EFFECT OF NH₄Cl ADDITIVES ON THE PHASE TRANSFORMATION AND MORPHOLOGY OF α-Al₂O₃

Abstract

To investigate the effects of NH 4 Cl doping and the calcination temperature on the phase transformation and microscopic morphology of Al 2 O 3 , Al 2 O 3 powders were obtained by introducing different mass fractions of NH 4 Cl into the Al(OH) 3 powders and were then calcined at different temperatures. X-ray diffractometry and scanning electron microscopy were used for the phase analysis and particle morphology observation, respectively. The results showed that the addition of NH 4 Cl could reduce the phase transition temperature of α-Al 2 O 3 . With an increase in the NH 4 Cl addition, the α-Al 2 O 3 phase transition temperature significantly decreased. The transition phase was completely converted to α-Al 2 O 3 at 1100 °C with the addition of NH 4 Cl at 20 % at 1100 °C, which reduced both the phase transition temperature and the complete phase transition temperature of α-Al 2 O 3 by 100 °C. Meanwhile, the introduction of NH 4 Cl had no effect on the microscopic morphology of α-Al 2 O 3 . The α-Al 2 O 3 phases were worm-like with or without NH 4 Cl, and the doping of NH 4 Cl did not lead to the transitional growth of the complete phase-changed α-Al 2 O 3 grains.