This paper gives an overview on the recent developments of high-thermal-conductivity silicon nitride ceramics. Some major factors lowering thermal conductivity of silicon nitride are clarified and some potential approaches to realize high thermal conductivity are described. Then, the recent achievements on the silicon nitride fabricated by a sintered reaction bonded silicon nitride (SRBSN) process are presented. Due to the reduction of the content of impurity oxygen dissolved in the lattice, the silicon nitride ceramics attained substantially higher thermal conductivities, compared to that of the conventional gas-pressure sintered silicon nitride, while the microstructures and bending strengths are similar to each other between these two types of materials. Moreover, further improvement of the thermal conductivity is possible by increasing the β/α phase ratio of the nitrided compact, and a silicon nitride with a thermal conductivity as high as 177 W/(m ? K) and a high fracture toughness of 11.2 MPa-m~(1/2) was developed.
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