I tried to use a common 900 W microwave oven melt some alloy with low melting point (138 deg C, eutectic bismut/tin).

The metal did not heat up, neither did the metal container, which makes me think the waves got reflected from it just like on the device inner walls.

The oven is working at 2.45 GHz, about 120 mm wavelength.

I expect it is possible to build some kind of antenna that would heat up?
What would be good shapes - thin and 120 mm long? Half and quater wavelength could work too?
Can the individual long parts be connected - like at the center?

There are microwave kilns available commercially. It's a heat resistant foam material container with an inner graphite-containing coating. I do not know whether they work based on a specific geometry of the coating.


closed as off-topic by CuriousOne, John Rennie, ACuriousMind, Waffle's Crazy Peanut, Kyle Kanos May 31 '15 at 19:28

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  • $\begingroup$ Why do you want to use a microwave oven instead of a simple oil bath? That would give much better control over temperature distribution, too. $\endgroup$ – CuriousOne May 31 '15 at 3:23
  • $\begingroup$ Mostly to see whether it's easy to work with. Generally, I use a hot air gun for small amounts, a gas flame for larger. Your points on the oil bath are useful. $\endgroup$ – Volker Siegel May 31 '15 at 3:28
  • 2
    $\begingroup$ It sounds more like an attempt at destroying Mom's microwave. The answer is that it's not easy to work with. Any type of resonator structure that does not have the correct impedance with reflect too much energy back into the microwave tube and you are risking the destruction of the part. Since I am not sure that you have the discipline not to open the box to see what you did there, the next step in the chain of unfortunate events will be the risk of serious electric shock and tissue burns. Don't go there, just because it's an appliance doesn't mean it's a safe device when mishandled. $\endgroup$ – CuriousOne May 31 '15 at 3:32
  • $\begingroup$ @CuriousOne - I had started writing a long and complex answer, but your comment is succinct and essentially what I was going to say: "This sounds like a really bad idea. Either it works and you end up with molten metal (and potentially fumes of unknown toxicity) in your microwave, or it does nothing..." $\endgroup$ – Floris May 31 '15 at 3:35
  • $\begingroup$ The kitchen microwaves are designed to the frequency of water molecule excitation. All foods contain water and it is optimized for that . here is a study of metal and microwaves that might help you jmpee.org/jmpee_site/Vol_44%281%29/JMPEE44-1-4Yoshikawa.pdf $\endgroup$ – anna v May 31 '15 at 3:40

For safety reasons, as pointed out in the comments, you should be using a kiln.

Looking at microwave kilns one finds a youtube DIY.

I found loads of videos on how to use this type of kiln on youtube but none on how to go about making it. So I decided to do it. Now if you are skilled enough to use it you are certainly skilled enough to make it and probably do a better job than me. It uses fire cement, vermiculite, magnetite, sugar and graphite and the only thing I had to buy was the fire cement. If you don't have any vermiculite yo can use perlite just as easily and this can be got from the net or a garden center for about £2 for a huge bag of the stuff - certainly more than you will ever need. Incidently the same process can be used to construct the tube of a muffler furnace - for those out there who are looking for ideas on how to go around Chemical Vapour Deposition at home. I might even get round to this at some future date. This thing can be used for sintering metal powders, ceramics, glass and high temperature chemistry - which is what i want it for..

Note, metal powders . That agrees with this reference

Because of small (order of micron or less) penetration depth of electromagnetic field into metals, temperature of a bulk metal cannot be raised

It is the Eddy currents on the surface that heat metals , so in that sense the geometry of powder allows heating.


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