High thermal conductivity silicon nitride ceramic

The thermal conductivity of Si3N4 ceramic at room temperature is basically governed by the lattice oxygen content in the β-Si3N4 crystal. Therefore, in order to improve thermal conductivity, it is important to purify the grains, as has been demonstrated in AlN ceramic. The purification of β-Si3N4 grains can be achieved through a solution re-precipitation reaction during sintering using sintering additives that have a great affinity for SiO2, such as Y2O3 and Yb2O3. As far as the authors know, Si3N4 ceramic with a high thermal conductivity of over 100 W m-1 K-1 has been fabricated only by gas-pressure sintering. From a commercial point of view, it is very important to fabricate high thermal conductivity Si3N4 ceramic by a conventional sintering technique such as pressureless sintering. Seeding, combined with careful control of grain-boundary composition, may be one of the processing strategies for this purpose. In addition, microstructure design for harmonizing high thermal conductivity with good mechanical and electrical properties (such as low dielectric constant) is also very important for the widespread use of Si3N4 ceramic as a high thermal conductivity material.