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How to analyse aluminium content in chromadizing tank

Q. Sir I work in a pretreatment manufacturing unit. Please tell me how to analyse the aluminium content in chrome tank.

Nirbhay Goswami
- Rudrapur, Uttrakhand, India
October 10, 2012

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Ed. note: the word "chromadizing" isn't used much in the USA to our knowledge, but we believe it means chromate conversion coating of aluminum.

A. I'm not familiar with chromadizing but from what I can gather it is just treating the metal with chromic acid. If so, take a 20 mL sample of the bath and dilute it to 100 mL with DI water, then titrate with .5N NaOH ⇦ on eBay or Amazon [affil links] to a pH of 3.2. Call this "A". Continue titrating to a pH of 4.8. Call this "B". To get your aluminum content it is
(B-A)x .430

Scott Merritt
- Eastman, Georgia, USA
October 12, 2012

A. My apologies, I forgot to include the factors for free and total chromium.
To determine free acid you multiply "A" x 0.334
To determine total acid multiply "B" x 0.334

Scott Merritt
- Eastman, Georgia, USA
October 30, 2012

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