[xchcui]

Hi.

I understand that muriatic acid can remove the oxide layer from copper/brass,
But if the contacts has a stubborn black dirt etc.will the muriatic acid clean that,while
leaving a clean shiny copper contacts.
BTW,i tried the vinegar+salt solution and citric acid solution with no success.

Thanks.

[Arkcon]

Yes.  HCl will clean the oxide off of copper, and leave the copper alone.  There's always son oxide, and it may B what the "dirt" is adhering to.  Or maybe the dirty is oxide, of some sort.  But the other acids should have done something for you.  You may have a really stubborn problem.

[xchcui]

I have several of tiny contacts that by mechanic cleaning(sand paper,steel wool etc)the dirt was removed,but since is so small,each one to clean,takes a lot of time and it is not comfortable.
So,if i will use the HCL(~30%),will it dissolve whatever
the dirt it is?even if it is not oxide?

[Enthalpy]

Hydrochloric acid HCl leaves copper surfaces that make good contacts. I suspect it's not clean copper, because the result is whiter than freshly cut or sanded copper.

Contacts using bare copper don't last. Depending on the needs, it would be useful to cover copper with a thin layer of gold or nickel, or at least tin or tin-lead (tin-silver oxidises more easily).

If your amounts permit it, contract a company to clean and cover your copper parts. It's a separate job and competence, they do it better.

[xchcui]

Hydrochloric acid HCl leaves copper surfaces that make good contacts. I suspect it's not clean copper, because the result is whiter than freshly cut or sanded copper.

Contacts using bare copper don't last. Depending on the needs, it would be useful to cover copper with a thin layer of gold or nickel, or at least tin or tin-lead (tin-silver oxidises more easily).

If your amounts permit it, contract a company to clean and cover your copper parts. It's a separate job and competence, they do it better.

Ok.so i understand that the HCL(~30%)will clean everything from the copper/brass contacts to make a good contacts,while it won't look the same fresh as sanded one.
When you said:"... (tin-silver oxidises more easily)",
Did you mean that the contacts with layer of tin-silver will corrode faster than layer of tin and tin-lead layer?

[Enthalpy]

That's what I observed with the older Sn63-Pb37 solder, and with the newer Sn95.5-Ag3.8-Cu0.7: the newer tarnishes in few days of water contact, while the older (prohibited in Europe by the RoHS rule) keeps brilliant.

Though, The SnAgCu stays brilliant in air, so it would suffice for normal uses.

And if the parts resist more heat, just plain Sn is cheaper.

[xchcui]

Thanks for your assistance

[xchcui]

Enthalpy,you mentioned before that:

Hydrochloric acid HCl leaves copper surfaces that make good contacts. I suspect it's not clean copper, because the result is whiter than freshly cut or sanded copper...

Refer to that quote:if i would like to plate the copper contacts with a thin layer of Nickel(as you suggested)using an electro-plating method,will it be good enough to dip the whiter copper contacts straight in the electrolyte(after removing them from the HCL)as they are (whitish)or i should bring them to a fresh copper color?
besides that,should i neutralize the contacts after removing them from the HCL,before dipping them to the electrolyte for nickel plating?

[Enthalpy]

I'd love to deduce such answers by numbers, logic and from a well-established body of knowledge...

But electrochemistry is black magic. Such answers are strictly experimental. The people who know them spend all their working day on it.

My bet is that if you try to make a nickel layer by yourself, you'll probably get an imperfect result, then invest much time and not obtain anything good. Surface treatment is like seal rings or gears: the knowledge is too specialized and too long to acquire. When you need a nickel layer, ask a specialized subcontractor.

[xchcui]

Okay,i understand what you mean.
But in general idea,after cleaning a copper object with HCL ,should i take other actions on the copper object before i dip it in the electrolyte?
Could the whitish copper(which turn to that color after the HCL cleaning) interfere to the ability of the nickel ions to chemically adhere to the copper?

[Enthalpy]

I'm completely outside my knowledge here, which is anyway very limited in chemistry.

Plating, electrochemistry and so on being often so extremely sensitive to surface contamination, I'd intuitively try to have the copper surface as clean as possible, and brush away any layer whose colour differs from blank copper. I'd do or redo it few seconds before dipping the copper part for plating.

Machines can sand you copper items automatically. Some let fine-grained sand bμmp against the items by shaking them vigorously together. They can treat several items simultaneously, even of moderately complicated shapes.

[xchcui]

Thanks,again,for your help.