[Physics] Teflon and induction cookware

electromagnetismeveryday-lifeinduction

I remember once getting new Teflon (non-stick) cookware; however, when I tried this new cookware on my induction cooker the cookware did not heat up. My regular steel cookware worked just fine on the induction cooker, both before and after trying the Teflon cookware. I've heard from at least two other people that they've noticed the same thing with Teflon cookware and induction cookers (at least one tried the same exact brand and style of cookware as myself). And so, I wonder:

Did my Teflon cookware not heat up with the induction cooker because of the Teflon or the process it went through to be Teflon coated? In other words, does Teflon cookware in general not work with induction cookers? Or is it possible that my Teflon cookware just happened to not be made of a ferrous material and thus the induction cooker had no effect on it, with or without the Teflon?

If it is the case that Teflon in no way affects the performance of the cookware on an induction cooker, is it possible that a majority (or all) of Teflon cookware is made of non-ferrous material (perhaps because it is easier to get the Teflon to stick to aluminum than is to stick to steel)? In this way Teflon cookware would not work on induction cookers but not because of the Teflon.

I unfortunately no longer live in the same apartment as the induction cooker or the Teflon cookware so I cannot verify whether the cookware is ferrous or not myself.

Best Answer

The coating has nothing to do with it - it's the metal of the pan that matters. As was mentioned in the comments, many Teflon coated pans are made of aluminum (or aluminium, depending on where you live...). The issue is skin depth: for a non-ferromagnetic material, at the frequencies of the induction heater a large fraction of the volume of the pan becomes a (good) conductor of the electrical current: and because the size of the (eddy) current is fixed by the geometry of the cooker, if you present it with a low resistance, the amount of power generated will be low, since $P=I^2 R$.

The following table of skin depths (at 24 kHz) shows you what is going on (adapted from http://en.wikipedia.org/wiki/Induction_cooking):

                      rho   mu    skin    R     effect
Copper                0.68    1   0.017  0.04    1.00
Aluminum              1.12    1   0.022  0.051   1.28
Stainless steel 304  29       1   0.112  0.26    6.5
Carbon steel 1010     9     200   0.004  2.25   56.25
Stainless steel 432  24.5   200   0.007  3.5    87.5

in this table

rho = resistivity (in 10^-6 ohm-inches)
mu = relative permeability
skin = skin depth in inches
R = surface resistivity (in 10-3 ohm/square)
effect = relative heating effectiveness compared to copper

As you can see, copper and aluminum make terrible materials for induction cooking pans: you need something with high electrical and high magnetic permeability to get the best heat transfer. 432 Stainless (which has high resistivity AND is ferromagnetic) is a lot better. Some copper pans adapted for induction heating have a coating of another material specifically for this reason.

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