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Volume 49, Issue 8
Displaying 1-19 of 19 articles from this issue
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Hirotaka Kato, Kazuo Washida, Yuji Soda2002 Volume 49 Issue 8 Pages 651-657
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSHigh speed steel and low alloy steel were bonded by powder sintering processes in order to investigate the effects of carbon content of high speed steel and sintering temperature on the bonding behavior. Two type bonding methods were studied, i.e. the process A in which high speed steel and low alloy steel green compacts were bonded by sintering without a bonding pressure, and the process B in which two-layer powders of the steels compacted and then sintered. The density, microstructure and four-point bending strength of the bonded specimens were examined. It was found in the process A that the two steels were not bonded at lower sintering temperature than the temperature (Ts) at which the relative density of sintered high speed steel reached 98%, and that bonded specimens showed the highest bending strength at higher sintering temperature than the Ts by 20K. In the process B, there was no significant influence of carbon content and sintering temperature on the bending strength, and the maximum bending strength was lower than that of the bonded specimens by the process A. This was considered to be due to both the micro-pores produced at the interface and the residual tensile stress of the bonded specimens.View full abstractDownload PDF (5486K) -
[in Japanese]2002 Volume 49 Issue 8 Pages 660
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSDownload PDF (130K) -
Atsuyuki Nakano, Takuya Aoki, Osamu Kimura2002 Volume 49 Issue 8 Pages 661-665
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSA one-chip type transformer is produced as an MHD (Multilayer-Hybrid-Circuit-Device) using a multilayer technology and it contributes to miniaturize of a DC/DC converter. In order to get high efficiency of this transformer, it is needed to reduce the residual magnetic flux neighborhoods of internal electrode. Therefore, the internal electrode is needed to cover with nonmagnetic oxide completely in MHD. However, the discrepancy of thermal expansion coefficient between these materials produces internal stress which causes a degradation of magnetic properties and internal cracks in the worst case. Many studies were reported about internal stress effect comes from the internal Ag electrode to produce high performance multilayer chip inductor. In this paper, a study about the thermal expansion coefficient of ferrites was performed to reduce the thermal expansion coefficient discrepancy between NiCuZn ferrite and CuZn ferrite. It was found that the thermal expansion coefficient was able to control by ferrite compositions and degree of raw materials mixing. And it was thought that the thermal expansion coefficient was affected by ferrite compositions as well as thermal vibration which was caused from imperfect match at the interface between a spinet structure and a residual unreacted oxide materials in sintered ferrite body.View full abstractDownload PDF (2885K) -
Fumitaka Baba, Koichi Kakizaki, Nobuyuki Hiratsuka2002 Volume 49 Issue 8 Pages 666-670
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThis study describes the effect of Pr6O11 addition on the magnetic properties and the microstructures of the sintered Mn-Zn ferrite for high frequency power transformer uses. After calcination of mixed raw materials at 1000°C in nitrogen gas, the calcined powders were mixed with Pr6O11 in the concentration ranging from 0 to 0.8wt.% and then compacted. The compacted powders were sintered in air at the various temperatures of 1125-1225°C for 3 hours. When sintered at 1175°C, the coreloss at 50 mT and 200 kHz of sample added with 0.1 wt.% of Pr6O11 decreased to about a quarter of that of the sample without addition. Moreover, the initial permeability of the former sample increased by. about twice that of the latter sample. The fact suggests the formation of Fe2+ ions in the former sample caused by the substitution of Fe3+ ions by added Pr4+ ions.View full abstractDownload PDF (1688K) -
Shinjiro Saigusa, Koichi Kakizaki, Nobuyuki Hiratsuka2002 Volume 49 Issue 8 Pages 671-676
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSAcicular Ni0.4Zn0.6Fe2O4 fine particles were made from acicular a-FeOOH, Ni(C5H7O2)2 and Zn(C5H7O2)2 by calcining at 750-950°C for 4 hours. The saturation magnetization and the aspect ratio of the obtained particles were 50 emu/g and 26, respectively. These particles were pressed in a die into a troidal shape. In the pressing process, they were grain-oriented by multi-layer formation or magnetic field application so that their <111> direction in the spinel structure could be aligned perpendicular to the top surface of the troidal core. In addition, the randomly oriented sample was also prepared as a reference. These pressed compacts were sintered at 1200-1300°C for 6h. The initial permeability of the grain-oriented samples were larger than that of the randomly oriented sample. Moreover, the frequency dependence of reflection loss in these grain-oriented samples were improved.View full abstractDownload PDF (1828K) -
Takeshi Tachibana, Kenji Izumi, Masataka Kanoh, Takashi Nakagawa, Taka ...2002 Volume 49 Issue 8 Pages 677-684
Published: August 15, 2002
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe cation distribution and magnetic structure of the Z-type hexagonal ferrite with various compositions (x=0, 0.2, 0.4 in Ba3Co2-xFe24+xO41) prepared under oxygen partial pressure, Po2=101.3 kPa, at 1573K, were studied by neutron powder diffraction analysis (wave length of the neutron was 1.006 Å). To examine magnetic Bragg reflections, neutron diffraction patterns were measured within temperature range between 294 and 773K for the sample with composition x=0.4. Two significant reflections were observed at 2θ=11.5 and 13.5°in the pattern at 294 K though no peaks at 773 K. These magnetic reflections were observed for any other samples at 294 K. The peak at 28 = 11.5° corresponded to the magnetic reflections of (0010), (101) and (104) planes and the other at 13.5° the magnetic reflections of (0012) and (106) planes, respectively. The cation distribution for all the samples was determined by the Rietveld analysis of the neutron diffraction patterns measured at 294 K. The preferential distributions of cobalt ions were found. Cobalt ions partially occupy 12k octahedral site at the boundary between S-block and T-block, 4e tetrahedral site in S-block, 2a octahedral site in T-block and 2c five fold (trigonal bypiramid) site in T-block for the sample of x=0.View full abstractDownload PDF (677K) -
Osamu Kimura, Yoshitaka Murakami, Masafumi Matsumoto, Mitsuo Sakakura, ...2002 Volume 49 Issue 8 Pages 685-690
Published: August 15, 2002
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSMagnetic properties were studied for magnetoplumbite type ferrites, namely, Z, W or Y type hexagonal ferrites, whose basal planes contain the easy direction of magnetization. Increase in the degree of crystal orientation of these ferrites is known as an effective method to enhance their permeabilities. Accordingly, we have already obtained highly crystal-oriented samples by applying a hot-forging process in air, using normally calcined powders as starting materials. Here, a molten-salt process is adopted to prepare new powders of the ferrites composed of plate-like particles. The degrees of crystal orientation of the hot-forged samples are expected to enhance by replacing the normally calcined powders with these powders.View full abstractDownload PDF (3707K) -
Masahiko Watanabe, Katsushi Yasuhara, Atsuyuki Nakano, Takeshi Nomura2002 Volume 49 Issue 8 Pages 691-695
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSFurther miniaturization and higher reliability of electronic devices are required for automobiles. The reliability of ferrites with high saturation magnetic flux-density, which is indispensable for automobiles, was investigated. A saturation magnetic flux-density of 450 mT at 100°C was obtained with substituting Ni for part of Mn in Fe-rich MnZn ferrite. However the deterioration of core loss was observed on the high temperature storage test at 150°C for 2000hr. The degradation degree of core loss increased on increasing the number of cation vacancy in sintered body. On optimizing the number of cation vacancy by controlling sintering atmosphere, MnNiZn ferrites with both high saturation magnetic flux-density and reliability at high temperature were obtained.View full abstractDownload PDF (313K) -
Hiroyuki Taketomi, Teruhiko Fujiwara2002 Volume 49 Issue 8 Pages 696-700
Published: August 15, 2002
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSPowder cores have relatively small permeability, and the enhancement of the permeability may be attained with improvement of particle properties. In this study, permeability and effective demagnetizing factor of a particle were estimated from a measured permeability of the powder core using the equation of Takajyo et al.
It was found that effective demagnetizing factor, N of a particle were 0.06, which were independent of particle size or heat treatment temperature of the powder core. It was also found that permeability of a particle, A increased exponentially with increasing heat treatment temperature: about 100, 300 and 600 for the temperature of 673, 773 and 873 K, respectively.
This study exhibited that the utilization of particle with higher aspect ratio rather than high temperature heat treatment was effective for the permeability enhancement.View full abstractDownload PDF (1664K) -
Atsushi Yamada, Isao Saeki, Shinichi Kikkawa2002 Volume 49 Issue 8 Pages 701-705
Published: August 15, 2002
Released on J-STAGE: November 19, 2010
JOURNAL OPEN ACCESSHigh purity Fe16N2 was obtained by nitridation of α-Fe fine powder with ammonia at 120°C for various duration up to 100 hours. Crystallite size of Fe16N2 fine powder became smaller with the nitridation duration. Its coercivity showed a maximum of 2 kOe at the crystallite size of 22 nm. Saturation magnetization decreased with a reduction of the crystallite size and the value at 4.2 K was 154 emu/g. Sputter deposited α-Fe thin film was directly nitrided without an exposure to ambient air. Any kinds of iron nitride was not formed below 200°C on the films thicker than 360 nm. A mixture of Fe2-3N, Fe3N and Fe4N was obtained at 250°C. This nitride formation temperature was reduced with the film thickness. A small amount of Fe3N was observed in the α-Fe film nitrided at 130°C with a thickness of 50 nm.View full abstractDownload PDF (408K) -
Shinji Hatanaka, Nobuhiro Matsushita, Masanori Abe2002 Volume 49 Issue 8 Pages 706-709
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSMagnetite ultrafine particles (-10nm in diameter) were synthesized from an aqueous solution of FeCl2+FeCl3, utilizing Fe2+→Fe3+ oxidation by air (oxygen). Their dispersibility in water was measured by absorbance of light recorded as a function of time. The magnetite ultrafine particles was found to be dispersed stably in aqueous solution when pH≥5 and pH≤11. The surfaces are charged positively and negatively at these acidic and alkaline conditions, respectively. This allows the magnetite ultrafine particles dispersed stably in water due to repulsive force of the surface charge. The bit pattern of a floppy disk was successfully observed using the magnetite ultrafine particles dispersed in water at pH=5.View full abstractDownload PDF (3383K) -
Nobuyuki Gokon, Noriko Hasegawa, Hiroshi Kaneko, Yutaka Tamaura, Takes ...2002 Volume 49 Issue 8 Pages 710-716
Published: August 15, 2002
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe Ni2+-substituting magnetite formation in the wet process in a high magnetic field from 0 to 8 T generated with a 10 T cryocooler-cooled superconducting magnet has been studied at iron ions concentration of 1500 mg/l at Fe2+/Fe3+(Rf) mole ratio of 1/2 and 2/1. The particle size (nanoparticles) of Ni2+-substituting magnetite was decreased with increasing magnetic field. Also, the magnetic field enhanced the reaction rate of ferrite formation. The Ni2+ content of Ni2+-substituting magnetite at Rf= 2/1 was lower than that at Rf=1/2. In the Ni2+-substituting magnetite, the lattice parameter decreases with an increase of magnetic field from 0 to 8 T, indicating that high magnetic fields enhance a formation of Ni2+-substituting magnetite (enhancement of solubility of Ni2+ into magnetite). This result is supported by the experimental result which the magnetite formed in a high magnetic field tends to adsorb Ni2+ in the reaction solution in a high magnetic field, indicating that a high magnetic field enhances the higher incorporation of Ni2+ into spinel structure.View full abstractDownload PDF (571K) -
Ken Makita, Shigeru Takaki2002 Volume 49 Issue 8 Pages 717-723
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe alignment of magnet powder such as Nd-Fe-B and Sr-ferrite under applied magnetic field was investigated. Initial magnetization curves of the unfixed powder showed sudden increase of magnetization at a field named Hrot which can be related to the beginning of rotation of the easy axis towards the applied field. Although the coercive force of Nd-Fe-B powder had changed by the substitution of Nd by Dy, the value of Hrot remained stable. When the volume proportion of powder capsulated in a sample holder had increased, the rotation was suppressed and the magnetization decreased. Nd-Fe-B powder formed many stable columns which are parallel to the applied field. The diameter of the columns are about few hundred microns. Inside the columns, magnet powder formed small chains aligned parallel to the applied field. Based on the model experiment where the powder particles are simulated by small magnets, the process of alignment was classified to three steps: technical magnetization; rotation/movement; alignment.View full abstractDownload PDF (3885K) -
Michiharu Ogawa, Takayoshi Shimizu, Tetsuo Yamamoto, Timihiro Ozaki, K ...2002 Volume 49 Issue 8 Pages 724-727
Published: August 15, 2002
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSThe powders of (Tb0.5Dy0.5)(Fe1-xCrx)1.8 (x=0-0.2) were synthesized by a mechanical alloying (MA) of the elemental Tb, Dy, Fe and Cr powders using a planetary ball milling for 360 ks, and they were consolidated at 1273 K by a pulsed current sintering (PCS). The Cr addition was very effective to improve compressive strength of the sintered alloys, which is thought to be attributed to the formation of ductile Fe-Cr phase. On the other hand, the Cr addition of x = 0.2 decreased magnetostriction of the alloys due to an excess amount of Fe-Cr phase. As a result, it was found that the optimum Cr content is x = 0.05 for achieving large magnetostriction (380 ppm at 112 kA/m) and high compressive strength (800 MPa) simultaneously.View full abstractDownload PDF (2089K) -
Gaku Obara, Hiroshi Yamamoto, Hideaki Ono, Tetsurou Tayu2002 Volume 49 Issue 8 Pages 728-731
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSSr-La-Co M-type ferrite fine particles with high coercivities can be prepared by mechanical compounding (M.C.) method using the planetary ball-mill and subsequent heat treatment. This experiment was carried out to investigate the magnetic properties of ferrite sintered magnets prepared by the hot-pressing process using M.C. powders. The anisotropic sintered magnets were obtained from the hot-pressing process without magnetic field pressing. Typical magnetic and physical properties of the sample obtained by this process are as follows; (BH)max=19.9 kJ/m3, Jr =0.330 T, HcJ=308kA/m, HcB=224kA/m, and density = 5.05 Mg/m3.View full abstractDownload PDF (4782K) -
Masashi Ohmura, Akihiro Tanaka, Hiroshi Yamamoto2002 Volume 49 Issue 8 Pages 732-737
Published: August 15, 2002
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSAn experiment was carried out to investigate the effects of stearic acid as a new reducing agent on the magnetic and physical properties of SrFe2-W type hexagonal ferrite. It was found that the magnetic properties of SrO⋅8.5Fe2O3 were considerably improved by simultaneous addition of 0.3 wt% stearic acid, 0.3 wt%SiO2, and 0.7 wt% CaO. The optimum conditions for making magnets and some typical properties of the obtained sample are as follows. Chemical analysis composition: Sr2+0.96Si4+0.11Ca2+0.17C4+0.21Fe2+0.72Fe3+16.61O27; semi-sintering condition: 1350°C×4.0h in nitrogen gas atmosphere; drying treatment condition: 200°C×3.0h in air; sintering condition: 1170°C×1.5h in nitrogen gas atmosphere. Magnetic and physical properties are Jm=0.48 (T), Jr=0.45 (T), HcJ=169.0 (kA/m), HcB=164.7 (kA/m), (BH)max=34.6 (kJ/m3), Tc=501.5 (°C), HA=1446 (kA/m), KA=3.3 (×105 J/m3), and ηB=29.8μB, a=5.888 (×10-10m), c=32.85 (×10-10m), and c/a=5.58.View full abstractDownload PDF (1824K) -
Kunio Okimoto, Katsuhisa Izumi, Kazuhisa Iwamoto, Tomotaka Kuroda, Sei ...2002 Volume 49 Issue 8 Pages 738-743
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe magnetic product produced by the conventional magnetically aligning press is restricted in its shape and size. To solve this problem, this paper presents a novel process, in which the pressing process is separated from the aligning one. As an example, strontium ferrite powder mixed with an MIM binder was compacted in a die, followed by alignment under a magnetic field. After then, effects of forming conditions on the magnetic properties of the compacts, for example, the degree of orientation, Br/Js, were examined. The maximum value of Br/Js reached 0.950, indicating that the well oriented magnetic compact could be obtained by this procedure.
The MIM binder is preferable to have a low viscocity for a high orientated compact and a good compactibility, a good shape stability as well as an easiness in mold release for the compact production. Moreover, simultaneous addition of zinc stearate with the MIM binder to the compact was found to improve the above behaviors of the binder for the compact.View full abstractDownload PDF (410K) -
Kunio Okimoto, Tomotaka Kuroda, Seiichi Hosokawa, Sachio Toyota2002 Volume 49 Issue 8 Pages 744-748
Published: August 15, 2002
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSTo investigate effects of shear stress and shear strain on the magnetic properties of Sr-ferrite powder, the powder was milled by a mechanofusion (MF) apparatus, and its magnetic characteristics were studied. Coercive force of the MF-milled powder was decreased with milling time, and it reached the constant value of 140 kA⋅m-1 as milling time was longer than 30 min. Reduction of the coercive force of the milled powder was found to slightly improve degree of powder particle alignment under applied magnetic fields. M-type ferrite phase of the original Sr-ferrite powder remains unchanged after the MF-milling treatment. The mean particle size of the powder was increased by a MF-milling treatment longer than 30 min due to aggregation of the powders. As a result, the optimum MF-milling time was in the range from 15 min to 30 min under the experimental conditions of this study.View full abstractDownload PDF (1941K) -
Kunio Okimoto, Tomotaka Kuroda, Seiichi Hosokawa, Sachio Toyata2002 Volume 49 Issue 8 Pages 749-752
Published: August 15, 2002
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSIt is well known fact that decrease in the coercive force of hard-ferrite powder occurs during its pulverizing and compacting processes. This study aims to elucidate the mechanism of this phenomenon. For this purpose, a strontium ferrite powder was compacted by a dry die compaction or a dry cold isostatic pressing (CIP) process. In addition, a wet CIP compaction was conducted for the powder preliminarily pulverized in a mechanofusion (MF) mill, which could introduce immediately larger shear stresses and strains into the particles of the powder. The magnetic properties of these compacted powders were measured as a function of the compacting pressure.
The experiments result suggests that decrease in the coercive force of the powder is caused by the internal strain in its particles due to solid contacts between them in the compacting process and the degree of the decrease is hardly affected by the utilized compacting process, namely, the dry die compaction, or the dry CIP compaction.View full abstractDownload PDF (302K)
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