Factors influence MgO-C bricks quality

 Magnesia carbon brick is a high melting point basic oxide magnesium oxide (melting point 2800 ° C) and a high melting point carbon material which is difficult to be infiltrated by slag as a raw material, and various non-oxide additives are added.

A non-burned carbon composite refractory material combined with a carbonaceous binder. Ladle Magnesia carbon brick is mainly used for the lining of converter, AC arc furnace, DC arc furnace, slag line of ladle and so on.

The process factors affecting the performance of magnesia carbon bricks are mainly refractory raw materials, binders and additives.

1. Magnesite

The high-purity sintered magnesia was used in the original production of magnesia carbon bricks abroad. With the in-depth study of the use of magnesia-carbon bricks, the following reactions were observed at high temperatures:

MgO+C→Mg↑+CO↑

This reaction generally starts at 1650 ° C, and the reaction is intensified at l750 ° C. This is one of the important reasons for the loss during the use of magnesia carbon bricks, and it is also the reason why the loss of magnesia carbon bricks at 1700 ° C or above is significantly increased. The impurities such as SiO2 and Fe2O3 in the magnesia have a promoting effect on the above reaction, and therefore, it is desirable that the magnesia has a high purity.

Compared with sintered magnesia, fused magnesia has a more complete crystal structure and a more stable carbon reduction. Especially the characteristics of large-crystal fused magnesia are more prominent, so the production of magnesia-carbon bricks begins to shift. Fused magnesia. The fused magnesia-sintered magnesia may also be used in combination in consideration of the bonding state of carbon and the wett ability of the binder.

The results of the use of magnesia-carbon bricks show that the best effect is on the production of magnesia-carbon bricks with magnesia with high MgO content, large magnesia phase crystal particles and calcium-silica ratio greater than 2.

2. Graphite

Graphite is another essential component in magnesia carbon bricks. Graphite has good basic properties of refractory materials. The main physical and chemical indicators are: fixed carbon 85%～98%, ash 13%～2% (main component SiO2, Al2O3, etc.), relative density 2.09～2.23, melting point 3640K ( Volatile). Since graphite is very 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 magnesia carbon bricks:
(1) Oxidation of graphite by oxygen in the air;
(2) 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 in the magnesia carbon brick react, the structure of the brick body is loose, the gas permeability is increased, and the strength is decreased, which is the internal cause of the damage of the magnesia carbon brick. Therefore, most of the magnesia carbon bricks used are graphites with high purity and large crystals of phosphorus.

3. Bonding agents

Bonding agents are essential for magnesium 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.

They are cured by bonding at room temperature. The binder is coked and carbonized, and carbon is combined with graphite at high temperatures. Generally, the binder refers to organic substances such as resins and asphalt. The high-temperature coking of the binder forms about 3% of carbon after carbonization.

Although this amount is not much, it is the most dynamic component in magnesia-carbon bricks or other carbon-containing products, and has an important influence on the high-temperature performance of the product. Magnesia-carbon brick binders can be generally divided into three types: phenolic resin, modified asphalt, and petroleum cracking by-products. Among them, phenolic resin is the best used and the most used.

4. Additives

The oxidation of graphite is one of the most important causes during the destruction of magnesia carbon bricks. Due to the loss of carbon from oxidation, the structure of the brick body is loose and the strength is lowered. The damage process follows the path of oxidative carbon loss → structural looseness → erosion → erosion and dissolution.

In order to improve the oxidation resistance of the ladle magnesia carbon brick, a certain amount of additives may be added, including silicon powder, aluminum powder, FeSi alloy, CaSi alloy, SiC, Si3N4, B4C and the like. Another effect of the additive is to "bridge" between the refractory oxide and the graphite to form a strong bond between the graphite and the refractory oxide, which is facilitated by the formation of a new mineral phase at a certain temperature.?For further details, please feel free to contact us, we would be your reliable partner.

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