Journal of Powder Materials

Chemical Leaching of Non-Equilibrium Al(Fe-Co) Powder Produced by Rod Milling: Hyun-Goo Kim; J Korean Powder Metall Inst. 2003;10(5):305-309.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.305

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Abstract PDF: We report on the formation and chemical leaching of non-equilibrium Al_0.6(Fe_75Co_25) alloy produced by rod milling. X-ray diffractometry, transmission electron microscopy, differential scanning calorimetry, scanning electron microscopy, and vibrating sample magnetometry were used to characterize the as-milled and leached specimens. After 400 h, only the Al_0.4Fe_0.6 peak of the body-centered cubic type was present in the XRD pattern. The entire rod milling process could be divided into three different stages of milling: agglomeration, disintegration, and homogenization. The saturation magnetization, M_s decreased with increased milling time, the M_s of the powders before milling was about 113.8 emu/g, the M_s after milling for 400 h was about 11.55 emu/g. Leaching of the Al in KOH of the Al at room temperature from the as-milled powders did not induce any significant change in the diffraction pattern. After the leached specimen had been annealed at 600°C for 1 hour, the nanoscale crystalline phases were transformed into the bcc Fe, cubic Co, and CoFe_2O_4 phases. On cooling the specimen from 850°C, the degree of magnetization increased slightly, then increased sharply at approximately 364.8°C, indicating that the bcc Al_0.4Fe_0.6 phase had been transformed to the Fe and Co phases.

Effect of Polymer Content on Synthesis Process and Microstructure of Alumina-Zirconia Composite: J Korean Powder Metall Inst. 2003;10(5):310-317.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.310

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Two-component ceramic (alumina-zirconia) composites were fabricated by a soft-solution process in which polyethylene glycol (PEG) was used as a polymeric carrier. Metal salts and PEG were dissolved in ethyl alcohol without any precipitation in 1:1 volume ratio of alumina and zirconia. In the non-aqueous system, the flammable solvent made explosive, exothermic reaction during drying process. The reaction resulted in formation of volume expanded, porous precursor powders by a vigorous decomposition of organic components in the precursor sol. The PEG content affected the grain size of sintered composites as well as the morphology of precursor powders. The difference of microstructure in sintered composite was attribute to the solubility and homogeneity of metal cations in precursor sol. At the optimum amount of the PEG polymer, the metal ions were dispersed effectively in solution and a homogeneous polymeric network was formed. It made less agglomerated particles in the precursor sol and affected on uniform grain size in sintered composite.

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Grain Growth Behavior and Characteristics of Multiphase Ceramic Composites Fabricated by Organic-Inorganic Solution Technique
Sang Jin Lee
Materials Science Forum.2007; 558-559: 1249. CrossRef

Crystallite Size Measurement of Uranium Oxide Fuel Powders by Neutron Diffraction: J Korean Powder Metall Inst. 2003;10(5):318-324.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.318

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Abstract PDF: The nano-scale crystallite sizes of uranium oxide powders in simulated spent fuel were measured by the neutron diffraction line broadening method in order to analyze the sintering behavior of the dry process fuel. The mixed UO_2 and fission product powders were dry-milled in an attritor for 30, 60, and 120 min. The diffraction patterns of the powders were obtained by using the high resolution powder diffractometer in the HANARO research reactor. Diffraction line broadening due to crystallite size was measured using various techniques such as the Stokes' deconvolution, profile fitting methods using Cauchy function, Gaussian function, and Voigt function, and the Warren-Averbach method. The non-uniform strain, stacking fault and twin probability were measured using the information from the diffraction pattern. The realistic crystallite size could be obtained after separation of the contribution from the non-uniform strain, stacking fault and twin.

The Effect of Extrusion Temperatures on Microstructures and Mechanical Properties of Ultra-Fine Structured and Extruded Al₈₁Si₁₉ Alloys: J Korean Powder Metall Inst. 2003;10(5):325-332.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.325

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Abstract PDF: The effect of extrusion temperature on the microstructure and mechanical properties was studied in gas atomized TEX>Al_81Si_19 alloy powders and their extruded bars using SEM, tensile testing and wear testing. The Si particle size of He-gas atomized powder was about 200-800 nm. Each microstructure of the extruded bars with extrusion temperature (400, 450 and 500°C) showed a homogeneous distribution of primary Si and eutectic Si particles embedded in the Al matrix and the particle size varied from 0.1 to 5.5 µm. With increasing extrusion temperature from 400°C to 500°C, the ultimate tensile strength (UTS) decreased from 282 to 236 ㎫ at 300 K and the specific wear increased at all sliding speeds due to the coarse microstructure. The fracture behavior of failure in tension testing and wear testing was also studied. The UTS of extrudate at 400°C higher than that of 500°C because more fine Si particles in Al matrix of extrudate at 400°C prevented crack to propagate.

Microstructure and Magnetic Properties of Nanostructured Fe-Co Alloy Powders Produced by Chemical Solution Mixing and Hydrogen Reduction Methods: J Korean Powder Metall Inst. 2003;10(5):333-336.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.333

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Abstract PDF: The purpose of this study is the fabrication of nano-sized Fe-Co alloy powders with soft magnetic properties by the slurry mixing and hydrogen reduction (SMHR) process. FeCl_20 and CoCl_2 powders with 99.9% purities were used for synthesizing nanostructured Fe-Co alloy powder. Nano-sized Fe-Co alloy powders were successfully fabricated using SMHR, which was performed at 500°C for 1 h in H_2 atmosphere. The fabricated Fe-Co alloy powders showed alpha' phase (ordered body centered cubic) with the average particle size of 45 nm. The SMHR powder exhibited low coercivity force of 32.5 Oe and saturation magnetization of 214 emu/g.

Synthesis of Cu/Al₂O₃ Nanostructured Composite Powders for Electrode Application by Thermochemical Process: J Korean Powder Metall Inst. 2003;10(5):337-343.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.337

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Abstract PDF: Nanostructured Cu-Al_2O_3 composite powders were synthesized by thermochemical process. The synthesis procedures are 1) preparation of precursor powder by spray drying of solution made from water-soluble copper and aluminum nitrates, 2) air heat treatments to evaporate volatile components in the precursor powder and synthesis of nano-structured CuO + Al_2O_3, and 3) CuO reduction by hydrogen into pure Cu. The suggested procedures stimulated the formation of the gamma-Al_2O_3, and different alumina formation behaviors appeared with various heat treating temperatures. The mean particle size of the final Cu/Al_2O_3 composite powders produced was 20 nm, and the electrical conductivity and hardness in the hot-extruded bulk were competitive with Cu/Al_2O_3 composite by the conventional internal oxidation process.

Characteristics of Tantalum Powder by Conditions of After Treatment: J Korean Powder Metall Inst. 2003;10(5):344-347.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.344

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Pure tantalum powder has been produced by combining Na as a reducing agent, K_2TaF_7 as feed material, KCl and KF as a diluent in a stainless steel (SUS) bomb, using the method of metallothermic reduction. And we examined various types of after-treatment that affect the high purification of powder. A significant amount of impurities contained in recovered powder was removed in various conditions of acid washing. In particular, 20% (HCl + HNO_3) was effective in removing heavy metal impurities such as Fe, Cr and Ni, 8% H_2SO_4 + 8% Al_2(SO_4)_3 in removing fluorides such as K and F from non-reactive feed material, and 2% H_2O_2 + 1 % HF in removing oxides that formed during reaction. Significant amounts of oxygen and part of light metal impurities could be removed through deoxidation and heat treatment process. On the other hand, because it is difficult to remove completely heavy metal impurities such as Fe, Cr, and Ni through acid washing or heat treatment process if their contents are too high, it is considered desirable to inhibit these impurities from being mixed during the reduction process as much as possible.

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Characteristics and production of tantalum powders for solid-electrolyte capacitors
Jae Sik Yoon, Byung Il Kim
Journal of Power Sources.2007; 164(2): 959. CrossRef

Production of Tantalum Powder and Characteristics by External Supply of Feed Material and Reductant: J Korean Powder Metall Inst. 2003;10(5):349-352.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.349

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This study examined the correlation of various operational factors including reaction temperature and the quantity of reductant and diluent with the characteristics of powder using K_2 TaF_7 as feed materials, Na as a reductant and KCl/KF as a diluent. Also to control the particle size and shape, external supply system developed, it can provide a feed material and a reductant at a fixed quantity and evaluated the characteristics of tantalum powder. When the external supply system was applied instead of the batch type process that charges feed material, reductant and diluent at the same time, it was possible to induce regular reduction reaction between feed material and reductant, which increased the recovery rate and reduced the mixture of impurities. In particular, the application of the external supply system enabled the control of reaction temperature and reaction speed according to the feeding rate of feed material during reduced reaction, and resultantly it enabled the manufacturing of granular-shaped powder with a regular granularity of 2∼3 µtextrmm and purity of 99.5%.

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The production of niobium powder and electric properties of niobium capacitors
Jae Sik Yoon, Sung Wook Cho, Yang Soo Kim, Byung Il Kim
Metals and Materials International.2009; 15(3): 405. CrossRef
Characteristics and production of tantalum powders for solid-electrolyte capacitors
Jae Sik Yoon, Byung Il Kim
Journal of Power Sources.2007; 164(2): 959. CrossRef

기상법에 의한 나노분말 합성의 최근 연구 동향: J Korean Powder Metall Inst. 2003;10(5):353-359.; DOI: https://doi.org/10.4150/KPMI.2003.10.5.353

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