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Monitoring of vitreous enamel degradation by electrochemical noise

By Estrela, P.; Migliorato, P.; Takiguchi, H.; Fukushima, H. & Nebashi, S.
Published in Surface and Coatings Technology 2002

Abstract

Vitreous coatings are widely used for protecting steel at temperatures up to 600 °C in applications where high oxidation- and wear-resistance are required. However, the action of alkaline chemical agents such as household cleaning products can cause the devitrification and spalling of these coatings, with the consequent loss of their protective properties. In such cases, corrosion of the substrate is accelerated due to the heat treatment applied during the manufacturing process of the coating -- tempering or curing. The present work characterizes the initial stages of this deterioration using the electrochemical noise technique (EN). When coatings are undamaged the current noise is very low, with current intensity values of the order of picoamperes. However, when defects appear as a result of chemical attack, the systems electrical activity changes considerably and there is an increase in both current and potential noise. This work also establishes the loss of the coatings protective nature as a function of spectral noise resistance, Rsn, finding good concordance with values obtained by other more conventional techniques such as electrochemical impedance.

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