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PublisherNACE InternationalLanguageEnglish
Document ID 07358
Content TypeConference Paper
TitleOrganic Corrosion Inhibitors for Interim Corrosion Protection
AuthorsFrank Dietsche, Manfred Essig, Ralf Friedrich, Michael Kutschera,Wolfgang Schrepp, Helmut Witteler,Product Development Metal Surface Treatment,BASF Aktiengesellschaft, Michael J. Anchor, Klaus Friedrich,Performance Chemicals Applications,BASF Corporation
SourceCORROSION 2007, March 11 - 15, 2007 , Nashville, Tennessee
Copyright2007. NACE International
Keywordscorrosion inhibitors, anticorrosive polymers, conversion coating, interim corrosion protection
PreviewABSTRACT

The prevention of uniform corrosion on metal parts subsequent to surface treatment operations is becoming a key problem, after increasingly complex legal requirements and ecotox issues have caused the ban or the de-facto abandonment of various well-tried corrosion inhibiting actives. In this presentation, the potential of organic corrosion inhibitors for interim corrosion protection is demonstrated. After a brief survey on structure and function of organic corrosion inhibitors, examples dealing with uniform corrosion as it occurs during manufacturing, storage, or transportation of metal parts are discussed. Immersion tests, weathering, electrochemical measurements, and microscopy are used to monitor the effect of different classes of organic inhibitors and their synergy with other additives.

INTRODUCTION

The ban or the de-facto abandonment of various well-tried corrosion inhibiting substances is caused by
  • legislation or legislation in preparation that prohibits the use of selected chemical species in specified applications and/or that specifies limits for selected chemical species in waste (for examples see ref. 1, 2)
    • (available in full paper)
  • non-legislative initiatives of manufacturers who proactively limit the use of particular compounds as feedstock (for example see ref. 3)
    • (available in full paper)
  • official records that summarize toxicological data of chemical compounds and that list compounds that are toxic, sensitizing, carcinogenic, mutagenic, and toxic for reproduction (for example see ref. 4)
    • (available in full paper)
  • independent studies that influence the perception of potential risks associated chemical compounds or groups of compounds (for examples see ref. 5).
    • (available in full paper)


Not only substances with overwhelming toxicological or ecological deficiencies, such as chromate, have been banned. Also species that are significantly less problematic are presently being discussed, such as zinc, phosponates and phosphate. In view of these facts, it appears reasonable to focus on substitutes that per se are expected to be less problematic. For instance, this is the case for polymers.

Corrosion inhibitors have been divided into many groups, such as cathodic and anodic inhibitors, inorganic and organic corrosion inhibitors, filming and non-filming inhibitors, and many more (Ref. 6) (available in full paper). The focus of this study is on organic corrosion inhibitors of polymeric nature that readily dissolve in water. These polymeric corrosion inhibitors act just as ordinary inhibitors while they are dissolved in the corrosive medium, i. e. they limit the corrosiveness of the organic medium. After an aqueous solution of the polymeric inhibitor has been used to impregnate a metal surface and the water has dried off, the inhibitor may act as an anticorrosive coating. Polymeric corrosion inhibitors are different from polymer coatings in that they exhibit a specific interaction with the surface before a dry film is formed. Polymeric corrosion inhibitors do not necessarily form a barrier against oxygen and water but they change the corrosion potential of a metal. In this respect, they are similar to low-molecular weight corrosion inhibitors, which make up the great majority of organic corrosion inhibitors.

Low-molecular weight corrosion inhibitors often affect the surface tension of water, they may in fact be surfactants, and they form a surfactant-like monolayer on metal surfaces, thus protecting the metal surface (Fig.1).
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