Journal of Powder Materials

Characteristics of L1₀ Ordered Fe₅₀Pt₅₀ Nanoparticles Synthesized by Chemical Vapor Condensation Process: Gyeong-Mo Lee, Ji-Hun Yu, Dong-Won Lee, Byung-Kee Kim, Hyeok-Don Kim, Tae-Suk Jang; J Korean Powder Metall Inst. 2007;14(5):281-286.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.281

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Abstract PDF: Ordered L1_0 to FePt nanoparticles are strong candidates for high density magnetic data storage media because the L1_0 phase FePt has a very high magnetocrystalline anisotropy (K_usim6.6-10times107erg/cm3), high coercivity and chemical stability. In this study, the ordered L1_0 FePt nanoparticles were successfully fabricated by chemical vapor condensation process without a post-annealing process which causes severe particle growth and agglomeration. The Fe_50Pt_50 nanopowder was obtained when the mixing ratio of Fe(acac) and Pt(arac) was 2.5 : 1. And the synthesized FePt nanoparticles were very fine and spherical shape with a narrow size distribution. The average particle size of the powder tended to increase from 5 nm to 10 nm with increasing reaction temperature from 800°C to 1000°C. Characterisitcs of FePt nanopowder were investigated in terms of process parameters and microstructures.

Synthesis of SnO₂ Powders by Oxidation Heat Treatment of Nano-sized Sn Powders and Their Microstructural Characteristics: Sung-Tag Oh, Sung-Il Lee, Yeon-Jun Joo; J Korean Powder Metall Inst. 2007;14(5):287-291.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.287

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Abstract PDF: Oxidation behavior and microstructural characteristics of nano-sized Sn powder were studied. DTA-TG analysis showed that the Sn powder exhibited an endothermic peak at 227°C and exothermic peak at 560°C with an increase in weight. Based on the phase diagram consideration of Sn-O system and XRD analysis, it was interpreted that the first peak was for the melting of Sn powder and the second peak resulted from the formation of SnO_2 phase. Microstructural observation revealed that the SnO_2 powder, heated to 1000°C under air atmosphere, consisted of agglomerates with large particle size due to the melting of Sn powder during heat treatment. Finally, fine SnO_2 powders with an average size of 50nm can be fabricated by controlled heat treatment and ultrasonic milling process.

Synthesis of TiB₂ Dispersed Cu Matrix Composite Material by the Combination of the Mechanical Milling and Plasma Activated Sintering Process: Kyong-Ju Kim, Gil-Geun Lee, Ik-Min Park; J Korean Powder Metall Inst. 2007;14(5):292-297.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.292

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Abstract PDF: The present study was focused on the synthesis of a TiB_2 dispersed copper matrix composite material by the combination of the mechanical milling and plasma activated sintering processes. The Cu/TiB_2 mixed powder was prepared by the combination of the mechanical milling and reduction processes using the copper oxide and titanium diboride powder as the raw material. The synthesized Cu/TiB_2 mixed powder was sintered by the plasma activated sintering process. The hardness and electric conductivity of the sintered bodies were measured using micro vickers hardness and four probe method, respectively. The relative density of Cu/TiB_2 composite material sintered at 800°C showed about 98% of theoretical density. The Cu-1vol%TiB_2 composite material has a hardness of about 130Hv and an electric conductivity of about 85% IACS. The hardness and electric conductivity of Cu-3vol%TiB_2 composite material were about 140 Hv and about 45% IACS, respectively.

Magnetic Properties of Fe Powder Core Fabricated by Warm Compaction: Se-Hoon Kim, Tae-Sun Jo, Min-Suh Park, Young-Do Kim; J Korean Powder Metall Inst. 2007;14(5):298-302.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.298

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In recent years, a rapid increase in demands for the soft magnetic composite parts has been created and it has been tried to improve their properties by various processing methods, alloying elements and compaction parameters. Warm compaction method has been used for the reduction of residual stress, the improvement of magnetic properties and the higher densities. In this work, the effects of warm compaction and polymer binder on magnetic properties of Fe powder core were investigated. The sintering powder, Fe oxide, was ball-milled for 30n hours. And then ball-milled Fe oxide powder was reduced through hydrogen reduction process. The hydrogen reduced Fe powder and polymer binder were mixed by 3-D turbular mixer. And then the mixed powder was warm-compacted. The magnetic properties such as core loss and permeability were measured by B-H curve analyzer.

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Warm Compaction of Fe-Si/Fe Powder Mixture and its Magnetic Property
Se-Hoon Kim, Myung-Jin Suk, Young-Do Kim
Journal of Korean Powder Metallurgy Institute.2009; 16(4): 249. CrossRef

Effect of the Surface Oxidation on the Electromagnetic Wave Absorption Behavior of a Fe-based Nanocrystalline Alloy: S.K. Koo, S.J. Woo, B.G. Moon, Y.S. Song, W.W. Park, K.Y. Sohn; J Korean Powder Metall Inst. 2007;14(5):303-308.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.303

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Abstract PDF: The oxidation of Fe_73Si_16B_7Nb_3Cu_1 nanocrystalline powder has been conducted to investigate its influence on the electromagnetic wave absorption characteristics of the soft magnetic material. Oxidation occurred primarily on the surface of nanocrystals. Oxidation reduced the real part of complex permeability due to the reduction of the relative volume of the powder, which otherwise contributes to the permeability. Oxidation reduced the absorption efficiency of the sheet at frequencies over 1GHz, indicating that the relative contribution of skin depth increments to the absorption was not significant. The pulverization and milling process lowered the optimum crystallization temperature of the material by 40sim50°C because of the internal energy accumulated during the fragmentation and powder thinning processes.

Synthesis and Characterization of Nanoporous Zirconia: Seung-Sik Woo, Ho-Kun Kim; J Korean Powder Metall Inst. 2007;14(5):309-314.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.309

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Zirconia powders with nano size pores and high specific surface areas were synthesized via aqueous precipitation and hydrothermal synthetic method using ZrOCl_28H_2O and NH_4OH under pH=11 and ambient condition. By this reaction. zirconia hydrate (ZrO_x(OH)_4-2x) was primarily synthesized and the obtained zirconia hydrate was heat treated hydrothermally using an autoclave at various temperatures under pH=11. X-ray diffraction, Scanning electron microscopy, Energy dispersive X-ray spectroscopy, FT-IR, Raman, Particle size analysis, DTA-TG, and BET techniques were used for the characterization of the powder. The synthesized zirconia showed an amorphous phase, however, the phase was transformed to the crystalline state during the hydrothermal process. The observed crystalline phase above 160°C was a mixed phase of monoclinic and tetragonal zirconia. By the BET analysis, it was found that the specific surface area was ranged in 126sim276m2/g and the zirconia had the cylindrical shaped pores with average diameter of 2sim7nm.

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Characteristics of Zirconia Nanoparticles with Hydrothermal Synthesis Process
Chi Wook Cho, Weon Pil Tai, Hak Sung Lee
Applied Chemistry for Engineering.2014; 25(6): 564. CrossRef

Consolidation of Binderless and Low-Binder WC hardmetal by Vacuum Sintering: Byoung-June Min, Young-Ho Park, Gil-Geun Lee, Gook-Hyeon Ha; J Korean Powder Metall Inst. 2007;14(5):315-319.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.315

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Abstract PDF: Pure WC or WC with low Co concentration less than 0.5 wt.% is studied to fabricate high density WC/Co cemented carbide using vacuum sintering and post HIP process. Considering the high melting point of WC, it is difficult to consolidate it without the use of Co as binder. In this study, the effect of lower Co addition on the microstructure and mechanical properties evolution of WC/CO was investigated. By HIP process after vacuum sintering, hardness and density was sharply increased. The hardness values was 2,800kgf/mm2 using binderless WC.

Ag-Cu Powders Prepared by Electrical Wire Explosion of Cu-plated Ag Wires: Won-Baek Kim, Je-Shin Park, Chang-Youl Suh; J Korean Powder Metall Inst. 2007;14(5):320-326.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.320

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Abstract PDF: Ag-Cu alloy nano powders were fabricated by the electrical explosion of Cu-plated Ag wires. Ag wires of 0.2mm diameter was electroplated to final diameter of 0.220 mm and 0.307 mm which correspond to Ag-27Cu and Ag-68Cu alloy. The explosion product consisted of equilibrium phases of alpha-Ag and beta-Cu. The particle size of Ag-Cu nano powders were 44 nm and 70 nm for 0.220 mm and 0.307 mm wires, respectively. The Ag-Cu nano powders contained less Cu than average value due to higher sublimation energy compared to that of Ag. As a result, micron-sized spherical particles formed from liquid droplets contained higher Cu content.

Process Optimization of Environment-Friendly Ag-SnO₂ Electric Contact Materials through a Powder Metallurgy: Jeong-Gon Kim; J Korean Powder Metall Inst. 2007;14(5):327-332.; DOI: https://doi.org/10.4150/KPMI.2007.14.5.327

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Abstract PDF: In a view point of environment, the advanced electric contact material without environmental load element such as cadmium has to be developed. Extensive studies have been carried out on Ag-SnO_2 electric contact material as a substitute of Ag-CdO contact materials. In the present study, powder metallurgy including compaction and sintering is introduced to solve the incomplete oxidation problems in manufacturing process of Ag-SnO_2 electrical contact material. The Ag-SnO_2 contact material, fabricated in this study, was actually set in an electric switchgear of which working voltage is 462V and current is between 25 and 40A, for the purpose of testing its performance. As a result, it exceeded the existing Ag-CdO contact materials in terminal-temperature ascent and main contact resistance.

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