937920.fig.007a
(a)
937920.fig.007b
(b)
937920.fig.007c
(c)
Figure 7: Potentiodynamic polarization curves of steel immersed in aerated 0.1 mol L−1 Na2SO4 solution (pH 2.5) in the presence of tannin ( 1 ) and absence of tannin ( 2 ) for (a) 1 day, (b) 3 days, and 7 days.