Ferrite grade iron oxides from ore rejects

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,J _s, 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.     

Dielectric properties of the system Ca1 −x La x Ti1 −x Co x O3

Dielectric behaviour of samples of the system Ca_{1 −x} La _x Ti_{1 −x} Co _x O₃ withx ⩽ 0·20 has been studied in the temperature range 300–525 K as a function of frequency. The strong dispersion ofɛ andD observed in these materials indicate the significant contribution of interfacial polarisation to the observed dielectric properties. The interfacial polarisation arises due to the presence of microscopic chemical heterogeneities arising out of the slow diffusion-controlled solid state sintering process used for their preparation.     

Dielectric behaviour of glasses and glass ceramics in the system BaO-PbO-TiO2-B2O3-SiO2

Glasses with varying molar ratios of PbO/BaO in the system BaO-PbO-TiO₂-B₂O₃-SiO₂ were prepared keeping (BaO + PbO)/TiO₂ ratio equal to one. The glasses were ceramized by two-stage heat treatment. X-ray diffraction indicates that PbTiO₃ crystallizes in lead-rich glasses while BaTiO₃ precipitates in barium-rich compositions. Solid solution (Ba, Pb)TiO₃ does not seem to crystallize over the entire range of compositions. Simultaneous presence of PbO and BaO in the initial glass composition reduces the yield of ferroelectric phase. Dielectric properties have been interpreted in terms of microstructural features.     

Dielectric properties of K2Zn2(SO4)3 and (NH4)2 Mg2(SO4)3

Dielectric constant (ɛ), dielectric loss (tan δ) and conductivity (σ) for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ have been measured over the frequency range 100 Hz — 100 kHz and in temperature range 30°C — 400°C. The values of static dielectric constant at room temperature are 7.67 and 4.80 for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively. The plots of log σ against reciprocal temperature at different frequencies of these samples merge into a straight line beyond 250°C and the activation energies calculated in this region are found to be 0.67 eV and 1.98 eV for K₂Zn₂(SO₄)₃ and (NH₄)₂ Mg₂(SO₄)₃ respectively.     

MexZn1-x Fe2O4复合氧化物的制备及电磁波损耗特性研究

通过固相化学反应合成了MexZn1-xFe2O4(Me=Co,Mn;x=0,0.5,0.6)三种复合氧化物,利用TG-DTA,XRD,SEM等对复合氧化物的热分解性质,物相和形貌进行了表征,同时测定了复合氧化物的相对复介电常数和相对复磁导率,以损耗角正切值表征了它们的吸波性能,结果表明MexZn1-xFe2O4复合氧化物在高频段对电磁波有较大的吸收,并且三种复合氧化物之间有明显差异.     

Dielectric,electrical and infrared studies of γ-Fe2O3 prepared by combustion method

This paper reports the electrical and spectroscopic investigation of the gamma ferrite synthesized through combustion route. The electrical study and dielectric behaviour showed a typical ferrite nature for the samples. The γ → α transition is observed from the electrical conductivity data. Infrared spectral study showed the transition of a typical ferrite. The effect of the presence of α-impurities in γ-Fe₂O₃ is also explained here.     

Dielectric, elastic, anelastic and conductivity behaviour of ferroelectromagnetic composites, Ni0·5Zn0·5Fe1·95O4?δ + Ba0·8Pb0·2TiO3

Ferroelectromagnetic composites with compositions, X Ni_0·5Zn_0·5Fe_1·95O_4−δ + (1 − X) Ba_0·8Pb_0·2TiO₃, in which X varies as 0, 0·005, 0·010, 0·015, 0·020, 0·040, 0·060, 0·080 and 1 in mole %, were prepared by conventional ceramic double sintering process. The presence of two phases was confirmed by X-ray diffraction. The temperature variation of dielectric constant, ɛ′, dielectric loss, tan δ, d.c. conductivity, a.c. conductivity, elastic and anelastic behaviour of ferrite-ferroelectric composites were studied in the temperature range 30–350°C. The a.c. conductivity measurements on these composites in the frequency range 100 Hz-1 MHz at room temperature reveal that the conduction mechanism is due to small polaron hopping. The dielectric and elastic data were discussed in the light of phase transitions.