On the Existence of Our Metals-Based Civilization

Abstract

The stability of the barrier layers of bilayer passive films that form on metal and alloy surfaces, when in contact with oxidizing aqueous environments, is explored within the framework of the point defect model using phase-space analysis, in which the rate of growth of the barrier layer into the metal ͑dL + /dt͒, and the barrier layer dissolution rate ͑dL − /dt͒, are plotted simultaneously against the barrier layer thickness. A point of intersection of dL − /dt with dL + /dt indicates the existence of a metastable barrier layer having a steady-state thickness greater than zero. If ͑dL − /dt͒ L=L ss Ͼ ͑dL + /dt͒ L=0 , the barrier layer cannot exist, even as a metastable phase, as the resulting thickness would be negative. Under these conditions, the surface is depassivated and the metal may corrode at a rapid rate. Depassivation due to potential-enhanced dissolution ͑transition to the transpassive state͒ and to acid attack on the barrier layer ͑"acid depassivation"͒ are explored. The boundaries for depassivation may be plotted in potential-pH space to develop kinetic stability diagrams as alternatives to the classical Pourbaix diagrams for describing the conditions under which metals or alloys exist in the passive state.

The Kinetics of Nucleation of Metastable Pits on Metal Surfaces: The Point Defect Model and Its Optimization on Data Obtained on Stainless Steel, Carbon Steel, Iron, Aluminum and Alloy-22

“…the number of pits grows at a maximum rate shortly after the first pit appears). It has been found 28,34 that, under some conditions (especially where concentrations of Cl − or the potential is high), criterion 17 holds very well and the nucleation of metastable pits on a metal surface may be regarded as being an "instantaneous nucleation" phenomenon. Nevertheless, t max increases dramatically as the chloride concentration decreases, as exemplified in Fig.…”

Modeling fretting-corrosion wear of 316L SS against poly(methyl methacrylate) with the Point Defect Model: Fundamental theory, assessment, and outlook

“…According to the Point Defect Model (PDM), a passive film is envisaged to be a bi-layer structure comprising a point defective, nano-crystalline barrier layer and a porous outer layer that is formed by the hydrolysis of cations that are transmitted through the barrier layer and are subsequently precipitated as a hydroxide, oxyhydroxide, or oxide, depending upon the local conditions [13][14][15][16][17][18][19][20][21]. The stoichiometric formula for the barrier layer oxide on the surface of the stainless steel can be represented as MO /2 , without specifying the exact defect structure.…”

“…In this paper, the authors have chosen to investigate the progression of damage from the perspective of the Point Defect Model (PDM) [13][14][15][16][17][18][19][20][21]. It is worth noting that, in order to use the PDM, values for many important physical parameters have been extracted from the literature, or have been determined experimentally (oxides layer thickness, for instance).…”

“…Other reactions, those at the bl/ol interface, depend upon the pH and applied potential, but not on the film thickness, because the relevant voltage at the point of application (the reference electrode in the solution, just outside the outer layer) has not been imposed across the barrier layer at the point of impact on the rate (the bl/s interface). Tables 3 and 4 summarize, for each reaction, the parameters involved in the rate constant expressions [13,14,21]. k : standard rate constant , as described by the PDM [24,25].…”

“…In this particular case, as with most chromium-containing alloys, the compact inner layer (barrier layer) adjacent to the metallic surface is a thin chromic oxide (defective chromia, Cr 2+x O 3-y ) [19,34,35], in which the principal defect is the metal interstitial (x > 0), or oxygen vacancies (y > 0), or both (x > 0, y > 0), with metal interstitials being commonly identified as the principal defect [19,21]. The barrier layers on a wide range of chromium-containing iron-and nickel-base alloys are invariably n-type in electronic character in a specific range of applied potentials [36][37][38][39][40][41], as expected from the defect assignment given above.…”