Low carbon magnesia carbon brick
In the traditional process, the carbon content of magnesia-carbon bricks is generally 14%-20%, and the source of carbon basically comes from graphite. This is because graphite is resistant to high temperatures, has small mass loss, small volume expansion and contraction, and poor wettability to slag. Traditional magnesium carbon refractory materials will gradually expose the following problems during long-term use:
(1) Carbon is easily oxidized during high-temperature smelting. After oxidation, it is easy to form a porous structure in the refractory material, which reduces the strength of the material and makes the material easily eroded and penetrated by slag;
(2) High thermal conductivity increases the temperature of molten steel, takes away more heat energy, increases energy consumption, and worsens the corrosion of refractory materials;
(3) High thermal conductivity deforms or damages furnace shells and metallurgical containers;
(4) Consuming a large amount of valuable graphite resources and increasing CO2 and CO emissions;
(5) When used as a lining material for VOD refining furnaces and other special converters, it will increase the carbon content of molten steel and fail to meet the smelting standards of low-carbon clean steel.
Therefore, reducing the amount of carbon used and preparing low-carbon magnesium-carbon refractory materials has become an inevitable trend in research. The carbon content of low-carbon magnesia-carbon bricks currently studied is generally not higher than 8%, because as the carbon content decreases, the thermal conductivity of magnesia-carbon bricks will decrease, the elastic modulus will increase, and the thermal shock stability will decrease. . Compared with high-carbon magnesia-carbon bricks, when the carbon content is reduced, molten slag will penetrate into the pores of the bricks, causing the magnesia-carbon bricks to have poorer slag and corrosion resistance. How to reduce the use of graphite while maintaining the superior properties of magnesia-carbon bricks, so that they can occupy an unmatched position in the steelmaking industry, has become a hot issue studied by scholars at home and abroad in today's world.
Low-carbon magnesia-carbon bricks are refractory materials with excellent performance obtained by reducing the carbon content in magnesia-carbon bricks without changing the traditional preparation process. Since the amount of graphite in low-carbon magnesia-carbon bricks has been halved, the advantages of graphite such as high thermal conductivity, extremely small thermal expansion coefficient and elastic modulus cannot be brought into play, resulting in the thermal stability and slag resistance of low-carbon magnesia-carbon bricks. Corrosion becomes worse. Therefore, how not to reduce the thermal stability, slag resistance and corrosion resistance of low carbon magnesia carbon bricks has become the key to research. We can control the matrix structure of magnesia carbon bricks by looking for carbon raw materials with better performance to achieve the purpose of improving the thermal stability, slag resistance and corrosion resistance of low carbon magnesia carbon bricks. A good matrix structure requires appropriate carbon particles to control the composition, shape, size and distribution of pores in the sample: at the same time, a good matrix structure can greatly affect the thermal conductivity, thermal expansion coefficient and elastic modulus of the material, thus Improve the material's oxidation resistance, thermal stability, slag resistance and corrosion resistance.
Some scholars use nanocarbon as the carbon source, add a small amount of nanocarbon in different proportions to graphite, and keep the total carbon content below half of the total carbon content in traditional magnesium carbon refractory materials to prepare new magnesium carbon refractory materials. Research shows that when 0.9% nanocarbon and 3% graphite are mixed, the performance of refractory materials reaches the best value. Because nanocarbon can be more evenly distributed in the matrix, it can fill the gaps between particles of different sizes in the starting material and the pores inside the nanocarbon, thus reducing the apparent porosity of the refractory material and increasing the volume density, Strength, corrosion resistance, etc. In addition, nanocarbon can also reduce the stress caused by the volume expansion or contraction of refractory materials, thereby improving the uneven distribution of thermal stress within the refractory materials and improving thermal stability. The low-carbon magnesia-carbon bricks prepared by this method reduce the carbon content while improving the performance of refractory materials and improving the quality of the bricks.
Modified graphite was added to magnesia-carbon bricks for ladle slag, and the effect of modified graphite on various properties of magnesia-carbon bricks was studied. Experimental results show that although adding 0-1% modified graphite will have an adverse effect on the volume density of magnesia-carbon bricks, the volume expansion produced by modified graphite at high temperatures can compensate for the matrix shrinkage of the bricks and fill the pores between materials. , thereby improving the slag resistance of magnesia carbon bricks. When 0.8% modified graphite is added, the gap between the aggregate and the matrix in the magnesia carbon brick is the smallest and the slag resistance is the best.
Environmentally friendly coal pitch was used to replace graphite, and phenolic resin was used as a binder to prepare magnesia-carbon bricks after heat treatment at different temperatures, and various performance indicators of the samples were tested. Experimental results show that with the gradual addition of environmentally friendly asphalt, the bulk density of the sample decreases, the apparent porosity increases, and the linear change rate becomes smaller, but the compressive strength increases significantly. Through microstructural analysis, it was found that at high temperatures, fibrous AlN and nano-magnesia-aluminum spinel are produced in magnesia-carbon bricks, and the higher the temperature, the more conducive to the formation of this structure.