The Formation of Mg-bearing Ferrite by the Air Oxidation of Aqueous Suspensions

Abstract

When the Mg2+/Fetotal molar ratio in the initial aqueous suspension is below 0.1 at pH 9.0 and 65 °C, almost all Mg2+ is incorporated into the spinel type ferrite by the air oxidation of Fe(OH)2. The chemical composition of the Mg-bearing ferrite thus obtained is not stoichiometric, and is expressed as the MgFe2O4–Fe3O4–γ-Fe2O3system. When the Mg2+/Fetotal ratio exceeds 0.1, the excess Mg2+ produces a basic magnesium sulfate which has a composition of [Mg1.002+, Na0.64+] [OH1.36−,(SO42−)0.64]. At pH 8.0, a small amount of the Mg2+ is incorporated into the ferrite, between pH 9.0 and 10.0 only the Mg-bearing ferrite is formed, and at pH 11.0, the α-FeOOH type compound is formed together with the Mg-bearing ferrite.

Extent and mechanism of metal ion incorporation into precipitated ferrites

“…Further chemical analyses were conducted in order to assess the moiety of the c-Fe 2 O 3 (maghemite) phase, which was reported by several authors [27,32,43,48] to form under similar synthesis procedures, alongside the magnetite phase, as result of excessive oxidation. The presence of maghemite is expected to affect both the incorporation extent of the divalent metals because of electro-neutrality considerations (maghemite is composed of trivalent cation only) and the unit cell dimension, which is later used to estimate the degree of Me content.…”

Effects of Reaction Conditions on Deposition of Ferrites from Alkaline Metal Hydroxide Gels

“…[4,5] These workers have shown that the sudden change in ORP at the end of the reaction coincides with the depletion of Fe(II) in the reaction mixture by oxidation to Fe(III). Typically the ORP starts at approximately -0.9 V vs. SCE and ends at approximately -0.1 V vs. SCE when the reaction is complete.…”

Microwave‐Hydrothermal Synthesis of Nanophase Ferrites

“…S PINEL ferrites are magnetic materials with a wide range of applications. There are numerous methods of ferrite powder preparation, such as hydrothermal, 1-3 coprecipitation and oxidation, [4][5][6][7][8] combustion, sol-gel, spray pyrolysis, evaporative decomposition of misted solutions, solid-state, and flux. Among these methods, the hydrothermal method is a lowtemperature method for ferrite powder preparation.…”