Replacing Hexavalent Chromium in Passivations on Zinc Plated Parts The use and benefits of passivations based upon hexavalent compounds, particularly on zinc plated parts, are well established and understood in finishing. Through the changing attitudes within society, the continued long-term use of this technology is under question and review. We examine the background and comment on the alternative strategies available that are most likely to commercially succeed . . . By Paul C. Wynn, Business Manager and Craig V. Bishop, Special Projects Director McGean-Rohco (UK) Ltd. TABLE IV—Passivation Strategies to Replace CrVI • CrIII - Difficult to build thickness on Zn but alloys do allow significant increases in thickness. Colors are different. Fate of CrIII is uncertain. • Organic films - Large variety. Coating thickness, uniformity, and color are concerns. • Inorganics - Salts/oxides of Al, Ti, Mo, W, Co, Ce, Zr, etc. produce colored coatings. Do poorly in salt spray. • Oxides - Silicates, phosphates, etc. Complement CrVI, CrIII, and organic coatings. Can't be used alone. • Organometallics - Stability in water is limited to a few compounds. Very expensive chemicals. • Multiple Steps - Combinations of the above, very promising, capital expense may be involved. TABLE V—Trivalent (CrIII) Observations • Salt spray on zinc not quite as good as conventional. • Iridescent colors aren't identical to CrVI. • Doesn't repair itself. • Still has chromium. • Salt spray on alloys is very good. • Easy application • Thin, conductive very long lived. • In most respects it is a suitable substitute for hexavalent chromium. TABLE VI—Trivalent (CrIII) Colors: Iridescent & Black