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topic 28708

Silver striking problem: coating is white


A discussion started in 2004 but continuing through 2019

2004

Q. Dear Sir,

I am a student. I research about striking silver plating on copper. After plating, quality of coating is not good. White layer appears on coating. Striking composition is:

AgCN 5 g/L
KCN 85 g/L
T 20 °C
Current density 2.5 A/dm2

Please guide me?

Thank you,

Hashemi [last name deleted for privacy by Editor]
student - Esfahan, Iran


2004

A. Immerse while the power is on.

Cair Shishani
Cair Shishani
aircraft maintenance
- Al Ain, UAE




March 23, 2018

Q. Sir,

I have the same problem. I used this solution and immersed with the power on but white layer also occurred. How can I overcome this problem? Can you offer any suggestion?

Caner BASARAN
- ANKARA,TURKEY


March 2018

A. Hi cousin Caner. Sometimes when people say they have 'the same problem', they just mean that they also got unacceptable results like the original poster -- not that they carefully holding to every other operational point as the original poster. If you did some things somewhat differently, without telling us what those differences were, it can be difficult to help :-)

Digital version
mfg_online

(No longer published, but Elsevier hasn't yet de-commissioned the online version of the Guidebook)
Download it before it disappears.

But maybe you should try a lower current density? Because rather than the 2.5 A/dm2 mentioned here, Lowenheim's "Modern Electroplating" [link is to info about book at Amazon] suggests 1.0-2.0 A/dm2 and the Metal Finishing Guidebook suggests 0.5-1.0 A/dm2 =>

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


March 26, 2018

Q. Sir thank you for your reply,

I used 1.883 A/dm^2.

I used below ingredients with 150 ml solution.

3 gr KAg(CN)2
4.5 gr Potassium cyanide
3 gr Potassium carbonate.
at room temp.

I did our experiments with 3.3*3.1 cm coupons with forty minutes (approximately 8 micron thickness).

All of my coupons plated with white, not gray, color.
I didn't solve my problem. I boiled my coupons in water for two hours, but I could not solve the cyanide compounds on the surface.

I did not use strike solution, I used rack work solution.

Please help me.

Caner BASARAN [returning]
- ANKARA,TURKEY


March 2018

A. Hi Caner. Although a reader might not realize it, this site has been running for 23 years and has over a quarter million metal finishing postings arranged under 50,000 topics. So we have many threads which address your problem of heavy silver plating for 40 minutes much better than this thread which was about the rather different process of silver striking for a few seconds.

Digital version
mfg_online

(No longer published, but Elsevier hasn't yet de-commissioned the online version of the Guidebook)
Download it before it disappears.

For starters, you seem to be attempting to do silver plating without addition agents and then are surprised by the resulting white deposits, whereas Alan Blair notes on the first page of his 'Silver Plating' chapter in the 'Metal Finishing Guidebook' ...

"The formulas above [similar to yours] will produce chalk-white deposits that are very soft. Additions of grain refiners or brighteners will modify deposits, causing them to become lustrous to full bright".

Blair also notes on page 2, that ...

"... it is essential to employ a silver-strike coating prior to plating ..."

Please review the silver plating chapter of that text before doing anything further. Also, be aware that you are dealing with truly deadly potassium cyanide chemistry, which must be done under adequate supervision. Good luck!

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha


March 27, 2018

A. I'm not sure what your problem is but, as far as I know, silver is the whitest metal there is.

Chris Owen
- Benton, Arkansas, USA



September 10, 2019 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Hi,
I don't know why there's a layer of white residue on the product after plating, and it's hard to wash off, what's that?

Dagan Du
- China


September 2019

A. Hi Dagan. We would need a lot of information from you to understand what this white residue looks like and where it might be coming from, but the first thing to realize is that if you are plating silver without the proper chemistry you should expect the plating to be white :-)

If you look at a mirror attached to a wall which is painted white, the mirror does not reflect a greater amount of light than the white wall; rather the difference is that the white wall scatters the light which impinges on it whereas the mirror preserves the image because the angle of reflection matches the angle of incidence. Silver electrodeposited without proper addition agents is microscopically rough and chalky and scatters the light, making it look white.

Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
Striving to live Aloha

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