Difference Between Trivalent and Hexavalent Zinc Plating

The key difference between trivalent and hexavalent zinc plating is that the trivalent zinc plating process has a high efficiency with a uniform distribution than the hexavalent zinc plating process.

Zinc plating is a common process of protecting a wide range of materials. It can act as a sacrificing coat. For example, if we do zinc plating on iron and if the coating is scratched somewhere, then the zinc acts as a sacrificial electrode to protect the inner iron material. There are two forms of zinc plating process; trivalent plating and hexavalent plating process. Among them, trivalent zinc plating is the latest.

1. Overview and Key Difference
2. What is Trivalent Zinc Plating
3. What is Hexavalent Zinc Plating
4. Side by Side Comparison – Trivalent vs Hexavalent Zinc Plating in Tabular Form
5. Summary

What is Trivalent Zinc Plating?

Trivalent zinc plating is a form of finishing method that uses chromium sulfate or chromium chloride as the main ingredient. Therefore, it is highly environmentally friendly. The main ingredients mentioned previously are less toxic, and we call this finishing a decorative chrome plating. It has most of the characteristics of hexavalent zinc plating. It provides materials with the resistance to scratch and corrosion. Moreover, it is available in many colors.

The advantages of this plating include the ability to create highly protective and bright deposits at very high current densities, extremely low stressed and blistered free deposits, excellent covering power, uniformity, environmental friendly plating, etc.

However, it is difficult to control this process and the chemicals used are highly expensive. Another disadvantage is that the colors are not identical. More importantly, the coating needs to be applied at high temperatures around 30-60 ◦C.

What is Hexavalent Zinc Plating?

Hexavalent zinc plating is an older version of zinc plating. The most common name for this method is chrome plating. We can use this process for decorative purposes and functional finishes. We can achieve this finish via submerging the substrate material in a bath of chromium trioxide (CrO3). This bath contains sulfuric acid as well. This plating provides the materials with corrosion and wears resistance.

However, this method is now replaced by trivalent method because of its disadvantages. More importantly, this process produces some hazardous waste products. Ex: lead chromate, barium sulfate. Moreover, hexavalent chromium is a carcinogen. Therefore, this process is harmful to the environment as well.

What is the Difference Between Trivalent and Hexavalent Zinc Plating?

Trivalent zinc plating is the latest version of zinc plating. The ingredients that we use for this process are chromium sulfate or chromium chloride. Importantly, it creates a more uniform coat and is an eco-friendly process. This is the main difference between trivalent and hexavalent zinc plating. On the other hand, hexavalent zinc plating is the older version of zinc plating. The ingredients that we use for this process are chromium trioxide and sulfuric acid. It creates a less uniform coat and is harmful to the environment. However, this process is less expensive, comparatively.

Summary – Trivalent vs Hexavalent Zinc Plating

The two major finishes of zinc plating are trivalent and hexavalent zinc plating. The key difference between trivalent and hexavalent zinc plating is that the trivalent zinc plating process has a high efficiency with a uniform distribution than the hexavalent zinc plating process.

Reference:

1. Wardell, Marcee. “Hexavalent vs. Trivalent Chrome Plating.” Electro Chemical Finishing, 30 May 2017. Available here
2. “Zinc Trivalent Plating.” Cadillac Plating. Available here