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Iron Content Test for Nitric Acid Passivation Baths
Q. I just started working in a small etch and pass process and I wanted to know how to verify that the pass baths were still good, mainly to check the iron content? What is the simple detailed titration test method for measuring the free iron content in nitric acid passivation baths?Kierra Porter
A. Dear Kierra :
Peace be upon you
You can use the next procedure,
1- take a known weight from the bath W(15-25 gm).
2- add 25 conc. HCl, then boil in w.p. for nearly one hour.
3-add 400 d.w., then 10 ml. cons H2SO4.
4- titrate against KMnO4 0.1 N, the color change from colorless to pink after X ml. titrant.
Fe % = Xml. of titrant*0.558/W gm
A. Are you working to a spec that limits the iron concentration?
If not, what will the concentration tell you?
Passivation baths dissolve very little iron.
Iron in a nitric solution is green and nitric acid is cheap.
If the solution is green - change it.
Salah, thank you so much for your response ... I have really been having a hard time trying to figure this simple method out! You have really saved my from any further headaches :)
Geoff, thanks for responding also, but I needed the method more for control measures than just evaluating solution color. I'm trying to follow our most stringent specs as well as AMS2700 [affil link] which states the iron content should be no more than 2% by weight. This will be most helpful in the event of an audit :)
I appreciate you both!
What does "w.p." mean?November 6, 2014
Q. Forgive me for my lack of understanding. I'm fairly new to the etching process but my company sends out samples and waits 2 weeks to find out % iron. This is information I've been looking for but I am stumped on what w.p. is?Dan Wise
A. Hi Dan. We'd probably have to see it used in context to know for sure, but I think it will mean "weight percentage" / percentage by weight.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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