Self-propagating high temperature synthesis and magnetic properties of Ni0.35Zn0.65Fe2O4 powders

Ni-Zn ferrite powders were synthesized by self-propagating high temperature synthesis (SHS) method. X-ray diffraction, TEM and vibrating sample magnetometry (VSM) were used to characterize the phase composition, microstructure and magnetic properties of the combustion products. The effect of the combustion temperature (T _c), the major parameter of the SHS process, on particle size, phase composition and magnetic properties of the products was also studied. The results showed that particle size grew with the increasing combustion temperature. The maximum saturation magnetization,M _s, increased with combustion temperature indicating the growth of grain size and high degree of ferritization, while residual magnetization,M _r, and coercive force,H _c, decreased. Compared with other methods, Ni_0.35Zn_0.65Fe₂O₄ ferrite powders with improved magnetic properties can be obtained by SHS at 1000°C.     

Self-propagating high temperature synthesis of Ni0.35Zn0.65Fe2O4 ferrite powders

The stoichiometric Ni_0.35Zn_0.65Fe₂O₄ ferrite powders were synthesized by SHS method. In the process of SHS, the effects of the molar ratio Fe/Fe₂O₃ in the starting mixture, oxygen pressure, grain size and relative density of the raw materials on combustion temperature, combustion wave velocity, phase composition and microstructure of the combustion products were investigated. X-ray diffraction, scanning electron microscope, TEM, vibrating sample magnetometry were used to characterize the microstructure and magnetic properties of the products. The results showed that as the molar ratio Fe/Fe₂O₃ increases, the combustion temperature and combustion wave velocity increased. The same results can be observed when the oxygen pressure increased from 0.1 to 0.9 MPa. The increase of grain size and relative density of raw materials resulted in the decrease of combustion temperature and combustion wave velocity. Compared with other methods, SHS process leads to ferrite powders with improved magnetic properties.     

Combustion synthesis and characterization of NiCuZn ferrite powders

In this paper, the feasibility of synthesizing NiCuZn ferrite powders by combustion synthesis (CS) reaction is demonstrated through igniting the mixtures of iron, iron oxide, copper oxide, zinc oxide and copper carbonate under different oxygen pressure values. The ferrite powders produced directly from the CS reaction and after annealing at 800 °C for 2 h are characterized by XRD, SEM, XPS and VSM. The results show that the spinel phase in the combustion products increases with the decrease of the diluent content and the increase of the oxygen pressure. Heating the as-synthesized ferrite at 800 °C for 2 h affords pure crystalline NiCuZn ferrite, which possesses better magnetic properties. XPS studies confirm that copper ions in the as-synthesized ferrite are present in the different ionic states of the A- and B-sites, while copper ion is divalent in the B-sites only for the annealed products.     

Phase transformation and the mechanism of combustion synthesis of ZnFe2O4 ferrite powders

The reaction mechanism of combustion synthesis of zinc ferrite, which belongs to the complex oxide combustion reaction was investigated using a combustion front quenching method (CFQM). Phase transformation and microstructural evolution of the quenched samples were observed by XRD, SEM, and Mössbauer spectroscopy. The results showed that the combustion proceeded by a dissolution-precipitation mechanism, viz the iron was burned to form Fe₂O₃ in an oxygen atmosphere and melting of the Fe₂O₃ led to the dissolving of the ZnO particles, then ZnFe₂O₄ precipitated out. In addition, a model of the mechanism was drawn.     

Structural and Magnetic Properties of Nanocrystalline Lithium–Zinc Ferrite Synthesized by Microwave-Induced Glycine–Nitrate Process

In this study, nanocrystalline Li–Zn ferrites with the chemical composition Li_0.5Zn _x Fe_2.5?x O₄ (where x=0, 0.1,0.2,0.3,0.4,0.5) were synthesized by the glycine–nitrate process using glycine as a fuel, nitrate as an oxidizer and microwave oven as a heat source. The combustion reaction was studied by differential thermal analysis and thermogravimetry. The experimentally determined combustion reaction is extremely exothermic and it occurs at 170 ^°C. The as-synthesized powders were characterized by X-ray diffraction technique. X-ray diffraction data shows that nanocrystalline Li–Zn ferrite powders with a spinel structure have been formed successfully in all samples. Morphological studies using scanning electron microscopy and field emission scanning electron microscopy show agglomerated clusters with a lot of pores attributed to the large amount of gases released during the combustion synthesis with the particle size of 20–40 nm. The magnetic measurements on the as-synthesized powders and compacted samples were carried out using a vibrating sample magnetometer and an inductance/capacitance/resistance meter, respectively. Saturation magnetization increases with the increase in zinc concentration up to x=0.2 and then it decreases with the increase in the zinc content. In addition, maximum magnetic permeability also obtained for the sample with x=0.2 at different frequencies.     

Microwave-induced combustion synthesis of Li0.5Fe2.5−xCrxO4 powder and their characterization

Li_0.5Fe_2.5−xCr_xO₄ (0 ≦ x ≦ 1.0) powders with small and uniformly sized particles were successfully synthesized by microwave-induced combustion, using lithium nitrate, iron nitrate, chromium nitrate, and carbohydrazide as the starting materials. The process takes only a few minutes to obtain as-received Cr-substituted lithium ferrite powders. The resultant powders annealed at 650 °C for 2 h and were investigated by thermogravimeter/differential thermal analyzer (TG/DTA), X-ray diffractometer (XRD), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermomagnetic analysis (TMA). The results revealed that the lattice constant decreases linearly with increasing of Cr content in Li_0.5Fe_2.5−xCr_xO₄ specimens. Moreover, the magnetic properties of Cr-substituted lithium ferrite were also strongly affected by Cr content. The saturation magnetization, remanent magnetization, and coercive force decrease monotonously with increasing of Cr content.     

Magnetic properties of magnesium-cobalt ferrites synthesized by co-precipitation method

The alternating current (a.c.) low field susceptibility vs temperature, magnetization and⁵⁷Fe Mössbauer effect measurements are reported for the spinel solid solution series Mg _x Co_1?x Fe₂O₄ synthesized by a wet-chemical method before and after high temperature annealing. The observed features for the wet samples, such as the coexistence of paramagnetic doublet and magnetic sextets in Mössbauer spectra and lower saturation magnetization values confirm small particle ferrite behaviour. Especially, Mössbauer spectra of wet samples reveal the presence of superparamagnetic particles which exist simultaneously with ferrimagnetic regions in the materials well supported by a.c. susceptibility data. The high temperature annealing changes the wet-prepared ferrites into the ordered magnetic structure of ceramic ferrites.     

Facile synthesis of nanocrystalline zinc ferrite via a self-propagating combustion method

Macroporous nanocrystalline zinc ferrite with single spinel-phase was prepared by a facile self-propagating combustion method using zinc nitrate, iron nitrate and glycine. The as-prepared ZnFe₂O₄ were characterized by X-ray diffraction (XRD) analysis, N₂ adsorption, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and energy dispersive X-ray spectrum (EDS). The magnetic properties of the prepared ZnFe₂O₄ were also studied.     

Structural and Magnetic Properties of Cobalt and Manganese Doped Ni-Ferrite Nanoparticles

This study reports that NiCoMn ferrite [Ni_(1?x)Co _x Mn _y Fe_(2?y)O₄ with (x=y=0.01,0.02)] powders are prepared by using the sol-gel combustion method. The effect of various calcination temperatures on their structural and magnetic properties is also investigated. Structural properties of the powders are carried out by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). According to XRD analysis, all samples of two compositions have cubic spinel structure, with an enlargement in crystalline size is observed with increasing of calcination temperature. The crystallite size of the nanopowders is estimated from (311) peaks using Scherrer’s formula. Spherical particles of nanocrystalline ferrite powders are shown in TEM photographs. The room temperature magnetic properties of particles are studied by using a vibrating sample magnetometer (VSM). The magnetization measurements also indicated that the saturation magnetization (M _s) increases as the calcinations temperature increases for both A and B samples in the range of 31.69 to 47.77 and 21.81 to 48.89 emu/gr, respectively. The value of coercivity fields (H _c) decrease with increasing the calcinations temperature. Furthermore, the properties of two samples synthesis at the optimum calcinations temperature (800 ^°C) compared together.     

Bulk magnetic properties of Co-Zn ferrites prepared by the co-precipitation method

The alternating current (a.c.) susceptibility versus temperature and magnetization measurements are reported for the disordered spinel ferrite system Zn _x Co_1-x Fe₂ O₄ prepared by a wet chemical method before and after high temperature annealing. The low field a.c. susceptibility measurements indicate that the low temperature synthesis of wet prepared Co-Zn ferrites aids the formation of spin-clusters and thereby increases the magnetic inhomogeneity. The X-ray analysis shows that the samples are single phase spinels and the variation of lattice constant with zinc concentration deviates from Vegard's law [1]. The high temperature annealing changes the wet prepared ferrites into the ordered magnetic structure of the ceramic ferrites.     

Synthesis, characterization and magnetic properties of nanocrystalline Ni-Zn-Co ferrites

Nanocrystalline magnetic particles of Ni_0.7−xZn_0.3Co_xFe₂O₄ with x lying between 0.0 and 0.3 were synthesized by combustion method using metal nitrates, sucrose and polyvinyl alcohol (PVA). The synthesized powders where characterized by X-ray diffraction and Transmission electron microscopy (TEM). The average crystallite size determined from XRD data using Scherrer formula lie in the range of 20-30 nm. TEM micrographs show a well defined nano-crystallite state with an average particle size of around ~ 10 nm. The electron diffraction patterns confirm the spinel crystal structure of the ferrite. Magnetic properties measured at room temperature by vibrating sample magnetometer (VSM) reveal an increase in saturation magnetization with increase in cobalt concentration. Non-linear increase in saturation magnetization is related to surface effects and method of preparation.     

Temperature dependence on the mass susceptibility and mass magnetization of superparamagnetic Mn–Zn–ferrite nanoparticles as contrast agents for magnetic imaging of oil and gas reservoirs

The mass susceptibility (χ_mass) and mass magnetization (M_mass) were determined for a series of ternary manganese and zinc ferrite nanoparticles (Mn–Zn ferrite NPs, Mn_xZn_1?xFe₂O₄) with different Mn:Zn ratios (0.08 ≤ x ≤ 4.67), prepared by the thermal decomposition reaction of the appropriate metal acetylacetonate complexes, and for the binary homologs (M_xFe_3?xO₄, where M = Mn or Zn). Alteration of the Mn:Zn ratio in Mn–Zn ferrite NPs does not significantly affect the particle size. At room temperature and low applied field strength the mass susceptibility increases sharply as the Mn:Zn ratio increases, but above a ratio of 0.4 further increase in the amount of manganese results in the mass susceptibility decreasing slightly, reaching a plateau above Mn:Zn ≈ 2. The compositional dependence of the mass magnetization shows less of a variation at room temperature and high applied fields. The temperature dependence of the mass magnetization of Mn–Zn ferrite NPs is significantly less for Mn-rich compositions making them more suitable for downhole imaging at higher temperatures (>100 °C). For non-shale reservoirs, replacement of nMag by Mn-rich Mn–Zn ferrites will allow for significant signal-to-noise enhancement of 6.5× over NP magnetite.     

Comparative Studies on the Structure and Magnetic Properties of Ni–Zn Ferrite Powders Prepared by Glycine-Nitrate Auto-combustion Process and Solid State Reaction Method

Ni–Zn ferrite compositions (Ni_1?x Zn _x Fe₂O₄) are well known due to their remarkable soft magnetic properties, which potentially have a broad range of applications in many areas. In this study, Ni–Zn ferrite with the chemical formula of Ni_0.64Zn_0.36Fe₂O₄ was prepared by the glycine-nitrate autocombustion process (GNP) and solid state reaction method (SSRM). In order to achieve a desirable particle size, the SSRM powders were milled for 3 h at a milling rate of 200 rpm. The structure and magnetic properties of the ferrite powders, which were synthesized by both methods, were characterized and their properties were compared. The results indicate that a significant amount (～?90 wt.%) of nanocrystalline Ni_0.64Zn_0.36Fe₂O₄ ferrite with the average crystallite size of 47 nm, particle size of 200 nm, saturation magnetization of 73 emu/g and coercivity of 54 Oe has been formed by means of the glycine-nitrate process. The results also show that not only the saturation magnetization of the GNP ferrite powder is relatively similar to that of the milled SSRM powders, but also it is synthesized at a much shorter duration than that of the solid state reaction method.     

Magnetism in V-Doped Tio2 Bulk Samples

Bulk samples of Ti_1?x V _x O₂ nominal composition with x=0.08 were fabricated with the standard solid-state reaction. Appropriate proportions of Titanium dioxide (TiO₂) and vanadium pentoxide (V₂O₅) high-purity powders were thoroughly mixed according to the desired stoichiometry. The solid-state reaction was conducted for 30?min. Pellets were formed applying 8 tons of pressure. Then, they were subjected to thermal process at 550?°C for 10?h in air. The samples were characterized by X-ray diffraction analysis. Magnetic properties were studied by measuring magnetization as a function of temperature and applied magnetic fields. Magnetization as a function of temperature without applied magnetic field showed that magnetization increases slowly with decreasing temperature from 300 to 42?K, but for temperatures below 42?K, it increases rapidly. Magnetization as a function of the applied magnetic field, at 5, 77, and 300?K revealed the ferromagnetic behavior of the samples.     

Microstructure, hysteresis and microwave absorption analysis of Ba(1 − x)SrxFe12O19 ferrite

M-type hexagonal ferrite series, Ba_(1−x)Sr_xFe₁₂O₁₉ (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0), has been synthesized by conventional ceramic method. Hysteresis parameters have been investigated at an applied field of 10 kOe and absorption has been studied at X-band as a function of thickness, substitution and frequency. Microstructure and X-ray diffraction confirmed hexagonal structure of ferrite. The substitution causes profound increase in absorption, coercivity and magnetization. The magnetic parameters have been characterized by taking into account microstructure and preferential site occupancy. Curie temperature decreases with substitution due to the formation of spin canting structure.     

Steady-shear magnetorheological response of fluids containing solution-combustion-synthesized Ni-Zn ferrite powder

Magnetically soft nickel-zinc ferrite (Ni_0.5Zn_0.5Fe₂O₄) powder with high saturation magnetization was synthesized by solution combustion route using metal nitrates as precursors and glycine as fuel. The particles were found to have irregular morphology. Three different concentrations of magnetorheological fluids (MRFs) were prepared by dispersing 10, 20 and 40?wt% of these particles in thin silicone oil. The behaviours of the MRFs were studied under steady shear conditions at different applied magnetic field strengths (B). The yield strength (τ_Y) and viscosity (η) of all the MRFs were found to increase with B and particle fill fraction ?, while the response of the MRFs was strongly influenced by the morphology, microstructure and saturation magnetization of the particles. Owing to the low density of the particles, the observed off-state viscosity is high. However, the excellent thermo-oxidative and chemical stabilities of these magnetic oxide particles than metallic magnetic particles make these MRFs dependable for applications in harsh working environments. In addition, the low cost and feasibility of large scale preparation of these magnetic oxides make these MRFs further attractive for industrial applications.     

Magnetic, dielectric, and complex impedance properties of nanocrystalline Mn-Zn ferrites prepared by novel combustion method

The electromagnetic and micro-structural properties of nanocrystalline spinel ferrite Mn_xZn_1 − xFe₂O₄ (x = 0.0-1.0) prepared by the novel route of combustion method were investigated. The microstructure and morphology were characterized by X-ray diffraction and scanning electron microscopy, respectively. The magnetic properties were measured using vibrating sample magnetometer. The analysis indicates that the permittivity, saturated magnetization and coercivity increase as the content of manganese rises. Further, the analysis of complex impedance spectra by an equivalent circuit model was used to investigate the AC electrical conduction mechanism. The results show that as-synthesized Mn-Zn ferrites with low conductivity and good magnetic properties have excellent potential for applications in electromagnetic devices.     

Spin canting phenomenon in cadmium doped cobalt ferrites, CoCd x Fe2−x O 4 ( x = 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), synthesized using sol–gel auto combustion method

Synthesis of non-collinear (spin canted) ferrites having the formula, CoCd _x Fe_2???x O ₄ (x?= 0·0, 0·2, 0·4, 0·6, 0·8 and 1·0), has been carried out using the sol–gel auto combustion method. The ferrite samples show an interesting magnetic transition from Neel to Yafet–Kittel configuration, as the Cd^2?+? concentration is increased beyond x?= 0·4. The FT–IR spectra confirm the formation of the metal oxide bond as they exhibit two frequency bands in the range of ~595 cm^???1 and ~450 cm^???1, corresponding to the tetrahedral and the octahedral stretching vibrations of the metal oxide, respectively. The structural evolutions of the nanophase investigated using powder X-ray diffraction (XRD) technique show that the average crystallite size is ~ 35 nm. The magnetic studies reveal that the saturation magnetization, M _s , increases up to x?= 0·4 and decreases when the value of x is >0·4. It is proposed that the incorporation of Cd^2?+? ion takes place into the tetrahedral sites and up to x?= 0·4, Neel’s model is followed. But for x?> 0·4, canting of spins occurs, as explained by Yafet–Kittel (Y–K) model. The d.c. resistivity decreases as a function of temperature, indicating semiconducting nature of the ferrites and the positive value of Seebeck coefficient establishes p-type conduction behaviour for all the ferrite samples.     

Self-propagating high-temperature synthesis of Al2O3-TiC-Al composites by aluminothermic reactions

Al₂O₃-TiC-Al composites were fabricated by self-propagating high-temperature synthesis process using aluminothermic reactions with titania, aluminum, and graphite powders. As the molar ratio x of the excessive aluminum in the reactants increases, the adiabatic temperature of the reaction and the melting rate of alumina in the products obviously decrease according to thermodynamics. This reaction is theoretically presumed to be ignited at preheat temperature of 900 K even though x is up to 13 mole. The experimental results revealed that the critical molar ratio of excessive Al, which the combustion reaction can self-sustain, is 7.66 mole with a preheat temperature of 400–500 K. The excessive aluminum favors to fill in the pores of the products, and a cylindrical Al₂O₃-TiC-Al composite with a relative density of 70% can be obtained, and its tensile strength is higher ten times than that of the Al₂O₃-TiC composite. Moreover, TiC and Al₂O₃ grains in the composites are fined as the excessive aluminum increases. Although the excessive aluminum does not take part in the combustion reaction, it strongly affects combustion process and microstructures of the products.     

Apatite-forming ability and magnetic properties of glass-ceramics containing zinc ferrite and calcium sodium phosphate phases

Fine particles of zinc ferrite (ZnFe₂O₄) and calcium sodium phosphate [NaCaPO₄] were crystallized in bulk x(ZnO, Fe₂O₃)(65?x)SiO₂20(CaO, P₂O₅)15Na₂O (6 ≤ x ≤ 21 mol %) glassy matrix by heat treatment. Initial magnetization curves reveal that samples with x = 6 and 9 mol % zinc–iron oxide exhibit both ferrimagnetic and paramagnetic contributions, whereas, samples with x > 9 mol % zinc–iron oxide exhibit only ferrimagnetic contribution. This observation is supported by the disappearance of the electron paramagnetic resonance (EPR) absorption line centered at g ≈ 4.3 in samples with x > 9 mol % zinc–iron oxide. Apatite-forming ability of the glass-ceramic samples was investigated by examining apatite formation on the surface of the samples treated in simulated body fluid (SBF). Increase in apatite-forming ability was observed with an increase in zinc–iron oxide content. The results obtained have been used to understand the evolution of the apatite surface layer as a function of immersion time in SBF and glass-ceramic composition. A good correlation has also been observed between the magnetic nature of the samples and their apatite-forming ability. These materials are expected to find application as thermo-seeds in hyperthermia treatment of bone cancer.