Final Report - Strategic Environmental Research and Development ...

Potential (mV vs. SCE)
Potential (mV vs. SCE)
the whole surface with significant amount of sulfur detected over the intermetallic particles
(Figure 2.26). SEM analysis also revealed that the S-phase particles were still intact underneath
the formed film. XPS characterization showed significant amounts of sulfur in the film with no
trace of Pr. The only source of sulfur in the solution is from H 2 SO 4 , which was added to adjust
the pH. These observations suggest that the film formed over the surface is not owed to
praseodymium inhibition but to the presence of this incidental sulfur concentration.
Figure 2.23. XRD pattern after 30 days immersion 0.1 M NaCl solution with 0.2 mM
Pr 3+ .
In high pH solution (pH 10), SEM analysis revealed the deposition of corrosion product across
the surface rich in Pr (Figure 2.27). Furthermore, thick-oxide precipitates rich in Pr were present
over both S-phase and FeMn(Si) intermetallic particles. Interestingly, virtually no inhibition was
observed electrochemically to correlate with the oxide precipitation (Figure 2.24b).
-400
-400
-600
-600
-800
-1000
No inhibitor
0.2 mM
-800
-1000
No inhibitor
0.2 mM
-1200
-1200
-1400
10 -9 10 -8 10 -7 10 -6 10 -5 0.0001 0.001 0.01
Current Density (A/cm 2 )
-1400
10 -10 10 -9 10 -8 10 -7 10 -6 10 -5 0.0001 0.001
Current Density (A/cm 2 )
(a)
(b)
Figure 2.24. Naturally aerated polarization curves in 0.2 mM Pr 3+ containing solution
at pH (a) 4 and (b) 10.
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