Gold pins with black/grey coat after HCL soak

Hello Dears,

Once again, I need your kind help:

I was trying to process around 0.25k of gold plated pins but with tin solder tips.

So, I started by soaking these pins in HCL and left it over 2 nights. While checking the patch i noticed that the tin solder tips were gone but also a black/grey coat is covering so many pins.

I think this black/grey coat is tin plated out the gold pins.

My question now, is how to remove this tin black/grey coat out out pins so they will be ready for processing ?

Hello ahmadbayoumi,

the visible tin solder tips contain not only tin, but also lead and zinc. The zinc dissolves readily in cold HCl creating much bubbles. The tin dissolves very slowly in cold HCl creating few and very tiny bubbles. Two nights are not enough to dissolve the tin. Also the tin continuous to dissolve when there are no bubbles more visible. To dissolve solder tin in cold HCl it would take weeks. Warming up the HCl the tin dissolves in a few days. The lead dissolves in hot HCl only very slowly and creates dissolved and precipitated lead chloride.

The black/grey coat on you pins is probably lead and tin which is precipitated from dissolving zinc.

To clean the pins there ist no other way to soak them in hot HCl until they remain completely shining, without no more visible base metals and no more visible precipitated salts. It takes a few days if the base metal of the pins is copper.
If the base metal of the pins is brass or bronce it takes much longer and you should trate the pins with Hot HCl and crockpot.

ahmadbayoumi said:

Hello Dears,

Once again, I need your kind help:

I was trying to process around 0.25k of gold plated pins but with tin solder tips.

So, I started by soaking these pins in HCL and left it over 2 nights. While checking the patch i noticed that the tin solder tips were gone but also a black/grey coat is covering so many pins.

I think this black/grey coat is tin plated out the gold pins.

My question now, is how to remove this tin black/grey coat out out pins so they will be ready for processing ?

Click to expand...

ahmadbayoumi


If the pins are from the same material as in the other thread....

1.Most high grade producing company's Don't use regular low grade solder's on there products.
2.Most high grade producing company's Use higher percentage silver solder.

With that being said,Black part is gold that was collected by silver and other base metal in solder at time of making solder joint.
This leaves the grey coat as silver chloride not zinc or lead.Hope this helps.Thanks in advance.



modtheworld44

I had this same event occuring last week when I was removing solder in HCl. After the HCl soak I treated them (the pins) in hot nitric without any problems. All the base metals dissolved and I could easely recover the gold foils. My guess is also that this is not tin that is plating out, it can't be. For this I have two reasons. First: tin dissolves pretty good in HCl, I don't think it will plate out that easy in hot concentrated HCl, second: there are other metals in solution that will plate out before tin does according to the reactivity series of metals. If there is tin, silver and lead in solution, the most nobel of these three wil plate out first becease it wants to be in a metallic state more than the other two. So silver is the most nobel one, after that it is lead, and finally tin.