Environmentally Friendly Zirconium Oxide Pretreatment

The Chemical Agent Resistant Coating (CARC) System application specification, MIL-C-53072, requires that metal surfaces be treated to improve the adhesion and corrosion resistance prior to coating with an epoxy primer and camouflage topcoat. In original equipment manufacturer (OEM) processes the surface treatment is generally a zinc phosphate as prescribed in TT-C-490.  In depot operations, and for OEM touch-ups, the surface treatment requirement is met through the pretreatment/wash primer, DOD-P-15328. This formulation contains 7.1% zinc chromate and has 6.5 lb/gal of volatile organic compounds (VOCs) which are classified as hazardous air pollutants (HAPs).

There is a current emphasis to develop coating systems which have reduced VOCs, and are free of regulated metals, for Department of Defense applications. This increased interest in environmentally friendly coatings is the impetus for the development of zirconium-based pretreatments intended for use with CARC coating systems that meet MIL-DTL-0053022C, MIL-DTL-0053030B, and MIL-DTL-64159. The intent of this work is to formulate a metal pretreatment which is free of VOCs and regulated heavy metals, yet is cost effective and exhibits corrosion performance equal to incumbent technologies. 

During the first phase of SERDP 1676, OEM application methods have been utilized to determine the feasibility of a zirconium-based pretreatment as an alternative to zinc phosphate or wash primers for metal pretreatment.  Immersion applied zirconium-based pretreatments performed similarly to Zn phosphate or wash primer in wet/dry adhesion (ASTM D3359), water resistance (ASTM D1308), JP8 (jet fuel) resistance, ASTM B-117 (neutral salt spray), and GMW14872 (cyclic corrosion testing); passing specifications outlined for the subsequent epoxy primer layer (MIL-DTL-0053022C for solvent-borne and MIL-DTL-0053030B for water-reducible). Work outlining the development and evaluation of a spray-applied pretreatment will also be presented.