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Staining of potassium dichromate sealing

We are currently experiencing problems with staining of finished Potassium Dichromate sealed jobs.we carry out sulfuric anodising process prior to Dichromate (Concentration 40-60 g/l and pH 5-6).

The staining is only happening after grease application to this particular jobs.Please advice on how to properly seal the surfaces to avoid this problem.

Robert Morrissa
Lab Technician - Middlesex, UK
2007

Obviously it is not "sealed" if grease is getting into the p-ores.

You did not mention temp - it should be 205 °F (99 °C) for 15 minutes, made-up with deionized water and maintained with careful and accurate pH control over 5.0.

Make up a new precision and perfect solution in the lab and try it to see if it will seal well enough to hold off the grease.

If that fails, then try double seal: 1, with nickel acetate at 160 for 5 minutes, followed by 2, good dichromate seal.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

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