Phase, microstructure and sintering of aluminum nitride powder by the carbothermal reduction-nitridation process with Y2O3 addition

Aluminum nitride powders were synthesized by carbothermal reduction-nitridation method using Al(OH)3, carbon black and Y2O3 as raw materials. The change of phase, microstructure and densification during the AlN synthesis and sintering process were investigated and the effects of Y2O3 was discussed. The results showed that Y2O3 reacted with Al2O3 to form yttrium aluminates of YAlO3 (orthorhombic and hexagonal phases), Y4Al2O9 and Y3Al5O12 at the low temperature of 1350 °C. YAlO3 could firstly be transformed into Y2O3 and then completely into YN when the firing temperature and holding time increased. However, YN could be oxidized into Y2O3 again after the carbon removal at 700 °C in the air atmosphere. There were two ways generating AlN when adding Y2O3 and the possible mechanism was proposed. Y2O3 from YN oxidation favored the densification of AlN ceramics because the liquid had better flowability and distribution in the sintering process at 1800 °C.