Papers by Author: Yoon Joo Lee

Abstract: Antimony doped tin oxide (ATO) is a typical p-type semiconductor and widely used due to its good properties such as electrical conductivity and transparency in visible range, while reflects infrared light. These features allow ATO to be used as transparent electrodes, heat mirrors and energy storage device, display panel. However, the use of tin oxide ceramics is limited by the low densification during sintering due to the dominance of non-densification mechanism such as surface diffusion or evaporation condensation. So, sintering agents such as Cobalt (II) oxide (CoO), zinc oxide (ZnO), manganese dioxide (MnO₂) used to improve the densification of SnO₂ by forming lattice solid solution or liquid phase. In this study, we studied the effect of the sintering agents. The antimony-doped tin oxide nanoparticles were synthesized by a sol-gel method. After sintering ATO with sintering agents such as MnO₂ and CoO, sintered body characteristics were investigated by XRD, SEM, thermal conductivity, resistivity and interesting characteristic.

Abstract: The formation of organic-inorganic hybrid composite with ceramic platelets and polymeric compound can have the higher strength and higher elasticity than metal, which is a nanocomposite with high strength and light weight. Ceramic platelet such as Al₂O₃ has been used to form organic-inorganic composite material using PMMA as an organic polymer. Bending strength and density of the composites prepared by infiltration and post-warm pressing were measured. FE-SEM and TG analysis were carried out to determine the microstructure of the organic-inorganic composite materials. Bending strengths and densities of the composites prepared by Al₂O₃ ceramic plate and PMMA after post-warm pressing were ~70MPa and ranged from 2.4 to 2.6, respectively.

Abstract: β-SiC powder was synthesized directly from silicon sludge with carbon black. Large amount of silicon sludge is generated from Solar Cell industry. In an environmental and economic point of view, recycling silicon sludge is important. In this study, two kinds of silicon sludge were characterized using XRD, SEM/EDS and FT-IR. SiC powder was synthesized by the reaction of ball-milled silicon powder for 3h in vacuum at different temperatures (1350 and 1600). Physical properties of the heat treated SiC have been characterized using a SEM, XRD, Particle size analyzer and FT-IR Spectroscopy.

Abstract: β-SiC powder was synthesized using silicon sludge from photovoltaic silicon-wafer production by varying heat treatment temperature and carbon contents. The synthesized β-SiC powder and silicon sludge was analyzed by XRD, SEM, FT-IR and Particle size analysis. It is known that the conversion of SiC from the mixture of Silicon and Carbon is mainly affected by the mole ratio of C/Si and heat treatment temperature. In this study, the influence of reaction temperature and carbon contents on the synthesis of β-SiC from silicon sludge was examined.

Abstract: Polyphenylcarbosilane (PPCS) was synthesized from thermal rearrangement of the polymethylphenylsilane around 350 ~ 430°C. Characterization of synthesized PPCS was performed with FT-IR spectroscopy analysis. From FT-IR data, the band at 1035cm^-1 is very strong and assigned to CH₂ bending vibration in Si-CH₂-Si group, indicating the formation of the PPCS. Ceramic thin film was fabricated onto stainless substrate by dip coating using a 20wt% PPCS in toluene. Heat treatment of the samples was performed at various temperatures (600°C and 800°C) under nitrogen atmospheres. The prepared PPCS samples and the coating layers on SUS316 after heat treatment were analyzed using FT-IR and XPS, respectively.

Abstract: The effects of the pair-minerializer (CaSO4,-CaF2) on the burnability of clinker and the formation of mineral are investigated. As experimental results, the addition of F as pair-mineralizer, the burnability of clinker was improved. Especially, the addition of F and SO3 components simultaneously as pair-mineralizer, total amount of free lime in clinker is rapidly decreased compared with the value which mineralizer was added separately. In case of adding K2O only to the raw mixes, the amount of free lime is increased. However, if alkali (K2O) and pair-minerializer (CaSO4,-CaF2) were added simultaneously, the produced amount of clinker mineral is increased due to the formation of stable calcium langbeinite by the combination of alkali (K2O) and sulfate