Black cement with copper

[metatp]

I'm inclined to think of as being silver, perhaps chloride. Does it dissolve in a drop of ammonium hydroxide? If, after dissolving the sample, what does a drop of DMG show?

Sadly, i do not have ammonium hydroxide or DMG. Can you point me to any sources? I do have a pool supply store near by if it is something they use for pools.

I'm still inclined to think of the gray material as silver and/or chloride. Neon greenish? Don't have a clue, although if there is nickel or copper present, that could be influencing the color.

I know there is silver, and it was cemented with copper so there may be some copper present.

Palladium is a bit of a chameleon, and will yield color combinations in keeping with what you experienced. If you have any DMG, test a drop of the solution. This test will be conclusive. Palladium yields a deep canary yellow precipitate, and it takes very little in solution for the precipitate to develop and be visible. If you get no reaction, you don't have palladium.

I am pretty sure i know what contacts are creating this situation. Problem is that I thought they were silver tungsten contacts so I put them all together. I did dissolve the rest (with a little silver) in nitric, but there is a lot of extra nitric in the solution. Will DMG be ok with excess nitric acid?

Besides, it's actually quite interesting!

That it is.

In order to satisfy the unknown, you should have the following:
Schwerter's solution
nitric acid
HCl
stannous chloride
DMG
Standard gold solution
ammonium hydroxide

Have everything but the DMG and ammonium hydroxide.

It would pay you to read Hoke's books on testing, too.

I have read this section, but have not played around with any of the testing she mentions.

I will reproduce what testing i did and take pictures tomorrow.

 

[eeTHr]

HTPatch;

See first paragraph, 12th sentence---
http://en.wikipedia.org/wiki/Ammonia

So you can get it at a grocery or drug store. 8)

 

[Anonymous]

Harold,
Am I missing something? I have been under the impression that copper can only replace precious metals.
And if thats the case then he should only have precious metals in that black mix.

I have used copper for shotgun replacement of precious metals when I had to dissolve everything from IC chips.
That was before I was able to get nitric only, so I had to use a variation of the poors mans AR to recover the metals.
Jim

 

[metatp]

Here are the pictures where the sample was soaked in HCL. It appears that the color change is disappearing over time.

 

[metatp]

Here are the pictures where the sample was soaked in a little NO3 and HCL. It appears that the color change is disappearing over time as well.

 

[metatp]

I took some of the suspect contacts and put it in some nitric acid for a few days. They did start to dissolve, but very slowly. There was no noticeable fizzing. There should be no silver (in don't think). The solution was clear with some reddish brown residue (same color as the final contacts) that was filtered out.

Stannous chloride test of the solution is a pale blue.

 

[Harold_V]

Harold,
Am I missing something? I have been under the impression that copper can only replace precious metals.
And if thats the case then he should only have precious metals in that black mix.

Yes, I agree, but if there was any copper oxide present, or if the material wasn't washed well, it's entirely possible that there would be traces of copper included. Just trying to cover all of the bases. Right now, I'm totally confused. I'm reading about (and seeing) reactions that I never experienced.

Edit:

I have never seen the bright green reaction, pictured above. The blue reaction I am inclined to attribute to tungsten. I recall that when washing silver cemented from contacts that came down quite dirty that the HCl solution turned a dark blue color. I do not recall testing with stannous in this case, secure in the knowledge that I didn't have any precious metals present. If the blue reaction is the result of a test with stannous, I'm still just as lost as I have been from the outset. (a second edit here: Now that I've had time to think on this, if the sample was tested with a stannous solution that has an excess of HCl, and the solution contains traces of tungsten, the blue reaction could well be attributed to the presence of tungsten, and has nothing to do with the fact that stannous chloride was introduced. That could be determined by adding a drop of HCl alone to the test sample to see if it reacts accordingly.) I clearly don't have a clue what the hell is going on at this point.

I wonder if GSP has followed this thread? He has a lot more experience than I do with silver, and may have seen these reactions before.

At this point in time, if there's the least question that the reaction may be palladium, a DMG test is a great idea.

Fading color reactions are often the result of an excess of nitric. There are instances where the reaction takes place and fades almost instantly. That may account for the slow degradation being experienced. Dunno!

Harold

 

[qst42know]

Cobalt blue was a common potent colorant for early pottery, however I don't have a clue how it would react to acids or stannous. As I remember reading it took very little cobalt to produce a deep blue glaze.

What say the chemists of the forum?

 

[lazersteve]

I've never seen blue with stannous tests. I've worked with gold plated tungsten/ copper alloy once and the result was a yellow powder and a orange yellow liquid.

Cobalt is another option I was considering, but I don't have any experience with stannous and it to say for sure.

I'm wondering if the orange/ green reaction may be a result of Pd, the only odd part is that the reaction typically starts orange and changes to green-blue with a minute or so depending on the concentration. The azure blue color on the stannous swab looks like copper nitrate or a cobalt compound to me.

Here's a few more test you can perform:

1) Rinse and dry a small sample of the material then try to melt is and see what happens.

2) Take a sample of the green acidic liquid and add in some solid copper, see if you get a cementation reaction.

This one is a new one to me also.

Steve

 

[metatp]

The blue reaction I am inclined to attribute to tungsten. I recall that when washing silver cemented from contacts that came down quite dirty that the HCl solution turned a dark blue color.

The blue ocurred with the nitric, not the HCL. the HCL only was yellow. I thought tungsten did not dissolve in nitric or HCL. The HCL does appear to remove the black and turn the solution to a yellowish green. There is definitely tungsten in the mix that was dissolved. The precipitant maybe a dark blue not black. Why would it cement on copper? I have another sample that I am cementing the black stuff with copper right now. There should be little or no silver in this batch. i will then redissolve making sure there is not excess nitric and test again to see if the same blue appears.

Now that I've had time to think on this, if the sample was tested with a stannous solution that has an excess of HCl, and the solution contains traces of tungsten, the blue reaction could well be attributed to the presence of tungsten, and has nothing to do with the fact that stannous chloride was introduced. That could be determined by adding a drop of HCl alone to the test sample to see if it reacts accordingly.

HCL does react. It formed a yellow solution that tended toward grean over time. I deffinitely get different results when HCL only or HCL with a drop on nitric. I will take the solution that was hcl and nitric and just add a drop of 32% hcl to see what happens

What about a contact with tungsten and some material other than silver? Has anybody seen a different alloy with tungsten for a contact?

At this point in time, if there's the least question that the reaction may be palladium, a DMG test is a great idea.

This appears to be key. I will persue getting some DMG. I only have one contact left that is giving these results, so all this learning may just be for learning sake. I will try to find the source of these contacts, but the guy I got them from says he collected them over the course of the last 25 years.

Fading color reactions are often the result of an excess of nitric.

Could this be true with excess HCL also? I know I had excess HCL.

Thanks again,
Tom

 

[qst42know]

I was doing some digging and tungsten is sintered with Co, Ni, Fe, Mo, Cu. In a variety of combinations and ratios for the desired properties.

You may be leaching binders for your base colors. If that helps any.

 

[metatp]

Cobalt is another option I was considering, but I don't have any experience with stannous and it to say for sure.

I was wondering about cobalt. I thought I read somewhere that it would show blue, but i can't remember if that was the solution or the stannous chloride test.

Here's a few more test you can perform:

1) Rinse and dry a small sample of the material then try to melt is and see what happens.

I am preparing a new sample that should have little of no silver in it. Copper is cementing the black stuff as we speak. I will redissolve some in a small amount of nitric and test with Stannous again. I will also dry it and try to melt it (though I only have MAPP).

2) Take a sample of the green acidic liquid and add in some solid copper, see if you get a cementation reaction.

I started this with the sample that is in HCL. There was not cementation reaction imediately. I will check when I get home.

This one is a new one to me also.

It is probably just me. I probably messed something up and the information is not getting on this forum. I am new, so maybe there is an important piece of information I am not aware of.

 

[T3sl4]

Tungsten, in the form of carbide cutting tools, is essentially powder brazed together with a matrix of cobalt. Something like 80% WC or W2C, balance cobalt. You can safely assume WC is insoluble: the damn stuff melts at 6000 degrees.

I've taken some carbide grindings, soaked in HCl and got a lovely pink solution: the color of cobalt chloride hydrate. That, and a lot of black sludge (the WC, and any Co that didn't dissolve). The solid salt might be recognized from dessicators, as it turns pink when hydrated, blue when dehydrated.

Stannous chloride is a reducing agent, right? Cobalt is already reduced, in the +II state, and it's somewhat unwilling to go any higher (though some complexes take it up to +4, as I recall). It's typically a pink color in chloride solution. The strength of color is typical of chlorides, including iron, copper, etc., and not overwhelming like the color of potassium permanganate. Only when cobalt is fused into a glassy substance does it get insanely blue (I think cobalt glass is to the tune of 2% Co).

Tim

 

[qst42know]

The color ranges of the different states of cobalt oxide are mentioned in these links.

http://en.wikipedia.org/wiki/Cobalt_oxide

 

[metatp]

OK. Here's what I think is happening. I preface this with I am not a chemist and don't know what I am talking about.

I think the black stuff is not really cementing with copper. I think that silver is cementing, and the black stuff is going for the ride. I think it is coating the silver powder. I also think that the black stuff is actually very very dark blue.

I just placed some copper in a nitric acid solution containing very little silver (just maybe some left overs). The blackish stuff started dropping off, but when i came home from work, the solution was black. After filtering and rinsing, the solution was still very dark with almost no powder left in the filter. After dipping a Q-tip in the solution, it is actually a dark blue. Stannous chloride did not change the solution color much. just made it a little bluer.

Warm water does not seem to remove all the dark blue/black material from powder. I don't this it is very water soluble. I am going to try a quick rinse of the silver rich black powder with dilute nitric acid of maybe dilute sulfuric acid to see if the black dissolved off. I see that it comes off in HCL, but appears to make silver chloride at the same time (it did not redissolve very well in nitric).

I don't think there is any values other than the silver. After I get some DMG (somewhere) and confirm no Palladium, i will abandon this learning experience. i will try a quick melt of the black powder first.

FYI. I read from I-Shor that Iridium turns blue-black when Stannous chloride is added.

Thanks all. It has been a fun ride.

 

[metatp]

This almost feel like I am blogging.

I rinsed and rinsed and rinsed. I still could not get the filter solution totally clear. i took a sample of the powder and add just water and nitric acid. After sitting for some time, the solution had only a slight green tint. Tested with Stannous and it turned a faint blue. the left over powder looks like silver. Tried to melt the rest. I got a small silver button that tested as a high purity silver with some black encrustation on it that would not melt (only got red hot with mapp). Tried to melt the left over contact that did not dissolve yet in nitric, and it would not melt as well. It is not like the tungsten/silver alloy contacts where they break easy after the silver is dissolved. Except for the really thin sections, I cannot break them by hand.