Passive iron

Nagayama, M. and Okamoto, G., The Anodic Behaviour of Passive Iron in Chromic Acid-Chromate Solutions , Corros. Sci., 2, 203 (1962)... 

The incorporation of anions from the electrolyte, such as borate and carbonate, into the oxide has also been shown to occur on iron and cobalt, such anions being restricted to the outer layers of the film. Attempts to find incorporation of chloride into passive iron surfaces from... 

Nitric acid is also withstood by high-silicon iron. The concentrated acid is believed to reinforce the silica film by the formation of a passive iron oxide... 

Passivation under a wide range of operating conditions and in all boiler designs is a goal of all BW treatment programs. It is achieved through the formation of a stable, continuous, uniform, self-limited, and nonporous magnetite film. (This objective also applies to the maintenance of cuprous oxide, the copper equivalent of a film of passive iron.)... 

Figure 14. In situ cell for performing EXAFS studies on passivated iron films. (From Ref. 72, with permission.)...

Figure 15. Derivatives of the near-edge region of spectra for nitrite- (A) and chromate- (B) passivated iron films under in situ ( 4-) and ex situ ( ) conditions. (From Ref. 72, with permission.)...

Adsorption of TU on active and passive iron electrodes was studied by Bockris et al. using radiotracer and Fourier Transform Infrared Spectroscopy techniques. The high values of AG° (the standard states 0° = 0.582 and c° = 1 mol T ) equal to -17.20 kJ/mol and -18.98 kJ/mol have been obtained for the active and passive iron electrodes, respectively. They are markedly higher than those obtained for other metals (Table 1). 

Hatva, T. (1989) Iron and manganese in ground-water in Finland Occurrence of glacifluvial aquifers and removal by biofiltration. Publ. Water environmental research institute. Nat. Board Waters Envir., Finland, No. 4, 99 p. Haupt, S. Strehlow, H.H. (1987) Corrosion layer formation and oxide reduction of passive iron in alkaline solution A combined electrochemical and surface analytical study. Langmuir 3 837-885... 

The specimen is transferred to concentrated nitric acid. A few bubbles of gas may escape at first, then no more, and the now passive iron is not attacked further. 

Figure 7.104 shows the plot of the value of J vs. S obtained for different potentials on the bare iron region from the data plotted in Fig. 7.103. A straight line obtained with an intercept much greater than 1 indicates that Oz reduction on reduced iron proceeds by the direct four-electron reaction pathway. Formation of HjOj as an intermediate in the consecutive reaction pathway is less than 1 % of the total reduction current Conversely, in the potential region corresponding to passive iron, the slope, S, of the /disk//ring plot is zero, and the intercept J = (l/N) indicates that 02 reduction on passive Fe is a two-electron process in which is the product, and not an intermediate, of the reaction.

PASSIVITY. When iron is immersed in concentrated nitric acid, there is no visible reaction (Keir, 1790). although dilute nitric acid results in a marked reaction with iron, Upon removal of the iron from the concentrated nitric acid and immersion in copper sulfate solution, the iron is not plated by copper, although this occurs with ordinary iron. Iron in such a condition is described as passive iron, and the phenomenon is known as passivity. See also Iron Metals, Alloys, and Steels... 

Gojkovic, S.L., Zecevic, S.K., and Drazic, D.M., Hydrogen peroxide oxidation on passive iron in alkaline solutions, Electrochim. Acta, 37(10), 1845-1850, 1992. 

Knowledge here is largely restricted to neutral solutions. It turns out (Jovan-cicevic, 1986) that the mechanism that best fits the facts for passive iron (see Table 7.15) is... 

A. Finkelstein, Z Physikal. Chem. 39 91 (1902). Impedance of passive iron. 

However, the application of the Split Ring Disc electrode especially with hydro-dynamic modulation of its rotation speed (HMRRD) will be mentioned briefly. The construction of appropriate ring disc electrodes including a modified commercial disc rotator and the necessary electronic tripotentiostat have been already described in detail elsewhere [25]. The investigations of K.G. Heusler on passive iron in 0.5 M sulphuric acid have been already mentioned [18]. Another example is shown for Cu in alkaline solution [26]. Two half rings permit determination of the formation of two Cu species simultaneously. The transfer efficiency from the disc to the ring has been... 

Fig. 1. Plot of flatband potential vs. pH for different iron(III) oxides in contact with aqueous electrolytes obtained by capacitance-potential measurements. O, Thermal a-Fe203 [24] , single crystal a-Fe203 [25] A, a, thermal a-Fe203 [26, 27] , passive iron [28] I, passive iron [29] x, passive iron [30],...

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