Fig. 1 Schematic of wet-dry acid corrosion test device

Fig. 2 SEM micrographs of the bare steels: a blank steel; b W steel; c Mo steel

Fig. 3 Corrosion loss of the steels in wet-dry acid corrosion environments with different O2 concentrations of a 1%; b 5%

Fig. 4 Potentiodynamic polarization curves of the bare steels in 0.01 M Na2SO4 solution with pH 3.0 and at temperature of 25 °C

Fig. 5 EIS plots of the bare steels tested in 0.01 M Na2SO4 solution with pH 3.0 and at temperature of 25 °C

Fig. 6 Equivalent circuit for fitting EIS plots of the bare steels tested

Fig. 7 EIS plots of rusted steels in 1% O2 wet-dry acid corrosion: a, b 14 CCT; c, d 28 CCT; e, f 42 CCT

Fig. 8 Equivalent circuit for fitting EIS plots of rusted steels

Fig. 9 EIS plots of the rusted steels in 5% O2 wet-dry acid corrosion: a, b 14 CCT; c, d 28 CCT; e,f 42 CCT

Fig. 10 SSA of the rust at 42 CCT in wet-dry acid corrosion with O2 concentrations of a 1%; b 5%

Fig. 11 Cross-sectional morphologies of the rusts at 42 CCT in wet-dry acid corrosion: a-c for the blank steel, W steel, and Mo steel under O2 concentration of 1%; d-f for the blank steel, W steel, and Mo steel under O2 concentration of 5%

Fig. 12 Distribution of the elements W and Mo in the rust at 42 CCT in wet-dry acid corrosion: a W 1% O2; b Mo 1% O2; c W 1% O2; d Mo 5% O2