Magnesium refractory materials have high refractory performance and are alkaline (MgO melting point 2805 ℃), thus having good resistance to alkaline slag. However, due to their high coefficient of linear expansion ((14-15) X 10-6 ℃ -1, 0~1500 ℃), their thermal conductivity is low at high temperatures (λ Mg0100 ℃=34.33 W/(m · K), λ Mg01000 ℃=6.70 W/(m · K)), and their resistance to thermal spalling is poor. Graphite is difficult to wet by slag, has good melting resistance (graphite melting point>3000 ℃), and has a small coefficient of linear expansion (3.34 × 10-6 ℃ -1, 25-1600 ℃). It also has excellent thermal conductivity (λ graphite, 1000 ℃=229W/(m · K)), making it resistant to thermal peeling, but prone to oxidation. The significant oxidation starting temperature TA of flake graphite is generally above 580 ℃. Introducing graphite into magnesium refractory materials improves their slag resistance and peel resistance.
When magnesia and graphite are combined to make magnesia carbon bricks, magnesia carbon refractory bricks exhibit excellent slag resistance, iron corrosion resistance, permeability, and thermal shock resistance. The main reason is:
(1) The matrix of magnesia carbon brick is mainly composed of graphite and magnesia powder. The graphite and magnesia particles, as well as the magnesia particles, are surrounded by a strong carbon carbon bonding network, which is not easy to slip. There is no eutectic relationship between C and MgO, and no liquid phase is produced. Only a small amount of liquid phase is generated by the impurities introduced by the graphite and magnesia raw materials. Therefore, during use, when the highly permeable * * * in the slag encounters carbon, it will be reduced to metallic iron. Due to the reducing effect, the melting point and viscosity of the slag increase, and the permeability is greatly reduced.
(2) The non wettability of slag and molten iron with graphite. Because the contact angle between slag and molten iron and graphite is above 90 °, the magnesium carbon brick made has excellent resistance to slag erosion.
(3) The protective effect of forming a dense square magnesium layer inside the magnesia carbon brick material; At temperatures above 400 ℃, MgO in magnesia reacts with carbon to generate Mg vapor. The Mg vapor flows out through the pores and reacts with FeO in the slag at the interface in contact with the slag, producing magnesium oxide again and forming a dense layer of magnesia, thereby preventing the infiltration of the slag.
(4) The influence of CO gas pressure. The infiltrated slag reacts with the carbon in the magnesia carbon brick to generate CO gas, and the pressure in the pore channel can reach over 0.2 MPa (2 atm), which can prevent or delay the infiltration of slag into the pores.
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