What metal is this?

[MGH]

These pieces and a few others were left over solids after processing a batch of mixed gold filled. I digested first with nitric, poured off, rinsed with DI water, then moved to AR - no, I did not incinerate, but wish I had :-(. They sat in hot AR for about 7 hours.

As expected, the karat foils left after the nitric digest dissolved in AR. These pieces remained, but I can’t figure out what they are. I tested them on the stone. They make a silver colored streak, but the streak remains under 10k, 14k, 18k, 22k, and platinum test acid.

My first guess is that they are stainless steel. But the other bits of stainless that I know were included in the mix did dissolve in AR and are nowhere to be seen. Even if they were solid karat gold, I would have expected them to dissolve to some degree in AR, but the markings and edges are clear and crisp, and I don't see any indication of a AgCl crust.

I’m assuming these pieces do not have any PM content, but obviously want to make sure. Has anyone else seen this before? Do you know what metal this is?

Thanks,
- Matt H.

 

[myfalconry76]

How many ml of acids did you use? Maybe your solution was exausted! I hear brass is a common metal in gold filled stuff.

 

[kurtak]

Its stainless steel

Kurt

 

[MGH]

How many ml of acids did you use? Maybe your solution was exausted! I hear brass is a common metal in gold filled stuff.

Come on now, give me a little credit. I'm sure I can identify brass. I'm also sure that brass would not have made it through the nitric (of which I used 3.55 mL per gram of GF along with an equal volume of DI water), and certainly would not have made it through the hot AR where all gold dissolved yet still come out with nothing more than a little discoloration.

Its stainless steel

Kurt

Thanks, Kurt. So would this be a grade of stainless that doesn't dissolve in AR? Every other bit of stainless I've had in AR solutions has dissolved - both in this batch and in previous batches. If this is just a certain grade, then I've learned something new yet again!

 

[Lou]

It says stainless on one of the pieces.

 

[Barren Realms 007]

It says stainless on one of the pieces.

If all else fails read the instructions. 8)

 

[Barren Realms 007]

How many ml of acids did you use? Maybe your solution was exausted! I hear brass is a common metal in gold filled stuff.

Come on now, give me a little credit. I'm sure I can identify brass. I'm also sure that brass would not have made it through the nitric (of which I used 3.55 mL per gram of GF along with an equal volume of DI water), and certainly would not have made it through the hot AR where all gold dissolved yet still come out with nothing more than a little discoloration.

Its stainless steel

Kurt

Thanks, Kurt. So would this be a grade of stainless that doesn't dissolve in AR? Every other bit of stainless I've had in AR solutions has dissolved - both in this batch and in previous batches. If this is just a certain grade, then I've learned something new yet again!

Put the pieces in HCL for a few days and you should see a weight difference in them.

 

[mls26cwru]

by putting it in nitric first, you would have passivated the surface... Its similar to bluing (which can be done a number of ways).

The theory is that you want to form an oxide layer that is resistant to a specific chemical attack (most often oxygen) to protect a piece of metal. Iron can form two types of oxide... if i recall correctly, they are Fe2O3 and FeO4... the first is rust, the second is much more inert and protects the metal underneath. This is essentially what you do when you expose it to nitric acid.

There is a whole industry devoted to the passivation of stainless steel... I use it regards to applying diamond like carbon coating to stainless steel by exposing the raw stainless to an oxygen plasma.

 

[MGH]

by putting it in nitric first, you would have passivated the surface... Its similar to bluing (which can be done a number of ways).

The theory is that you want to form an oxide layer that is resistant to a specific chemical attack (most often oxygen) to protect a piece of metal. Iron can form two types of oxide... if i recall correctly, they are Fe2O3 and FeO4... the first is rust, the second is much more inert and protects the metal underneath. This is essentially what you do when you expose it to nitric acid.

There is a whole industry devoted to the passivation of stainless steel... I use it regards to applying diamond like carbon coating to stainless steel by exposing the raw stainless to an oxygen plasma.

Thank you! That makes more sense now.

My confusion came after searching led me to the couple of links below (I think there are a couple more) that seem to imply that IF one were to put stainless and gold in AR together, that with enough time and acids everything would eventually dissolve. As with many details in refining - not so simple.

http://www.goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=49&t=23128
http://goldrefiningforum.com/~goldrefi/phpBB3/viewtopic.php?f=49&t=10338

Thanks again to everyone.

 

[Lou]

You had too much nitric relative to HCl.