Aluminum Carbon Brick
Aluminum carbon bricks are mainly composite refractory materials produced by combining alumina (such as sintered/fused white corundum, sub-white corundum, brown corundum, plate-shaped alumina, sintered bauxite, etc.) and carbon/graphite raw materials. In most cases, additives (such as SiC, Si, Al, etc.) are also added to improve their performance.
According to the production method, Al2O3-C refractories can be divided into shaped Al2O3-C refractories (bricks) and amorphous Al2O3-C refractories. The former can be further divided into fired Al2O3-C refractories (fired aluminum carbon bricks) and unfired Al2O3-C refractories (unfired aluminum carbon bricks).
The bonding of unfired Al2O3-C refractories (unfired aluminum carbon bricks) after carbonization treatment or use is based on the adhesion of the coke network to the refractory particles, as well as the direct bonding of some atoms in the coke network, negative valence bonding and van der Waals forces.
Fired aluminum carbon bricks belong to ceramic bonding materials, or ceramic-carbon composite bonding materials. Fired aluminum carbon bricks are widely used as sliding bricks, long nozzle bricks, immersed nozzle bricks, upper/lower nozzle bricks, integral plugs, etc. for sliding nozzles for continuous casting;
Unfired aluminum carbon bricks belong to carbon bonding materials. Because aluminum carbon bricks have high oxidation resistance and resistance to corrosion by Na2O slag, they are also widely used in molten iron pretreatment equipment and as refractory materials for ladle lining.
In addition, Al2O3-C amorphous refractory materials (ramming materials, plastic materials, castable materials, vibrating materials, etc.) are also widely used. The following is a brief introduction to aluminum carbon bricks for ladle.
Aluminum Carbon Bricks for Ladle
Traditional high-aluminum ladle lining bricks are made of sintered bauxite as the main raw material. Due to their inherent disadvantages as described below, their usage is not much:
(1) High-aluminum bricks shrink in volume, resulting in more severe penetration and erosion of molten steel and slag, and the formation of a thicker slag layer at the joints between bricks.
(2) The inherent brittleness of high-aluminum bricks and their structural characteristics cause the ladle lining to form a thicker denudation zone and slag layer.
(3) The inherent wettability of high-aluminum bricks to molten steel and slag causes more severe erosion and penetration of slag, and produces flaking.
In order to overcome the above disadvantages of high-aluminum bricks, graphite is added to the ingredients to produce Al2O3-C bricks to replace traditional high-aluminum bricks for ladle lining.
This type of aluminum-carbon brick is made of corundum, sintered bauxite and graphite as the main raw materials, phenolic resin as a binder and antioxidants. Usually, the amount of graphite added is less than 12%, which basically belongs to low-carbon aluminum-carbon bricks.
Development of magnesia carbon bricks
The development and application of MgO-C composite refractories have a history of more than 40 years. They began with the tar/asphalt combined dolomite refractory developed for converters in the 1950s.
At first, the service life of this carbon-containing refractory was about 100 furnaces in some steel plants.
To this end, fine magnesia powder was added to the tar/asphalt combined dolomite refractory to manufacture the so-called magnesia-dolomite bricks, which made great progress.
Around the 1970s, fired oil-immersed magnesia bricks with a small number of pores became the standard lining bricks for the impact zone and other high-wear parts of the converter. At the same time, the implementation of “comprehensive lining” was implemented, that is, the implementation of zoned lining, which achieved balanced erosion and increased service life.
In the late 1970s, magnesia-carbon bricks were successfully tested on converters, thus creating a precedent for the application of MgO-C composite refractories on converters.
In the 1980s, resin-bonded magnesia carbon bricks were developed, and the amount of carbon added was increased. At the same time, in order to reduce the burning rate of carbon, antioxidants were added to protect the carbon.
Since magnesia carbon bricks 100% utilize the characteristics of natural graphite (flakes) that are difficult to wet with slag, have high thermal conductivity and large stress relaxation capacity, they maximize the high corrosion resistance of MgO, so this type of refractory material is a revolutionary refractory material.
Later, fused magnesia, large-grained sintered magnesia, high-purity (sintered/fused) magnesia and high-purity graphite were introduced into magnesia carbon bricks to improve the material’s corrosion resistance, thereby greatly increasing the service life of the converter.
Performance advantages of magnesia carbon bricks
The advantages of magnesia carbon bricks are: good resistance to slag erosion and thermal shock.
The disadvantage of MgO-Cr2O3 bricks and dolomite bricks in the past was that they absorbed slag components, caused structural spalling, and led to premature damage. Magnesium carbon bricks have eliminated this disadvantage by adding graphite. Their characteristics are that the slag only penetrates into the working surface, so the reaction layer is limited to the working surface, the structure is less spalling, and the service life is long.
Now, in addition to traditional asphalt and resin-bonded magnesia carbon bricks (including fired oil-impregnated magnesia bricks), the magnesia carbon bricks sold on the market include:
(1) Magnesium carbon bricks made of magnesia containing 96% to 97% MgO and graphite containing 94% to 95% C;
(2) Magnesium carbon bricks made of magnesia containing 97.5% to 98.5% MgO and graphite containing 96% to 97% C;
(3) Magnesium carbon bricks made of magnesia containing 98.5% to 99% MgO and graphite containing 98% to 98% C.
According to the carbon content, magnesia carbon bricks are divided into:
(I) Sintered oil-impregnated magnesia bricks (carbon content less than 2%);
(2) Carbon-bonded magnesia bricks (carbon content less than 7%);
(3) Synthetic resin-bonded magnesia carbon bricks (carbon content of 8% to 20%, and in a few cases up to 25%). Antioxidants are often added to asphalt/resin-bonded magnesia carbon bricks (carbon content of 8% to 20%).
Magnesia carbon bricks are produced by combining high-purity MgO sand with flaky graphite, carbon black, etc. The manufacturing process includes the following steps: crushing, screening, and grading of raw materials, mixing according to the material formula design and product performance setting, heating to nearly 100~200℃ according to the type of binder, and mixing with the binder to obtain the so-called MgO-C mud (green body mixture).
MgO-C mud made of synthetic resin (mainly phenolic resin) is formed in cold state;
MgO-C mud made of asphalt (heated to fluid state) is formed in hot state (at about 100℃).
According to the batch and performance requirements of MgO-C products, vacuum vibration equipment, die molding equipment, extruder, isostatic press, hot press and heating equipment, ramming equipment can be used to process MgO-C mud into an ideal shape.
The formed MgO-C body is placed in a kiln at 700~1200℃ for heat treatment to convert the binder into carbon (this process is called carbonization).
In order to increase the density of magnesia carbon bricks and strengthen the bonding, fillers similar to the binder can also be used to impregnate the bricks.
At present, synthetic resins (especially phenolic resins) are mostly used as binders for magnesia carbon bricks. The use of synthetic resin bonded magnesia carbon bricks has the following basic advantages:
(1) The environment allows the processing and production of these products;
(2) The products can be produced under cold mixing conditions, saving energy in the process;
(3) The products can be processed under non-curing conditions;
(4) There is no plastic phase compared to tar pitch binders;
(5) Increased carbon content (more graphite or bituminous coal) can improve wear resistance and slag resistance.
