Passive films on stainless steels—chemistry, structure and growth

Grain refinement is known to lead to improvements in strength and wear resistance. Inherent processing involved in grain refinement alter both the bulk and the surface of a material, leading to changes in grain boundary density, orientation, and residual stress. Ultimately, these surface changes can have an impact on electrochemical behavior and, consequently, corrosion susceptibility as evidenced by the large number of studies on the effect of grain size on corrosion, which span a range of materials and test environments. However, there has been limited work on developing a fundamental understanding of how grain refinement and more generally how grain size affects the corrosion resistance of an alloy. Existing literature is often contradictory, even within the same alloy class, and a coherent understanding of how grain size influences corrosion response is largely lacking. A survey of previous work related to the relationship between grain size and corrosion resistance for a number of light meta...

Effect of Grain Size on Corrosion: A Review

Revealing the relationship between grain size and corrosion rate of metals

The history of the Point Defect Model for the passive state: A brief review of film growth aspects

We report on the anodic formation of a self-standing 720 μm thick TiO2 nanotubular membrane by complete consumption of a 250 μm thick titanium foil sample. By employing double sided electrochemical oxidation of titanium in an electrolyte comprised of water, NH4F, and ethylene glycol, we obtain two highly ordered, hexagonal close-packed titania nanotube arrays 360 μm in length that are separated by a thin compact oxide layer; the individual nanotubes in each array have an aspect ratio of ∼2200. The potentiostatic anodization of titanium in an ethylene glycol, NH4F, and water electrolyte dramatically increases the rate of nanotube array growth to approximately 15 μm/h, representing a growth rate ∼750−6000% greater than that seen, respectively, in other polar organic or aqueous based electrolytes previously used to form TiO2 nanotube arrays. We consider the effects of electrolyte composition, applied potential, and anodization duration on the length and diameter of the resulting nanotubes in terms of a growt...

A new benchmark for TiO2 nanotube array growth by anodization

Nature of the passive film on nickel

A new method for estimating the diffusivities of vacancies in passive films

Despite intensive investigations, the nature of the passive state is one of the most complex and unresolved subjects in the electrochemistry of zinc in alkaline solutions. In this paper, we explore the electrochemistry of the passive state on zinc in 0.1 M sodium borate/1 M sodium hydroxide solution of pH 10.5. During the course of passivation, several characteristic features in the anodic region are observed, including a wide passive range extending over >2 V and a secondary passivation phenomenon that occurs at high anodic potentials. The steady-state current in the passive state is found to be independent of the applied voltage, which is consistent with the barrier layer being an interstitial zinc conductor or an oxygen vacancy conductor (or both) with interstitial zinc being the most likely defect. This model is also consistent with the well-known n-type character of the passive film on zinc.

Characterization of the Passive State on Zinc

The effect of EDTA (ethylenediaminetetraacetic acid, added as ) on the electrochemical behavior of iron and on the semiconducting properties of passive films formed on this metal in borate buffer solution (pH 8.4) was studied. Electrochemical studies, including potentiodynamic and galvanostatic reduction experiments and capacitance measurements coupled with Mott‐Schottky analysis, were carried out over the entire passive range in borate buffer solutions in the presence and absence of 0.01 M EDTA. Passive films formed in the presence of EDTA were thinner and showed higher donor concentrations. EDTA present in the borate buffer solution effectively inhibited the formation of the Fe(III) outer layer, thereby rendering the defective inner layer to direct examination. The barrier layer is found to be an n‐type semiconductor, which is consistent with the oxide being a defective magnetite in which the principal defects are oxygen vacancies and cation interstitials. EDTA effectively competes with chloride ion for adsorption into oxygen vacancies at the barrier layer/solution interface, thereby suggesting that the chelating agent might be an effective inhibitor of passivity breakdown. © 2000 The Electrochemical Society. All rights reserved.

https://iopscience.iop.org/article/10.1149/1.1394024/pdf

Elzbieta Sikora

Papers

Nature of the passive film on nickel

A new method for estimating the diffusivities of vacancies in passive films

Characterization of the Passive State on Zinc

The Passivity of Iron in the Presence of Ethylenediaminetetraacetic Acid I. General Electrochemical Behavior

The electronic structure of the passive film on tungsten