by Roger Sowinski
Vice President of Technology, Asterion
Q: What is the best way to increase the bath life and quality of trivalent passivates on zinc plate?
A: One of the more significant developments of the last 20 years in the metal finishing industry is the commercial development and application of trivalent passivates on zinc electroplate. These developments have allowed applicators to eliminate the use of toxic hexavalent-chromate conversion coatings, thereby safeguarding the health of all involved in the handling and processing of zinc-plated parts. Further, these trivalent passivates have a substantially positive impact on the environment. The following information addresses issues involved with producing a consistent blue-bright, thin-film passivate on electrodeposited zinc.
Trivalent passivates are typically acidic in nature and operate at a pH between 1.6 and 2.2, under most operating situations. Therefore, during the passivation step, both zinc and iron will be dissolved in the passivate solution, and their concentration in the passivating solution will increase. Read more.