V M S Verenkar
Articles written in Bulletin of Materials Science
Volume 24 Issue 1 February 2001 pp 39-45 Magnetic Materials
Iron(II) carboxylato–hydrazinates: Ferrous fumarato–hydrazinate (FFH), FeC4H2O4.2N2H4; ferrous succinato–hydrazinate (FSH), FeC4H4O4.2N2H4;ferrous maleato–hydrazinate (FEH), FeC4H2O4.2N2H4;ferrous malato–hydrazinate (FLH), FeC4H4O5.2N2H4;ferrous malonato–hydrazinate (FMH), FeC3H2O4.1.5N2H4.H2O; and ferrous tartrato–hydrazinate (FTH), FeC4H4O6.N2H4.H2O are being synthesized for the first time. These decompose (autocatalytically) in an ordinary atmosphere to mainly 𝛾-Fe2O3, while the unhydrazinated iron(II) carboxylates in air yield 𝛼-Fe2O3, but the controlled atmosphere of moisture requires for the oxalates to stabilize the metastable 𝛾-Fe2O3. The hydrazine released during heating reacts with atmospheric oxygen liberating enormous energy, $$N_2H_4 + O_2 \rightarrow N_2 + H_2O;\Delta H_2O = – 621 kJ/mol,$$ which enables to oxidatively decompose the dehydrazinated complex to 𝛾-Fe2O3. The reaction products N2 + H2O provide the necessary atmosphere of moisture needed for the stabilization of the metastable oxide.
The synthesis, characterization and thermal decomposition (DTA/TG) of the iron(II) carboxylato–hydrazinates are discussed to explain the suitability of 𝛾-Fe2O3 in the ferrite synthesis.
Volume 24 Issue 3 June 2001 pp 323-330 Chemical Beneficiation
Chemically beneficiated high silica/alumina iron ore rejects (27–76% Fe2O3) were used to synthesize iron oxides of purity 96–98% with SiO2/Al2O3 ratio reduced to 0.03. The major impurities on chemical beneficiations were Al, Si, and Mn in the range 2–3%. A 99.73% purity Fe2O3 was also prepared by solvent extraction method using methyl isobutyl ketone (MIBK) from the acid extracts of the ore rejects. The magnesium ferrite, MgFe2O4, prepared from these synthetic iron oxides showed high resistivity of ∼ 108 ohm cm. All ferrites showed saturation magnetization, 4𝜋𝑀s, in the narrow range of 900–1200 Gauss and the Curie temperature, 𝑇c, of all these fell within a small limit of 670 ± 30 K. All ferrites had low dielectric constants (𝜀'), 12–15, and low dielectric loss, tan 𝛿, which decreased with the increase in frequency indicating a normal dielectric dispersion found in ferrites. The presence of insignificant amount of polarizable Fe2+ ions can be attributed to their high resistances and low dielectric constants. Impurities inherent in the samples had no marked influence on the electrical properties of the ferrites prepared from the iron ore rejects, suggesting the possibility of formation of ferrite of constant composition, MgFe2O4, of low magnetic and dielectric losses at lower temperatures of 1000°C by ceramic technique.
Volume 24 Issue 3 June 2001 pp 331-338 Chemical Beneficiation
Iron oxyhydroxides and hydroxides were synthesized from chemically beneficiated high SiO2/Al2O3 low-grade iron ore (57.49% Fe2O3) rejects and heated to get iron oxides of 96–99.73% purity. The infrared band positions, isothermal weight loss and thermogravimetric and chemical analysis established the chemical formulas of iron-oxyhydroxides as 𝛾-FeOOH.0.3H2O; 𝛼-FeOOH.0.2H2O and amorphous FeOOH. The thermal products of all these were 𝛼-Fe2O3 excepting that of 𝛾-FeOOH.0.3H2O which gave mainly 𝛾-Fe2O3 and some admixture of 𝛼-Fe2O3. The hydrazinated iron hydroxides and oxyhydroxides, on the other hand, decomposed autocatalytically to mainly 𝛾-Fe2O3. Hydrazine method modifies the thermal decomposition path of the hydroxides. The saturation magnetization, 𝐽s, values were found to be in the range 60–71 emu g–1 which are close to the reported values for 𝛾-Fe2O3. Mechanism of the 𝛾-Fe2O3 formation by hydrazine method is discussed.
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