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Refractory materials containing Cr2O3 have good high temperature corrosion resistance. Among all the oxide additives for refractory materials found so far, Cr2O3 can be said to be one of the most superior in performance. The main reasons for the superior corrosion resistance of Cr2O3 are:
1) Cr2O3 can form a solid solution with some main oxides in refractory materials to form a solid solution with a high melting point and a low eutectic point.
2) The main reasons for the damage caused by the interaction between refractory castables and high-temperature melts can be summarized as follows:
Mechanical action, slag chemical erosion and thermal stress, usually the damage of refractories is the result of the combined action of the three. Mechanical action mainly refers to the erosion and wear of refractory materials by furnace charge, high-temperature melt and high-temperature airflow; chemical erosion refers to the damage caused by chemical reactions, and refractory materials will be in contact with slag, melt, smoke Physical and chemical reactions occur when gas and dust and other substances cause its structure to be destroyed. The main process is the dissolution and infiltration of the liquid phase, and the main manifestations are infiltration, slag erosion and dissolution.
Cr2O3 can reduce the wettability of slag to refractory materials, reduce the erosion of slag to refractory materials, and at the same time reduce its penetration on refractory materials. Li Yong et al. studied the contact angles of 61.5%SiO2-17.8%Al2O3-20.7%MgO slag on magnesia refractories and magnesia chromium-containing refractories respectively, and found that after holding at 1370°C for 2 hours, the slag on chromium-containing refractories The contact angle on the surface is larger, indicating that the wettability of the slag to it is poor.
The erosion of slag on refractory materials is mainly through penetration into the refractory material to form an erosion layer. When the temperature changes drastically, the minerals in the erosion layer expand and generate structural stress, resulting in the formation of cracks inside the material, resulting in refractory Structural spalling of material. When a certain amount of Cr2O3 is added to the refractory material, it can effectively reduce the penetration of slag in the refractory material, even the copper smelting slag containing S and O with strong penetration ability can also play the same role, thereby reducing The resulting spalling of the structure.
When the refractory material contains Cr2O3, it will interpenetrate with the slag, and Cr2O3 will affect the viscosity of the slag after entering the slag. Wang Chengxun and others studied the relationship between the viscosity of silicate slag and the content of Cr2O3, showing that Cr2O3 not only has a low solubility in silicate slag, but also significantly increases the viscosity of slag and reduces the fluidity of slag, so it can reduce slag. Corrosive action on refractory materials. The increase of the viscosity of the slag can slow down its penetration to the refractory material and reduce the formation of a permeable layer in the refractory material, thereby reducing the structural spalling of the refractory material. Therefore, chromium-containing refractories are widely used in non-ferrous metallurgy, iron and steel metallurgy, coal-water slurry gasifier and glass industry. Among all basic refractory materials, chromium-containing refractory materials are regarded as the best performing refractory materials.
Although chromium-containing refractories have excellent performance, their usage has been greatly reduced since the late 1980s, mainly because the trivalent chromium in Cr2O3 may be oxidized to be toxic during the service of chromium-containing refractories. Hexavalent chromium, which is very harmful to the human body and the environment. People began to use some chromium-free refractory materials instead of chromium-containing refractory materials, but in some environments with harsh service conditions, chromium-containing refractory materials are still irreplaceable because of their excellent performance, such as the high-temperature firing zone of cement rotary kiln, Chromium-containing refractories are still widely used in the lining of refining furnaces outside the furnace, coal-water slurry gasifiers, etc.
In the cement industry, in order to reduce the pollution of hexavalent chromium, people have used dolomite, iron-aluminum spinel, magnesium dolomite, magnesium-aluminum spinel and magnesium-calcium-zirconium refractories to replace the original magnesium-chromium refractories. But its effect is all unsatisfactory, and there is one or another problem that has not been solved yet. First of all, materials such as dolomite, magnesia dolomite and magnesia aluminum spinel have poor kiln skin performance and high thermal conductivity. The use of refractory materials made of these materials will increase the overall temperature of the furnace shell by 20-50 ℃, affecting the kiln itself. The overall structure of the dolomite also increases the requirements for tire expansion compensation; secondly, due to the high content of active calcium oxide in dolomite, which is easy to absorb water and hydrate, there are special requirements in the process of transportation and storage, especially The hydration of dolomite is particularly serious during the shutdown of the cement rotary kiln; although the iron-aluminum spinel refractory material has excellent kiln skin-hanging properties, the change in the atmosphere of the cement rotary kiln will cause the iron to refractory in the second phase during use. The transition between valence and trivalence leads to the loosening of the structure of refractory materials, which affects the normal use of refractory materials. Based on the above reasons, magnesium-chromium refractories are still widely used in the high-temperature firing zone of cement rotary kilns due to their advantages such as high-temperature strength and good kiln skin hanging performance.
In the iron and steel industry, chrome-free environment-friendly refractory materials can be used in many parts, but the refractory materials in some places are severely eroded by molten steel and slag or need to withstand severe temperature changes and environmental atmosphere changes, such as furnace In the external refining furnace, ordinary refractory materials are difficult to resist steel erosion and atmosphere changes.
In the non-ferrous metallurgical melting furnace, compared with the traditional steelmaking furnace, the non-ferrous metal melting furnace has a higher oxygen partial pressure. Although magnesia-carbon refractories have shown good performance in converters, due to the high oxygen partial pressure in non-ferrous metallurgical smelting furnaces, magnesia-carbon refractories are easily oxidized and damaged. In contrast, chromium-containing refractory materials are ideal refractory materials for non-ferrous metal smelting furnaces because of their good slag resistance and high temperature strength.