noble metal underplating?

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justinhcase

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Feb 12, 2014
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I have had in an unusual piece,It was a white ceramic aviation circuit board.
One side was gold plated circuitry the reverse was completely plated(sample 5 in Pic a/)a.JPG
The plating striped off for testing and was indeed Au (Pic b/)but there was a slight dark containment visible in the Stannious test.b.JPG
I noted that there was still a bright silver plating left under the Au which did not look like it had reacted to any thing at all..It took two day's to digest even heated.
The second digestion's stannious test has given a gray/blue result??(pic c/)c.JPG
I dropped the Au from the first solution and the percipitent is very dark almost black,the spent solution no longer give a reaction to stannous testing.
Any ideas??
 
If the gold is dull, as opposed to bright and shiny, it has been applied as paste in a silk screen process and is quite thick (called thick film circuit). If shiny, it was applied by evaporation and is quite thin (thin film circuit).

It doesn't sound like the undercoat is silver. What color was the undercoat solution? I assume you used nitric? What strength? I've run across that blue/gray stannous color before and my best guess on pin-pointing it was that it was cobalt. Don't quote me on that. If I remember right, this was once discussed on the forum and someone had a different answer. If you didn't heat the nitric or it was weak, cobalt (or nickel) can go slow at room temp.
 
goldsilverpro said:
If the gold is dull, as opposed to bright and shiny, it has been applied as paste in a silk screen process and is quite thick (called thick film circuit). If shiny, it was applied by evaporation and is quite thin (thin film circuit).

It doesn't sound like the undercoat is silver. What color was the undercoat solution? I assume you used nitric? What strength? I've run across that blue/gray stannous color before and my best guess on pin-pointing it was that it was cobalt. Don't quote me on that. If I remember right, this was once discussed on the forum and someone had a different answer. If you didn't heat the nitric or it was weak, cobalt (or nickel) can go slow at room temp.

I did soak the hole part in hot Nitric for some time hoping the Au would come away but got no reaction so went on to A.R.
The gold was thick and dull so must have been applied as a paste.
The under coat of plate was silver in color ,bright and reflective.it took two day's to digest in a strong A.R. that I let heat on the side of my plate while I was working on a larger flask .the long digestion and lack of dulling through out the digestion was why it puzzled me.The resulting solution was yellow.
I was expecting a red reaction from stannous for Rhodium form the way it react but got the gray/blue as in pic C/.
I did also test with D.M.G. but got no precipitate so do not think it is Nickle.what is a good spot test for cobalt?
Thank you for you reply.
Regards as ever.
Justin
 
justinhcase said:
goldsilverpro said:
If the gold is dull, as opposed to bright and shiny, it has been applied as paste in a silk screen process and is quite thick (called thick film circuit). If shiny, it was applied by evaporation and is quite thin (thin film circuit).

It doesn't sound like the undercoat is silver. What color was the undercoat solution? I assume you used nitric? What strength? I've run across that blue/gray stannous color before and my best guess on pin-pointing it was that it was cobalt. Don't quote me on that. If I remember right, this was once discussed on the forum and someone had a different answer. If you didn't heat the nitric or it was weak, cobalt (or nickel) can go slow at room temp.

I did soak the hole part in hot Nitric for some time hoping the Au would come away but got no reaction so went on to A.R.
The gold was thick and dull so must have been applied as a paste.
The under coat of plate was silver in color ,bright and reflective.it took two day's to digest in a strong A.R. that I let heat on the side of my plate while I was working on a larger flask .the long digestion and lack of dulling through out the digestion was why it puzzled me.The resulting solution was yellow.
I was expecting a red reaction from stannous for Rhodium form the way it react but got the gray/blue as in pic C/.
I did also test with D.M.G. but got no precipitate so do not think it is Nickle.what is a good spot test for cobalt?
Thank you for you reply.
Regards as ever.
Justin
There are several different metal pastes that are found on thick film circuits. Most common are the PMs - Au, Ag, Pt, and Ru. There are probably certain non-PM metals used as well although I don't know which ones (if there are any). It all depends on what is best for that particular application.
 
justinhcase said:
I did also test with D.M.G. but got no precipitate so do not think it is Nickle.what is a good spot test for cobalt?

Justin

Justin

DMG is used to test for both palladium & nickel - if the solution is acidic & nickel is in the solution (but no Pd) then you will not get a precipitate - the solution needs to be made basic (with ammonia) to detect the nickel

on the other hand if the solution is acidic & it has Pd then you will get a precipitate

Read Hokes pg. 97 for DMG test Pd and DMG test Ni

Kurt
 
kurtak said:
justinhcase said:
I did also test with D.M.G. but got no precipitate so do not think it is Nickle.what is a good spot test for cobalt?

Justin

Justin

DMG is used to test for both palladium & nickel - if the solution is acidic & nickel is in the solution (but no Pd) then you will not get a precipitate - the solution needs to be made basic (with ammonia) to detect the nickel

on the other hand if the solution is acidic & it has Pd then you will get a precipitate

Read Hokes pg. 97 for DMG test Pd and DMG test Ni

Kurt
I always evaporate down my solutions,as much to reduce the solubility of impurity's as to remove nitric acid.I then use a tiny bit of Sulphamic acid to test and make sure there is none left,no bubbles means no more free Nitric.
I had thought ammonia was necessary for testing Nickle as the conventional advice was to use a cotton bud with ammonia to rub a suspected nickle before testing with D.M.G.
But our great an knowledgeable friend Mr Lino informed me that that is not so and D.M.G. should act as a reliable test without an alkali solvent.
 
justinhcase said:
I had thought ammonia was necessary for testing Nickle as the conventional advice was to use a cotton bud with ammonia to rub a suspected nickle before testing with D.M.G.
But our great an knowledgeable friend Mr Lino informed me that that is not so and D.M.G. should act as a reliable test without an alkali solvent.
To my knowledge, that's not true. If you test without the ammonium hydroxide, DMG won't reveal the presence of nickel, which it does with a beautiful pink display when it is present, and ammonia is used. It helps to distinguish between copper and nickel, each of which results in a vivid blue solution when ammonia is added.

Can you share with us the expected reaction when testing without the ammonium hydroxide?

Harold
 
I did raise the subject before and we had a good discussion
http://goldrefiningforum.com/phpBB3/viewtopic.php?f=37&t=21256&p=219377#p219377
At which point MrLino1406 advised
Lino1406 said:
Nickel ions will react with DMG, no matter what anion
I have read some of his papers and they are far above my understanding of the interaction of elements so I take his word as gospel when it comes to the reaction of ions.
If the reaction was expected to be out side the norm I would expect he would have informed us at that time.
But if this is incorrect I would love to have the point explained in more detail.
Some of my source malarial has been giving me impurity's I have as yet not been able to identify properly.
Regards
Justin
 
justinhcase said:
Lino1406 said:
Nickel ions will react with DMG, no matter what anion

But if this is incorrect I would love to have the point explained in more detail.
.
Regards
Justin

Other then Lino's comment here --- EVERYTHING I have ever read about testing for nickel says to adjust the PH up with ammonia --- thats called protocol - for the sake of being sure --- I would follow protocol

Edit to ad --- it only takes a drop of solution a drop of ammonia & a drop of DMG to do the test - per protocol

Kurt
 
I have ordered Two samples .one of cobalt and one of nickle 99.99%.
I am going to run a complete set of test's against them to educate my self of the possible test results.P.H. variation's concentration's ,compounds.
Not having much in the way of pure metals available to me locally I have never been able to discount impurity's before.
It should be interesting.
I do love Hoke but have to hope over a century of inquiry may have improved our understanding on some subjects particularly P.G.M.'s as they where only just coming into every day use when she wrote her book.
Mrs Hoke never had to take thing's like molybdenum, niobium, rhenium, yttrium, vanadium into account which you will find in industrial setting's now a day's,
or any of the possible new P.G.M.'s like Hassium,Meitnerium ,Darmstadtium which may start coming into use in the near future.
Mr Lino from what I have read about his work specializes in P.G.M.'s along with some very fine work I will not mention in case he wishes to hide his light under a bushel.
But I know he would like to invite donation's to children cancer patient's.so you can probably work it out for your self's
he is what I would call a rock solid source of information . if he took the time from his very important work to suggest some thing it should be investigated fully.
I am looking forward to seeing for my self.I will also try again with ammonia to see if that changes the results in hand.
Regards
Justin
 
With all due respect to Lino, in my experience the ammonia is necessary in detecting nickel. It also may require more than one drop of ammonia, and possibly more than one drop of DMG, depending on how concentrated you've managed to get your DMG test solution. Start with one drop of the solution you wish to test in a spot plate or a white plastic spoon. Add a drop or two of DMG solution. I don't believe you'll see any reaction. Then start adding ammonia, drop by drop. When you've added enough ammonia, the solution should turn pink. If you look closely, you'll see there are actually tiny red specks in the solution, which gives it an overall pink color.

Usually, you add ammonia to the solution to be tested before adding the DMG, but it works both ways and you'll be able to see the difference the ammonia makes.

Dave
 
Nickel ions will react with DMG, no matter what anion
I think what Lino meant was that the nickel could be there as, say, nickel chloride or nickel sulfate or nickel nitrate, etc., etc. and the DMG would still work. If he said that ammonia wasn't needed, I must have missed it.
 
Thank you very much chap's
The discussion it's self in which Mr Lino made the suggestion was about if Ammonia was needed and if there was a second testing agent that could be used with out the need for ammonia.
It is great to have your help to learn.so very much appreciated.
J
 
Justin

It's not just Hokes that says to adjust Ph with ammonia for the nickel test - you will find that as THE standard method in all info about it

I have a book that give's "many" instructions for testing to determine "many" different metals in many alloys - the book was written back before the advent of the XRF & was written for scrape yards so they could test metals coming in & then maximize there profits by better sorting & sales of there metals --- the test for nickel is explained exactly the same in this book

IF - I get time I will dig the book out & maybe do a thread on procedures & chems for testing for metals other then PMs

Kurt
 
kurtak said:
Justin

It's not just Hokes that says to adjust Ph with ammonia for the nickel test - you will find that as THE standard method in all info about it

I have a book that give's "many" instructions for testing to determine "many" different metals in many alloys - the book was written back before the advent of the XRF & was written for scrape yards so they could test metals coming in & then maximize there profits by better sorting & sales of there metals --- the test for nickel is explained exactly the same in this book

IF - I get time I will dig the book out & maybe do a thread on procedures & chems for testing for metals other then PMs

Kurt
Thank you Kurt that would be most helpful.
When you find it I have a friend in London who found me an immaculate first edition from Hoke ,I will see if he can find me a copy.
Regards
Justin
P.S. :oops: I tried adding the ammonia with D.M.G.and got a heavy brown for the concentrated sample and red return for the weak.
Thank's for all the input and help.
 
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