Carbon-bonded alkaline material—magnesia carbon brick
Magnesia-carbon bricks are carbon-bonded alkaline bricks prepared with magnesia, carbon materials, organic binders and admixtures, after mixing, high-pressure forming and low-temperature treatment. Because the bricks give full play to the advantages of alkaline materials and carbon materials, they have excellent thermal shock resistance, spalling resistance, slag resistance and high temperature creep resistance. It is an ideal lining material for metallurgical smelting furnaces.
alkaline material, magnesia carbon brick, magnesia, binders
Realed product：magnesia carbon brick
All countries attached great importance to it and formed a black whirlwind in the 1980s, which improved the age of the furnace and gained benefits. At present, China can produce ordinary and high-strength magnesia-carbon bricks, as well as functional products such as magnesia-carbon breathable bricks, which can basically meet the needs of the development of the metallurgical industry.
The main raw material for the production of magnesia carbon bricks is magnesia, and its technical requirements are high purity, less impurities, complete development of granular crystals, uniform texture, low porosity and high volume density. Magnesia is divided into fused magnesia and sintered magnesia, each of which is divided into several grades: carbon materials are also the main raw materials of magnesia-carbon bricks, and natural flake graphite is generally used. It has no eutectic relationship with oxides such as MgO, and does not form a low-melting substance. Its thermal conductivity is large, the elastic modulus is small, the thermal expansion coefficient is low, and it has the characteristics of non-wetting. The carbon atoms of this type of graphite are multi-layer laminated crystals of hexagonal ring-shaped flakes, with a well-developed structure and a certain degree of oxidation resistance: the binder is the key material for the production of magnesia carbon bricks. Due to the pyrolysis or polycondensation of the binder, a carbon bond bond is formed, so that the brick gains strength. Its technical requirements: (1) Wetting of the carbon material is small, and the affinity is better (2) The residual carbon rate is high (3) The content of impurities and water is small. Commonly used binders include phenolic resin, modified phenolic resin and tar pitch, etc. The admixtures mainly include AL, Si powder and curing agent. When producing high-strength magnesia-carbon bricks, high-quality raw materials should be selected and additives should be added. When producing ordinary magnesia-carbon bricks, the grade of raw materials can be lower, and tar pitch is allowed as a binder, and additives are generally not mixed.
The critical particle size of magnesia-carbon brick refractory aggregate is 8 or 5mm: refractory powder <0.088mm should account for more than 90%: the particle size of flake graphite is generally less than 100 mesh, when it is made into mixed powder, its fineness is 0.09mm: AL , Si, SiC and CaSi and other additives are also mixed with fine powder. General mixing ratio of magnesia carbon brick: refractory aggregate 60%~70%, mixed powder 30%~40%, binder 4%~5%, curing agent 0.2%~0.4%, admixture 2%~5%, next The table shows the performance of ordinary magnesia carbon bricks.
There are two parts of carbon in magnesia carbon bricks, one is graphitic carbon, and the other is carbon brought in by the binder, which is called bound carbon. At room temperature, magnesia particles and graphitic carbon rely on the viscosity of organic binders to obtain strength through pressure forming: After heat treatment, the resin is cured to form a bonded carbon film, which forms a spatial carbon network, which envelops the particles, and at the same time The graphite carbon and other materials are connected to form a dense structure, so the magnesia carbon brick has higher strength.