Abstract:The electrochemical behavior of mild steel in bicarbonate solution at different dissolved oxygen (DO) concentrations and immersion times has been studied under dynamic conditions using electrochemical techniques. The results show that both DO and immersion times influence the morphology of the corrosion products. In comparative tests, the corrosion rate was systematically found to be lower in solutions with lower DO, lower HCO 3 − concentrations and longer immersion time. The SEM analyses reveal that the iron dissolution rate was more severe in solutions containing higher DO. The decrease in corrosion rate can be attributed to the formation of a passive layer containing mainly α-FeO (OH) and (γ-Fe 2 O 3 /Fe 3 O 4 ) as confirmed by the X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). Passivation of mild steel is evident in electrochemical test at ≈ −600 mV SCE at pH ≥8 in dearated (≤0.8 ppm DO) chloride bicarbonate solution under dynamic conditions.

No abstract

It has been found that vortex shedding can occur from long cylinders at small angles of yaw, i.e. in near-axial flow. The range of Reynolds number over which this can take place has been determined for yaw angles between 0° and 10°. Results for vortex-shedding frequencies are also presented, and compared with existing data for larger yaw angles. It is suggested that the phenomenon may be relevant to turbulence-generation mechanisms in thick axisymmetric turbulent boundary layers.

The effect of potassium iodide (KI) and sodium nitrite (NaNO2 inhibitor on the corrosion inhibition of mild steel in chloride bicarbonate solution has been studied using electrochemical techniques. Potentiodynamic polarisation data suggest that, when used in combination, KI and NaNO2 function together to inhibit reactions at both the anode and the cathode, but predominantly anodic. KI/NO2− concentration ratios varied from 2:1 to 2:5; inhibition efficiency was optimized for a ratio of 1:1. The surface morphology and corrosion products were analysed using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). The latter shows that the addition of I− to NO2 facilitates the formation of a passivating oxide (γ-Fe2O3) as compared to NO2− alone, decreasing the rate of metal dissolution observed in electrochemical testing. The synergistic effect of KI/NO2− inhibition was enhanced under the dynamic conditions associated with testing in a rotating disc electrode.

No abstract