July 30 - August 5, 2012
What is the effect of using a lower-metallic-content zinc-rich epoxy on the life of a paint system?
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Derek Righinni of Certified Coating Inspection Ltd on
August 30, 2012:
To my knowledge zinc-rich epoxy is not, as a rule, loaded with zinc to the critical pigment concentration where the zinc pigments are touching and in electrical contact, and so it is not considered a true sacrificial coating unless the binder is electrically conductive. There may be some confusion here with zinc-rich ethyl silicate paints loaded with zinc to 90% by dry weight, which is truly sacrificial. The zinc pigment in zinc-rich epoxies may be adding to the barrier properties of a coating and may offer some galvanic protection. The question above needs clarifying about quantities: lowering the metallic content from what % to what % and what is the proposed paint system? I hope this helps. (ICorr 3, NACE 3)
Greg Girard of The Chidley and Peto Company on
August 8, 2012:
Studies have shown that there is a lower zinc content than current levels that can be highly effective while maintaining zinc-to- zinc contact. The accelerated, long-term testing shows equal to improved performance, due to improved flow and the ability to maintain the zinc-to-zinc electrochemical connections. Many real world testing applications have been done and these are showing consistent good performance at two years. Testing continues. Based on accelerated testing, it would appear that a lower zinc level would not necessarily decrease performance.
Dennis Snijders of APS Dubai on
August 3, 2012:
In atmospheric conditions, your coating will have a shorter expected service life.
Jay Mitchell of James Hardie Building Products on
August 28, 2012:
Other factors affect the ability of a sacrificial coating to provide substrate protection. For example, permeability, resin matrix and auxiliary pigment conductivity, as well as mechanical properties such as adhesion, flexibility, and sometimes even UV- and free-radical-degradation resistance. The nominal level of zinc required is a function of the coating properties, the environmental exposure and the level of expectation of product performance and longevity. This must be determined empirically for new technologies rather than relying on accepted levels from prior art.
jonathan arguelles of megapaint and coating corp. on
August 1, 2012:
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It will not be effective as cathodic protection compared to high zinc content since corrosion protection depends on its zinc content. The contact between zinc-to-zinc particles and zinc-to-metal substrate plays a vital role for corrosion protection; therefore, the more zinc content, the more "contacts" it would create.
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