I am working on melting of metals in microwave oven and even after exposing it to microwaves for 20 mins, I am unable to reach a temperature above 95°C. So I had a doubt whether the oven has some kind of temperature control device thats cuts off the magnetron supply when a certain temperature limit is reached? If anyone has idea about it please guide me through.
Hi Niraj,
no, usual kitchen microwave ovens don't have temperature control.
I guess the main problem is your metal itself: While microwave radiation of about 2.5 GHz has a penetration depth of a few cm in water - please find a table here:
http://www.pueschner.com/en/microwave-technology/penetration-depths
- the penetration depth in metals is of the order of some micrometers; as a consequence, nearly all of the radiation (and hence the power) is reflected by metals.
The walls of the oven chamber are metallic, too, so if the oven chamber is empty except for the metal you are trying to melt then the radiation inside the chamber builds up until the small percentage share of power absorbed by the walls and your piece of metal equals the power delivered by the magnetron.
(I never dared to do such an experiment because I was afraid that the magnetron might get damaged by the reflected energy; but perhaps I was too timid.)
You can melt metals electromagnetically but at a much lower frequency = much larger wavelength. Therefore the metal is located in the near field of the source, and the transfer of power is not based on radiation but on induction. For a short overview, please see:
https://en.wikipedia.org/wiki/Induction_furnace
You may be able to melt metal in a microwave if you make it very thin. This probably won't be useful for you though.
I think that if you put china plates with metal decoration in a microwave it ruins them because the metal decoration melts and sparks.
You could check out the following paper:
MICROWAVE SINTERING, BRAZING AND MELTING OF METALLIC MATERIALS by Dinesh Agrawal from 2006.
They worked on a microwave metal melting furnace and used very fine powedered materials.
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