Influence of MgO/CaO ratio on the properties of MgO–CaO–Al2O3–SiO2 glass–ceramics for LED packages

The crystallization behavior and thermal properties of diopside/cordierite based glass–ceramics fabricated from a MgO–CaO–Al2O3–SiO2 (MCAS) glass composition system were studied as a function of the CaO/MgO ratio. The crystallization behavior of the glass–ceramics was investigated in a non-isothermal analysis using a differential thermal analysis performed with various heating rates (5–20 °C/min) and by applying John–Mehl–Avrami and Kissinger equations. The activation energy and Avrami constant were calculated as 332 kJ/mol and 1.0, respectively, indicating that the surface crystallization is preferred. The main peak intensity in the XRD patterns for glass–ceramics is linearly proportional to the thermal diffusivity, density and bending strength. Thus, the crystallinity is, in this case, a more important factor than the ratio of the two crystal phases. The glass–ceramics of CaO/MgO = 1.5 had the highest bending strength of 148 MPa and thermal conductivity of 2.6 W/mk−1due to its high crystallinity.