A study on eco-friendly chromate-free passivation of galvanised steels

Abstract

Although chromate passivation is commerciaily used most effectively in preventing white rust and giving a long life to galvanised steels or zinc-plated parts. It is not eco-friendly, as it contains hexavalent chromium. Hexavalent chromium is very toxic and carcinogenic and its maximum permissible limit in drinking water is 0.05 ppm as per WHO as well as Indian Standard (IS 10500-1983). Hence there is a need to find alternate chromate-free passivation with similar or better properties. This paper attempts to compare and evaluate an alternative molybdate-phosphate based passivation method with chromate-passivation on hot-dip galvanized and electrogalvanised steel. From the observationsandresults,it is clearthatbothmoly-phos(0.66)and moly-phos(0.33)are effective as passivating solutions, but it requires more research work to make it work commercially as an alternative to chromate passivation. However, they do have great potential to replace the toxic chromate passivation. Original References are cited for detailed information to the Literature.