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

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 -Al 2 O 3 .With an increase in the NH 4 Cl addition, the -Al 2 O 3 phase transition temperature significantly decreased.The transition phase was completely converted to -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 -Al 2 O 3 by 100 C.Meanwhile, the introduction of NH 4 Cl had no effect on the microscopic morphology of -Al 2 O 3 .The -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 -Al 2 O 3 grains.