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Different functions of binders in magnesia carbon brick — improving the distribution of carbon

At present, the low carbon magnesia carbon brick is still made of phenolic resin. Although it has strong binding capacity and high carbon residue rate, the isotropic glass carbon formed by its carbonization will make the magnesia carbon brick brittle. This is not conducive to the thermal shock stability of the low carbon magnesia carbon brick, but also reduces the high temperature strength. At the same time, due to its amorphous structure, its oxidation resistance is insufficient.

Therefore, many researches and improvements have been made on the bond of low carbon brick at home and abroad. Behera and Sarkar introduced graphitized carbon precursor into phenolic resin for modification. The composite binder can be carbonized into secondary carbon with flowing or inlaid structure, or form nano carbon fiber in situ when magnesia carbon brick is used. The thermal shock stability and high temperature strength of low carbon magnesia carbon brick can be improved by improving the carbon structure and strengthening effect of nano carbon fiber. The results show that the strength of the brick increases with the increase of its concentration, especially when its content is 0.4% mass fraction, the strength of the brick is about 2.2 times higher than that of the sample without addition. The SEM shows that the network structure of the nano carbon fiber is formed in the matrix of the magnesia carbon brick, and the increase of the strength is due to the network structure In addition, through the introduction of nano scale composite graphitized carbon black into the binder, it is possible that the binder can be carbonized to form nano scale and partially graphitized secondary carbon, which may improve the bonding strength and elasticity of MgO-C brick. Li et al. Tested the effect of adding different content of nano carbon black on the mechanical properties of low carbon magnesia carbon brick. The results showed that the increase of nano carbon black content made the mechanical properties of magnesia carbon brick improved in many aspects, but it also made the viscosity of composite binder increase rapidly, which brought about the problem that it is not easy to disperse. In addition, some scholars considered to solve the problem from the perspective of graphitization of phenolic resin Modification problems.

Jansen uses a reflaflex catalytic activation technology to add catalytic active substances and special manufacturing and curing processes to the bricks, so as to reduce the graphitization temperature of phenolic resin to below 1000 ℃, so as to reach the temperature conditions in the preheating and heating process area of ladle and converter. The final result is that magnesia carbon bricks have excellent strength and toughness. The use of nano modified binders can improve the low temperature The properties of carbon magnesia carbon brick, but the problems such as poor dispersion of nano modifier in binder, poor interfacial compatibility and high cost limit the large-scale production, which need to be further studied. Liao Qingling et al. Introduced that nano carbon black particles were oxidized on the surface of mixed acid to make its surface rich in organic functional groups, and then modified phenolic resin was formed in situ by blending method Compared with the common phenolic resin, the thermal decomposition temperature and the carbon oxidation temperature of the phenolic resin were increased by 170 ℃ and 178 ℃ respectively.

Tang Guangsheng et al. Used KH-550 coupling agent and high-speed stirring method to uniformly disperse nano carbon black N220 in phenolic resin, made nano carbon black phenolic resin composite binder, and prepared low-carbon magnesium carbon sample with ω (c) = 3%. The results show that the graphitization degree of nano carbon black phenolic resin composite increases after carbonization at 1500 ℃, and the flexural strength, high temperature flexural strength and normal temperature compressive strength of low carbon magnesia carbon samples increase with the increase of nano carbon black content.

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