Preparation of AlN powder of low oxygen content via carbothermal reduction and nitridation by active gas exchange technique

Abstract

By generating a periodic impulse-like pressure (2.0–4.4 kPa, 84 s) to actively exchange the gas in synthesis furnace, pure AlN powder of low oxygen content was synthesized via additive free carbothermal reduction and nitridation (CRN) of Al2O3 powder. Compared with the conventional CRN method, the proposed extra gas exhaust process can more effectively remove the side-produced CO from the reaction sites to accelerate nitridation process and decrease the residual oxygen content in the obtained AlN powder. For example, with 39 wt% activated carbon loaded in the raw material at 1650 °C for 4 h, the prepared AlN powder by the proposed synthesis scheme has only 0.68 wt% residual oxygen. The effects of carbon content, synthesis temperature and holding time on the residual oxygen content in AlN powder by the proposed synthesis scheme were also studied. The ball-milled as-prepared AlN powder was pressureless sintered at 1880 °C for 2.5 h to obtain a translucent AlN ceramics (37.6% at ~5700 nm), which demonstrates the excellent sinterability of the as-prepared AlN powder.