• Journal of the Korean Ceramic Society
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• v.34 no.4
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• pp.380-386
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• 1997

The tribological properties of ceramics are very important in the application to engineering ceramic parts such as seal rings, pump parts, thread guides, and so on. In this study, the effects of graphite addition on the mechanical and tribological properties of alumina/graphite composites were investigated. The composites were prepared by the adding of graphite powder to the mixture of Al2O3, talc and calcium carbonate. Bending strength, water absorption, friction coefficient, the amount of worn out material at a certain time, and maximum surface roughness(Rmax) of the prepared composites were measured. Crystalline phases and microstructure were examined with XRD and SEM. The melt of Al2O3-CaO-MgO-SiO2 system was shown over 10 vol% graphite composition. As the amount of the graphite is increased, needle like crystals of mullite were formed and grown. We obtained the good properties of friction coefficients and wear resistance at the powder composition containing 15 vol% of graphite.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.9
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• pp.1323-1329
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• 2015

The WO₃/Ag/WO₃ transparent thin films are fabricated by the RF magnetron sputtering. This has a transmittance of front and rear about 90% in the visible light range and surface resistance of 6.41Ω/□. In this paper, we analyzed the surface characteristics caused by the working pressure and O₂ plasma surface treatment to apply a transparent electrode that was prepared to the laminated structure with other materials. The working pressure was changed in the WO₃ film to 10mTorr, 7mTorr, and 5mTorr, it showed a lower than roughness of conventional ITO. In addition, by 55.5774 J/m² at 5mTorr, it shows the hydrophobic property with lower process pressure. O₂ plasma surface treatment was changed at the condisions of the RF power to 150W, 100W, and 50W and the process time to 240s, 180s, 120s, and 60s. The surface roughness are the maximum roughness(Rmax) 6.437nm and the average roughness(Rq) 0.827nm at RF power 150W, and the maximum roughness (Rmax) 6.880nm and the average roughness (Rq) 0.839nm at process time 240sec. It showed a lower value than the surface treatment. also about working pressure and process time is increased, it showed the hydrophobic.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.827-831
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• 1997

Conductive veramic matrix composite(CMC) workpiece of TiC 33%/Al /sab 2/O /sab 3/ 66% Y /sab 2/ O /sab 3/ was machined by die sinking electrical discharge machining(EDM) according to different pulse duration and suty factor for reverse polarity of electrode. Material removal rate(MRR) was examined by process under various operating conditions. The surface morphology was evaluated by surface roughness values and scanning electron microscopy(SEM) research. The more MRR was obtained according to increase pulse duration and duty factor. Also the maximum surface roughness(Rmax) of EDMed surface was slightly changed with increased pulse duration and duty factor. The SEM photographs of EDMed surface showed wide recast wide recast distribution region of melting materials in purse duration 0.130(ms) than 0.048(ms).

• Journal of the Korean Society for Precision Engineering
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• v.9 no.4
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• pp.72-77
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• 1992

In this study, using in-process tool failure detecting system by AE method in turning machining, we measured AE signal from the tool, and the surface roughness of workpiece and then compared it with tool wear. As a result, we found that tool failure can be predicted by means of surface roughness of the workpiece and it can be predicted more precisely by the arithmetical average roughness (Ra) than by the maximum height of irregularities (Rmax) of the workpiece. Also, we found that we could judge whether it was sudden failure or the wear by means of the shape of AE signal and the range distri- bution of power spectrum frequency when tool danage was happened.

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.479-484
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• 1996

The tribological properties of ceramics are very important in the application to engineering ceramic parts such as mechanical seal slurry valve disc and so on. In this study the effect of graphite addition on the mechanical and tribological properties of RBSC/graphite composites were investigated. The composites were prepared by adding graphite powder to the mixture of SiC powder metallic siliconcarbon black and alumina. Bending strength water absorption friction coefficient the amount of worn out material at a certain time and maximum surface roughness(Rmax) of the prepared composites were measured and crystalline phases were examined with XRD. The composite containing 5 vol% graphite powder showed improved bending strength due to high green density and decreased friction coefficient and wear resistance. The friction coefficient and the wear resistance of the composite were increased by adding graphite powder up to 10 vol% They decreased however as increasing the amount of graphite powder more that 10vol% There was no linear relationship between the tribological properties and bending strength of the composites.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.1
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• pp.31-42
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• 1997

This study was performed to investigate the surface roughness of the Cerec Vita Mark II polished by various polishing techniques, compare with that of the Vintage enamel porcelain glazed by high temperature glazing technique. All of the Cerec specimen were finished with sequential use of high speed diamond burs(grit 45, 30 and $15{\mu}m$). The groups were divided into 5 groups : Group I : Cerec Vita Mark II block specimens polished with Sof-lex discs. Group II : Cerce Vita Mark II block specimens polished with Two Striper MPS. Group III : Cerce Vita Mark II block specimens polished with Enhance. Group IV : Cerce Vita Mark II block specimens polished with Porcelain laminate polishing FG kit. Group V : Vintage enamel porcelain glazed by high temperature glazing Technique. Each group was consisted of 10 specimens. The surfaces produced were examined quantitatively using a laser specular reflectance machine(Perthen RM600-s, Feinpruf Perthen GmbH., Germany) and qualitatively under SEM(JSM-5400, JEOL, Japan). The Results were as follows : 1. The arithmetic mean roughness value(Ra) in groups 1, 2, 3 and 4 was higher than that of group5. There was statistically significant difference(P<0.05). 2. The arithmetic mean roughness value(Ra) decreased in the following orders : group 1, group 2, group 4, group 3 and there was no statistically significant difference between group 1 and group 2, group 3, and group 4. There was statistically significant difference among group 1, 2, and group 3, 4 and group 5(P<0.05). 3. The maximum individual peak-to-valley-height(Rmax) decreased in the following orders : group 2, group 1, group 4, group 3, group 5 and there was no statistically significant difference between group 1 and 2, group 1 and group 4, group 3 and group 5. There was statistically significant difference among group 1, 2, and group 1, 4 and group 3, 5(P<0.05). 4. The treated surfaces of group 5 had smoother surface than that of groups 1, 2, 3, 4 with SEM.