A pulse-echo ultrasonic technique for the localization of the solid-liquid interface during directional solidification of silicon ingots

A special ultrasonic technique is discussed and experiments in a solidification process for 24 kg ingots are 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 bears 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-liquid interface were received with transmission rods made of SiC, Al₂O₃, and monocrystalline Si