Papers by Author: Myeong Sang Ahn

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: Fiber-reinforced plastics consist of fibers of high strength and modulus embedded in, or bonded to a matrix with distinct interfaces between them. Because fiber configuration plays a key role in determining mechanical strength of fiber-reinforced plastic rods, especially bending strength of fiber-reinforced plastic rods was measured and simulated numerically in variation with winding angles. Also, stress distribution in fiber-reinforced plastic rods was simulated numerically under the condition of constant bending load to fiber-reinforced plastic rods. The measured bending strength of fiber-reinforced plastic rods in variation with winding angles was different from that of simulated. The difference between measured and simulated results was due to the effect of shear stresses on the strength of fiber-reinforced plastic rods.

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: Two kinds of colloidal silica(CS)/silane sol solutions were prepared. Two sol solutions are involved with the kinds of silane such as methyltrimethoxysilane(MTMS) and
-Glycidoxypropyl trimethoxysilane(ETMS) using LS CS. MTMS was added to two sol solutions. Whether ETMS was added or not, two kinds of sol solutions were synthesized. Using two kinds of sol solutions, sol-gel coating films were formed on glass substrates via dip-coating process. Here, seasoning effect of for enhancing properties of sol-gel coating layer on glass was investigated while such sol-gel solutions were left for 7days. Also, their properties such as surface free energy, roughness, thermal property, potential hardness and elastic portion were characterized in order to understand the effect of addition of ETMS. In this case of LS/MTMS sol, the coating film had low surface free energy and more enhanced flat surface than that of the case of LS/MTMS/ETMS sol. ETMS forms hydrophilic hydroxyl group in sol solution, then surface free energy of LS/MTMS/ETMS coating film increased. In the beginning of reaction sol solution seemed to be unstable, but 4days later their coating film properties such as surface free energy and roughness enhanced. The elastic portion of coating films obtained from LS/MTMS/ETMS sol increased with addition of ETMS, but thermal stability decreased.

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.