Binding Agent of MgO-C

The matrix and the binder system are the two weak links of mgo-c in actual production and use.
Due to the particularity of graphite, one of the raw materials of mgo-c brick, that is, the wetting Angle (contact Angle) of the liquid is large, and its surface is difficult to be wetted by the liquid, the requirements of binder for the preparation of mgo-c brick are different from the requirements of general refractory materials. The binder requirements for mgo-c brick production are as follows:
(1) has a certain viscosity and fluidity at room temperature, and has a good wettability to magnesia and graphite;
(2) the binder can further condense in the process of heat treatment, so that the product has a higher strength;
(3) in the process of heat treatment, the binder will not cause excessive expansion and contraction of products to avoid product cracking;
(4) the content of F.C should be high, and the carbon polymer after coking has good high-temperature strength;
Types of binders used to produce mgo-c bricks
Coal pitch, coal tar, special carbon resin, polyol, asphalt denatured phenolic resin, synthetic phenolic resin, etc.
Because of the good mixing and molding performance of synthetic phenolic resin, it can be directly mixed and formed at room temperature, and the pressed brick has high strength. During heat treatment, mgo-c brick can be further condensed, which can further improve the strength of the finished product, form a firm carbon bond in the reducing atmosphere, and maintain a high thermal strength at high temperature. It is widely used as a binding agent in the production of mgo-c brick.
When asphalt is used as binder, its fixed carbon content is higher than that of synthetic phenolic resin. In addition, the graphitization degree and oxidation temperature of carbonized structure of asphalt are higher than that of synthetic phenolic resin. Graphitization: from amorphous carbon to graphite, the process of putting the atoms in order is called graphitization. Graphitization degree is a parameter that indicates that the crystal structure of carbon raw materials is close to the size of ideal graphite crystal. It is also used as the binder for mgo-c brick production by many manufacturers, but corresponding environmental measures should be taken.
antioxidants
The excellent performance of mgo-c brick depends on the existence of carbon in the brick. In the process of use, the oxidation of carbon is easy to cause the deterioration of the product structure, so that the slag invades into the brick along the gap, corrodes MgO particles, and reduces the service life of mgo-c brick. Therefore, how to inhibit carbon oxidation has become the key technology of mgo-c brick production.
Choose antioxidants.
(1) judge the possible condensate phase and vapor pressure of each gas phase according to thermodynamic data and service conditions;
(2) compare the affinity between each condensed phase and oxygen and the possibility of reaction with CO
(3) the effects of various reactions on the microstructure of bricks were analyzed
Thermodynamic and kinetic mechanism of antioxidants
At working temperature, the affinity of additives or products reacting with carbon with oxygen is greater than that between carbon and oxygen, which is prior to the oxidation of carbon, thus playing the role of protecting carbon. At the same time, the additives react with oxygen and carbon monoxide to change the microstructure of carbon composite refractories, such as increasing density, blocking pores, and preventing the diffusion of oxygen and reaction products.
The commonly used antioxidants in mgo-c production process are metal aluminum powder, silicon powder, aluminum magnesium alloy powder, B4C, CaB6, etc.