Mn-Zn Ferrite Powder Research Articles

Self-propagating high-temperature synthesis of MnZn-ferrites for inductor applications

The self-propagating high-temperature synthesis (SHS) route is evaluated for the synthesis of MnZn-ferrite powders that are subsequently processed towards the manufacturing of high initial magnetic permeability polycrystalline specimens for inductor applications. The conditions for the synthesis of particular phases by SHS reactions between iron metal and oxide powders were optimized and the effects of the synthesis parameters on ignition and propagation characteristics were studied. By “fine-tuning” the synthesis parameters, products of a wide spectrum of phases from single-phase, pure and well crystallized (MnxZny)Fe2+δO4 to the oxide of the divalent metals (Mnx′Zny′Fe1−x′−y′)O could be controllably synthesized. Advantages of the synthesis route are demonstrated by tests on properties of merit on final products: combustion powder products were subsequently pressed to torroids, sintered and characterized with respect to their magnetic properties, in comparison to conventionally synthesized samples of the same composition. When sintered under appropriate schedules of oxygen partial pressure profile to avoid phase oxidation at 600°C, SHS powders could be processed to high permeability MnZn-ferrites. At equal average particle sizes SHS powders exhibit higher reactivity and grain growth compared to conventionally synthesized powders. This advantage can be utilized in the manufacturing of high permeability MnZn-ferrites with shorter firing schedules and thus all associated advantages in terms of productivity, production costs or zinc evaporation loss.

Fabrication of a Common-mode Noise Filter for Balanced-mode Signal Transmission using Mn-Zn Ferrite Particle/Polyimide Composite Thick Film

To develop a common-mode noise filter for balanced-mode digital signal interfaces such as USB ver. 2 and IEEE 1394, a Mn-Zn ferrite/Polyimide composite thick film was fabricated and applied to the filter device. The polycrystalline Mn-Zn ferrite powder and polyimide precursor liquid solution were used as the starting materials for the composite thick film. The composite film had a large imaginary part of complex permeability at high frequencies over 1GHz, and high permittivity. The common-mode noise filter using the composite film exhibited the common-mode suppression of over 10dB in the frequency range over 1GHz.

Structure and magnetic properties of rf thermally plasma synthesized Mn and Mn–Zn ferrite nanoparticles

Plasma synthesis has previously been shown to be a viable route to producing nanocrystalline magnetite and Ni ferrite nanoparticles. In this work nanocrystalline powders of Mn and Mn–Zn ferrites have been synthesized using a 50 kW–3 MHz rf (radio frequency) induction plasma torch. We investigate these materials for soft magnetic applications. High-energy ball milled Mn + Fe powders and (Mn+Zn) +Fe powders (<10 μm) in the stoichiometric ratio of 1:2 were used as precursors for the ferrite synthesis. Compressed air was used in the oxygen source for oxidation of metal species in the plasma. X-ray diffraction patterns for the plasma-torched Mn ferrite and MnZn ferrite powders were indexed to the spinel ferrite crystal structure. An average grain size of ∼20 nm was determined from Scherrer analysis confirmed by transmission electron microscopy studies. The particles also exhibited faceted polygonal growth forms with the associated truncated cuboctahedral shapes. Room-temperature vibrating sample magnetometer measurements of the hysteretic response revealed saturation magnetization Ms and coercivity Hc of Mn ferrite are 23.65 emu/g and 20 Oe, respectively. The Néel temperatures of Mn ferrite powders before and after annealing (500 °C, 30 min) were determined to be 200 and 360 °C, respectively. Inductively coupled plasma chemical analysis and energy dispersive x-ray analysis data on the plasma-torched powders indicated deviations in the Mn or Zn contents than the ideal stoichiometry. MnZn ferrite was observed to have a Néel temperature increased by almost 400 °C as compared with as-synthesized Mn ferrite but with a larger coercivity of ∼35 Oe.

Effect of Aggregates on the Microstructure in Manganese Zinc Ferrite

To study the effect of aggregates on the microstructure of sintered bodies, Mn-Zn ferrite powders were prepared by an alcoholic dehydration method. Aggregate powders and reground powders were used as seeds and matrices, respectively. The mixing ratios for the aggregate and reground powders were varied with the sintering temperatures. Green densities were measured with changes in forming pressure and they were related to the microstructures of the sintered bodies. The aggregates proved to be capable of acting as seeds for abnormal grain growth. When the green density difference between the aggregate and the matrix was large, the aggregate could become the seed of abnormal grain growth. As the forming pressure increased, the more aggregates became seeds of abnormal grain growth.

Dispersant-assisted hydrothermal synthesis of MnZn ferrites from raw oxides

MnZn-ferrite powders were prepared using hydrothermal syntheses of a homogenous mixture of the raw oxides, i.e., Fe2O3, ZnO and Mn3O4, at 280°C in air. The hydrothermal synthesis was performed in the presence of various amounts of an anionic dispersant. The final results of the hydrothermal reaction between the raw oxides were fine powders with a heterogeneous phase composition mostly composed of iron oxide and spinel products. The composition of the spinel products depended to a great extent on the amount of dispersant in the hydrothermally treated suspension. Without the dispersant addition, Zn ferrite and Zn manganate spinel products were formed, while in the presence of the dispersant, the ferrimagnetic MnZn-ferrite spinel product was obtained. A larger amount of the dispersant in the reaction mixture increased the conversion rate of the raw oxides into the Mn,Zn ferrite spinel product. Additionally, polyvinyl alcohol (PVA) was used during the hydrothermal synthesis in order to bind the chlorine impurities, introduced into the hydrothermally prepared powder with the raw Fe2O3. With the PVA burnout, the level of chlorine impurities was decreased by approximately 50%.

Characteristics of powder and sintered bodies of hydrothermally synthesized Mn-Zn ferrites

To improve the sinterability of powders fabricated by the conventional mixed-oxides method, ultrafine Mn-Zn ferrite powders were hydrothermally synthesized from metal nitrates solution using ammonia as a precipitant. The R value (alkalinity) was introduced to adjust the amount of added OH− in the reaction suspension. The characteristics of the powders synthesized at different hydrothermal conditions and the properties of the sintered bodies were investigated. The results show that the R value and hydrothermal time have a great effect on the compositions and phases of hydrothermally synthesized Mn-Zn ferrite powders. Powders synthesized from a starting suspension with a higher content of Zn ions (or lower content of Mn2+) may approach to a stable spinel structure with a lower Mn/Zn ratio as the hydrothermal time is longer. Factors affecting the position of the diffraction angle (2θ) of the spinel Mn-Zn ferrite (311) of powders may include both the compositions of spinel ferrite structure and crystallite sizes (or particle sizes) of powders. Some possible reasons were suggested to explain the dependence of composition and phase of hydrothermally synthesized Mn-Zn ferrite powders on the R value and hydrothermal time. The temperature that the green compact begins to shrink at increases with increasing R value, and ranges from 510°C (R = 2) to 650°C (R = 6). After being sintered at 950°C for 2 h in N2 atmosphere, the relative sintered density of each specimen reaches a value of 94.5–99.8%.

Preparation and Sinterability of Mn-Zn Ferrite Powders by Hydrothermal Method

Preparation and Sinterability of Mn-Zn Ferrite Powders by Hydrothermal Method

Sintering of MnZn-ferrite powders prepared by hydrothermal reactions between oxides

Abstract The sintering of ferrite powders prepared by a hydrothermal treatment of starting oxides was studied in comparison with conventional pre-sintered powders. Two hydrothermal powders were prepared, one with a similar degree of conversion into spinel products as the pre-sintered powder but with a larger specific surface, and the other with a lower specific surface area and a high degree of conversion into MnZnFe2O4. In the first powder, non-homogeneity caused primarily by the agglomeration of the Mn-rich particles (Mn3O4 and ZnMn2O4) resulted in the formation of Kirkendall porosity, which significantly influenced the densification process.

硫酸イオンがＭｎＺｎフェライトの粒界構造に及ぼす影響

The effect in MnZn ferrite of sulphate ion on grain boundary chemistry and core loss was studied. When MnZn ferrite powder with additives (SiO2, CaCO3) is milled in water, CaSO4 · 1/2 H2O forms from a sulphate ion impurity and the added CaCO3. In the case of sintered specimens of powder rich in sulphate ion content, Ca is not located uniformly along the grain boundary. These specimens have relatively higher coercive force, lower electric resistivity, and in consequence, higher core loss. In MnZn ferrite, it is well known that the grain boundary chemistry depends heavily on phase equilibria of the CaO-SiO2-Fe2O3 system. Thermogravimetry data show that it is very hard to decompose CaSO4 into CaO and SO3. We consider that the formation of CaSO4 prevents the uniform spread of Ca along the grain boundary in MnZn ferrite at sintering.

Powder Characterization and Sinterability of Hydrothermally Synthesized Mn-Zn Ferrites.

Ultrafine Mn-Zn ferrite powders were synthesized under mild hydrothermal conditions by precipitation from metal nitrates with an aqueous ammonia. R value (alkalinity) was introduced to adjust the amount of added ammonia. A method of controlling the desired compositions and crystallite sizes of synthesized powders was proposed in this paper. In addition, the effect of R value and hydrothermal time on powder characterization, such as the Mn/Zn ratio in spinel structure of synthesized powders, variation of X-ray diffraction angle of spinel ferrites, crystallite size and the loss ratio of Zn2+ for different starting suspensions during hydrothermal process, was also investigated. Powders upon hydrothermal treatment exhibited superior sinterability as compared to powders which were not subjected to hydrothermal treatment. High densities, 99.4-99.8% of theoretical densities, were obtained upon sintering green ferrite powders at relatively low temperature (900-950°C) in N2 atmosphere without any sintering aids.

Microstructures and magnetic and electric properties of low-temperature sintering Mn–Zn ferrites without and with addition of lithium borosilicate glass

Highly sinterable Mn–Zn ferrite powder consisting of submicrometer-size particles (∼0.18 μm) with structural distortion has been prepared by grinding a coprecipitated powder with a media agitation mill. Dense pure Mn–Zn ferrites (>98% of theoretical) can be fabricated by heating at 900°C in a nitrogen atmosphere. They show magnetic and electric properties in which their permeability μ and electric resistivity ρ are 520–635 and 0.8–1.6 Ω m, respectively. These properties have been further improved by adding small amounts of lithium borosilicate glass; especially, high values of μ=1015 and ρ=474 Ω m are achieved in ferrites (900°C/12 h) with 0.1 wt% glass addition. The microstructures consist of large grains (∼35 μm) with high resistive layers at grain boundaries.

Preparation of phase homogeneous Mn–Zn ferrite powder by spray pyrolysis

Two kinds of aqueous precursor solutions are used to synthesize Mn–Zn ferrite powders: (i) nitrate (NO) precursor—derived from solutions of Mn(NO3)2, Zn(NO3)2, and Fe(NO3)3; and (ii) acetate (AC) precursor—derived from solutions of Mn(CH3COO)2, Zn(CH3COO)2, and Fe(NO3)3. The composition of the powders synthesized from the precursor AC is very uniform, whereas powders derived from the precursor NO have Mn and Zn segregated on the particle surfaces. In addition, the powders synthesized from precursor AC are solid spherical particles with fine porosity, whereas many hollow and fragmented particles are observed in the powder derived from precursor NO. Overall, the properties of Mn–Zn ferrite cores prepared from the precursor AC are superior to those prepared from the precursor NO. The reasons for the differences are explained and described in detail. The AC precursor powders synthesized by spray pyrolysis produced Mn–Zn ferrite cores with good magnetic properties.

Hydrothermal Synthesis of Manganese Zinc Ferrite Powders from Oxides

Manganese zinc (MnZn) ferrite powders were prepared via the hydrothermal treatment of a homogeneous mixture of the raw oxides (i.e., Fe2O3, ZnO, and Mn3O4 or MnO) at temperatures of 220°‐320°C in air or an inert atmosphere. The final results of the hydrothermal reactions between the raw oxides were fine powders with a heterogeneous phase composition. In addition to lower concentrations of the residual reactants (Fe2O3, Mn3O4), two types of spinel‐structure‐based reaction products‐ferrite ((Mn2+,Zn)Fe2O4) and manganate ((Zn,Mn2+)Mn23+O4)‐were detected after the synthesis. The composition of the ferrite products, as well as the ratio of ferrite products to manganate products, were mainly functions of the oxidation state of the manganese that was present during treatment. The oxidation state of manganese during reaction was dependent on the valence of the manganese in the starting manganese oxide and on the atmosphere in the autoclave during reaction. When the hydrothermal reaction was conducted in air, almost‐pure zinc ferrite was identified, whereas during reaction in an inert atmosphere, MnZn ferrite was formed. The kinetics of the hydrothermal reactions also were dependent on the oxidation state of manganese, as well as the temperature and specific surface area of the starting Fe2O3.

Experimental study on magnetic and heating characteristics of magnetic wood

Magnetic wood, wood which demonstrates magnetic characteristics, was introduced by the Oka group in 1991. Based on previous studies, we have proposed that magnetic wood can be used as a heating board by induction heating, applying a high frequency magnetic field. This article covers experimental magnetic and heating characteristics for three types of magnetic wood: an impregnated type (the wood is impregnated with a water-based magnetic fluid), a powder type (Mn–Zn ferrite powder and wood powder are mixed and pressed into boards), and a coating type (Mn–Zn ferrite powder is coated onto a fiber board). Our results showed that the coating-type magnetic wood had the highest surface temperature when using a solenoid excitation coil. In this case the surface temperature rose 50 °C. The heating board we propose can be used in furniture and medical equipment that require a warm and smooth surface.

Phase formation and composition of Mn–Zn ferrite powders prepared by hydrothermal method

Mn–Zn ferrite powders were prepared by hydrothermally aging the coprecipitates of compositional metal ions using ammonium hydroxide as a precipitant. R value (alkalinity) = (moles of added OH−)/[(moles of added Zn2+) × 2 + (moles of added Mn2+) × 2 + (moles of added Fe3+) × 3] was introduced to adjust the amount of added ammonia. The results show that the R value of starting suspension and hydrothermal time have similar and dominant effects on the composition, spinel ratio, and crystallite size of synthesized powders. From the analyses of x-ray diffraction (XRD) and inductively-coupled plasma (ICP), it notes that no α–Fe2O3 peak in the XRD patterns of powders synthesized at R = 2–3, 150 °C × 2 h, may be due to lower degree of crystallinity and less amount of α–Fe2O3 existing in these powders. Both the increase of hydrothermal time and of R value can promote the crystallinity of powders and also cause a significant loss of zinc, hinting that in the hydrothermal process, the loss of zinc may play a crucial role in the crystallinity of hydrothermally synthesized powders.

Electric and Magnetic Properties of Low-Temperature Sintering Mn-Zn Ferrite by Addition of Lithium Borosilicate Glass

Mn-Zn ferrites (spinel-type structure, cubic), which are sintered at 1250 to 1350 8C under a controlled partial oxygen pressure, are widely used in electronic applications such as transformers, choke coils, and noise ®lters because of their high permeabilities and low magnetic losses at high frequencies. Recently, low-temperature sintering of Mn-Zn ferrites have been developed to meet a demand for the miniaturization of electronic components [1]. The ferrite needs to be sintered at ,950 8C in order to co-heat with silver internal electrodes (T m 962 8C) during the manufacture of multilayer chip inductors and LC ®lters [2, 3]. The most important subject is the preparation of the reactive powder, which can be sintered at low temperatures. It has previously been shown that co-precipitated Mn-Zn ferrite powder treated for 30 min with a media agitation mill was highly sinterable; dense Mn-Zn ferrites could be fabricated by heating for 2 h at 900 8C in N2 [1]. However, the permeability at 100 kHz was 520 because of their small grain size ( 1.3 im). The purpose of the present study is to improve the electric and magnetic properties of low-temperature sintering Mn-Zn ferrites by adding lithium borosilicate glass. As-received co-precipitated Mn-Zn ferrite powder [4] (Toda Kogyo Co., Ltd.), with the composition of 51.4Fe2O3 24.3MnO 24.3ZnO (mol %) and lithium borosilicate glass (Senyo Glass Co., Ltd.), consisting of 3Li2O, 37B2O3 and 60SiO2 (mol %), were used as starting materials. To prepare reactive Mn-Zn ferrite powder, the former was ground for 30 min using a media agitation mill with zirconia balls (1 mm in diameter) and ethanol. The grinding conditions were the same as described in the earlier paper [1]. The latter, having a low melting point ( 850 8C) [5], was selected as a liquid-phase forming additive. It was ground and then screened (400 nominal open size). A weighed quantity of both powders was then mixed for 30 min in ethanol, using an agate mortar and pestle. The resulting wet powder was dried at 80 8C under a reduced pressure. Five specimens, denoted A through E, were chosen in this study (Table I). The specimens were uniaxially pressed into toroidal compacts (14 mm outer and 10 mm inner diameters) at 75 MPa. Densi®cation was performed for 12 h at 900 8C in N2; heating and cooling rates were 300 and 200 8C=h, respectively. Phases were identi®ed by X-ray diffraction (XRD) analysis using Mn-®ltered FeKa radiation. Bulk densities were measured by the Archimedes method and relative densities were calculated using the theoretical density (5:13 g=cm) of pure Mn-Zn ferrite with the same composition [1]. An electron probe micro-analyzer (EPMA), equipped with a wavelength dispersive X-ray (WDX) detector, was used for the microstructural observation and elemental distribution analysis of the sintered compacts. The sintered compacts with silver electrodes were subjected to the measurements of electrical resistivity r and complex impedance Z. The permeability i was measured in a magnetic ®eld of 0:8 A=m at 0.01 to 10 MHz with an impedance analyzer. The Curie temperature Tc was determined from the temperature dependence of i. All sintered compacts consisted of only Mn-Zn ferrites. The characteristics of Mn-Zn ferrites with and without glass addition are presented in Table I. The bulk and relative densities of ferrite A without glass addition were 4:96 g=cm and 96.6%, respectively. Ferrites with glass addition increased in density; ferrite B and ferrites C through E showed 97.5 and 98% of theoretical density, respectively. Microstructures were classi®ed into two groups: (1) ferrites A and B, and (2) ferrites C through E. The former consisted of ®ne grains (3 im) with small pores at grain boundaries (Fig. 1). On the other hand, the microstructures of the latter were

Sintering of Nanosized MnZn Ferrite Powders

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 alpha‐Fe2O3 in the spinel lattice.

Low Loss of Fine Grained Mn-Zn Ferrite

Mn-Zn ferrite with grain size or 1.5μm was obtained by sintering hydrothermal-precipitated powders with uniform dispersion or additions. The fine grain size and high density were realized simultaneously by the use of fine particle ferrite powder and fine particle additives, planetary ball mill mixing of MnZn ferrite powder and additives and low temperature sintering. The core loss of a newly developed ferrite with fine grain was significantly reduced to that of a commercial ferrite.

Readout Characteristics of Magnetic-Ink-Printed Bar Codes with Anisotropic Permeabilities

Invisible bar codes such as magnetic ones play an important role in systems requiring security. The magnetic bar code system described in this paper uses magnetic anisotropy as a carrier of information. Three kinds of magnetic ink were used, containing iron base alloy, Mn-Zn ferrite powder, and carbonyl iron powder. Although the level of the output voltage needs subsequent amplification, all of these magnetic ink can be used for making magnetic bar codes, especially the one containing iron base alloy. We explain a possible mechanism for two sub-peaks occurring berfore and after the main peak.

Particle size and morphology of hydrothermally processed MnZn ferrites observed by atomic force microscopy

Atomic force microscopy (AFM) was employed to analyse ultrafine MnZn ferrite powders, obtained by precipitation from metal sulphates and sodium hydroxide at 110 and 190 °C, under hydrothermal conditions. Particle sizes measured on AFM images taken at the surfaces of pressed samples ranged from 10 to 40 nm, as a function of synthesis temperature, and were in good agreement with measurements made using X-ray diffraction and the Brunnauer–Emmett–Teller (BET) technique. Direct observation also showed that the particles were monodispersed and approximately spherical in shape, meeting the requirements for the production of high density sintered components. Using a straightforward sample-preparation technique, AFM proved to be a powerful tool for direct analysis of ceramic powder particles on the nanometre scale.