Journal of Powder Materials

Changes in Mechanical and Electrical Properties as a Function of Unidirectional Pressure Changes in Preforming While Isostatic Pressing for Graphite Block Fabrication: Tae-Sub Byun, Dong-Pyo Jeon, Sang-Hye Lee, Sang-Woo Lee, Jae-Seung Roh; J Powder Mater. 2023;30(1):35-40. Published online February 1, 2023; DOI: https://doi.org/10.4150/KPMI.2023.30.1.35

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In this study, a graphite block is fabricated using artificial graphite processing byproduct and phenolic resin as raw materials. Mechanical and electrical property changes are confirmed due to the preforming method. After fabricating preforms at 50, 100, and 150 MPa, CIP molding at 150 MPa is followed by heat treatment to prepare a graphite block. 150UP-CIP shows a 12.9% reduction in porosity compared with the 150 MPa preform. As the porosity is decreased, the bulk density, flexural strength, and shore hardness are increased by 14.9%, 102.4%, and 13.7%, respectively; and the deviation of density and electrical resistivity are decreased by 51.9% and 34.1%, respectively. Therefore, as the preforming pressure increases, the porosity decreases, and the electrical and mechanical properties improve.

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Effect of Microstructural Change under Pressure during Isostatic Pressing on Mechanical and Electrical Properties of Isotropic Carbon Blocks
Tae-Sub Byun, Sang-Hye Lee, Suk-Hwan Kim, Jae-Seung Roh
Materials.2024; 17(2): 387. CrossRef
Effect of Pressure and Holding Time during Compression Molding on Mechanical Properties and Microstructure of Coke-Pitch Carbon Blocks
Sun-Ung Gwon, Sang-Hye Lee, U-Sang Youn, Jae-Seung Roh
Applied Sciences.2024; 14(2): 772. CrossRef

Influence of α-SiC Seed Addition on Spark Plasma Sintering of β-SiC with Al-B-C: Microstructural Development: Kyeong-Sik Cho, Hyun-Kwuon Lee, Sang-Woo Lee; J Korean Powder Metall Inst. 2010;17(1):13-22.; DOI: https://doi.org/10.4150/KPMI.2010.17.1.013

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The unique features of spark plasma sintering process are the possibilities of a very fast heating rate and a short holding time to obtain fully dense materials. beta-SiC powder with 0, 2, 6, 10 wt% of alpha-SiC particles (seeds) and 4 wt% of Al-B-C (sintering aids) were spark plasma sintered at 1700-1850°C for 10 min. The heating rate, applied pressure and sintering atmosphere were kept at 100°C/min, 40 MPa and a flowing Ar gas (500 CC/min). Microstructural development of SiC as function of seed content and temperature during spark plasma sintering was investigated quantitatively and statistically using image analysis. Quantitative image analyses on the sintered SiC ceramics were conducted on the grain size, aspect ratio and grain size distribution of SiC. The microstructure of SiC sintered up to 1700°C consisted of equiaxed grains. In contrast, the growth of large elongated SiC grains in small matrix grains was shown in sintered bodies at 1750°C and the plate-like grains interlocking microstructure had been developed by increasing sintering temperature. The introduction of alpha-SiC seeds into beta-SiC accelerated the grain growth of elongated grains during sintering, resulting in the plate-like grains interlocking microstructure. In the alpha-SiC seeds added in beta-SiC, the rate of grain growth decreased with alpha-SiC seed content, however, bulk density and aspect ratio of grains in sintered body increased.

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Effect of Sintering Temperature on Microstructure and Mechanical Properties for the Spark Plasma Sintered Titanium from CP-Ti Powders
Kyeong-Sik Cho, In-Beom Song, Min-Hyeok Jang, Ji-Hye Yoon, Myung-Hoon Oh, Jae-Keun Hong, Nho-Kwang Park
Journal of Korean Powder Metallurgy Institute.2010; 17(5): 365. CrossRef

Battery Electrode Characteristics of Si-based Composite by Mechanical Alloying Method: Churl-Kyoung Lee, Jong-Ho Lee, Sang-Woo Lee; J Korean Powder Metall Inst. 2009;16(6):389-395.; DOI: https://doi.org/10.4150/KPMI.2009.16.6.389

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Abstract PDF: A Si-CuO-graphite composite was prepared by a mechanical alloying (MA) method. The Si-CuO composite has a mixture structure, where CuO is homogeneously dispersed in Si. Also, Cu_2O and Cu_3Si phases were formed during MA and heat treatment. Graphite with the Si-CuO composite was mixed in the same mill for 30 minutes with weight ratio of Si-CuO composite and graphite as 1:1. The Si-CuO composite was homogeneously covered with graphite. SiC phase was not formed. Electrochemical tests of the composite have been investigated, and the first charge and discharge capacities of the material were about 870mAh/g and 660mAh/g, respectively. Those values are about 76% of the first cycle efficiency. The cycle life of the composite showed that the initial discharge capacity of 660 mAh/g could be maintained up to 92% after 20 cycles.

Thermal Stability of Al-Fe-X Alloy System Prepared by Mechanical Alloying and Spark Plasma Sintering: I. Al-Fe: Hyun-Kwuon Lee, Sang-Woo Lee, Kyeong-Sik Cho; J Korean Powder Metall Inst. 2005;12(1):70-78.; DOI: https://doi.org/10.4150/KPMI.2005.12.1.070

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Mechanical alloying using high-energy ball mill and subsequent spark plasma sintering (SPS) process was applied to understand mechanical alloying processing of Al-Fe alloy system. The thermal stability of mechanically alloyed Al-Fe alloy was intended to be enhanced by SPS process. Various analytical techniques including particle size analysis, density measurement, micro-Vickers hardness test, SEM, TEM, and X-ray diffractometry were adopted to find optimum processing conditions for mechanical alloying and subsequent SPS and to estimate thermal stability of the prepared alloy. It was found from the treatment of mechanically alloyed Al-8wt.%Fe powder mixture that needle-shaped Al_3Fe precipitates was formed in the Al-Fe matrix, and the alloy compact showed enhanced densification and reached its full density with little loss of its fine microstructure. After heat treatment at 500circC, it was also shown that the thermal stability of Al-8wt.%Fe alloy fabricated in the present study was enhanced, which was due to its fine microstructure developed by fast densification of SPS.

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Effect of Sintering Temperature on Microstructure and Mechanical Properties for the Spark Plasma Sintered Titanium from CP-Ti Powders
Kyeong-Sik Cho, In-Beom Song, Min-Hyeok Jang, Ji-Hye Yoon, Myung-Hoon Oh, Jae-Keun Hong, Nho-Kwang Park
Journal of Korean Powder Metallurgy Institute.2010; 17(5): 365. CrossRef

Thermal Stability of Al-Fe-X Alloy System Prepared by Mechanical Alloying and Spark Plasma Sintering: II. Al-Fe-Cr and Al-Fe-Mo: Hyun-Kwuon Lee, Sang-Woo Lee, Kyeong-Sik Cho; J Korean Powder Metall Inst. 2005;12(1):43-50.; DOI: https://doi.org/10.4150/KPMI.2005.12.1.043

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Mechanical alloying using high-energy ball mill and subsequent spark plasma sintering (SPS) process was applied to Al-Fe-Cr and Al-Fe-Mo powder mixture to investigate effects of Cr and Mo addition on thermal stability of Al-Fe, and thereby to enhance its thermal stability up to 500circC. Various analytical techniques including micro-Vickers hardness test, SEM, TEM, X-ray diffractometry and corrosion test were carried out. It was found that addition of Cr and Mo to Al-Fe system played a role of grain growth inhibitor of matrix Al and some precipitates such as Al_3Fe during SPS and subsequent heat treatment. The inhibition of grain growth resulted in increased Vickers hardness and thermal stability up to 500circC comparing to those of Al-Fe alloy system.

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A Constitutional Framework of a Future Palestinian State - Synthesis of Leading Palestinian Thinking and Public Perceptions
Asem Khalil
SSRN Electronic Journal.2009;[Epub] CrossRef

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