Passivity stability constants

A. Passive binding of Fe(III)—Lm complex and Fe(III) to ligands (acceptor sites) of the outer membrane and the outer phase of the inner membrane. Fe(III)-Ln represents a soluble chelate complex of Fe(III) with a sufficiently low stability constant, e.g., polynuclear Fe(III)-sucrose complex(es). B. reduction of membrane-bound Fe(III) to Fe(II) by the respiratory chain at the level of cytochrome c/cytochrome a and energy-dependent active transport of Fe(ll) across the inner membrane. See text. This model is based on Refs. 23, 24, 27-32. 

A key assumption about the ability of small complexes to cross membranes passively relates to their overall charge uncharged complexes cross membranes more easily than do highly charged complexes. Thus much effort has been directed toward determining the structures of AP+-citrate complexes and their corresponding stability constants. 

Passivation current density (A cm j Stability constant of a complex... 

For solving heterogeneous models it is necessary to take into account the effect of such processes as dissolution and mineral formation, surface complex formation and ion exchange. That is why beside stability constants of complexes in water it is necessary to have values of ion exchange coefficients, solubility products and also surface acidity and constant of surface complex formation for individual minerals. For nonpolar and chemically passive components are needed values of partition coefficients or solubility. Due to the shortage of these data and complexity of computations at... 

Stability constants of their iron complexes as presented in Table 7.1 [30,45-47]. The stability constants with one anion are given, which refers to the reaction order one that has usually been found for the dissolution of passive layers under the influence of the aggressive anions. The reaction of Fe + with HP to form FeF " and F1+ yields the more realistic value of log Kj = 2.28 due to the small dissociation constant of FIF (pFC = -log = 2.98). Table 7.1 also contains the constants K- for Ni +- and Cr3+-halide complexes. Their falling values from fluoride to iodide and Fe + to Ni + support the decreasing tendency for enhanced dissolution of the passive layer and localized corrosion. These data can be referred to the situation at the oxide surface. The fluoro complexes are very stable and form in high concentrations at all surface sites. Therefore their much faster transfer to the electrolyte yields enhanced general dissolution, whereas the attack of the other halides is locally restricted and much less pronounced. Besides the thermod5mamically based values, i.e., the stability constants, the kinetics of complex formation and of the complex transfer to the electrolyte are another decisive factor for the attack of the passive layer. In this sense, the situation of Cr is very special and will be discussed separately. 

Other important properties for photovoltaic materials are their refractive index, stability, brittleness, toxicity, crystal lattice constant, thermal expansion coefficient, temperatures required for processing into cells, energy investment for cell production, ability to be doped both types, level of technological knowledge and industrial maturity, cost, and abundance. Issues particular to passivation and the trapping of weakly absorbed light include the availability of compatible and affordable passivation and surface texturing methods. ... 

Aromatic polyimides have found extensive use in electronic packaging due to their high thermal stability, low dielectric constant, and high electrical resistivity. Polyimides have been used as passivation coatings, (1) interlayer dielectrics, (2) die attach adhesives, (3) flexible circuitry substrates, (4) and more recently as the interlevel dielectric in high speed IC interconnections. (5) High speed applications require materials with a combination of low dielectric constant, flat dielectric response versus frequency and low water absorption. 

The stability of the passive him has been checked also in aqueous solution and in ultrahigh vacuum conditions. In the case of iron, the unstable hlms thicken up to a constant thickness of... 

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