Czochralski furnace

A Czochralski furnace is a device for growing single crystals by slowly [~10mm/hr] pulling a crystal from a melt while rotating it. I constructed this one to grow single crystals of potassium bromide, which is useful in infrared optics. It used a liquid-cooled induction heater to bring the salt to 770°C before lowering a seed crystal into the melt and beginning to draw. A key challenge in this type of furnace is precisely controlling the temperature—too hot and the crystal you're drawing will melt—too cold and your whole melt will solidify. To solve this problem without expensive temperature probes I used stainless steel and a convenient property of induction heating. Stainless steel has a Curie temperature (above which it is no longer magnetic) of 750°C, while my salt had a melting point of 734°C. Above the Curie temperature, the steel would be heated much less by the magnetic induction heater, so the steel's temperature would remain stable at 750°C. By adding stainless steel directly to the crucible I was able to maintain consistent temperatures and draw crystals.