Chromate Primer Alternatives

Current Usage   

Chromated primers are used to provide corrosion protection to aircraft skins and airframe components.
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Typical Applications
  • Aircraft skins
  • Al airframes
  • Steel airframe components

ESOH Issues

Cr6+ (CrVI, hexavalent chromium) is a known carcinogen that is heavily regulated.

  • EPA Clean Air Act rules
  • OSHA Occupational Exposure to Hexavalent Chromium (Cr6+ PEL is currently 5μgm-3)
  • European Union laws (RoHS, WEEE, ELV, REACH)
  • OSD-ATL Memo, Minimizing the Use of Hexavalent Chromium (2009)
  • DFARS Minimizing the Use of Hexavalent Chromium, Federal Register /Vol. 76, No. 87 /Thursday, May 5, p 25569 (2011)

Exposure 

Personnel may be exposed at the OEM level and during depot overhaul, repaint, and operational level touch-up and repair.

  • OEM and depot personnel may be exposed in painting operations.  Emission controls, PPE required.
  • Maintainers are exposed in scuff sand and paint operations.  PPE required.

Alternatives, Applications, Status 
Primary alternatives are barium chromate and non-chrome products.  Barium chromate is considered to be less toxic than other chromates used in primers and is a Class C1 in MIL-PRF specifications. Non-chrome primers contain alternative inhibiters such as rare earth metals. Zn-rich primers have long been used for steel infrastructure, and are now used on some USMC MRAPs, and new Mg-rich primers are under development and evaluation for DoD use.  A number of alternatives are commercially available and some have been authorized and implemented.

Common Alternatives Examples of Developments, Authorizations, and Implementations Specifications
Barium Chromate primers  
  • MIL-PRF-85582 Class C1
  • MIL-PRF-23377 Class C1
Chrome-free primer approvals
  • USN aircraft skins, scuff sand, and touch-up of existing paint systems
  • MIL-PRF-23377 Class N
Chrome-free primer implementations
  • F-35 Lightning II Joint Strike Fighter (rare earth primer)
  • Apache helicopter upgrade, repair (rare earth primer)
  • All new Boeing commercial fuselages
  • Some USMC vehicles – Zn-rich primer
Lockheed-Martin and Boeing specs
Mg-rich primer
  • In development and testing
 
Powdercoats, e-coats, UV cured paints
  • Low temperature cure powdercoat, for Al and high strength steel, e-coats for components