The negative-difference effect during the localized corrosion of magnesium and of the AZ91HP alloy

Galvanostatic tests with pure magnesium and with the AZ91HP alloy were performed in NaCl solutions, and the volume of hydrogen evolved during the tests was measured. In order to examine the negative-difference effect, a concept was developed to separate the hydrogen evolution (H.E.) on the passive s...

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Bibliographic Details
Published in:	Journal of the Brazilian Chemical Society Vol. 14; no. 4; pp. 584 - 593
Main Authors:	Weber, Cristina R., Knörnschild, Gerhard, Dick, Luís F. P.
Format:	Journal Article
Language:	English
Published:	Sociedade Brasileira de Química 01-08-2003
Subjects:	AZ91HP alloy CHEMISTRY, MULTIDISCIPLINARY localized corrosion magnesium negative-difference effect magnesium localized corrosion AZ91HP alloy negative-difference effect
Online Access:	Get full text
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Summary:	Galvanostatic tests with pure magnesium and with the AZ91HP alloy were performed in NaCl solutions, and the volume of hydrogen evolved during the tests was measured. In order to examine the negative-difference effect, a concept was developed to separate the hydrogen evolution (H.E.) on the passive surface and the H.E. inside the pits. An analysis of the volumetric data showed that the current density of H.E. inside the pits is much higher for Mg than for the AZ91HP alloy. With the assumption, that the ratio between the hydrogen reduction rate and the rate of the anodic metal dissolution, expressed by the factor k, does not change with the polarization, a k value of ca. 0.5 for pure Mg was found, while for the AZ91HP alloy this value was only ca. 0.3.
ISSN:	0103-5053 1678-4790
DOI:	10.1590/S0103-50532003000400015