# Silver Powder Won't Melt In Electric Kiln/Furnace - Why Not?



## Anonymous (Nov 18, 2014)

Hello members,

I have been using an electric kiln/furnace with a temp rating of 2400 degrees F, that has a graphite crucible. The thing that I haven't figured out is why the silver powder won't melt in the crucible?

The crucible is 30oz. I filled it up after it warmed up to the required temp, then I added the powder to it, then I closed the lid. After 10 minutes I opened up the lid and saw that the crucible and the powder was red... well the crucible hot red, and the silver powder dull red. So after closing the lid and letting it work for about 20 more minutes (30 minutes now) the powder never budged, even after stirring with the graphite rod. 

So, I decided to try something. I added about 4ozT of solid silver to the crucible, and within 5 minutes the solid silver started molting and then it was liquid and I didn't see it on top anymore. I let it heat for 5 more minutes, and I decided to take it out. When I took out the crucible and poured it into a mold, the solid silver I put in it poured right out into the mold, but the powder poured over top of it, without even absorbing into the molten silver at all. I even stirred the silver and powder while it was still in the furnace. But the powder stayed at a powder, but the solid silver melted.

My question is why won't silver powder melt in the furnace? I'm sure you're going to say I need an induction furnace. I even turned the furnace up to 2000 degrees F before the pour, when I only needed 1763 degrees to melt it.

So now, I am melting the powder in my melting dish, then putting the melted silver in the furnace to make 25oz bars. I'm using electricity and gas (propane or mapp) to do a single melt.

Any help appreciated.

Kevin


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## Harold_V (Nov 18, 2014)

testerman said:


> My question is why won't silver powder melt in the furnace?


Because it's not pure. The oxide film surrounding the silver powder prevents the silver from coalescing. Inside each miniscule piece there is likely molten silver. Fluxing solves the problem, but flux and graphite crucibles are a poor mix. Your big mistake was thinking that the electric furnace was a good idea. It's not. I owned one of them and regret having spent the money. It sat idle for years once I understood how poorly they are matched to this kind of application. 



> I'm sure you're going to say I need an induction furnace.


Then you'd be wrong, as I never suggest that ANYONE needs an induction furnace. Further, unless one owned one with quite high operational frequency, it may not melt silver powder, either. They are charge and feed sensitive, so one must procure the proper furnace for the particular application. Melting powder is totally different from melting pieces. 

What I would suggest is that you need either an adequate torch and a large melting dish in which you can heat the silver powder and add flux (borax, with either anhydrous or borax glass being the best choice), or, better yet, a crucible in which you can add the powder, then introduce anhydrous borax or borax glass when the charge is up to heat. You'd witness an immediate coalescence of the silver. Once melted, this charge is best poured to a cone mold, so the flux can be easily separated. The resulting button(s) are then remelted so they can be poured to an anode mold for parting. 



> So now, I am melting the powder in my melting dish, then putting the melted silver in the furnace to make 25oz bars.


I expect the quality is questionable, depending on the source and process involved. If fluxing yields slag that has color, that should be proof enough that the material is not pure. If it is free of color, it may well be quite pure, but I would expect that it would also melt adequately without flux if that was the case. I may be wrong. 

Harold


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## g_axelsson (Nov 18, 2014)

If there is any silver oxide on the surface in the beginning then it should be gone when reaching melting temperature of the silver. Silver oxide starts to decompose at temperatures above 200 C and melts at 300 C. At 1000 C it should all be gone.

Apparently there is something on the surface of the silver powder that stops it from coalesce into a larger molten mass or the temperature isn't enough. I know you said the crucible temperature was high but your description of "dull red" of the powder hints of a lower temperature.
I guess that this silver powder is a result from your "proprietary" process and then it's hard to help you as we don't know what you have done with it.

And as Harold and others have written many times, that small electrical furnace isn't a good tool for what we are doing.

Göran


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## Anonymous (Nov 18, 2014)

Thanks for the reply.

The silver is pure. No question about that. Also, the furnace isn't mine. Someone bought it to do some melting and I wanted to test it out on my powder. I have no problem at all melting it in my melting dish using propane or mapp, but, in my own experience, propane melts the powder easier. That's my opinion.

Also, there isn't a crud of flux on my silver. I melt in a seasoned refractory melting dish, a large one, and I pour the melted silver in a 5 gallon bucket of water. The silver looks better than minted silver, or just the same. I do the cone sometimes and it does separate the flux from the silver easily, verses trying to let the silver cool a bit in the melting dish and then using tweezers to take it out.

I'm thinking that I may have to have a insulated fire oven/kiln designed to put a torch on each side and melt it that way. I may need to look into doing it that way.

On another note, what is the biggest refractory melting dish you know of? I believe mine is the 4" or so. It can hold about 10ozt silver powder, melted down in increments and more added to it. When I do it that way, the powder gets melted much quicker because the other molten silver heats it very fast, using propane gas. 

Kevin


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## kurtak (Nov 18, 2014)

Kevin 

I don't know how much silver you are wanting to melt at a time but if you are talking a pound (14.4 ozt) or more you need to look into get a good propane fired furnace like this

This one takes a #4 crucible I use it for pouring 2 pound anode bars (it will melt more that's just the size of my mold) this one use's compressed air for the air/gas (propane) mix

I have a bigger one that takes up to a #40 crucible & has a self aspirating burn for adjusting air/gas mix instead of compressed air

Kurt


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## Anonymous (Nov 18, 2014)

Loving the view Kurt!


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## philddreamer (Nov 18, 2014)

These are the ones I use for melting my material:
http://www.ebay.com/itm/221022450014?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=20855&p=214632&hilit=furnace#p214632

Phil


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## Anonymous (Nov 18, 2014)

kurtak said:


> Kevin
> 
> I don't know how much silver you are wanting to melt at a time but if you are talking a pound (14.4 ozt) or more you need to look into get a good propane fired furnace like this
> 
> ...


I saw that setup the other day in another post that you did. It looks great. I am trying to melt 25ozt of silver per run. The powder isn't covered with anything, and I'm saying that because when I do a torch to it, the fire doesn't get green or any other color. In the furnace, it just glows a dull red. I'm almost tempted to take some solid silver, then dissolve it in nitric and drop it with copper and rinse and dry, and try it that way to see if my method is the reason why it won't melt. Although I doubt that's my problem, I'll have to at least check it out to see.

Now, on the same note... have anyone actually melted silver powder in a electric furnace and it melted as expected?

And i never used an oxy/gas torch before, but I've seen some videos about it, but I would definitely need some of your expert advice as to the kind I should start off with. I have seen some new on eBay starting around $80 USD for the cutting torches. But like I said, I'm not experienced at all with them and I will need advice as to what I should buy.

There is a person that sells firebrick locally (12 for $30) and he has two different sizes too. I bought some from him, but I am going to buy a dozen of each size he has so I can build an oven. But I need to get some refractory cement or powder to seal it. I still have some refractory insulation sheet to line or insulate it somehow.

Being as cold as it is now outside (in the 20's) a melting dish won't cut it. 

Oh, also, to make sure my powder is free of any impurities (I'm thinking) I put the powder in a 9" x 13" cake pan and torch it until it glows. I don't have to do it that way, but I've been doing it that way because the furnace just won't melt it.

But like *g_axelsson* said, it may be possible the furnace isn't getting hot enough to melt the silver powder. But, it will melt the metal within 5 minutes. So, with that in mind, I'm thinking the silver powder need to be heated to an even higher temp in the furnace?.... Oh, and for the sake of it, I even took my torch to the inside of the crucible while in the furnace heating it and the powder still never budged.

*[ADDED INFO]* I was just now brainstorming and I was thinking about insulating the crucible without the use of the furnace and then put the powder in it and melt it with the torch. I'm sure that will work. That's an idea I think I'll give a try if no other solution can work for me for what I have to work with right now.

Kevin


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## Anonymous (Nov 18, 2014)

To answer one of your questions Kevin. Harold has already alluded to the problems of trying to melt silver powder in an electrical furnace. From experience.


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## Anonymous (Nov 18, 2014)

spaceships said:


> To answer one of your questions Kevin. Harold has already alluded to the problems of trying to melt silver powder in an electrical furnace. From experience.


Yes, I know, and I believe him too. Also, I've learned from being on this forum that it will take longer for powder to melt into a solid than to take a solid and melt it back into a solid.

I think the insulating of the crucible alone may work with the torch.

Kevin


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## Anonymous (Nov 18, 2014)

Mapp gas torch + melting dish + powder = metal. Metal + crucible + decent furnace = larger lumps of metal.


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## Barren Realms 007 (Nov 18, 2014)

spaceships said:


> Mapp gas torch + melting dish + powder = metal. Metal + crucible + decent furnace = larger lumps of metal.



+ Experience.


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## solar_plasma (Nov 18, 2014)

> Oh, and for the sake of it, I even took my torch to the inside of the crucible while in the furnace heating it and the powder still never budged.



If the silver powder is from your keyboard mylars and never has been dissolved and cemented or precipitated and converted, it could still be the problem of impurities. Yes it is hard to believe, I myself do not know, where the impurities should come from, but without dissolving you can't be sure and it is a assumption it is pure. My first succeses with melting silver happened first after I learned to produce it in a good purity.

In my poor (silver melting) experience I learned one thing: Pure silver melts reliably even with a five dollar bunsen burner, if the probe isn't too big and well isolated. Give it a try.


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## Harold_V (Nov 19, 2014)

To be clear, I stand my ground. Like it or not, the problem is an oxide on the surface of the silver (not a silver oxide), or some other contaminant. All the other nonsense that has been speculated is just that---nonsense. If the furnace will melt solid silver, there's not one good reason why the same temperature won't melt finely divided silver. All it would take is the introduction of a trace of borax for the silver to coalesce. Been there, done that, and should have the T shirt, although I do not. 

And----if your plan is to flux in a graphite crucible, be prepared to buy a new one for the furnace owner, for it will be destroyed by fluxing. Have a chair near when you price the crucible. They are not cheap. 

Harold


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## kurtak (Nov 19, 2014)

Harold_V said:


> And----if your plan is to flux in a graphite crucible, be prepared to buy a new one for the furnace owner, for it will be destroyed by fluxing. Have a chair near when you price the crucible. They are not cheap.
> 
> Harold



Correct - you will only get 2 or 3 melts & after that the graphite becomes porous & the flux will bleed through the crucible wall get on the heating element & destroy the elements & your furnace is then dead --- ask me how I know

Even with pure metal by the 4th melt the crucible is getting real iffy for further use

Return the furnace before you end up owing the guy a new crucible &/or even a new furnace

Kurt


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## kurtak (Nov 19, 2014)

testerman said:


> Now, on the same note... have anyone actually melted silver powder in a electric furnace and it melted as expected?
> 
> And i never used an oxy/gas torch before,
> 
> Kevin



Yes I bought one of those electric furnaces about 3 years ago along with a couple extra crucibles & it melted my silver cement no problem --- the problem was short (expensive) crucible life --- I tried to squeeze one to many melts out of a crucible & both silver & flux ended up bleeding through the crucible walls got on the elements & destroyed the furnace

When I was talking about air/gas mix I was not talking about an oxy/gas torch - you don't need oxy/gas when torch melting silver - a MAPP gas torch works fine 

The air/gas mix I was talking about the burners for gas fired furnace's - you need to mix oxygen with the gas (propane) to get it hot enough - that's because you are not trying to melt a small amount of metal in a small melting dish - but you also need to heat the large surface area of the refractory walls in the furnace - the larger heavier walled crucible & a larger amount of metal

So you need to increase burning temp to heat all these things that are acting as heat sinks - that's done by mixing air with the gas - that can be done with ether compressed air (don't need much - only between 3 - 7 psi) or by what is called self aspirating in the furnace burner design

Here are pics of my 2 furnace burners - the small one is compressed air design the big one is self aspirating - the air mix on the self aspirating is adjusted by adjusting the slide

Kurt


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## kurtak (Nov 19, 2014)

philddreamer said:


> http://goldrefiningforum.com/phpBB3/viewtopic.php?f=61&t=20855&p=214632&hilit=furnace#p214632
> 
> Phil



8) Very cool Phil - some how I missed that thread till now --- I REALLY like that cone/bar mold you have there - do you have any more detailed pics on the construction of it :?: 

I assume as heavy as the walls are on it the bottom is 2 flat bar stock welded together (not angle iron) & what type/grade iron/steel did you use ?

Edit ; to also ask - where did you get that refractory lining ?

Kurt


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## kurtak (Nov 19, 2014)

spaceships said:


> Loving the view Kurt!



I live on 40 acres mostly wooded with a creek & pond - my nearest neighbor is 1/3 mile down the road - dinner (deer, wild turkeys, etc.) walk through the yard all the time :mrgreen: 

Kurt


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## philddreamer (Nov 19, 2014)

> Very cool Phil - some how I missed that thread till now --- I REALLY like that cone/bar mold you have there - do you have any more detailed pics on the construction of it
> 
> I assume as heavy as the walls are on it the bottom is 2 flat bar stock welded together (not angle iron) & what type/grade iron/steel did you use ?
> 
> ...



Thanks Kurt!
The mold is made of 3/8" 3 x 3 mild steel angle and some scrap plate welded at each end. It's a simple set-up. The pic's shows another type I have for pouring heavier bars.

The refractory is kaowool ceramic bars I got from e-bay, from an outfit here in Washington.

Phil


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