The Research On Improving the property Of Magnesia Refractories by Adding graphite

March 18, 2019

Magnesia refractories with high refractory properties and are alkaline, so they have better resistance to alkaline slag. However, because of the high linear expansion coefficient, the thermal conductivity at high temperature is low, and the thermal spalling resistance is poor. Graphite is difficult to be wet by slag and has good melting resistance, low linear expansion coefficient  and good thermal conductivity. Therefore, the producers introduce graphite into magnesia refractories, which improves slag resistance and spalling resistance of magnesia refractories.

When magnesia and graphite are combined to make magnesia-carbon bricks, magnesia-carbon bricks show excellent slag resistance, iron corrosion resistance, permeability and thermal shock resistance. Why? Jundao refractory material tell you the reasons:

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(1) The matrix of magnesia-carbon brick is mainly composed of graphite and magnesia powder. The graphite and magnesia particles and magnesia particles are surrounded by a solid carbon-carbon bonding network, which is not easy to slip. There is no co-solubility between C and MgO, and there is no liquid phase. Only the impurities introduced by graphite and magnesia materials produce a small amount of liquid phase. Therefore, in the using process, iron oxide with strong permeability in slag will be reduced to metallic iron when it meets carbon. Due to reduction, the melting point and viscosity of slag increase, and the permeability decreases greatly.

(2) Slag and hot metal are not wettable with graphite. Because the contact angle between slag and hot metal and graphite is above 90 degrees, so that the magnesia-carbon brick with excellent corrosion resistance to slag.

(3) The protective effect of compact periclase layer can be formed in magnesia-carbon brick material; MgO in magnesia reacts with carbon to form Mg vapor above 400 C, and Mg vapor overflows along with the pore. Magnesium oxide reacts with FeO in the slag at the interface contacted with the slag to form a compact periclase layer, which will prevent the slag from penetrating.

(4) The influence of CO gas pressure. The permeated slag reacts with carbon in magnesia-carbon brick to produce CO gas. The pressure in the pore passage can reach more than 0.2 MPa (2atm), which will prevent or delay the slag from penetrating into the pore.

These excellent properties of magnesia carbon bricks are closely related to the existence of graphite in magnesia-carbon bricks, so the quality of graphite has a great influence on the properties of magnesia-carbon bricks. If you wanna get more details about high quality magnesia refractory, please contact us. Jundao New Materials Co.,LTD. is one leading China refractory manufacturer & supplier, professional in lightweight clay bricks, alumina silicate fire brick, high alumina fire bricks, ladle refractory materials, boiler insulation bricks, magnesia refractory brick, refractory castables.

 

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