Stuttgart, Germany
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Rammelt U.,EXCOR Korrosionsforschung GmbH | Koehler S.,EXCOR Korrosionsforschung GmbH | Reinhard G.,EXCOR Korrosionsforschung GmbH
Corrosion Science | Year: 2011

Electrochemical measurements (electrochemical impedance spectroscopy (EIS), polarisation and open circuit potential (OCP) measurements) were used to study the corrosion protection of mild steel in aerated neutral solution of selected dicarboxylates. It was shown that all investigated carboxylates are effective in the presence of air. Most of the carboxylates act predominantly at local defects in the primary oxide layer by forming of weakly soluble Fe(III) compounds, in agreement with the pore plugging concept. As known, carboxylates, which can also be adsorbed on the oxide covered mild steel surface, should own an enhanced efficiency. It was found that the adsorption ability of dicarboxylates their selves are weak, but the corrosion protective effect could be improved considerably, if mixtures of dicarboxylates with monocarboxylates are used. The additional inhibition effect was ascribed to the ability of monocarboxylates to adsorb stronger on the oxide covered mild steel surface than dicarboxylates. The sebacate/caprinate mixture provides the best protection comparable with the synergistic effect observed with carboxylate in the presence of benzotriazole, too. © 2011.


Rammelt U.,EXCOR Korrosionsforschung GmbH | Koehler S.,EXCOR Korrosionsforschung GmbH | Reinhard G.,EXCOR Korrosionsforschung GmbH
Corrosion | Year: 2011

The ability of some typical vapor phase corrosion inhibitors (VCI) to protect mild steel toward corrosion in neutral and alkaline solutions was studied. The inhibition mechanism was investigated by electrochemical methods such as open-circuit potential (OCP) measurements, polarization curves, and electrochemical impedance spectroscopy (EIS) exemplary in aerated cyclohexylamine salt solutions with different weak and strong acid anions. It was found that weak acid anions like benzoate play a dual role in the inhibition mechanism: under near-neutral conditions they can occlude defects in the airformed oxide layer by precipitation of insoluble salts or basic salts with ferric ions, and in strong alkaline solutions they act as a buffer of pH inside the defect sites and limit the localized accumulation of protons. However, in the pH range between 9.0 and 10.3, passivation of mild steel is not possible with all investigated cyclohexylamine salts. © 2011, NACE International.


Koehler S.,EXCOR Korrosionsforschung GmbH | Rammelt U.,EXCOR Korrosionsforschung GmbH | Reinhard G.,EXCOR Korrosionsforschung GmbH
European Corrosion Congress 2011, EUROCORR 2011 | Year: 2011

In general, polymer based packaging materials are used in order to protect metallic equipment during transport and storage against atmospheric corrosion. This temporary corrosion protection is achieved by incorporation of vapour phase corrosion inhibitors (VCIs, volatile corrosion inhibitors) in the polymer film, whereby the packaging material functions as a VCI source. Protection is necessary especially during the time of wetness, where the metal surface can corrode due to the formation of a thin electrolyte layer on the surface. Therefore, the efficiency of a compound used as VCI mainly depends on two parameters: 1. its vapour pressure ( more exactly: its tendency to sublimate) under atmospheric conditions is high enough allowing significant vapour phase transport of the inhibitor within an enclosed space to the metal surface; 2. the VCI adsorbed directly on the metal surface or dissolved in a condensed water film on the metal surface inhibits the metal corrosion during storage and transport by interaction with the surface. Within this paper calculations should be presented to estimate the minimum need of VCI in dependence on the volume of closed packages, the surface roughness of the goods and the exposed temperature. Further, the transport of the VCI in the atmosphere of a densely closed package by diffusion and natural convection should be discussed. These findings can be used to approximate the conditioning time. In the second part results of electrochemical measurements like the measuring of the free corrosion potential and recording of electrochemical impedance spectra should be presented characterizing the interaction of VCIs like benzotriazole or benzoic acid/ benzoate with oxide covered metal surfaces in the presence of a condensed water layer. Thereby, mechanisms of action (e.g. adsorption and/or formation of insoluble salts to seal defects in the oxide layer) shall be derived from the data. Finally, the efficiency of VCI containing package materials should be demonstrated by self-developed climatic tests. Here, decreased mild steel test panels are packed into VCI containing package materials as well as in respective VCI free reference materials. Both kinds of packages are exposed to an alternating climate according to IEC 60068-2-30. Comparison of surfaces' quality after a defined number of cycles allows evaluating the efficiency of the respective VCI containing package material.

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