Concentration levels should be as low as possible because they will compete against CHEMEON TCP-HF to be a part of the coating and some of them will cause micro-galvanic coupling on the surface. It is very difficult to give an exact number for the upper limit of these elemental contaminants, but
Iron: 10 ppm, preferably 5 ppm, more preferably 0 ppm.
Zinc: 50 ppm, preferably 25 ppm, more preferably 5 ppm.
Aluminum: 75 ppm, preferably 25 ppm.
Aluminum Zinc combined: less than 100 ppm would be great.
Again, please keep in mind that these are the findings we have based on the lab and field tests. If the customer has been failing, then we need to look at the combination of the pre- and post-processing details. Decanting might be an alternative to reduce the contaminant concentration, but this needs to be evaluated well before decanting.