Fig. 1. (a) Typical samples for SVET/SIET experiments (b) SVET/SIET scanning chamber showing the sample-probe (electrodes) arrangement.

Fig. 2. Typical polarization curves of the Q-phase (anodic branch) and pure Al in 0.1 M NaCl solution at different pH values.

Fig. 3. Typical polarization curves of the Q-phase (cathodic branch) and pure Al in 0.1 M NaCl solution at different pH values.

Fig. 4. Variation of galvanic current and potential between the Q-phase and pure Al in 0.1 M NaCl solutions in pH 2, 6 and 12 solutions. (The surface area of each electrode is 1 cm2).

Fig. 5. SVET current density distribution over the Q-phase/Al couple in 0.1 M NaCl solution at pH 2 after (a) 1 h, (b) 6 h, (c) 24 h and (d) optical micrograph after 24 h.

Fig. 6. SVET current density distribution over the Q-phase/Al couple in 0.1 M NaCl solution at pH 6 after (a) 1 h, (b) 6 h, (c) 24 h and (d) optical micrograph after 24 h.

Fig. 7. SVET current density distribution over the Q-phase/Al couple in 0.1 M NaCl solution at pH 13 after (a) 1 h, (b) 6 h, (c) 24 h and (d) optical micrograph after 24 h.

Fig. 8. SVET current density distribution over the uncoupled Q-phase in 0.1 M NaCl after 1 h solution at (a) pH 2, (b) pH 6, (c) pH 13 and the corresponding optical micrographs at (d) pH 2, (e) pH 6, (f) pH 13.

Fig. 9. Comparison of the average negative current densities on the surface of coupled and uncoupled Q-phase after SVET tests at (a) pH 2, (b) pH 6 and (c) pH 13.

Fig. 10. Consecutive SIET-SVET scan of the Q-phase/Al couple after 1 h in 0.1 M NaCl solution at pH 6: (a) SVET current density map, and (b) SIET pH map.

Fig. 11. EDX evaluation of the relative atomic percentages of the component elements in the Q-phase surface after 24 h of SVET test in 0.1 M NaCl solution at pH 2, 6 and 13.