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On the anodic reaction of the co2 corrosion process, Iron carbonate nucleation and crystal grow
- 1. On the anodic reaction of the CO2 corrosion process Iron carbonate nucleation and crystal growth, Surface finish effect Omar Yepez, Nihal Obeyesekere and Jonathan Wylde
- 2. Outline • Introduction • State of the art • What is nucleation? • Experimental • Potentiodynamic transients • Simulations • Surface after cleaning the scale • Effect of a more acidic pH • Confirmation with weight loss • Conclusions
- 3. State of the art. Study of FeCO3 nucleation M. H. Sk, A. M. Abdullah, M. Ko, B. Ingham, N. Laycock, R. Arul and D. E. Williams, “Local supersaturation and the growth of protective scales during CO2 corrosion of steel: Effect of pH and solution flow” Corr. Sci. 126 (2017) 26.
- 4. State of the art. Study of FeCO3 nucleation M. H. Sk, A. M. Abdullah, M. Ko, B. Ingham, N. Laycock, R. Arul and D. E. Williams, “Local supersaturation and the growth of protective scales during CO2 corrosion of steel: Effect of pH and solution flow” Corr. Sci. 126 (2017) 26.
- 5. State of the art. Study of FeCO3 nucleation S. Nešic, K. L. J Lee, V. Ruiz, “A mechanistic model of rion carbonate film growth and the effect on CO2 corrosion of mild steel”, CORROSION 2002, paper 237”
- 7. What is nucleation. 2D nucleation of cadmium on silver 2 exp tBtAJ J t
- 9. Experimental Electrochemical cell for Nucleation
- 10. Potentiostatic transients on 15 µm at pH 6.5
- 12. Simulations. Nucleation of FeCO3 on 15 µm carbon steel 111 µm
- 14. Simulations. Nucleation of FeCO3 on 0.06 µm carbon steel 27 µm
- 16. Surface after cleaning the scale 15 µm 0.06 µm
- 17. Effect of a more acidic pH 4
- 18. Nucleation of FeCO3 on carbon steel at pH 4 15 µm 0.06 µm 0.44 µm 4.8 µm
- 19. Same surface finish but different pHs
- 20. Experimental
- 22. Conclusions • FeCO3 formation is required but not sufficient to produce a protective siderite scale. This is because it still needs to nucleate the scale. • Even after producing such scale, it needs to grow certain thickness to offer any protection. • Higher pH and rougher surfaces help to achieve good protection.
- 23. Conclusions continue • Surface finish controls the nucleation law occurring on the surface. • It was found that 0.06 µm finish is required to do not influence nucleation by an uncontrolled amount and kind of surface defects, which increase with rougher finishes. • Corrosion rates in autoclave experiments are also controlled by the siderite nucleation phenomena occurring at the interphase.
Editor's Notes
- This is the outline of the talk
- This is an example of 2D nucleation and the equation that described it. At the beginning the current growth with time because the aggregates are being formed. This occurred until the critical nucleus is produced. Then, the new phase precipitate on the substrate and the crystal growth. As the 2D crystal growth it cover the substrate quickly and the current drop dramatically. In this case with an exponential of the square of the time!
- Figure 1: Photograph of the jacketed cell for siderite nucleation measurements. From left to right: 1) Graphite counter-electrode, 2) Gas bubbler, 3) Saturated Calomel Electrode, 4) Working electrode, 5) Thermocouple.
- Figure 3: Potentiostatic transients for siderite nucleation on UNS G10180. This was performed at pH = 6.5, under 100 % CO2, 50 °C, 15 µm finish and static conditions. The over-potential applied against SCE is in the legend.() () 1 mA/cm2 = 456 mpy. Thus, the currents in this graph are between 1000-7000 mpy.
- Figure 4: Effect of surface texture on siderite nucleation experiments performed at pH = 6.5. This was under 100 % CO2 at -533 mV vs OCP (SCE), 50 °C and static conditions. The total charge (mC/cm2) of each experiment is also depicted.
- a) Simulation of the current (red) obtained with the electrode polished to 15 µm , three different nucleation events occurred at different times (cut lines). Their addition (green line) fit the experimental current. This is instantaneous nucleation described by equation (7).
- Thus, FeS nucleate under a 2 Dimensional instantaneous law with Troilite, cubic FeS and Mackinawite nucleating at the same time with different nucleation rates.
- Figure 5: b) Simulation of the current (red) obtained with the electrode polished to 0.06 µm, one nucleation event occurred (cut line). This is progressive 2D nucleation described by equation (8).
- Thus, FeS nucleate under a 2 Dimensional instantaneous law with Troilite, cubic FeS and Mackinawite nucleating at the same time with different nucleation rates.
- Figure 6: Photos of the surfaces after removing the siderite scale. On the left is the 15 µm surface: Left top with x500; left bottom x2500, pit depth = 6 µm. On the right is the 0.06 µm surface: Right top with x500; right bottom x2500, pit depth = 11 µm. pH = 6.5.
- Figure 7: Effect of surface texture on siderite nucleation experiments performed at pH = 4.0. This was under 100 % CO2 at -595 mV vs OCP (SCE), 50 °C and static conditions. The total charge of each experiment is depicted in the Figure.
- Figure 8: a) Partial simulation of the current obtained (red) with the electrode polished to 15 µm showed in Figure 7, five different nucleation events (cut lines) contributed to the total current (green line). This is instantaneous nucleation described by equation (7). b) Simulation of the experimental current (red) obtained with the electrode polished to 0.06 µm presented in Figure 7, one nucleation event occurred (cut line). This is progressive 2D nucleation described by equation (8).
- Figure 9: Siderite nucleation experiments. Both experiments were performed with 15 µm finish, 100 %CO2 at -595 mV vs OCP (SCE), 50 °C and static conditions.
- Figure 2: a) 3 Lt. Autoclave used for weight loss measurements. It has means to pressurize with CO2, a thermocouple controlled heating mantle and it can hold up to 3000 psi. It also has a rotator that can reach 1500 RPM; b) Cylinder coupons packed into a cylindrical PEEK holder. The numbers are the finished of each coupon.
- Figure 10: Weight loss experiment performed with UNS G10180 coupons. This is in 0.6 M NaCl, 1 atm CO2, 50 °C and 500 RPM. pH = 4.0.