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- Volume 8(1); February 2001
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- Effect of Fuel on Synthesis of Nanocrystalline Ni particles by a Combustion Synthesis Process
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J Korean Powder Metall Inst. 2001;8(1):13-19.
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Abstract
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- Ni and NiO particles were made by a combustion synthesis process. The characteristics of synthesized powders were investigated with various kinds and amounts of fuels such as urea, citric acid and glycine. Ni phase particles without NiO phase were obtained through combustion synthesis process in air atmosphere with-out further calcinations process, when the content of glycine was 2.44 times of the stoichiometric ratio in the precursor solution. Primary particle sizes of synthesized Ni and NiO particles were about 20∼30 nm.
- Characteristics of Magnetic Polishing with Magnetic Abrasive Powder Fabricated by Plasma Melting Method
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J Korean Powder Metall Inst. 2001;8(1):20-25.
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Abstract
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- Most of mold manufacturing procedures have been automated by the introduction of NC machine tool and CAD/CAM system. But the three-dimensional surface curvature of the mold must be done by hand work of well-skilled workers. Magnetic abrasive polishing powders were investigated for surface polishing for 3D curvature. This study aims to investigate homogeneously distributed hard phase in Fe matrix and strong bonding between Fe-matrix and hard phase. The NbC powder, B_4C powder and Al_2O_3 powder were mixed in Fe-matrix respectively. Mixed Fe-hard phase powders were compacted by press and then these were melted by plasma melting. According to SEM, XRD and OM observation, Fe-NbC magnetic abrsive powder had the most homogeneous distribution and strong bonding. As a result of magnetic polishing, the surface roughness before magnetic polishing, 1 µm R_max, was reduced to 0.2 µm R_max over the entire inner surface of the tube.
- Effect of Ni Content on Activated Sintering of Sub-micron Tungsten Powder Compact
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J Korean Powder Metall Inst. 2001;8(1):26-34.
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Abstract
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- In the present study, the effect of Ni content on densification and grain growth in Ni doped W compacts was investigated by using the dilatometric analysis. The Ni-doped W compacts with various amount of Ni activator from 0.02 to 0.4 wt％ were sintered in hydrogen atmosphere up to 1400°C. As the amount of Ni and heating rates, the Ni-doped W compacts show a greatly different dilatometric behavior during the sintering. The sintered specimen was densified over 98％ of theoretical density by adding only 0.06 wt％ Wi in sub-micron W powder and the appropriate heating rate. It was also observed that the microstructure development strongly depended on the change of the Ni amount. In addition, it was found that the critical content of Ni showing large grain growth in microstructure was below 0.1 wt％.
- Characterization of Hydrothermally Synthesized BaTiO_3 Powder and Spark Plasma Sintering(SPS)
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J Korean Powder Metall Inst. 2001;8(1):35-41.
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Abstract
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- BaTiO_3 fine powder was synthesized by hydrothermal process from the mixture of titania-hydroxide(TiO_2cdotxH_2O) and barium hexa-hydroxide (Ba(OH)_2cdot8H_2O) as starting materials. Fine powder(< 100 nm) was made under the reaction conditions of 180°C,10 atm, 1.5 hr in autoclave and showed cubic structure. The powders were sintered by a spark plasma sintering technique from 1050~1150°C for 5 min. The grains of sample sintered at 1100°C were about 0.9µm in average size and showed the mixture of cubic and tetragonal structures.
- The Effect of Milling Conditions on Microstructure and Phase Transformation Behavior of Ti-Ni Based Alloy Powders
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J Korean Powder Metall Inst. 2001;8(1):42-49.
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Abstract
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- Ti-50Ni(at%) and Ti-40Ni-10Cu(at%) alloy powders have been fabricated by ball milling method, and their microstructure and phase transformation behavior were investigated by means of scanning electron microscopy/energy dispersive spectrometry, differential scanning calorimetry (DSC), X-ray diffractions and transmission electron microscopy. In order to investigate the effect of ball milling conditions on transformation behavior, ball milling speed and time were varied. Ti-50Ni alloy powders fabricated with the milling speed more than 250 rpm were amorphous, while those done with the milling speed of 100rpm were crystalline. In contrast to Ti-50Ni alloy powders, Ti-40Ni-10Cu alloy powders were crystalline, irrespective of ball milling conditions. DSC peaks corresponding to martensitic transformation were almost discernable in alloy powders fabricated with the milling speed more than 250 rpm, while those were seen clearly in alloy powders fabricated with the milling speed of 100 rpm. This was attributed to the fact that a strain energy introduced during ball milling suppressed martensitic transformation.
- Synthesis and Characteristics of W-Ni-Fe Nanocomposite Powder by Hydrogen Reduction of Oxides
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J Korean Powder Metall Inst. 2001;8(1):49-54.
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- The synthesis and characteristics of W-Ni-Fe nanocomposite powder by hydrogen reduction of ball milled W-Ni-Fe oxide mixture were investigated. The ball milled oxide mixture was prepared by high energy attrition milling of W blue powder, NiO and Fe_2O_3 for 1 h. The structure of the oxide mixture was characteristic of nano porous agglomerate composite powder consisting of nanoscale particles and pores which act as effective removal path of water vapor during hydrogen reduction process. The reduction experiment showed that the reduction reaction starts from NiO, followed by Fe_2O_3 and finally W oxide. It was also found that during the reduction process rapid alloying of Ni-Fe yielded the formation of gamma-Ni-Fe. After reduction at 800°C for 1 h, the nano-composite powder of W-4.57Ni-2.34Fe comprising W and gamma-Ni-Fe phases was produced, of which grain size was35nm for W and 87 nm for gamma-Ni-Fe, respectively. Sinterability of the W heavy alloy nanopowder showing full density and sound microstructure under the condition of 1470°C/20 min is thought to be suitable for raw material for powder injection molding of tungsten heavy alloy.
- Preparation of Hard Magnetic Sm_2Fe_17N_x Compound by Mechanical Alloying
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J Korean Powder Metall Inst. 2001;8(1):55-60.
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- Mechanical alloying technique was applied to prepare hard magnetic Sm_2Fe_17N_x compound powders. Staring from pure Fe and Sm powders, the formation process of hard magnetic Sm_2Fe_17N_x phase by mechanical alloying and subsequent solid state reaction was studied. As milled powders were found to consist of Sm-Fe amorphous and alpha-Fe phases in all compositions of Sm_xFe_100-x(x = 11, 13, 15, 17). The effects of starting composition on the formation of Sm_2Fe_17 intermetallic compound was investigated by heat treatment of mechanically-alloyed powders. When Sm content was 15 at.％, heat-treated powders consisted of nearly Sm_2Fe_17 single phase. For preparation of hard magnetic Sm_2Fe_17N_x powders, additional nitriding treatment was performed under N_2 gas flow at 450°C. The increase in the coercivity and remanence was proportional to the nitrogen content which increased drastically at first and then increased gradually as the nitriding time was extended to 3 hours.
- Densification Behavior of the Oxidation-treated Spherical Fe-powder Compact during Spark-Plasma Sintering Process
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J Korean Powder Metall Inst. 2001;8(1):61-69.
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- Spark-Plasma Sintering(SPS) is one of the new sintering methods which takes advantages both inconventional pressure sintering and electric current sintering. It is known that SPS is very effective for the densification of hard-to-sinter materials like refractory metals, intermetallic compounds, glass and ceramics without grain growth. However, a clear explanation for sintering mechanism and an experimental evidence for the formation of weak plasma during SPS are not given yet. In this study, fundamental study on sintering behavior and mechanism of SPS was investiged. For this study, various spherical Fe powders were prepared such as as-received, as-reduced, and as-oxidized and then sintered by SPS facility. In order to confirm the surface cleaning effect during SPS neck region and fracture surface of sintered body was observed and analyzed by SEM/EPMA. Densification behavior was analyzed from the data of deflection along the pressure axis. Some specimens were additionally produced by Hot Pressing and the results were compared with those of SPS.
- 생체재료의 연구개발 및 산업화 현황
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Yeong-Geun Chung, Gyeong-Ja Kim, Gyun Choi
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J Korean Powder Metall Inst. 2001;8(1):70-77.
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