profile is possible by B–P codoping method. In this work, the basic characteristic of 8 in silicon single crystal grown using codoping method is studied and whether proposed method has advantage for the silicon crystal growth is discussed.     

Efficient adaptive phase field simulation of directional solidification of a binary alloy

Efficient adaptive phase field simulation based on a finite volume method is carried out to study the morphological development during directional solidification of a nickel/copper alloy. The adaptive nature of the method allows the calculation to cover different length scales for the interface, solute diffusion, and heat conduction. With the frozen temperature approximation, our calculated results are in reasonable agreement with previous ones (J. Crystal Growth 200 (1999) 583). However, the use of a much larger domain allows us to perform simulation at low speed near the onset of constitutional supercooling, where both solutal boundary layer and cell wavelength are large. For the same domain size, the calculated results without using the frozen temperature approximation remain about the same, even though the release of latent heat lowers the steady interface position and the thermal gradient in the melt side.     

Modulating dopant segregation in floating-zone silicon growth in magnetic fields using rotation

The feasibility of modulating dopant segregation using rotation for floating-zone silicon growth in axisymmetric magnetic fields is investigated through computer simulation. In the model, heat and mass transfer, fluid flow, magnetic fields, melt/solid interfaces, and the free surface are solved globally by a robust finte-volume/Newton's method. Different rotation modes, single- and counter-rotations, are applied to the growth under both axial and cusp magnetic fields. Under the magnetic fields, it is observed that dopant mixing is poor in the quiescent core region of the molten zone, and the weak convection there is responsible for the segregation. Under an axial magnetic field, moderate counter-rotation or crystal rotation improves dopant uniformity. However, excess counter-rotation or feed rotation alone results in more complicated flow structures, and thus induces larger radial segregation. For the cusp fields, rotation can enhance more easily the dopant mixing in the core melt and thus improve dopant uniformity.     

激光诱导击穿光谱法对钢铁偏析样品的分析

经典判断钢铁样品是否存在偏析带方法有金相显微及硫印方法,其缺点在于分析速度慢,且无法提供元素的含量分布信息。文中在最佳实验条件下,采用激光诱导击穿光谱(LIBS),在空间横向分辨率约为100 μm左右对两块钢铁中低合金板坯及均匀样品扫描分析,在建立校准曲线的基础上,将元素强度二维分布转化为含量二维分布。研究表明,编号为86#样品C,Si,Mn,P,S及Cu等元素存在明显的偏析,编号为174#样品C,Si,P,Ti等元素存在明显的偏析,并对偏析带的宽度进行估算,其偏析带的位置及宽度与金相显微分析方法相吻合。对均匀样品扫描分析,C,Si,Mn,P,S等元素均匀分布,不存在偏析带,通过元素强度或含量二维分布图可间接反映样品的均匀性。与传统的金相分析方法相比较,LIBS不仅可快速准确体现样品偏析带位置及宽度,而且还可同时提供元素含量分布(如C,Si,Mn,P,S等元素)等方面的信息。此方法可用于快速对钢铁样品是否存在偏析带及其宽度进行表怔,从而为钢铁冶炼工艺的改进提供理论依据。     

Mixing and segregation of solid particles in a conical spouted bed: Effect of particle size and density

In this work, the mixing and segregation of binary mixtures of particles with different sizes and densities in a pseudo-2D spouted bed were studied experimentally. A binary mixture of solid particles including sand, gypsum, and polyurethane was used. To determine the particles mass fraction, and their mixing and segregation in the bed, an image-processing technique was developed and used. Important hydrodynamic parameters, such as the axial and radial segregation profiles of the solid particles, were measured. The effects of air velocity, particle size, and particle mass fraction were also evaluated. The flow regime in the spouted bed and the time required for reaching the equilibrium state of the solid particles were discussed. The results showed that the segregation of solid particles and the time to equilibrium both decreased when the air velocity increased to much larger than the minimum spouting velocity. The axial segregation increased with the diameter ratio of the particles. Upon completion of the test, coarse particles were concentrated mainly in the spout region, while fine particles were aggregated in the annulus region. Examination of the flow pattern in the spouted bed showed that the particles near the wall had longer flow paths, while those near the spout region had shorter flow paths.     

Mechano-chemical coupling in the adhesion of thin-shell structures

Nonlinear coupling between mechanical and chemical fields at material interfaces can result in complex phenomena that include segregation-driven interface strengthening or weakening and bistability. Spatial nonuniformity of those fields is driven by elastic stresses that develop in the conforming bodies and from surface topography that is the result of patterning or inherent roughness. In this paper, equilibrium states are analyzed as a function of geometrical, material, and chemical properties to understand coupling mechanisms that impact interface strength. In particular, a theoretical model is presented for the finite deformations of a shallow spherical cap adhering to a rigid substrate that is either flat or has topography. The adhesive interactions are taken to be a continuous function of the local shell-substrate separation and the local concentrations of strengthening or weakening chemical species. Equilibrium states characterized by contact radii and energies are presented as a function of the average concentration of surface species (closed system) and the ambient chemical potential (open system). Bistable equilibria, snap transitions, and nonuniform energy, traction, and concentration fields are salient features of the numerical solutions. Interface separation under edge loading conditions is also investigated to determine the geometrical, material, chemical, and rate of the pull-off load and the work of separation. Additionally, adhesion to substrates with sinusoidal topography is analyzed to investigate the impact of patterning or inherent roughness. Important predictions of the later analysis are topography-induced segregation patterns and bistability.     

Effect of curvature on interfacial segregation: Electronic contribution to the point defect/interface binding energy

The electronic contribution to the driving force for segregation to a curved interface between a cylindrical fiber of insulator embedded in a metal matrix is calculated. The solute/curved-interface binding energy is shown to vary as the inverse of the radius of curvature of the interface in the limit of a small radius. This result implies that the propensity for segregation of curved interfaces is larger than that of planar interfaces.     

Atomistic modeling of surface and bulk properties of Cu, Pd and the Cu–Pd system

The BFS method for alloys is applied to the study of the Cu–Pd system. A variety of issues are analyzed and discussed, including the properties of pure Cu or Pd crystals (surface energies, surface relaxations), Pd/Cu and Cu/Pd surface alloys, segregation of Pd (or Cu) in Cu (or Pd), concentration dependence of the lattice parameter of the high temperature fcc CuPd solid solution, the formation and properties of low temperature ordered phases, and order–disorder transition temperatures. Emphasis is made on the ability of the method to describe these properties on the basis of a minimum set of BFS universal parameters that uniquely characterize the Cu–Pd system.     

Hydrodynamic model for particle size segregation in granular media

We present a hydrodynamic theoretical model for “Brazil nut” size segregation in granular materials. We give analytical solutions for the rise velocity of a large intruder particle immersed in a medium of monodisperse fluidized small particles. We propose a new mechanism for this particle size-segregation due to buoyant forces caused by density variations which come from differences in the local “granular temperature”. The mobility of the particles is modified by the energy dissipation due to inelastic collisions and this leads to a different behavior from what one would expect for an elastic system. Using our model we can explain the size ratio dependence of the upward velocity.