Reactivity of Tannic Acid with Common Corrosion Products and Its Influence on the Hydrolysis of Iron in Alkaline Solutions

To ascertain the role of tannic acid in the anticorrosive protection of steels, the reaction between 5% tannic acid aqueous solutions with lepidocrocite, goethite, superparamagnetic goethite, akaganeite, poorly crystalline maghemite, magnetite and hematite was studied using color changes, infrared a...

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Bibliographic Details
Published in:Hyperfine interactions 2003, Vol.148/149 (1-4), p.199-209
Main Authors: Jaén, J. A., Araúz, E. Y., Iglesias, J., Delgado, Y.
Format: Article
Language:English
Subjects:
Acids
Alkalinity
Aqueous solutions
Chemical precipitation
Color
Coordination compounds
Corrosion prevention
Corrosion products
Crystal structure
Crystallinity
Degree of crystallinity
Hematite
Infrared analysis
Iron compounds
Magnetite
Mossbauer spectroscopy
Nanoparticles
Reaction products
Tannic acid
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Summary:To ascertain the role of tannic acid in the anticorrosive protection of steels, the reaction between 5% tannic acid aqueous solutions with lepidocrocite, goethite, superparamagnetic goethite, akaganeite, poorly crystalline maghemite, magnetite and hematite was studied using color changes, infrared and Mössbauer spectroscopy. After three months of interaction with lepidocrocite, the formation of an iron tannate complex was detected by its dark blue color and confirmed by infrared and Mössbauer analysis. Evidence for the chemical transformation was obtained for goethite in nanoparticles and poorly crystalline maghemite after reaction for six months. The other iron compounds do not transform to another oxide or phase upon treatment with the tannic acid solution. These results showed that lepidocrocite is the most reactive phase and that the size and degree of crystallinity have strong influence on the formation of the tannate complexes. The precipitation of iron phases from alkaline solutions of iron (II) sulfate heptahydrate containing different amount of tannic acid and potassium nitrate as oxidative agent was also studied. Mössbauer and infrared results show that in the absence of tannic acid some common rust components are obtained (viz. goethite, superparamagnetic goethite, maghemite and non-stoichiometric magnetite). The presence of 0.1% tannic acid in a low alkalinity solution results in the precipitation of iron oxyhydroxides and some iron tannates. Concentrations of 1% tannic acid are required for the formation of the tannates complexes as main reaction product.
ISSN:0304-3843
1572-9540
DOI:10.1023/B:HYPE.0000003781.45888.28