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Claudie

Claudie

Well-known member
Joined
Aug 17, 2010
Messages
1,853
Location
Iowa
There is such a difference between the weight of Gold foils verses the weight of the button they produce, it makes me have to know what happened to the missing Gold.
The contest Geo had recently is a great example of the difference. He started with 128.3g of foils, but ended up with a final melt of 42.8g. That is approximately 1/3 of the starting weight.
If the foils are close to 24K, where is this lost weight?
Does this missing Gold get lost as colloidal Gold and end up in the stock pot? Do elves come and steal it in the night? Is there anything we can do to get those two numbers (starting foil wt / final wt) closer together?
 
Claudie said:
There is such a difference between the weight of Gold foils verses the weight of the button they produce, it makes me have to know what happened to the missing Gold.
The contest Geo had recently is a great example of the difference. He started with 128.3g of foils, but ended up with a final melt of 42.8g. That is approximately 1/3 of the starting weight.
If the foils are close to 24K, where is this lost weight?
Does this missing Gold get lost as colloidal Gold and end up in the stock pot? Do elves come and steal it in the night? Is there anything we can do to get those two numbers (starting foil wt / final wt) closer together?
Click to expand...
If he did them in AP, I would guess that most of the nickel plating was still attached to the back of the gold foils. I would imagine that, if he had then boiled the foils in nitric to dissolve the nickel backing, and then rinsed, dried, and weighed them, the weight loss would be similar.
 
I did recover the foils using copper(II) chloride. I did everything that I would normally do. When I gathered the foil, I kind of rolled the foils around but couldn't find any lumps or solids. I can't say what it is but it seems to me a lot of members have the same issue.
 
Seems to me like there would have to be quite a bit of Nickel in the mix to out weigh the Gold 2:1.
After decanting solution from dropping Gold from HCL/Bleach, I have let that same solution set in a beaker and after a week or more, there would be a thin film of dust on the bottom of the container. I know this is missed Gold that some may move to the stock pot, but not in the quantities of the 67% loss.
With Stannous test negative for Gold, I would be leaning more toward some colloidal Gold that gets missed in settling. Add that to the weight of the Nickel and we're getting closer.
 
I was skimming through a PDF about Gold plated contacts and according to the file, the Nickel must be have a minimum thickness of 1.3 microns (50 microinches). It also tells the general thickness of Gold on the contacts.
So the loss may very well be in the weight of the Nickel.

Link to file I was referring to: http://www.te.com/documentation/whitepapers/pdf/aurulrep.pdf
 
This company uses 120-240 micro" (3-6 microns) of nickel.
http://www.eurocircuits.com/index.php/eurocircuits-printed-circuits-blog/gold-plating-for-edge-connectors

This one uses 100 micro" (2.5 microns).
http://www.epectec.com/articles/pcb-surface-finish-advantages-and-disadvantages.html

This one uses 150-200 micro" (3.75 - 5 microns)
http://www.pcbuniverse.com/pcbu_faq.php

This one 125-150 micro" (3.125 - 3.75 microns).
http://www.pcbontime.com/compliance.html
 
I see the Gold they use also has some Cobalt in it.

Edit: Thanks for the link, very informative site.
 
Claudie said:
I see the Gold they use also has some Cobalt in it.

Edit: Thanks for the link, very informative site.
Click to expand...
All of the gold plating you find on fingers has been hardened to improve wear resistance by co-depositing very small amounts of nickel or cobalt with the gold. However, in most all cases, the gold is still between 99% to 99.9% pure (0.1% - 1% Ni or Co). Besides hardening, the addition of Ni or Co also produces stress in the deposit. If more Ni or Co were added, than the amounts given, stress fracturing could occur. This could cause cracking and even peeling of the deposit.
 
You're welcome. You ask good questions.

Nickel dissolves much, much more slowly in HCl than copper. I used to process a lot of pure palladium contact points from telephone switching equipment. The points had a nickel backing on them that was probably about the same thickness as what we've been talking about. I removed the Nickel by boiling the points in concentrated HCl. It literally took all day to remove the nickel.

I would think that the easiest way to test for nickel on the foils is to use a magnet.
 
I would think that the easiest way to test for nickel on the foils is to use a magnet.
Click to expand...

I have some hard drive magnets and some foils. I will have to check that idea out tomorrow. Thanks again!
 
It might interest you guys to know that I had a very unhappy customer, long ago. who brought me what he said was a pound of foils. I've told the story before, and I may not remember it exactly the same at this point, as I'm getting old and goofy, but here's how it went, at least as I recall.

A fellow in Utah was stripping gold plated pins, using nitric acid. He was older than I was, likely near 60 years old at the time. He heard about me, although I don't recall how. We talked, then he brought a small plastic container to me, partially filled with gold foils. The container, as I recall, was one of those used for a whipped cream substitute.

I weighed the container and found it to be right at one pound. The foils were not perfectly clean, as there were bits of insulation included, although not a lot.

I'm really struggling right now with the end result. I recall it to be about six troy ounces. He was furious. He just "knew" that I had ripped him off.

The hard facts:

His fouls were wet, although there was no standing water in the vessel. Those hollow shells can hold a considerable amount of water.
They were dirty, as I implied.

I filled the container with the resulting gold ingot, the filter paper, and added water to the line where the foils had filled the container. It weighed a pound. That wasn't good enough for him, and he stormed off, never to be seen or heard from again. There was no way I could convince him he hadn't been ripped off. He wasn't.

The lesson should be learned from these experiences that what you have before refining isn't what you're going to have afterwards, and the loss can be significant. There's a huge amount of surface area in those thin foils, which is quite adept at holding on to matter.

Harold
 
As has been mentioned by GSP - the gold flakes themselves by weight can't produce anything like an informed guesstimate of yield there are too many other factors and contaminants to factor in. Which leads me to Harold's post which was pretty close to my take on it which is that water and all kinds of things mess up the figures before you even discuss other materials.

Take "dried gold powder" for example. It isn't always the true weight of the metallic gold. Even if there's 1% moisture in there then you're a gramme per hundred out. Foils hold water in all kinds of weird places. Even when you think they are dry.

So overall my advice would be to never make any assumptions or calculations of yield based upon foils.

Regards

Jon
 
When ever you, as a refiner, have to answer to a customer about yield it is always wise to melt the material to a bar before processing, if nothing else it will give you an accurate start weight. While it is true foils will dissolve easier than a granulated gold alloy, listening to a customer accuse you of stealing is never easy and the extra time spent digesting is a small price to pay.

I always would melt and sample. Then you have a true start weight and a sample that you retain long after the job is finished. If there are any questions, you have a sample which can verify that the gold assay is truly reflected in the yield. Then any nickel, cobalt or copper in with the gold can be explained. Assays don't lie.

Think of the retained sample as insurance. Later on when you accumulate a pile of metallic samples from settled jobs you can always process a house lot to get your money out.
 

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