Alejandro Samaniego

Hydrogen Evolution During Anodic Polarization of Mg Alloyed with Li, Ca, or Fe

The origin of high rates of hydrogen evolution (HE) on dissolving Mg, the so-called negative difference effect, remains of practical interest. Recent studies have suggested that the ability of Mg to support the cathodic reaction is enhanced during dissolution and that enrichment of noble impurity elements at the dissolving Mg surface may also play a role in enhanced rates of HE. To begin to uniquely address the role played by other elements, Mg was intentionally alloyed with Li, Ca, or Fe. Hydrogen collection was performed during anodic galvanostatic polarization tests. An Mg-Li alloy containing 33 at% Li exhibited similar rates of anodic HE as pure Mg. Because Li dissolves with a valence of 1, any mechanism of anodic HE involving a lower valence state such as Mg+, is therefore ruled out. Mg-Ca and Mg-Fe alloys exhibited higher rates of anodic HE than pure Mg. They also exhibited a minimum of the HE rate under cathodic polarization instead of at the open-circuit potential, the latter being the case for pu...

Effect of Native Oxide Film on Commercial Magnesium Alloys Substrates and Carbonate Conversion Coating Growth and Corrosion Resistance

Possible relations between the native oxide film formed spontaneously on the AZ31 and AZ61 magnesium alloy substrates with different surface finish, the chemistry of the outer surface of the conversion coatings that grows after their subsequent immersion on saturated aqueous NaHCO3 solution treatment and the enhancement of corrosion resistance have been studied. The significant increase in the amount of aluminum and carbonate compounds on the surface of the conversion coating formed on the AZ61 substrate in polished condition seems to improve the corrosion resistance in low chloride ion concentration solutions. In contrast, the conversion coatings formed on the AZ31 substrates in polished condition has little effect on their protective properties compared to the respective as-received surface.

Different Performance of Factors Affecting the Estimation of the Corrosion Rate in Magnesium Alloys by Implementation of the Common Methods for Electrochemical Measurements

financial support for this work from the Ministry of Science and Innovation of Spain (MAT n2009-13530)