The black barrier: Characteristics of high-performance black passivates for zinc substrates

The use of chromium conversion coatings for the corrosion protection of zinc surfaces has a long history. The vast majority of this history has been dominated by the use of hexavalent chromates, which provided an easy-to-operate means to achieve high corrosion protection figures on zinc and zinc alloy surfaces. Also, high decorative demands were satisfied with yellow, olive drab, and black hexavalent chromium conversion coatings. But the toxicity of chromium(VI) is much higher than that of chromium in other oxidation states, especially compared to that of chromium(II).