Zn vs. Mn Phosphatization

A. Mr Asif,

For someone to answer your question he has to go a long way. But in short, zinc and iron phosphate is often used for better corrosion protection and good bonding of top coating.

Mn phosphate is used for lubrication purpose usually in bearing and similar accessories.

The principle metal they are used on is mild steel.

A. Mr. Saify has given a good short answer. I would add that Iron phosphate is easiest and cheapest to apply, and zinc phosphate is more expensive and more capable -- with both used as pretreatments before painting and powder coating. Detailed investigation can be found in W. Rausch's "Phosphating of Metals" ⇦[this on Amazon or AbeBooks affil links] or in Samuel Spring's Preparation of Metal for Painting ⇦[this on Amazon affil links]. Good luck.

A. You received a brief description, Muhammed, plus the names of two books that have the complete answers. I don't know how to answer your original question to your full satisfaction, in a posting of reasonable length rather than book length, but maybe this will help...

Iron phosphating is simplest and cheapest usually only requiring a one-step cleaning-plus-phosphating step and two rinses; it's sometimes called the 3-step process; it's only applicable to steel parts.

Zinc phosphating is more expensive and thicker, requiring separate cleaning and phosphatizing steps, but resulting in a heavier and better paint base, sometimes called the 7-step process. It is also applicable to galvanized parts, and can be used on aluminum parts. But there are many variations like tri-cationic zinc phosphating.

Manganese phosphate is usually oiled rather than painted; often engine and machine parts will be manganese phosphated for a measure of dry lubricity during the break-in period before oil can lubricate them.

Apologies, but actual formulations must be obtained from books, patents, or published articles. In much of the world, these formulations are considered closely-guarded proprietary trade secrets. Considering the anonymity of the internet, there is unfortunately no practical way for us to know the legitimacy of a poster's knowledge of this subject so we usually cannot post formulations for fear of abetting the theft of trade secrets. That's why they must come from some non-anonymous source, not an internet posting. Sorry.

"Electrolytic and Chemical Conversion Coatings"
by Biestek & Weber

on AbeBooks

or Amazon

(affil links)

A. Hi Umit. We appended your inquiry to a thread where we have mentioned two books. A third is Freeman's "Phosphating & Metal Pretreatment" ⇦[this on Amazon or AbeBooks affil links], and an excellent fourth one is "Conversion Coatings" by Biestek & Weber.
You can probably do a free patent search for zinc phosphating that will be helpful, and maybe a scholar.google.com one. And you might contact "Metal Finishing Information Service" in England (www.surfacequery.com), as they can do a search through their database of metal finishing technical literature for you. Good luck.

Regards,

A. Good Day
The normal polyester powder can use Iron Phosphating or Zinc Phosphating but with special applications we should go to Manganese Phosphating because this type gives you the target you need.

A. Hi, Baldev.

A short but simplistic answer is that zinc phosphate is a pretreatment for components that will be painted or powder coated, and manganese phosphate is an oil-retentive final coating normally used for lubricated components such as internal engine parts.

But we live in technologically competent times, so as soon as someone says that either zinc or manganese is better for this or for that, then new hybrid formulations spring up that try to counter any such argument :-)

Regards,

A. Hi Hamid. I think people would like to help, but there are two issues ...

First, in the West, no shop formulates their own phosphates; they buy them from companies who have done the R&D over a course of decades. This means very few people know the formulations and for those who do, keeping food on their own table requires that they sell the formulated product and retain their knowledge to themself. We can't print stuff on this site that might be trade secret, finding ourselves crowd-sourcing industrial espionage; we can only print links to published literature on the subject. Please try to locate some books on phosphating if you don't have any.

Secondly, this is a terribly broad subject. When a friend of mine passed away he left me a half dozen cardboard file boxes crammed full of old patents on phosphating processes. Times changed and I threw them away because this stuff is all available for free on the internet these days. Please go to any patent site, including
patft.uspto.gov/netahtml/PTO/search-bool.html or https://patents.google.com
and search for phosphating formulations and you should easily find dozens. Best of luck!

Regards,

A. For far better wet paint, powder coating, rubber to metal adhesive application, adhesion, and corrosion resistance a 7-stage microcrystaline Zinc Phosphating process is it.
It is not the heavy phos, similar to the Mn phosphate good for holding part and oil lubricity -- however, it has many disadvantages for coating applications.

Sometimes the US govt is fooled; however, the specs I have seen for all coatings is Zinc Phosphating.

A. Hi Randall. We appended your letter to one which already addresses the question. Zinc phosphate is a premium pretreatment for subsequent painting or powder coating. Manganese phosphate is intended for parts that will hold oil -- it's a great coating for internal engine parts, and helps parts break in.

But neither is really designed to be used as a permanent final finish. I think zinc plating with black chromate will prove more satisfactory. Good luck.

Regards,

A. When you mention "silver" zinc I think you are referring to a brighter deposit which is typically plated out of an acid electrolyte. Due to the nature of that electrolyte it takes large volumes of organic brighteners to get a satisfactory deposit when compared to alkaline zinc deposits. The end result is a bright part, but it does not accept the passivate (clack chromate) easily. Unsatisfactory coloring could be due to low zinc thickness (lower than .0003"), too low a passivate temp, too low a passivate concentration, improper activation of zinc layer prior to passivate or improper pH of the passivate.