Densification and properties of glass/cordierite composites

Five borosilicate glass/cordierite composite samples were prepared from pure chemicals such as H3BO3, Al2O3, MgO, silica sand, Na2CO3 and K2CO3. The glass and cordierite were separately prepared at 1500–1550 °C before mixing the composite batches. These composite batches composed of 50/50, 40/60, 30/70, 20/80 and 10/90 wt.% of glass/cordierite, respectively. The composite samples were sintered at 1100 and 1300 °C. Densification parameters, XRD, microstructure, thermal expansion and dielectric constant were addressed. The results revealed that, for the composites with ≥60 wt.% cordierite, no crystallization of cristobalite from the glass took place. The presence of cristobalite results in an undesirable high coefficient of thermal expansion. The thermal expansion of all the composites was in a range of 4.2 × 10−6/K to 3.8 × 10−6/K. It was also found that the bulk density decreases with the increase of cordierite content at the used sintering temperature due to the lower amount of liquid phase produced from the glass. The dielectric constant of the obtained composites was between 4.7 and 5.8. The precipitation of cristobalite did not affect the dielectric constant of the resulting composites because the dielectric constant of cristobalite itself is 3.8 as compared with that of glass (4.6) and cordierite (5.3).