Metal finishing Q&As since 1989

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Testing for Iron Oxide RFH

I have a 303 stainless steel miniature fitting that appears to have rust on it. I need to find out if it is indeed rust or not.
I am wondering if there is a chemical test to determine if the material is Iron Oxide or not.

Austin Ganly
- Greenland, New Hampshire
2003

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You could use a mixture of acids conc. nitric and 50% sulfuric acid to digest a sample of the stuff you intend to test for about an hour. Dissolve the digested stuff in water. then use ammonia [on eBay or Amazon] to neutralize the acid. Once neutralised make slightly acidic by adding hydrochloric acid. 0.9 Molar. Add 5 mls of ammonium acetate buffer. Add 2 mls of hydroxylamine hydrochloride a complexing agent. Add 5 mls of dipyridil.

The solution should turn red if there is presence of Iron oxide. The dipyridil solution will go red in presence of iron.

Evans [last name deleted for privacy by Editor]
- Nairobi, Kenya
2003

Use a single drop of 10% hydrochloric acid (1 drop of acid to 9 drops distilled water) onto the brown material and dab dry with tissue. Dab only once so that the acid + some brown material is in one spot. Leave to dry for an hour and look for yellow/green colour, which is a positive id for iron oxide. However, no colour does not indicate the absence of iron oxide, just that for some reason the test has not worked.

Simon Deadman BSc MSc MCSM
- Aberdeen, Scotland
September 9, 2010