The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Behavior of Nickel Strike

I would like to understand the nature of how the constituents, specifically hydrochloric acid and nickel, behave in a nickel strike bath. Is it safe to assume that through the plating process the hydrochloric acid will deplete and the nickel concentration will rise due to the anodes being in the tank?

Jennifer Friesen
Chemistry Lab Technician - Winnipeg, Manitoba, Canada
2004

Why? In other words, what is your vesting in the issue, Ms. Friesen. Some answers may depend on that.

Theoretically, in a perfect world, strike and plating baths last forever as an equilibrium process. Nickel dissolves from the anodes and deposits on the cathode, and everything else just stays there. But in reality, strike baths are low efficiency, so hydrogen is released at the cathode, leaving behind OH ions that raise the pH, requiring additions of acid to maintain the pH. This causes a buildup of the anions of the acid.

Nickel does not dissolve in the acid without power, but can be electrolytically oxidized from the anodes as well as electrochemically reduced at the cathode. The nickel content will tend to rise because of the inefficiency of the cathodic process, but limiting the anode area can cause it to go partially passive as well, slowing the excess dissolution. You need less anode area in a strike bath than a plating bath.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

---

There is no such thing as "never" for a plater. First assumption is that you are not using SD nickel which will definitely dissolve in a high HCl strike. Rolled depolarized nickel will dissolve very slowly and acid content drop with a corresponding increase in nickel "as metal". Electrolytic nickel would probably dissolve even slower. Based on experience of a second strike tank that would set idle for several weeks, several times a year. Yes, the liquid level was brought up to the same mark for each analyses.

James Watts
- Navarre, Florida
2004