JPS593069A - Alumina-silicon carbide-carbon refractories - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

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

Recently, at the hot metal stage, soda ash (Nas Os) +
Or the fluxing agent fluorite (CaF2) vf-added quicklime (
A pretreatment method for hot metal that performs dephosphorization and desulfurization using refining agents such as carbs has been studied, but these 7 lacs, which are excellent refining agents, are not suitable for refractories in hot metal processing furnaces.

It acts as a strong corrosive agent. For example, alumina (
A40s).

Therefore, in order to achieve 1100% corrosion resistance of refractory materials, it is desirable to use all materials with low impurities, especially not to contain impurities in the matrix part, but on the other hand, refractories whose main raw material is alumina are currently in use. It has the drawback that it is susceptible to thermal spalling, that is, surface cracks occur due to temperature changes during use, and peeling phenomenon is likely to occur due to this. For example, as shown in Table 1, alumina has a high coefficient of hot linear expansion of 0.86%, a low thermal conductivity of 5.0, and a high melting point (2050°G), so it is in a liquid state at the operating temperature. (Glass layer) Due to no t-formation, thermal spalling is likely to occur.

Table 1 Therefore, in order to improve such thermal spalling property, carbon (Q or silicon carbide (StC) is added to the main raw material.
), it has been conventional practice to add both.

This is due to the following reason. In other words, carbon is usually added in the form of graphite, but as shown in Table 1, graphite has a coefficient of hot linear expansion that is half that of alumina, and a thermal conductivity that is 20 times higher than alumina. It has excellent heat spalling resistance.

Furthermore, graphite belongs to the hexagonal crystal structure and has a layered structure, and the bonds between carbon atoms in the regular hexagonal ring planes are strong covalent bonds, but the bonds between the layers are weak van der Waals bonds, and because the layers are slippery, they are generated by thermal changes. This is because it has the property of relieving thermal stress.

Furthermore, as shown in Table 1, silicon carbide has a lower coefficient of thermal expansion than graphite and a higher thermal conductivity than alumina, making it a material with excellent heat spalling resistance.

In this way, alumina-silicon carbide-carbon based refractories have been used that are based on alumina raw materials and have improved heat spalling properties. Tar, pitch, phenolic resin, etc. are mixed as binding materials at all compounding stages, and the above binding materials are carbonized by mixing, molding, drying, and firing, or by heating during use without firing, so-called carbon. It is a combination.

However, the aforementioned graphite and silicon carbide, which are added to improve the heat spalling properties of alumina and suppress slag infiltration, originally have poor corrosion resistance against soda-based 7 lux. 10. Poor corrosion resistance to CaO-based flux. Furthermore, the quality of the refractory deteriorates due to oxidation of carbon and silicon carbide, including the bonded portion. Therefore, in alumina-silicon carbide-carbon refractories, as a result of the IJx being worn out first, the alumina aggregate separates from the structure of the refractory brick before it reacts significantly with the slag. The result is that the characteristics of the alumina raw material, which has high corrosion resistance against slag, cannot be effectively utilized.

As a result of considering the composition of the composition that should completely prevent the detachment of alumina aggregate due to such wear and tear of the matrix and exhibit all 100 degrees of corrosion resistance of the alumina aggregate, we found that the conventional matrix gold bonded only by carbon bonding and ceramic bonding by hot bonding. The conclusion was reached that it is effective to reinforce with a matrix created by

Furthermore, the requirements for the ceramic bonded matrix part are that it must have very strong corrosion resistance against slag, that even a relatively small amount of alumina aggregate should have a bonding effect with the matrix, and that the formation of ceramic bonds should create a refractory structure. There should be no change in volume that could cause damage to the material.

This invention is based on the above knowledge, and is based on alumina-carbonized, alumina (A4), which is the main raw material for silicon-carbon refractories.
Spinel (MgO, AtzOs
) to strengthen the matrix and reduce the wear rate of the refractory. Periclese (MgO) is added to the total amount of fine powder of 100 microns or less.
) is added in a weight ratio of 0.5 to 4.0 to make the matrix part a structure of carbon bonds and spinel bonds.

Here, the term "magnesia-enriched spinel" refers to a spinel containing periclase that is manufactured so that the magnesia content is greater than the stoichiometric ratio of spinel. As is well known, spinel (mineral name spinel) has a melting point of 2135°C.
is the chemical formula Mg0At20! The theoretical component ratio is Mg02B, 3T Atz Os 71.7%,
The magnesia-enriched spinel used in this invention preferably contains 13% or more of the MgO component, has few impurities, and uniformly contains periclase.

First, in this invention, in the matrix of alumina-silicon carbide-carbon refractory to which magnesia powder or magnesia-enriched spinel powder has been added, magnesia and alumina are bonded together with carbon by high-temperature heating during use, and the magnesia and alumina are heated to 1250°C.
The above reaction occurs, spinel (MgO”At鵞Os)t”
It forms the matrix part of the ceramic bond.

That is, the density (specific gravity) of AtzOs is '5.8 and M
Reacts from g03.6 to Mg0-ALtOs 55t
= The volume expands to form a dense and strong matrix that is a composite of carbon bonds and ceramic bonds.

Magnesia powder used in this invention includes fused magnesia, sintered magnesia, and calcined magnesia.

Magnesia hydroxide etc. can be used. It is desirable that the particle size of the magnesia-enriched spinel powder and magnesia powder is as fine as possible in consideration of dispersibility, and the amount added is the same as that required to form the ceramic bond in the matrix based on spinel 1 expandability. It is desirable to keep it at the lowest level.

Therefore, the particle size to be added is preferably 50 microns or less, but
The fine powder normally obtained as a raw material for refractories is 100 microns or less (equivalent to passing through a 150-mesh Tyler standard sieve). In addition, the addition ratio is MgO (
It is desirable that the amount of periclase is in the range of 0.5 to 4.0% by weight. If it is less than 0.5% by weight, the amount of spinel produced is small and a dense connective tissue cannot be obtained;
If it is more than that, the amount of expansion of spinel generated is large and the connective tissue is destroyed, which is not preferable. In addition, compared to magnesia powder,
Since magnesia-enriched spinel powder is mixed in a large amount when adding the same amount of Vericles, uniform dispersion is facilitated.

Various materials can be considered as the alumina-silicon carbide-carbon raw materials used in this invention.

For example, fused alumina and sintered alumina, which are usually used for refractories, can be used, but in addition to these, calcined alumina,
Aluminum hydroxide etc. can be used. The amount of alumina blended is preferably 70 to 90% by weight.

Next, carbon is necessary to suppress the intrusion of slag and obtain spalling resistance, and scaly graphite, earthy graphite, etc. can be used, but scaly graphite with few impurities and good crystal development is preferable. The blending amount of carbon is preferably 5 to 15% by weight, and 5 to 15% by weight.
If it is less than 155% by weight, it is difficult to impart spalling resistance, and if it is more than 155% by weight, the decarburization phenomenon on the working surface increases and the corrosion resistance against slag decreases. It is preferable that the amount of Naori-bon added is about 1.5 to 2.0 times the amount of silicon carbide added.

In addition, silicon carbide is effective in imparting spalling resistance by reducing the expansion of refractories and suppressing carbon oxidation, and is preferably used as a fine powder, with a blending amount of 3 to 10% by weight.
is desirable. If the weight is less than 6, the effect of imparting spall resistance and suppressing carbon oxidation is small. Moreover, if the weight exceeds 100, the corrosion resistance of the matrix portion decreases.

The alumina-silicon carbide-carbon refractory of the present invention is produced by adding a clay mixture containing aluminum-based silicon carbide and magnesia or magnesia-enriched spinel to form a spinel bond to a carbon raw material, as described above, using an organic binder in a conventional manner. For example, phenol resin, furan resin, coal tar, tar pitch, etc. are added, kneaded, and dried to produce an unfired product. Alternatively, it can be produced as a fired product by firing in a non-oxidizing atmosphere at about 1400°C.

By adding periclase in this way and making the matrix part a composite structure of spinel bonds and carbon bonds, preliminary damage to the matrix part is suppressed, thereby preventing the detachment of the alumina aggregate and ensuring sufficient corrosion resistance of the alumina aggregate. It is something that can be demonstrated.

Next, Table 2 shows examples and test results of this invention.

It is shown in Tables 6 and 4. Table 2 shows the chemical composition of magnesia and magnesia-enriched spinel. Table 3 shows compounding examples. 5 weights of thermosetting phenolic resin was added to each compound, kneaded, and molded at a molding pressure of 1000° C./300° C.
It was dried for 10 hours. Table 4 shows the test results of the above-mentioned example and the conventional product and the results of use in a hot metal pretreatment furnace.

Table 6 Formulation table Table 4 Usage results Note) Physical properties were measured according to the JIS test method after treatment in a coke pleat at 1400°C for 3 hours.

The conventional examples in Table 4 are carbon bonded conventional alumina
It is a silicon carbide-carbon based refractory, and the average loss amount is the average loss amount when 200 in all cases is used as a lining material in a hot metal processing furnace, and the hot metal is mainly desulfurized and dephosphorized.

As is clear from Table 4, the refractory of the present invention, whose matrix portion is a composite structure of carbon bonds and ceramic bonds, has a greatly increased bending strength compared to the conventional example, and the average wear loss in an actual furnace is approximately 20%. % reduction.

Agent: Patent Attorney Sanro Kimura

Claims (1)

[Claims] 100 of either magnesia or magnesia-enriched spinel
An alumina-silicon carbide-carbon refractory whose matrix part has a structure of carbon bonds and spinel bonds by adding 0.5 to 4.0 percent of periclase to the total amount of fine powder of less than a micron.