In order to improve silicon crystal quality, better understanding of heat and masstransfer process during crystal growth through numerical modelling is indispensable. More accurate thermophysical property data are required for numerical modelling. Combining levitation and microgravity, which can supply a contamination-free and under-cooled condition, is receommended as a novel tool to supply a lot of missing thermophysical property data for undercooled melts.
The principle of electromagnetic levitaion is reviewed. To allow electromagnetic levitation, a sample must be electrically conductive, because levitaion force and heating power are supplied to the sample through electromagnetic induction. Various processes, such as preheating or heavy doping, must be applied to make them capable of electrical conductivity. The design and function of electromagnetic levitation facilities are shown.
An electrostatic levitator furnace (ELF) for Japanese Experiment Module of Space Station is now under development. This electrostatic levitator furnace consists of heating section, positioning section, observation section, atmosphere control section and automatic sample-exchange robotics. In ELF, samples will be heated by four lasers, and each laser power can be controlled independently, which enables both uniform and nonuniform heating. The charged samples are positioned between electrodes, and their position-control is achieved by changing electrode voltages in accordance with position signals from detectors . ELF has three equipments for observing samples during processing, which are a pyrometer, a thermal imaging system and a video camera . ELF can provide containerless processing under micro-gravity environment for various materials including metals, glass, ceramics, and so on. This report describes the features, expected environment for processing and development status of ELF.
Space-DRUMS™ is a new approach for positioning, manipulating and shaping samples in both gravity and microgravity environments. It relies on the direct acoustic radiation force from many equivalently- positioned ultrasonic beams under dynamic feedback control to levitate or position large samples1•2l . The technology was conceived and developed for the Canadian Space Agency by Guigne International Limited.
The aero-acoustic levitator combines aerodynamic and acoustic forces to achieve stable levitation and precise positioning of samples. The levitation force is primarily aerodynamic and is stabilized by the smaller acoustic forces to obtain precise control of the position of levitated solid and liquid samples. Laser beam heating and melting become possible to allow liquid phase processing and property measurement experiments under containerless conditions at very high temperatures. A wide range of glass and molten ceramic materials have been investigated. In this paper we discuss the design and operation of the aero-acoustic levitator with examples from experiments on liquid phase processing of oxide glasses and ceramics. The method enables valuable earth -based experiments in support of microgravity research.