- The role of carbon in refractories
Applications in refractories are not uncommon, and many new products have been developed in the past year to accommodate new metallurgical processes and developments in refractories.Refractory experts have long known that different forms of carbon exhibit excellent properties in refractories.In refractory oxide, carbon can reduce the wettability of slag, steel and refractory, increase its thermal conductivity and reduce its expansion, so that refractory has excellent thermal shock resistance.In addition, carbon has high thermal stability, and its sublimation temperature is about 4000℃.At the pressure of 110~140bar, the solid liquid gas at the three-phase point of the carbon in the phase diagram is close to 4020℃. Therefore, when the pressure is below 110bar, the carbon sublimates without melting.Since carbon is oxidized at high temperature, the above results can only be applied under specific conditions.
At present, the most important application fields of carbon-containing refractories are:
- Converter, electric furnace and ladle working lining
- A crucible for smelting metal
- Key parts for continuous casting
- Refractory for blast furnace ironmaking
A variety of refractory bricks can be produced by adding carbon, especially magnesium-carbon advanced alkaline refractory.
There are several ways to add carbon to a refractory:
- Impregnated with tar pitch or synthetic resin
Sintered oxide refractories have an open porosity of about 12%, most of which can be filled with tar pitch or resin.Due to the relatively low volatilization and density of volatilized components, the carbon residue rate of these products is about 2%~3%.
- Tar pitch or resin combination
Generally speaking, in the production of magnesium-carbon refractories, the amount of binder is 3%~5%, the carbon residue rate is about 50%, and the carbon content is reduced to 1.5%~3% after carbonization. At the same time, in order to increase the carbon content of the products, carbon black of 1%~3% is added, so that the carbon content of the final products is 3%~6%.
- Add solid carbon
In addition to tar pitch or resin binder, 5% to 15% graphite can be added to make the carbon content in the final product 6% to 18%.
Magnesium-carbon brick is a typical composite material, which combines the excellent fire-resistance properties of carbon material and the excellent properties of the secondary dense layer MgO.
Carbon plays a decisive role in the erosion mechanism of magnesium-carbon refractory.The mechanism is that carbon is difficult to be wetted by silicate slag, so it is difficult to be permeated by melt. MgO is reduced by carbon, and the formed Mg vapor reoxidizes to form MgO layer at the interface between slag and refractory, which inhibits further oxidation of carbon.The possibility and extent to which this process can be affected by electric currents is the subject of current research at the institute of ceramics, glass and structural materials.