JPS6048467B2 - Alumina-svinel-carbon refractories - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to the composition of refractory formulations used in the steel industry, particularly in the pretreatment stage of hot metal.

Recently, soda ash (Na) has been used as a scouring agent in the hot metal stage.

Pretreatment methods for molten pig iron are being considered, in which dephosphorization and desulfurization are performed using quicklime (CaO) containing fluorite (CaF0) and fluorite (CaF0) as a flux, but these fluxes, which are excellent scouring agents, are It acts as a strong corrosive agent for refractories in hot metal processing furnaces. Table 1: Alumina (A
l.

03) and spinel (MgO-Al.

O0) can be mentioned. However, in order to fully demonstrate the corrosion resistance of these refractory materials, it is desirable to use materials with few impurities, especially not to contain impurities in the matrix part. Bricks have the disadvantage that they are susceptible to thermal spalling during use, that is, they are susceptible to flaking due to temperature changes.

For example, regarding alumina, as shown in Table 1, its coefficient of hot linear expansion is as high as 0.86%, and because of its high melting point, it does not form a liquid phase at the operating temperature, which causes thermal spalling. easy. In the case of spinel, the expansion rate and melting point are even higher. Carbon C, silicon carbide (SIC), or both are added to the main raw material in order to improve such thermal spalling properties.

This is due to the following reason. In other words, carbon is usually used in the form of graphite (graphite), but as shown in Table 1, graphite has a coefficient of thermal expansion that is half that of alumina, and a thermal conductivity of 2 K, making it extremely superior to alumina. Graphite belongs to a hexagonal crystal structure and has a layered structure, with strong covalent bonds between carbon atoms in the regular hexagonal ring plane, but weak bonds between layers due to van der Waals bonds. This is because silicon carbide is slippery and has the property of relieving thermal stress caused by thermal changes.Also, as shown in Table 1, silicon carbide has a lower coefficient of thermal expansion than alumina and a higher thermal conductivity. Therefore, it is a material with excellent heat spalling resistance. However, as mentioned above, when carbon is added to improve the heat spalling resistance of alumina and spinel, deterioration of the refractory due to oxidation of carbon becomes a problem. Therefore, it is possible to make the brick structure denser in order to suppress carbon oxidation.
As mentioned above, the layers of graphite are slippery and lamination is likely to occur when high-pressure molding is performed. There is a method of using a binder or a molding aid to improve the molding and filling properties.

There is also a method of adding antioxidants such as glazes,
In any case, the use of these additives is undesirable because it reduces the durability of the refractory brick. Therefore, it is known from experience that adding carbon and silicon carbide simultaneously without taking such measures to densify the structure is effective in preventing oxidation of carbon, but this action and effect have not been elucidated. It has not been.

4 The inventors conducted various experiments on the anti-oxidation effect of silicon carbide (SIC) and analyzed used refractory bricks, and as a result, they found that an alumina-spinel-carbon refractory made of alumina and spinel as main raw materials and added with carbon. We have found that adding a small amount of ultrafine silicon carbide is extremely effective in preventing oxidation of carphone.

That is, the purpose of this invention is to prevent quality deterioration of refractories due to oxidation of carbon and reduce the degree of wear and tear caused by the use of refractories by simultaneously adding a specific fine powder and a specific amount of silicon carbide with carbon. , the gist of which is that alumina (A
l2Oa) and spinel ((MgO-Al.

O. ) 80 to 95% by weight of one or two kinds of raw materials, 3 to 15% by weight of carbon, and 2 to 5% by weight of silicon carbide (SiC), of which 85% or more is fine particles of 2 to 30 microns. It is an alumina-spinel-carbon based refractory. First, to discuss the behavior of SiC at high temperatures, carbon C coexists in refractory bricks, and 1
In the atmosphere inside the brick at 000 to 1,400°C and in an equilibrium state, the oxygen partial pressure is 10-'' to 10-atm) CO.

Partial pressure is 10-2 ~ 10-゜atmNc0 partial pressure is approximately 1
It is atmospheric pressure. Oxygen partial pressure fluctuates in micropores, but even if it rises to 10 to 10 atm, in the low oxygen range below this, SiC will not decompose into SiO gas. It was found that the SIC particles eventually undergo the following reaction on their surface: SlCfCO
=SIO↑+f This reaction accompanies the generation of SiO gas and the deposition of C.

The CO consumed there is generated when FeO in the slag and soda ash (Na2CO), a scouring agent, react with carbon C in the bricks under the operating conditions of the bricks. The carbon that has been oxidized and lost from Si
It is reprecipitated in the brick by the decomposition reaction of C. Furthermore, the SiO gas generated in the above reaction becomes SiO at a location where the oxygen partial pressure is high in the brick, and this becomes SiO in the brick aggregate Al.
'.

0.

Al around. O3-SlO2-based compounds such as mullite (3Ae203.2Si02) fill the pores,
Densify the matrix part. This densification of the matrix works to prevent the oxidation of carbon in bricks.
The functions of SiC can be summarized as follows.

1 Carbon Feedback Mechanism As a result of oxidative wear of carphone on the operating surface of the brick, CO gas is generated in the brick, which reacts with SIC to precipitate 2 moles of C per mole of SIC1, resulting in a densified structure.

2 Generation of new compounds SiO gas, another reaction product, is SIO in the brick pores.

So, Al. O. Al on the surface of the raw material. O. -SIO.
Generates system compounds and fills the pores. 3. Preventing oxidation of carphone in bricks The production of the compound in 2 is a reaction from a gas phase to a solid phase, and the matrix becomes dense, thereby preventing the oxidation of carbon.

Although there are several types of SIC decomposition reactions, it has been clarified by microscopic examination of the head and other microscopic analyzes of tissues that the reaction mechanism described above proceeds under the conditions described above.

It was also found that the same holds true not only when the aggregate is alumina, but also when it coexists with spinel or spinel. Based on the above analysis results, it was concluded that the strengthening of the matrix and the prevention of carbon oxidation by adding SIC do not depend on the amount added, but are proportional to the total specific surface area of the SIC particles.

Therefore, the finer the particle size of the SIC to be added, the greater the effect, so it is most desirable to use a fine powder that is 100% fine particles of 2 to 30 microns, but the currently industrially available fine powder is 2. It was confirmed that the ratio of particles of ~30 microns was about 85% to 93%, and that even with such a particle size, the above-mentioned effects of SiC could be sufficiently exhibited.

Further, ultrafine particles of less than 2 microns are decomposed and cannot become particles before the reaction occurs after the bricks are operated as described above, so the smaller the number, the better. Further, coarse particles exceeding 30 microns are difficult to react with and at the same time are harmful to the corrosion resistance of refractory bricks, so the smaller the better. Further, if the amount of SiC added is less than 2% by weight based on the total amount of bricks, the above-described effects of the present invention cannot be achieved.

It has also been found that the corrosion resistance of bricks decreases when m weight % is added, so the most desirable amount of SiC to be added is 5 weight % or less. As mentioned above, the purpose of adding carbon (graphite) is to improve heat spalling resistance, but if it is added in a small amount less than 3.0% by weight, the resulting brick will have poor heat spalling resistance, and if it exceeds 15% by weight, it will result in a brick with poor heat spalling resistance. When added, the decarburization phenomenon on the working surface increases and the corrosion resistance against slag decreases.

The amount of Naorihon added is 1.5 to 2 times the amount of silicon carbide added.
．． It is preferable to increase the number to about 0 times. Next, the results of the example in which the refractory brick of the present invention and the conventional alumina 5-bon silicon carbide brick were lined in a 2-ton hot metal pretreatment furnace, and the hot metal was mainly subjected to dephosphorization and desulfurization treatment, are shown in the second example. Shown in the table.

− 11i ψH ÷ ″Gll As is clear from Table 2, the refractory brick of the present invention has an average loss amount representing the degree of achievement of oxidation prevention of carbon in the brick, that is, the amount of loss of the brick calculated for each charge of hot metal treatment. The amount of wear and tear has decreased significantly.

Claims (1)

[Claims] 1 Alumina (Al_2O_3) and spinel (Mg
O・Al_2O_5) One or two kinds of raw materials are 80 to 9
Silicon carbide (SiC) with 5% by weight, 3 to 15% by weight of carbon, and 85% or more of fine particles of 2 to 30 microns.
An alumina-spinel-carbon-based chemical resistant material containing 2 to 5% by weight of