Hematite FejO

Few comparative studies have been made on the reductive dissolution of different mineral phases. In one such study, the order of reaction with seven organic and transition metal reductants was found to be the same hematite (a-Fe203)>magnetite (FejO,/,)>nickel ferrite (NiFe204) (43). Magnetite is an interesting case, since both Fe(III) and Fe(II) are present in the lattice prior to reaction. Evidence indicates that Fe(IIl) sites reduced to Fe(II) sites by redox reaction dissolve more quickly than Fe(II) sites originally present in the mineral lattice (6). 

Stewart, C. (1985) Spectral and other physicochemical properties of submicron powders of hematite (a-Fe203), maghemite (y-Fe203), magnetite (FejO ), goethite (a-FeOOH), and lepidocrocite (y-FeOOH). J. Geophys. Res., 90, 3126-44. 

FeO- Fe304(magnetite)- y-Fe203(magJiemite)670 K - a-FejO, (hematite)... 

FejOs hematite, reagent 0.001 mol 1CM5 mass titration... 

FejO., hematite, monodispersed, from chloride 0.001-0.01 mol dm NaNO, 25... 

FejO., of FeClj at 100 "C, washed hematite synthetic dm NaCl 0.01 mol dm ... 

Iron is extracted from ores hematite (FcjOj), magnetite (FejO, limonite... 

Bicrystalline nanowires of hematite (a-FejOs) have been synthesized by the oxidation of pure Fe"" Single-crystalline hexagonal a-FejO, nanorods and nanobelts can be prepared by a simple iron-water reaction at 673 K. Mesoporous quasi-single crystalline... 

X-Ray Diffraction. Diffractograms of the catalysts containing iron only show that crystalline phases containing iron are formed upon calcination at 750 C. In catalysts supported on titania as well as on zirconia hematite (a-FejO,) is formed. Only in the catalyst samples with good iron distributions, the most intense diffraction peak (hematite (104)) is hardly discernible... 

II. Hematite—830 °C endotherm, hematite undergoes a polymorphic transformation from a-FejO, to y-Fe203. 

Independent of the synthesis route, iron(III) oxide crystallizes in the a-modifi-cation (hematite) after calcination. Brilliant, intense colors are obtained with 50-150 nm layers of FejO, (hematite) on muscovite (see Figure 7.4c). Absorption and interference colors are produced simultaneously and vary with layer thickness. The red shades are especially intense because interference and absorption enhance each other. An intense green-red flop with different viewing angles is possible at a FejOj layer thickness producing green interference. 

In nature most metals have a greater tendency to exist in ores than as neutral metals. Therefore, when metals are mined they are already in oxidized states. To be useful in industry, they must be reduced to the neutral metals. Iron, for example, is most commonly foimd in the minerals hmonite (FeO), hematite (Fe Oj), magnetite (FejO ), or in iron ores mixed with other metals. With hmonite, metallic iron is produced in a blast furnace by reacting FeO with carbon monoxide (CO) at elevated temperatures, as shown ... 

Hemingway, B.S. (1990) Thermodynamic properties for bunsenite, NiO, magnetite, FejO, and hematite, FejOj, with comments on selected oxygen buffer reactions. Am. Mineral., 75, 781—790. 

---