**4. Conclusion and perspective**

In conclusion, this chapter presents the recent advances on the carbothermal synthesis of spherical AlN fillers. The influence of various synthetic parameters on the morphology and particle size of final products is summarized. During the CRN process, the elevated N2 gas pressure favored the growth of the particle size and the formation of the uniform spherical morphology, but hampered the nitridation rate. The relatively high reaction temperature could result in the increasing nitridation rate, the growth of the particle size, and the sphericity of AlN particles, but a too high temperature above 1900°C was not beneficial for the spherical morphology due to the decreasing liquid content. Prolonging the reaction time properly was also conducive to the formation of large spherical AlN particles. As for the raw materials, increasing the additive content tended to enhance the sphericity and particle size of AlN particles; excessive carbon black reduced the nitridation rate and particle size, but increased the sphericity of AlN particles; the use of the additive with a large particle size could slow down the nitridation rate and reduce the AlN particle size.

In summary, the liquid aluminates forming from the reaction between Al2O3 and additives played an important role in the carbothermal synthesis of spherical AlN fillers by improving the nitridation rate, increasing the particle size, and promoting the formation of smooth spherical appearance. The condition that AlN particles were completely wrapped with liquid aluminates during the growth stage was necessary for the spherical morphology.

Although the micron-sized spherical AlN particles, which showed great potentiality to be used as fillers, were successfully synthesized by the CRN method, further research is still necessary aiming at evaluating the actual thermal conductivity of the AlN fillers and the performance of the as-prepared thermal interface materials.
