Magnesia-carbon bricks are made of fused magnesia (sintered magnesia) and flake graphite (mainly crystallized graphite) as raw materials, using resin as a binding agent to prepare and press, and heat treatment. Electric furnace magnesia carbon brick
In order to improve the oxidation resistance, anti-oxidants such as metals are often added. Magnesia-carbon bricks form a carbon skeleton bond when used at high temperatures. Because magnesium oxide and carbon do not have a mutual soluble relationship, the excellent fire resistance of the original components is retained. Carbon has good thermal conductivity, low thermal expansion coefficient and low elasticity coefficient, which can effectively prevent high temperature spalling and slag penetration, and is not prone to structural spalling, which greatly changes the fatal weakness of degraded structure spalling caused by slag penetration of magnesia refractories. Coupled with the non-wetting of carbon to the slag, the corrosion resistance is also good.
These series of characteristics of magnesia carbon brick make it an ideal charge material with good thermal shock resistance, corrosion resistance and spalling resistance. Magnesia-carbon bricks have a wide range of uses, and can be used in key parts of thermal equipment such as steel-making converters, electric arc furnaces, ladles, and out-of-furnace refining furnaces. Converter magnesia carbon brick
Electric furnace magnesia carbon brick
The chemical attack of slag on magnesia-carbon bricks is mainly through the dissolution of magnesia and the oxidation of carbon in the matrix of magnesia-carbon bricks. Under the combined action of the following factors, the magnesia-carbon bricks are damaged:
1. The effect of alkalinity: the lower the alkalinity of the slag, the more beneficial it is to the erosion of magnesia carbon bricks. If the alkalinity of the slag increases, the activity of SiO2 in the slag will decrease, which can reduce the oxidation of carbon. With the increase of the temperature, the FeO activity in the slag decreases, which relatively slows down the corrosion behavior of the slag on the magnesia carbon brick;
2. The influence of MgO: When analyzing the composition of the LF slag line, Osbom et al. found that the MgO content in the slag layer was 30%. High, also slows down the erosion of magnesia carbon bricks by slag.
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 refractory materials, make the slag easier to penetrate from the magnesia grain boundary, and make the periclase separate from the magnesia carbon brick matrix .
4. The influence of FeO: FeO in the first slag can easily oxidize with the graphite in the magnesia-carbon brick at high temperature, and produce bright white iron beads to form a decarburized layer. Secondly, the periclase in the magnesia-carbon brick will also be in the slag. The FeO reaction produces low melting point products.
In the process of repeated heating and cooling of the ladle, due to the inconsistency of the thermal expansion rate between the formed mafic composite low melting point product and the mafic ore, the magnesium oxide on the surface of the refractory material is broken, which in turn leads to the dissolution of the brick body. Foreign scholars also believe that the increase of iron content in steel slag is detrimental to the life of magnesia-carbon bricks. Iron FeO accelerates the oxidation of carbon on the surface of magnesia-carbon bricks, and then FeO reacts with MgO to loosen the structure of the magnesia-carbon brick working surface. The joint action of the magnesia carbon bricks accelerates the erosion.
