Influence of Ga content on electrochemical behavior of Mg-5 at%Hg anode materials

The effects of Ga content on the electrochemical behavior of Mg-5 at%Hg alloys which contain a small amount of Ga was investigated by the measurement of polarization curves and galvanostatic test. The microstructure of the alloys and the surface of the specimens corroded in galvanostatic test were observed by using scanning electron microscopy, energy spectrum analysis and X-ray diffraction analysis. It can be concluded that with the content of Ga increasing, the alloys come into Mg-Mg3Hg, Mg-Mg-7.2(Hg, Ga)(2.8) and Mg-Mg5Ga2 binary phase fields sequentially. The best electrochemical activity occur in the Mg-5 at%Hg-1 at%Ga alloy, with open circle potential -2.124 V and mean potential -1.992 V. The corrosion resistance of the alloys is in the sequential order from big to small: Mg-5 at%Hg-5 at%Ga, Mg-5 at%Hg-22 at%Ga, Mg-5 at%Hg-1 at%Ga, Mg-5 at%Hg. The lowest corrosion current density is 0.418 mA.cm(-2) The activation mechanism of the magnesium alloy produced by Hg and Ga was concluded: the dissolution of Hg and Ga atoms leads to the back accumulation of liquid Hg and Ga, which makes a true metallic contact with a-Mg. Magnesium atoms diffuse through the liquid mercury and gallium to form magnesium amalgam and undergo severe oxidation at the amalgam/electrolyte interface. The reaction produces pure Hg and Ga again which continue the activation process.