Characteristics and Applications of Magnesia-Carbon Bricks
2025-11-04 09:27:20
Magnesia-carbon bricks are made from dead-burned or fused magnesia and carbon materials (mainly fully crystalline graphite) as raw materials, formulated with resin as a binder, and then heat-treated. To improve oxidation resistance, metals or other antioxidants are often added to magnesia-carbon bricks. The melting points of refractory oxides in magnesia-carbon bricks, as well as MgO forming composite oxides or binary systems with some oxides, vary. Among all commonly used refractory oxides, MgO has the highest melting point, and it can form high-melting-point compounds or solid solutions with many oxides or components in slag. The eutectic temperature of binary systems formed by MgO and some oxides is also very high. Therefore, MgO-containing magnesia-based refractories are the preferred refractory materials for steelmaking.
With the development of iron and steel smelting, the magnesia-based refractories used are mostly magnesia-composite materials, such as magnesia-carbon bricks, magnesia-calcium-carbon bricks, magnesia-calcium bricks, magnesia-alumina spruce bricks, and magnesia-chrome bricks.
Magnesia refractories have a long history of application, but magnesia bricks have a high coefficient of thermal expansion, making them prone to spalling during use. Magnesia-carbon bricks were developed by adding graphite to magnesia bricks. Because graphite has a low coefficient of thermal expansion and is not easily wetted by slag, it can improve the spalling resistance of magnesia-carbon bricks and slow down the penetration of slag into the brick interior, thus improving its erosion resistance.
Currently, magnesia-carbon bricks are widely used in steelmaking furnaces and ladles. Some attribute the role of carbon in preventing slag penetration to the following reasons:
(1) The wetting angle between carbon and slag is large, preventing carbon from being wetted by slag;
(2) Iron oxide in the slag is reduced to metal, increasing the viscosity of the slag.
In my country and Japan, except in special cases, resin-bonded magnesia-carbon bricks with a carbon content of 12% to 20% are generally used. In Europe, bitumen-bonded magnesia-carbon bricks are more commonly used, with a carbon content generally around 10%. Low-carbon magnesia-carbon bricks generally refer to a type of material with a total carbon content of no more than 8%, which is made of magnesia sand and graphite bonded together by an organic binder.