School of Materials and Metallurgy, Northeastern University, Shenyang 110004, China The results show that the MgO dense layer is formed on the surface of the refractory that is in contact with the molten metal and cannot be formed on the surface that is in contact with the slag; the MgO dense layer is formed by Mg(g) that diffuses to the surface of the refractory in the magnesium oxide particle. The surrounding oxides are deposited so that the magnesium oxide particles grow up and are connected to one another.
When used at a high temperature above °C, MgO and C undergo an oxidation-reduction reaction, and Mg(g) and CO gas are generated to loosen the internal structure and cause damage. However, if out-diffused Mg(g) is capable of oxidative deposition on the surface of the magnesium carbon refractory and forms a dense layer of MgO, then the resistance to slag corrosion of the magnesium-based refractories is improved and the redox of MgO and C is effectively suppressed. The reaction will have a significant impact.
With regard to the formation of MgO dense layers in MgO-based refractories, there have been many reports on whether the Mg(g) generated in the interior of the refractory can diffuse to the surface, mainly depending on the partial pressure difference between the Mg(g) inside and the surface of the refractory. . In this. As can be seen from the figure, since Mg(g) has a large concentration gradient in the interior and the surface of the refractory material, Mg(g) generated inside the refractory material will diffuse toward the surface of the refractory material.
In the presence of a molten metal, the equilibrium partial pressure of the refractory surface Mg(g) of the part in contact with the molten metal is determined by the following formula: The oxygen potential in the molten metal and the oxygen potential in the furnace gas should be equal. Therefore, the middle curve (2) can also be regarded as the equilibrium partial pressure of the refractory surface Mg(g) of the portion in contact with the molten metal.
2.3 Formation of compact layer of MgO Mg (g) diffused on the surface of the refractory To discharge from the slag and the molten metal, bubbles must first be formed in the slag and the molten metal. The conditions for bubble formation are as follows: The smaller the diameter, the greater the partial pressure of Mg gas required.
When the surface of the refractory material is in contact with the molten metal, most of the pores on the surface of the refractory material, especially the pores with larger pore diameters, will be immersed in the molten metal due to the better wetting of the molten metal with magnesia and graphite. The volume of pores that can be occupied by the formation and growth of bubbles is relatively reduced. It can be known from formula (6) that the resistance to formation of Mg(g) bubbles is large at this time, and Mg cannot be discharged from the pores in time, when the oxygen in the molten metal When diffused into the pore, it reacts with Mg(g) to form MgO(s). When the pores are surrounded by magnesium oxide particles, the resulting MgO(s) will precipitate on the surface of the magnesium oxide particles, causing the magnesium oxide particles to grow continuously, and finally connecting the adjacent particles to form an MgO dense layer. The formation model of the MgO dense layer is shown.
When the surface of the refractory material is in contact with slag, the slag cannot generally be immersed in the pores on the surface of the refractory material due to the poor wetting of the slag and the refractory material. Therefore, Mg(g) diffused into the surface of the refractory contacting with the slag is easily discharged without forming a dense layer of MgO on the surface.
The magnesium oxide ultrafine particle layer on the outside of the MgO dense layer is presumed to be an ultrafine particle layer of magnesium oxide. In fact, electron probe analysis also showed that the magnesium oxide ultrafine particles contained a certain amount of slag components.
3 Conclusion The MgO dense layer is formed on the surface of the refractory material in contact with the molten metal and cannot be formed on the surface of the refractory material in contact with the slag.
The dense MgO layer is formed by oxidation deposition of Mg(g) diffused on the surface of the refractory material around the magnesium oxide particles, and the MgO particles grow and connect to each other.
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