Journal of Powder Materials

Volume 13(5); October 2006

Synthesis of Carbon Nanotubes by Chemical Method at Warm Temperatures: Jung-Ho Ahn, Sang-Hyun Lee, Yong-Jin Kim, Byung-Sik Chung; J Korean Powder Metall Inst. 2006;13(5):305-312.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.305

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Abstract PDF: Amorphous carbon nanotubes were synthesized by a reaction of benzene, ferrocene and Na mixture in a small autoclave at temperatures as low as 400°C. The resulting carbon nanotubes were short and straight, but their inner hole was filled with residual products. The addition of quartz to the reacting mixture considerably promoted the formation of carbon nanotubes. A careful examination of powder structure suggested that the nanotubes in this process were mainly formed by surface diffusion of carbon atoms at the surface of solid catalytic particles, not by VLS(vapor-liquid-solid) mechanism.

Thermoelectric Properties of Bi_0.4Sb_1.6Te₃ Sintered Body Fabricated by Mechanical Grinding Process: Gil-Geun Lee, Sung-Chul Shin, Woo-Yeol Kim, Gook-Hyun Ha; J Korean Powder Metall Inst. 2006;13(5):313-320.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.313

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Abstract PDF: The present study is to analyze the thermoelectric properties of Bi_0.4Sb_1.6Te_3 thermoelectric materials fabricated by the mechanical grinding process. The Bi_0.4Sb_1.6Te_3 powders were prepared by the combination of mechanical milling and reduction treating methods using simply crushed pre-alloyed Bi_0.4Sb_1.6Te_3 powder. The mechanical milling was carried out using the tumbler-ball mill and planetary ball mill. The tumbler-ball milling had an effect on the carrier mobility rather than the carrier concentration, whereas, the latter on the carrier concentration. The specific electric resistivity and Seebeck coefficient decreased with increasing the reduction-heat-treatment time. The thermal conductivity continuously increased with increasing the reduction-heat-treatment time. The figure of merit of the Bi_0.4Sb_1.6Te_3 sintered body prepared by the mechanical grinding process showed higher value than one of the sintered body of the simply crushed powder.

Carbon-Nanofiber Reinforced Cu Composites Prepared by Powder Metallurgy: H. Weidmueller, T. Weissgaerber, T. Hutsch, R. Huenert, T. Schmitt, K. Mauthner, S. Schulz-Harder; J Korean Powder Metall Inst. 2006;13(5):321-326.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.321

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Electronic packaging involves interconnecting, powering, protecting, and cooling of semiconductor circuits fur the use in a variety of microelectronic applications. For microelectronic circuits, the main type of failure is thermal fatigue, owing to the different thermal expansion coefficients of semiconductor chips and packaging materials. Therefore, the search for matched coefficients of thermal expansion (CTE) of packaging materials in combination with a high thermal conductivity is the main task for developments of heat sink materials electronics, and good mechanical properties are also required. The aim of this work is to develop copper matrix composites reinforced with carbon nanofibers. The advantages of carbon nanofibers, especially the good thermal conductivity, are utlized to obtain a composite material having a thermal conductivity higher than 400 W/mK. The main challenge is to obtain a homogeneous dispersion of carbon nanofibers in copper. In this paper, a technology for obtaining a homogeneous mixture of copper and nanofibers will be presented and the microstructure and properties of consolidated samples will be discussed. In order to improve the bonding strength between copper and nanofibers, different alloying elements were added. The microstructure and the properties will be presented and the influence of interface modification will be discussed.

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Heat Exchange Structures Based on Copper/CNT Composite
André Schlott, Thomas Hutsch, Silke Hampel, Julius Lohse, Thomas Weißgärber, Bernd Kieback
Key Engineering Materials.2019; 809: 106. CrossRef

Hydrogenation and Electrochemical Characteristics of Amorphous-nanostructured Mg-based Alloys: A. Gebert, B. Khorkounov, L. Schultz; J Korean Powder Metall Inst. 2006;13(5):327-335.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.327

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Abstract PDF: In the development of new hydrogen absorbing materials for a next generation of metal hydride electrodes for rechargeable batteries, metastable Mg-Ni-based compounds find currently special attention. Amor phous-nanocrystalline Mg_63Ni_30Y_7 and Mg_50Ni_30Y_20 alloys were produced by mechanical alloying and melt-spinning and characterized by means of XRD, TEM and DSC. On basis of mechanically alloyed Mg-Ni-Y powders, complex hydride electrodes were fabricated and their electrochemical behaviour in 6M KOH (pH=14,8) was investigated. The electrodes made from Mg_63Ni_30Y_7 powders, which were prepared under use of a SPEX shaker mill, with a major fraction of nanocrystalline phase reveal a higher electrochemical activity far hydrogen reduction and a higher maximum discharge capacity (247 mAh/g) than the electrodes from alloy powder with predominantly amorphous microstructure (216 mAh/g) obtained when using a Retsch planetary ball mill at low temperatures. Those discharge capacities are higher that those fur nanocrystalline Mg_2Ni electrodes. However, the cyclic stability of those alloy powder electrodes was low. Therefore, fundamental stability studies were performed on Mg_63Ni_30Y_7 and Mg_50Ni_30Y_20 ribbon samples in the as-quenched state and after cathodic hydrogen charging by means of anodic and cathodic polarisation measurements. Gradual oxidation and dissolution of nickel governs the anodic behaviour before a passive state is attained. A stabilizing effect of higher fractions of yttrium in the alloy on the passivation was detected. During the cathodic hydrogen charging process the alloys exhibit a change in the surface state chemistry, i.e. an enrichment of nickel-species, causing preferential oxidation and dissolution during subsequent anodization. The effect of chemical pre-treatments in 1% HF and in 10;mg/l;YCl_3/1%;H_2O_2 solution on the surface degradation processes was investigated. A HF treatment can improve their anodic passivation behavior by inhibiting a preferential nickel oxidation-dissolution at low polarisation, whereas a YCl_3/H_2O_2 treatment has the opposite effect. Both pre-treatment methods lead to an enhancement of cathodically induced surface degradation processes.

Synthesis of Nanostructured Fe-Co Alloy Powders from Metal Salts: Young-Jung Lee, Jea-Sung Lee, Young-Ik Seo, Young-Do Kim; J Korean Powder Metall Inst. 2006;13(5):336-339.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.336

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Abstract PDF: Magnetic properties of nanostructured materials are affected in complicated manner by their microstructure such as pain size (or particle size), internal strain and crystal structure. Thus, studies on the synthesis of nanostructured materials with controlled microstructure are necessary fur a significant improvement in magnetic properties. In the present work, nanostructured Fe-Co alloy powders with a grain size of 50 nm were successfully fabricated from the powder mixtures of (99.9% purity) FeCl_2 and CoCl_2 by chemical solution mixing and hydrogen reduction.

How to Improve the Ductility of Nanostructured Materials: J. Eckert, C. Duhamel, J. Das, S. Scudino, Z. Zhang, K. B. Kim; J Korean Powder Metall Inst. 2006;13(5):340-350.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.340

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Abstract PDF: Nanostructured materials exhibit attractive mechanical properties that are often superior to the performance of their coarse-grained counterparts. However, one major drawback is their low ductility, which limits their potential applications. In this paper, different strategies to obtain both high strength and enhanced ductility in nanostructured materials are reported for Ti-base and Zr-base alloys. The first approach consists of designing an in-situ composite microstructure containing ductile bcc or hop dendrites that are homogeneously dispersed in a nanostructured matrix. The second approach is related to refining the eutectic structure of a Ti-Fe-Sn alloy. For all these materials, the microstructure, mechanical properties, deformation and fracture mechanisms will be discussed.

Spark Plasma Sintering of the Ductile Cu-Gas-atomized Ni Bulk Metallic Glass Composite Powders: Jin-Chun Kim, Yong-Jin Kim, Byoung-Kee Kim, Ji-Soon Kim; J Korean Powder Metall Inst. 2006;13(5):351-359.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.351

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Abstract PDF: Ni based(Ni_57Zr_20Ti_18Si_2Sn_3) bulk metallic glass(BMG) powders were produced by a gas atomization process, and ductile Cu powders were mixed using a spray drying process. The Ni-based amorphous powder and Cu mixed Ni composite powders were compacted by a spark plasma sintering (SPS) processes into cylindrical shape. The relative density varied with the used SPS mold materials such as graphite, hardened steel and WC-Co hard metal. The relative density increased from 87% to 98% when the sintering temperature increased up to 460°C in the WC-Co hard metal mold.

Effect of Grain Size and Heat-treating Atmosphere on the Phase Stability of Y-TZP: Tai-Joo Chung, Seung-Su Ahn, Eun-Wha Song, Kyung-Sik Oh, Jong-Sook Lee, Young-Sik Kim; J Korean Powder Metall Inst. 2006;13(5):360-365.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.360

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The phase stability of tetragonal phase in Y-TZP was investigated in terms of the distribution of grain sizes and heat-treating atmosphere. Y-TZP with various grain sizes were prepared using duration time at 1600°C as experimental parameter. Accumulated grain size distributions were built from the SEM micrographs and the amount of tetragonal phase were measured using XRD. Both results were compared to determine the critical grain size before and after heat-treatment in vacuum. The critical grain size drastically decreased compared with the small increase of average grain size due to the autocatalytic effect which critically affects the tetragonal to monoclinic phase transformation. After heat-treatment in reductive atmosphere critical grain size relatively increased due to the stabilization of tetragonal phase. The formation of oxygen vacancies during heat-treatment was ascribed to the increase of stability.

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Direct Observation on the Low Temperature Degradation Due to Surface Treatment in Y-TZP
Tai-Joo Chung, Hye-Sung Kim
Journal of Korean Powder Metallurgy Institute.2010; 17(3): 197. CrossRef

Effect of Sintering Temperature on Microstructure and Mechanical Properties of Cu Particles Dispersed Al₂O₃ Nanocomposites: Young-Keun Jeong, Sung-Tag Oh, Yong-Ho Choa; J Korean Powder Metall Inst. 2006;13(5):366-370.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.366

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Abstract PDF: The microstructure and mechanical properties of hot-pressed Al_2O_3/Cu composites with a different sintering temperature have been studied. The size of matrix grain and Cu dispersion in composites increased with increase in sintering temperature. Fracture toughness of the composite sintered at high temperature exhibited an enhanced value. The toughness increase was explained by the thermal residual stress, crack bridging and crack branching by the formation of microcrack. The nanocomposite, hot-pressed at 1450°C, showed the maximum fracture strength of 707 MPa. The strengthening was mainly attributed to the refinement of matrix grains and the increased toughness.

Mechanical Alloying and Milling: C. Suryanarayana, In-Seop An; J Korean Powder Metall Inst. 2006;13(5):371-372.; DOI: https://doi.org/10.4150/KPMI.2006.13.5.371

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Scientific Reports.2023;[Epub] CrossRef
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Transactions of the Indian Institute of Metals.2023; 76(3): 849. CrossRef
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Sukanto, Wahyono Suprapto, Rudy Soenoko, Yudy Surya Irawan
EUREKA: Physics and Engineering.2022; (1): 103. CrossRef
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