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.% we re produced by a hot pressing technique in reducing (CO) and neutral (Nz) a tmospheres. The experimental data of the electrical resistivity for conduct ive, 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, X-c as a function of the radius of dielectric partic les to the radius of conductive particles ratio. R-d/R-m, in a two and thre e-dimensional (bulk) structure. The electrical resistivity of CMC was predi cted using the computed X-c parameter by applying the percolation theory an d the general effective media (GEM) equation. Finally, the predicted values were compared with the obtained experimental data. Both values were in goo d agreement. It was proved that the resistivity of electroconductive cerami cs is strongly affected by the amount and morphology of the filling phase a nd is slightly affected by the filling phase's formula. An evident influenc e of the grain size distribution of TaN powders and morphology of particles of the conductive phase on some electrical and mechanical properties was a scertained. A small quantity of BN powder was added to the starting composi tion for stabilisation of the porosity level in the manufactured composites which is essential for the production of reproducible electroconductive co mposites. (C) 2001 Elsevier Science Ltd. All rights reserved.