Magnesia-carbon bricks are made of high-melting alkaline oxide magnesium oxide (melting point 2800℃) and high-melting carbon materials that are difficult to be infiltrated by slag, and various non-oxide additives are added. A non-burning composite refractory material combined with a carbon binder. Magnesia-carbon bricks are mainly used for the lining of converters, AC electric arc furnaces, and DC electric arc furnaces, and the slag line of ladle.
As a composite refractory material, magnesia carbon brick effectively utilizes the strong slag erosion resistance of magnesia and the high thermal conductivity and low expansion of carbon, which compensates for the biggest shortcomings of poor spalling resistance of magnesia.
Its main characteristics are: 1 Good high temperature resistance 2 Strong slag resistance 3 Good thermal shock resistance 4 Low high temperature creep
The influence of raw materials on the performance of magnesia carbon bricks
The main raw material for the production of magnesia carbon bricks, the quality of magnesia has an extremely important influence on the performance of magnesia carbon bricks. How to choose magnesia reasonably is the key to the production of magnesia carbon bricks. Magnesia has fused magnesia and sintered magnesia, which have different characteristics. Fused magnesia: large grains, less impurities, less silicate phase, high degree of direct grain bonding, and less grain boundaries.
Sintered magnesia: small grains, relatively large amounts of impurities and silicate phases, and poor direct bonding.
For magnesia raw materials, in addition to chemical composition, high density and large crystals are also required in terms of organizational structure. Therefore, as the quality index of magnesia raw materials for the production of magnesia carbon bricks, the following content should be investigated 1. Magnesium oxide content (purity) 2 The types of impurities, especially the content of C/S and B2O3. 3 The density, pore diameter, and pore morphology of magnesia (sinterability).
The purity of magnesia has a significant impact on the slag resistance of magnesia carbon bricks. The higher the magnesium oxide content, the lower the relative impurities, the lower the degree of silicate phase separation, the higher the degree of direct bonding of periclase, and the higher the resistance to slag penetration and the slag melting loss. The squeezed juices in magnesia mainly include calcium oxide, silicon dioxide, and iron oxide.  If the content of impurities is high, especially boron oxide compounds, it will adversely affect the refractoriness and high temperature performance of magnesia.
The impurities in magnesia mainly have the following inseparable influences: 1. Reduce the direct bonding degree of periclase 2. Form a low-melting substance with magnesium oxide at high temperature 3. Iron oxide, silicon dioxide and other impurities are at 1500-1800°C. Because magnesium oxide reacts with carbon, leaving pores, the slag resistance of the product deteriorates.
For magnesia raw materials, in addition to the total amount of impurities, the type and relative content of impurities also have a significant impact on the performance of magnesia. Among them, the ratio of CaO/SiO2 and the content of B2O3 have the most obvious influence. General magnesia refractories usually require CaO/SiO2≥2 to improve the high temperature stability of magnesia carbon bricks.