Manufacturing of phosphating chemicals

A. Hi Aswin. Theoretically, a zinc phosphate process could be a 30 to 90 minute immersion in 3% zinc phosphate plus phosphoric acid at near boiling temperature, with the ratio determined by what delivers a good "free acid to total acid ratio" (you titrate to a still-low pH to determine the free acid, then continue the titration to a higher pH to calculate the total acid). You adjust the amount of phosphoric acid to give you the desired ratio. You can search the site for how to conduct this two-step test, what indicators to use for the two-step titration, and what are reasonable FA/TA ratios to shoot for.

But, while people regularly conduct this FA/TA titration, virtually nobody, not even the largest automobile manufacturers, formulate their own process from raw chemicals because there is too much benefit from proper proprietary addition agents to not use them. Without addition agents the process is terribly slow (nitrate, nitrite, chlorate and/or peroxide accelerators are needed), the coatings are too thick, too much sludge results, insufficient adhesion and corrosion resistance results, etc. So people buy a proprietary formulation and follow the vendor's instruction because practical phosphating profits so greatly from modifying the formulation in different ways, as well as from pretreatment activators and post-treatment passivators.

TSN Sankara offers -- linked from this page -- the full text of a paper with great insights into what these additives are and what each type does, and with over 400 references on the subject. And you can use scholar.google.com with search terms like "improved zinc phosphate process" to find countless other papers on the subject.

But if your situation is that you actually need to phosphatize something for your project, the way you do it is by buying a commercially available process, not by mixing raw zinc phosphate and phosphoric acid. You'll might also want a proprietary activator before the phosphate and possibly a proprietary passivator after it. Any good phosphating book will explain the dynamics of the process and the general value of various sorts of accelerators and other addition agents, but none that I personally know of tell us the exact formulation of even one practical zinc phosphatizing bath.

Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Dear Sir,

I would like to guide you. Please provide the ratio of these chemicals in 1 liter or per Kg basis. The answer lies in the correct ratios and the correct chemicals. You seem to be missing on both the fronts. Cheers!

A. Dear Mr. Khan,

Please refer the following book:

W. Rausch, "Phosphating of Metals" ⇦[this on Amazon or AbeBooks affil links], published by Finishing Publications Ltd.
Now this book comes with CD-ROM Database Update! with 3,500 abstract records.

For a recent review on phosphate coating, you can refer to
www.ipme.ru/e-journals/RAMS/no_2905/narayanan.pdf ⇩

Since "Reviews in Advanced Materials Science" is an e-journal, I believe that the article will be accessible for many readers.

[Ed. update 2024: The above link is broken. Thankfully, the Internet Archive preserved a copy here
These days information often appears on the internet, then disappears forever. If that is a concern to you please consider a donation to The Internet Archive.

A. Hi Touseef. You posted a similar question last year and you received a link from T.S.N. Sankara Narayanan to an outstanding paper he wrote on the subject. I suspect that our reply went to your spam folder, or something might have been "lost in the mail" and you are not aware of his response. Please don't miss it!

Although you can get some general hints in the standard texts like The Metal Finishing Guidebook, you might be better with a specialty book like the Rausch book he suggested, or

• "Modern Technologies of Thin Films Deposition: Chemical Phosphatization"
by Sandu & Bejinariu ⇦[this on Amazon or on AbeBooks affil links]

• "Phosphating of Metals"
by Guy Lorin [on Amazon or on AbeBooks affil links]

• Freeman's "Phosphating & Metal Pretreatment" ⇦[this on Amazon or AbeBooks affil links]

• [on eBay or Amazon affil links] or

• "Electrolytic and Chemical Conversion Coatings"
by Biestek & Weber [on Amazon affil links].

But please introduce yourself and your situation to help avoid misunderstandings because the short answer is that if you are a researcher, there are thousands of papers on different aspects of zinc phosphate coating formulation, but if you are a user, almost nobody formulates their own process, they buy one from a supplier who has invested decades of research into viable proprietary processes. Good luck.

Hi, Cousins.

Unfortunately, a question as general as how to formulate a better phosphatization bath is a bit like asking how to make more tasty cookies or a more reliable can: it can quickly scatter the thread in many directions and render it incoherent :-)

Please post your formulation, or refer to the article by TSN Sankara, or the dozens of threads on line here about the formulation of phosphatizing processes. Please search the site and scan them, get hold of the books and the on-line papers that have been recommended, and ask specific questions about any remaining questions you have, and you may get some answers. Although people won't throw away their business advantage by publishing the secrets to their own successful formulations, if you describe specific difficulties they are usually quite generous in offering very important hints.

Good luck and Regards,

A. Hi Rina. My dear friend Joe Mazia (dec.) designed such formulations for Parker+AmChem for decades before there was an internet, and he kept many large file drawers full of patents on the subject. After you've read a couple of books about Phosphatizing and understand the generalities, a great source of good information would be the patents, and it is so easy today with them all being on line.

But by all means, start with TSN Sankara's terrific paper, available through the link on this page. Good luck.

Regards,

A. Hi folks. Please obtain and skim some of the books & some of the papers that have been suggested, then download a few patents to understand the acknowledged weaknesses of certain formulations and the claimed advantages of the various tweaks. Then knowledgable formulators may be willing & able to offer a little help with highly specific questions.

But most people spend decades, and many people have spent their whole careers, in the design of phosphatizing processes; the idea that people can compete in a field they know little about, with a recipe posted on an internet forum is unfortunately ridiculous. Best of luck.

Regards,