Yurian Kim

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.

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.

Light‐emitting‐diode ( LED ) encapsulants, such as epoxy and silicone resin, have a lower refractive index than YAG :Ce phosphor, and this is usually one of the major causes of LED inefficiency. To improve LED performance, a glass encapsulant is considered. In this study, the SiO ₂ – B ₂ O ₃ – ZnO glass system containing La ₂ O ₃ and WO ₃ was investigated as an encapsulant to minimize total internal reflection and to increase the light extraction efficiency of LED packages. The characterization of glass encapsulants was performed using a differential scanning calorimeter, a pycnometer, a prism coupler, X ‐ray photoelectron spectroscopy, and integrating spheres. The refractive index increased linearly with increasing molar volume of glass because La ₂ O ₃ and WO ₃ act as modifiers in the glass, creating more nonbridging oxygen. The refractive index of glass increases with the content of La ₂ O ₃ and WO ₃ , which is attributed to the increase in polarizability of oxide ions in the glass. When the refractive index between glass and phosphor matched, light extraction efficiency was maximized because total internal reflection decreased.

Composition of calcium zinc borosilicate glass has been designed from the viewpoint of achieving high thermal expansion for low temperature co‐firing ceramic applications. Coefficient of thermal expansion (CTE) of the glass increased with the total percentage of CaO plus ZnO up to 70 mol%, and it also increased with CaO/ZnO ratio up to 50/20 under the constraint of 70 mol% of total CaO plus MgO, beyond which glass forming was impossible. All the CTE behaviors were qualitatively well correlated by the prediction of Hormadaly's model and the simple rule of mixture based on Appen's constant, while the former was shown to be a better tool on a quantitative base for the design of glass composition. Dielectric constant of the developed glass was generally within the range predicted by the Appen's constant. The designed glass, 50CaO·20ZnO·20B ₂ O ₃ ·10SiO ₂ , demonstrated CTE of 12.8 × 10 ⁻⁶ /K and dielectric constant of 13.5. ?>