Preparation and dielectric properties of porous silicon nitride ceramics
(State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, China)
Abstract: Porous silicon nitride ceramics with difference volume fractions of porosity from 34.1% to 59.2% were produced by adding different amount of the pore-forming agent into initial silicon nitride powder. The microwave dielectric property of these ceramics at a frequency of 9.36 GHz was studied. The crystalline phases of the samples were determined by X-ray diffraction analysis. The influence of porosity on the dielectric properties was evaluated. The results show that a-Si3N4 crystalline phase exists in all the samples while the main crystalline phase of the samples is b-Si3N4, indicating that the a/b transformation happens during the preparation of samples and the transformation is incomplete. There is a dense matrix containing large pores and cavities with needle-shaped and flaky β-Si3N4 grains distributing. The dielectric constant of the ceramics reduces with the increase of porosity.
Key words: silicon nitride; pore-forming agent; porosity; geometry; dielectric properties