Die Korrosion der Metalle

Chemisorption model of electrochemical passivity of metals and thermodynamic calculation of the flade potential of metals Ni and Cr taking into account their surface Gibbs energy

“…(4) gives much more negative values (by 0.5, 0.35, and 0.35 V, respectively) than the experimental values. These discrepancies between the predictions of the film theory and the experiment have long been known, and there have been attempts to minimize the discrepancies without changing the gen eral concept of film theory [13]. In this study, a ther modynamic model of chemisorption is proposed; this model, along with taking into account the energy of the chemical bond between the metal atom and the oxygen of water, makes allowance for the energy of breaking of the bond between the surface atom and the bulk of the metal.…”

“…In the case of nickel passivation, it is proposed to consider that the passive state of the metal is deter mined by the reversible reaction (13) where the forward reaction is passivation to form a Ni=O oxide having chemisorption bonds, while the reverse reaction is the decomposition (depassivation) of nickel. Electrochemical reactions involving ada toms are known from the literature, e.g., [21].…”

“…Next, in terms of the chemisorption model, a for mula of the equilibrium electrode potential of reaction (13) is derived assuming that this potential is a theoret ical value of the Flade potential of the chemisorption reaction, which is denoted by The Vetter scheme [2] for metal passivation (14) in which the Me z+ ions directly pass into an oxide characteristic of a given metal, was taken as a basis. In terms of the chemisorption model of passivity, the metal oxidation reaction occurs via another path: a successive transition of the Me z+ metal ion from the bulk (b) into the SL of the metal (S) and finally into the monomolecular layer of surface oxide Ox(S) as fol lows: (15) Using this method, consider the equilibria at the interfaces for this scheme: (16) In terms of electrochemical thermodynamics, each of these transitions is thought of as passing through an equilibrium state that occurs under the condition of equality of the electrochemical potentials.…”

Properties of aluminum oxide thin film obtained by metal plasma immersion ion implantation and deposition after zirconium-based pretreatment

“…The aluminum-to-oxygen atomic ratio indicates a highly oxidized aluminum layer, exceeding the ratio for the alumina stoichiometry (Al 2 O 3 ), which is present in amorphous g-Al 2 O 3 on technological aluminum surface at moderate environment (pH 4-pH 9) [19,20]. Oxygen excess associated with the hydrogen content (12% of the film) indicates the presence of aluminum hydroxide, which might be present in the amorphous state Al(OH), or Al 2 O 3 $H 2 O, similar to the aluminum hydroxide state found in technological aluminum alloys [19,20]. The uncertainty of the measured elements is 1.9%, 1.9% and 2.6%, respectively for Al, O and H.…”

Grain boundary corrosion of the surface of annealed thin layers of gold by OH· radicals

“…Grain boundary corrosion is certainly one of the most intensively studied topics [19,20] of corrosion. There are several reasons why an increased corrosion rate may be observed at grain boundaries, for example a high defect concentration, the specific nature of the defects at grain boundaries, composition differences between adjacent grains and resulting potential differences, the existence of interphases, stress, etc.…”