The determination of pH,potential and chloride concentration in corroding crevices on 304 stainless steel and 7475 aluminium alloy |
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| Affiliation: | 1. Centro de Quimica Estrutural, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa, Portugal;2. Magnesium Innovation Centre MagIC, Institute of Materials Research, Helmholtz-Zentrum Geesthacht, 21502, Germany;3. Department of Materials Science and Engineering, Delft University of Technology, The Netherlands;1. Polo Universitario de Tecnología Avanzada (PUNTA), Facultad de Química, Universidad Nacional Autónoma de México (UNAM), Apodaca, Nuevo León 66629, Mexico;2. Facultad de Ciencias, Universidad Nacional Autónoma de México (UNAM), CDMX 04510, Mexico;3. Centro Nacional de Investigaciones Metalúrgicas (CENIM), CSIC, 28040 Madrid, Spain |
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| Abstract: | The conditions in a simulated crevice have been studied for type 304 stainless steel and for 7475 T651 AlZnMg alloy in 0.6 M NaCl bulk solutions. The pH has been measured with a palladium/hydrogen diffusion electrode, and the chloride concentration with a silver/silver chloride electrode. For stainless steel the results conform with the expectations of the classical crevice corrosion model, with the crevice becoming a net anode, and the pH falling as a result of chromium ion hydrolysis. For the aluminium alloy more complex results are obtained, with parts of the crevice becoming mildly acidic (pH 3–4), while the deeper parts of the crevice become slightly alkaline (pH 8). The latter observation is not readily explained in terms of the chemistry and electrochemistry of the crevice. |
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