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

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Discussion Overview

The discussion revolves around the challenges faced when using a ZVS inductive heater to melt polycrystalline silicon, particularly in relation to its conductivity and the heating process. Participants explore the effectiveness of the heater with silicon compared to other metals and the implications of preheating and frequency settings.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant reports that the silicon workpiece does not melt or heat sufficiently despite preheating to 100°C, contrasting its performance with other metals like iron and aluminum.
  • Another participant expresses skepticism about the conductivity of polycrystalline silicon at 100°C and requests material references to support this claim.
  • A later reply clarifies that the silicon becomes fully conductive at 300°C and mentions that even with a stronger torch for preheating, the inductive heater fails to take over.
  • Concerns are raised about whether the frequency of the ZVS heater is suitable for heating silicon, with a noted lack of information on the necessary frequency range for effective inductive heating of silicon.
  • One participant suggests that setting up the frequency and coil design is complex and recommends contacting a specific company for more information.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the effectiveness of the ZVS inductive heater for melting silicon, with multiple competing views regarding the material's conductivity and the importance of frequency settings remaining unresolved.

Contextual Notes

There are limitations regarding the assumptions about silicon's conductivity at various temperatures and the specific frequency requirements for effective inductive heating, which remain unclear.

Patrick Underwood
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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.
 
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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?
 
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.
 
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)..
 

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