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Magnesia-carbon brick status, existing problems and future research directions

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In recent years, as the scope and amount of magnesia-carbon bricks have become larger and larger, the in-depth research on magnesia-carbon bricks has been promoted, and the research scope and direction have become more and more extensive. The research direction at this stage is mainly the development of new binding agents, antioxidants, and additives, and many aspects have achieved great results.Magnesia-carbon brick status

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The use of phenolic resin as a binder to produce magnesia-carbon bricks is a major leap forward in the development of magnesia-carbon brick binders. Phenolic resin can be used at room temperature, with high viscosity and strong adhesion, which can well combine the raw materials used for magnesium carbon brick. After high temperature carbonization, low-melt impurities are less and the amount of residual carbon is about 50%. At this stage, research on phenolic resins for refractory materials is mainly focused on the modification of resins. On the one hand, it tends to improve the structure and performance of resin residual carbon. On the other hand, it tends to synthesize new high-performance interpenetrating phenolic resins to improve the structure of the resin itself. After curing, it can form more complex network structures, thereby increasing the strength of magnesium carbon bricks and reducing the production cost of phenolic resins.- Magnesia-carbon brick status

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Graphite is insoluble in water, insoluble in dilute acid, alkali, organic solvents and high-temperature slag, so graphite has a very strong resistance to slag, but graphite is easily oxidized at high temperatures. After graphite is oxidized, the product structure is damaged, and its performance is significantly reduced. Therefore, in order to prevent graphite from being oxidized, it is necessary to appropriately add an antioxidant. After the antioxidant is added, the anti-corrosion ability of the magnesium carbon brick is significantly improved when it is used in the field. Commonly used antioxidants are metal silicon powder and metal aluminum powder. Zou Ming et al. Used LF slag as an experiment to determine the oxidation resistance of various antioxidants in magnesium carbon bricks. It was found that the antioxidant metal aluminum powder and metal silicon powder in the magnesium carbon brick have priority over the reaction between oxygen and carbon dioxide in graphite and air. The oxidized product of the antioxidant produces volume expansion to block the pores, which can effectively protect the graphite in the magnesium carbon brick from further oxidation, and improve the slag resistance of the magnesium carbon brick. SiC and B4C are also excellent antioxidants for magnesium carbon bricks. Ye Xiaoye studied the antioxidant capacity of various antioxidants such as Al, Si, SiC and B4C at 1300 ℃ and 1500 ℃, and found that B4C has the best antioxidant effect at these two temperatures. The magnesium borate composite produced after the B4C reaction will become liquid after 1360 ° C. The liquid magnesium borate composite fills the open pores and has a positive effect on the oxidation resistance of magnesium carbon bricks;-Magnesia-carbon brick status

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In order to continuously improve the performance of magnesium carbon bricks, researchers are constantly looking for new additives, adding TiCC composite powder to low carbon magnesium carbon bricks to improve the thermal shock resistance of low carbon magnesium carbon bricks. The slag resistance of TiN was added to the magnesium carbon brick. It was found that CaTiO3 with high melting point was formed in the slag corrosion layer, which increased the viscosity of the slag and reduced the slag penetration. High melting point mineral phases such as Ti (C, N) solid solution have a positive effect on the slag resistance of magnesium carbon bricks.-Magnesia-carbon brick status

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Since the advent of magnesia carbon bricks, with its excellent properties, it has quickly replaced the lining materials on various steelmaking furnaces, and has been widely used. With the continuous updating of smelting technology, the requirements for refractory materials are becoming more and more severe. Low-carbon magnesium-carbon bricks have begun to be adopted by more and more enterprises. At the same time, aluminum oxide has been introduced into carbon-containing refractories to improve the special properties of carbon-containing products. The carbon content of traditional magnesium carbon bricks is 10% wt to 20% wt. In the long-term use process, more and more companies have found the following problems:

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  • Magnesia-carbon bricks have high thermal conductivity and high heat loss, so it is necessary to increase the tapping temperature, resulting in large energy consumption, and the high tapping temperature increases the erosion of refractory materials;
  • When smelting special steels such as ultra-low carbon steel and high-quality clean steel, due to the problems of the magnesium carbon brick material itself, the molten steel will increase carbon.
  • Consume a lot of precious graphite resources.

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In order to solve these problems, in recent years, research has begun on magnesium carbonate bricks with excellent properties and low carbon content to replace ordinary magnesium carbon bricks on refining ladle. Research in this area has received increasing attention from domestic and foreign industries. Breakthrough results have been achieved.

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The main problems caused by the low carbonization of magnesia carbon bricks are the decrease in thermal shock stability and slag resistance. When the carbon content is reduced to a certain range, a series of chain problems will be caused. After the carbon content is too low, a continuous carbon network cannot be formed inside the magnesium carbon brick, which will cause the thermal conductivity of the magnesium carbon brick to decrease and the elastic modulus to increase. The thermal shock resistance of magnesia-carbon bricks deteriorates. Another problem after the carbon content is too low is to enhance the wettability of magnesium carbon bricks with molten steel and slag. Due to the reduced graphite content, the resistance of Mg-C bricks to the penetration of molten steel and slag becomes worse, which leads to the poor permeability of molten steel and slag, which makes the Mg-C bricks wear faster when used.

[/vc_column_text][vc_separator][vc_column_text]It is found through research that these problems are mainly solved through the following aspects:[/vc_column_text][vc_column_text]

  • The thermal shock stability of magnesia-carbon bricks is improved by improving the properties of the binder and changing the residual carbon structure of the binder. Phenolic resin is a widely used binder now. The structure of residual carbon after carbonization of the currently used phenolic resin is glassy. Therefore, after carbonization, magnesium carbon brick has poor toughness, high elastic modulus, brittleness, low temperature strength, and thermal shock stability Poor sex. The carbon precursor that can be graphitized in the binder. When this composite binder is carbonized, it can form secondary carbon or nano-carbon fibers. With this improved carbon structure, it can strengthen low-carbon magnesium carbon bricks. Thermal shock stability and high temperature strength;

  • Optimize the matrix structure. It is found that the thermal shock stability and slag resistance of Mg-C bricks are mainly determined by the composition and structure of the matrix. After the Mg-C bricks are decarbonized, in order to improve their thermal shock stability, the contact between aggregate and carbon particles is increased. Probability is one of the important measures, that is, the carbon particles are refined and highly dispersed. Secondly, by adjusting the particle size and composition of the ingredients and controlling the size and distribution of the pores, the thermal shock stability and slag resistance of the low carbon magnesium carbon brick can also be improved.

  • Use highly effective antioxidants. With the low carbonization of magnesia-carbon bricks, the oxidation protection of carbon is more important. The damage of magnesia-carbon refractory materials during use has two main reasons. One is that the carbon in the material is oxidized by the oxides in the slag, resulting in magnesium oxide. The particles directly react with the slag to form a low-melting phase and are lost; the second is that the slag penetrates directly into the refractory material and causes damage to the refractory material, so it is very important to choose a suitable high-efficiency antioxidant. At present, researchers have done a lot of research on the combination of antioxidants Work and achieved some results.

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  • The introduction of nano-carbon sources in carbon-containing materials, improving the dispersion of carbon in the materials, so that the product can form a carbon network in a low-carbon environment; the introduction of composite carbon sources in carbon-containing materials, and increasing the slag resistance And crack propagation resistance

  • Study the way that antioxidants and carbon sources exist with each other to enhance the oxidation resistance of the product;

  • Investigate new high-strength environmentally friendly binders, improve the structure of the residual carbon of the binder, and enhance the oxidation resistance of the residual carbon.

  • By adjusting the physical and chemical composition of the carbonaceous material, controlling the in-situ ceramic phase formation and morphology and other methods to increase the toughness and thermal shock resistance of the material.

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