Metal finishing Q&As since 1989

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In ASTM A967 Passivation, Does the 25% by Vol. Nitric Represent Industrial (65%) or Full Strength Nitric?

Q. Many formulas such as the passivation formula in ASTM A967 call for a certain percentage of Nitric, but usually no mention is made of whether the Nitric is the standard industrial grade from a drum (65%) or is assumed to be 100%. We'd appreciate it especially if someone knew specifically what A967 requires.

Tim Crutchfield
plating company - Jackson Mississippi
November 19, 2008

A. Tim The specification is referring to a solution that is 25% by volume, nitric acid. Perform your titration on solutions that are made up with 65% and 100% nitric to see which gives you a 25% solution. Willie Alexander - Colorado Springs, Colorado November 21, 2008 A. This is not exactly a weakness in ASTM A967: bear in mind the requirement from paragraph 5.2.1 is that the acid meet the performance needed. So if you can show it works you can use the standard 42 degrees baumé stuff, or perhaps 40 degree baumé, or some other concentration. If you look at Letter 2183, you'll find others before you have asked about this. Part of the confusion comes from the fact that nitric acid, in it's pure HNO3 form, is a gas. You have to dissolve it in water to get a useful liquid. The standard grade, from the O-N-350 federal specification that was called out in QQ-P-35C [from DLA] , was 61% to 68% nitric acid. Since the recipes found in ASTM A967 pretty well match those in QQ-P-35 and it's successors AMSQQP35 [canceled] and AMS2700, then I'd argue strongly that the proper nitric acid strength is 42 degrees baumé. Lee Gearhart metallurgist - E. Aurora, New York November 21, 2008

Q. Thank you for your responses to my initial question, posted Nov. 19. I will now assume that the amount of nitric acid which is called for in specs stemming from QQ-P-35 represents industrial grade Nitric, unless stated otherwise.

I have a further question -- in A967, sodium dichromate is mentioned as an ingredient in passivation and/or post-cleaning formulas. Does anyone know whether we can substitute potassium dichromate? It should produce the same reaction, but the time needed could be different -- maybe not. Any ideas? Thanks again.

Tim Crutchfield
plating company - Jackson, Mississippi
December 3, 2008

A. Ancient people used to say in such a case: amicus Plato sed magis amica veritas.

Sorry, I can't agree. 100 % nitric acid is not a gas, but a real fuming liquid I've used many times in my lab. Boiling point 82 deg, melting point 42 deg, and density 1,52 kg/L. For such reason concentrated nitric acid is extremely dangerous as a very strong oxidizer, we usually prefer using it's 65% solution. The solution is an azeotropic form of nitric acid with a boiling point at 120 deg and density 1,42 kg/L. Regards

JANUSZ LABEDZ
- WARSAW, POLAND
December 10, 2008

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 Thanks Janusz, for correcting a long-held misunderstanding of mine! (Gosh, that's embarrassing, but now at least I won't make that mistake again!)

I stand by the answer that the passivation specs want you to use 61-68% nitric acid in water.

Lee Gearhart
metallurgist - E. Aurora, New York
December 19, 2008

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Q. To how many parts water should I add 30 parts 42 baumé concentrated nitric acid to prepare a 33% by volume Type VI passivation solution?

Chris Jurey, Past-President IHAA
Luke Engineering & Mfg. Co. Inc.

Wadsworth, Ohio

February 13, 2010

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ASTM976 ^^{ASTM A967} Nitric Mixture Question (volume vs weight)

December 12, 2018

Q. We run a small EP business with a passivation bath.

I have a customer who is requesting a passivation to something close to Nitric 4. They want the mixture to be 50%/vol.(ASTM calls for 45-55 by vol.)
In maintaining our normal passivation bath to type 2 (we target 28% vol) we have always factored in the strength of the raw acid of 42 baume at 67% strength. So to meet the 28% we would be adding about 42 gallons Nitric and 58 gallons water (for a 100 gal tank).

But this customer is insisting that this is wrong. They are saying that the raw acid is assumed to be 67% (42 baume) and to factor it in the mix by volume at 100% strength. So their 50/50 bath would be exactly 50 gal nitric and 50 gal water. And looking at the standard towards the bottom states:
"X2.2 Acid Content:
X2.2.1 Nitric acid to be used in the formulations described in Section 6 is understood to be the typical commercially available concentrated aqueous solution of nitric acid containing 61.0 to 68.2 weight percent of HNO3 (also referred to as 42° Baumé)."

That tells me we have been doing it wrong I believe and the customer is correct.
Problem is I have talked to another EP place and they are doing it like we have been. And I have a few chemists that agree with them. And on the other hand there is the customer and my supplier who are insistent that its just 50/50 and the ASTM standard considers the raw acid to be 100%

Any help would be appreciated.

Michael J [last name deleted for privacy by Editor]
QC - Detroit, Michigan