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Research progress on oxidation resistance of low carbon magnesia carbon bricks

Desicription: In recent years, low-carbon magnesia-carbon bricks using nanotechnology have been greatly developed. LMM engineers conducted research on the oxidation resistance of low-carbon magnesia-carbon bricks.

Title: Research progress on oxidation resistance of low carbon magnesia carbon bricks

Keywords: Low carbon, magnesia carbon brick, oxidation resistance, research progress

The low-carbon magnesia-carbon bricks used can be roughly divided into two categories:

① Under the conditions of use, low-carbon magnesia-carbon bricks combined with nano-carbon fibers are formed in situ. The wc =1% in this kind of brick, the service life on the VOD ladle is twice that of the traditional magnesia chrome brick;

②Nano-structured matrix low-carbon magnesia-carbon brick, wc=3%5% in the brick. In Japan, this kind of brick has been widely used in RH refining furnace as a substitute product of magnesia chrome brick, and its service life is obviously better than traditional magnesia chrome brick.


Great progress has also been made in the development and application of low-carbon magnesia carbon brick in China. Al powder was added to low carbon magnesia carbon brick, and its effect on the oxidation resistance of the material was studied. It is found that when the content of metal Al powder is less than 6wt%, the oxidation resistance of the material increases with the increase of Al powder. The added metal Al powder will eventually react with the substances in the material to form magnesium aluminum spinel, so as to form a dense layer in the decarburization layer. In the oxidation process, the dense decarburization layer can inhibit the further invasion of gaseous or liquid oxidizing substances into the material. Therefore, the greater the amount of metal Al powder added and the more spinel generated, the thicker the dense layer generated, the stronger the ability to prevent oxidizing substances from further invading the interior of the material, and the better the oxidation resistance of the material.

The research shows that if the low carbonization of carbon containing refractory can be realized, the oxidation resistance of the material can also be improved. Compared with the materials with higher carbon content, the spacing between MgO particles in the materials with lower carbon content is smaller, and it is easier to form MgO rich dense layer (protective layer) on the working surface of the material, which can make the oxidized tissue more dense, further hinder the transmission of oxidizing atmosphere, and inhibit the oxidation of carbon in the material.

For magnesia carbon refractories with low carbon content, the effect of oxidation process on the microstructure is also relatively small. Compared with magnesia carbon bricks with high carbon content, the distance between magnesia particles in low-carbon magnesia carbon refractories is smaller, which is beneficial to form MgO rich dense layer and improve the oxidation resistance of materials by adding antioxidants.

LMM engineers studied the effect of adding MgB2 to magnesia carbon refractories. It is found that when the temperature is higher than 1000 ℃, MgB2 reacts with CO to form MgO, C and B2O3, and MgO reacts with B2O3 to form mg3b2o6; When the temperature is higher than 1340 ℃, mg3b2o6 melts into liquid phase and is filled between MgO aggregate and matrix, which makes the structure of MgO-C refractory compact and is beneficial to improve the oxidation resistance of the material;

In addition, B2O3 (L) will react with MgO to form mg3b2o6, forming a dense layer on the surface of magnesium carbon refractory to inhibit the oxidation of the material. The antioxidant effect of MgB2 is lower than that of B4C, which is better than that of metal Al powder and elemental Si powder. The optimal addition of MgB2 in magnesia carbon refractory is about 3wt%. It is also found that adding Al + 10wt% MgB2 to magnesia carbon refractories has achieved good antioxidant effect.

LMM engineers have studied the synthesis of SiC-Al2O3 composite powder and its application in low-carbon magnesia carbon brick. It is found that adding SiC-Al2O3 composite powder to low-carbon magnesia carbon brick can significantly improve its corrosion resistance and permeability to oxidizing slag. This is because the particles of the added SiC-Al2O3 composite powder are very small. When the slag is in contact with the refractory, the Al2O3 in the added SiC-Al2O3 composite powder is easy to integrate into the slag, and the SiC particles in the composite powder also enter the slag together. Because the solubility of SiC in oxide slag is very small and the reaction speed between SiC and slag is very slow, SiC particles exist in the slag in the form of solid phase, which increases the apparent viscosity of slag and delays the corrosion of slag to refractory. However, the addition of SiC-Al2O3 composite powder has little effect on its oxidation resistance.

LMM engineers studied the preparation of Al4SiC4 and its effect on the oxidation resistance of magnesia carbon brick. It was found that when the addition amount of Al4SiC4 was 3 ~ 5wt%, the carbon loss decreased by 50 ~ 60wt% (1500 ℃, 6h).

Al4SiC4 can reduce the oxidized carbon and add its own C as free C to magnesia carbon brick to supplement the carbon source. In addition, Al2O3 and SiC generated by Al4SiC4 decomposition react with MgO to finally generate magnesia alumina spinel and forsterite, so as to form a protective layer on the surface of the brick to prevent further oxidation of the material.

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