Measures to prolong the service life of magnesia carbon bricks used in slag lines

The researchers fabricated crucible samples of slag-line MgO-C bricks with an inner diameter of 60 mm x 50 mm and an outer diameter of 120 mm x 100 mm. They then placed low-iron LF slag and high-iron LF slag into the crucibles, held at 1600°C for 3 hours, and used the static crucible method to test the slag-erosion resistance of the MgO-C bricks. They ground two types of LF furnace slag into a 200-mesh fine powder and, using thermoplastic phenolic resin as a binder, pressed the powder into cylindrical samples measuring 6 mm x 5 mm. These samples were placed on a gasket made of slag-line MgO-C bricks and placed in a DRH-III refractoriness tester. The wetting angle between the slag and the MgO-C bricks was measured when the samples reached hemispherical temperature, thereby characterizing the wetting properties of the slag on the MgO-C bricks.

The researchers further discovered that LF slag first wets the surface of the magnesia carbon brick, then penetrates into the matrix of the magnesia carbon brick along the pores left after graphite oxidation, fills around the magnesia sand particles, and chemically erodes and dissolves the magnesia sand particles to produce a low-melting-point liquid phase containing Ca, Si, and Al, which gradually erodes the magnesia sand particles. From this, it can be inferred that as the reaction time increases, a cemented structure will form in the magnesia carbon brick, the magnesia sand particles will be embedded in the liquid phase, and the edges of the magnesia sand particles will be dissolved by the slag, becoming smooth, resulting in a significant difference in the composition and properties of the eroded layer and the original brick layer of the magnesia carbon brick, especially the thermal expansion coefficient. When subjected to thermal shock and thermal shock during use, the working surface of the magnesia carbon brick will peel off and be damaged. Under the conditions of LF refining outside the furnace, due to the high refining temperature, the viscosity of the slag is reduced, and the temperature inside the furnace lining is also high, the slag can penetrate deeper into the refractory material, forming a thicker reaction layer, which will aggravate the melting loss of the magnesia carbon brick lining and cause serious peeling and damage. Therefore, the impact of LF slag on MgO-C bricks is mainly manifested as chemical erosion and the resulting poor thermal shock stability, resulting in spalling damage.

Carbon products are another type of neutral refractory material. Based on the composition of the carbon-containing raw materials and the mineral composition of the finished product, they are divided into three categories: carbon bricks, graphite products, and silicon carbide products. Carbon bricks are made from high-grade petroleum coke, with tar and asphalt as binders, and fired at 1300°C in an airless environment. Graphite products (except natural graphite) are made from carbon materials through a graphitization process in an electric furnace at 2500-2800°C. Silicon carbide products are made from silicon carbide, with binders such as clay and silicon oxide fired at 1350-1400°C. Silicon carbide can also be combined with silicon powder in an electric furnace under a nitrogen atmosphere to create silicon nitride-silicon carbide products.

Carbon products have a very low coefficient of thermal expansion, high thermal conductivity, excellent thermal shock resistance, and high-temperature strength. They remain resistant to long-term use at high temperatures, are resistant to acid and alkali corrosion, have excellent salt resistance, and are not wetted by metals or slag. Their lightweight nature makes them excellent high-temperature resistant materials. Its disadvantage is that it is easily oxidized at high temperatures and is not suitable for use in oxidizing atmospheres. Carbon products are widely used for linings of high-temperature furnaces (such as the furnace bottom, hearth, and lower portion of the furnace body) and for smelting non-ferrous metals. Graphite products can be used to line reactor tanks and autoclaves in petrochemicals. Silicon carbide and graphite products can also be made into crucibles for smelting copper, gold, and light alloys.

Magnesia Carbon Bricks