Magnesium-chromium refractory is a refractory mainly composed of magnesia and supplemented by chromite. Depending on the process and raw materials, magnesia-chromium refractories form different degrees of secondary composite spinel and periclase-secondary spinel composites during the cooling process, forming a structure of magnesia-wrapped chrome ore.
Magnesium-chromium refractories will produce harmful chromium-containing compounds (Cr6+) under the current state of production and use. This compound is a strong carcinogen and has strong corrosion to human skin, mucous membranes and upper respiratory system. effect. However, magnesia-chromium refractories are still widely used in copper smelting industrial systems due to their high strength, good volume stability and slag corrosion resistance in high temperature environments.
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Special failure mechanism of magnesia-chromium refractory bricks for copper smelting
Although different oxides in magnesia-chromium refractory bricks for copper smelting can also affect the properties of the material to a certain extent, and thus the destruction of heterogeneous materials, such as chromium oxide, alumina, zirconia, etc., magnesia-chromium refractory bricks for copper smelting The special failure mechanism of high-quality refractory bricks lies in the special damage of copper slag, iron-silicon slag and sulfur elements to the material. First, copper slag and copper melt can gradually penetrate into the interior along the pores of magnesia-chrome brick, and the slag and The copper melt fills the pores and cracks, causing thermal breakdown of the furnace lining and expansion and spalling.
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Secondly, for the special damage of iron-silicon slag, MgO in magnesia-chromium brick and FeO in slag generate magnesia-iron spinel solid solution. With the increase of SiO2 content in the brick body, magnesia-iron solid solution is gradually replaced by low melting point magnesium The fayalite is replaced, and the periclase is eroded by the iron-silicon slag, thereby forming the structure of the main crystal phase magnesia-chromium spinel in the forsterite and forsterite; and the viscosity of the iron-silicon slag is relatively low, and the magnesia-chromium brick The iron-silicon slag infiltrated into the medium forms a continuous network, forming a metamorphic layer. The metamorphic layer causes the thermal expansion of the brick body to be different. Cracks are formed in the brick body and gradually expand, resulting in the peeling of the brick body, and SO2 is oxidized when migrating in the brick body. The reaction generates SO3, and with alkaline oxides, low-melting alkaline metal salts are formed. The density of the reaction product is small, which leads to an increase in volume, which intensifies the penetration and erosion of the slag. Most experts and scholars believe that the main reason for the failure of magnesia-chromium bricks is due to iron-silicon slag.
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For the special destruction of sulfur element:
1. At 1500°C, when the sulfur content in the slag is relatively high, in the process of SO2 magnesia-chrome brick migration, there is a process in which sulfate is generated first and then decomposed, which will cause the expansion of the pores of the brick body and structural changes. Loosening and deepening the erosion of magnesia-chromium refractories by converter copper slag: the presence of an appropriate amount of CaO can absorb SO2 gas and reduce the generation of MgSO4, while a small amount of MgSO4 is generated, and when the porosity is large, the volume expansion caused by it will not destroy The structure of the brick body actually blocks the pores and prevents the further erosion of the magnesia-chromium refractory brick by the converter copper slag.
2. At 1300°C, the corrosion resistance of the directly combined magnesia-chrome brick is better than that of the fused semi-recombined magnesia-chrome brick. to be superior;
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These results show that the selection of refractory bricks needs to consider many factors in the process of erecting copper converters. For general copper smelting converters, since the working temperature is generally 1100~1300°C, direct-bonded magnesia-chrome bricks are selected at this time. Due to the existence of SO2 gas, the direct-bonded magnesia-chrome bricks with higher CaO content and higher porosity are more suitable. On the contrary, for converters with higher melting temperature, it is advisable to use electro-melting semi-recombined magnesia-chrome bricks with better performance to form electro-melting and re-combined magnesia-chrome bricks.
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