Improving the electrical and thermal conductivities of Si3N4 based composite materials

The aim of this PhD dissertation is to improve the electrical conductivity of Si3N4 based ceramics for expanding the application areas of this materials. For this purpose, basic conductivity theories and segregated network concept taken as basis and an innovative, easy and cost effective process is developed. Appart from traditional particulate reinforced composite approach, spherical SiAlON based granules are coated with nano sized oxide (TiO2) and non-oxide powders(TiCN, SiC) in the range of 2.5-10 vol. % by mechanical mixing. Depending on the additive type gas pressure sintering (GPS), spark plasma sintering (SPS) and pressureless sintering (PS) techniques are employed to densify composites. Even coating with very low amounts such as 2.5 vol. % highly conductive segregated network of particles are achieved without detoriating the mechanical and physical properties of Si3N4 based matrix material. For comparison and to emphasis the importance of production route, composites produced by particle reinforcement concept are also prepared. In addition to electrical conductivity, high termal diffusivity values are obtained. Instead all within this process other properties of the materials such as thermal conductivity is also improved.