The present study demonstrates the effect of freezing conditions on the pore structure of porous Cu-10 wt.% Sn prepared by freeze drying of CuO-SnO₂/camphene slurry. Mixtures of CuO and SnO₂ powders are prepared by ball milling for 10 h. Camphene slurries with 10 vol.% of CuO-SnO₂ are unidirectionally frozen in a mold maintained at a temperature of -30°C for 1 and 24 h, respectively. Pores are generated by the sublimation of camphene at room temperature. After hydrogen reduction and sintering at 650°C for 2 h, the green body of the CuO-SnO₂ is completely converted into porous Cu-Sn alloy. Microstructural observation reveals that the sintered samples have large pores which are aligned parallel to the camphene growth direction. The size of the large pores increases from 150 to 300 μm with an increase in the holding time. Also, the internal walls of the large pores contain relatively small pores whose size increases with the holding time. The change in pore structure is explained by the growth behavior of the camphene crystals and rearrangement of the solid particles during the freezing process.

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• Fabrication of Porous Ni by Freeze Drying and Hydrogen Reduction of NiO/Camphene Slurry
  Jae-Hun Jeong, Sung-Tag Oh, Chang-Yong Hyun
  Journal of Korean Powder Metallurgy Institute.2019; 26(1): 6.     CrossRef
• Fabrication of Al2O3 Dispersed Porous Cu by Freeze Drying of CuO-Al2O3/Camphene Slurry
  Hyunji Kang, Doh-Hyung Riu, Sung-Tag Oh
  journal of Korean Powder Metallurgy Institute.2018; 25(1): 25.     CrossRef
• Porous W-Ni Alloys Synthesized from Camphene/WO3-NiO Slurry by Freeze Drying and Heat Treatment in Hydrogen Atmosphere
  Sung Hyun Park, Seong-Min Park, So-Jeong Park, Bo-Yeong Park, Sung-Tag Oh
  Korean Journal of Materials Research.2018; 28(2): 108.     CrossRef

The effect of sublimable vehicle composition in the camphor-naphthalene system on the pore structure of porous Cu-Ni alloy is investigated. The CuO-NiO mixed slurries with hypoeutectic, eutectic and hypereutectic compositions are frozen into a mold at -25°C. Pores are generated by sublimation of the vehicles at room temperature. After hydrogen reduction at 300°C and sintering at 850°C for 1 h, the green body of CuO-NiO is completely converted to porous Cu-Ni alloy with various pore structures. The sintered samples show large pores which are aligned parallel to the sublimable vehicle growth direction. The pore size and porosity decrease with increase in powder content due to the degree of powder rearrangement in slurry. In the hypoeutectic composition slurry, small pores with dendritic morphology are observed in the sintered Cu-Ni, whereas the specimen of hypereutectic composition shows pore structure of plate shape. The change of pore structure is explained by growth behavior of primary camphor and naphthalene crystals during solidification of camphor-naphthalene alloys.

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• Freeze Drying Process and Pore Structure Characteristics of Porous Cu with Various Sublimable Vehicles
  Gyuhwi Lee, Sung-Tag Oh, Myung-Jin Suk, Young-Keun Jeong
  Journal of Korean Powder Metallurgy Institute.2020; 27(3): 198.     CrossRef
• Interaction of Solid Particles with the Solidifying Front in the Liquid-Particle Mixture
  Ho-Suk Lee, Kyu-Hee Lee, Sung-Tag Oh, Young Do Kim, Myung-Jin Suk
  Journal of Korean Powder Metallurgy Institute.2018; 25(4): 336.     CrossRef

This study reports a simple way of fabricating the porous Cu with unidirectional pore channels by freeze drying camphene slurry with Cu oxide coated Cu powders. The coated powders were prepared by calcination of ballmilled powder mixture of Cu and Cu-nitrate. Improved dispersion stability of camphene slurry could be achieved using the Cu oxide coated Cu powders instead of pure Cu powders. Pores in the frozen specimen at -25°C were generated by sublimation of the camphene during drying in air, and the green bodies were sintered at 750°C for 1 h in H₂ atmosphere. XRD analysis revealed that the coated layer of Cu oxide was completely converted to Cu phase without any reaction phases by hydrogen heat treatment. The porous Cu specimen prepared from pure Cu powders showed partly large pores with unidirectional pore channels, but most of pores were randomly distributed. In contrast, large and aligned parallel pores to the camphene growth direction were clearly observed in the sample using Cu oxide coated Cu powders. Pore formation behavior depending on the initial powders was discussed based on the degree of powder rearrangement and dispersion stability in slurry.

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• Effect of Freezing and Sintering Condition of CuO-SnO2/Camphene Slurries on the Pore Structure of Porous Cu-Sn
  Joo-Hyung Kim, Sung-Tag Oh, Chang-Yong Hyun
  Journal of Korean Powder Metallurgy Institute.2016; 23(1): 49.     CrossRef
• Fabrication of Cu-30 vol% SiC Composites by Pressureless Sintering of Polycarbosilane Coated SiC and Cu Powder Mixtures
  Yeon Su Kim, Na-Yeon Kwon, Young-Keun Jeong, Sung-Tag Oh
  Korean Journal of Materials Research.2016; 26(6): 337.     CrossRef
• Synthesis of Aligned Porous Sn by Freeze-Drying of Tin Chloride/camphene Slurry
  수룡 방, 승탁 오
  Korean Journal of Materials Research.2015; 25(1): 27~31.     CrossRef

Cu-Ni alloys with unidirectionally aligned pores were prepared by freeze-drying process of CuO-NiO/camphene slurry. Camphene slurries with dispersion stability by the addition of oligomeric polyester were frozen at -25°C, and pores in the frozen specimens were generated by sublimation of the camphene during drying in air. The green bodies were hydrogen-reduced at 300°C and sintered at 850°C for 1 h. X-ray diffraction analysis revealed that CuO-NiO composite powders were completely converted to Cu-Ni alloy without any reaction phases by hydrogen reduction. The sintered samples showed large and aligned parallel pores to the camphene growth direction, and small pores in the internal wall of large pores. The pore size and porosity decreased with increase in CuO-NiO content from 5 to 10 vol%. The change of pore characteristics was explained by the degree of powder rearrangement in slurry and the accumulation behavior of powders in the interdendritic spaces of solidified camphene.

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• Enhancement in electrical conductivity of pastes containing submicron Ag-coated Cu filler with palmitic acid surface modification
  Eun Byeol Choi, Jong-Hyun Lee
  Applied Surface Science.2017; 415: 67.     CrossRef
• Investigation for Microstructure and Hardness of Welded Zone of Cu-Ni Alloy using W92-Ni-Fe Sintering Tool
  Tae-Jin Yoon, Sang-Won Park, Myung-Chang Kang, Joong-Suk Noh, Sung-Wook Chung, Chung-Yun Kang
  Journal of Korean Powder Metallurgy Institute.2015; 22(3): 181.     CrossRef
• Controlling Structural and Electrical Properties of Pt Nanopowder-Dispersed SiO2Film
  Jae Ho Lee, In Joo Shin, Sung Woo Lee, Hyeong Cheol Kim, Byung Joon Choi
  Journal of Korean Powder Metallurgy Institute.2014; 21(5): 355.     CrossRef

In order to fabricate the porous Al₂O₃ with dispersion of nano-sized Cu particles, freeze-drying of camphene/ Al₂O₃ slurry and solution chemistry process using Cu-nitrate are introduced. Camphene slurries with 10 vol% Al₂O₃ was frozen at -25°C. Pores were generated by sublimation of the camphene during drying in air. The sintered samples at 1400 and 1500°C showed the same size of large pores which were aligned parallel to the sublimable vehicles growth direction. However, the size of fine pores in the internal walls of large pores decreased with increase in sintering temperature. It was shown that Cu particles with the size of 100 nm were homogeneously dispersed on the surfaces of the large pores. Antibacterial test using fungus revealed that the porous Al₂O₃/1 vol% Cu composite showed antifungal property due to the dispersion of Cu particles. The results are suggested that the porous composites with required pore characteristics and functional property can be fabricated by freeze-drying process and addition of functional nano particles by chemical method.

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• Collection of Industrial Oil Using Nanoparticles and Porous Powders of Silica
  Y.-S. Cho, J.-W. Moon
  Archives of Metallurgy and Materials.2017; 62(2): 1371.     CrossRef
• Fabrication and Mechanical Properties of STS316L Porous Metal for Vacuum Injection Mold
  Se Hoon Kim, Sang Min Kim, Sang Ho Noh, Jin Pyeong Kim, Jae Hyuck Shin, Si-Young Sung, Jin Kwang Jin, Taean Kim
  Journal of Korean Powder Metallurgy Institute.2015; 22(3): 197.     CrossRef