Magnesium alloys have high strength/weight ratios, but poor corrosion resistance affects the viability of increased magnesium usage in aerospace and other applications. This review approaches the p...

Corrosion of magnesium

The aim of the present article is to review some of the common corrosion phenomena and describe the predominant corrosion mechanisms in high-temperature and supercritical water. Corrosion in aqueous systems up to supercritical temperatures is determined by several solution-dependent and material-dependent factors. Solution-depending factors are the density, the temperature, the pH value, and the electrochemical potential of the solution, and the aggressiveness of the attacking anions. Material-dependent parameters include alloy composition, surface condition, material purity, and heat treatment. Corrosion phenomena that are observed include intergranular corrosion, pitting, general corrosion, and stress corrosion cracking. The solubility and dissociation of both attacking species and corrosion products play the most important role for corrosion in high-temperature water. Both solubility and dissociation processes are strongly influenced by the density, or the ionic product, respectively, of the solvent. High values of both parameters favor ionic reactions, and thus, accelerate electrochemical forms of corrosion. At low densities, water behaves like a non-polar solvent, and thus, ions associate. In these cases, the concentation of e.g. aggressive H + drops down and thus, solutions containing species such as HCl become neutral and thus less aggressive. Further, corrosion products plug the surface and material loss stops. Materials parameters have influence especially on the initiation of corrosion. In the present article, these factors are linked with the physical and chemical properties of high-temperature and supercritical water. An outlook is also given for future research needs.

Corrosion in high-temperature and supercritical water and aqueous solutions: a review

The present review surveys studies on physical-chemical properties and biological response of living tissues to NiTi (Nitinol) carried out recently, aiming at an understanding of the place of this material among the implant alloys in use. Advantages of shape memory and superelasticity are analyzed in respect to functionality of implants in the body. Various approaches to surface treatment, sterilization procedures, and resulting surface conditions are analyzed. A review of corrosion studies conducted both on wrought and as-cast alloys using potentiodynamic and potentiostatic techniques in various corrosive media and in actual body fluids is also given. The parameters of localized and galvanic corrosion are presented. The corrosion behavior is analyzed with respect to alloy composition, phase state, surface treatment, and strain and compared to that of conventional implant alloys. Biocompatibility of porous Nitinol, Ni release and its effect on living cells are analyzed based on understanding of the surface conditions and corrosion behavior. Additionally, the paper offers a brief overview of the comparative toxicity of metals, components of commonly used medical alloys, indicating that the biocompatibility profile of Nitinol is conducive to present in vivo applications.

Surface, corrosion and biocompatibility aspects of Nitinol as an implant material.

Corrosion behavior of an equiatomic CoCrFeMnNi high-entropy alloy compared with 304 stainless steel in sulfuric acid solution

The coordination chemistry of weathering: III. A generalization on the dissolution rates of minerals

Passive film of 18-8 stainless steel structure and its function

It is common knowledge that metallic iron and nickel placed in acidic solutions corrode with evolution of hydrogen gas. In concentrated nitric acid, however, they suddenly become protected against corrosion some time after violent metal dissolution and gas evolution have occurred. A sudden decrease of metal dissolution is also observed when they are anodically polarized in acid and neutral solutions. The unstable surface of actively corroding metals in aqueous solutions can thus sometimes be made stable in the presence of a strong oxidant or by polarizing the electrode potential in the anodic (positive) direction. The phenomena, which was found in the days of Faraday,(1) is called the electrochemical passivation of metals, and the corrosion-resistance state of the stable surface is called the passive state, as contrasted with the active state of the corroding surface; the term chemical passivation is sometimes used for the passivation caused by oxidants and the anodic passivation for the anodic formation of passivity.

Electrochemical Passivation of Metals

It has been considered that the corrosion of passive metals and alloys is not caused by the active metal-dissolution but the dissolution of a nonporous passive oxide film in aqueous solution. The corrosion current density of iron(1)(2), chromium(3) and their alloys(4) is independent of the potential in all the range of passivity, although depending upon the pH of solution. Vetter(1) explained such a corrosion behavior by assuming that the dissolution rate of the passive oxide film is electrochemically controlled by the potential difference at the filmsolution interface, which is determined soley by the pH of solution. Recent studies of passivated stainless steels in acid solutions by means of X-ray photo electron spectroscopy(5) and Auger electron spectroscopy(6) have proved the high enrichment of chromium component in the passive oxide film, which seems to explain the high corrosion resistivity of stainless steels in acid solutions. The passive oxide film has an amorphous structure with a chemically bound water (7). Hydrous chromium oxide prepared by precipitation in aqueous solution according to the X-ray diffraction data(8), has also an amorphous structure. Therefore it is expected that the structure of hydrous chromium oxide is similar to that of the passive chromium oxide on stainless steels. In this study, hydrous chromium oxide prepared by precipitation is adopted as a model material of the passive oxide film on stainless steels and the dissolution of hydrous chromium oxide in acid solutions is investigated and the dissolution mechanism is discussed from the electrochemical point of view.

Dissolution of Hydrous Chromium Oxide in Acid Solutions

Changes in the power spectral density of noise current on type 304 stainless steels during the long time passivation in sulfuric acid solutions

https://www.jstage.jst.go.jp/article/jcorr1954/21/6/21_6_263/_pdf

Go Okamoto

Papers

Passive film of 18-8 stainless steel structure and its function

Electrochemical Passivation of Metals

Dissolution of Hydrous Chromium Oxide in Acid Solutions

Changes in the power spectral density of noise current on type 304 stainless steels during the long time passivation in sulfuric acid solutions

Effect of the Potential of Etching Treatment and Passivation Treatment on the Stability of Passive Stainless Steels