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Research progress of matrix structure in low carbon magnesium-carbon bricks

Carbon materials determine the matrix structure, thermal conductivity, coefficient of thermal expansion, elastic modulus and other factors of low-carbon magnesium-carbon bricks. Therefore, the selection of carbon materials with special structure to improve the thermal shock stability and slag permeability of low-carbon magnesium-carbon bricks has attracted the attention of scholars all over the world. Tsuboietal. [6] studied the effect of the use of micro-refined special graphite to replace the commonly used flake graphite on the thermal peeling resistance of magnesium-carbon bricks.When the carbon content is less than 4%, there is no difference in thermal spalling resistance between the two samples.When the content of graphite is above 6%, the thermal spalling resistance of magnesium-carbon brick containing fine graphite is obviously better than that of flake graphite.The main reason for this difference is that compared with large flake graphite, fine graphite powder is more easily dispersed and its structure tends to be uniform.Fuchimoto [7] believes that the thermal stress of ultra-low carbon magnesium-carbon brick can be solved by two methods: “three-dimensional structural graphite” and nanofiber technology.It has the microstructure of natural graphite and three dimensional structure stone ink ultra-low carbon magnesia carbon brick.The results show that the ultra-low carbon magnesium-carbon brick with carbon content of 3% and the carbon content of 10%~15% magnesium-carbon brick have basically the same elastic modulus, and the iron-oxygen slag resistance is improved

Li Lin et al. [8] studied the effect of the addition of nano carbon black on the properties of low-carbon magnesium-carbon bricks.By comparison, the strength of low carbon magnesium-carbon brick predispersed in resin was higher than that of carbon black directly added into low carbon magnesium-carbon system.With the increase of nano carbon black in the resin, the viscosity of the resin increased rapidly.At the same time, it has been proved that when the temperature is above 50 ℃, the resin added with nano carbon black has a low viscosity and is feasible to be constructed.With the increase of nano carbon black content in the resin, the flexural strength, compressive strength and high temperature flexural strength of the samples gradually increased.When the addition of nano carbon black reaches 0.6%, its strength at room temperature and thermal state is about 40% higher than that of samples without nano carbon black.V. Stein1 [9] et al. studied the effect of nano TiO2 addition on the substrate properties of low carbon magnesium-carbon bricks.Solid resin and liquid resin were used to combine graphite and carbon black as carbon source and aluminum as anti-oxidant.After 5 thermal earthquakes, no. 1, 3, 5, 7 and 9 samples had different degrees of strength loss. Samples containing TiO2 had relatively good strength retention rate and final strength, while samples containing TiO2 and metal aluminum had relatively good strength retention rate and final strength.XRD and SEM results show that when TiO2 and Al co-exist, Ti(C,N), spinel and AlN are formed in situ in the matrix after treatment at 1 500 ℃, and Ti(C,N) whiskers evenly distributed in the matrix are the reason for good thermal shock stability (figure 8).If there is only TiO2 but no Al, Mg2TiO4 will eventually be formed.If only metal aluminum without TiO2, tiny and transparent AlN and Al3C4 whiskers will be formed.In addition, the addition of TiO2 can significantly improve the wet pulverization of products after heat treatment, and significantly improve their hydration resistance.Therefore, low carbon magnesium carbon products with nano TiO2 and aluminum have good thermal shock stability and hydration resistance, which can be applied in skateboard and other fields.

Zhu qiang et al. [10] used wax stone and natural graphite as raw materials to synthesize SiC-Al2O3 composite powder through carbon thermal reduction, and added the composite powder into low-carbon magnesium-carbon brick as an additive.The results show that the heating temperature has an important effect on the synthesis of composite powders: it is easy to synthesize SiC-Al2O3 composite powders by adding proper amount of natural graphite to paraffin and heating the mixture of paraffin and graphite to 1 650 ℃ in an inert atmosphere.The addition of SiC-Al2O3 composite powder to low carbon magnesium carbon brick can obviously improve the corrosion resistance and permeability of oxidized slag, but it has no effect on the oxidation resistance.This is because the compound powder of SiC-Al2O3 is easy to enter into the slag when it is in contact with the slag, which greatly increases the viscosity of the slag at the contact interface, preventing further erosion and penetration of the slag into the refractory.

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