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We are currently using a nichrome (80/20) wire based heater to surround a sample chamber that we wish to heat by radiation. Maximum sample temperature is 400degC in an atmosphere of air that may be high humidity. That means the wires get red hot. Our specific problem is that there is corrosion occurring that alters the emissivity of the wires, making temperature control difficult.

Is there a better alloy, or is there some kind of coating we can apply which will not alter through thousands of hot/cold cycles?

The type of thing I am thinking about is (for example) platinum coating the wire. Alternatively, any suggestions for a solution?

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  • $\begingroup$ Nichrome is what's generally used in space heaters. $\endgroup$
    – Safdar Faisal
    Commented Oct 26, 2022 at 16:05
  • $\begingroup$ Depending on what your sample chamber looks like, you may want to look into the heating tapes that are typically used for baking out vacuum systems. Very brief search gives you this, in the $100 range, rated up to 500 C if installed permanently (says it requires a controller as well but you could probably hack something together for less, depending on relative value of time and money to you) briskheat.com/applications/… $\endgroup$
    – llama
    Commented Oct 26, 2022 at 19:33
  • $\begingroup$ @llama Thanks, but it must be non contact $\endgroup$
    – Dirk Bruere
    Commented Oct 26, 2022 at 21:02

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Nichrome routinely operates at red heat (roughly 1500 °F) with very long life. 400 °C is no problem, moisture is no problem. Look for some contamination if you are getting corrosion.

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  • $\begingroup$ Well, the wire is certainly not bright and shiny after a number of hours of use $\endgroup$
    – Dirk Bruere
    Commented Oct 27, 2022 at 9:27
  • $\begingroup$ Nichrome generally has a black surface ( presumably oxide). Such as an electric stove heating element. New stock from the mill is dull grey; this alloy is not polished like a stainless. $\endgroup$
    – blacksmith37
    Commented Oct 27, 2022 at 15:57
  • $\begingroup$ Our wire is quite bright and polished before we insert it into the heater. $\endgroup$
    – Dirk Bruere
    Commented Oct 27, 2022 at 16:23
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    $\begingroup$ The starting material would be cleaned to avoid wear in the wire dies. Then in drawing the finished wire has a natural burnished surface . And possibly the finished wire is polished. New stock we had was primarily sheet, no wire. $\endgroup$
    – blacksmith37
    Commented Oct 27, 2022 at 20:21

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