• Journal of Powder Materials
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• v.28 no.1
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• pp.7-12
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• 2021

The change in the open porosity of bulk graphite as a function of the uniaxial molding pressure during manufacturing is studied using artificial graphite powder. Subsequently, the graphite is impregnated to determine the effect of the open porosity on the impregnation efficiency and to improve the density of the final bulk graphite. Bulk graphite is manufactured with different uniaxial molding pressures after mixing graphite powder, which is the by-product of processing the final graphite products and phenolic resin. The bulk density and open porosity are measured using the Archimedes method. The bulk density and open porosity of bulk graphite increase as the molding pressure increases. The open porosity of molded bulk graphite is 25.35% at 30 MPa and 29.84% at 300 MPa. It is confirmed that the impregnation efficiency increases when the impregnation process is performed on a specimen with large open porosity. In this study, the bulk density of bulk graphite molded at 300 MPa is 11.06% higher than that before impregnation, which is the highest reported increase. Therefore, it is expected that the higher the uniaxial pressure, the higher the density of bulk graphite.

• Carbon letters
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• v.15 no.2
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• pp.142-145
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• 2014

Isotropic synthetic graphite scrap and phenolic resin were mixed, and the mixed powder was formed at 300 MPa to produce a green body. New bulk graphite was produced by carbonizing the green body at $700^{\circ}C$, and the bulk graphite thus produced was impregnated with resin and re-carbonized at $700^{\circ}C$. The bulk density of the bulk graphite was $1.29g/cm^3$, and the porosity of the open pores was 29.8%. After one impregnation, the density increased to $1.44g/cm^3$ while the porosity decreased to 25.2%. Differences in the pore distribution before and after impregnation were easily confirmed by observing the microstructure. In addition, by using an X-ray diffractometer, the degrees-of-alignment (Da) were obtained for one side perpendicular to the direction of compression molding of the bulk graphite (the "top-face"), and one side parallel to the direction of compression molding (the "side-face"). The anisotropy ratio calculated from the Da-values obtained was 1.13, which indicates comparatively good isotropy.

• Journal of the Korean institute of surface engineering
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• v.54 no.3
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• pp.144-151
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• 2021

In the present work, planar-type ZnO powder of [0001] plane with a high aspect ratio range of 20:1 to 50:1 was synthesized. Ag or CuO could be coated on the planar-type ZnO powder by wet methods such as centrifugation or ball milling. During the coating, the average size of the powder was slightly increased while maintaining the shape and XRD pattern of ZnO. When Ag or CuO was coated, the absolute value of the zeta potential, as well as the concentration of oxygen vacancy, was increased. Ag or CuO coated planar-type ZnO power exhibited excellent antibacterial performance, which seems to be related to their high electrostatic attraction force. They could be made into a masterbatch by mixing with ABS resin, and their applicability to antibacterial substances was confirmed by manufacturing the caps of a keyboard.

• Journal of the Korean Society of Safety
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• v.23 no.5
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• pp.43-48
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• 2008

The magnetic polishing is the useful method to finish some machinery fabrications by using magnetic power. This method is one of the precision polishing techniques and has an aim for clean technology in the transportation of the pure gas in the clean pipes. The magnetic abrasive polishing method is not so common in the field of machine that it is not known to widely. There are only few researchers in this field because of non-effectiveness of magnetic abrasive. Therefore, in this paper deals with development of the magnetic abrasive using Ba-Ferrite. In this development, abrasive grain GC and CBN has been made by using the resin bond fabricated at low temperature. And magnetic abrasive powder was fabricated from the Ba-Ferrite which was crushed into 200 mesh. The XRD analysis result shows that only GC, CBN and Ba-Ferrite crystal peaks were detected, explaining that resin bond was not any more to contribute chemical reaction. From SEM analysis, we found that GC, CBN abrasive and Ba-Ferrite were strongly bonding with each other.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.35 no.6
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• pp.610-615
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• 2022

BaTiO₃ is one of the ferroelectric materials with excellent dielectric properties such as high dielectric constant, low dielectric loss, and is widely used for the manufacturing of capacitors, piezoelectric converters, microsensors, and ferroelectric memories. Inkjet printing is a technology which uses digital and contactless methods which significantly improves flexibility associated with material and structural design, reducing manufacturing costs. Therefore, the top and bottom electrodes, BaTiO₃ ink, and photocurable resin were all printed by an inkjet to produce a BaTiO₃ capacitor. The properties of the printed thin film were analyzed. It was confirmed that the photocurable resin ink was well-infiltrated between the BaTiO₃ powder particles printed by inkjet. The dielectric properties of the capacitor such as dielectric constant which varies in accordance with frequency, polarization and tunability that changes with voltage, were measured.

• Journal of the Speleological Society of Korea
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• no.79
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• pp.77-81
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• 2007

In this paper deals with behavior of the magnetic abrasive using Sr-Ferrite on polishing charateristiccs in a internal finishing of staninless steel pipe a tying magnetic abrasive polishing. The magnetic polishing is the useful method to finish some machinery fabrications by using magnetic power. This method is one of the precision techniques and has in aim for clean technology in the transportation of the pure gas in the clean pipes. The magnetic abrasive polishing method is not so common in the field of machine that it is not known to widely. There are rarely researcher in this field because of non-effectiveness of magnetic abrasive. Therefore, in this paper we deals with the development of the magnetic abrasive with the use of Sr-Ferrite. In this development, abrasive grain SiC has been made by using the resin bond fabricated at low temperature. And magnetic abrasive powder was fabricated from the Sr-Ferrite which was crushed into 200 mesh. The XRD analysis result shows that only SiC abrasive and Sr-Ferrite crystal peaks were detected, explaining that resin bond was not any more to contribute chemical reaction. From MACRO analysis, we found that SiC abrasive and Sr-Ferrite were strongly bonding with each other.

• Journal of Ceramic Processing Research
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• v.20 no.4
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• pp.411-417
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• 2019

Graphene doped zinc oxide nanoparticles (G-ZnO) were prepared using modified hummer's technique together with the ultrasonic method and characterized by field emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), fourier-transform infrared spectroscopy (FTIR) and high-resolution transmission electron microscopy (HRTEM). Different samples of epoxy resin nanocomposites reinforced with G-ZnO nanoparticles were prepared and were marked as F1 (without adding nanoparticles), F2 (1% w/w G-ZnO), and F3 (2% w/w G-ZnO) in combination of ≈ 56:18:18:8w/w% with epoxy resin/hardener, ammonium polyphosphate, boric acid, and Chitosan. The peak heat release rate (PHRR) of the epoxy nanocomposites was observed to decrease dramatically with the increasing G-ZnO nanoparticles. However, the LOI values increased significantly with the increase in wt % of G-ZnO nanoparticles. From the UL-94V data, it was confirmed that the F2 and F3 samples passed the flame test and were rated as V-0. The results obtained in the present work clearly revealed that the synthesized samples can be used as efficient materials in fire-retardant coating technology.

• Journal of the Korean Ceramic Society
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• v.56 no.4
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• pp.360-364
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• 2019

PZT suspensions for photo-curable 3D printing were fabricated and their characteristics were evaluated. After mixing the PZT, photopolymer, photo-initiator, and dispersant for 10 min by using a high-shear mixer, the viscosity characteristics were investigated based on the powder content. To determine an appropriate dispersant content, the dispersant was mixed at 1, 3, and 5 wt% of the powder and a precipitation test was conducted for two hours. Consequently, it was confirmed that the dispersibility was excellent at 3 wt%. Through thermogravimetric analysis, it was confirmed that weight reduction occurred in the photopolymer between 120? and 500?, thereby providing a debinding heat treatment profile. The fabricated suspensions were cured using UV light, and the polymer was removed through debinding. Subsequently, the density and surface characteristics were analyzed by using the Archimedes method and field-emission scanning electron microscopy. Consequently, compared with the theoretical density, an excellent characteristic of 97% was shown at a powder content of 87 wt%. Through X-ray diffraction analysis, it was confirmed that the crystallizability improved as the solid content increased. At the mixing ratio of 87 wt% powder and 13 wt% photo-curable resin, the viscosity was 3,100 cps, confirming an appropriate viscosity characteristic as a stereolithography suspension for 3D printing.

• Journal of Adhesion and Interface
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• v.2 no.1
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• pp.1-8
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• 2001

In this study, wasted stone powders (WSP) obtained from sludge and Wasted Tire Chips (WTC) as fillers have been used to formulate polymer hybrid composites based on Unsaturated Polyester (UPE) resin. To further enhance not only the interfacial bond between the inorganic filler and the polymer matrix, but also the filler dispersion by wetting the particulate surfaces to uniformly spread the resin during the mixing, silane coupling agent[${\gamma}$-methacryloxy propyl trimethoxy silane (${\gamma}$-MPS)] was used. The influences of organic recycled fillers contents and the concentrations of coupling agent in polymer hybrid composite formulations have been investigated from a mechanical and microstructural point o view through Mercury Porosimeter and SEM.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.2
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• pp.131-138
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• 2014

Highly conductive bipolar plate for polymer electrolyte membrane fuel cell (PEMFC) was prepared using phenol novolac-type epoxy/graphite powder (GP)/carbon fiber filament (CFF) composite, and a rubber-modified epoxy resin was introduced in order to give elasticity to the bipolar plate graphite fiber (GF) was incorporated in order to improve electrical conductivity. To find out the cure condition of the mixture of novolac-type and rubber-modified epoxies, differential scanning calorimetry (DSC) was carried out and their data were introduced to Kissinger equation. And tensile and flexural tests were carried out using universal testing machine (UTM) and the surface morphology of the fractured specimen and the interfacial bonding between epoxy matrix and CFF or GF were observed by a scanning electron microscopy (SEM).