# do someone know what is that black crust from melting



## ericrm (Aug 13, 2013)

i have been melting scrap brass, iron, nickel, silver and whatever else i could find with eater copper or pm in it to make anode and i have ended up with that black material that refuse to melt... i have pushed the furnace to its maximum and still refuse to mix with the other melted metal . it is anoying because it acumulate in the crucible or endup screwing my anode surface. i have grinded it and it nevershine ,it seem to be realy hard ,could it be some kind of iron or copper oxide? i dont use any borax in the crucible... anyway look at the pix , if someone has a clue about what it could be i would love to know it.


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## NobleMetalWorks (Aug 13, 2013)

Something oxidized, you don't get that colorized layer without something having had oxidized. 

What did you use as a flux, I can see you had a boil over, it could possible have something to do with a secondary reaction that took place with your flux, whatever it might have been composed of.

Whenever you alloy two or more metals together, they take on different properties, melting temperatures, oxidizing states, etc. Literally, your alloy composition could have been anything according to what you have stated. It looks like you have some type of oxidation, but that doesn't mean it's the problem, it could be that you have a metal with a higher melt temperature that didn't melt. If the other metals did, and left the metal behind that couldn't melt you it could have protected other metals from melting, and caused your problem. I don't know enough about pyrometallurgy to comment anything further than a guess.

Maybe there was Tungsten? It seems like if you were able to melt iron though, that it should have readily alloyed with tungsten. I'm just not sure.

One thing I would be careful of is your boil over, it looks like you had a fairly substantial one. If that metal you cannot melt splattered on the inside of your furnace, you are going to want to remove it, carefully. 

Can you describe a little bit more about the conditions that produced that kind of result? The flux composition, temperature, metals etc?

I think maybe Lou or 4Metals might be able to help you further.

Scott


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## ericrm (Aug 13, 2013)

thank for the fast reply

i think you mean by a boil over because of the buble around the crucible, but it is normal i guess, i have about 20 melt in it and it become uglyer each time.since im only melting to make anodes and not trying to 'clean" the metal content i dont use any flux, . i might be totaly off the track on this...
temperature would be between 1200c and 1600c , metal were anything from silver plated item (epns, copper, brass),gold plated pin(copper,brass),just plain copper and mixed unknow magnetic and non magnetic pin.


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## Lou (Aug 13, 2013)

Melt with 1 part borax, half part carbonate. Adding more carbonate if necessary to get the metal to prill.

Those are oxides, mostly of copper, that form a skull on the crucible wall.


L


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## ericrm (Aug 13, 2013)

ok i will try that
thank you Lou


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## rusty (Aug 13, 2013)

Your crucible looks to be near the end of it's useful life expectancy.


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## ericrm (Aug 13, 2013)

rusty, i dont think i will see the end of it... for now it is still 1/4 inch over all around and when he will be too thin i will use it for easier job like Pb melting


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## rusty (Aug 13, 2013)

ericrm said:


> rusty, i dont think i will see the end of it... for now it is still 1/4 inch over all around and when he will be too thin i will use it for easier job like Pb melting



Ah, suit yourself.

The crucible will look fine in the furnace until you pick it up with your tongs then having it crumble to pieces in transit - had it happen.


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## ericrm (Aug 13, 2013)

good to know , thank you


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## rusty (Aug 13, 2013)

ericrm said:


> good to know , thank you



Your welcome ecrim, When you start using flux in your melts do not expect to get 20 melts from a crucible, the thin walls of an over used crucible become pliable like putty when extremely hot.


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## bswartzwelder (Aug 14, 2013)

Back when I lived in Southwestern PA, I saw a lot of stuff that reminded me of your crucible. One, was slag from the steel mills. I suppose slag could be considered anything (usually undesirable) left over from melting metals. The other was what was called clinker, which was the ash left over from burning coal. Back then, (I was born in 1950) in that area, we used an awful lot of coal for heating our homes and producing electricity. Don't want to bring politics into it, but there aren't very many coal miners left.


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## Imran (Aug 15, 2013)

@ericrm
I believe that black crust is copper (II) oxide. Next time you melt copper you should add some powdered charcoal. Hope it helps.


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## MysticColby (Aug 15, 2013)

I had my first crucible fail on me a few months ago. Didn't crumble or fall apart. I was melting copper powder (copper nitrate cemented with iron), then I looked into the crucible and was shocked at how little there was, then noticed it had drained out a small hole in the side of the crucible. I was able to pick up the crucible (it was still 3/8"+ thick in most places) and pour out what was in it, then I turned off the furnace, waited for it to cool, then picked up the copper that had poured out (along with the ITC-100 layer of my furnace). the next day I added all the recovered copper to a new crucible and kept melting.
I had added sodium carbonate to limit oxidation (does it reduce copper oxide to copper, or just stop it from becoming copper oxide?), and that's supposed to eat through crucibles. probably why mine failed so quickly (it wasn't new, but was pretty thick still). now I use powdered carbon (charcoal)

if it won't melt in a furnace, it's likely an oxide.


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