Papers by Author: Dong Pil Kang

Abstract: Three kinds of colloidal silica (CS)/silane sol were prepared. Sols are involved with the kinds of silane with different organic group. Methyltrimethoxysilane (MTMS) has the three methoxy groups and a methyl group. γ-Glycidoxypropyltrimethoxysilane (GTMS) has the three methoxy groups and a bulky epoxy group. GTMS was added to two sols with different amount. When sol reacted for 10 days, viscosity increased dramatically. Trasnmittance of sols reacted for 10 days decreased rapidly, too. It indicated the stability of sol degraded. Sol-gel coating films were formed on glass substrate using spin coating procedure with reaction time for 10 days. Coating films were flat and transparent without cracking. CS/MTMS coating films showed high contact angle. When large amount of GTMS was added, contact angle decreased due to its epoxy group. No thermal degradation of CS/MTMS coating film occurred up to 600 oC. CS/MTMS/GTMS coating film degraded at 400 oC for decomposition of epoxy group which has long organic chain which easily degraded by the thermal shock.

Abstract: Several sol solutions were synthesized by using two kinds of nanosized boehmite and methyltrimethoxysilane (MTMS) according to the changing amount of MTMS at different reaction time. To understand their physical and chemical properties, sol-gel coating films were fabricated on glass. The sol solutions were prepared from boehmite of spherical shape (boehmite1)/MTMS and mixed boehmites of spherical and fibrous shapes (boehmite2)/MTMS. The soluble stability of boehmite1/MTMS was observed in the sol solution left for 24 h, however, that of boehmite2/MTMS was observed in the sol solution left for 48 h. The contact angle of sol-gel coating films from boehmite/MTMS increased with MTMS contents and reaction time. The films formed a flat surface with the increasing MTMS contents and decreasing reaction time. The electrical resistivity of films increased with MTMS contents. The thermal degradation of films occurred at approximately 400 oC.

Abstract: Organic/inorganic hybrid materials synthesized from acrylic resin and silane-terminated colloidal silica(CS). The silane-terminated CS was prepared in variation with the kind of silane to CS. The CS treated with methyltrimethoxysilane(MTMS) and then treated with vinyl trimethoxysilane(VTMS), 3-glycidoxypropyltrimethoxysilane(ATMS) or 3-methacyloxypropyl trimethoxysialne(ETMS) by sol-gel method, respectively. The variation of silane-terminated CS and acrylic resin were hybridized by thermal-polymerization. Thin films of organic/inorganic hybrid materials were prepared using spin coater on the glass and aluminum sheets. Their contact angle, surface electric resistivity and thermal resistance improved with the amount of silaneterminated CS. The contact angle and surface electric resistivity of hybrid thin film with VTMS were enhanced. The surface of hybrid thin film with VTMS was homogeneous through FE-SEM.

Abstract: This paper presents the effects of ceramic fillers on light reflectance and arc resistance of PTFE(polytetrafluoroethylene) for nozzle of circuit breaker. In arc environment of a circuit breaker, radiation generated from arcing is considered to play a key role in transport mechanism of arc energy to the wall. Adding some ceramic fillers into PTFE material is expected to be efficient for improving the endurance against arc radiation. In this experiment, three kinds of ceramic fillers for achieving good endurance in the high temperature were used. Light reflectance and arc resistance of PTFE composites were investigated. The arc resistance of PTFE composites increased with the amount of ceramic fillers. The light reflectance of PTFE composites filled with ceramic fillers increased in the long wavelength region and decreased largely in the short wavelength region in comparison with that of pure PTFE.

Abstract: Three kinds of colloidal silica (CS)/silane sol solutions were synthesized in variation with parameters such as different acidity and reaction time. Sol solutions were prepared from HSA CS/ methyltrimethoxysilane (MTMS), LS CS/MTMS and LS CS/MTMS/γ -Glycidoxypropyltri methoxysilane (ES) solutions. In order to understand their physical and chemical properties, sol-gel coating films were fabricated on glass. Coating films on glass, obtained from LS/MTMS sol, had high contact angle, also, much enhanced flat surface in the case of LS/MTMS sol was observed in comparison with HSA/ MTMS sol. From all sol-gel solutions, seasoning effect of for enhancing properties of sol-gel coating layer on glass was observed while such sol-gel solutions were left for 7days. In initial stage of sol-gel reaction, all most of sol solutions used in this work seem to be unstable, formation of coating films was a little hazy and rough. However, improved coating films as observed in 4days later. LS/MTMS/ES sol solutions were synthesized with ES, adding to LS/MTMS sol. Contact angle of LS/MTMS/ES sol-gel coating films decreased, since ES played a role in forming hydrophilic hydroxyl sol. The elastic portion of coating films prepared from LS/MTMS/ES sol increased with addition of ES, but thermal stability decreased a little.

Abstract: This paper presents the effects of fillers on electrical properties of PTFE composites for nozzle of circuit breaker. PTFE has been used widely as a material for circuit breaker nozzle. Adding some filler into PTFE material is expected to be efficient for improving the endurance against arc radiation. In this experiment, effects of fillers on electrical properties such as dielectric constant, dissipation factor, electrical resistivity, dielectric strength and corona resistance of PTFE composites were investigated.

Abstract: Nanocrystalline nickel powders were prepared by chemical reduction of nickel chloride hydrate with different surfactant at moderate temperature in a pressurized vessel. Nickel nanosheets were generated successfully through reducing the nickel ion complexes, formed by sodium tartrate, at alkaline condition by hydrazine hydrate. The nanosheets and nanowires were characterized by the means of an X-ray diffractomer (XRD), a field emission scanning electron microscopy (FESEM), an energy dispersive X-ray spectrometer (EDS) and a high sensitive magnetometer (HSM).

Abstract: Colloidal silica/silane sol solutions were prepared in variation with the ratio of silane to colloidal silica. Such sol solutions were synthesized from colloidal silica/tetramethoxysilane (TMOS)/methyltrimethoxysilane(MTMS). Sol solutions were prepared by sol-gel reaction through two step reactions. To understand their physical and chemical properties, dip coating of sol solutions was performed on the glass substrates. Contact angle and thickness of coating films increased with increasing the amount of MTMS. The surface free energy of coating films decreased with increasing amount of MTMS. Coating films were stable until 550°C. Thermal degradation temperature of coating films decreased with increasing amount of MTMS. Plastic hardness decreased with increasing amount of MTMS. Elastic portion increased with increasing amount of MTMS.

Abstract: Organic-inorganic hybrid blends were prepared in variation with the ratio of sol solution to urethaneacrylic resin. Such sol solutions were synthesized from colloidal silica (CS)/ methyltrimethoxysilane(MTMS)/vinyltrimethoxysilane(VTMS) by sol-gel reaction through two step reactions. Thin films of organic-inorganic hybrid blends were prepared using spin coater on the glass and aluminum sheets. In order to understand surface properties of thin films, contact angle and roughness were measured. Surface contact angle and roughness of thin films increased as the amount of sol solution increased. Thermal dissociation temperature of thin films was observed using TGA. Thin films were stable until 270 oC. Thermal dissociation temperature of thin films improved with increasing sol solution. In order to observe insulation property of thin films, electrical resistance measurements were performed. Surface and volume resistance of thin films increased as the amount of sol solution increased.