The authoritative public forum
  for Metal Finishing since 1989
  

  -----

Difference between Yellow, Green and White Passivation

Dear All,

I would like to know the difference between the various passivation used after zinc plating. Currently we are using yellow passivation and want to shift to white passivation. The base metal is Galvanised Iron sheet, manufactured by pressing operations.

I. Vijayasankar
- India
2006

---

2006

Sir,
30 years ago I did fundamental work on hexavalent chrome to protect hot dip galvanized work in Canada. First we found which worked better chromic acid (CrO3) or sodium dichromate (Na2Cr2O7). Then we used various acids to control pH to the correct pH. From our work we found that sulfuric acid pH control gave gold, nitric acid gave light yellow, hydrochloric acid plus acetic acid ⇦ this on eBay or Amazon [affil links] gave clear with a slight sky-blue where the chromate quench had not dried and did not fully drain. The last formulation was by far the best looking and always passed the Canadian government 40 hour salt-spray test.
Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA