Donor Density Of Passive Film Research Articles

Effect of passive film on the galvanic corrosion of titanium alloy Ti60 coupled to copper alloy H62

Ti alloys exhibit high potential because of the compact passive film. However, the effect of passive film on galvanic corrosion is not clear. On the one hand, the great potential difference can accelerate the galvanic corrosion of other metals with low potential. On the other hand, the passive film can hinder the electrochemical reactions, inhibiting the galvanic corrosion. To clarify this question, the galvanic corrosion of titanium alloy Ti60 coupled to copper alloy H62 was studied using zero‐resistance ammeter, scanning vibrating electrode technique, scanning electron microscopy, and potentiodynamic polarization measurements. The chemical composition and electrical properties of the passive film on Ti60 were detected using X‐ray photoelectron spectroscopy and Mott‐Schottky plots. The results indicate the galvanic corrosion of Ti60‐H62 coupling is ignorable in spite of the great galvanic potential difference between them. It can be attributed to the low electron donor density of passive film, which inhibits the electron charge transfer process at the film/solution interface, causing the slow cathodic reaction rate on Ti60.

Surface corrosion enhancement of passive films on NiTi shape memory alloy in different solutions

The corrosion behaviors of NiTi shape memory alloy in NaCl solution, H2SO4 solution and borate buffer solution were investigated. It was found that TiO2 in passive film improved the corrosion resistance of NiTi shape memory. However, low corrosion resistance of passive film was observed in low pH value acidic solution due to TiO2 dissolution. Moreover, the corrosion resistance of NiTi shape memory alloy decreased with the increasing of passivated potential in the three solutions. The donor density in passive film increased with the increasing of passivated potential. Different solutions affect the semiconductor characteristics of the passive film. The reducing in the corrosion resistance was attributed to the more donor concentrations in passive film and thinner thickness of the passive film.

Modeling interactive effects of Pb contamination, Ca2+ and Mg2+ on passivity of alloy 800 in simulated crevice chemistries at high temperature

A phenomenological model is postulated to interpret the interactive impacts of dissolved Pb contamination, Ca2+ and Mg2+ on passivity of Alloy 800 in simulated crevice chemistries at 300°C. Passivity degradation is characterized by the retarded dehydration during passivation and increased donor density in passive film. Ca2+ and Mg2+ can cause the passivity degradation in the Pb-free chemistries but, if the Pb-contamination concentration exceeds a critical value, would reduce the detrimental effect of Pb-contamination. This behavior may be related to the extremely strong adsorption capacity of Pb contamination. Finally, the applications in the water management strategy of nuclear power plants are discussed.

A Comparative Study of Semiconducting Behavior of Passive Film of High Nitrogen and Ni and Mn Free Stainless Steels in 3.5 wt. % NaCl

The semiconducting property of passive films formed on Alloy 1 (18Cr-2Mo-1N)], Alloy 2 (17.5Cr-3Mo-0.5N)] and Alloy 3 (Type 316 SS) were studied by using the Mott-Schottky (M-S) approach in 3.5 wt. % NaCl solution of pH 2, 7 and 12. The M-S analysis shows that the film acts as n - type and p - type semiconductors across the potential range. The donor density of Alloy 1 has been found to be lower by about 31 %, 11 % and 6 % as compared to that of Alloy 2 at pH 2, 7 and 12 respectively. However; Alloy 3 has higher donor density 44 %, 27 % and 30 % in comparison with Alloy 1. The donor density of Alloy 3 found to be greater about 21 %, 18 % and 25 % to the Alloy 2 at pH 2, 7 and 12 respectively. These results indicate that the sensitivity of electrolyte composition and the presence of alloying elements like nitrogen and nickel on the donor density of passive film. High nitrogen stainless steels exhibited a lower donor density that corresponds to good protectiveness, more stable passive film which is in agreement with a low passive current density (ipass), higher pitting potential (Epit) and polarization resistance (Rp).

The role of inhibitors on the repassivation of pitting corrosion of carbon steel in synthetic carbonated concrete pore solution

The semiconductive properties and pitting susceptibility of passive films formed on carbon steel in synthetic carbonated concrete pore solution containing Cl − ions were studied by Mott–Schottky (M–S) plots and electrochemical noise (EN). The results show that both nitrite and tetraethylenepentamine (TEPA) can reduce the donor density in passive film, leading to a more positive film breakdown potential. Moreover, nitrite can rehabilitate metastable pits and passivate the broken passive film more quickly than TEPA. Polarization curves also show that nitrite can increase the pitting potential more than TEPA at same concentration. Atomic force microscopy (AFM) imaging shows that Cl − ions could induce large metastable pits on passive film, but the size of pits decreases and the density of pits increases with addition of nitrite. However, AFM imaging fails to detect the metastable pits under TEPA adsorbed film in spite of a smooth-like image on the steel surface is observed. The force curves of AFM indicate a stiffness (elasticity) order of films: nitrite oxidation film > original passive film > enamine adsorbed film.

Effect of Sn content on the properties of passive film on PbSn alloy in sulfuric acid solution

The effect of Sn content on properties of anodic film formed on PbSn alloys in sulfuric acid solution was investigated using linear sweeping voltage (LSV), cyclic voltammetry (CV), and a.c. voltammetry (ACV), based on the Mott-Schottky analysis. The results revealed that the addition of Sn into lead alloys can promote the corrosion resistance property and could decrease the impedance of anodic film; these results were more remarkable with enhancing the Sn content. The over potential of oxygen evolution on lead alloys enhanced with the increase of Sn content. The Mott-Schottky analysis indicated that the passive film appeared an n-type semiconductor, and the donor density of passive film increased with increasing Sn content. The increased vacancies in the passive film with Sn content increasing could illustrate this trend.

Effect of hydrogen charging on the stability of SAE 10B22 steel surface in alkaline solutions

The influence of hydrogen charging into a quenched and tempered boron steel membrane electrode (SAE 10B22) was studied using borate buffer (pH 8.4) and NaOH solutions (pH 12.7), with or without the addition of 0.01 M EDTA. At the hydrogen input side, hydrogen charging influenced cyclic voltammograms increasing the anodic charge of iron(II) hydroxide formation, and decreasing the donor density of passive films. These results suggest that the hydrogen ingress caused instability of metallic surface, increasing the surface area activity.