Corrosion of Mg alloy in the presence of ammonium ion. Evidence of hydride sub-products

• Published in: Corrosion science Vol. 104; pp. 173 - 186
• Main Authors: Buggio, Davide, Trueba, Monica, Trasatti, Stefano P.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2016
• Subjects: A. Magnesium; C. Hydrogen absorption; C. Negative difference effect; A. Magnesium; C. Hydrogen absorption; C. Negative difference effect
• ISSN: 0010-938X; 1879-0496
• DOI: 10.1016/j.corsci.2015.12.008

•Remarkable reactivity of Mg/NH4+ system manifested by copious evolution of hydrogen over a dark corrosion film.•Complex hydride corrosion subproducts favored by the alteration of the dissociation equilibrium of water.•Chemical recombination of hydrogen atoms composing the complex hydrides as kinetically determinant process. Corrosion of AZ31 Mg alloy was systematically investigated by different experimental approaches in the presence and in the absence of NH4+. Remarkable reactivity of Mg/NH4+ system was manifested by copious evolution of hydrogen over a dark corrosion film, associated to active deprotonation of complex Mg hydrides, more likely bridged {Mg2+(AlH4−)2Mg2+(H−)2} complexes covered by a skin of MgO. Metastability of hydride phases is favored in the presence of species that alter the equilibrium dissociation of water, such as NH4+ and SO42−. Chemical recombination of hydrogen atoms of oxidic Mg hydrides is proposed as the kinetically determinant process.