How are magnesia carbon bricks fired?

Magnesia-carbon bricks are made of fused magnesia (sintered magnesia) and flake graphite (mainly fully crystallized graphite), prepared and pressurized with resin as a binder, and then heat-treated. magnesia brick

In order to improve the oxidation resistance, antioxidants such as metals are often added. When magnesia-carbon bricks are used at high temperature, they form a carbon skeleton bond. Since magnesia and carbon do not have a mutual solubility relationship, they retain the excellent refractory properties of the original components. Carbon has good thermal conductivity, low thermal expansion coefficient and elastic coefficient, which can effectively prevent high temperature spalling and slag infiltration, and is not prone to structural spalling. In addition, the non-wetting of carbon to slag has good corrosion resistance. Electric furnace magnesia carbon brick

This series of properties of magnesia-carbon bricks make it an ideal charge material with good thermal shock resistance, erosion resistance and spalling resistance. Magnesia-carbon bricks are widely used and can be used in key parts of thermal equipment such as steel-making converters, electric arc furnaces, ladles, and refining furnaces outside the furnace. Converter 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, and the damage of magnesia-carbon bricks is caused by the combined action of the following factors:

1. Effect of basicity: The lower the basicity of the slag, the more favorable the erosion of magnesia-carbon bricks. If the basicity of the slag increases, the activity of SiO2 in the slag will decrease, which can reduce the oxidation of carbon. As the temperature increases, the activity of FeO in the slag decreases, which relatively slows down the erosion behavior of slag on magnesia-carbon bricks; ladle magnesia-carbon bricks

2. Influence of MgO: Osbom et al. found that the content of MgO in the slag layer was 30% when analyzing the composition of the LF slag line, and believed that the higher the content of MgO in the slag, the slower the erosion of magnesia-carbon bricks and the higher the basicity. high, which also slows down the erosion of slag on magnesia-carbon bricks.

3. 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 magnesia grain boundary, and make the periclase separate from the magnesia-carbon brick matrix .

4. Influence of FeO: FeO in the first slag is easily oxidized with the graphite in the magnesia-carbon brick at high temperature, and produces 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.

During the repeated heating and cooling of the ladle, the magnesia on the surface of the refractory material is broken due to the inconsistency of thermal expansion rates between the formed low-melting-point magnesia-iron composite product and the mafic ore, 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 not conducive to the life of magnesia-carbon bricks. The first iron FeO accelerates the oxidation of carbon on the surface of magnesia-carbon bricks, and the second is that FeO will react with MgO to make the working surface of magnesia-carbon bricks loose. Under the joint action of the points, the erosion of magnesia-carbon bricks is accelerated.