The production and characterization of silicon nitride having high thermal conductivity

Si3N4 ceramics are widely used various applications such as electronic devices and industrial robots. This devices capable of converting electrical power and which can control effectively. Mechanical and thermal properties of materials determine performance of the device in the electronic circuit. Internal stresses due to the high heat causes crack initiation in the ceramic substrates. Therefore, high strength, high thermal conductivity and electrical insulation are necessary for this substrates. In this thesis, cost effective Si3N4 powders were used instead of Al2O3 and AlN which are used in both thermal conductivity and insulation applications. Also, determination of fabrication parameters and their characterizations were purposed. Economic Silzot and Yantai Si3N4 powders were used as alternative powder instead of expensive UBE powder. Effect of the powder type, particle size, sintering method, sintering temperature, time and pressure on thermal conductivity were investigated. Moreover, effect of the heat treatment after sintering, sintering additives as Y2O3 and Yb2O3 on thermal properties was analyzed. Finally, addition of high thermal conductive secondary phases as SiC, effect of the amorphous and crystalline grain boundary phases on thermal properties was determined. As a result of study, thermal conductivity of the silicon nitride ceramics has been increased with SiC addition and sintering temperature (due to high density and grain growth). Also, thermal properties were decreased with the crystalline phases.