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Journal of Coatings Technology and Research

, Volume 15, Issue 6, pp 1201–1215 | Cite as

Diffusion cell investigations into the acidic degradation of organic coatings

  • Victor Buhl Møller
  • Ting Wang
  • Kim Dam-Johansen
  • Sarah Maria Frankær
  • Søren Kiil
Article
  • 148 Downloads

Abstract

Protective organic coatings work by preventing contact between an aggressive environment and a vulnerable substrate. However, the long required lifetime of a barrier coating provides a challenge when attempting to evaluate coating performance. Diffusion cells can be used as a tool to estimate coating barrier properties and lifetime. In this work, a diffusion cell array was designed, constructed, and compared to previous designs, with simplicity being the most important design parameter. Sulfuric acid diffusion through five different coatings was monitored using a battery of cells, and a mathematical model was developed to simulate the experimental data and to study diffusion mechanisms. The diffusion cells allowed an objective and fast analysis of coating barrier properties. It was found that sulfuric acid deteriorated these properties as it diffused through the films. This was also expressed in the modeling results, where a three-step time dependency of the diffusion coefficient was required to simulate both acid breakthrough time and the subsequent steady-state flux. A vinyl ester-based coating proved to be the most effective barrier to sulfuric acid diffusion, followed by a polyurethane coating. Amine-cured novolac epoxies provided the least effective protection.

Keywords

Permeation rate Failure mechanism Diffusion coefficient Barrier properties Mathematical modeling 

Nomenclature

A

Effective diffusion area (m\(^2\))

\(\alpha\)

Plasticization power (l/mol)

C

Concentration (mol/l)

D

Diffusion coefficient (m\(^2\)/s)

\(D_0\)

Zero-concentration diffusion coefficient (m\(^2\)/s)

F

Ion flux (mol/m\(^2 \cdot\)s)

\(l_0\)

Coating thickness (m)

t

Time (s)

V

Volume (m\(^3\))

l

Position in the coating film (m)

Subscripts

B

Breakthrough

D

Donor chamber

degraded

Acid exposed

dry

Dry

i

Initial

lag

Time lag

sat

Saturated

R

Receiver chamber

SS

Steady state

T

Transient state

virgin

Nonacid exposed

Notes

Acknowledgments

This work is part of the project ‘Minerals and Cement Process Technology—MiCeTech’ funded by Innovation Fund Denmark, FLSmidth A/S, Hempel A/S, the Hempel Foundation, and Technical University of Denmark (DTU). Performed at the Hempel Foundation center for Coating Technology and Research (CoaST).

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Copyright information

© American Coatings Association 2018

Authors and Affiliations

  1. 1.CoaST, Department of Chemical and Biochemical EngineeringTechnical University of Denmark (DTU)Kgs. LyngbyDenmark
  2. 2.Hempel A/SKgs. LyngbyDenmark

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