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Electrochemical Modeling of Anodic Metal-Rich Primers

Description:

 
 

TECHNOLOGY AREA(S): Air Platform, Ground/Sea Vehicles, Materials/Processes

ACQUISITION PROGRAM: POM17 FNC - Advanced Topcoat Systems; NAVAIR 4.3.4 Air Vehicle Engineering Materials Division

OBJECTIVE: Develop innovative models and analysis tools that support the maturation of metal-rich coatings, including their interaction with metallic and non-metallic surfaces and prediction of performance in the laboratory and naval operating environment.

DESCRIPTION: Metal-rich primers using anodic materials, such as the newly-developed Al-rich systems, are showing a great deal of promise for replacement of legacy chromated primers in aircraft. However, development and optimization of these primer systems is inhibited by a lack of understanding of how the entire system behaves and protects coated aircraft components, and assemblies in which they are used. Furthermore, the technology to manufacture these primers is quite advanced with regards to particulate size, loading and a number of other parameters that can be manipulated. Consequently, given this capability to customize the manufacturing process of such metal filled primers, a model-based analysis/optimization tool is required that can provide guidance on how to adjust these numerous parameters in order to optimize coating system performance.

Accurate electrochemical modeling is needed that explicitly accounts for the chemistry and structure of these metal-filled primers. This would make it possible to predict the behavior of the primer in a primer/topcoat system as a function of resin system chemistry, solvents, additives, metal particle alloy, particle size and shape, surface chemistry, and loading. This detailed modeling of the paint system must then be able to be used for guiding the choice of primer/particulate parameters for manufacture and an upfront prediction of how painted components will behave in aircraft galvanic assemblies.

This modeling must incorporate both the initial condition of the substrate/primer system, and changes that occur over time, including degradation of the polymer matrix in which the particles reside, corrosion and dissolution of the particles themselves, corrosion products, and voids and other changes created in the system by the dissolution of the particles. This modeling must include charge transfer through the resin system, electrochemical surface reactions at resin matrix/particle interfaces, electrochemical surface reactions at the substrate/resin interface (including interactions with the substrate conversion/passivation coating), and electrochemical reactions at the primer/electrolyte interface of a non-topcoated paint system, and at the primer/topcoat interface of a system with supplementary coatings like a topcoat. It must also be able to model interactions between the primer materials and damage such as porosity, scratches, and holidays.

PHASE I: The small business will develop and demonstrate a proof-of-principle model for the electrochemical interactions of a metal-rich primer that incorporates interactions between the metal particles, substrate, and electrolyte based on the measured electrochemical properties of the metal rich primer system, including its polarization behavior and electrochemical impedance, using microscopic structure information and electrochemical measurements supplied by NAVAIR, augmented if necessary with additional test data.

PHASE II: Based on the results of the Phase I effort, the company will extend and fully develop a prototype software tool/model to include the explicit primer/substrate and primer/topcoat interactions, including modeling of scratches and other coating damage. The small business will incorporate this prototype paint-system model into an accurate electrochemical model of an assembly of components painted with Al-rich and Zn-rich primers, with and without topcoats, on aluminum and steel. The company will model how these primers will behave in the short and long-term in the presence of protection system damage and adjacent galvanically-coupled components of the assembly, such as stainless steels coupled to metal-rich painted aluminum. The company will apply this modeling to prediction of the behavior of assemblies such as the NAVAIR galvanic test assembly or actual representative aircraft assemblies.

PHASE III DUAL USE APPLICATIONS: The company will apply the knowledge gained in Phase II to optimize the model for certification which can be used by the Navy and commercial entities to accelerate the development, implementation and characterization of metal-rich primers and supporting materials like topcoats. The small business will support the Navy for test and validation to certify and qualify the model for Navy use. The company shall explore the potential to transfer the model to other military and commercial applications. Market research and analysis shall identify the most promising applications and the company shall develop validation plans to facilitate a smooth transition to the Navy, DOD and commercial M&P industry. Private Sector Commercial Potential: Metal-rich primers are used extensively in the commercial markets for the protection of transportation, storage, energy, facilities, and other structures. Advanced modeling capability will enable new and improved protective materials which are less costly to develop and faster to transition.

REFERENCES:

  • "Aluminum-Rich Primer" B. Skelley, 2015 DOD-Allied Nations Technical Corrosion Conference Proceedings.
  • "Reducing Stress-Corrosion Cracking with an Aluminum-Rich Primer" C. Matzdorf, 2015 DOD-Allied Nations Technical Corrosion Conference Proceedings.

KEYWORDS: metal-rich primer; protective materials; models; electrochemistry of coatings; degradation of coatings; lifetime prediction

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