2019 Volume 127 Issue 11 Pages 810-817
We propose a facile and continuous direct nitridation method for synthesizing fine aluminum nitride (AlN) particles using a drop tube furnace. Aerosolized Al powder as the raw material was continuously supplied through the top of the furnace together with N2 as a carrier gas. Once in the furnace, the Al powder reacted with the N2 to form AlN. A particular advantage of this process is that it allows the continuous synthesis of fine AlN particles. In this study, either a mullite (Al2O3–SiO2) or an alumina tube was used to fabricate the furnace, and the products were collected in a crucible placed at the bottom. Upon heating the mullite tube from 1200 to 1400°C, AlN was formed once the temperature exceeded 1250°C, and its product content increased with temperature. When the flow rate of the N2 carrier gas was decreased from 4 to 2 L min−1, the amount of AlN formed increased due to the increased residence time in the reactor. The morphology of the particles obtained was radially aligned nanofibers with droplets on the tips of the fibers. Transmission electron microscopy revealed that the Si in the mullite tube reacted with Al to form eutectic Al–Si droplets on the Al surface, in which these droplets acted as a catalyst of vapor–liquid–solid AlN fiber growth. When the alumina tube was used (1800°C), nitridation of Al was enhanced and radially aligned AlN nanofibers with no droplets on the tips were collected, mainly in a filter at the exhaust port. These AlN nanofibers are thought to form via vapor–solid growth and are easily carried along with the N2 gas flow, resulting in their deposition on the filter. The products collected in the crucible contained coarse Al particles, which are formed via Al particle agglomeration and coarsening through melting.