Phase change and structural change of properties during calcination of aluminum hydroxide
Phase change
1. Removal of adhesive water
The industrial production of aluminum hydroxide contains 8%~12% of the attached water, and the temperature of removal of the attached water is between 100℃~110℃.
2. Remove crystal water
Three stages of removal of crystalline water
Under dynamic conditions, the remaining 0.05~0.1 water molecules were removed by heating from 600℃ to 1050℃.
3. Crystal transformation
Aluminum hydroxide is generally transformed into -Al2O3 at 1200℃, accompanied by crystal transformation during dehydration.
Structural and performance changes
1. Change of specific surface area
The change of specific surface area with temperature in the process of calcination is shown in the figure. The specific surface area increases sharply at 240℃ and reaches its maximum value at about 400℃.
The specific surface area of alumina is related to the original material. Although the crystal shape of alumina obtained by different methods is basically the same after calcining, the structure and specific surface area are quite different.
2. Change of burning rate
The dehydration of aluminum hydroxide was mostly completed before 400℃, and the main dehydration was between 100 ℃ and 300℃.
3. Changes in granularity
The particle size of alumina is an important index, which depends on the particle size, strength, roasting temperature, heating rate and fluid dynamics conditions in the calcination process of the raw material (aluminum hydroxide). The particle size will change with the change of temperature.
