Core Tips: Price of Magnesia Carbon Bricks Magnesia Carbon Bricks are based on high melting point basic oxide magnesium oxide (melting point 2800 ℃) and high melting point carbon materials that are difficult to be infiltrated by slag as raw materials. additive. Today, the editor of China Insulation Net compiled and analyzed the process factors that affect the performance of magnesium carbon bricks.

       Magnesia carbon brick is based on high melting point basic oxide magnesium oxide (melting point 2800 ° C) and high melting point carbon material which is difficult to be infiltrated by slag as raw materials, and various non-oxide additives are added. Non-burning carbon composite refractory material combined with a carbonaceous binder. Magnesia carbon bricks are mainly used in converters, AC electric arc furnaces, DC electric arc furnace linings, ladle slag lines and other parts.

       The main factors affecting the properties of magnesia-carbon bricks are raw materials, binders and additives.

        1.Magnesia

       High-purity sintered magnesia was used in the initial production of magnesia-carbon bricks abroad. With in-depth research on the use of magnesia-carbon bricks, it was found that the following reactions occur at high temperatures:

MgO + C → Mg ↑ + CO ↑. This reaction generally starts at 1650 ° C, and the reaction intensifies to 1750 ° C. This is one of the important reasons for the loss of magnesia-carbon bricks during use, and it is also the reason that the loss of magnesia-carbon bricks is significantly increased above 1700 ° C. The impurities in the magnesia, such as SiO2 and Fe2O3, can promote the above reaction. Therefore, the magnesia is expected to have a higher purity.

       Compared with sintered magnesia, fused magnesia has a more complete crystalline structure and more stable reduction of carbon. In particular, the characteristics of large-crystalline fused magnesia are more prominent, so the production of magnesia-carbon bricks has shifted to use. Fused magnesia. Considering the bonding state of carbon and the wettability of the binder, fused sintered magnesia can also be used. Magnesia-carbon bricks in China basically use fused magnesia.

       The results of the use of magnesia-carbon bricks show that the use of magnesia with high MgO content, large periclase phase crystal grains and a calcium-silicon ratio greater than 2 produces magnesia-carbon bricks with good results.

        2.Graphite

            Graphite is another basic component in magnesia-carbon bricks. Graphite has good basic properties of refractory materials. The main physical and chemical indicators are: fixed carbon 85% to 98%, ash 13% to 2% (main components SiO2, Al2O3, etc.), relative density 2.09 to 2.23, melting point 3640K ( Volatile). Because graphite is easily oxidized, it has not attracted much attention for a long time.

       There are three reasons for the oxidation of graphite during the use of magnesium carbon bricks:

        (1) Oxidation of graphite by oxygen in the air;

        (2) the oxidation of graphite by oxides in the slag;

        (3) Oxidation of graphite by impurity oxides contained in graphite itself. These oxides mainly refer to SiO2 and Fe2O3.

        After the impurity oxide and graphite react in the magnesium carbon brick, the structure of the brick is loosened, the air permeability is increased, and the strength is reduced. This is the internal cause of the damage of the magnesium carbon brick. Therefore, most of the magnesium-carbon bricks are produced by using graphite with high purity and large crystal flakes.

        3.Binder

        Binders are essential for magnesia-carbon bricks and other carbon-containing refractory products. There is no mutual solubility relationship between graphite and refractory oxide, and it is impossible to sinter each other. At room temperature, they must be bonded and cured by a bonding agent. At high temperatures, the binding agent must be coked and carbonized to form a carbon bond with graphite. Generally, this binding agent refers to organic substances such as resins and asphalts. After the high-temperature coking and carbonization of the binder, about 3% of carbon is formed. Although this amount is not large, it is a dynamic component in magnesia-carbon bricks or other carbon-containing products, which has an important impact on the high-temperature performance of the product. The production process and product quality of magnesium-carbon bricks or other carbon-containing products in China are not stable. One of the important reasons is the instability of the binder.

       Magnesium-carbon brick binders can be roughly divided into three types: phenolic resins, modified asphalts, and petroleum cracking by-products. Among them, the phenolic resins have the best effect and the most used.

       4.Additives

       During the damage process of magnesia-carbon bricks, graphite oxidation is one of the main reasons. Due to oxidative loss of carbon, the brick structure becomes loose and its strength decreases. The damage process follows the path of oxidative carbon loss → structural looseness → erosion → erosion and dissolution. In order to improve the oxidation resistance of magnesium carbon brick, a certain amount of additives can be added, including silicon powder, aluminum powder, FeSi alloy, CaSi alloy, SiC, Si3N4, B4C and so on. Another effect of the additive is to “bridge” between the refractory oxide and graphite, so that the graphite and the refractory oxide form a strong bond. This effect is caused by the addition of a new mineral phase at a certain temperature.

      China produces magnesium carbon bricks and other phosphorous refractory products. The most commonly used additives are aluminum powder, silicon powder and SiC powder.