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smurali1 (Automotive) (OP)
27 Jul 10 14:26
Hello all,

I am looking for a chemical test which will help me to detect the presence or absence of Manganese phosphate coating on steel part.

Your feedback please.

Thanks

smurali1
CoryPad (Materials)
27 Jul 10 15:47
A simple non-chemical test is visual observation.  Steel is light gray or steel, while manganese phosphate is dark gray to black.

Concentrated hydrochloric acid will remove manganese phosphate.  So, put a drop of HCl on your unknown piece.  If there is no change, it was uncoated steel.  If you wipe away the drop area and it is lighter than it was, you removed the phosphate coating.
cloa (Petroleum)
27 Jul 10 21:55
Wouldn't conc HCL instantly react with steel- it would form Fe3+. I haven't such an experiment since university or high school but I bet the heat evolved would evaporate the water in the HCL.   
CoryPad (Materials)
27 Jul 10 22:54
If you put a drop of concentrated HCl on a CLEAN steel surface, not much happens within 5 seconds.  On a contaminated surface, reactions, bubbling, etc. can happen.
Helpful Member!  redpicker (Materials)
28 Jul 10 15:14
Do you need a test to verify that the part has been coated vs. non-coated, or a test to verify the coating on the part is manganese phosphate as opposed to some other coating (such as zinc phosphate)?

If it is the first case, then the visual process or the chemical process CoryPad mentioned will work.

The second case is a bit more complex.  While I am sure there are spot tests for manganese phosphate, I am not aware of any specific ones.  

If I were given the problem, I'd control the process and verify coating immediately after it was applied.  It the part comes out of a manganese phosphating bath, and is covered with an acceptable coating, you can be pretty sure is has a manganese phosphate coating on it.

rp
smurali1 (Automotive) (OP)
29 Jul 10 1:16
Hello redpicker and corypad,

Thanks for the feedback.

The case is of first type i.e. to check presence of Manganese Phosphate or no coat.

Let me explain some more background:
We assemble Manganese Phosphate coated part with slight interference on to a shaft. We see some powders (presumably Mn Phosphate) coming out during assembly process.
So, we dis-assembled one pc to check if all of the Mn phosphate has been removed (bare steel is exposed) or still some amount of coating is remaining on the part.

Thanks,

SPM
CoryPad (Materials)
29 Jul 10 10:27
Another option is using SEM + EDS.
DABwilldo (Materials)
23 Aug 10 14:57
With an interference fit you can bet that at least some of the manganese phosphate is removed during assembly.  In my experience iron and manganese phosphates are good for preventing rust in storage, and as a carrier for a rust preventative oil, or as a base for paint.  But for long term corrosion resistance, especially in situations where the coating is scratched/rubbed/abraded, you're better off with another means to prevent corrosion.

David Benson
Benson's Mobile Welding & Fabrication
www.bensonmobilewelding.com

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