Journal of Powder Materials

산화물 초전도체의 응용기술: J Korean Powder Metall Inst. 2003;10(4):221-227.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.221

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Synthesis of TiC/Co Composite Powder by the Spray Thermal Conversion of Metallic Salt Solution: J Korean Powder Metall Inst. 2003;10(4):228-234.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.228

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In the present study, the focus is on the synthesis of titanium carbide/cobalt composite powder by the spray thermal conversion process using metallic salt solution as the raw materials. Two types of oxide powders of Ti-Co-O system were prepared by the spray drying of two types of metallic salt solutions : titanium chloride-cobalt nitrate and TiO_2 powder-cobalt nitrate solutions. These oxide powders were mixed with carbon black, and then these mixtures were carbothermal reduced under a flowing argon atmosphere. The changes in the phase structure and thermal gravity of the mixtures during carbothermal reduction were analysed using XRD and TG-DTA. In the case of using the titanium chloride-cobalt nitrate solution, it could not be obtained TiC/Co composite powder due to contamination of the impurities during the spray drying of the solution. However, in tile case of using the TiO_2 powder-cobalt nitrate scullion, TiC-15 wt. %Co composite powder could be synthesized by the spray thermal conversion process. The synthesized TiC-15 wt. %Co composite powder at 1200°C for 2 hours has average particle size of 150 nm.

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Synthesis of Ultra Fine Titanium-Tungsten Carbide Powder from Titanium Dioxide and Ammonium Metatungstate
Gil-Geun Lee, Gook-Hyun Ha
MATERIALS TRANSACTIONS.2009; 50(1): 187. CrossRef
Carbothermic Reduction of Oxide Powder Prepared from Titanium Dioxide and Cobalt Nitrate
Gil-Geun Lee, Gook-Hyun Ha
MATERIALS TRANSACTIONS.2006; 47(12): 3007. CrossRef

Mechanical Properties and Texture after Thermomechanical Treatment of Al/Al₂O₃ Composite Fabricated by Powder-in Sheath Rolling Method: J Korean Powder Metall Inst. 2003;10(4):235-240.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.235

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Abstract PDF: The Al/Al_2O_3 composites fabricated by powder in sheath rolling method were cold-rolled by 50% reduction and annealed for 1.8 ks at various temperatures ranging from 200 to 500°C, for improvement of the mechanical properties. The mechanical properties and texture of the composites after rolling and annealing were investigated. The tensile strength of the composites increased significantly due to work hardening after cold rolling, however it decreased due to restoration after annealing. The strength of the composites was improved by thermo mechanical treatment. On the other hand, the texture evolution with annealing temperatures wa,i different between the unreinforced material and the composites. The unreinforced material showed a deformation (rolling) texture of which main component is ｛112｝<111> at annealing temperatures up to 300°C. However, the composites have already exhibited a recrystallization texture of which main component is ｛001｝<100> after annealing at 200°C. This proves that the critical temperature for recrystailization is lower in the composites than in the unreinforced ones.

Fabrication of Biaxially Textured Ni Tapes from Ni Powder Compact Rods: J Korean Powder Metall Inst. 2003;10(4):241-248.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.241

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Biaxially textured Ni tapes were fabricated by a cold working and recrystallization heat treatment processes from powder compact rods. The processing parameters associated with the cube texture formation in Ni tapes were systematically investigated by using X-ray diffraction and pole-figure analysis. The Ni powder used in this study was 5 mum in size and 99.99% in purity. To find the optimum sintering temperature, tensile tests were performed for Ni rods sintered at various temperatures. The Ni rods sintered at 1000°C showed poor elongation and low fracture strength, while the Wi rods sintered above 1000°C revealed good mechanical properties. The higher elongation and fracture strength of the Ni rods sintered at higher temperatures than 1000°C are attributed to the full densification of the sintered rods. The sintered Ni rods were cold-rolled with 5% reduction to the final thickness of 100 mum and then annealed for development of rube texture in rolled Ni tapes. The annealed Ni tapes depicted strong cube texture with FWHM(full-width at half-maximum) of in-plane and out-of-plane in the range of 8° to 10°. The NiO deposited on the Ni tapes by MOCVD process showed good epitaxy with FWHM=10°, which indicates that the Ni tapes can be used as a substrate for YBCO coated conductors.

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Processing condition for the development of cube texture in Ni and Ni alloy tapes fabricated by powder metallurgy process
Bong Ki Ji, Dong-Wook Lee, Min-Woo Kim, Byung-Hyuk Jun, Pyeong Yeal Park, Kyu-Dong Jung, Chan-Joong Kim
Physica C: Superconductivity.2004; 412-414: 853. CrossRef

Microwave Sintering of WC-Co Hard Metals: J Korean Powder Metall Inst. 2003;10(4):249-254.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.249

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Abstract PDF: WC-6wt%Co hard metal powders were sintered by a 2.45 GHz multimode microwave applicator in Ar atmosphere. Microwave sintering of WC-6wt%Co powder lowered the sintering temperature and shortened the processing time in less than two hours than by a conventional method. Microstructures of the sintered specimen were studied with scanning electron microscope (SEM) and no abnormal grain growth was observed. Mechanical properties were similar to the values of the specimens sintered by a conventional method. Specimen sintered at 1350°C for 30 minutes ,hewed 99%, 20.5 GPa and 8.1 MPasqrtm of theoretical density, hardness and fracture strength, respectively.

Synthesis of Ultrafine TaC-5%Co Composite Powders using Tantalum Oxalate Solution: J Korean Powder Metall Inst. 2003;10(4):255-261.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.255

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Abstract PDF: Ultrafine TaC-5%Co composite powders were synthesized by spray conversion process using tantalum oxalate solution and cobalt nitrate hexahydrate(Co((NO_3)_2 . 6H_2O). The phase of Ta-Co oxide powders had amorphous structures after calcination below 500°C and changed Ta_2O_5, TaO_2 and CoTa_2O_6 phase by heating above 600°C. The calcined Ta-Co oxide powders were spherical agglomerates consisted of ultrafine primary particles <50 nm in size. By carbothermal reaction, the TaC phase began to form from 900°C. The complete formation of TaC could be achieved at 1050°C for 6 hours. The observed size of TaC-Co composite powders by TEM was smaller than 200 nm.

Fabrication of Nano-Sized Ni-ferrite Powder from Waste Solution Produced by Shadow Mask Processing: J Korean Powder Metall Inst. 2003;10(4):262-269.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.262

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Abstract PDF: Nano-sized Ni-ferrite powder was fabricated by spray pyrolysis process using the waste solution resulting from shadow mask processing. The average particle size of the powder was below 100 nm. The effects of the concentration of raw material solution, the nozzle tip size and air pressure on the properties of powder were studied. As the concentration increased, the average particle size of the powder gradually increased and its specific surface area decreased, but size distribution was much wider and the fraction of the Ni-ferrite phase greatly increased as the concentration increasing. As the nozzle tip size increased from 1 mm to 2 mm, the average particle size of the powder decreased. In case of 3 mm nozzle tip size, the average particle size of the powder increased slightly. On the other hand, in case of 5 mm nozzle tip size, average particle size of the powder decreased. Size distribution of the powder was unhomogeneous, and the fraction of the Ni-ferrite phase decreased as the nozzle tip size increasing. As air pressure increased up to 1 kg/cm2, the average particle size of the powder decreased slightly, on the other hand, the fraction of the Ni-ferrite phase was almost constant. In case of 3kg/cm2 air pressure, average particle size of the powder and the fraction of the Ni-ferrite phase remarkably decreased, but size distribution was narrow.

Microstructure and Sintering Behavior of W-15 wt%Cu Nanocomposite Powder Prepared from W-CuO Mixture: J Korean Powder Metall Inst. 2003;10(4):270-274.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.270

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Abstract PDF: Recently, the fabrication process of W-Cu nanocomposite powders has been researched to improve the sinterability by mechanochemical process (MCP), which consists of ball milling and hydrogen-reduction with W- and Cu-oxide mixture. However, there are many control variables in this process because the W oxides are hydrogen-reduced via several reduction stages at high temperature over 800°C with susceptive reduction conditions. In this experiment, the W-15 wt%Cu nanocomposite powder was fabricated with the ball-milling and hydrogen-reduction process using W and CuO powder. The microstructure of the fabricated W-Cu nanocomposite powder was homogeneously composed of the fine W particles embedded in the Cu matrix. In the sintering process, the solid state sintering was certainly observed around 850°C at the heating rate of 10°C/min. It is considered that the solid state sintering at low temperature range should occur as a result of the sintering of Cu phase between aggregates. The specimen was fully densified over 98% for theoretical density at 1200°C for 1 h with the heating rate of 10°C/min.

In-situ Particle Characterization of Cu Nanopowder using Scanning Mobility Particle Sizer in Pulsed Wire Evaporation Method: J Korean Powder Metall Inst. 2003;10(4):275-280.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.275

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Abstract PDF: Synthesis and characteristics of Cu nanopowder were considered by in-situ characterization method using SMPS in pulsed wire evaporation process. With increasing pressure in chamber, particle size and degree of agglomeration increased by increase of collision frequency. Also, it was found from the XRD analyses and BET measurements that crystallite size and particle size decreased with elevating applied voltage. However, SMPS measurements and TEM observation revealed the increase of particle size and degree of agglomeration with increase of applied voltage. These results suggested that particle growth and agglomeration depend on overheating factor in chamber at the early stage and thermal coagulation in filtering system during powder formation until collection.

Synthesis of Ultrafine TiC-15%Co Powder by Thermochemical Method: J Korean Powder Metall Inst. 2003;10(4):281-287.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.281

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Abstract PDF: Ultrafine TiC-15%Co powders were synthesized by a thermochemical process, including spray drying, calcination, and carbothermal reaction. Ti-Co oxide powders were prepared by spray drying of aqueous solution of titanium chloride and Ti(OH)_2 slurry, both containing cobalt nitrate, fellowed by calcination. The oxide powders were mixed with carbon powder to reduce and carburize at 1100~1250°C under argon or hydrogen atmosphere. Ultrafine TiC particles were formed by carbothermal reaction at 1200~1250°C, which is significantly lower than the formation temperature (~1700°C) of TiC particles prepared by conventional method. The oxygen content of TiC-15%Co powder synthesized under hydrogen atmosphere was lower than that synthesized under argon, suggesting that hydrogen accelerates the reduction rate of Ti-Co oxides. The size of TiC-15%Co powder was evaluated by FE-SEM and TEM and Identified to be smaller than 300 nm.

Amorphization Process of Cr-N Alloy System by Mechanical Alloying: J Korean Powder Metall Inst. 2003;10(4):288-293.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.288

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Abstract PDF: Mechanical alloying (MA) by high energy ball mill of Pure chromium Powders was carried out under the nitrogen gas atmosphere. Cr-N amorphous alloy powders have been produced through the solid-gas reaction subjected to MA. The atomic structure during amorphization process was observed by X-ray and neutron diffractions. An advantage of the neutron diffraction technique allows us to observe the local atomic structure surrounding a nitrogen atom. The coordination number of metal atoms around a N atom turns out to be 5.5 atoms. This implies that a nitrogen atom is located at both of centers of the tetrahedron and octahedron formed by metal atoms to stabilize an amorphous Cr-N structure. Also, we have revealed that a Cr-N amorphous alloy may produced from a mixture of pure Cr and Cr nitrides powders by solid-solid reaction during mechanical alloying.

DBM 공정에 의한 구형 솔더볼 분말의 제조기술 연구동향: J Korean Powder Metall Inst. 2003;10(4):294-300.; DOI: https://doi.org/10.4150/KPMI.2003.10.4.294

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