Influence of Al2O3 additions on the crystallization mechanism and properties of diopside/anorthite hybrid glass-ceramics for LED packaging materials

The crystallization mechanism and properties of diopside (CaMgSi2O6)/anorthite (CaAl2Si2O8) hybrid glass-ceramics fabricated from a CMSA (CaO-MgO-SiO2-Al2O3) glass system were studied as a function of Al2O3 additions. The parent glass prepared was pressed to pellets isostatically and was sintered to produce glass-ceramics. A non-isothermal analysis was performed to study the crystallization behavior of diopside/anorthite hybrid glass-ceramics using differential thermal analysis (DTA) with various heating rates (5-20 K min−1) and John-Mehl-Avrami and Kissinger equations. The occupying ratio of diopside and anorthite phases, crystal identification and microstructure in the glass-ceramics containing various Al2O3 contents were analyzed. Also the thermal conductivity and density of diopside/anorthite composites were measured to apply to LED packaging materials. The main crystalline phases for CaO-MgO-SiO2-Al2O3 glass-ceramics system containing 8.6 wt% or less Al2O3, and 15.9 wt% or more Al2O3 were the diopside and anorthite, respectively. The difference (ΔT) of initiation temperature for crystallized (Tx) and glass transition temperature (Tg), calculated from the DTA curve for a glass is inversely proportional to the density of glass-ceramics fabricated from the glass. The highest crystallization temperature was 946 °C for the glass-ceramics containing 27.4 wt% Al2O3, which is low enough to apply the LTCC process. The glass-ceramics of diopside base with no Al2O3 added had the highest thermal conductivity of 2.372 W/m °C among all specimens fabricated in this study.