Yurian Kim

Effect of transmittance on luminescence properties of phosphor-in-glass for LED packaging

The transmittance of phosphor-in-glass (PIG) color converter material was studied as a factor affecting the luminescence properties of light emitting diode packaging; it is closely related to the residual pores of sintered glass. In this study, the correlation between porosity and optical properties of the glass and PIG plates was investigated. The transmittance, luminescence properties, and porosity were measured by UV-visible spectrometer, integrating sphere and scanning electron microscope, respectively. Transmittance of the sintered glass plate and the luminous efficacy of the PIG plate both increase with decreased porosity, while the light scattering coefficient decreases. Luminescence properties such as emission intensity and color coordinates are also influenced by transmittance of the PIG plate.

Measurement of hardness and friction properties of pencil leads for quantification of pencil hardness test

We have investigated the various properties of different types of pencil leads in order to quantify a pencil hardness test for reliability. The chemical composition and mechanical properties for different types of pencils (F, 2H, 4H, 6H and 8H) were measured using X-ray diffraction, nano-indentation and a tribometer. The values for nano-indentation hardness of the pencil leads are in the range of 0.3–0.8 GPa. A higher hardness grade in the pencil lead leads to a wider error range. The clay content of the lead seems to be proportional to the hardness of the pencil lead. Different crystalline phases in clays for each grade of pencil lead result in variations in the degree and distribution of the hardness. Consequently, the content of the crystalline phases in the clay affects deviations in the hardness.

Size Effect of CaCO3 Filler on the Mechanical Properties of SMC Composites

SMC composites consist of chopped glass fiber as a reinforcements, polyester and mineral fillers. Among them, filler is one of the important factors for improving mechanical and thermal properties of composites, but it has not drawn much attention for SMC composites. In this study, the size effect of calcium carbonate as mineral filler on mechanical properties of SMC composites was discussed using five different sizes of commercial calcium carbonates without chopped fiber reinforcement, to focus on the size effect itself. The SMC process was modified to be suitable for a laboratory scale composed of three steps. The mean sizes of the calcium carbonates were 3 – 20 μm, and the specific surface areas were calculated to be 1 – 5 m2/g by BET. Small size of calcium carbonate having high surface area up to 4 m2/g showed high thermal resistance, and showed higher strength comparing to the large fillers because it affected to form a dense packed microstructure.

Purification and particle size control of β-SiC powder using thermocycling process

Abstract Recently, SiC single crystal growth has been of interest for the development of an alternative semiconducting material. The aim of this study was to purify and grow β-SiC particles for use as a single crystal source. First, a β-SiC powder with a particle size of about 10 μm and a purity of 99·5% was prepared from a phenyl-containing silica sol. Then, three different of heat treatment process were applied to grow the β-SiC particles and evaluate the effects of heat-treatment time and temperature. After three thermocycling processes carried out from 1850 to 2000°C in 1 h, the β-SiC particles had diameters over 100 μm because of a vaporisation–recrystallisation process that accelerated the β-SiC particle growth. Moreover, the thermocycling process improved the purity of β-SiC by eliminating metallic impurities.

Fabrication of nanoporous silicon carbide fibres by thermal treatment

Abstract Nanoporous silicon carbide fibres were prepared by curing and heat treatment of melt spun polycarbosilane (PCS) fibres. During the curing process, green PCS fibres were thermally oxidised at the temperature between 180 and 220°C and time between 2 and 10 h for cross-linking among the molecule chains in the PCS and controlling the oxygen concentration and distribution. After thermal oxidation, fibres were heat-treated between 1200 and 1600°C for the conversion to SiC phase. About 15–20 wt-% of oxygen was analysed after heat treatment at 1200°C and it can be possible to pyrolyse without melting or deformation of fibre. At a temperature above 1400°C, the uniform distribution of nanopores was observed on the fibre surface, and the size of pores was increased with curing and heating condition. This type of nanoporous SiC fibre is expected to be a good candidate for high temperature catalyst or catalytic supports.

Microstructures and thermal conductivities of reaction sintered SiC ceramics

Abstract Reaction sintered SiC ceramics were prepared by the silicon melt infiltration method over temperatures of 1450−1550°C. The effects of the carbon and silicon contents of the starting materials as well as the sintering temperature and time on the thermal conductivities and microstructures of the ceramic materials were studied. The thermal conductivities and microstructures of the samples were characterised using thermal conductivity measurements, X-ray diffraction analysis, scanning electron microscopy, energy-dispersive X-ray spectroscopy and mercury injection porosimetry. The results showed that sintering temperature and time as well as the carbon and silicon contents of the green specimens are the main factors affecting the microstructure and porosity of reaction bonded SiC ceramics. Increasing the reaction temperature and time decreased the porosity of the ceramics. This was due to the infiltration of the silicon melt into the ceramic specimens. The thermal conductivity and porosity of the sample sintered at 1550°C for 3 h in an argon atmosphere were 102·5 W m K−1 and 0·3% respectively.

Bio-Inspired Synthesis of Al2O3/Polymer Composite

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.

Mechanical and dielectric properties of silicon dioxide film fabricated from polyphenylcarbosilane

Abstract Abstract Silicon dioxide film derived from polyphenylcarbosilane (PPCS) is being investigated for electronic ceramics and applications to dielectric materials. Polyphenylcarbosilane was heat treated under oxygen atmosphere to fabricate SiO2 film. The mechanical property and dielectric constant of the film were measured using a nanoindenter and a semiconductor parameter analyser with metal–insulator–semiconductor structure. The chemical behaviour and structure were analysed with an X-ray photoelectron spectrometer and a differential thermal analyser. From the results, the silicon oxide film was synthesised from PPCS due to proper heat treatment. Elastic modulus values of the fired PPCS film were from 8·9 to 27·9 GPa and hardness values of the fired PPCS film were from 0·47 to 2·29 GPa with increasing firing temperature. Change in mechanical properties is related to intermolecular binding strength in the film.