Low-temperature synthesis of AlN powder with multicomponent additive systems by carbothermal reduction–nitridation method

AlN powders were synthesized at low temperatures (1300 and 1400 {sup o}C) by the carbothermal reduction-nitridation (CRN) method using multicomponent additive systems. The synthesis treatments were conducted in a graphite furnace with flowing nitrogen gas between 1200 and 1500 {sup o}C using powder mixtures with Al{sub 2}O{sub 3}:C molar ratio of 1:3 and 0.5-3 wt% of CaF{sub 2}, Y{sub 2}O{sub 3}, Li{sub 2}CO{sub 3} and/or SrCO{sub 3} as additives. In relation to the conventional CRN process, the use of multicomponent additive systems reduced the synthesis temperature in 200 {sup o}C (CaF{sub 2}-SrCO{sub 3}), 100 {sup o}C (CaF{sub 2}-Li{sub 2}CO{sub 3} and CaF{sub 2}-Y{sub 2}O{sub 3}-Li{sub 2}CO{sub 3}) or <100 {sup o}C (CaF{sub 2}-Y{sub 2}O{sub 3} and CaF{sub 2}-Y{sub 2}O{sub 3}-Li{sub 2}CO{sub 3}-SrCO{sub 3}). X-ray diffraction patterns showed that the additives reacted with the alumina powder forming aluminate phases, which vaporized with the increase of synthesis temperature. The enhanced AlN conversion rate was discussed in terms of the vaporization of aluminates in the reducing atmosphere.