Flake graphite has the following characteristics
1. The melting point and boiling point of high-temperature resistant graphite are 3850 50 and 4250 respectively. Even if the magnesia-carbon brick is burned by ultra-high arc, the loss of quality is very small and the coefficient of linear expansion is very small. The strength of graphite increases with the increase of temperature. At 2000 C, the strength of graphite increases twice as much as that of magnesia-carbon brick manufacturers.
2. Conductivity and thermal conductivity. The conductivity of graphite is twice as high as that of non-metallic ores. The thermal conductivity exceeds that of steel, iron, lead and other metal materials. The thermal conductivity decreases with the increase of temperature, even at extremely high temperatures, graphite is adiabatic.
3. Lubrication. The lubricity of graphite depends on the size of graphite flakes. The larger the flakes, the smaller the friction coefficient and the better the lubrication performance.
4. Chemical stability. Graphite has good chemical stability at room temperature. It can resist acid, alkali and organic solvent corrosion.
5. Plasticity. Graphite has good toughness and can be rolled into very thin sheets.
6. Thermal shock resistance. When graphite is used at high temperature, it can withstand the drastic change of temperature without destroying. When the temperature changes abruptly, the volume of graphite does not change much and no cracks will occur.
Binder plays the role of linking matrix and particle. In the actual production and use process, matrix and binder system are two weak links of magnesia-carbon brick.
The requirement of the binder for the production of magnesia-carbon bricks is as follows:
1. It has certain viscosity and fluidity at room temperature, and has good wettability to magnesia and graphite.
2. Binder can further condensate during heat treatment, so that the products have higher strength.
3. Binders do not cause excessive expansion and contraction of products during heat treatment to avoid cracking of products.
4. High C content and good high temperature strength of coked carbon polymer
Generally, the binders used in the production of magnesia-carbon bricks are coal tar, coal tar, special carbon resin, polyols, asphalt modified phenolic resin, synthetic phenolic resin, etc.
The excellent properties of magnesia-carbon bricks depend on the existence of carbon in the bricks. The oxidation of carbon in the bricks can easily lead to the deterioration of product structure, which makes slag invade the bricks along the crevice, erodes magnesia particles and reduces the service life of magnesia-carbon bricks. At present, the oxidation resistance of magnesia-carbon bricks is mainly improved by adding antioxidants.
Principles for Selecting Antioxidants
1. Judging the possible condensed phase and vapor pressure of each vapor phase according to thermodynamic data and operating conditions
2. Comparing the affinity of each condensate with oxygen and the possibility of CO reaction.