Letter 38067

Phosphorus higher than 12 % [Argentina] 

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We use to plate nickel phosphorus between 10-12% P. What is the matter with acetic acid spray saline when the phosphorus is higher than 12 %? (about 13-15%)

Roberto Capria
plating ENickel - Pilar, Argentina

Why, is it failing a qc test? Higher P EN solutions cost more, are harder to control and do not get as many tank turnovers as lower P. Some shops have no problem, but more do have problems with it. (opinion)

James Watts
- FL

Salt fog type tests (whether neutral or acetic acid) are mostly porosity tests. The phosphorus content of a high phosphorus coating does not have a significant effect of its results. If you are seeing reduced performance, I would suggest that you look at other factors like bath age or substrate quality, and not whether the coating is 11% or 14% phosphorus.

Most commercial high phosphorus EN Bath will not produce coatings with more than 12%P, unless they are plating at a very slow rate.

Ron Duncan Palm International, Inc. - LaVergne, TN

Ed. note: It is our sad duty to alert the readers to the passing of Ron Duncan on Dec. 15, 2006. For those who would like to know more about him, a brief obituary opened Update No. 13 of our Metal Finishing Industry Update Podcast.

Always we work about 10-12 %P. But two months ago we discovered a serious corrosion (with acetic salt spray). At different laboratories, they informed us 7%, 11% and 15%!!!
I guess initially the 7% is a problem, but then when appears 15 %... I don't know now. So, I ask you if the 15 % is a probably cause to the corrosion.

Roberto Capria
- Pilar, Argentina

Not enough information, so some general suggestions for determining the problem. As noted above, the P content isn't the root cause.

Poor corrosion results can be caused by inadequate surface preparation, insoluble impurities (inadequate filtration) or soluble impurities (buildup with metal turnovers and impure chemicals).

First, does the EN pass adhesion (bend) testing? If so, surface preparation may be OK.

Second, do porosity testing of as-plated specimens. E.g., feroxyl test on ferrous substrate, alizarin test on aluminum, per ASTM B733 [link is to spec at TechStreet]. Failure would suggest better filtration is required.

Since your bath is quite old, the buildup of soluble impurities seems likely. How many metal turnovers?

Ken Vlach - Goleta, California

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