Iron oxide activation energy

The corrosion of iron occurs particularly rapidly when an aqueous solution is present. This is because water that contains ions provides an oxidation pathway with an activation energy that is much lower than the activation energy for the direct reaction of iron with oxygen gas. As illustrated schematically in Figure 19-21. oxidation and reduction occur at different locations on the metal surface. In the absence of dissolved ions to act as charge carriers, a complete electrical circuit is missing, so the redox reaction is slow, hi contrast, when dissolved ions are present, such as in salt water and acidic water, corrosion can be quite rapid. 

Horne and Axelrod have suggested that this exchange may not be first order with respect to each iron oxidation state at high thiocyanate concentrations. A lower value for the rate coefficient kg and a slightly higher activation energy than that quoted previously have been reported ... 

It should be noted that the choice of Fe0 950 (wustite) rather than FeO in the preceding reactions is not arbitrary [10]. The steam-iron reaction would produce very little hydrogen at these temperatures if magnetite were reduced to FeO instead of Fe095O. Hacker et al. [55] determined that the activation energy of magnetite reduction with H2 and CO is equal to 95 and 98 kj/mol, respectively. The energy of activation of wustite oxidation with steam was found to be 29 kj/mol. 

Monitoring solid state reactions that play a role in catalyst activation forms a useful application of XRD. The example discussed above concerns a catalyst with large iron oxide particles as is used in the water gas shift reaction, and represents a particularly favorable system for XRD analysis. Similar studies with small particles are certainly also feasible, although it may be advisable to use laboratory X-ray sources of higher energy, such as Mo Ka, or a synchrotron [13]. 

Iron nitrosyls coordination, 28 146, 148 nucleophilic attack, 28 153, 154 Iron oxide, 32 54-55 activation energy, 27 16, 17 in catalytic converter, 24 62 coatings containing, 40 103-105 CO conversion, 28 263 on silver, 27 14-17... 

The desorption of anions from iron oxides as a result of changing the anion concentration in solution is often very slow. It can be accelerated by increasing the pH. The partial irreversibility of anion adsorption has been attributed by some authors to a high activation energy of adsorption resulting from the formation of multiden-tate surface complexes, whereas others attribute it to a slow diffusion out of micropores. 

Tab. 12.6 Average dissolution rate, activation energy and frequency factor for the dissolution of various iron oxides in 0.5 M HCl at 25 °C (Sidhu et al., 1981).

Torrent, J. Schwertmann, U. (1987) Influence of hematite on the color of red beds. J. Sediment. Petrology 57 682-686 Torrent, J. (1987) Rapid and slow phosphate sorption by Mediterranean soils effect of iron oxides. Soil Sci. Soc. Am. J. 51 78-82 Torrent, J. (1991) Activation energy of the slow reaction between phosphate and goethites of different morphology. Aust. J. Soil Res. 29 69-74... 

Finally, Arrhenius treatments of the catalytic data were examined for the HTAD synthesized substitutional series, Bi(2-2x) 2x 030i2, and the binary bismuth molybdate series where Bi/Mo ratios were varied fi-om pure Mo oxide to pure Bi oxide. The noteworthy aspect of the oxidation results is that in the most reactive regime of x = 0-5% atom fi-action Fe, before separate phase Fe3Mo30j2 begins to dominate the catalyst composition in the iron series, the apparent activation energies were all in the range of 19-20 kcal/mol. Furthermore, the activation energies for the pure Bi-Mo series were between 19-20 kcal/mol while the activities were considerable different. Thus, the chief difference in the reactivities in both series is in the preexponential factor, i.e. the number of active sites. 

In fact, the polymer is quite stable with respect to precipitation. Once isolated it can be kept in aqueous solution indefinitely (37). This stability is presumably kinetic in origin. Since all evidence points to a different internal structure for the polymer from all crystalline ferric oxide or hydroxide phases, the reorganization required for precipitation would be expected to have a high activation energy. Addition of base to pol5maer solutions does produce an immediate precipitate, presumably by cross-linking the polymer particles. In hydrolyzed ferric nitrate solutions with less than 2.5 base equivalent per mole of iron the eventual precipitates observed are probably formed directly from low molecular weight components. The low rate of dissociation would then be another factor in polymer stability. 

Apparent Activation Energies of S02 Oxidation over Iron Oxide Supported by Silver and... 

Pyrite is the most common sulfide mineral. It is a major contributor to the formation of mine drainage and sulfate-rich natural runoff. The oxidation of pyrite and other Fe(II) sulfides (e.g. marcasite and pyrrhotite) involves both iron and sulfur, as well as any arsenic impurities. Activation energies suggest that surface reactions dominate the oxidation of pyrite (Lengke and Tempel, 2005). Furthermore, evidence from pyrites in coal and ore deposits suggests that arsenian pyrite is more susceptible to oxidation from weathering than low-arsenic pyrite (Savage et al., 2000, 1239). 

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