Passivates versus Chromates and the Effect on the Environment – A Finishing and Protection Process Discussion

At DeKalb Metal Finishing we strive to be as environmentally friendly as possible in what we do. Because we work with Zinc Nickel Alloy, Zinc Iron Alloy and Pure Zinc for metal finishing, we talk a lot about finishing specifications and finishing protection. Related to the environmentally friendly side of things, when we talk about finishing protection, we’re talking about post treatment of Zinc Nickel Alloy, Zinc Iron Alloy and Pure Zinc for protection and often colors, for example, clear, blue/clear, black or yellow passivates.

When we hear the word chromate instead of passivate, however, we want to establish a clear distinction between the two and why we use a passivate treatment process versus chromate.

Zinc Nickel / Zinc Iron / Zinc Finishing:  Chromates

In the post treatment of these finishes, we stay away from chromate as it is very harmful to people and the environment. In the Oxford dictionary, “chromate” is a salt in which the anion contains both chromium and oxygen, especially one of the anion CrO42−. In our industry, chromate refers to hexavalent chromium or Cr6.

OSHA describes hexavalent chromium [Cr(VI)] as one of the valence states usually produced by an industrial process involving chromium which can result in worker exposure to toxic hexavalent chromium. They can also be used to electroplate chromium onto metal parts to provide a decorative or protective coating. As a metal finishing company, despite its benefits, “chromate” has been a negative word and its usage is a bad actor for the environment as it also results in byproducts considered hazardous waste.

Zinc Nickel / Zinc Iron / Zinc Finishing:  Passivates

A passivate is also known as a protective surface treatment made inert or less active. However, in our industry of automotive plating Zinc Nickel, Zinc Iron and Pure Zinc, a passivate generally is referred to as a conversion coating on top of the plating utilizing trivalent chrome or Cr3. So now we are talking about hexavalent chrome chromates versus trivalent chrome passivates. Trivalent chrome differs from hexavalent chrome in the bath chemistry and is considered 500 times less toxic.

Instead of using chromium trioxide, trivalent chromium passivates are comprised of chromium sulfate or chromium chloride as its main ingredient. The result is a trivalent chrome conversion coating resistant to corrosion. We also have extended corrosion resistance from trivalent based “passivate” conversion coatings that impart self-healing characteristics with nano technology that will repair scratching of the coating.

DeKalb Metal Finishing:  Trivalent Chrome Passivates

Trivalent chrome passivates are considered environmentally friendly which is why DeKalb Metal Finishing has used this finishing process well before others raised the alarm on the negative effects of associated to chromates. In our daily routines, language is important such as when we are asked about clear, clear/blue, yellow or black passivates versus earlier generations of chromates.

We want to provide the education behind why we are so passionate about the distinction between Passivates (Trivalent Chrome Compounds) and Chromates (Hexavalent chromium) and their use in our finishing processes.

To speak to an expert about your Zinc Nickel, Zinc Iron or Zinc finishing project, give DeKalb Metal Finishing a call.

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