Moreover, it is required that the dissolution rate of alumina in the cryolite melt is fast, the bottom of the electrolytic cell tank is deep and deep; the heat insulation of the shell on the electrolyte is good; the moisture is not absorbed in the air, the flying loss is small, the fluidity is good, and the transportation is convenient. It is convenient to automatically feed the electrolytic cell. All of these properties depend on the physical properties of the alumina.
The indicators used to characterize the physical properties of alumina are: angle of repose, α-Al203 content, bulk density, particle size and specific surface area, and wear coefficient.
1. The angle of repose. The alumina angle of repose refers to the inclination of the material naturally accumulating on a smooth plane. The alumina with a larger angle of repose is more soluble in the electrolyte, and can be well covered on the electrolyte crust during the electrolysis process, and the flying loss is also small.
2. a-Al2O3 content. The content of a-Al2O3 in alumina reflects the degree of alumina roasting. The higher the degree of calcination, the more a-Al2O3 content, the hygroscopicity of alumina decreases with the increase of a-Al2O3 content. Therefore, alumina for electrolysis is required to contain a certain amount of a-Al2O3. However, the solubility of a-Al2O3 in the electrolyte is inferior to that of Υ-Al203.
3. Tolerance. The bulk density of alumina refers to the weight of a unit volume of material in a natural state. Aluminium, which generally has a small bulk density, facilitates dissolution in the electrolyte.
4. Particle size. The particle size of alumina refers to the degree of its thickness. The particle size of alumina must be appropriate, too coarse in the electrolyte to dissolve slowly, or even precipitate; the rules are easy to fly loss.
