The effects of drying temperature on the microstructure of porous W fabricated by the freeze-casting process of tert-butyl alcohol slurry with WO₃ powder was investigated. Green bodies were hydrogen-reduced at 800°C for 1 h and sintered at 1000°C for 6 h. X-ray diffraction analysis revealed that WO₃ powders were completely converted to W without any reaction phases by hydrogen reduction. The sintered body showed pores aligned in the direction of tertbutyl alcohol growth, and the porosity and pore size decreased as the amount of WO₃ increased from 5 to 10v ol%. As the drying temperature of the frozen body increased from -25°C to -10°C, the pore size and thickness of the struts increased. The change in microstructural characteristics based on the amount of powder added and the drying temperature was explained by the growth behavior of the freezing agent and the degree of rearrangement of the solid powder during the solidification of the slurry.

In this study, porous Mo-5 wt% Cu with unidirectionally aligned pores is prepared by freeze drying of camphene slurry with MoO₃-CuO powders. Unidirectional freezing of camphene slurry with dispersion stability is conducted at -25°C, and pores in the frozen specimens are generated by sublimation of the camphene crystals. The green bodies are hydrogen-reduced at 750°C and sintered at 1000°C for 1 h. X-ray diffraction analysis reveals that MoO₃-CuO composite powders are completely converted to a Mo-and-Cu phase without any reaction phases by hydrogen reduction. The sintered bodies with the Mo-Cu phase show large and aligned parallel pores to the camphene growth direction as well as small pores in the internal walls of large pores. The pore size and porosity decrease with increasing composite powder content from 5 to 10 vol%. The change of pore characteristics is 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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  Korean Journal of Materials Research.2020; 30(12): 672.     CrossRef
• Effect of α-lath size on the mechanical properties of Ti–6Al–4V using core time hydrogen heat treatment
  Gye-Hoon Cho, Jung-Min Oh, Hanjung Kwon, Jae-Won Lim
  Materials Science and Technology.2020; 36(7): 858.     CrossRef

The improvement of dispersion stability for the primary polishing slurry in a CMP process is achieved to prevent defects produced by agglomeration of the slurry. The dispersion properties are analyzed according to the physical characteristics of each silica sol sample. Further, the difference in the dispersion stability is confirmed as the surfactant content. The dispersibility results measured by Zeta potential suggest that the dispersion properties depend on the content and size of the abrasive in the primary polishing slurry. Moreover, the optimum ratio for high dispersion stability is confirmed as the addition content of the surfactant. Based on the aforementioned results, the long-term stability of each slurry is analyzed. Turbiscan analysis demonstrates that the agglomeration occurs depending on the increasing amount of surfactant. As a result, we demonstrate that the increased particle size and the decreased content of silica improve the dispersion stability and long-term stability.

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• Surface Defect Properties of Prime, Test-Grade Silicon Wafers
  Seung-Hwan Oh, Hyeonmin Yim, Donghee Lee, Dong Hyeok Seo, Won Jin Kim, Ryun Na Kim, Woo-Byoung Kim
  Korean Journal of Materials Research.2022; 32(9): 396.     CrossRef

Metallic porous materials have many interesting combinations of physical and geometrical properties with very low specific weight or high gas permeability. In this study, highly porous Cu foam is successfully fabricated by a slurry coating process. The Cu foam is fabricated specifically by changing the coating amount and the type of polyurethane foam used as a template. The processing parameters and pore characteristics are observed to identify the key parameters of the slurry coating process and the optimized morphological properties of the Cu foam. The pore characteristics of Cu foam are investigated by scanning electron micrographs and micro-CT analyzer, and air permeability of the Cu foam is measured by capillary flow porometer. We confirmed that the characteristics of Cu foam can be easily controlled in the slurry coating process by changing the microstructure, porosity, pore size, strut thickness, and the cell size. It can be considered that the fabricated Cu foams show tremendous promise for industrial application.

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• Preparation and comparative evolution of mechanical behavior of Fe and Fe2O3 foams and their polymer composites
  Vemoori Raju, Roy Johnson, Asit Kumar Khanra
  Journal of Alloys and Compounds.2018; 750: 71.     CrossRef

Metal foams have a cellular structure consisting of a solid metal containing a large volume fraction of pores. In particular, open, penetrating pores are necessary for industrial applications such as in high temperature filters and as a support for catalysts. In this study, Fe foam with above 90% porosity and 2 millimeter pore size was successfully fabricated by a slurry coating process and the pore properties were characterized. The Fe and Fe₂O₃ powder mixing ratios were controlled to produce Fe foams with different pore size and porosity. First, the slurry was prepared by uniform mixing with powders, distilled water and polyvinyl alcohol(PVA). After slurry coating on the polyurethane( PU) foam, the sample was dried at 80°C. The PVA and PU foams were then removed by heating at 700°C for 3 hours. The debinded samples were subsequently sintered at 1250°C with a holding time of 3 hours under hydrogen atmosphere. The three dimensional geometries of the obtained Fe foams with an open cell structure were investigated using X-ray micro CT(computed tomography) as well as the pore morphology, size and phase. The coated amount of slurry on the PU foam were increased with Fe₂O₃ mixing powder ratio but the shrinkage and porosity of Fe foams were decreased with Fe₂O₃ mixing powder ratio.

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• 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

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