Date of Defense
21-11-2024 2:30 PM
Location
F3-032
Document Type
Thesis Defense
Degree Name
Master of Science in Chemistry
College
COS
Department
Chemistry
First Advisor
Dr. Ahmed Alshamsi
Keywords
Corrosion, 304 austenitic stainless steel, NaCl, molybdate (MoO42-), tungstate (WO42-), passive film, pitting corrosion, concentration of Cl-, inorganic inhibitor, sulfuric acid.
Abstract
In this study, the corrosion behavior of 304 austenitic stainless steel was investigated in H2SO4 solutions, H2SO4 as a function of Cl- ions concentration, H2SO4 as a function of MoO42- ions concentration, and H2SO4 + Cl- ions as a function of MoO42- ions concentration. Moreover, the synergistic inhibition of MoO42- and WO42- ions was investigated in 0.1 M H2SO4, with the solution pH adjusted to 3.0. The findings show that the corrosion current density (icorr) increases while the polarization resistance (Rp) decreases with increased H2SO4 concentrations in the absence of Cl- ions. In the presence of Cl- ions, icorr increases whereas Rp decreases with increasing Cl- concentration in ≤1M H2SO4 solutions. In contrast, in concentrations ≥ 2M H2SO4, icorr decreases while Rp increases with increasing Cl- ions concentration up to ~ 0.5-1.0 M Cl- ions concentration, while the trend is reversed in concentrations ≥ 1M NaCl as the Rp decreases and icorr increases with increasing Cl- ions concentration. The pitting potential (Epit) decreases as Cl- ions concentration increases in a given H2SO4 concentration as expected; however, no correlation is found between Epit and [Cl-]/[H2SO4] ratio or Epit and [Cl-] when solutions of different concentrations of H2SO4 + Cl- were taken into consideration.
The MoO42- ions acted as an excellent corrosion inhibitor in H2SO4 solutions in the absence of Cl- ions, with the IE% exceeding 99%. However, in H2SO4 solutions in the presence of Cl- ions, MoO42- ions acted both as a corrosion accelerator and a corrosion inhibitor depending on the concentrations of H2SO4, Cl- ions, and MoO42- ions, with the inhibition tendency increasing with the decrease in the Cl- concentration and the increase in the MoO42- concentration. For the MoO42- ion to effectively induce inhibition in H2SO4 + NaCl solutions, its concentration must be high enough to shift the corrosion potential to the passive range in the polarization curves. Finally, both MoO42- and WO42- ions acted as excellent corrosion inhibitors of 304 stainless steel in 0.10 M H2SO4 (pH = 3.0), with the two ions showing a synergistic inhibition effect, with the maximum corrosion inhibition occurring when a 1:1 concentration ratio was used.
Included in
CORROSION BEHAVIOR OF 304 STAINLESS STEEL IN H2SO4/NACL IN THE ABSENCE AND PRESENCE OF MOLYBDATE AND TUNGSTATE
F3-032
In this study, the corrosion behavior of 304 austenitic stainless steel was investigated in H2SO4 solutions, H2SO4 as a function of Cl- ions concentration, H2SO4 as a function of MoO42- ions concentration, and H2SO4 + Cl- ions as a function of MoO42- ions concentration. Moreover, the synergistic inhibition of MoO42- and WO42- ions was investigated in 0.1 M H2SO4, with the solution pH adjusted to 3.0. The findings show that the corrosion current density (icorr) increases while the polarization resistance (Rp) decreases with increased H2SO4 concentrations in the absence of Cl- ions. In the presence of Cl- ions, icorr increases whereas Rp decreases with increasing Cl- concentration in ≤1M H2SO4 solutions. In contrast, in concentrations ≥ 2M H2SO4, icorr decreases while Rp increases with increasing Cl- ions concentration up to ~ 0.5-1.0 M Cl- ions concentration, while the trend is reversed in concentrations ≥ 1M NaCl as the Rp decreases and icorr increases with increasing Cl- ions concentration. The pitting potential (Epit) decreases as Cl- ions concentration increases in a given H2SO4 concentration as expected; however, no correlation is found between Epit and [Cl-]/[H2SO4] ratio or Epit and [Cl-] when solutions of different concentrations of H2SO4 + Cl- were taken into consideration.
The MoO42- ions acted as an excellent corrosion inhibitor in H2SO4 solutions in the absence of Cl- ions, with the IE% exceeding 99%. However, in H2SO4 solutions in the presence of Cl- ions, MoO42- ions acted both as a corrosion accelerator and a corrosion inhibitor depending on the concentrations of H2SO4, Cl- ions, and MoO42- ions, with the inhibition tendency increasing with the decrease in the Cl- concentration and the increase in the MoO42- concentration. For the MoO42- ion to effectively induce inhibition in H2SO4 + NaCl solutions, its concentration must be high enough to shift the corrosion potential to the passive range in the polarization curves. Finally, both MoO42- and WO42- ions acted as excellent corrosion inhibitors of 304 stainless steel in 0.10 M H2SO4 (pH = 3.0), with the two ions showing a synergistic inhibition effect, with the maximum corrosion inhibition occurring when a 1:1 concentration ratio was used.