Hexavalent Chromium is found in many legacy sealers used during surface finishing processes to prevent corrosion and extend the service life of a Department of Defense (DoD) weapons system. Hexavalent chromium is a known carcinogen, posing health risks upon inhalation of vapors or dust. Normally, post treatment sealers are required to protect against corrosion and fill in porosity of the surface treatment.

SERDP and ESTCP have continued to invest in research and demonstrations dedicated to reducing or eliminating the use of chromium in processes and materials and providing safe and effective replacements for chromium. While researchers have successfully developed and demonstrated chromium-free alternatives for select processes, identifying a chromium-free sealer that can perform multiple functions would simplify and streamline DoD operations.

In 2021, SERDP selected the following projects to develop chromium-free, high-performance sealers and pretreatments that can be applied across multiple surface finishing processes. 

• At TDA Research Inc, Jeannine Elliott is leading an effort to develop a chromium-free sealer that can fill in pores and defects left from prior plating and anodizing surface finishing processes. The team will carry out a multi-pronged corrosion inhibitor approach that uses the driving force of corrosion itself to generate a corrosion inhibiting protective layer. When put into a sol-gel coating, this novel inhibitor package has the potential to be an effective, chromate-free post-treatment sealer. Dr. Elliott and her team will test the sealant on zinc (Zn) and zinc-nickel (ZnNi) plated substrates and on Cd plated and anodized (MIL-A8625F (Type II, III)) AA2024 (Project Overview).
• Zn or ZnNi plating is one of the highest priority processes for chromium-free sealers. Dr. Waynie Schuette at Boeing and her team aim to create chromium- free post-treatment finishing solutions for zinc and zinc-nickel, as well as for cadmium (Cd) plating, and anodized aluminum (Al) and ion vapor deposition (IVD) Al coatings. To accomplish this, they will develop and mature organic Schiff base (SB) containing passivating and sealing post-treatment solutions. The team will also conduct a lifecycle analysis of the SB passivating solution to facilitate technology transition and implementation across DoD depots (Project Overview).
• Alexander Westbrook at the Naval Air Warfare Center, Aircraft Division will also focus on ZnNi-plated steel, as this metal finish is particularly important in naval aviation applications as a cadmium alternative. The team will electrolytically deposit inhibitor-doped fluorozirconate coatings, focusing on high strength applications. They will measure the sealer’s effectiveness on zinc-nickel plated steel by observing corrosion resistance, electrochemical properties, paint adhesion, hydrogen embrittlement, and plating adhesion (Project Overview). 

Chromium-free sealers that can be used in a variety of applications could dramatically cut costs for depot operations and eliminate health risks for workers. To learn more about other SERDP and ESTCP efforts to develop and implement chromium-free alternatives across the Services, visit the SERDP and ESTCP website.