Fig. 3

Chemical stability diagram showing the equilibrium conditions for the most stable corrosion product compounds (thick solid lines) for the Zn²⁺/ZnO (red, line 8.3) and Mg²⁺/Mg(OH)₂ (blue, line 8.1) systems, respectively. The trajectory lines describing the evolution of solution pH and metal ion concentration (thin dashed lines) with respect to [Zn²⁺] (red, 1.1) and [Mg²⁺] (blue, 1.2) are shown. The trajectory for Zn dissolution follows line 1.1 and then the equilibrium boundary for Zn²⁺/ZnO equilibrium line 8.3 upon intersecting it as noted by the red arrow. The Mg chemical trajectory follows the paths indicated; one path prior to the intersection of the Zn dissolution and equilibrium boundary (line 1.2) and a different path after that intersection (line 2), as noted by the blue arrow. The boundaries between the regions of pH where different aqueous Zn-based ions are predominantly stable are indicated by thin vertical dotted lines at the pH value for which the two ions are equal in concentration