Development and application of carbon brick/graphite brick
Carbon and graphite can constitute refractory materials or serve as important raw materials for refractory materials mainly based on their following properties:
(1) Graphite has high heat resistance, the highest temperature can reach 3850 ℃, graphite in ultra-high temperature arc, its mass loss is small.
(2) Graphite has high chemical stability, is not easy to react with other inorganic materials and molten metals, and is difficult to be wetted by oxide slag, and has strong resistance to penetration.
(3) The thermal conductivity of graphite is large, but it decreases with the increase of temperature, and it is in adiabatic state even at extremely high temperatures.
(4) Graphite has an anisotropic structure and a small linear expansion coefficient, so it has good thermal shock resistance.
Carbon and graphite refractories have been used in iron-making blast furnaces for a long time, and have continued to develop with the development of iron-making blast furnaces. For example, Germany began to use carbon bricks in blast furnaces in 1920.
Later (from the 1940s to the 1950s), all countries competed to use carbon bricks in blast furnaces. At present, the large blast furnaces in the world use carbon bricks (charcoal blocks) to build from the bottom, hearth to the hearth and other parts of the furnace. Some blast furnaces have been built up to the shaft or even the tapping hole. With the adoption of the water-cooled furnace wall, the interior of the blast furnace bell is also built with carbon bricks.
Early carbon bricks mainly used metallurgical coke as the main raw material, asphalt as a binder, and were produced by extrusion molding. However, this kind of carbon brick tends to cause local abnormal erosion during use. For this reason, the metallurgical coke was changed to roasted anthracite coke with good corrosion resistance to molten iron to improve the performance, as shown in Table 1. It shows that the amount of melting increases in the order of roasted anthracite coke <natural cryptocrystalline graphite <artificial graphite <pitch coke. However, although roasted anthracite coke has the advantage of good corrosion resistance to molten iron, it has the disadvantage of poor alkali resistance due to its high ash content. In order to overcome this shortcoming of roasted anthracite coke, artificial graphite is also used.
Table 1 Corrosion resistance of carbon immersed in hot metal at 1550℃ for 5h
Main raw materials of carbon bricks
Corrosion index
Anthracite coke
100
amorphousgraphite
225
Artificial graphite
438
Pitch coke
713
In order to reduce the damage of the carbon bricks caused by the penetration of molten iron into the pores, various improvements have been made to the carbon bricks:
(1) In order to improve the corrosion resistance of molten iron, alumina is added to the ingredients.
(2) In order to reduce the pore diameter, metallic silicon is added to the ingredients, which reacts to form whiskers during firing, which makes the pores finer and prevents the intrusion (infiltration) of molten iron.
(3) In order to improve the cooling effect, the graphite blending ratio has been increased.
(4) Change the binder from asphalt to resin to improve the high temperature strength.
(5) By adding SiC, the pores are made finer and the penetration of molten iron is prevented.
(6) At the bottom of the furnace, in order to improve the cooling effect, graphite bricks and C-SiC bricks with high thermal conductivity are used on the outside of the furnace.
The largest user of carbon and graphite refractories is the metallurgical industry, mainly used for lining refractories in blast furnaces (carbon and graphite refractories for blast furnaces), ferroalloys, and metal refining (including electric furnaces and iron furnaces). Among them, more than 70% of blast furnaces are used (75% in Japan). In the steel-making electric furnace, the use of artificial graphite bricks in harsh parts has the effect of prolonging the life. In addition, carbon bricks are used as refractory materials for the lining of electric furnaces in the production of phosphorus and soluble phosphate fertilizers.
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