Processing of steatite ceramic with a low dielectric constant and low dielectric losses

Abstract

Steatite ceramic was processed from natural raw materials talc, clay and dolomite. They were stabilised in water electrostatically and electrosterically with polyacrylic acid at pH 9. The suspensions were spray dried and the resulting powders contained granules with a mean size of 10 µm. The powders were dry-pressed and sintered at 1275 °C and 1300 °C for 2 hours. The effect of type of stabilisation and sintering temperature on the phase composition, microstructure and dielectric properties of the ceramic was studied. The X-ray powder diffraction analysis revealed that the orthorhombic protoenstatite and tetragonal cristobalite were present in all the ceramic samples. The microstructures of the samples investigated by scanning electron microscopy were homogenous with grains surrounded with a glass phase and some pores. By energy dispersive X-ray spectroscopy we identified Mg, Si, Al and O in the grains and Mg, Si, O and minor amount of Al, Ca and Fe in the glassy phase. The dielectric constant of the ceramic measured at room temperature and 1 MHz decreased from about 8 to about 5 with increasing sintering temperature from 1275 °C to 1300 ^oC, while the dielectric losses were between 0.001 and 0.003. The dielectric properties of the steatite ceramic were related to the chemical composition of the glassy phase. The results show that the chemical composition of the phases and the dielectric properties of the ceramic depend on the processing temperature while the type of stabilization of raw materials in water has only a minor influence on these parameters.