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Coatings 2015, 5(4), 816-829; doi:10.3390/coatings5040816

Natural Deposit Coatings on Steel during Cathodic Protection and Hydrogen Ingress

1
National Structural Integrity Research Centre, Granta Park, Cambridge CB21 6AL, UK
2
TWI, Granta Park, Cambridge CB21 6AL, UK
*
Author to whom correspondence should be addressed.
Academic Editor: Alessandro Lavacchi
Received: 29 September 2015 / Revised: 27 October 2015 / Accepted: 6 November 2015 / Published: 12 November 2015
(This article belongs to the Special Issue Trends in Coatings and Surface Technology—Feature Papers)
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Abstract

The calcareous coating formed during cathodic protection (CP) in seawater is known to reduce the current demand by hindering the transport of species required to support the cathodic reactions and, thereby, improve the economic performance of CP systems. There is, however, uncertainty as to whether the coating reduces hydrogen uptake or indeed enhances it. To ascertain this, two sets of samples were polarized at −1.1 V (standard calomel electrode, SCE) in 3.5% w/v NaCl and synthetic seawater (ASTM D1141) at 20 °C and the diffusible hydrogen content measured over a period of 530 h. Under such conditions reports suggest a deposit with two distinct layers, comprising an initial brucite layer followed by an aragonite layer. Contrary to other findings, a fine initial layer containing Ca and Mg followed by a brucite layer was deposited with a few specks of Ca-containing zones in synthetic seawater. The hydrogen uptake was found to occur within the initial 100 h of exposure in synthetic seawater whilst it continued without the benefit of a deposit coating, i.e., in 3.5 wt % NaCl solution. View Full-Text
Keywords: natural; coating; cathodic protection; hydrogen; brucite; calcareous deposit natural; coating; cathodic protection; hydrogen; brucite; calcareous deposit
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Smith, W.R.; Paul, S. Natural Deposit Coatings on Steel during Cathodic Protection and Hydrogen Ingress. Coatings 2015, 5, 816-829.

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