Realization of the Zone Length Measurement during Zone Refining Process via Implementation of an Infrared Camera

Abstract

Zone refining, as the currently most common industrial process to attain ultrapure metals, is influenced by a variety of factors. One of these parameters, the so-called "zone length", affects not only the ultimate concentration distribution of impurities, but also the rate at which this distribution is approached. This important parameter has however neither been investigated experimentally, nor ever varied for the purpose of optimization. This lack of detections may be due to the difficult temperature measurement of a moving molten area in a vacuum system, of which the zone refining methodology is comprised. Up to now, numerical simulation as a combination of complex mathematical calculations, as well as many assumptions has been the only way to reveal it. This paper aims to propose an experimental method to accurately measure the molten zone length and to extract helpful information on the thermal gradient, temperature profile and real growth rate in the zone refining of an exemplary metal, in this case aluminum. This thermographic method is based on the measurement of the molten surface temperature via an infrared camera, as well as further data analysis through the mathematical software MATLAB. The obtained results show great correlation with the visual observations of zone length and provide helpful information to determine the thermal gradient and real growth rate during the whole process. The investigations in this paper approved the application of an infrared camera for this purpose as a promising technique to automatically control the zone length during a zone refining process.

Zonal Refining and Bridgman Technique for CsI:Tl Scintillation Crystal Growth

“…Zonal refinement is a technique for purifying solid materials by liquefying a small region capable of dragging impurities to the ends of the solid material. [14,15] According to Figure 1-(a), it is possible to observe the solid formed after the zonal refining.…”

The Influence of Initial Purity Level on the Refining Efficiency of Aluminum via Zone Refining

“…The zone refining apparatus at IME/RWTH Aachen University with an inductive heater and an infrared camera (details presented in [16]) was utilized in this work, as shown in Figure 2. It is capable of generating up to 45 kW with a maximum frequency of 10 kHz.…”

“…Moreover, the zone length frequently varied even under the stable heater power and a constant heater movement velocity due to the high thermal conductive charge and crucible, leading the frequent failure of heat balance at the solid/liquid interface [6]. Therefore, a frequent adjustment of the power had to be carried out manually, according to the real zone length detected by an Infrared camera [16,22]. This allowed for a comparatively stable zone length as the heater moved.…”

A Review on the Zone Refining Process Technology toward Ultra‐Purification of Gallium for GaAs/GaN‐based Optoelectronic Device Applications

“…a) A vertical zone refining system [139] and b) a horizontal zone refining system with a single induction heater along with an infrared camera set up at a particular angle to focus on the molten zone. [177] [Both irregular crystallization due to the faster velocity of the zone and there is also a possibility of cross-growth that traps more impurities. Therefore, modest zone speed is typically used in practice.…”

“…Induction heating is a useful technique for creating a molten zone in a metal bar. [13,177,178,180] Another inherent benefit of this process is the automatic stirring of the molten zone, which helps with the diffusion of impurity atoms from the solidifying interface into the melt. The only materials that can be treated with this procedure are those that conduct electricity.…”