Low-Temperature Synthesis of α-Al₂O₃ Powder via Calcining Aluminum Ammonium Sulfate Double Salt Process: Effects of Glucose and Pre-Pressing

Aluminum is a widely used material in the industries of electronics, automobiles, and aviation due to its excellent properties. However, the synthetic temperature of commercial α-Al₂O₃ powder is high, and the obtained powder has coarse particles, low activity, serious agglomeration, and it is not easy to disperse, which affects its subsequent applications. Therefore, the synthesis of α-Al₂O₃ powder at a low temperature is challenging. In this paper, α-Al₂O₃ powder was synthesized by calcining NH₄Al(SO₄)₂·12H₂O with different added glucose contents. The effects of glucose content and sample pre-pressing on the synthetic temperature of α-Al₂O₃ powder were investigated. The results showed that the presence of glucose changed the phase transition process and significantly decreased the synthetic temperature. With 30% (mass fraction) glucose added, α-Al₂O₃ powder could be synthesized at 950 ℃, which was about 200 ℃ lower than that of the glucose-free control. With 75% glucose added, the synthetic temperature of α-Al₂O₃ further decreased to 900 ℃. The presence of glucose is believed to accelerate the thermal decomposition of NH₄Al(SO₄)₂·12H₂O, and make NH₄Al(SO₄)₂·12H₂O be dispersed evenly and amorphous. The results also showed that pre-pressing further decreased the synthetic temperature of α-Al₂O₃ by 25—50 ℃, which might be a result of the attenuation of agglomeration and the further homogenization of powder dispersion. Moreover, single-phase α-Al₂O₃ with a uniform distribution of particle size (average particle size 110 nm) were obtained at 850 °C by using 25 MPa pre-pressing and 75% (mass fraction) glucose process.