(1) Erosion of slag on magnesia carbon bricks:
In the ladle, due to the complex physical and chemical environment of the slag line, the lining of slag is most easily damaged. The chemical erosion of magnesia by the slag mainly through the dissolution of magnesium oxide and the oxidation of carbon in the matrix of magnesia carbon brick. Under the combined effect of the following factors, the damage of magnesia carbon bricks is caused:
1. The effect of alkalinity: the lower the alkalinity of the slag, the more favorable the erosion of the magnesia carbon brick. If the alkalinity of the slag is increased, the activity of SiO2 in the slag is lowered, the oxidation of carbon can be reduced, and the alkali degree increases, the activity of FeO in the slag decreases, which relatively slows the erosion behavior of the slag on the magnesia carbon brick.
2. The influence of MgO: When the composition analysis of the LF slag line was carried out, it was found that the content of MgO in the slag layer was as high as 30%, and the higher the content of MgO in the slag, the slower the erosion of the magnesia carbon brick and the higher the alkalinity. Also, the erosion of the slag on the magnesia carbon bricks is slowed down.
3. The influence of Al2O3: Al2O3 in the slag will reduce the melting point and viscosity of the slag, increase the wettability of the slag and the refractory material, make the slag more easily penetrate from the grain boundary of the magnesia, and remove the magnesite from the magnesia carbon brick matrix.
4. The influence of FeO: Firstly, FeO in the slag is easily oxidized with graphite in magnesia carbon brick at high temperature, and produces bright white iron beads to form a decarburized layer; then the periclase in the magnesia carbon brick is also in the same slag. The FeO reaction produces a low melting point product. During the repeated heating and cooling of the ladle, the thermal expansion coefficient between the formed magnesium iron composite low melting point product and the mafic iron is inconsistent, causing the magnesium oxide on the surface of the refractory material to be broken, thereby causing the dissolution of the brick body. Foreign scholars also believe that the increase of iron content in steel slag is not good for the life of magnesia carbon brick. First, iron FeO accelerates the oxidation of carbon on the surface of magnesia carbon brick, followed by FeO reaction with MgO, which makes the structure of magnesium carbon brick work surface loose. The combination of points will accelerate the erosion of magnesia carbon bricks.
(2) Oxidation of carbon in magnesia carbon bricks:
When the magnesia carbon bricks is in contact with the slag, the carbon will decarburize with the oxide such as FeO in the slag, and the decarburization layer is formed under certain conditions, so that the structure of the working surface of the magnesia carbon brick is loose, which is damaged by the magnesia carbon brick. main reason. The carbon reacts with oxides such as CO2, O2 and SiO2 and is continuously oxidized by the iron oxides in the slag; the loose structure formed by the second decarburization layer generates larger cracks and voids under the action of thermal expansion and slag, so that the slag is easily infiltrated. And forming a low melting point phase with MgO, and at the same time, the surface layer structure of the magnesia carbon brick changes under the action of the mechanical agitation of the molten pool and the violent erosion of the steel slag, and eventually the outer layer is gradually damaged, causing the magnesia carbon brick to be seriously damaged. After the temperature exceeds a certain value, the brick structure will be damaged and then sharply eroded, which is due to the self-consumption of MgO and graphite at high temperature.
(3) Influence of stomata
The erosion of magnesia carbon bricks is more likely to occur due to the presence of micropores inside and on the magnesia carbon brick. During the use of magnesia carbon bricks, the pores play an accelerating role in the formation of the decarburization layer, which in turn makes the erosion of the slag on the refractory polishing of the magnesia carbon bricks more serious. The outside air enters the pores in the magnesia carbon brick for cooling, and the oxygen in the air reacts with the surrounding carbon to produce CO gas and is discharged through the micropores. The continuous occurrence of the two processes causes the porosity and the pore size to gradually increase. The most important factor in the generation of pores is the choice of binder in magnesia carbon bricks. The binder is generally selected from phenolic resins. If a small amount of phenolic resin is added to the magnesia carbon brick, the porosity will not be too high in the cold state of about 3%, but the phenolic resin will decompose to produce water, argon, methane, carbon monoxide, carbon dioxide and the like after heating. And pores are formed under the flow of these gases, increasing the porosity. Therefore, the magnesia carbon brick is eroded by the slag passing through the pores, so that the oxidation of carbon and the dissolution of MgO are more intense, thereby causing damage to the magnesia carbon brick. Due to the repetitive nature of the gas generation process, the damage of magnesia carbon bricks is increasing.
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Article Source:Erosion mechanism of magnesia carbon brick in slag in LF
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