Chile customer order 300 tons magnesia carbon bricks.
The main raw materials of magnesia carbon bricks include fused magnesia or sintered magnesia, flake graphite, organic binders and antioxidants.
magnesium oxide
Magnesia is the main raw material for the production of magnesia carbon bricks and can be divided into fused magnesia and sintered magnesia. Compared with sintered magnesia, fused magnesia has the advantages of coarse periclase grains and heavy particle volume, and is the main raw material for production. The production of ordinary magnesia refractory materials mainly requires high-temperature strength and corrosion resistance of magnesium raw materials. Therefore, attention should be paid to the purity of magnesium oxide and the C/S ratio and B2O3 content in its chemical composition. With the development of the metallurgical industry, smelting conditions are becoming more and more severe. Large crystals of magnesia used in MgO-C bricks for metallurgical equipment (converters, electric furnaces, ladles, etc.).
carbon source
Both traditional magnesia carbon bricks and widely used low carbon magnesia carbon bricks use flake graphite as the carbon source. Graphite, as the main raw material for the production of MgO-C bricks, mainly benefits from its excellent physical properties: ① It does not wet slag. ②High thermal conductivity. ③ Low thermal expansion. In addition, graphite and refractory materials are not eutectic at high temperatures and have high refractory resistance. The purity of graphite has a great influence on the performance of MgO-C bricks. Typically, graphite should be used with a carbon content greater than 95%, preferably greater than 98%.
In addition to graphite, carbon is also commonly used in the production of magnesia carbon bricks. Carbon black is a highly dispersed black powdery carbonaceous material obtained by thermal decomposition or incomplete combustion of hydrocarbons. 99%, high purity, high powder resistivity, high thermal stability, low thermal conductivity, and is a difficult-to-graphitize carbon. The addition of carbon black can effectively improve the spalling resistance of MgO-C bricks, increase the amount of residual carbon, and increase the density of the bricks.
Adhesive
Commonly used binders in the production of MgO-C bricks include coal tar, coal pitch and petroleum asphalt, as well as special carbonaceous resins, polyols, asphalt-modified phenolic resins, synthetic resins, etc. The following types of adhesives are used:
1) Asphalt material. Tar pitch is a thermoplastic material that has the characteristics of high affinity with graphite and magnesium oxide, high carbon residual rate after carbonization, and low cost. It was widely used in the past; however, tar pitch contains carcinogenic aromatic hydrocarbons, especially benzo-beta content. High; the use of tar pitch is now declining due to increased environmental awareness.
2) Resinous substances. Synthetic resin is produced by the reaction of phenol and formaldehyde. It can be fully mixed with refractory particles at room temperature. The carbon residue rate after carbonization is high. It is the main binder currently used in the production of MgO-C bricks. The glassy network structure is not ideal for the thermal shock and oxidation resistance of refractory materials.
3) Substances modified based on asphalt and resin. If the binder can form a mosaic structure and in-situ carbon fiber material after carbonization, the binder will improve the high-temperature performance of the refractory material.
Antioxidants
In order to improve the oxidation resistance of MgO-C bricks, a small amount of additives are often added. Common additives include Si, Al, Mg, Al-Si, Al-Mg, Al-Mg-Ca, Si-Mg-Ca, SiC, B4C, BN and recently reported additives such as Al-BC and Al-SiC-C [5-7]. The working principle of additives can be roughly divided into two aspects: First, from a thermodynamic point of view, that is, at the working temperature, additives or additives react with carbon to generate other substances whose affinity with oxygen is greater than that of carbon and oxygen. It is oxidized prior to carbon to protect carbon; on the other hand, from a kinetic point of view, the compounds generated by the reaction of additives with O2, CO or carbon will change the microstructure of carbon composite refractory materials, such as increasing density, blocking pores, Hinder the diffusion and reaction of oxygen, etc.