Effect of sintering temperature on the thermal properties of diopside-based glass-ceramics of varying CaO/MgO ratio.

The thermal properties of diopside (CaMgSi2O6)-based glass-ceramics of varying CaO/MgO ratio were investigated as a function of sintering temperature. The crystallization behavior of the glass was studied by a non-isothermal method using a differential thermal analysis (DTA) with various heating rates. Diopside, as a main crystalline phase, and cordierite, as a minor phase, were formed in the glass-ceramics with an - 0.67-2.23 CaO/MgO ratio. The X-ray diffraction peak for diopside in the glass-ceramic becomes higher with an increase of the CaO/MgO ratio. The crystallization volume fraction with sintering temperature was calculated showing that both the initiation temperature for crystallization and a temperature range of crystallization increased with an increased heating rate. The microstructure of all glass-ceramics had a lump area composed of several tens-of-nanometer particles and a matrix composed of rows of particles, and the matrix area decreased with a decreasing CaO/MgO ratio. The thermal conductivity of glass-ceramics of CaO/MgO = 2.23 was 44% higher than that of CaO/MgO = 0.67 owing to the higher crystallinity and less voids in a microstructure. All glass-ceramics fabricated in this study were sintered at below 955 degrees C, which makes them applicable to the LTCC process for light-emitting diode packaging.