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Sn-Ca Plating

Dear All,

Has anyone heard of adding Calcium (Ca) into a Tin plating?
What is the advantage of that and how can we add Ca into a Sn plating?

We did some EDX analysis on a Tin-plated hook and found that it contains 5% calcium. And the salt spray test result is much better than that of normal Tin coating.

Please advise.

Kenny Kam
Plating Industry - Hong Kong
2005

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You cannot electroplate calcium as a metal or alloy. I suspect you have a coating on the tin that contains calcium. Remember EDX is a very sensitive analytical tool and works ont he surface on the material. Try cleaning the tin sample with the electron beam and see if the calcium is still there. I would expect the calcium peak to disappear, unless it is very heavy contamination.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005

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Dear All,

Actually we asked a professional lab to do the analysis for us and they have cleaned the surface very thoroughly and they said that they were analyzing the composition at 10 µm under the plating so the calcium is not just at the surface.

Any comment will be highly appreciated.

Kenny Kam [returning]
- Hong Kong
2005

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It is possible that the plater has used tap water and not pure (i.e., distilled or de-ionised or reverse osmosis) water. Hence the plating bath will contain a miriad of cations. If he uses "hard water" there will be a high level of calcium in it. Now, if he uses an acid tin bath that contains sulphate, he will produce calcium sulphate that may be co-deposited as a fine suspension. Thta is, hew is producing a composite deposit of tin and calcium sulphate (or some other insoluble calcium salt) What other peaks are showing in the EDX? Perhaps if we have the full details, we can answer your problem. Rest assured, though, you CANNOT electrodeposit calcium from an aqueous system.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005

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2005

Dear All,

The average measurement over 5 pts are:

Sn: 94.4%
Ca: 5.2%
Fe: 0.3%

The standard deviations are less than 0.2 for all.

And I don't think the plating was done using tap water. I
am pretty sure they used DI water for that.

Thank you for your attention.

Kenny Kam [returning]
- Hong Kong

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An interesting poser! I just wonder if there is some mis-intepretation of the peaks here. The main peak for tin is the K alpha at 25.27KeV, but there is a L alpha peak at 3.44KeV; this is much smaller, but I do not know how much smaller. The main peak for calcium is the K alpha one at 3.69KeV. I know it is quite a distance from the tin L alpha, but it is worth a longshot and I wonder if the peaks have been misunderstood! There is also a L alpha peak for antimony at 3.60KeV, although there should be a stronger peak at 26.35 KeV for its K alpha peak. Since you do not mention it in your previous reply, I presume it is not there. I could understand there being antimony present, as a tramp element in impure tin amd this could be co-deposited. It would also provide the opportunity for a galvanic couple to be set up that could (perhaps) enhance the corrosion resistance! Antimony is more electropositive than tin, but it does alloy with tin and the alloy could offer enhanced resistance for the tin. It is also interesting that you do not mention any sulfur being present, so that eliminates the possibility of calcium sulphate being codeposited.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK
2005