Factors Influencing the Texture and Stability of Maghemite Obtained from the Thermal Decomposition of Lepidocrocite

Abstract

The thermal decomposition of a series of lepidocrocite samples has been monitored by means of the Constant Rate Thermal Analysis (CRTA). This method allows controlling the reaction temperature in such a way that both the reaction rate and the partial pressure of the water vapor generated in the reaction are maintained constant at values that can be arbitrarily selected by the user. The final products obtained from the thermal dehydroxylation of the lepidocrocite precursors under residual pressures of water vapor ranging from 5 × 10 -5 mbar to 10 mbar have been characterized by TEM, XRD, and Mo ¨sbauer spectroscopy. It has been concluded that they preserve the shape and size of the corresponding precursors. The precise control of the partial pressure of the water vapor self-generated in the above reaction allows tailoring the internal porosity of the maghemite-hematite mixture obtained as final product. It has been shown that the larger the particle size of the starting lepidocrocite is, the larger the porosity of the iron oxide obtained. The ratio γ-Fe 2 O 3 /R-Fe 2 O 3 is strongly dependent on both the texture of the starting lepidocrocite and the partial pressure of water vapor selected for performing its dehydration. Thus, the percentage of maghemite increases by decreasing the particle size of the starting lepidocrocite and by increasing the residual pressure of water vapor. An interpretation of this behavior is given.

γ-Fe2O3/SiO2 nanocomposites for magneto-optical applications: Nanostructural and magnetic properties

“…nitrogen, is needed to observe the transformation to c-Fe 2 O 3 phase [24], while oxygen favors the appearance of a-Fe 2 O 3 . Furthermore, the presence of water vapor either generated in the sample surroundings during water evacuation from the xerogel pores or contained within the employed gas flow, also enhances the formation of a-Fe 2 O 3 , as demonstrated in dedicated experiments with water saturated gas flows [25]. Finally, the temperature was reduced at 0.5°C/min down to room temperature, and iron oxide doped silica xerogels resulted, with physical and mechanical properties dependent of processing conditions.…”

Adsorption/Reduction of NO2 on Graphite Oxide/Iron Composites

“…Additional peaks at about 17 and 27°found only for Fe-n indicate the presence of ferrihydrites, particularly γ-FeOOH. 39,40 The FTIR spectra of the composite materials and iron samples are presented in Figure 4. Several bands are revealed on these spectra.…”

Synthesis based on the wet impregnation method and characterization of iron and iron oxide-silica nanocomposites

“…4 shows the DSC trace at a heating rate of 10 C/min, in air, for the composite obtained at 300 C. The reactivity of γ-Fe 2 O 3 regarding its transformation to α-Fe 2 O 3 is greatly affected by the method of preparation and pre-treatment of samples, by impurity content and the morphology of particles, etc. [33][34][35]. The temperatures reported in the literature for this transformation range from 250 to 900 C. In Fig.…”