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Ammonium molybdate tetrahydrate as accelerator in iron phosphate


Q. We get an excellent results by using the ammonium molybdate as an oxidizing agent in the iron phosphate tank, but due to the formation of a complex the solution turned to blue.
How to avoid this blue color?
We only need to get a blue color on the substrate only?

Ahmed Fouad Serag Eldin
Ahmed Fouad Serag Eldin
Ein Shams - Cairo - Egypt


A. Hi Ahmed,

If you say that your phosphating bath is giving you excellent results, why are you concerned that the color of the bath is blue?  ;-)

There are many types of accelerators used in phosphating baths that do not turn the solution blue. You could switch to one of those products.

George Gorecki
- Naperville, Illinois


A. Dear Serag,

The blue colour is called "molybdenum blue".

In fact this is one of the tests to check for the presence of phosphate coating on steel.

If molybdenum ions are there it will give the colour.

T.S.N. Sankara Narayanan
T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India
(ed.note Nov. 2017: The good doctor has a fascinating blog at https://advancementinscience.wordpress.com)


thumbs up signMany thanks Mr. George Gorecki for your reply. I read from you many valuable replies on this great site.
We tried many accelerators -- all of them succeed to form the iron phosphating layer with golden, violet and blue shades but the problem is the presence of the intense blue shade giving too much confidence in our market about the product.
So we found that the ammonium or sodium molybdate gives this feature.
The presence of Nitric acid in the formula decreases the formation of the blue color in the solution but does not prevent it.

Ahmed Fouad Serag Eldin
Ahmed Fouad Serag Eldin
Ein Shams - Cairo - Egypt


A. Molybdenum +4 is blue (oxidized state). It is harmless.

don baudrand
Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [affil link to the book on: Amazon or AbeBooks ])


A. Hi Ahmed,

I'm not sure I understand your problem. Your customers like the blue color, but you want to eliminate it?

You can continue to use the molybdate-accelerated product, but the color can be altered by changing the pH. If you are getting a deep blue color, I am assuming your pH is around 4.2. You can try running at 4.5 - 5.0 and see if that helps. The color will probably tend toward gold.

If I am misunderstanding your problem, please re-state.

George Gorecki
- Naperville, Illinois


Q. Dear Mr George Gorecki

The phosphated steel surface color is excellent blue shade but the problem in the color of the phosphating solution itself.

The solution turned from colorless to blue after spraying several times.

All that I need is to prevent the formation of a blue solution.

Ahmed Fouad Serag Eldin
Ahmed Fouad Serag Eldin
Ein Shams - Cairo - Egypt


A. Hi Ahmed,

Why does your customer object to the color of the solution? As I mentioned before, the color of the solution is not related to the performance of the phosphated work.

I suggest to contact the manufacturer of the phosphating product and see whether alternative chemistries can be used here.

George Gorecki
- Naperville, Illinois


A. Dear Ahmed
In the acid-molybdate method orthophosphate reacts with molybdate to form phosphomolybdic acid. Phosphomolybdic acid is reduced by acid to form a blue complex.
So I think your work in acidified media.

Ahmed Morad
- Egypt

October 27, 2008

A. You can use sodium nitrite , but I see that it is not problem if the result good

Dr. Amal
- Cairo, Egypt

May 1, 2015

A. I read somewhere that addition of edta prevents the solution from turning blue or green, due to the formation of a Mo-EDTA Complex.

Gokul Malik
- Chandigarh, India


I ask of you defined DETERGENTS (ANIONIC / NONIONIC), and defined percentage(%) of accelerator in iron phosphate (ammonium molybdate tetrahydrate ).

Thank you very much .

Soltan [last name deleted for privacy by Editor]


Q. Dear Mr. GEORGE, please tell me what will be estimated future life of the properly phosphated mild steel in normal climate? As I visit phosphating unit as salesman and I can't answer them properly. {lease help me. thanks.

Satish D Deshpande.
chemicals - Satara, Maharashtra, India

July 1, 2010

Q. Dear sir
I am working on iron phosphating solution. Examining a variety of formulations, I have gotten no results yet. So, I would like to ask you some questions:
1- percentage(%) of accelerator in iron phosphate?
2- combination of sodium nitrite and nitrate is suitable?
3- sodium dihydrogen phosphate is needed?

Thank you in advance.

Afshin Radmanesh
Master student - Tehran, Iran

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