Iron Phosphate vs. Phosphoric Acid?

[swpruett]

Well......I've been searching through all the posts I can find on pretreatment with Iron Phosphate looking to educate myself on the product. I understand the principles involved in it's use, but I have thoroughly confused myself on another hand.

Specifically, I am having a hard time understanding the difference between common phosphoric acid used as a metal "prep" before painting and "iron phosphate" used in p.c. pretreatment. I'm no chemist, but it seems iron phosphate is the byproduct of the reaction that results from the application of phosphoric acid on ferrous metals (but I don't know).

The ultimate question I have is this: Is Iron Phosphate simply a phosphoric acid incognito? If so, can I use the commercially (and locally) available phosphoric acid and achieve the same results?

I appreciate any help you folks can provide.

Regards,

Sven

[CarWiz]

Iron phosphate is FePO4. Phosphoric acid is H3PO4. As a coating, they work differently. You can get IP by visiting a garden shop. It's sold as a slug killer. Look for Sluggo & Escar-Go brands. They are two that consist of Iron phosphate.

[swpruett]

Originally Posted by CarWiz

Iron phosphate is FePO4. Phosphoric acid is H3PO4. As a coating, they work differently. You can get IP by visiting a garden shop. It's sold as a slug killer. Look for Sluggo & Escar-Go brands. They are two that consist of Iron phosphate.

Thanks for the lesson. If I can't expect the same results between the two, then I am inclined to go ahead and buy some of the "industrial" product made for P.C. Kind of a pain as I was hoping I might have a local source at less cost. Never that lucky........

Regards,

Sven

[jazzcornet]

i would like to be more familiar with how it works. or more specifically, how do you use it. i have the iron phosphate primer, but im not sure how to use it or when to use it. can anyone give me a pointer or two? perhaps a simply chemistry lesson on how it works would be sufficient as well.

[Harleydad]

Originally Posted by jazzcornet

i would like to be more familiar with how it works. or more specifically, how do you use it. i have the iron phosphate primer, but im not sure how to use it or when to use it. can anyone give me a pointer or two? perhaps a simply chemistry lesson on how it works would be sufficient as well.

How Iron phosphate works.


http://www.powder-coater.com/phosphating.htm

[jazzcornet]

very helpful thanks!!!

[swpruett]

The thing that worries me is flash rusting after the rinse. In my limited past experience with phosphating, most attempts to rinse after coating with phosphoric acid-based products result in flash rusting almost before your eyes. Is iron phosphate similar and does it leave the "powdery" residue that some phosphateting products do on steel?

Thanks!

Sven Pruett

[jazzcornet]

i would also like to know how to apply the iron phosphate primer

[Harleydad]

The stuff I use is mixed with water. There's more to it, but you really need to watch the ph, you want it around 4.0-4.5. Lower will give you flash rust. The white powdery residue is from too long a dwell time or too heavy a coating. Section 1.2 of Tigers trouble shooting guide lists a few problems and correction suggestions.
http://www.tiger-coatings.com/filead...guide2_usa.pdf