Reasons for variegation in tabular alumina production
The crystal grains of tabular alumina are large, and the particle size is mostly 40~200μm. There are many circular closed pores of 5~15μm inside the crystal, and there are few open pores. Because no additives are added and the purity is high, tabular corundum has a high melting point, high grain hardness, high thermal strength, low thermal shrinkage, high density, low air permeability, and good wear resistance; especially due to the presence of Many closed small pores have good thermal shock resistance; and most alkalis and inorganic acids do not react with tabular alumina, which is resistant to chemical attack. Due to the series of properties of tabular corundum, it becomes an ideal refractory raw material and is widely used in various types of refractory materials.
In the production process of tabular alumina, after the alumina balls are calcined at a high temperature in a high-temperature shaft kiln, they should be pure white when they leave the kiln, but occasionally mixed with variegated balls. The common colors of these variegated balls are black (gray), rose red, blue, yellow, etc. The cases of black (gray), rose red, and blue balls appear occasionally in small amounts and irregularly; The situation is very different, once it occurs, it lasts for a long time and the number is large. These yellow balls are mixed into the white tabular corundum, which will affect the appearance of tabular alumina products. If they are used in fired refractory products, they will also affect the appearance of refractory products.
(1) The rose red particles, blue particles and black (gray) particles appearing in the production of tabular alumina have very high Fe2O3 content. Controlling the stainless steel impurities mixed in the production process can effectively reduce the occurrence of variegated balls such as red, blue and black.
(2) The lower the sulfur content in industrial alumina, the better. Excessive sulfur content will lead to yellowing of the tabular alumina balls, and the larger the crystal growth of tabular alumina balls, the more likely it is that the balls turn yellow.
(3) Among the broken particles of tabular alumina, there is not much difference in physical index and phase composition between yellow particles and white particles.
