Re: Low Temperature / Phosphate-free Conversion Coatings

A cost effective high performance environmentally friendly alternative to iron phosphate

By Chris Klingenberg and David Jones
EnviroServe Chemicals Inc.

Energy costs are a major concern for metal finishing operations as well as issues of environmental compliance. Waste water treatment facilities in certain areas of the country are tightening phosphate and heavy metal discharge limits on metal finishers. To address these concerns, a line of inorganic conversion coating products has been developed. They focus on temperature reduction and phosphate discharge elimination while improving corrosion resistance.

Formulated to replace traditional iron phosphate, these products require no or very little heat to deposit an inorganic conversion coating. Conventional iron phosphate products, on the other hand, can require temperatures of 130-160 F. Another benefit of this new technology is usage; a maximum of about 2% by volume is needed in the bath compared to approximately 2-4% by volume with conventional iron phosphates.

These conversion coatings provide a microcrystalline surface in the nanometer (10-9m) range and require a short contact time of 15 to 30 seconds. Conventional iron phosphate coatings are usually in the micrometer (10-6m) range and require at least 45 to 60 seconds contact time. The “nanocrystals” formed increase the surface area of the substrate thus enhancing paint adhesion, corrosion protection and consequently salt-spray results.  These inorganic conversion coatings do not require a post treatment seal to achieve high performance adhesion, under film corrosion and salt-spray resistance.

The corrosion resistance performance of these inorganic conversion coatings is compared below to conventional iron phosphate coatings (organic accelerator) with TGIC polyester and hybrid powder paint systems on cold-rolled steel and aluminum substrates.


As the table indicates, the inorganic conversion coatings outperformed conventional iron phosphate coatings in under film corrosion resistance.
In actual production on cold rolled steel panels, this new type of inorganic conversion coating with a DI water rinse has been proven to outperform Bonderite 1000 / P60 Chrome / DI rinse in corrosion resistance after 504 and 1008 hours of neutral salt-spray exposure (ASTM B-117) as the table below indicates:


These new technology coatings contain no regulated heavy metals and eliminate phosphate from the process bath. Sludge is also reduced to a minimum while waste treatment costs and other effluent issues are greatly diminished. Reduced sludge formation results in considerably lower maintenance costs since fewer bath dumps are needed and the incidence of plugged nozzles and other problems are reduced.  Rinse water consumption is also reduced because of the lower amount of total dissolved solids present in these new coating baths.  Lower total dissolved solids means less rinse water overflow is needed to maintain proper rinse integrity.

The benefits of these new types of conversion coatings are real and tangible. Energy consumption is reduced, the process is consistent and easy to control while parts quality and performance are improved. The process produces much less sludge than conventional iron phosphates and when the tanks need to be pumped out, about once a year, there is no need for a tanker truck to haul away the sludge as hazardous waste, all that is required is to neutralize the pH. 

To sum up, these new products offer a cost effective high performance and environmentally friendly alternative to traditional iron phosphates. For more information on these new technology inorganic conversion coatings, please contact EnviroServe Chemicals Inc. by phone at 910-892-1791 or by e-mail at sales@enviroserveinc.com or visit the web site at www.enviroservechemicals.com.

This article was published in Southern Metal Finishing Newsletter, November 2006.

EnviroServe Chemicals, Inc.


Re: Low Temperature / Phosphate-free Conversion Coatings

I know this is an old post, but I have a question if you are still on or if someone else would like to comment.

We bonderize and nickel plate steel tape. However, we are having high scrap issues with rusty steel and "over plating". We believe these are caused by either not cleaning/prepping the steel properly and/or from sitting in the chemicals for extended periods of time. Is there anything you could offer that would reduce or eliminate these issues?

Are there other methods or processes that anyone knows of to eliminate these issues?


Re: Low Temperature / Phosphate-free Conversion Coatings

Please describe your process and your defects in more detail.

-Dustin Gebhardt, CEF

Advanced Manufacturing/Finishing Engineer


Sanford, NC