Passive iron oxide

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... 

To what extent can our concepts of the coordination chemistry of the oxide-water interface and our knowledge of the factors that enhance and retard dissolution of Fe(III) oxides contribute toward an understanding of the properties of passive iron oxides A review of the corrosion literature yields much phenomenological information that could be accounted for by surface-chemical theory. However, present passivity theories appear, with few exceptions, to be rather oblivious to the concepts of chemical surface reactivity. Thus, some perhaps speculative chemical ideas on the factors that enhance or reduce iron oxide passivity may be exposed to examination and discussion. 

The passive iron oxide layer is destroyed when pH is reduced to about 11.0 or below, causing the porous oxide layer (rust) to form during corrosion. 

Fig. 10.12 - Plots showing the dependence of (a) A and (b) Ij on the charge passed during the reduction of passive iron oxides. The passive films were formed for 300 s at (A) 0.75 V and (B) 1.35 V and then reduced at —0.25 V vs NHE. The wavelength was 460 nm and the angle of incidence 68°. Reproduced with permission from C. T. Chen B. D. Cahan, J. Electrochem. Soc., 129, (1982), 17.

Fig. 19.68 X-ray photoelectron spectroscopic (XPS) analysis of passive iron oxide layers form in the presence of doped polyaniline. (From Ref. 83.)...

The composition of the passivating iron oxide film on steel usually has properties of an /i-type semiconductor with excess negative charge carriers [46]. The electronic... 

Flg. 31.35 Structures determined for passive iron oxide films formed on the surface of steel. 

Fig. 31.36 XPS spectrum of the passive iron oxide layer formed on steel under doped polyaniline coating. (From Ref. 26.)...

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