H. C. Lin

Effects of AC-Modulated Passivation and Post-Treatment on Composition and Stability of Passive Films

Abstract An investigation of the effects of alternating voltage modulated passivation (AC-modulated passivation) and post-treatment on the composition and stability of passive films on 302 and 316 stainless steels by ellipsometry, electrochemistry, and surface Auger electron spectroscopy analysis was carried out. AC-modulated passivation increases the concentration of elements O, and the ratio Cr/ (Cr + Fe) in the passive film, changes the depth composition profile of the film, roughens the surface of the passive film and makes it more favorable to the adsorption of molybdenum-containing ions during post-treatment. Hence, the resistance against the chemical dissolution of the passive film increased and the stability of the passive film improved.

The stability of the transpassive film on 304 stainless steel with post-treatment

Abstract Investigation on the stability of transpassive film on 304 stainless steel was carried out by ellipsometric measurement, AES and XPS analyses and examination of the breakdown potential, E b , in a Cl − -containing solution and the active dissolution time t a in an acidic medium. It is found that the t a of properly transpassivated film is almost 2 orders of magnitude longer than that of normally passivated film, and that the E b of the film which is post-treated in a molybdate-containing solution is much higher than that of the passive film formed in the passive region with the same post-treatment. The results of ellipsometric measurement show that the thickness of the film on the stainless steel increases with the positive shift of the anodic polarization potential, especially in the transpassive region, and the thickness of the transpassive film increases much more sharply than in the passive region. Moreover, AES and XPS analyses indicate that the transpassivated film consists of much more Fe 3+ and much less Fe 2+ than the passivated one, and this film with proper post-treatment contains much more Mo than the film formed in the passive region with the same post-treatment. It is believed that the increase of stability of the surface film obtained by transpassivation and post-treatment is ascribed to the increase of film thickness, the rise of the ratio Fe 3+ /Fe 2+ and the adsorption of Mo into the film during the post-treatment.

Inhibition Effects of l− and l2 on Stress Corrosion Cracking of Stainless Steel in Acidic Chloride Solutions

Abstract Stress corrosion cracking (SCC) of AISI 321 (UNS S32100) stainless steel (SS) in 0.5 mol/L sodium chloride (NaCl) + 0.5 mol/L hydrochloric acid (HCl) solution and the inhibition effects of...

Electrochemical impedance spectroscopy study on the diffusion behavior of water through epoxy coatings

The diffusion behavior of water through epoxy coatings with micaceous iron oxide (MIO) at different pigment volume concentration (PVC) was studied by EIS techniques. Experimental results showed that, in the initial diffusion period, the diffusion processes of water through epoxy coatings immersed in 0.5 M sodium chloride (NaCl) solution followed Ficks second law. The diffusion coefficients of water through the coatings were also calculated. Within the PVC values that were studied, the diffusion coefficients of water through epoxy coatings decreased with increasing PVC, indicating that the barrier property of the pigment was the main factor affecting the water diffusion behavior.

Quantum chemistry study on the effect of Cl- ion on anodic dissolution of iron in H2S-containing sulfuric acid solutions

The effect of Cl- ion on the anodic dissolution of iron in H2SO4 solutions containing low H2S level has been studied by electrochemical polarization curve measurements. The total energy and binding energy of the competitive adsorption for Cl- and HS- ions have been calculated with CNDO/2 method, as well as the net charge distribution of iron atoms at an anodic potential. The results showed that certain concentration of Cl- ion inhibit the anodic reaction of iron accelerated by HS-. However, when Cl- ion reached saturated adsorption, it began to promote the anodic reaction of iron due to the increased negative charge of iron atoms

Inhibitive effect of benzotriazole on the stress corrosion cracking of 18cr-9ni-ti stainless steel in acidic chloride solution

The SCC susceptibility of 18Cr-9Ni-Ti austenitic stainless steel in 0.5 mol.dm(-1) HCl + 0.5 mol.dm(-3) NaCl solution and the inhibiting effect of benzotriazole (BTA) on SCC and general corrosion were investigated by slow strain rate testing (SSRT), transient current measurements during fast strain rate testing (FSRT) under potentiostatic condition, scanning electron microscopy (SEM), potentiodynamic polarization measurements and electrochemical impedance spectroscopy (EIS) measurements. The results indicated that the inhibitive action of BTA can be attributed to its adsorption and inhibiting the anodic dissolution of the metal by the effect of blocking the active sites on the metal surface

A kinetic model for the potential oscillation phenomenon of mild steel in conc. H2SO4

The phenomenon of oscillation of potential for mild steel in concentrated sulfuric acid in the vicinity of Flade potential under galvanostatic condition can be elucidated based on the theory of dissipative structure. The necessary condition for the occurrence of the oscillation phenomenon is an autocatalytic process being involved. A kinetic model is proposed.

Regression analysis of the transient process of an electrode perturbed by a potential step

It is deduced that any n + 1 consequent points on a transient current curve of an electrode system with n time constants perturbed by a small amplitude of potential step can be correlated by a linear equation. Through regression of the linear equation, the electrochemical parameters and the number of time constants of the transient system can be easily obtained without a curve fitting process.

A New Technique for Correlation of Underground Corrosion

Abstract Fuzzy clustering analysis, a new branch of mathematics, was applied to correlation of soil corrosiveness for the first time. It was proven that the fuzzy technique could succeed in evaluat...

Electrochemical potential noise of AISI type 321 stainless steel under stress in acid sulphate solutions

Abstract An investigation was carried out on the features of potential fluctuations of AISI type 321 stainless steel under various constant loads in acidic sodium sulphate solutions with or without the addition of chloride ions. The probability of occurrence of potential noise was found to be affected by the stress level, the concentration of Cl− and the acidity of the solution. It increased with increasing stress and concentration of Cl−. However, increasing acidity led to a decrease in the potential noise level. The probability of potential noise fluctuations decayed gradually with increasing time after loading. Based on a mechanism of the breakdown and repassivation, a statistical analysis has been undertaken of the potential fluctuations recorded in the present study.