Magnesia calcium China carbon bricks have many excellent properties and are well used in out-of-furnace refining. However, there are still some problems in the use of magnesia-calcium carbon bricks. This passage we will talk the first problem about that.
1. High temperature reaction of magnesium oxide and resistance to slag penetration
After the temperature reaches 1500 ℃, the MgO in the magnesium calcium carbon refractory matrix （China carbon bricks）is easy to react with the C in the matrix as shown in the following formula, when the temperature reaches 1600 ℃, the reaction becomes violent, in which MgO is reduced to Mg vapor, and C is oxidized to CO gas. Escape from the adobe, causing serious weight loss of the adobe, which is one of the important reasons for the damage of Mg-C bricks.
MgO+C→Mg(g)+CO(g)
In addition, during the use of magnesia-calcium China carbon bricks, SiO2 in the slag first reacts with free CaO to form C2S and C3S. Their formation can increase the viscosity of the slag, making it difficult for the slag to further penetrate into the magnesia-calcium China carbon bricks. However, the graphite on the surface of the brick is oxidized, resulting in decarburization of the surface layer to form voids, so that the slag further penetrates into the brick, and the MgO in the magnesia-calcium sand reacts with the CaO-SiO2 slag to form a MgO-CaO-SiO2 low melting phase, so MgO is magnesium. The weak link of calcium China carbon bricks resistance to slag corrosion.
MgO is the weakest link in magnesium-calcium-carbon refractories, so it is necessary to reduce the content of MgO in magnesium-calcium China carbon bricks, to a certain extent inhibit the weight loss problem caused by the reaction of MgO with C at high temperature; and use CaO to form a continuous phase distribution of magnesia-calcium sand, so that MgO does not react directly with the CaO-SiO2 slag.
Generally, when fused magnesia-calcium sand is selected as the raw material of magnesia-calcium, the CaO grains of the sintered magnesia-calcium sand form a continuous phase to wrap the MgO grains, which can protect the MgO. And the fused magnesia-calcium sand is denser than the sintered magnesia-calcium sand, which also strengthens the slag penetration resistance of the magnesia-calcium China carbon bricks. However, the CaO grains of sintered magnesia-calcium sand are covered by MgO grains, which makes it difficult for CaO to contact the air and thus be hydrated by the water vapor in the air, while the fused magnesia-calcium sand just has the disadvantage of easy hydration of CaO, and sintering Compared with fused magnesia-calcium sand, magnesia-calcium sand is more economical. Therefore, the selection of different types of magnesia-calcium sand raw materials has its own advantages and disadvantages.
