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1991
Conference Paper
Titel
A pulse-echo ultrasonic technique for the localization of the solid/liquid interface during directional solidification of silicon ingots
Abstract
For photovoltaic applications multicrystalline silicon is produced by directional solidification of large silicon melts. One of the quality determining parameters is the uniformity of the solidification velocity. In order to control the velocity, in situ observation of the solid/liquid interface position is essential. Ultrasonic techniques appear to be suited best because X-ray radiography is problematic in production processes. In this paper a special ultrasonic technique will be discussed and experiments in a solidification process for 24 kg ingots will be reported. The ultrasonic signal is generated and received by the same piezoelectric transducer. As direct contact of the transducer with the silicon melt is impossible, a transmission rod is used. It is dipped into the melt at one end and is bearing the transducer at its cold end. This rod is the most critical part of the system. Several materials were under consideration and some of them were tested. Clear echoes from the solid/li quid interface were received with transmission rods made of SiC, Alsub2Osub3 and monocrystalline Si. The actual position of the interface is calculated from time differences between the echoes from the hot end of the transmission rod and the echoes from the solid/liquid interface.
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