KITCHEN, Matthew Paul (2021). A study into the formation of patina on copper-containing antifouling marine coatings. Doctoral, Sheffield Hallam University. [Thesis]
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31019:610435
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Kitchen_2022_PhD_StudyIntoTheFormation.pdf - Accepted Version
Available under License Creative Commons Attribution Non-commercial No Derivatives.
Kitchen_2022_PhD_StudyIntoTheFormation.pdf - Accepted Version
Available under License Creative Commons Attribution Non-commercial No Derivatives.
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Abstract
Antifouling (fouling control) coatings are used to protect underwater marine structures from the colonisation by organisms which can increase a structure's mass and reduce the efficiency of vessels. Antifouling coatings, which are used to present their attachment, contain biocidal pigments, such as cuprite (CU20) readily realising CU2+ ions into the environment, which are toxic to fouling organisms at concentrations of 10 µg. cm−2. day−1. However, these coatings may form a blue-green patina surface
layer, leading to unnecessary maintenance operations due to the perceived reduction
in protection and aesthetics, costing both time and money. Therefore, accelerated
testing methodologies are required to reproduce naturally formed patina, allowing the
patination characteristics of different coating formulations to be observed, with the
aim of reducing patina formation.
While patination of copper in the marine environment has been extensively researched, there is less information on the patination of antifouling coatings. The analysis of patinated paint flakes removed from in-service vessels found that clinoatacamite Cu2Cl(OH)3 was the most commonly detected copper patina.
DC electrochemical tests were then carried out to determine the most appropriate
environments that would result in an acceleration in antifouling coating patination.
Clinoatacamite developed in chloride containing electrolytes, with the 10% sodium
chloride electrolyte having the highest corrosion rate, while a further increase in
corrosion rate was observed in elevated temperatures up to 55°C. Analysis of the
Pourbaix diagrams for the different sodium chloride concentrations and temperatures
also found that the stability domain for Cu2Cl(OH)3 occurred between pH 6 and 8.5
with a neutral pH being selected for testing of the coatings.
The blue-green clinoatacamite patina found on in-service vessels was reproduced
when testing under immersion, evaporation, and salt spray laboratory conditions. The
quickest patination rate and highest levels of clinoatacamite were observed in the
neutral 10% sodium chloride electrolyte under immersion conditions. This was
associated with the increase in clinoatacamite density due to the reduction in patina
particle size and an overall increase in the thickness of an adherent patina layer. This
testing procedure allows for the rapid qualification of different antifouling coating
formulas and their resistance to patina formation, and therefore reduce the need for
the reapplication of coatings prior to their expected end of service life.
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