Recent numerical studies by the authors concerning bulk single crystal growth under microgravity fields were reviewed. For the InGaSb alloy crystal growth by temperature gradient method, it was found that the growth rate was not affected by gravity level although the dissolution of GaSb seed crystal before growth process was enhanced by solutal natural convection under normal gravity field. For the Si/Ge alloy crystal growth by floating zone method, transport structure including wave number was changed by coexistence of solutal and thermal Marangoni convections. For the hydrothermal wave in a shallow annular melt, the combination of crucible rotation and magnetic field was efficient for suppression of unsteady transport phenomena even though weak external forces.
It is becoming increasingly clear that nucleation processes in liquids and glasses are more complicated than previously thought, often coupling to other phase transitions and ordering processes. Experimental and theoretical studies show the development of icosahedral shortrange order in many supercooled transition metal and alloy liquids, which in some cases extends beyond nearest neighbor distances. This atomic and chemical ordering couples to the nucleation barrier, and may play a role in glass formation in some cases. Select experimental results are presented to demonstrate these points. These are discussed in light of nucleation theories, including the commonly used Classical Theory of Nucleation, diffuse interface theories, and coupled-flux theory, which takes account of the interaction between interfacial processes at the surface of the crystal nuclei and long-range diffusion fluxes.
We discuss the face stability of a growing basal face of an ice disk in supercooled water. The local supercooling is largest at the face center and smallest at the periphery of the basal face. For the basal face to remain maroscopically flat, the step distribution on the basal face must compensate for the nonuniformity in local supercoolong. We show that the local slope of the periphery of basal face increases with time.
The phase-field models developed in the field of solidification and crystal growth are explained with a focus on the models for dendritic growth in pure substances and alloys. The diffuse interface description, free energy functional, and variational derivation of phase-field equation with inclusion of anisotropy of solid-liquid interfacial energy are described. In addition,the essential points of the Kim-Kim-Suzuki’s model and the quantitative phase-field model for alloy solidification are briefly discussed.
Despite its tremendous importance for the understanding of underlying mechanisms and for the input in modeling and simulation of processes alike, accurate experimental diffusion data in liquid metals and alloys are rare. Common techniques exhibit several drawbacks that in most cases prevent an accurate measurement of diffusion coefficients - convective contributions during diffusion annealing are the most prominent ones. Recently, we advanced the field of liquid diffusion experiments through the use of quasielastic neutron cattering (QNS) on levitated metallic droplets for accurate measurements of self-diffusion coefficients in high-temperature metallic liquids. For the accurate measurement of interdiffusion coefficients we combine long-capillary experiments with an in-situ monitoring of the entire interdiffusion process by the use of X-ray and neutron radiography. These experiments are accompanied by diffusion experiments in space in order to benefit from the purely diffusive transport under microgravity conditions. Recent experimental results are discussed in the context of the relation of self- and interdiffusion (Darken’s equation) and of the relation of self-diffusion and viscosity (Stokes-Einstein relation).
Since physico-chemical properties of liquid alloys, molten salts and molten slags affects various phenomena in crystal-growth process, the information on those properties is indispensable to control and design the new technical processes. We sometimes,however, come across a situation of lacking those information, and we have to estimate the properties from some fundamental physical quantities. This paper describes some procedures to predict the surface tension of liquid alloys, molten salts and molten slags. In addition, some useful literatures will be given on the prediction of the properties.
It is expected to manufacture new materials with containerless processing by levitation technique. However, it is
indicated that the levitated droplet with levitation technique has nonlinear behavior. In this study, nonlinear bynamics of the levitated droplet is experimentally and analytically investigated. The levitation experiments with electrostatic levitator and the ultrasonic levitator are conducted under the normal gravity condition. Based on the experimental results,theoretical and numerical analyses are conducted to clarify the nonlinear dynamics of the levitated droplet. Furthermore,new technique to measure the viscosity in high viscosity region is proposed.
Electromagnetic levitation of electrically conductive droplets by alternating magnetic fields is a technique used to measure the physical properties of liquid metallic alloys as heat capacity and thermal diffusivity, among others. In order to reduce electromagnetic stirring and shaping of the molten sample, experiments are conducted in microgravity 1). Measurement is performed by using the modulation calorimetry technique . Here we test both numerically and experimentally a new measurement protocol, which aim is to eliminate calibration. We use this procedure to demonstrate that the use of a levitator in a DC magnetic field overcomes the negative effects of the electromagnetic stirring inside the sample on the accuracy of the modulated calorimetry technique.
This article contains a review of research activity in the University of Greenwich to model the effects of static or DC magnetic fields on the characteristics of EM-levitated melts. The general idea is that the presence of a DC field will damp out the velocities inside a levitated droplet and so lead to more accurate thermophysical property measurements, especially those of viscosity and thermal conductivity that will otherwise
be affected by turbulence. The technique is in fact used successfully in terrestrial experiments, and this study sets out to examine its applicability in the case of microgravity. An accurate spectral-collocation numerical scheme is used to couple dynamically the velocity, temperature and magnetic fields, so that internal velocity and liquid envelop changes of a suspended “spherical” droplet can be observed as a function of applied AC and DC fields, with or without gravity.
The lecture introduces how to make a microcomputer-controlled, electronic device for a beginner. A series of lectures provides not only how to measure a physical property with an electronic sensor, convert it to a digit (analog digital conversion), switch on and off an electronic circuit with FET (Field Effect Transistor), and control those with a microcomputer but also practical know-how to design an actual electronic circuit, choose appropriate electronic parts, and mount those to a PCB (printed-circuit board), with explaining how to make “an acceleration switch”. The switch can automatically turn on and off a connected device according to an acceleration level measured with an acceleration sensor and contribute to parabolic flight experiments through size reduction of an apparatus, less operation, and precise control of the experiments.