Effects of the addition of alumina on the crystallization, densification and dielectric properties of CaO–MgO–Al2O3–SiO2 glass in the presence of ZrO2

The alumina addition effects on the crystallization, sintering behaviors and dielectric properties of CaO–MgO–Al2O3–SiO2 glass (CMAS) and CaO–MgO–Al2O3–SiO2–ZrO2 (CMASZ) were investigated using the differential thermal analyzer (DTA), dilatometer, scanning electron microscopy (SEM) and X-ray diffractometer (XRD). For CMAS glass, the phyllosiloxide crystallized first and then anorthite crystallites were observed during sintering at 800–950°C. The crystallization temperature of phyllosiloxide shifted from 800°C to 850°C after adding ZrO2 to the glass. For CMAS glass added with 10vol% alumina, the acicular phyllosiloxide phase, intergrowth anorthite and subrounded alumina particles were observed. For CMASZ glass added with 10vol% alumina sintered at 900°C for 1h, homogeneously distributed zirconia precipitates, subrounded alumina particles and a small amount of acicular phyllosiloxide were found in the dense glass matrix. The CMASZ glass added with 10vol% alumina sintered at 900°C exhibited a dense microstructure, a low dielectric constant of 7.5 and a dielectric loss tangent of below 5×10−3, which provides a promising candidate for LTCC applications.