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51316-7214-40 Years of José R. Galvele´s Localized Acidification Pitting Model: Past Present and Future

In the present work a brief description of the mechanism development and examples of the pitting and crevice systems that have confirmed the validity of this localized acidification mechanism for stable pitting growth. Potential future lines of work are also briefly suggested.

Product Number: 51316-7214-SG
ISBN: 7214 2016 CP
Author: Alberto Keitelman
Publication Date: 2016
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The localized acidification mechanism for stable pitting growth was the result of the pitting research performed in the Corrosion Laboratory of the CNEA led by Dr. J.R. Galvele. The key point of the mechanism is that there is a pH drop on the anode surface and that this pH drop is a necessary condition to sustain pitting.The idea that aggressive anions lead to pitting by causing the pH at the anode to fall to values where no solid products would be formed on the metal surface has been already supported by various authors. Galvele and co-workers modified those mechanisms by taking into account the hydrolysis of the metal ions inside the pit. The analysis of the transport processes taking place inside a pit allowed to explain the pitting potentials of such metals as zinc cadmium aluminum or iron. It has also been shown that these transport process studies give a quantitative explanation of the influence of solution pH reducible ions buffer ions and inhibitors on the pitting potential and they also give an explanation of the existence of a pitting repassivation potential. In the present work a brief description of the mechanism development and examples of the pitting and crevice systems that have confirmed its validity are going to be presented.Potential future lines of work that would advance (using Galvele´s model)present understanding of several issues of pitting and crevice phenomena not yet elucidated mechanistically are also briefly suggested.

Key words: downloadable, pitting, mechanism, acidification

The localized acidification mechanism for stable pitting growth was the result of the pitting research performed in the Corrosion Laboratory of the CNEA led by Dr. J.R. Galvele. The key point of the mechanism is that there is a pH drop on the anode surface and that this pH drop is a necessary condition to sustain pitting.The idea that aggressive anions lead to pitting by causing the pH at the anode to fall to values where no solid products would be formed on the metal surface has been already supported by various authors. Galvele and co-workers modified those mechanisms by taking into account the hydrolysis of the metal ions inside the pit. The analysis of the transport processes taking place inside a pit allowed to explain the pitting potentials of such metals as zinc cadmium aluminum or iron. It has also been shown that these transport process studies give a quantitative explanation of the influence of solution pH reducible ions buffer ions and inhibitors on the pitting potential and they also give an explanation of the existence of a pitting repassivation potential. In the present work a brief description of the mechanism development and examples of the pitting and crevice systems that have confirmed its validity are going to be presented.Potential future lines of work that would advance (using Galvele´s model)present understanding of several issues of pitting and crevice phenomena not yet elucidated mechanistically are also briefly suggested.

Key words: downloadable, pitting, mechanism, acidification

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