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We are exploring the idea of using induction to heat up a small platinum crucible (height x diameter x wall thickness is 20mm x 6mm x 1mm) to 1400 °C in vacuum. The Pt crucible will be placed in an evacuated quartz tube of c. 20 mm o.d., the entire assembly is then placed in the coil. The heating should be stable (say ±50 °C) for at least 30 minutes.

Induction is a new field to us. Which specifications of the heater would you recommend for this task? (e.g. frequency, current and other important things I might be missing).

So far it seems that a 1-2 kW machine with a frequency between 100 and 500 kHz could do the trick. Due to chemical constraints in the experiment, the frequency must stay less than 1000kHz. We're happy for any input that get us on track. thanks!

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  • \$\begingroup\$ I'm curious about your chemical constraints \$\endgroup\$
    – BeB00
    Jun 19 '20 at 2:33
  • \$\begingroup\$ A part of the experiment will use oxygen. It apparently produces a plasma in the mHz frequency, which will disturb our measurements. We'd like to avoid that. \$\endgroup\$
    – Curious
    Jun 19 '20 at 2:44
  • \$\begingroup\$ An iridium crucible is the way to go. Of course, it only is found in meteorites. But good stuff. Used to use them for sapphire melts, though I think today acoustic levitation is perhaps more in use. That's just talking off the cuff, though. Ignore it. I'll assume you mean fused quartz given the temps here. What I'm curious about is how you intend to monitor and control that temperature. Have you contacted others who have been successful with what you are trying to achieve? Or is this a unique situation, never yet achieved? Have you calculated the radiated energy that must be stably returned? \$\endgroup\$
    – jonk
    Jun 19 '20 at 2:51
  • \$\begingroup\$ Iridium could work too, I'll keep that in mind. Temperature-control would be a second question. Thermocouples are likely not going to work, but we have high quality pyrometers on hand that we're considering to use. What we try to do is usually done with SiC furnaces or similar. We try to avoid that, so, it's kind of a unique situation (as far as I am aware of). There a few old papers describing similar methods, but they don't state the specs of the induction furnace. \$\endgroup\$
    – Curious
    Jun 19 '20 at 3:04
  • \$\begingroup\$ @Curious All I've done for decades is pyrometry. Generally, and with RTP FAB circumstances, in particular. And I can tell you from experience that every case has its problems that must be resolved. If you want accuracy (and most do) and not just precision, then you have still more problems to resolve and regular calibration steps that must be performed often. There is no such thing as "set it once and forget about it" in my experience. 30 minutes is obviously doable, though. Though my experience is with lamp-heating, not induction. \$\endgroup\$
    – jonk
    Jun 19 '20 at 3:40
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Results are in. As expected, a 2.5 kW machine with 100 kHz frequency easily heats the platinum crucible to 1500 °C within seconds.

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