Influence of hydrothermal powder morphology on the sintered microstructure of MnZn ferrites (original) (raw)
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Sintering of Nanosized MnZn Ferrite Powders
Journal of the American Ceramic Society, 2005
The sintering and microstructural evolution of nanosized MnZn ferrite powders prepared by a hydrothermal method were investigated. The microstructure of sintered ferrite compacts depends strongly on the strength of the agglomerates formed during the compacting of nanosized ferrite powders. It was found that at 700°C the theoretical density of sintered compacts can almost be reached, while above 900°C an increase of porosity was identified. The formation of extra porosity at higher sintering temperatures is caused mainly by the oxygen release which accompanies the dissolution of relatively large grains of residual ␣-Fe 2 O 3 in the spinel lattice.
Materials Research Bulletin, 1998
The hydrothermal process was employed to produce single-phase submicrometric NiZn ferrites. The materials were sintered in air at different temperatures and times (1100 to 1400°C, 5 to 240 min). After sintering, highly dense ceramic bodies with different microstructures were obtained. X-ray diffraction, helium pycnometry, nitrogen adsorption technique, and optical and scanning electron microscopy were used to determine the microstructural parameters of the samples. The modeling of the sintering process demonstrates a crossover between the densification mechanisms from grain boundary diffusion to lattice diffusion with increasing sintering temperature. It is also shown that, in the final-stage sintering, the grain growth kinetics is controlled by pore drag.
Sintering studies of hydrothermal NiZn ferrites
Journal of Physics and Chemistry of Solids, 1997
The isothermal sintering behavior of submicrometer-sized (< 50 nm) powders of Nii.ssZnss3Fe2,~04, prepared by hydrothermal process, was investigated under different sintering conditions. The powders were characterized by chemical analysis, energy-dispersive spectrometry (EDS), X-ray powder diffraction and scanning electron microscopy. The powders were compacted uniaxialiy with polyvinylalcohol and sintered at different times and temperatures, under constant heating and cooling rates. The characterization of the ceramic bodies was conducted by X-ray diffraction, optical and scanning electron microscopy, helium picnometry and EDS. The investigations showed high density ferrites with different porosity and microstructures depending on the sintering conditions. The results have been explained in terms of a qualitative model, which indicates the relative intluence of the densification and grain growth rates. 0 1997 Elsevier Science Ltd. All rights reserved
Acta Physica Polonica A, 2018
In this paper sol-gel method was used to synthesize Cu1−xZnxFe2O4 samples. Nitrates of magnesium, zinc and iron with purity of 97.00% were mixed with 80 ml of distilled water. To homogenize the resulting solution a constant stirring was used. The pH of the mixture was adjusted to 7 by ammonia while heating on a hot plate at 60 • C for 30 min. This procedure was followed by raising the temperature to 80 • C and continuous heating for 3 h to form the gel, which was dried at 120 • C to a complete burn out resulting in formation of fluffy structure. The fluffy structure was ground for 3 min using electric grinder to form fine ferrite powder. Powder was calcined at 500 • C for 4 h and sintered at 1000, 1100 and 1200 • C. The influence of sintering temperature on physical and magnetic properties of samples was studied by measurement of the absorbance of microwaves and the attenuation coefficient. The structure and morphology of prepared samples have been determined using XRD analysis and SEM.
Hydrothermally prepared nanocrystalline Mn–Zn ferrites: Synthesis and characterization
Microporous and Mesoporous Materials, 2008
Nanocrystalline particles of Mn x Zn 1Àx Fe 2 O 4 were prepared by chemical precipitation of hydroxides, followed by hydrothermal processing and freeze-drying. The synthesis involves the hydrolysis of aqueous metal precursors by using ammonia as precipitating agent. The chlorine ion concentration in the solution and the pH of the precipitation, are shown to play a crucial role in retaining the initial stoichiometry of the solution to the nanoparticles. The obtained products exhibited some interesting and unique features: they consisted of nanoparticles with sizes ranging from 5 to 25 nm, they had surface areas between 60 and 110 m 2 g À1 and pore sizes in the mesopore region (i.e. 8-20 nm). The produced materials were examined by powder X-ray diffraction for crystalline phase identification, scanning electron microscopy for grain morphology, high resolution transmission electron microscopy for particle size distribution and nitrogen sorption for surface area, pore volume and pore size distribution determination. The sintering of the ferrite powders was also studied by thermogravimetric analysis and dilatometry of the powders mixed with an organic binder to improve their compaction properties.
Field-Assisted Sintering of FeCo/MnZn Ferrite Core-Shell Structured Particles
JOM, 2021
Core-shell FeCo/MnZn ferrite powders were prepared by the sol-gel method with ferrite contents ranging from 5.01 wt.% to 17.10 wt.%. The target composition for the MnZn ferrite shell was Mn 0.8 Zn 0.2 Fe 2 O 4. The powders were compacted into bulk composites with FeCo separated by an oxide matrix using the field-assisted sintering technique (FAST) at 800°C for 10 min. All resulting compacts achieved relative density > 95%. As the MnZn ferrite content in the original core-shell powder increases from 5.01 wt.% to 17.10 wt.%, the saturation magnetization of the compacts decreases from 222 Am 2 /kg to 165 Am 2 / kg, and the coercivity increases from 772 A/m to 1654 A/m. XRD of the compacts indicates that a chemical reaction dissociates the spinel-structured MnZn ferrite into a rocksalt structured phase. Thermodynamics calculation indicates that the reaction happens between FeCo and MnZn ferrite at 800°C, but favors MnZn ferrite at temperatures £ 400°C. This prediction was substantiated by FAST consolidation at 400°C.
2005
Abstract MnZn ferrites are conventionally produced by the ceramic method that involves the solid state reaction of metallic oxides or carbonates at high temperatures. The particles obtained by this method are rather large and non-uniform in size. In order to overcome the difficulties arising out of the ceramic process, the coprecipitation method has been used as an alternative route to produce chemically homogeneous powders with fine particle size. In this work MnZn ferrites powders were produced by the coprecipitation method.
Heat treatment effects on microstructure and magnetic properties of Mn–Zn ferrite powders
Journal of Magnetism and Magnetic Materials, 2010
Mn-Zn ferrite powders (Mn 0.5 Zn 0.5 Fe 2 O 4 ) were prepared by the nitrate-citrate auto-combustion method and subsequently annealed in air or argon. The effects of heat treatment temperature on crystalline phases formation, microstructure and magnetic properties of Mn-Zn ferrite were investigated by X-ray diffraction, thermogravimetric and differential thermal analysis, scanning electron microscopy and vibrating sample magnetometer. Ferrites decomposed to Fe 2 O 3 and Mn 2 O 3 after annealing above 550 1C in air, and had poor magnetic properties. However, Fe 2 O 3 and Mn 2 O 3 were dissolved after ferrites annealing above 1100 1C. Moreover, the 1200 1C annealed sample showed pure ferrite phase, larger saturation magnetization (M s =48.15 emu g À 1 ) and lower coercivity (H c = 51 Oe) compared with the auto-combusted ferrite powder (M s =44.32 emu g À 1 , H c = 70 Oe). The 600 1C air annealed sample had the largest saturation magnetization (M s = 56.37 emu g À 1 ) and the lowest coercivity (H c = 32 Oe) due to the presence of pure ferrite spinel phase, its microstructure and crystalline size.