Why won't my silicon melt with a zvs inductive heater?

[Patrick Underwood]

I’m using a zvs inductive heater to try to melt some 99.85% polycrystalline silicon, as would occur in the Czochralski process, but the silicon workpiece is not melting let alone even getting hot. The silicon workpiece is about the size of a playing dice, and becomes fully conductive after preheating to about 100* C. Even after preheating the workpiece while in the coil to achieve adequate conductivity, the inductive heater still doesn’t “take over” to raise the temperature. The inductive heater works fine with other conductive materials such as iron and aluminum and heats them quite effectively. A Czochralski process patent I came across claims that the silicon must be preheated to at least 1000* C, but many other Czochralski process
diagrams and research papers make no mention of any necessary preheating.

 

[Windadct]

Honestly I would not have expected PC Si to conduct above 100c... do you have a material reference for this?

What can you melt in your heater?

 

[Patrick Underwood]

Thank you Windadct for the reply.
The silicon is mostly conductive at room temp, but doesn't become fully conductive until 300 C. (I ran the test again). I used a stronger torch for preheating; I was able to get the silicon workpiece to glow red, but the inductive heater still isn't taking over. I purchased the silicon from eBay titled "99.85% polycrystalline silicon chunks". I doubt conductivity is the issue. Could it be that the frequency for silicon is out of range of the zvs heater I'm using? After searching the web, I can't find any info on the necessary frequency range for heating silicon inductively.

 

[Windadct]

Setting up the frequency, coil design and other factors is apparently pretty involved - REFERENCE. I worked with Ambrel before (good people)- you may be able to get some quick info by contacting them - as a hobbyist(I assume)..