A Study of Densification and Enhanced Microwave Dielectric Properties of Al2O3-Polystyrene Ceramic Composites

Enhanced microwave dielectric properties of Al2O3-polystyrene (PS) ceramic composites with volume fractions up to 40% of PS and their inexpensive processing, densification, and microstructure are presented. Ceramic composite powders with different volume percentages of PS (10-40%) have been processed using toluene as a solvent. Bulk ceramic composites obtained by the simultaneous application of 600 MPa pressure and 175 & DEG;C temperature showed 68-99% of their theoretical densities. Fractographs of the ceramic composite were recorded through field-emission scanning electron microscopy (FESEM). The influence of PS content, pressure, and temperature on the microwave properties of the ceramic composites was investigated. The microwave dielectric properties-relative permittivity (& epsilon;(r)), quality factor (Q(u) x f), and temperature coefficient of resonance frequency (& tau;(f))-have been measured by standard resonance methods near 13 GHz. The densified ceramic composite with 40% volume fraction of PS exhibited & epsilon;(r) = 6.07, Q(u) x f = 30800 GHz, and & tau;(f) = + 10 ppm/K, respectively. The measured relative permittivity values of the composites were comparable with theoretical values using various theoretical models. Additionally, the thermal conductivity and linear coefficient of thermal expansion of the ceramic composites were also investigated. The thermal conductivity varied from 0.74 Wm(-1) K-1 to 1.9 Wm(-1) K-1 for volume fractions up to 40% of PS, whereas the coefficient of thermal expansion (CTE) values varied from 9 ppm/K to 37 ppm/K.