Relationship between various iron oxides

But this structure is unstable and usually accompanied with the defects of metal ions. As a consequence, there would be certain amounts of Fe + cations to maintain the charge-neutrality. These Fe + cations often enter into the original unoccupied tetrahedral interspaces. For example, when the defect concentration of metal ions is X, the wiistite could be expressed as Fei j 0, where x 1. And if x = 0.1, according to the principle of charge-neutrality, then  

If Fe + cations are replaced with appropriate amounts of Fe +, the rest of that is equal to 1/4  

This is Feo.TsO, i.e., Fc304 and Fe + (Fe +Fe +) O4, which is the formula of ions distribution in inverse spinel of magnetite. 

It is seen from Table 3.9 that any iron oxides could be expressed as aFeO- -bFe203 in chemistry, while as Fe203, Fe304, FeO or Fei xO in crystal structure, respectively. 

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Clayton RN, Epstein S (1958) The relationship between 0/ 0 ratios in coexisting quartz, carbonate and iron oxides from various geological deposits. J Geol 66 352-373 Clayton RN, Kieffer SW (1991) Oxygen isotope thermometer calibrations. In Taylor HP, O Neil JR, Kaplan IR (eds.) Stable isotope geochemistry A tribute to Sam Epstein. Geochem Soc Spec Publ 3 3-10... 

Isomorphous substitution of iron oxides is important for several reasons. In the electronics industry, trace amounts (dopants) of elements such as Nb and Ge are incorporated in hematite to improve its semiconductor properties. Dopants are also added to assist the reduction of iron ores. In nature, iron oxides can act as sinks for potentially toxic M", M and M heavy metals. Investigation of the phenomenon of isomorphous substitution has also helped to establish a better understanding of the geochemical and environmental pathways followed by Al and various trace elements. Empirical relationships (e. g. Fe and V) are often found between the Fe oxide content of a weathered soil profile and the levels of various trace elements. Such relationships may indicate similarities in the geochemical behaviour of the elements and, particularly for Al/Fe, reflect the environment in which the oxides have formed (see chap. 16). 

Figure 5.7 demonstrates the relationship between isomer shift and quadrupole splitting for iron in various environments. In oxidic components of iron catalysts, one usually only encounters the high-spin configurations of Fe2+ and Fe3+ ions. 

FOLLOWING A SHORT introduction dealing with the relationship between diffusion process and field transport phenomena in tarnishing layers on metals and alloys, the mechanism of oxidation of iron is discussed. Epitaxy plays an important role on the gradient of the concentration of lattice defects and, therefore, on the validity of the parabolic rate law. Classical examples of metal oxidation with a parabolic rate law are presented and the various reasons for the deviation observed are elucidated on the systems Iron in CO/CO2 and CU2O in <>2. In addition, the oxidation of alloys with interrupted oxide-metal interfaces is treated. Finally, attention is focussed on the difficulties in explaining the low temperature-oxidation mechanism. 

In this chapter the experimental physicochemical and the theoretical thermodynamic data enabling us to obtain an overall picture of the relationships between the ions and molecules in the solutions and the various sediments are examined. All the thermodjmamic calculations were made on the basis of the systems of consistent constants first worked out by us (Mel nik, 1972b), including the oxides, carbonates, and silicates of iron. As new experimental data have been obtained, the constants have been refined and supplemented (Tardy and Garrels, 1976 Klein and Bricker, 1977, Mel nik and Radchuk, 1977b). The consistent thermodynamic constants used in this work are given in the Appendix. The plotting of the stability ... 

Fig. 39. Relationships between iron compounds in various primary sediments for activity of Uf g-ion/I A = oxide B = silicate C = carbonate D = sulfide (Uj = 10 g ion/1).

In order to estabHsh the relationship between the structure of the prosthetic group and its reactivity toward NO in various hemoproteins in vivo, many efforts have been devoted to reveal the influence of the porphyrin microenvironment in the iron(III) porphyrin systems (i.e., the identity and charge of the substituents in the porphyrin periphery) on the dynamics of both the binding and release of nitric oxide. In this context, several new water-soluble iron(III) porphyrin models, i.e., a highly negatively charged ((P )Fe = [5", 115", 20" -tetra-ief i-butyl-5, 5 , 15, 15 -tetrakis-(2,2-biscarboxylato-ethyl)-... 

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