Corrosion costs over $300 billion per year in the US, and as much as $4 billion per year to the Navy alone.  The most cost effective method for preventing rust is to paint the surface.  This protection, however, is only temporary, as paint inevitably develops scratches.  The ability to make more durable coatings must be balanced against the convenience of spray painting.  The latter effectively limits the feasible options to polymeric coatings, which, in turn, constrains the maximum achievable wear resistance.  Rather than pursuing incremental improvements in damage resistance under these constraints, greater gains may be made through the development of damage tolerant coatings.  To this end, we present a paint additive that confers self-healing properties to commercial-off-the-shelf (COTS) primers.  Used in conjunction with zinc-rich primers, it can prolong the lifetime of galvanic protection afforded by the sacrificial zinc.  Whether the self-healing agent in the microcapsule is able to protect the exposed surface from corrosion depends upon three steps: i) How long the agent takes to wet the exposed metal; ii) How long the agent takes to form an effective barrier layer; and iii) What happens to the surface before the first two steps complete.  Under the right conditions, passivation of exposed steel delays the onset of corrosion for 6 weeks in a salt fog chamber, which compares to hours for a conventional paint and 1 week for a zinc-rich paint.  Electrochemical impedance spectroscopy reveals how the mechanism of chemical passivation working in conjunction with cathodic protection is better than either strategy alone.

Before, during, and after the scratch: Damage-tolerant paints with self-healing microcapsules

248th National Meeting (2014)

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