Metal finishing Q&As since 1989

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Neutralization requirements When Passivating per AMS2700

March 29, 2011

Hi,

We are setting up a Passivation Line - Nitric Acid and Sodium DiChromate.
We will be working to various Prime specifications

MOOG Spec MS100.CP.005 calls up AMS2700 which states that when a post treatment is specified then immerse in 4-6% Sodium Dichromate
Section 8.2 states when post treatment not specified, parts should be neutralized, "preferably" in a solution of 2-5% sodium hydroxide [affil links]

My question is - Does Sodium Dichromate do the same job? (i.e., neutralize). As AMS2700 does not tie us down to Sodium Hydroxide, can we utilise the Sodium Dichromate tank instead? Or does this not have a neutralizing effect?

Please excuse my ignorance if the answer seems obvious as I am a newbie to this process :)

Jonathan Fletcher
Quality Engineer - Special Processes - Birmingham. U.K.

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Hi Jonathan,

The sodium dichromate may have the effect of diluting, but it will not be neutralising. To neutralise the acid from the passivation process you need an alkaline solution. If you don't want to use sodium hydroxide you could consider a solution of sodium hydrogen carbonate.

Brian Terry
Aerospace - Yeovil, Somerset, UK
March 30, 2011