Description: In the final analysis, the damage factor of magnesia carbon brick, a refractory material for ladle slag line, is the oxidation of carbon, including gas phase oxidation, liquid phase oxidation, indirect oxidation, and the influence of pores. The detailed analysis is as follows:
Keyword: magnesia carbon brick for ladle furnace
Gas phase oxidation
That is, the direct oxidation of carbon. Graphite is oxidized at high temperature due to coexistence with air (O2), water vapor (H2O) and carbon dioxide. Graphite begins to oxidize significantly above 560°C, which causes decarburization of carbon-containing products. In the decarburization zone, many diffusion channels are formed due to the oxidation of carbon. Oxygen and slag enter the brick through the diffusion channels. Reaction, the reaction product diffuses out through the diffusion channel. At 1000°C, the system mainly exists in the form of CO gas, and the generated CO gas diffuses outwards, preventing the entry of O2 and other gases, thereby acting as a gaseous “antioxidant”, so carbon can exist stably, but It may be oxidized by air during cooling after tapping. At the same time, there is a slag layer on the surface of the lining brick of carbon-containing products, which can prevent the oxidation of carbon caused by air and play the role of a protective film. This protective effect is especially obvious above 1000 °C.
Liquid Phase Oxidation
MgO + C = Mg + CO
Refers to the oxidation of carbon caused by iron oxides and manganese oxides in the slag. Usually, the slag contains a large amount of iron oxide during the smelting process. With the increase of the total iron content in the slag, the damage rate of MgO-C lining bricks becomes larger. At the same time, after the decarburization layer is formed on the surface of carbon-containing products, the slag easily penetrates and reacts with the particles, which promotes the dissolution and dissolution of the particles into the slag, resulting in loose structure and accelerated product damage.
Indirect oxidation
The reaction between MgO and carbon at high temperature forms a decarburization layer, which leads to the deterioration of the structure of magnesia-carbon bricks, promotes the erosion of slag to the decarburization layer, and reacts with magnesia to form a reaction layer. Cause erosion and erosion. The standard free energy of formation of MgO(s) and CO(g) is equal at 1850°C, and they are in equilibrium at 1850°C, that is, these four substances coexist. But the above condition is that both PMg(g) and PCO(g) are 1 atm, and in practical application, PMg(g) is very low, so MgO(S) and C(S) start to react at very low temperature. This is extremely harmful to the damage of magnesia carbon bricks.
Influence of porosity on damage of magnesia carbon bricks (h3)
The pores in magnesia carbon bricks, especially the open pores, have an important influence on the damage of magnesia carbon bricks. During the use of magnesia carbon bricks, the oxidative damage of carbon is mainly promoted through pores, which in turn intensifies the erosion of slag on the brick lining, resulting in damage to magnesia carbon bricks. The open pores in the brick absorb air from the outside when it is cooled, and the oxygen in the air reacts with the surrounding carbon to generate CO to be discharged when it is reheated. This process repeats itself and increases the porosity. In addition, the binder present in the magnesia carbon brick is an important factor for the generation of pores. As a binder for magnesia-carbon bricks, generally 3% to 4% of phenolic resin is added, and the porosity after molding is as low as about 3%. However, during use, the phenolic resin is heated and decomposed to produce H2O, H2, CH4, CO, CO2 and other gases to evaporate and discharge, and the passage of gas evaporation forms pores, which also increases the porosity. In this way, the oxygen in the air and the oxides in the slag erode the brick through the pores, which promotes the oxidation and damage of carbon on the one hand, and intensifies the reaction between the slag and MgO in the brick on the other hand, resulting in the magnesia carbon brick. damaged.