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How to raise pH in ferrous sulphate Iron Plating bath?
Q. We are currently using a ferrous fluoborate bath to iron plate parts. We are now experimenting with a ferrous sulphate ferrous sulphate [affil links] bath. The bath composition includes ferrous chloride and ammonium chloride. The book that we are using suggests a pH of 4.5 to 6.0. Our current pH is 2.4. We have added some ammonium chloride and the pH stayed the same. Should I add more? My question is how to raise the pH in the bath to meet the book's specification.
Jason Kyleplating shop employee - Salt Lake City, Utah, United States of America
June 21, 2011
A. Hi, Jason. It sounds like you are using a home-brew bath based on an old book, and that's okay. But just in case you didn't know, proprietary baths are available, and offer you the advantage of technical service help.
It is possible to calculate the approximate pH of the solution based on the concentrations of the ions (see www.chem.purdue.edu/gchelp/howtosolveit/Equilibrium/Salt_Solutions.htm#phofsalts), but it looks like you'd need to add an impractical amount of ammonium chloride to get your current bath from its pH of 2.4 to 4.5-6.0. Anything above 4.5 sounds pretty high though; the baths listed in the Metal Finishing Guidebook seem closer to your present pH than your target pH.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
June 21, 2011
A. It is unlikely that ammonium chloride will have much effect on the pH. Ammonium carbonate could be used but the simple answer is to use ammonia, ammonium hydroxide (diluted).
However Ted may be right in that you may not need to raise the pH. Have you buffered your pH meter correctly? If you feel you must raise the pH, it would be wise to try a small volume first and check the plating results.
If you need to lower the pH use hydrochloric acid.
Remember that with pH, a small addition can have a large effect
Geoff Smith
Hampshire, England
June 27, 2011
Thank you for your responses. We ended up plating without raising the pH. The bath worked well for awhile. We now have a problem with hydrogen generation. It is causing hydrogen bubbles that result in nonuniform plating. We are using agitation. Are there any suggestions to help with our problem? Does anybody have a general idea of how long this iron bath would last?
- Salt Lake City, Utah, United States of America
January 12, 2012
Composition of a ferrous chloride based iron plating bath
Q. Hi.
Sir. can I know the ferrous chloride bath composition?
What to do for smooth ferrous plating?
- surat, gujrat, India
July 18, 2014
A. Hi Umesh. Per the Metal Finishing Guidebook (1998), the generic formula for a ferrous chloride bath is:
- Ferrous chloride dihydrate 40-60 oz/gal
- Calcium chloride 20-25 oz/gal
- Hydrochloric acid to pH 0.2-1.8
Iron plating is not a popular bath, so an Iron Plating chapter is included in only certain years of the MFG, and it's not in the on-line version. I'm sure you know that in much of India and most of the western world, plating shops do not use home-brew for iron plating, but proprietary baths offered by plating process suppliers.
Luck and Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
July 2014
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