Wustite disproportionation

Ferrous oxide is known as wustite (FeO), and it has the NaCl (rock salt) crystal structure. Accurate chemical analysis demonstrates that it is non-stoichiometric it is always deficient in iron. The FeO phase diagram (Figure 5.25) illustrates that the compositional range of wustite increases with temperature and that stoichiometric FeO is not included in the range of stability. Below 570 "C, wustite disproportionates to a-iron and Fe304. 

Fe(OH)2 is thermodynamically unstable with respect to magnetite (eq. (8.2) and (8.3)) and other Fe " compounds. It can, however, exist as a mestable phase for limited periods. Wustite, FeO, is only stable at temperatures greater than 570 °C. At lower temperatures it disproportionates to Fe° and Fe304. Figure 8.1 shows the stability domains for wustite, iron and magnetite as a function of temperature and oxygen content. The phase boundaries of wustite at high pressures have been estab-... 

The samples were treated at 400° C or 60 h at vacuum conditions and the quantitative analysis of phase was conducted with XRD. The XRD spectra of samples are shown in Fig. 3.12. The disproportionating ratio of wustite is calculated with the following equation ... 

The main results can be summarized as follows. Activation occurs as a complicated process involving the presence of more than one oxide species. The formation of metallic iron commences at ca 600 K, far below the onset of the main reduction process. This can be seen as direct experimental proof for the iron nucleation mechanism by disproportionation and prereduction of wustite. The... 

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