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Influence of metal aluminum powder on carbon-containing refractories

wallpapers Industry 2020-12-30
Under normal circumstances, the main function of adding metal aluminum powder to carbon-containing refractories is to improve the oxidation resistance of the material, reduce the oxidation of graphite, and extend the service life of carbon-containing products.
At the same time, after high-temperature treatment of aluminum powder-containing materials, the aluminum powder will undergo chemical changes to form a certain ceramic phase, which improves the performance of refractory materials. Under a neutral atmosphere (argon), it is effective against alumina-graphite composite refractories and magnesium. When carbon refractories are heat treated at different temperatures (500-1500℃), the addition of metal aluminum powder has a local effect, and the infiltration phenomenon is caused by the influence of metal aluminum at the added position, thereby increasing the strength of the refractory;
In the magnesia-carbon refractory containing metal aluminum powder, after the metal aluminum powder is heated to the melting point, the aluminum liquid will burst the aluminum oxide shell surrounding the metal aluminum powder and react with the surrounding carbon to form aluminum carbide;
When the temperature reaches 1100°C, the aluminum powder will completely disappear, and two new phases can be seen-a large number of interlaced plate-shaped aluminum carbide and magnesium aluminum spinel;
When the temperature exceeds 1100°C, small spinel crystals are formed in the aluminum carbide position, and the aluminum carbide begins to disappear, forming aluminum oxide and reacting with magnesium oxide to form magnesium aluminum spinel;
The aluminum carbide disappears completely at 1500°C, forming a fine lattice-like ceramic bond composed of spinel.
Aluminum carbide can be produced by different liquid-solid or gas-solid reactions, but at this time, the reaction of liquid aluminum and surrounding carbon to produce aluminum carbide is the easiest thermodynamically. Due to the difference in carbon activity, metallic aluminum has different reactivity.
In alumina-graphite composite refractories, when the temperature is less than 1100°C, the effect is the same as that in magnesia-carbon refractories. When the temperature is greater than 1300°C, oxygenated aluminum carbide will be produced, which reduces the permeability of the material and improves the refractory The erosion resistance.
After the carbon embedded heat treatment at 1200℃, aluminum oxide and aluminum carbide are formed around the original metal aluminum, and there are fibrous aluminum nitride formed between graphite or on the surface of aluminum carbide.
Some of the products are aluminum oxide surrounded by aluminum carbide, some are aluminum oxide shells surrounded by metal aluminum, and aluminum carbide or aluminum oxide shells have pores or holes.

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