Views: 96 Author: SEPPE Publish Time: 2021-04-22 Origin: SEPPE Technologies
Among unshaped refractories, bauxite clinker is commonly used to process refractory aggregates and powders.
First of all, what is bauxite clinker.
It is made of bauxite ore calcined at a high temperature of 1450℃-1600℃. The content of Al2O3 should be greater than 50%. Its main mineral composition is mullite, α-corundum and trace cristobalite.
Second, the chemical and mineral composition of bauxite.
The chemical components of bauxite are mainly Al2O3, SiO2, Fe2O3, and TiO2, which account for about 95% of the total composition. The minor components are CaO, MgO, K2O, Na2O, MnO2 and trace organic matter. The mineral composition of bauxite mainly consists of diasporite, boehmite, gibbsite and a small amount of sillimanite series, kaolinite and other minerals.
Third, the calcination of bauxite (the formation of bauxite clinker).
The heating change of raw bauxite mainly has three stages:
⑴Decomposition stage (400-1200℃), in this stage, diasporite dehydration forms the corundum pseudomorph, kaolinite dehydration forms metakaolinite, and metakaolinite is transformed into mullite and cristobalite. At this stage, there is a large volume shrinkage.
⑵Secondary mulliteization stage (1200-1400℃ or 1500℃). Above 1200℃, corundum formed from diasporite dehydration and free SiO2 decomposed from kaolinite continue to react to form mullite. This process is called Second Morai Petrochemical. This stage is accompanied by a volume expansion of about 10%.
⑶ Recrystallization stage (1400-1500℃). Above 1400-1500℃, the secondary mulliteization in bauxite has completed and entered the recrystallization stage. The crystals of mullite and corundum become larger, and the pores shrink and disappear. The impurities form a liquid phase and fill the pores in the material block. Due to the dissolution and crystallization of the solid phase in the liquid phase and the diffusion between solid phase molecules, the material block gradually becomes dense.
Identification of bauxite clinker.
Through physical and chemical analysis.
Choose alumina clinker with high aluminum content and less impurities. Impurities such as TiO2, K2O, and CaO must meet the index requirements. These impurities will increase the liquid phase and affect the high-temperature mechanical properties of alumina clinker. Body density and water absorption are also very important indicators, especially water absorption, which reflects whether the bauxite clinker is calcined completely. If the calcination is not complete, undersintering material will be generated (undersintering materials are more harmful to the product, and if there are undersintering materials, indicating that the first and second stages of sintering have not completed the reaction, volume shrinkage and expansion have not been completed. Such as using under-fired materials , will bring a large volume change to the product), will seriously affect the product performance.
However, it is impossible to do physical and chemical analysis of every piece of material. The following are some of our commonly used and effective identification methods:
One. Look, observe the appearance, if it is whitish, blue or off-white, it means that the aluminum content is high; if it is brownish yellow or light red, it contains more iron; observe the cross section, it is dense and there are no visible pores, it means bauxite Calcined completely, no undersintering material;
Two. Touch, hold it in your hand, if it feels heavy, it means it is dense and has a high aluminum content;
Three. Lick, lick the smooth side of the broken bauxite clinker with your tongue. If you can feel the tongue being sucked, it means that the quality of the bauxite material is good and the calcination process is complete.