• Journal of Powder Materials
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• v.27 no.4
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• pp.325-332
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• 2020

In this study, the effects of kaolin addition on the properties of reticulated porous diatomite-kaolin composites are investigated. A reticulated porous diatomite-kaolin composite is prepared using the replica template method. The microstructure and pore characteristics of the reticulated porous diatomite-kaolin composites are analyzed by controlling the PPI value (45, 60, and 80 PPI) of the polyurethane foam (which are used as the polymer template), the ball-milling time (8 and 24 h), and the amount of kaolin (0-50 wt. %). The average pore size decreases as the amount of kaolin increases in the reticulated porous diatomite-kaolin composite. As the amount of kaolin increases, it can be determined that the amount of inter-connected pore channels is reduced because the plate-shaped kaolin particles connect the gaps between irregular diatomite particles. Consequently, a higher kaolin percentage affects the overall mechanical properties by improving the pore channel connectivity. The effect of kaolin addition on the basic properties of the reticulated porous diatomite-kaolin composite is further discussed with characterization data such as pore size distribution, scanning electron microscopy images, and compressive strength.

• Journal of Powder Materials
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• v.4 no.2
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• pp.100-105
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• 1997

In this study the changes of the hardness and microstructures during aging at 120$^{\cire}C$ of an RS-P/M Al-5.6wt%Zn-2.0wt%Mg-1.3wt%Zr-1.0wt%Mn-0.25wt%Cu alloy were studied using a transmission electron microscopy. The hardness increased rapidly at early stage of aging and reached the maximun when the specimen was aged for 24 hr. The many irregular-shaped $Al_4Mn$ and rod-shaped $Al_6Mn$ dispersoids with 0.1-0.4 $\mu$m in length were observed in the as-extruded alloy. The dark particles with 2-3 nm in size were observed in aged specimen for 5hr and those are thought to be G.P.zones or precursor of $\eta'$ precipitates. In aged specimen for 24 hr, the $\eta'$ phases were distributed homogeneously within the matrix and the PFZ with 30-40 nm in width was observed along the grain boundary. With further aging, the width of PFZ increased and $\eta$ phases were also detected within the matrix.

• Journal of Powder Materials
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• v.1 no.1
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• pp.21-26
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• 1994

Aluminum was deposited on aluminum oxide powders using a fluidized bed reactor at atmospheric pressure. The aluminum oxide powders were irregular flakes with acute angles and the average particle size was 26 $\mu\textrm{m}$. The fluidized bed was formed by flowing argon gas at the velocity of 60 cm/sec. The optimal fluidization condition was obtained with the reactor designed to be tapered so that the fluid velocity decreases as the fluidizing gas goes up along the reactor. Aluminum was deposited by flowing TiBA(Triisobutylaluminum) evaporated at$250^{\circ}C$ through the fluidized bed reactor heated to 350~$450^{\circ}C$. The result from the analysis by XRD and EDAX confirmed the coating of aluminum and an SEM micrograph showed the conformality.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1107-1108
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• 2006

The coating of conductive polypyrrole (Ppy) on nonconductive ceramic substrates was performed by polymerization of pyrrole (Py) in an aqueous solution. The Ppy film was characterized by scanning electron microscopy and conductivity measurements. Electrophoretic deposition of bimodal alumina suspension prepared with a phosphate ester was performed using Ppy film as a cathode. Fabrication of alumina ceramics with irregular shapes or complicated patterns were also attempted by sintering the deposits together with the Ppy coated substrates in air.

• Journal of Powder Materials
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• v.22 no.2
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• pp.129-133
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• 2015

Porous W with controlled pore structure was fabricated by thermal decomposition and hydrogen reduction process of PMMA beads and $WO_3$ powder compacts. The PMMA sizes of 8 and $50{\mu}m$ were used as pore forming agent for fabricating the porous W. The $WO_3$ powder compacts with 20 and 70 vol% PMMA were prepared by uniaxial pressing and sintered for 2 h at $1200^{\circ}C$ in hydrogen atmosphere. TGA analysis revealed that the PMMA was decomposed at about $400^{\circ}C$ and $WO_3$ was reduced to metallic W at $800^{\circ}C$. Large pores in the sintered specimens were formed by thermal decomposition of spherical PMMA, and their size was increased with increase in PMMA size and the amount of PMMA addition. Also the pore shape was changed from spherical to irregular form with increasing PMMA contents due to the agglomeration of PMMA in the powder mixing process.

• Journal of Life Science
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• v.25 no.6
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• pp.615-623
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• 2015

This study investigated the effects of dissolved cement powder on Zacco koreanus by analyzing morphophysiological changes. The gills exposed to dissolved cement powder developed abnormal shapes in their secondary lamellae and increased numbers of mucous cells after long-term exposure. Additionally, clubbing, edema, and exfoliation of the epithelial cells were observed in the secondary lamellae. In the kidney tissue, the space in Bowman’s capsule was widened, and in the integument tissue the arrangement of the dermis was irregular due to the thinned epidermis. These results suggest that long-term exposure to cement powder can significantly affect morphological change, resulting death. The activities of antioxidant enzymes and LDH tended to increase commensurately with the duration of cement exposure. It was concluded that up-regulated proteins were the stress proteins involved in myofibrillar-protein production and down-regulated proteins were involved in glycolysis and energy metabolism after the integument’s exposure to cement. According to these results dissolved cement powder is a serious threat to the survival of fish because it causes morphological changes and weakens physiological activity in Z. koreanus tissues.

• Journal of Powder Materials
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• v.21 no.2
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• pp.97-101
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• 2014

The 304 stainless steel powders were prepared by high energy ball milling and subsequently sintered by spark plasma sintering, and the microstructural characteristics and micro-hardness were investigated. The initial size of the irregular shaped 304 stainless steel powders was approximately 42 ${\mu}m$. After high energy ball milling at 800 rpm for 5h, the powders became spherical with a size of approximately 2 ${\mu}m$, and without formation of reaction compounds. From TEM analysis, it was confirmed that the as-milled powders consisted of the aggregates of the nano-sized particles. As the sintering temperature increased from 1073K to 1573K, the relative density and micro-hardness of sintered sample increased. The sample sintered at 1573K showed the highest relative density of approximately 95% and a micro-hardness of 550 Hv.

• Journal of Korea Foundry Society
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• v.10 no.5
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• pp.435-443
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• 1990

By using the centrifugal atomization, which is one of the rapid solidification processes, Al-5,10wt%Pb alloys which are monotectic alloys were melted at 150K over two liquid phase line in the phase diagram. The melted alloy was poured on the rotating disk, being made into atomized powders, and then the solidified microstructure and morphology of the powder were investigated. This study converted the produced powders into strips by strained powder rolling. According to sintering temperature, the microstructure and hardness were investigated. The solidified structure of the powders were almost cellular dendritic structure. Pb particles ($2.0-3.0{\mu}m$) were fairl distributed in the Al matrix. Powder shapes were irregular. Rolling property and the compacting was good, respectively, because of increasing mechanical interlocking and surface area in the small size powders. With increasing temperature, the boundarys of powders were in porous form due to the diffusion. Pb particles which were surrounding the pores were inverse-segregated at the surface of the powders. With increasing of sintering temperature, the hardness of the powders and the strips decreased. In particular rolling-strip, the hardness abruptly decreased due to the release of work-hardening.

• Korean Journal of Materials Research
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• v.14 no.5
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• pp.358-362
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• 2004

$Si_3$$N_4$ ceramics have been identified as one of the promising structural ceramics. This study has been carried out to investigate of the synthetic behaviors of $Si_3$$N_4$ derived from domestic silica-stone by direct nitriding method. The silicon nitridation reaction has been studied in the temperature range of $1300～1550^{\circ}C$. Below the $1400^{\circ}C$, the nitriding rate was measured to be 16%. For the temperatures higher than the $1400^{\circ}C$, $\beta$-$Si_3$$N_4$ phase was formed mainly, and the nitriding rate showed above 98%. With the increasing of sample weight of silicon powder, the nitriding rate and $\beta$-$Si_3$$N_4$ phase increased at $1400^{\circ}C$ for 2 hours. The shape and particle size of$ Si_3$$N_4$ powder synthesized at $1400^{\circ}C$ for 2 hours showed the irregular angular-type and 10 $\mu\textrm{m}$, respectively.

• Journal of Powder Materials
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• v.21 no.2
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• pp.108-113
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• 2014

Flake-like $LiCoO_2$ nanopowders were fabricated using electrospinning. To investigate their formation mechanism, field-emssion scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were carried out. Among various parameters of electrospinning, we controlled the molar concentration of the precursor and the PVP polymer. When the molar concentration of lithium and cobalt was 0.45 M, the morphology of $LiCoO_2$ nanopowders was irregular and round. For 1.27 M molar concentration, the $LiCoO_2$ nanopowders formed with flake-like morphology. For the PVP polymer, the molar concentration was set to 0.011 mM, 0.026 mM, and 0.043 mM. Irregular $LiCoO_2$ nanopowders were formed at low concentration (0.011 mM), while flake-like $LiCoO_2$ were formed at high concentration (0.026 mM and 0.043 mM). Thus, optimized molar concentration of the precursor and the PVP polymer may be related to the successful formation of flake-like $LiCoO_2$ nanopowders. As a results, the synthesized $LiCoO_2$ nanopowder can be used as the electrode material of Li-ion batteries.