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Iron Phosphatization Treatment Process

Q. I want to know details about iron phosphate treatment for corrosion protection. Specifically, the pre-treatment of a mild steel surface, the phosphate itself (any hazards in handling?) and any necessary post wash treatment. The parts are oily coming to the process and I am washing off the oil with a powder cleaner that makes a very strong solution and can burn my skin. Also, if the parts are not treated with an additional rust inhibitor for storage, they will rust within a week in the shop.

Sally Clark
- Columbus, Ohio

A. Hi Sally,

Your question is somewhat lacking in details, but I can try to answer anyway.

I assume that you want a suggestion for a pretreatment operation that utilizes iron phosphating. How many stages does your system contain? Is it spray or immersion?

The best phosphating scenario would be clean in Stage 1 (sounds like you're already doing this), water rinse in Stage 2, iron phosphate in Stage 3, water rinse in Stage 4, post-treatment in Stage 5.

How you set this up depends on the end use of your parts. You say that the parts rust after a short period of storage. This is not unusual because an iron phosphated surface does not have a great deal of corrosion resistance in and of itself. Iron phosphating is a widely used pre-paint treatment. Ideally, you would paint the parts right after applying the phosphate coating. If the parts are not going to be painted, then you can apply some kind of rust inhibitor that can act as a barrier to corrosion.

As far as handling the iron phosphate, these are strong acid products; protective glovesamazoninfo and eye protection (gogglesamazoninfo) are the minimum equipment. Check your chemical supplier's MSDS for details.

George Gorecki
- Naperville, Illinois

April 27, 2009

Q. I want to make a solution for degreasing and phosphating in one step (spraying). Can you help me?
Thank you.

James ebram
chemist - cairo egypt

April 28, 2009

A. Hi, James. That would be an "iron phosphating solution". Although the best of these are patented or trade secret, yes, you can formulate your own. Please try to get hold of a few expired patents on the iron phosphating processes (it's so easy today), and also look into the principles behind the process in "Preparation of Metal for Painting" [link is to info about the book at Amazon] or "Phosphating of Metals" [link is to info about the book at Amazon].

Just remember that oils & soils are best removed in hot alkalies, so it's not ideal to try to remove them with the cooler, acidic iron phosphatizing solution; and an iron phosphatizing solution won't work its best when oils & soils are floating around in it. You can toss the apple pie into the chicken soup to save a bowl and a step, but no matter how well you do it, it's just not going to work as well as keeping the soup and the desert separate. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey


Q. I need a kind of anti-rust powder when cast iron part is phosphated, it enhances the antirust effect, to form a pattern in black and grey. How to get it? What is the price? Thanks a lot!

John River
machining - Hanzo, Zejon, China


A. Sorry, John, I don't understand the question. Are you suggesting that the phosphatizing that you are presently providing is not corrosion resistant on cast iron, but you have seen phosphatizing done that was corrosion resistant, and you are wondering what chemical you saw someone add to their tank to adjust theirs and tailor it to cast iron?

Two possible solutions are:
- to order a phosphatizing process from a reputable supplier, which will include technical data sheets (you will find a number of suppliers listed in our directory of Chemicals and Consumables, or
- to learn phosphatizing in more detail from one of the books previously mentioned. Best of luck.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


Q. I want to know whether it is possible to increase the iron phosphate coating weight to Minimum 0.6 gm/sq.m. for better corrosion protection by means of increasing concentration, trying different additives, accelerators or any speciality chemicals?

Nilesh Baraskar
Employee - Mumbai, Maharashtra, India


A. Hi Nilesh,

You can increase coating weight by increasing contact time, temperature and concentration. But increasing the coating weight will not necessarily improve corrosion protection. Corrosion resistance is related to the composition of the coating, and not the amount.

George Gorecki
- Naperville, Illinois


A. Dear Nilesh Baraskar,

If corrosion resistance is your only concern then try zinc phosphating.

T.S.N. Sankara Narayanan
- Chennai, Tamilnadu, India

February 1, 2013

Q. Our surface is metal for interior of car bodies.
I need to reinforce passivation in pretreatment line. I use iron phosphating. I use Cr6 for passivation but I need to increase corrosion resistance.
Some of my friends say if I use TETA (Triethylenetetramine) in Cr6 tank, it will give better corrosion resistance than before.

Nader Bayrami
- Iran

March 7, 2013

A. Hi, Nader. I feel you should be eliminating Cr6 passivation, because of its toxicity, rather than trying to reinforce it. I'm not familiar with TETA as an additive to Cr6 passivation, but I think you probably need to improve the iron phosphating itself or move to zinc phosphating rather than look for a magic final rinse additive to fix it. Good luck.


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Ted Mooney, P.E. RET
Pine Beach, New Jersey

March 15, 2013

Q. Iron Phosphate treatment was meant to increase adhesion of paint for steel drum.
Chinese and Japanese industrial packaging manufacturers use iron phosphate to increase drum's interior cleanliness.
I heard this might be shorten the shelf life of steel product, because the oil residual washed away. What's the pros and cons you think of this treatment?

Sean Kern
Industrial packaging steel drums - Shanghai, China

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