Why do FeOOH co-exist with Fe3O4 when the [Fe+2]/[Fe+3] doesn't maintain 1:2?
Dear Antonio, I use co-precipitation method. Gamma-FeOOH or Alpha-FeOOH comes into picture depending upon the synthesis conditions. What i want to know is why people take 1:2 ratio for synthesis of Fe3O4, if it deviates from 1:2 is it not possible to lend up with non stoichiometric Fe3O4?
It is stoichiometric for the conversion.
2.3. Procedure
Nanofluid sample was prepared by the
coprecipitation technique. The synthesis of Fe3O4
magnetic nanoparticles (MNP) is based in the
mixture of FeCl3 6H2O and FeCl2 4H2O salts in the
molar ratio 1:2. The reaction in this process is as
follows:
2Fe3+ + Fe2+ 4OH- ---> Fe3O4 + 4H+
from http://www.cenm.org/productos/articulos/articulos/233.pdf
Iron ions are your limiting reagents so as to prevent other oxide/oxyhydroxides from forming
where as
In the laboratory goethite can be formed through nucleation from solution by slow hydrolysis of Fe3+(OOH)6 at room temperature.
Lepidocrocite ... formed synthetically by oxidation of Fe(II) salt solutions at pH 5-7. The formation of Lepidocrocite is influenced by a number of factors such as the concentration of Fe(II) in solution, pH, partial pressure of CO2, the rate of oxidation and the presence of various solutes in the soil solution.
(http://www.kurdishscientist.com/ironoxides.html)
So, more Fe3+ --> more gamma FeOOH
More Fe2+ ---> more alpha FeOOH
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