Silica powder
The anti-oxidation mechanism of adding Si powder is: in magnesia-carbon refractory materials, the added Si powder will react with C(s) in the environment to form β-SiC. When the heat treatment temperature exceeds 1100°C, this reaction will be violent occur. When the heat treatment temperature is around 1200°C, Si will also react with N2 in the environment to form Si3N4. In addition, when the heat treatment temperature is in the range of 1100℃-1500℃, glassy SiO2 will also be generated. SiC and Si3N4 in the material react with CO to generate SiO(g), which will be further oxidized to generate SiO2, which is deposited in the pores. , blocks the pores, reduces the diffusion flow of oxidizing gas, thereby improving the oxidation resistance of magnesia carbon bricks; when the heat treatment temperature is higher than 1500°C, Si will eventually generate forsterite, and M2S will also block the pores, while also Will increase the strength of the material.
silicon carbide powder
The anti-oxidation mechanism of adding SiC is as follows: SiC is added to magnesium-carbon refractory materials. Although SiC cannot be oxidized prior to C to improve the oxidation resistance of the material, the process of SiC being oxidized to SiO2 is accompanied by a large volume expansion. At the same time, SiC will eventually be converted into forsterite phase and deposited in the pores, blocking the pores, reducing the diffusion flow of oxidizing gases, and improving the oxidation resistance of magnesia-carbon refractory materials.
Aluminum powder
The anti-oxidation mechanism of adding Al powder is as follows: in magnesia-carbon refractory materials, when the heat treatment temperature is 660°C, the added metal Al powder reacts with the carbon in the material or nitrogen in the air to generate Al4C3 and A1N. These two substances will transform in a CO atmosphere, namely Al→Al4C3→Al2O3, Al→AlN→Al2O3, Al→Al4C3→AlN→Al2O3. And no matter which process occurs, it will eventually be converted into the stable phase Al2O3. On the one hand, this change process is accompanied by changes in gas phases such as Al(g), Al2O(g), AlO(g), A1O2(g), A1N(g), and A1C(g), which can block pores and reduce the material’s The apparent porosity makes the material structure more dense and reduces the effective contact area between oxidizing gas and the material. On the other hand, A1 and Al4C3 will react with CO, releasing C and Al2O gas, and Al2O(g) will continue to diffuse outward. When the gas diffuses to the surface of the refractory material, due to the high oxygen partial pressure, Al2O(g) will It is transformed into Al2O3 and deposits in the pores to form a protective layer. At the same time, it blocks the pores, inhibits further diffusion of gas, and plays an antioxidant role. Al2O3 will also react with MgO in the material, and the resulting magnesia-aluminum spinel, MA, will also block the pores and improve the oxidation resistance of the material.