Microwave synthesis of Ti₄O₇ or AlN nanoparticles by rapid carbothermal reduction process

Microwave processing was used to fabricate nanoparticles having a desired particle size and morphology by a simple method, carbothermal reduction method. By microwave processing, Ti₄O₇ nanoparticles (∼ 60 nm) maintaining the morphology of a pristine material were fabricated at 950 °C for 30 min. Since grain growth was observed in conventional processing, rapid heating (250 °C/min∼) and rapid cooling, which are features of the microwave processing, are also effective in maintaining the particle diameter even though this carbothermal reduction reaction proceeds in the high temperature region. In addition, we successfully synthesized spherical AlN nanoparticles with high nitridation rate, maintaining the morphology of pristine material by microwave processing. It is considered that the crystal structure of transition alumina (which is advantageous for formation of intermediate AlON but phase transition over 1200 °C) was maintained over 1300 °C by microwave rapid heating. In addition, by optimizing the nitrogen flow rate, spherical AlN nanoparticles having a nitridation ratio of 0.88 could be fabricated at 1200 °C for 180 min and a nitrogen flow rate of 0.2 L/min.