The Effect of MgO Addition on Mullite Substrate

Abstract

The effects of MgO addition on thermal expansion coefficient and dielectric constant of mullite substrate were studied. Thermal expansion coefficient and dielectric constant decrease with increasing MgO content and exhibit a minimum value at 1wt% MgO. However, above 5wt% MgO content both values increase. Results of X-ray diffraction analysis show that mullite compositions which include more than 0.5wt% MgO form cordierite. Spinel is also formed as well as cordierite in the compositions containing more than 5wt% MgO. These results indicate that addition of MgO affects the thermal expansion coefficient and dielectric constant of mullite substrates because of the formation of new phases; cordierite and spinel. The thermal expansion coefficient and dielectric constant are affected mainly by cordierite and spinel in the regions containing less than and more than 5wt% MgO, respectively.