# Microwave melting



## Lou (Jan 7, 2015)

Something I've been thinking about for a while has been building a microwave melting furnace for assay and/or flux testing purposes.

Here's some existing work people have done:

http://www.popsci.com/diy/article/2003-09/smelting-microwave

http://www.instructables.com/id/microwave-smelter/


I think the best implementation would be to build an enclosure of insulating refractory brick and then get a small silicon carbide crucible (like such: http://www.ebay.com/itm/Silicon-Carbide-Crucible-125ml-Free-Shipping-/121516548449?pt=LH_DefaultDomain_0&hash=item1c4af36161 ) and wrap that in kaowool. 

Some larger microwaves approach 1.5 kW. This should be sufficient to melt perhaps a kg of silver and 500 or so grams of gold.

This guy is melting small amounts:
https://www.youtube.com/watch?annotation_id=annotation_758176&feature=iv&src_vid=Aa2uQgMMVUc&v=9gRiNM2P3dA

Lou


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## GotTheBug (Jan 7, 2015)

You'll have better results with microwave transparent materials. A fused silica crucible and ceramic blanket are a good start. Heat the material rather than the crucible itself. You'll also probably blow up a few microwaves in the learning process.


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## Barren Realms 007 (Jan 7, 2015)

About 2-3 years ago there were some links to people doing this. The one guy that stood out with success was using light weight fire brick and pouring the material into one of the small cone molds.


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## Barren Realms 007 (Jan 7, 2015)

Here you go this might be what you are looking for.

http://www.ebay.com/itm/Amana-Wdyrc22-Commercial-Microwave-220V-Stainless-Steel-2000-Watts-/181518494714?pt=BI_Commercial_Ovens_Ranges&hash=item2a43586bfa


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## solar_plasma (Jan 8, 2015)

http://goldrefiningforum.com/~goldr...f=39&t=16968&p=197261&hilit=microwave#p197248

Here is some more information.


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## Lou (Jan 8, 2015)

GotTheBug said:


> You'll have better results with microwave transparent materials. A fused silica crucible and ceramic blanket are a good start. Heat the material rather than the crucible itself. You'll also probably blow up a few microwaves in the learning process.




I would disagree. Heating the powder would work insofar as sintering but not once it forms a monolithic semi-solid piece. I think the way to go is to get a silicon carbide crucible. 

Lou


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## Palladium (Jan 8, 2015)

Lou said:


> GotTheBug said:
> 
> 
> > You'll have better results with microwave transparent materials. A fused silica crucible and ceramic blanket are a good start. Heat the material rather than the crucible itself. You'll also probably blow up a few microwaves in the learning process.
> ...



Their was a day when i would have read that and just took it for the words. Even though i still don't understand it completely i do understand the science behind it. I've been studying nano silver here lately and the difference between how things act on the order of scale or size. The difference in behavior between silver crystals of one size or another is amazing! It's like the difference in weak gravitational forces and strong nuclear forces when it come to the laws that govern them. Here is an interesting read i had a few days back.


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## GotTheBug (Jan 8, 2015)

Lou, I can tell you from personal experience that a very liquid melt is more than possible. Also note, keep an eye on the temperature. It takes awhile to get over 2000 degree F, but very little time to exceed 3000, and you can have a runaway melt that will go through the crucible, the bottom of the microwave, the table it's sitting on, and onto the concrete floor. Yes I've gone through the crucible with a runaway, and a friend had the "all the way to the floor experience. I'm playing now with a sensor and cutoff to shut down the magnetron when the temp gets to 2200 degrees. The arcs formed by the magnetron cause the melting to begin, and once the metal gets to a liquid state, it absorbs the microwaves VERY readily.


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## g_axelsson (Jan 8, 2015)

Lou said:


> GotTheBug said:
> 
> 
> > You'll have better results with microwave transparent materials. A fused silica crucible and ceramic blanket are a good start. Heat the material rather than the crucible itself. You'll also probably blow up a few microwaves in the learning process.
> ...


I totally agree with you, Lou. A micro wave oven is designed to vibrate polar molecules with the electrical field of the microwave. As heat isn't anything else than vibrations and random motion of atoms and molecules the vibrations of the molecules is transformed into heating the object. But larger metal objects conducts electricity and only reflects the micro waves. That's why the inside of the micro is made of steel but doesn't heat up.
Any metal piece of size will just reflect the waves making it impossible to melt. Even if you would get localized heating by corona effects and arcing between metal grains the effect is probably quite low and larger pieces would be impossible to remelt.
The way the silicon carbide crucibles works for melting metals is that SiC is a great absorber of microwaves and heats up by the absorbed energy. If you make a crucible out of SiC the metal will be shielded from the microwaves and heated from the crucible. All the energy will be absorbed by the crucible and conducted to the metal inside it. That would give a faster and more even heating curve, probably also easier to control the temperature by adjusting the timing.

A silicon carbide crucible should be able to melt even non-metallic materials, for example catalytic converters or silver chloride if you would like to.

Ref : Silicon carbide absorbing microwaves http://pubs.acs.org/doi/abs/10.1021/ar300318c

Göran


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## Lou (Jan 8, 2015)

I should think 1200/2350F should be no issue with it. I think I'll have to build one.


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## goldandsilver123 (Aug 16, 2015)

Lou said:


> I should think 1200/2350F should be no issue with it. I think I'll have to build one.



Lou, you proceeded with this idea?? Curious to know!


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## Herman (Sep 15, 2016)

I watched a guy using a common house hold microwave melt gold in it.He had what looked like a little brick house inside that he made from I think firebrick and the crucible was inside that>i saw him put his brown powder in and then set on high for 1/2 hour got his gold in the end.I tried it with some other precipitated material but only the top melted and the bottom was still powder.Ill have to play around with it and maybe increase my insulation or get another microwave as the one i was using is real old.
Herman


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## Herman (Sep 15, 2016)

I forgot to mention I did my thing outside.There is a lot of smoke that came out the vent during the time it was running.
Herman


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