• Title/Summary/Keyword: High-energy milling

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Effect of High-Energy Ball Milling on Thermoelectric Transport Properties in CoSb3 Skutterudite (고에너지 볼 밀링이 Skutterudite계 CoSb3의 열전 및 전하 전송 특성에 미치는 영향)

  • Nam, Woo Hyun;Meang, Eun-Ji;Lim, Young Soo;Lee, Soonil;Seo, Won-Seon;Lee, Jeong Yong
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.28 no.12
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    • pp.852-856
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    • 2015
  • In this study, we investigate the effect of high-energy ball milling on thermoelectric transport properties in double-filled $CoSb_3$ skutterudite ($In_{0.2}Yb_{0.1}Co_4Sb_{12}$). $In_{0.2}Yb_{0.1}Co_4Sb_{12}$ powders are milled using high-energy ball milling for different periods of time (0, 5, 10, and 20 min), and the milled powders are consolidated into bulk samples by spark plasma sintering. Microstructure analysis shows that the high-energy ball milled bulk samples are composed of nano- and micro-grains. Because the filling fractions are reduced in the bulk samples due to the kinetic energy of the high-energy ball milling, the carrier concentration of the bulk samples decreases with the ball milling time. Furthermore, the mobility of the bulk samples also decreases with the ball milling time due to enhanced grain boundary scattering of electrons. Reduction of electrical conductivity by ball milling has a decisive effect on thermoelectric transport in the bulk samples, power factor decreases with the ball milling time.

Effect of Initial Silicon Scrap Size on Powder Refining Process During High Energy Ball Milling (HEBM) (폐실리콘의 고에너지 밀링 과정에서 초기 입자 크기가 분말의 미세화에 미치는 효과)

  • Song, Joon-Woo;Kim, Hyo-Seob;Kim, Sung-Shin;Koo, Jar-Myung;Hong, Soon-Jik
    • Journal of Powder Materials
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    • v.17 no.3
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    • pp.242-250
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    • 2010
  • In this research, the optimal manufacturing conditions of fine Si powders from Si scrap were investigated as a function of different initial powder size using the high-energy ball milling equipment, which produces the fine powder by means of an ultra high-energy within a short duration. The morphological change of the powders according to the milling time was observed by Scanning electron microscopy (SEM). With the increasing milling time, the size of Si powder was decreased. In addition, more energy and stress for milling were required with the decreasing initial powder size. The refinement of Si scrap was rapidly carried out at 10min ball milling time. However, the refined powder started to agglomerate at 30 min milling time, while the powder size became uniform at 60 min milling time.

BRAZEABILITY AND MICROSTRUCTURE OF Ag-28Cu MICROJOINING FILLER PRODUCED BY HIGH ENERGY BALL MILLING

  • ASHUTOSH SHARMA;MYOUNG JIN CHAE;BYUNGMIN AHN
    • Archives of Metallurgy and Materials
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    • v.65 no.4
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    • pp.1323-1327
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    • 2020
  • In this paper, we have studied the evolution of morphology and brazing behavior of Ag-28Cu alloy filler processed by high energy ball milling. The milling of the powder mixture was carried out for 40 h. The structural and morphological analyses were performed by the X-ray diffraction and scanning electron microscopy. The melting temperature of the braze filler was determined by differential thermal analysis. The filler wetting properties were assessed from the spread area ratio measurements on various Ti substrates. The results indicate that the ball milling can effectively depress the filler melting point and enhance the brazeability. The milled powder mixture showed Ag(Cu) solid solution with a crystallite size of 174-68 nm after 40 h. It was shown that the high energy ball milling can be a potential method to develop low temperature brazing fillers for advanced microjoining applications.

Surface Modification of $AB_2$ Type Hydrogen Storage Alloys by Ball Milling for Ni-MH Battery (Ni-MH 전극용 $AB_2$계 수소저장합금의 볼밀링 처리에 의한 표면개질 연구)

  • Moon, Hong-Gi;Park, Choong-Nyeon;Yoo, Joung-Hyun;Park, Chan-Jin;Choi, Jeon
    • Journal of Hydrogen and New Energy
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    • v.17 no.4
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    • pp.418-424
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    • 2006
  • In order to improve the activation properties of the $AB_2$ type hydrogen storage alloys for Ni-MH battery, the alloy surface was modified by employing high energy ball milling. The $Zr_{0.54}Ti_{0.45}V_{0.54}Ni_{0.87}Cr_{0.15}Co_{0.21}Mn_{0.24}$ alloy powder was ball milled for various period by using the high energy ball mill. As the ball milling time increased, activation of the $AB_2$ type composite powder electrodes were enhanced regardless of additives. When the ball milling time was small discharge capacities of the $AB_2$ type composite powder electrodes increased with the milling time. On the other hand for large milling time it decreased with increasing milling time. The maximum discharge capacity was obtained by ball milling for 3-4 min.

Synthesis of MnFeP1-xAsx Nanocrystalline Powders by High-Energy Ball Milling (고에너지볼밀링을 이용한 MnFeP1-xAsx 나노분말의 합성)

  • 조영환
    • Journal of Powder Materials
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    • v.10 no.2
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    • pp.129-135
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    • 2003
  • Nanocrystalline powders of $MnFeP_{1-x}As_x$(x=0.45-0.6) have been synthesized by mechanochemical reaction at room temperature using high-energy ball milling from mixtures of Mn, Fe, P, and As Powders. It has been found that a mechanically induced self-propagating reaction (MSR) occurs within 2 hours of milling and it produces very fine polycrystalline powder having a hexagonal $Fe_2P$ structure. Further milling up to 24 hours did not change the crystalline and average particle sizes or the phase composition of the milling product. When x is 0.65, no reaction among the reactants has been observed even after 24 hours of milling. As the P content decreases in $MnFeP_{1-x}As_x$, the incubation time for the MSR has increased and the lattice constants in both a and c axes have changed.

Characterization of the High Energy Milled Boron Precursor Powders in the Synthesis of $MgB_2$ Superconductor ($MgB_2$ 초전도체의 합성에 미치는 고에너지 밀링에 의한 초기 보론 분말의 특성)

  • Lee, J.H.;Shin, S.Y.;Kim, C.J.;Park, H.W.
    • Progress in Superconductivity
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    • v.9 no.1
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    • pp.74-79
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    • 2007
  • We characterized the highly refined boron precursor powders which were attrition milled for different milling times. $MgB_2$ powder precursor was formed from elemental crystalline Mg and amorphous B powder. The microstructure was investigated by SEM. SEM results indicate that the size of the milled powders was reduced with increasing milling time, which were varied from 0 to 8 hours. We also studied thermal behavior of the starting precursor by DSC as a function of milling time. The thermal behavior of the powder precursors was influenced by milling time. In order to determine the thermal events at DSC peaks, we annealed the milled powder mixture at $600^{\circ}C$ and $650^{\circ}C$ under protective gas and then analyzed the formation of $MgB_2$ by the XRD. We observed that superconducting $MgB_2$ phase was formed at lower temperature by the longer high energy milling. These results show that the high energy milling of the boron precursor powder can improve the reactivity for the formation of $MgB_2$.

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Microstructure of W-Cu Composite Powders with Variation of Milling Method during Mechanochemical Process (기계화학적 공정의 밀링 방법에 따른 W-Cu 복합분말의 미세조직)

  • 이강원;김길수;김대건;김영도
    • Journal of Powder Materials
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    • v.9 no.5
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    • pp.329-335
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    • 2002
  • Recently, the fabrication process of the W-Cu nanocomposite powders has been studied to improve the sinterability through the mechanical alloying and reduction of W and Cu oxide mixtures. In this study. the W-Cu composites were produced by mechanochemical process (MCP) using $WO_3-CuO$ mixtures with two different milling types of low and high energy, respectively. These ball-milled mixtures were reduced in $H_2$ atmosphere. The ball-milled and reduced powders were analyzed through XRD, SEM and TEM. The fine W-Cu powder could be obtained by the high energy ball-milling (HM) compared with the large Cu-cored structure powder by the low energy ball-milling (LM). After the HM for 20h, the W grain size of the reduced W-Cu powder was about 20-30 nm.

Prepration and Properties of Blue Tungsten Oxide Nanopowders by High Energy Ball-Mill (고 에너지 볼밀을 이용한 Blue 텅스텐산화물 나노입자의 제조와 특성)

  • Kim, Myung-Jae;Lee, Kwang-Seok;Kim, Kyung-Nam
    • Korean Journal of Materials Research
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    • v.31 no.1
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    • pp.23-28
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    • 2021
  • The purpose of this study is to prepare WO3 nanopowders by high-energy milling in mixture gas (7 % H2+Ar) with various milling times (10, 30, and 60 min). The phase transformation, particle size and light absorption properties of WO3 nanopowders during reduction via high-energy milling are studied. It is found that the particle size of the WO3 decreases from about 30 ㎛ to 20 nm, and the grain size of WO3 decreases rapidly with increasing milling time. Furthermore, the surface of the particles due to the pulverization process is observed to change to an amorphous structure. UV/Vis spectrophotometry shows that WO3 powder with increasing milling times (10, 30, 60 min) effectively extends the light absorption properties to the visible region. WO3 powder changes from yellow to gray and can be seen as a phenomenon in which the progress of the color changes to blue. The characterization of WO3 is performed by high resolution X-ray diffractometry, Field emission scanning electron microscopy, Transmission electron microscopy, UV/Vis spectrophotometry and Particle size analysis.

Microstructural Evolution of AlCuFeMnTi-0.75Si High Entropy Alloy Processed by Mechanical Alloying and Spark Plasma Sintering

  • Minsu Kim;Ashutosh Sharma;Myoung Jin Chae;Hansung Lee;Byungmin Ahn
    • Archives of Metallurgy and Materials
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    • v.66 no.3
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    • pp.703-707
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    • 2021
  • In this work, we have designed a new high entropy alloy containing lightweight elements, e.g., Al, Fe, Mn, Ti, Cu, Si by high energy ball milling and spark plasma sintering. The composition of Si was kept at 0.75 at% in this study. The results showed that the produced AlCuFeMnTiSi0.75 high entropy alloy was BCC structured. The evolution of BCC1 and BCC2 phases was observed with increasing the milling time up to 60 h. The spark plasma sintering treatment of milled compacts from 650-950℃ showed the phase separation of BCC into BCC1 and BCC2. The density and strength of these developed high entropy alloys (95-98%, and 1000 HV) improved with milling time and were maximum at 850℃ sintering temperature. The current work demonstrated desirable possibilities of Al-Si based high entropy alloys for substitution of traditional cast components at intermediate temperature applications.

Refinement Behavior of Coarse Magnesium Powder by High Energy Ball Milling (HEBM) (고에너지 밀링공정을 이용한 조대 마그네슘 분말의 미세화 거동)

  • Song, Joon-Woo;Kim, Hyo-Seob;Kim, Hong-Moule;Kim, Taek-Soo;Hong, Soon-Jik
    • Journal of Powder Materials
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    • v.17 no.4
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    • pp.302-311
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    • 2010
  • In this research, the refinement behavior of the coarse magnesium powders fabricated by gas atomization was investigated as a function of milling time using a short duration high-energy ball milling equipment, which produces fine powders by means of an ultra high-energy within a short duration. The microstructure, hardness, and formability of the powders were investigated as a function of milling time using X-ray diffraction, scanning electron microscopy, Vickers micro-hardness tester and magnetic pulsed compaction. The particle morphology of Mg powders changed from spherical particles of feed metals to irregular oval particles, then platetype particles, with increasing milling time. Due to having HCP structure, deformation occurs due to the existence of the easily breakable C-axis perpendicular to the base, resulting in producing plate-type powders. With increasing milling time, the particle size increased until 5 minutes, then decreased gradually reaching a uniform size of about 50 micrometer after 20 minutes. The relative density of the initial power was 98% before milling, and mechanically milled powder was 92~94% with increase milling time (1~5 min) then it increased to 99% after milling for 20 minutes because of the change in particle shapes.