# Microwave Smelting?



## kane333 (Jan 19, 2013)

http://youtu.be/tB3oQeTG-Mc

I found this video on Youtube today and was wondering if anyone has tried this method yet. Sounds interesting and would save on having to get the Acetylene Bottle refilled.


----------



## damezbullion (Jan 20, 2013)

why cant i believe this, this is amazing, what was that powder he added do you know?


----------



## NobleMetalWorks (Jan 20, 2013)

I spoke with someone who has used this method.

Microwaves are used in industry to do everything from dry lumber, to transmitting signals over vast distances.

However, using a regular microwave oven to smelt with, is not going to work for very long. When you smelt, you use caustic ingredients, and over time the fumes will ruin the microwave. Unless you have a steady stream of working, scrapped microwave ovens, but then there are many other considerations besides.

Or maybe a better way of thinking about this would be to ask this question. If this is such a wonderful way to smelt, why isn't industry using this technology to do so themselves?

Smelting involves far more than throwing something in the microwave and waiting for the beep. It takes watching and knowing your melt, observing certain aspects, like making sure it's homogenous. Taking pin samples in some cases. Spooning off slag. Stirring with a carbon rod. And the list goes on and on.

Back to the person I spoke with that was using this method. He stated that besides all the points I just made, there is also the issue of being able to pull the refractory blocks containing the crucible out of the microwave, and being able to pour it, and doing so fast enough so that the metal doesn't harden. He was never able to get a good bar, and had several accidents attempting to hurry the process.

If anyone has used a crucible furnace before you will understand about the cooling. You have to move fairly quickly and confidently to pour molten metal out of a crucible you just pulled out of a melt furnace, before it hardens, specially when smelting. Considering the dangers involved, why would you want to use any method that would require you to rush to make up for the extra steps involved to get to the point you could pour?

I wouldn't even use this method to melt precious metals, let alone smelting anything.

There have been a few people who have posted about this in the past, but as of yet, I have not seen anyone post about this working well for them.

Seems to me everyone is trying to re-invent the wheel when it comes to recovering and refining. And always they come back to the tried and true methods, the things that work, those things that this board has literally hundreds of years worth of accumulated experience in the form of experienced people whom readily give advice on these methods and processes.

You could build a top of the line propane melt furnace that will smelt extremely well, for right around $400 USD. You can buy complete kits for smaller melt furnaces for even less. I wouldn't waste my time with the microwave method.

Scott


----------



## kane333 (Jan 20, 2013)

damezbullion said:


> why cant i believe this, this is amazing, what was that powder he added do you know?




Looking on MicrowaveGoldKiln.com, it appears to be called Chapman Recipe Flux.

_Chapman Recipe Gold & Silver Smelting / Refining Flux. Contains 40% Borax, 20% each: Soda Ash, Manganese Dioxide, Silica. Can be used with or without litharge_


----------



## kane333 (Jan 20, 2013)

SBrown said:


> I wouldn't even use this method to melt precious metals, let alone smelting anything.
> 
> You could build a top of the line propane melt furnace that will smelt extremely well, for right around $400 USD. You can buy complete kits for smaller melt furnaces for even less. I wouldn't waste my time with the microwave method.
> 
> Scott




That's why I put the question out there to see if it was worth looking into. It appears to work, though.


Reading through the Microwavegoldkiln website, it seems this method is geared more towards people who are panning and sluicing. He's got some interesting reading in the "Smelting Tips" section.


----------



## NobleMetalWorks (Jan 20, 2013)

kane333 said:


> SBrown said:
> 
> 
> > I wouldn't even use this method to melt precious metals, let alone smelting anything.
> ...



Sure, it works, you can also smelt in an electric melt furnace, for awhile, until the caustic gases created by smelting ruin the heating elements.

It's not a cost effective, nor good way of smelting!

Scott


----------



## kane333 (Jan 20, 2013)

If only Borax is used during the microwave melt, would Borax emit caustic gases? Any video I've seen of the melting process shows Borax being used with torches but no warnings about caustic gases.


----------



## butcher (Jan 20, 2013)

Sodium carbonate (borax) alone would hurt the microwave, unless maybe spilled. But borax and metal would not melt in a microwave, it would just burn up the magnetron, if you were lucky maybe just blow the fuse or burn out the high voltage diode. These would not absorb the microwave radiation, it would not create any heat to melt the metal, the metal would just reflect the microwaves and remain cold solid metal, the reason food heats up is because of water or moisture in the food will receive the microwaves and the water molecules movement creates heat, bread will not cook properly in a microwave, well they figured out if the made a paper envelope doped with microwave susceptors (hot pocket envelope) they could receive the microwave energy with the susceptor (in the paper) and convert the energy to heat baking the outside of the bread.
Flux to melt metals in a microwave, would need a microwave susceptor, mixed in the flux, like silicon carbide, graphite, magnetite, or a similar susceptor to absorb the microwave radiation and convert it to heat to melt the metal. 

http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=39&t=8483
http://en.wikipedia.org/wiki/Susceptor
http://www.talisman.org/~erlkonig/misc/microwave-metal-casting.html
http://nanotecnologia.com.br/redecmdmc/lab/arquivos_publicacoes/1260_Domestic%20microwave%20oven%20adapted%20for%20fast%20heat%20treatment%20PDF.pdf


----------



## creek (Jan 20, 2013)

I know one person that uses the microwave smelting thing. He took ex spading foam and used it to firm up the back wall of the microwave and laid it on its back. He cut down refractory board to fit sung in the bottom.

With the door opening to the top he just has to remove the lid to the kiln to get out the crucible. I think he has only used it 4 or 5 times, but it does work.


----------



## bswartzwelder (Jan 22, 2013)

I bought one of the microwave gold kilns. Paid something like $49 for the microwave they reccomend on the Internet. Used the flux and put in some crushed black sand. There wasn't enough gold in it to talk about. I over filled the crucible (put in more than about 2/3 of its volume) and with the boiling and expansion, it overflowed. Did a little damage to the kiln liner. Did it work? You bet it did. You have to use welding gloves and remove the kiln one layer at a time. After about an hour, I removed the kiln liner and found the crucible glowing almost yellow hot. The inside of the microwave stayed remarkably cool. There was no problem using crucible tongs to grab the now bright red hot crucible and pour the contents into a conical cast iron mold. I didn't find any gold until I put several small nuggets into the mix. Then I found a small button on the bottom of the cone mold.

The flux is most likely a form of a Chapman flux and their price for it is a bit steep. I will give them credit. They supplied an MSDS sheet which pretty much told you exactly what you need to make more flux, unlike the MSDS sheets supplied by Shor. Once the cone harden and cools, you have some really neat looking stuff which looks like obsidian glass. The people who sell the kiln also tell you that the black sand you process should have about 30% gold in it.


----------



## lazersteve (Feb 4, 2013)

Butcher,

For the record borax is Sodium Borate, not Sodium Carbonate,

Here's wiki's take on it:

Wiki Borax

All this alternate melting and smelting stuff really reminds me of the cat chasing her own tail. So much effort is being put into getting no improved results. I'll never understand why so many people work so hard to prove there is a 'better way' when the current proven ways work great! I understand the whole everything can be improved upon concept, but I can't see spending so much effort on such a fundamental task. Is the goal to say 'I did it; Do you want to buy one', or just to prove it can be done?

Can microwave ovens smelt precious metals if done properly? Yes, but it's more expensive to set up and maintain than an ordinary gas furnace for Gold and Silver or induction melter for PGMs. I'm all for a better tool, but I won't replace my current tools for lesser ones.

As Harold has eloquently put it in the past, "The wheel is not sufficiently round for some people", or something like that.

Steve


----------



## butcher (Feb 4, 2013)

Steve, 
Thanks for noting my mistake in how I stated that above.

I know borax and soda ash are different chemicals.

I know Borax is a borate salt compound sodium tetra borate Na2B4O7 that forms a glass slag when heated as a flux to absorb oxides of metals into the glass slag, it improves the viscous fluid of the melt and becomes a strong acid in the melt dissolving and fluxing most all metal oxides both acidic and basic, the borax glass cover not only absorbing the metal oxides but can also act as a shield from the atmosphere.

I do not confuse borax with sodium carbonate, and understand these are two different chemicals that are both commonly used in flux.

Sodium carbonate Na2CO3, which is also, called soda ash or washing soda, a powerful basic flux, which can act as a reducer of metals in a flux when it decomposes in the melt forming carbon dioxide gas which can also help to convert oxides of metals reducing them as it absorbs oxygen from the oxides of metals and which can aiding reduction of the oxides to elemental metal producing CO2 gas in the process, the soda ash which can also improve the property of the borax slag glass and melt properties , with ore it also acts as a desulfurizing agent or acts on silicates or aluminates as it forms an alkali. Sulfides and sometimes sulfates with ore in presence of its alkali are formed for this reason it is considered an oxidizer or desulfurizing agent, since the soda ash liberates alkali during melt it can also react with the acidic nature of ore, metal salts and the acidic nature of borax in the melt, the free alkali also reacting with silica or alumina in ore or your crucible forming silicates or aluminates dissolving away your crucible or melting dish


I did make a mistake in how I wrote what I did, which could have left the impression that these were the same, for members who do not know the difference.
I am sorry if this has caused any confusion.

I should have stated differently or written it different, with what I was trying to describe or what I was trying to say.

It should have written more like sodium carbonate or borax ingredients in flux alone would not…….
Not sodium carbonate (borax) alone.....


----------



## lazersteve (Feb 4, 2013)

Don't sweat it Butcher, we are all only human. I read your post as borax = sodium carbonate.

I just want to make sure no one else interpreted it the same way I did.

I know you are well aware of the differences between the two.

Steve


----------



## Chad_B (Oct 21, 2013)

i'm quite new to this forum so i'll apologize if i come off as too new but here's what i've found after a few days of researching this.

1) there are quite a few ways of doing this
2) finding the safest way may not be the easiest
3) the microwavegoldkiln people have a good idea, but aren't willing to acknowledge that there are other ways.

Search youtube for "microwave kiln" and you'll see people using crucibles of varying types lined with graphite and magnetite to smelt anything from glass to brass and silver. The combination of graphite and magnetite specifically because graphite reacts well at lower temperatures but doesn't get hot enough, while the magnetite works great at higher temperatures.

As for safety, I'm not sure about you but I'd like to have something that I can move about easily, especially if it is going into and out of a microwave. I like the idea that creek's acquaintance had as it makes the whole process easier.

As for the premade kit, they use a 2300F rated rigidized silica board. This is fine but I'd prefer something that provides a greater safety margin, and possibly some containment in case of failure. Also they use (most likely a graphite/magnetite blend?) additive in their custom flux and consider this to be the best option. However I've found an alternative that I really like in my search.

I've found this link from a government study that used a SiC crucible as a heating element, with another crucible inside it using a lab grade microwave.
http://www.osti.gov/scitech/servlets/purl/5671871
Admittedly the frequencies were tuned in this microwave and probably more directional but SiC is a good susceptor and with either more time, or a stronger microwave (and probably including rotation) this should be a good working 'blueprint'.
I've contacted a few insulation manufacturers to inquire about high density Alumina plates and tubes to use as an insulator for the whole process because they are microwave transparent AND stable to nearly 3600F, thought this is above the operational temperature of the SiC crucible it does give that safety factor I was looking for. It would also remove the need for custom flux.

As to any metals inside the crucible (which is inside the SiC crucible) sparking - it won't happen as the SiC absorbs almost 100% of the microwaves converting them to thermal energy.

So, basically an Alumina chamber with a SiC crucible that is slightly larger than your working crucible should work to (s)melt most things up to 1200C (@2200F) (without much risk of the SiC crucible failing) and up to 1600C(@2900F) for short periods, though the microwaves may severely affect it at higher temperatures.

I don't want to reinvent a wheel, I just don't have the desire to drag around 200lbs of gear to smelt my placer gold on site when 50lbs will do.
When I get everything together and test it I'll let you know how it goes!


----------



## butcher (Oct 22, 2013)

It sounds like you have been doing your homework on this subject, I would be interested in hearing how your progress goes.


----------



## bswartzwelder (Oct 23, 2013)

Several things concerning this process. First, not just ANY high powered microwave will work. It takes a certain type. They are readily available and like I said in a previous post, relatively cheap. It was the shipping charges that really made the one I ordered much more expensive. The people who make the microwave gold kiln list the type of microwave and even the makes and model numbers which should work, so that's a good place to start. If you know what you are looking for (make and model), you just might be able to pick one up at a flea market or second hand store for next to nothing. 

Second, it is not really a fast process. Once everything is loaded into the microwave, if memory serves me correctly, it takes about 60 to 90 minutes of continuous running. The last time I used it, my microwave seemed to be cycling on and off. Could be that the 5 or 6 times I used it destroyed it, or maybe it was a normal thing. 

If you just put everything in the crucible and turn it on, if you don't wait the full amount of time that they recommend, the gold does not have time enough to settle to the bottom of the crucible. In my experience, the flux was very thick and viscous. Even after I added more material to make it thinner, it still poured like molasses. This means that when poured into a mold, the gold may not have enough time to settle out before everything solidifies.

The people selling it are very friendly and do return calls and/or emails. Unlike another unmentioned company, they are free with their information and do not take common chemicals and give them names to hide what they have. When my one crucible overflowed, it damaged the inside of the kiln. Not too badly, but I was able to order replacement parts from them. 

The parts of the kiln appear to be professionally made. No nasty looking saw cuts, all smooth edges, and on the layers with holes in the center, the holes are clean and smooth as well. Everything from them came well packaged. Having said that, if you could find the source of the material they use, I would bet you could make your own unit and save a little (maybe a lot) of money. If you have a lot of material to smelt, I would think there are better methods which would handle larger volumes and probably work faster.

Their website offers a lot of free information, but, like this forum, you have to do your homework and read through everything. As with anything related to recovery and refining of precious metals, there are options. You must study the methods and determine which option best suits you for what it is you are trying to do. It would be nice if we could recover gold from scrap circuit boards by pouring whiskey over them and not having to use harsh acids or cyanide. But that just aint going to happen.


----------



## solar_plasma (Oct 23, 2013)

I think it's again like that dill. sulfuric/dill.H2O2-dripping-thing. There are well-experienced common methods and there are other methods, which also work in some way if properly done.

I like this diy microwave thing. Not because it is a more round wheel, - it is not. So, why? Since you easily can get an old microwave for free, why not? As long it doesn't harm and as long it causes no loss of values...

And I don't think the sulfuric method has been shot down. 

At this occasion I'd like to show a link I posted before in order to add an important point: Finding the hot spots of the microwave.

http://www.chf.de/eduthek/mikrowelle-experiment07.html

Knowing this link, this killn above seems too expensive to me. Everything I need for this project I have in my garage.

Another thing for discussion: Is it possible, to use the microwave standing on its back or would the glas get too hot? The advantage would be, that you are not forced to take all the stones out of it, when you want to stir the molten metal.

EDIT: But if I had nearly 400 bugs to spend, I would buy an acetyleneoxyweldingtorch, - well, I'll get one soon for free, but I could buy gas and a lot of nice equipment for the money.


----------



## Platdigger (Oct 24, 2013)

Solar, there is a post in this thread by "creek" that claims some one is doing just that, laying the micro on it's back.
good idea


----------



## solar_plasma (Oct 24, 2013)

> I know one person that uses the microwave smelting thing. He took ex spading foam and used it to firm up the back wall of the microwave and laid it on its back. He cut down refractory board to fit sung in the bottom.
> 
> With the door opening to the top he just has to remove the lid to the kiln to get out the crucible. I think he has only used it 4 or 5 times, but it does work.



Thanks, now I see. But what means "ex spading foam" and "to fit sung"? I could not translate it.


----------



## Platdigger (Oct 24, 2013)

I think he meant to say "expanding foam"

And "snug" the same as a good tight fit.


----------



## solar_plasma (Oct 24, 2013)

Thanks, Platdigger!


> After about *an hour*,


Using the hot spots they did it *in 5 min* to make brass from copper and zinc powder:
http://www.chf.de/eduthek/mikrowelle-experiment10.html

here once again the prepared crucible:
http://www.chf.de/eduthek/mikrowelle-experiment09.html

I don't see this as an alternative to any professional setup, ofcourse not. It's just for the fun of making this work.


----------



## Platdigger (Oct 24, 2013)

Looks cool, wish I could read German. Just a taste of what you all must go through on an English site like this.
Are those flower pots with perhaps a graphite based cement in the second one.


----------



## solar_plasma (Oct 24, 2013)

No, they use common graphite spray, which has to be sprayed onto the refractory mortar inside the flower pot before each melt. The refractory mortar form has to fit exactly to the crucible.


----------



## niteliteone (Oct 24, 2013)

Platdigger said:


> Looks cool, wish I could read German. Just a taste of what you all must go through on an English site like this.
> Are those flower pots with perhaps a graphite based cement in the second one.


Since Solar likes to post links written in German I have found that "Google Translate" is actually pretty good. You can copy/paste whole paragraphs and get an accurate translation with-in seconds.
here is the link;
http://translate.google.com/#auto/en/


----------



## jpdriver1 (Oct 26, 2013)

niteliteone said:


> Platdigger said:
> 
> 
> > Looks cool, wish I could read German. Just a taste of what you all must go through on an English site like this.
> ...



for me google automatically asked if I wanted to translate -- 

thanks for the info on smelting --- I too just purchased one from an outfit in Canada --- gas or microwave ---


----------



## jpdriver1 (Oct 26, 2013)

niteliteone said:


> Platdigger said:
> 
> 
> > Looks cool, wish I could read German. Just a taste of what you all must go through on an English site like this.
> ...



for me google automatically asked if I wanted to translate -- 

thanks for the info on smelting --- I too just purchased one from an outfit in Canada --- gas or microwave ---


----------



## Neb87 (Jul 9, 2020)

This works well for relatively clean precious metal powders. Using a graphite crucable, no flux is required. Takes me about 3 minutes to melt gold. I made mine myself using soft firebrick and silicon carbide powder + sodium silicate. The silicon carbude ring heats up as it absorbs the microwaves to around 1700*F. A graphite crucable is also important because it also absorbs microwaves and heats up beyond the melting point of the precious metal you are melting. Shortly after you have a nice metalic bead waiting for you.


----------

