Iron(III) Oxides from Thermal ProcessesSynthesis, Structural and Magnetic Properties, Mössbauer Spectroscopy Characterization, and Applications

Abstract

Structural and magnetic properties, methods of synthesis, and applications of seven iron-(III) oxide polymorphs, including rare beta, epsilon, amorphous, and high-pressure forms, are reviewed. Thermal transformations resulting in the formation of iron oxides are classified according to different parameters, and their mechanisms are discussed. 57 Fe Mo ¨ssbauer spectroscopy is presented as a powerful tool for the identification, distinction, and characterization of individual polymorphs. The advantages of Mo ¨ssbauer spectroscopy are demonstrated with two examples related to the study of the thermally induced solid-state reactions of Fe 2 (SO 4 ) 3 . Lead-InIron(III) oxide is not only a strategic industrial material but also a convenient compound for the general study of the polymorphism and the mutual polymorphous changes in nanoparticles. The existence of amorphous Fe 2 O 3 and four polymorphs (alpha, beta, gamma, and epsilon) has been established. Their discoveries as well as the majority of formation processes are connected with thermal transformations of iron-bearing materials in an oxidizing atmosphere. 57 Fe Mo ¨ssbauer spectroscopy is a unique method that allows one to distinguish and identify individual structural forms, amorphous and nanostructured Fe 2 O 3 particles, to analyze their magnetic properties and to study their formation mechanism during thermally induced solidstate reactions. In this review, thermal processes resulted in the Fe 2 O 3 formation are classified from different viewpoints and their mechanism is discussed. Applications, structural and magnetic properties, and methods of synthesis of all known forms of iron(III) oxide and their Mo ¨ssbauer characterization are also summarized. A detailed survey of the properties of rare forms (amorphous Fe 2 O 3 , β-Fe 2 O 3 , -Fe 2 O 3 , and highpressure Fe 2 O 3 ) is presented for the first time. With respect to the more known R-Fe 2 O 3 and γ-Fe 2 O 3 , the presented data spring from a series of previous works, including the excellent book by R. M. Cornell and U. Schwertmann. 1 Some unresolved problems, such as the relation between the properties of the original ferrogenous precursor and the structure of the formed iron-(III) oxide, or the experimental possibility to distinguish the amorphous Fe 2 O 3 from nanostructured γ-Fe 2 O 3 or R-Fe 2 O 3 particles are discussed. The value of Mo ¨ssbauer spectroscopy for the characterization of iron(III) oxides produced by thermal processes is demonstrated with two experimental examples taken from our work in the field. † Dedicated to R. L. Mo ¨ssbauer on the occasion of the 40 th jubilee of Nobel Prize presentation.

Magnetic and Mössbauer Study of Cerium-Based Reactive Sorbent

“…The last doublet, δ ∼ 0.40 mm/s and ∆ ∼ 0.70 mm/s, could represent dpositions in β-Fe 2 O 3 even if the doublet corresponding to b-positions cannot be resolved in the measured spectra due to its low intensity. Two quadrupole split components represent the crystallographically non-equivalent cation b-and d-positions in the structure [8]. The relative ratio of the fm and pm phases A f m /A pm slightly changes in dependence on treatment temperature for the benefit of fm from 2.17 (S0) to 4.68 (S673).…”

Sol–gel synthesis of iron(III) oxyhydroxide nanostructured monoliths using Fe(NO3)3·9H2O/CH3CH2OH/NH4OH ternary system

“…The results of elemental analysis are shown in Table 1 The preceding scenarios represent, in the case of Hypothesis 1, the exclusive existence of oxo bridges in the iron phase (in other words, a situation of complete condensation) and, in the case of Hypothesis 2, the coexistence of oxo and hydroxo bridges in equal 12 proportion. In both cases, it was considered that other substances or impurities have completely evaporated.…”

“…Other applications include torches for underwater or atmospheric cutting and perforation, hardware destruction devices, gas generators for airbags, the production of alumina-iron liners in-situ for pipes, and portable heat sources [10]. On the other hand, the iron(III) oxides, by themselves, are important materials in various fields of application [12]. They are used as inorganic pigments, both natural and synthetic, and as efficient catalysts for the manufacture of styrene, the Fisher-Tropsch synthesis of hydrocarbons, the selective oxidation of polyaromatic hydrocarbons and the burning of fuels, among other reactions.…”

Formation mechanism of nano-crystalline β-Fe2O3particles with bixbyite structure and their magnetic properties

“…The lattice parameter is a 0 =9.398 Å [2]. The cubic unit contains 24 Fe 3+ ions with C 2 symmetry (d site) and 8 ions with C 3i Symmetry (b site) [3][4][5]. The Néel temperature (T N ) of magnetic transition was reported between 110 K and 119 K [2,3].…”

“…There are several reports about the preparation of β-Fe 2 O 3 [1][2][3][4][5][6][7][8][9]. However there are only few reports obtaining the single phase β-Fe 2 O 3 [2] and concerning about the magnetic properties of β-Fe 2 O 3 [2,3].…”