Densification, microstructure and properties of electroconductive Si3N4–TaN composites. Part II: Electrical and mechanical properties

Dense Si3N4–TaN composites with the TaN phase in the range of 5–50 vol.% were produced by a hot pressing technique in reducing (CO) and neutral (N2) atmospheres. The experimental data of the electrical resistivity for conductive, TaN-reach areas and insulating Si3N4-based matrix are presented. A new numerical simulation was conducted to compute a threshold concentration of the conductive phase, Xc as a function of the radius of dielectric particles to the radius of conductive particles ratio, Rd/Rm, in a two and three-dimensional (bulk) structure. The electrical resistivity of CMC was predicted using the computed Xc parameter by applying the percolation theory and the general effective media (GEM) equation. Finally, the predicted values were compared with the obtained experimental data. Both values were in good agreement. It was proved that the resistivity of electroconductive ceramics is strongly affected by the amount and morphology of the filling phase and is slightly affected by the filling phaseʹs formula. An evident influence of the grain size distribution of TaN powders and morphology of particles of the conductive phase on some electrical and mechanical properties was ascertained. A small quantity of BN powder was added to the starting composition for stabilisation of the porosity level in the manufactured composites which is essential for the production of reproducible electroconductive composites.