关键词: 碳酸铝铵, α-Al₂O₃, 超细粉, 合成, 烧结

Abstract: By using ammonium aluminium sulfate and ammonium hydro-carbonate as the starting materials, the synthesis of ammonium aluminium carbonate hydroxide (NH₄AlO(OH)HCO₃)
was studied. It was found that NH₄AlO(OH)HCO₃ can be synthesized by adding ammonium aluminium sulfate solution to ammonium hydro-carbonate solution
with a adding rate less than 1.2L·h^-1. Under other conditions the precipitate was γ-AlOOH in the experimental range. The sequence of phase transformation of
γ-AlOOH during heating was found to be γ-AlOOH →γ-Al₂O₃→δ-Al₂O₃→θ-Al₂O₃→α-Al₂O₃; while that of NH₄AlO(OH)HCO₃ was found to be NH₄AlO(OH)HCO₃ →amorhous Al₂O₃→θ
-Al₂O₃→α-Al₂O₃. The transformation temperatures of NH₄AlO(OH)HCO₃ to θ-Al₂O₃ and α-Al₂O₃ were both about 100→ lower than those of γ-AlOOH. γ-AlOOH can transform to
α-Al₂O₃ completely by calcining at 1200℃ for 1h, and the obtained powder,with a particle size of 150nm, can be sintered to 84.46% relative density at 1450→
for 2h. NH₄AlO(OH)HCO₃ can transform to α-Al₂O₃ completely by calcining at 1100℃ for 1h, and the obtained powder, with a particle
size of 70nm, can be sintered to 97.80% relative density under the same sintering condition.

Key words: NH₄AlO(OH)HCO₃, α-Al₂O₃, ultrafine powder, synthesis, sintering