| Metallic iron is expected to be produced by disproportionation of Fe(,2)SiO(,4) at high pressure. However, due to the small concentration and dispersed nature of the metallic iron, it is not detectable by conventional techniques. Detectable metallic iron at high temperature and pressure is produced not by disproportionation mechanism but by chemical reduction or contamination.;The Hugoniot data of wustite (Jeanloz and Ahrens 1980) are reinterpreted in the light of the tendency for the stoichiometry of Fe(,x)O to decrease with increasing pressure above 100 kbar. A mixture of Fe(,x)O and metallic iron can explain the density of the outer core under the T-P conditions of the core. A nearly constant oxygen content required in a wide pressure range in the outer core, while x in Fe(,x)O varies, is consistent with the present model and satisfies the geodynamo and geochemical constraints. The possibility of the wustite--(magnetite (high pressure form) plus iron) boundary extending to higher pressures and temperatures and accounting for the wiggle in the Hugoniot is discussed. Further static experiments at pressure greater than 700 kbar (70 GPa) are important to clarify these models.;Static heating in the diamond anvil cell yields evidence that wustite (Fe(,.924)O and Fe(,.947)O) disproportionates to magnetite plus metallic iron at pressures up to 200 kbar (20 GPa) at 300(DEGREES)C. The disproportionation is usually incomplete and the residual metastable wustite is nonstoichiometric close to the disproportionation boundary. Further below the disproportionation boundary, the residual wustite, however, has a lattice parameter of a(,0) = 4.332 (ANGSTROM) which is consistent with stoichiometric FeO according to the relationship of Jette and Foote 1933. Thermodynamic calculations suggest that stoichiometric wustite may have a stability field at temperatures lower than 300(DEGREES)C and at high pressure but because of slow reaction rates, experimental confirmation is difficult. |
