Yingkou refractories---Characteristics of magnesia-carbon bricks

Flake graphite has the following properties

The melting point of type 1 graphite is 3850 ℃ ± 50 ℃, and the boiling point is 4250 ℃. Even if it is burned by an ultra-high arc, the loss of quality is very small, and the coefficient of linear expansion is also very small. The strength of graphite increases with the increase of temperature. At 2000℃, the strength of graphite doubles

2 Electrical and thermal conductivity. The conductivity of graphite is twice as high as that of ordinary non-metallic minerals. The thermal conductivity exceeds that of metal materials such as steel, iron, and lead. The thermal conductivity decreases as the temperature increases, and even at extremely high temperatures, graphite is a hot body. Burnt magnesia brick

3 Lubricity. The lubricity of graphite depends on the size of the graphite flakes. The larger the flakes, the smaller the friction coefficient and the better the lubricating performance.

4 Chemical stability, graphite has good chemical stability at room temperature, acid resistance, alkali resistance, solvent corrosion resistance

5 Plasticity. Graphite is very tough and can be rolled into very thin sheets.

6 Thermal shock resistance. When graphite is used at high temperature, it can withstand severe changes in temperature without damage. When the temperature changes suddenly, the volume of graphite changes little, and cracks will not occur.

The binder plays the role of connecting the matrix and the particles. In the actual production and use process, the matrix and the binder system are the two weak links of magnesia-carbon bricks.

The requirements for the binder in the production of magnesia-carbon bricks are:

1. It has the best viscosity and fluidity under high temperature, and has good wettability to magnesia and graphite.

2 During the heat treatment process, the binder can be further condensed, so that the product has a higher strength

3 During the heat treatment process, the binder does not cause excessive expansion and contraction of the product to avoid cracking of the product

The content of 4F.C should be high, and the carbon polymer after coking treatment has good high temperature strength

Generally, the binders used in the production of magnesia-carbon bricks include coal tar pitch, coal tar, special carbonaceous resins, polyols, pitch-modified phenolic resins, and synthetic phenolic resins.

old magnesia brick

The excellent performance of magnesia-carbon bricks depends on the presence of carbon in the bricks. The oxidation of carbon during its use can easily cause the deterioration of the product structure, so that the slag intrudes into the bricks along the gaps, erodes the magnesia particles, and reduces the service life of the magnesia-carbon bricks. At present, the oxidation resistance of magnesia-carbon bricks is mainly improved by adding antioxidants.

Principles of choosing antioxidants

1 Judging the possible condensed phase and the vapor pressure of each gas phase according to the thermodynamic data and operating conditions

2. Compare the affinity of each condensed phase with oxygen and the possibility of CO reaction.

3 Analysis of the influence of various tomb team bricks on the microstructure