Kinetic Calculation And Low-temperature Calcination Process Of Al（OH）₃ Prepared Al₂O₃

As an important material in the future industrial and scientific fields,high-purity alumina is of great importance to alumina research.This paper studied the aluminum hydroxide powder produced by Qinghai Shengnuo Optoelectronics Technology Co.,Ltd.,using differential scanning calorimeter,X-ray diffractometer,particle size analyzer and scanning electron microscope were used to study the phase inversion process and calcined product of aluminum hydroxide.The kinetic calculation of the calcination process of aluminum hydroxide was carried out by Popescu method,and various seed crystals were studied.The effect on the alumina phase inversion process shows that:During the calcination of aluminum hydroxide,the weight loss is 28wt%,during which it experiences Al（OH）₃→AlOOH+H₂O_（g）,AlOOH→δ-Al₂O₃+H2O_（g）,δ-Al₂O₃→η-Al₂O₃,η-Al₂O₃→θ-Al₂O₃,θ-Al₂O₃→α-Al₂O₃ various crystal transformation process.The final calcined alumina D50 is 15um,and its microstructure is unevenly distributed.The agglomeration behavior is called severe.The alumina has a hexagonal column shape,and many cracks are formed on the surface,and there is a large gap between the grains.The kinetic calculation results of aluminum hydroxide show that the first-stage weight loss of aluminum hydroxide is D1 model,the average activation energy is101.9KJ/mol,and the pre-exponential factor is between 0.2376-1.5379×10⁹min^-1.The second stage and three stage weight loss of aluminum hydroxide is D3 model,the average activation energy of the second stage is 136.285KJ/mol,the pre-exponential factor is between 0.62-1.12×10⁹min^-1,and the average activation energy of the three stages is 72KJ/mol.The pre-finger factor is between 1.468-2.385×10³min^-1.Alumina seed crystal,ammonium fluoride and aluminum fluoride seed crystal can effectively reduce the phase transition temperature ofα-Al₂O₃,and 10wt%alumina seed crystal can reduce the crystallization temperature ofα-Al2O3 by 100degrees,and oxidize by sintering.The aluminum particle size is reduced,the alumina particle size range is reduced from 0-100 um to 0-60 um,D50 is 8.5 um,and the microstructure distribution is uniform,and the agglomeration behavior is greatly reduced.Under the aluminum hydroxide powder with 5wt%ammonium fluoride or aluminum fluoride content,the conversion temperatures ofθ-Al₂O₃ andα-Al₂O₃ are about 780°Cand 1120°C,respectively.XRD test showed that 5wt%content of ammonium fluoride and aluminum fluoride can reduce theα-Al₂O₃ phase transition temperature by 200-250°C,and the particle size is significantly reduced,and 3 wt%aluminum fluoride seed crystal or 2 wt%fluorination Ammonium seeds can transform the microstructure of alumina from a hexagonal prism to a sheet structure.