S. Music

Synthesis of acicular α-FeOOH particles at a very high pH

Abstract The acicular α-FeOOH particles were synthesized from FeCl3 solutions at a very high pH using tetramethylammonium hydroxide as a precipitating agent. Samples were characterized by X-ray powder diffraction, FT-IR spectroscopy and transmission electron microscopy. α-FeOOH precipitated as a single phase from room temperature to 160 °C in a broad aging time interval. The ratio of the length to the width of α-FeOOH particles depended on the temperature and concentration of the starting FeCl3 solution. Multidomainic character of α-FeOOH particles gradually decreased with an increase in the temperature and time of aging.

Formation of nanocrystalline magnetite by thermal decomposition of iron choline citrate

Abstract Thermal decomposition of iron choline citrate (C 33 H 57 Fe 2 N 3 O 24 ) has been investigated using X-ray powder diffraction, Fourier transform infrared and 57 Fe Mossbauer spectroscopies. The starting compound was heated in a furnace at selected temperatures between room temperature and 460°C, and cooled down afterwards either by quenching in bidistilled water or by cooling in air. Final decomposition products were iron oxides Fe 3 O 4 (magnetite) and α-Fe 2 O 3 (hematite). In all samples quenched in bidistilled water magnetite was found to be a dominant crystalline phase. Self-propagating burning of iron choline citrate in air was observed. The unit-cell parameter of the obtained magnetite decreased gradually with the increase in temperature of thermal treatment of the starting compound regardless of the cooling procedure. Crystallite size of magnetite varied from 10(1) to 21(2) nm, whereas the crystallite size of hematite varied between 25(2) and 39(3) nm. FT–IR spectra showed a significant amount of organic fraction in the samples containing magnetite as a dominant crystalline phase. In absence (or presence of a small quantity) of organic phase, a transformation of magnetite to hematite occurred. The Mossbauer spectrum of iron choline citrate at RT showed a single line with pronounced broadening. On heating the starting compound at 270°C and quenching in bidistilled water a quadrupole doublet was recorded at RT. This quadrupole doublet was ascribed to amorphous iron(III)-(hydrous) oxide. For samples thermally treated at higher temperatures Mossbauer spectroscopy showed magnetite and hematite. Mossbauer spectra also showed substoichiometric magnetite, Fe 3− x O 4 , which was very pronounced in samples produced at the highest temperatures, and this was in agreement with XRD investigations.

X-ray diffraction and57Fe Mössbauer spectra of the system Fe2O3−Ga2O3

The influence of gallium substitution on the chemical and structural properties of haematite, α-Fe2O3, has been studied using X-ray diffraction and57Fe Mössbauer spectroscopy. The presence of only α-(GaxFe1−x)2O3 phase is detected for the compositions withx between 0.01 and 0.90. A gradual decrease of the unit-cell parameters of α-(GaxFe1−x)2O3 with the increase of gallium substitution is measured.57Fe Mössbauer spectra showed that the value of the magnetic hyperfine field of pure α-Fe2O3 decreases with increasing gallium for iron substitution. The hyperfine magnetic structure, which is observed for α-(GaxFe1−x)2O3 at room temperature, collapsed for the composition withx≃0.50. The changes in the57Fe Mössbauer spectra of the α-(GaxFe1−x)2O3 phase are discussed in the sense of the electronic relaxation and the superparamagnetic effects.

Formation and properties of oxide phases in the system Er2O3Fe2O3

Abstract Mixed hydroxide, 3Er(OH) 3 +5Fe(OH) 3 , was prepared by chemical coprecipitation. X-Ray diffraction showed that the samples obtained by heating the mixed hydroxide at 650°C were amorphous, and contained Er 2 O 3 , α-Fe 2 O 3 , ErFeO 3 and Er 3 Fe 5 O 12 (ErIG) at 750°C. The changes in phase composition of the samples were also monitored by FT-IR spectroscopy. The Mossbauer spectrum of mixed hydroxide, 3Er(OH) 3 +5Fe(OH) 3 , at RT was characterized with a quadrupole doublet ( δ Fe =0.38, Δ =0.80, and Γ =0.50 mms −1 ). After heating the starting material up to 650°C, the superposition of two quadrupole doublets and of a sextet of very small intensity with H =506 kOe was observed. This result indicated that the amorphous fraction, as detected by XRD, actually contained additional Fe-bearing oxide phase of very fine particles and probably of poor crystallinity. The sample obtained at 1300°C was characterized by two hyperfine magnetic fields at RT with H d =394 and H a =489 kOe corresponding to ErIG. The results of magnetometric measurements of selected samples were discussed.