Hyungsun Kim

Thermal and electrical properties of BaO–B2O3–ZnO glasses

Abstract Glasses in the BaO–ZnO–B2O3 system were examined as potential replacement for PbO glass frits with low firing temperature (500–600 °C) for the dielectric layer of a plasma display panel (PDP). The glasses were evaluated for glass transition temperature (Tg), thermal expansion coefficient (α) and dielectric constant e. The electrical and the thermal properties were also compared with theoretical data calculated by a known empirical equation. Tg of the glasses varied between 480 and 560 °C, and α was in the range of 7–9×10−6 K−1. The dielectric constant ranges from 14 to 19 and the theoretical data showed lower α and e than the experimental data. The results suggest that BaO–ZnO–B2O3 glasses would be suitable as an alternative to Pb-based dielectric layer in PDPs.

Measurement of hardness on traditional ceramics

Abstract To reveal quantitatively the hardness of clayware and stoneware, Mohs, Vickers (micro and macro) and superficial Rockwell indentation measurements were applied to roofing tiles with different porosity. This work discusses the comparison of different indentation results, indentation size effect on porous clayware and the effect of microstructure on hardness of tiles. As a result, for Vickers indentation test, the critical indent load was found to 0.5 and 1 kg for soft and hard tiles, respectively, and indentation size/load effect (ISE) appeared clearly in hard tiles. The relationship between load (P) and indent size (d) on tiles was very close to a modified Myer’s law. The PSR (proportional specimen resistance) model gave P/d=0.67+0.02d, P/d=1.33+0.1d for soft and hard tiles, respectively. It was found that there were no difference in hardness of tiles mounted with epoxy or copper and as-received sample under superficial Rockwell indentation. These concepts on the harness evaluation of tiles would be applicable to other clayware.

Sintering and crystallization phenomena in Silceram glass

An investigation has been carried out on the feasibility of employing a CaO-MgO-Al2O3-SiO2 glass-ceramic (known as Silceram) as a matrix for a fibre composite produced by a powder route. Some important properties of the parent glass, e.g. surface energy, viscosity, have been measured as well as the kinetics and structural aspects of the sintering and crystallization processes. It was found that the crystallization of the main phase, diopside, occurred from the surface of individual particles and internally with activation energies of 392 to 452 kJ mol−1 and 258 to 323 kJ mol−1 respectively. However, the surface crystallization was only dominant when the glass powder was fine (<38μm). The work has demonstrated that this glass-ceramic shows promise as the matrix component of a composite because(i)both sintering and crystallization may be achieved by a single stage heat treatment at relatively low temperatures of 900° C to 1000° C, because the glass powder can be compressed and sintered by viscous flow before crystallization commences, and(ii)the resulting microstructure is fine, and in the case of the hot-pressed material there is negligible porosity.

Effect of anorthite and diopside on dielectric properties of Al2O3/glass composite based on high strength of LTCC substrate

The green sheet of an alumina filler/glass matrix, which is a glass–ceramic based on an anorthite and diopside composite, is a low-fired substrate material for microelectronic packaging. In this study, alumina/glass sheets were prepared using a tape-casting process. The mechanical and dielectric properties of the sintered bodies were examined as a function of the sintering temperature. The volume of the crystalline phases was considered with the peak area of the XRD intensity for evaluating the alumina/glass composite. The flexural strength and dielectric properties of the sintered alumina/glass composites were 167.2 ± 13.1 MPa for the four-point bending test, 5.51 for the dielectric constant and 2,078 MHz for the quality factor, respectively. The dielectric constant was dependent on the volume of crystalline phases present.

Effects of alloying elements on the electrochemical characteristics of iron aluminides

Effects of alloying elements on the electrochemical characteristics of iron aluminides in the H2SO4, H2SO4+KSCN and HCl solutions were investigated using electrochemical tests. The corrosion morphologies in iron aluminides were analysed by utilising optical microscopy. It was found that the addition of Cr and Mo to iron aluminides increased the corrosion potential, pitting potential and repassivation potential. The active current density, passive current density and reactivation current density decreased as Cr and Mo were added. In the case of Mo addition, the passive current density was slightly higher in the H2SO4 solution than in solutions containing SCN- and Cl-. When B was added to samples, the corrosion potential and repassivation potential decreased, whereas the active current density, passive current density, reactivation current density and pitting potential increased. Iron aluminides containing Mo and Cr showed remarkably improved intergranular and pitting corrosion resistance to SCN- and Cl- solution. On the other hand, B addition accelerated granular and intergranular corrosion by precipitation of borides.

Effect of Mg on the evolution of non-metallic inclusions in Mn–Si–Ti deoxidised steel during solidification: experiments and thermodynamic calculations

Abstract The effects of Mg on the evolution of non-metallic inclusions in Mn–Si–Ti deoxidised steels during solidification were investigated in a study based on experiments and thermodynamic calculations. The inclusions were composed of the MgO–MnO–Ti2O3–TiO2 oxide, MnS, and TiN. With the increase of Mg concentration in steels, the phases of oxide inclusions were changed, in the order of pseudobrookite (Ti3O5–MnTi2O5), ilmenite (MgTiO3–MnTiO3–Ti2O3), spinel (Mg2TiO4–MgTi2O4–Mn2TiO4–MnTi2O4) and MgO. Thermodynamic calculations for inclusion evolutions were in good agreement with the experimental results.

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.

Surface crystallization of rare-earth aluminosilicate glasses

Abstract Surface crystallization in a rare-earth aluminosilicate glass (Nd 2 O 3 –Al 2 O 3 –SiO 2 –TiO 2 ) was studied using an isothermal method and the crystal growth rate of the glasses was evaluated as a function of the composition. For measuring the surface crystal growth rate, two different methods: measurement of the crystal layer in the longitudinal and lateral growth direction. It was found that crystallization proceeded by surface crystallization only and TiO 2 did not act as a nucleating agent. The growth rate was strongly dependent on the viscosity of glass and agreed with prediction from the Preston model using the known viscosity and melting temperature. As the Si/Nd and Si/Al ratios decreased, the crystal growth rate increased. TiO 2 and Nd 2 O 3 played the role of network modifier, which decreased the viscosity of the glass, facilitating crystallization of the rare-earth aluminosilicate glass.

Microstructure and properties of CaO-ZrO2-SiO2 glass-ceramics prepared by sintering

Abstract For the development of a new wear resistant and chemically stable glass-ceramic glaze, the CaO–ZrO 2 –SiO 2 system was studied. Compositions consisting of CaO, ZrO 2 , and SiO 2 were used for frit, which formed a glass-ceramic under a single stage heat treatment in electric furnace. In the sintered glass-ceramic, wollastonite (CaSiO 3 ) and calcium zirconium silicate (Ca 2 ZrSi 4 O 12 ) were crystalline phases composed of surface and internal crystals in the microstructure. The internal crystal formed with nuclei having a composition of Ca 1.2 Si 4.3 Zr 0.2 O 8 . The CaO–ZrO 2 –SiO 2 system showed good properties in wear and chemical resistance because the Ca 2 ZrSi 4 O 12 crystals positively affected physical and mechanical properties.

Erosion Behavior of YAG Ceramics under Fluorine Plasma and their XPS Analysis

Chemical composition and status of chemical bonding of the YAG(