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

• Main Authors: Danilo C. Curtolo, Xiaoxin Zhang, Martin J. R. Rojas, Semiramis Friedrich, Bernd Friedrich
• Format: Article
• Language: English
• Published: MDPI AG 2018-05-01
• Series: Applied Sciences
• Subjects: zone refining; zone length; growth rate; infrared camera; aluminum; fractional crystallization; high purity; ultrapure aluminum; zone melting
• Online Access: http://www.mdpi.com/2076-3417/8/6/875

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.