CA1189093A - Carbon-containing refractory - Google Patents
Carbon-containing refractoryInfo
- Publication number
- CA1189093A CA1189093A CA000421635A CA421635A CA1189093A CA 1189093 A CA1189093 A CA 1189093A CA 000421635 A CA000421635 A CA 000421635A CA 421635 A CA421635 A CA 421635A CA 1189093 A CA1189093 A CA 1189093A
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- CA
- Canada
- Prior art keywords
- refractory
- graphite
- weight
- carbon
- parts
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
ABSTRACT OF THE DISCLOSURE
Carbon in the form of graphite is commonly used in refractories for metallurgical purposes because of its ability to increase resistance to corrosion. However, if the graphite in the refractory becomes oxidized, it greatly loses this ability. For this reason, it is very important for a refractory to have good resistance to oxidation, but there are at present no refractories fully satisfactory from the standpoints of re-sistance to oxidation and hot strength. The present invention is a carbon-containing refractory having excellent resistance to oxidation and hot strength. These favorable properties are obtained by the addition in the refractory of both boron carbide and metal powder, the powder comprising at least one metal selected from A?, Si, Fe, and Ni.
Carbon in the form of graphite is commonly used in refractories for metallurgical purposes because of its ability to increase resistance to corrosion. However, if the graphite in the refractory becomes oxidized, it greatly loses this ability. For this reason, it is very important for a refractory to have good resistance to oxidation, but there are at present no refractories fully satisfactory from the standpoints of re-sistance to oxidation and hot strength. The present invention is a carbon-containing refractory having excellent resistance to oxidation and hot strength. These favorable properties are obtained by the addition in the refractory of both boron carbide and metal powder, the powder comprising at least one metal selected from A?, Si, Fe, and Ni.
Description
il~9~)~3;3 A CARBON-CONTAINING REFRACTORY
BACKG~OUND OF THE INVENTION
The present invention relates to an improved type of carbon-containing refractory and more specifically to burned and umburned AQ203-C, MyO-C, and MgO-AQ203-C
refractories having improved resistance to oxidation, spalling, and corrosion, in addition to improved hot strength.
Refractories containing carbon in the form of graphite are widely used in metallurgy. When in contact with molten iron, molten steel, or slag, these refractories exhibit excellent resistance to corrosion. Since graphite itself is resistant to wetting by slag, its presence in refractories prevents the penetration of slag into the refractories. Further, because of the presence of graphite, the refractories can not be over-sintered, and therefore thermal spalling does not readily occur. This, too, contributes to the high refractoriness of graphite-containing refractories.
However, graphite is very easily oxidized by oxygen in its surroundings, which causes a graphite-containing refractory to lose its excellent characteristics. In order to obtain a refractory with good characteristics, it is extremely important to decrease the oxidation of graphite.
Various methods have been proposed of increasing the resistance to oxidation of this type of refractory, but at present no satisfactory method has been found.
11~90~3 Japanese Patent Laid Open No. 50-69106 disclosed covering the surface of a carbon-containing molded refractory material with a nitride or carbide of silicon and further coating it with a borosilicate glass comprising boron ~arbide and silicon dioxide in order to prevent oxidation. However, these covering layers are not resistant to attack by molten iron, molten steel, or slag, and if worn through by chemical attack will lose their anti-oxidizing effect. Accordingly, this method is not desirable.
Another method of preventing oxidation in carbon-containing refractories is to uniformly disperse metcll powder in a carbon-containing molded refractory material.
Japanese Patent Laid Open No. 55-1077q9 disclosed adcling magnesium powder, aluminum powder, and silicon powder to carbon-containing reEractory bricks, and Japanese Patent Laid Open No. 54-39422 disclosed adding to carbon-containing refractories a metal powder having a greater affinity for oxygen than carbon. In the latter invention, at least one type of metal powder selected from AQ, Si, Cr, Ti, and Mg is added. However, the resistance to oxidation and the hot strength of the resulting carbon-containing refractory are not fully satisfactory.
SUMMARY OF THE INVENTION
It is the object of the present invention to overcome the drawbacks of carbon-containing refractories of the prior art and provide a carbon-containing refractory with excellent resistance to oxidation and hot strength.
These properties are obtained by the addition of boron 39~
carbide and metal powders to the refractory, the metal powder comprising at least one metal selected from AQ, Si, Fe, and Ni.
Accordingly, the present invention provides a carbon-containing refractory comprisin~: 3 to 30 parts by weight of graphite; 70 to 97 parts by weight of re~ractory raw materials;
1 to 7 parts b~ weight of a metal powder, said powder compris-ing at least one metal selected from aluminum, silicon, iron, and nickel; and 0.3 to 5 parts by weight of boron carbide.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The carbon-containing refractory of the present in-vention comprises 3 to 30 parts by weight of graphite, 70 to 97 parts by weight of refractory raw materials, 1 to 7 parts by weight of metal powder, the metal powder comprising at least one metal selected from -the group consisting of AQ, Si, Fe and Ni, and 0.3 to 5 parts by weight of boron carbide.
It is not fully clear what is the bonding structure of the resulting refractory. However, it is thought that when the fine grains of the refractory raw material, the fine grains of graphite, the metallic powder, and the boron carbide are heated, the product of the reaction between the me-tallic powder and the boron carbide binds together the matrix part of brick which is constituted from fine grains of graphite and refrac-tory raw materials. Further, it is thought that only a portion of the surface of the boron carbide powder is converted to boron oxide by oxygen contained ln the pores of the refractory, promoting the sintering of the refractory and forming a compact, dense, and strong bonding structure. Aluminum metal has the drawback that it forms aluminum carbide (AQ4C3) in the tempera-ture range of 800-1400 C. ~his aluminum carbide is undesirable because it is decomposed by water or by moisture in the air, causing the refractory to become brittle. However, after the refractory of the present invention was kept in a reducing ~9~?3 atmosphere at 1500C for 3 hours, aluminium carbide was not identified by X-ray analysis. The combined presence in the refractory of boron carbide with the aluminum powder effectively prevents the formation of alum:inum carbide.
~hen only boron carbide was added to the refractory raw materials and graphite, without any metal powder, the hot strength and the strength after heating were low. Therefore, in the present invention, the metal powder and boron carbide are indispensable components.
When the surface of the refractory is exposed to molten metal, boron carbide is oxidized to form oxide.
Boron oxide together with oxides of the metal powder and the refractory raw material form a melt of high viscosity which covers the surface of the refractory and prevents oxidation of the graphite.
The refractory raw materials employed in the present invention comprise oxides such as magnesia, spinel, alumina, silica, zircon, and zirconia, and non-oxides such as silicon carbide, silicon nitride, and boron nitride.
There are no particular limits on the components, but it is desirable that the main components be magnesia, spinel, and alumina. The graphite may be a natural graphite such as amorpous graphite or crystalline graphite, or it may be an artificial graphite such as that derived from electrode scraps, oil coke, or carbon black. However, it is preferable to use crystalline graphite with few impurities. The relative proportion of graphite used depends upon the type of refractory raw materials used and the intended use for the refractory. However, it is generally preferable to employ 9C~3 3 - 30 parts by weight of graphite per 100 parts by weight of the reEractory aggregate consisting of graphite and refractory raw materials. If the amount oE graphite in the aggregate is less than 3 parts by weight, the graphite will not exhibit good resistance to wetting by slag, in which case the entire refractory will have poor resistance to slag. Further, if the graphite exceeds 30 parts by weight, the desired strength can not be obtained and it becomes difficult to obtain a compact structure constitution.
Commercial boron carbide abrasive material is satisfactory for use as the boron carbide in the refractory.
In order to achieve good reactivi-ty and uniform dispersion of the boron carbide, it is desirable that the grain size be at most 0.125 mm. Per 100 parts by weight of refractory aggregate, 0.3 to 5 parts by weight of boron carbide should be used. If less than 0.3 parts by weight of boron carbide are used, its addition has no effect. If it exceeds 5 parts by weight, the refractory exhibits resistance to oxidation, but its hot strength and durability decrease. As for the metal powder, it may comprise any desired metal selected from AQ, Si, Cr, Ni, or it may comprise a mixture of more than one of these metals. The effects of AQ are particularly excellent. Per 100 parts by weight of refractory aggregate, the amount of metal powder should be 1 to 7 parts by weight.
If less than 1 part by weight is used, the addition of the metal powder produces no effect, and if more than 7 parts by weight are used, the resistance to corrosion of the reEractory decreases.
11~90~3 The yrain size-regulated refractory aggregate, boron carbide and metal powder are blended in the above described ratios. A binder such as tar, pitch, phenolic resin, cr furan resin is added. Using conventional methods, this mixture is molded. After being dried at around 200C, an unburned refractory is obtained. If it is instead burned at 900 - 1500C in a reducing atmosphere, a burned refractory is obtained.
The following examples of a refractory according to the present invention illustrate the effects pro~uced by various combinations of components.
Example 1 80 parts by weight of magnesia, 20 parts by weight of graphite, 3 parts by weight of aluminum powder, 0.5 parts by weight of boron carbide, and 5 parts by weight of resol-type phenolic resin as a binder were blended together and then molded under a pressure of 1000 kg/cm2 into standard bricks (230 x 114 x 65 mm) which were then dried at 200C
for 5 hours. At 1400C, the completed unburned bricks had a high hot modulus of rupture of 225 kg/cm2. After oxidizing burning at 1000C for 3 hours, the bricks had a decrease in weight of only 2.8~.
Example 2-5 Using the same method as used for Example 1, carbon-containing refractories having various compositions were prepared and formed in-to unburned standard bricks. The components and physical properties of these refractories according to the present invention are shown in Table 1.
~ 9~3 Comparative Examples 1-3 For the purpose of comparison, three refractories having the compositions shown on the right side of Table 1 were blended and molded in-to standard bricks using the same method as was used in Example 1. Unlike the refractory of the present invention, they did not contain boron carbide and metal powder in combination. As can be seen from the table, these refractories had a much lower hot modulus of rupture and a much greater weight loss during burning at 1000C than does the present refractory, clearly illustrating the beneficial effect of the combination of boron carbide and metal powder.
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BACKG~OUND OF THE INVENTION
The present invention relates to an improved type of carbon-containing refractory and more specifically to burned and umburned AQ203-C, MyO-C, and MgO-AQ203-C
refractories having improved resistance to oxidation, spalling, and corrosion, in addition to improved hot strength.
Refractories containing carbon in the form of graphite are widely used in metallurgy. When in contact with molten iron, molten steel, or slag, these refractories exhibit excellent resistance to corrosion. Since graphite itself is resistant to wetting by slag, its presence in refractories prevents the penetration of slag into the refractories. Further, because of the presence of graphite, the refractories can not be over-sintered, and therefore thermal spalling does not readily occur. This, too, contributes to the high refractoriness of graphite-containing refractories.
However, graphite is very easily oxidized by oxygen in its surroundings, which causes a graphite-containing refractory to lose its excellent characteristics. In order to obtain a refractory with good characteristics, it is extremely important to decrease the oxidation of graphite.
Various methods have been proposed of increasing the resistance to oxidation of this type of refractory, but at present no satisfactory method has been found.
11~90~3 Japanese Patent Laid Open No. 50-69106 disclosed covering the surface of a carbon-containing molded refractory material with a nitride or carbide of silicon and further coating it with a borosilicate glass comprising boron ~arbide and silicon dioxide in order to prevent oxidation. However, these covering layers are not resistant to attack by molten iron, molten steel, or slag, and if worn through by chemical attack will lose their anti-oxidizing effect. Accordingly, this method is not desirable.
Another method of preventing oxidation in carbon-containing refractories is to uniformly disperse metcll powder in a carbon-containing molded refractory material.
Japanese Patent Laid Open No. 55-1077q9 disclosed adcling magnesium powder, aluminum powder, and silicon powder to carbon-containing reEractory bricks, and Japanese Patent Laid Open No. 54-39422 disclosed adding to carbon-containing refractories a metal powder having a greater affinity for oxygen than carbon. In the latter invention, at least one type of metal powder selected from AQ, Si, Cr, Ti, and Mg is added. However, the resistance to oxidation and the hot strength of the resulting carbon-containing refractory are not fully satisfactory.
SUMMARY OF THE INVENTION
It is the object of the present invention to overcome the drawbacks of carbon-containing refractories of the prior art and provide a carbon-containing refractory with excellent resistance to oxidation and hot strength.
These properties are obtained by the addition of boron 39~
carbide and metal powders to the refractory, the metal powder comprising at least one metal selected from AQ, Si, Fe, and Ni.
Accordingly, the present invention provides a carbon-containing refractory comprisin~: 3 to 30 parts by weight of graphite; 70 to 97 parts by weight of re~ractory raw materials;
1 to 7 parts b~ weight of a metal powder, said powder compris-ing at least one metal selected from aluminum, silicon, iron, and nickel; and 0.3 to 5 parts by weight of boron carbide.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The carbon-containing refractory of the present in-vention comprises 3 to 30 parts by weight of graphite, 70 to 97 parts by weight of refractory raw materials, 1 to 7 parts by weight of metal powder, the metal powder comprising at least one metal selected from -the group consisting of AQ, Si, Fe and Ni, and 0.3 to 5 parts by weight of boron carbide.
It is not fully clear what is the bonding structure of the resulting refractory. However, it is thought that when the fine grains of the refractory raw material, the fine grains of graphite, the metallic powder, and the boron carbide are heated, the product of the reaction between the me-tallic powder and the boron carbide binds together the matrix part of brick which is constituted from fine grains of graphite and refrac-tory raw materials. Further, it is thought that only a portion of the surface of the boron carbide powder is converted to boron oxide by oxygen contained ln the pores of the refractory, promoting the sintering of the refractory and forming a compact, dense, and strong bonding structure. Aluminum metal has the drawback that it forms aluminum carbide (AQ4C3) in the tempera-ture range of 800-1400 C. ~his aluminum carbide is undesirable because it is decomposed by water or by moisture in the air, causing the refractory to become brittle. However, after the refractory of the present invention was kept in a reducing ~9~?3 atmosphere at 1500C for 3 hours, aluminium carbide was not identified by X-ray analysis. The combined presence in the refractory of boron carbide with the aluminum powder effectively prevents the formation of alum:inum carbide.
~hen only boron carbide was added to the refractory raw materials and graphite, without any metal powder, the hot strength and the strength after heating were low. Therefore, in the present invention, the metal powder and boron carbide are indispensable components.
When the surface of the refractory is exposed to molten metal, boron carbide is oxidized to form oxide.
Boron oxide together with oxides of the metal powder and the refractory raw material form a melt of high viscosity which covers the surface of the refractory and prevents oxidation of the graphite.
The refractory raw materials employed in the present invention comprise oxides such as magnesia, spinel, alumina, silica, zircon, and zirconia, and non-oxides such as silicon carbide, silicon nitride, and boron nitride.
There are no particular limits on the components, but it is desirable that the main components be magnesia, spinel, and alumina. The graphite may be a natural graphite such as amorpous graphite or crystalline graphite, or it may be an artificial graphite such as that derived from electrode scraps, oil coke, or carbon black. However, it is preferable to use crystalline graphite with few impurities. The relative proportion of graphite used depends upon the type of refractory raw materials used and the intended use for the refractory. However, it is generally preferable to employ 9C~3 3 - 30 parts by weight of graphite per 100 parts by weight of the reEractory aggregate consisting of graphite and refractory raw materials. If the amount oE graphite in the aggregate is less than 3 parts by weight, the graphite will not exhibit good resistance to wetting by slag, in which case the entire refractory will have poor resistance to slag. Further, if the graphite exceeds 30 parts by weight, the desired strength can not be obtained and it becomes difficult to obtain a compact structure constitution.
Commercial boron carbide abrasive material is satisfactory for use as the boron carbide in the refractory.
In order to achieve good reactivi-ty and uniform dispersion of the boron carbide, it is desirable that the grain size be at most 0.125 mm. Per 100 parts by weight of refractory aggregate, 0.3 to 5 parts by weight of boron carbide should be used. If less than 0.3 parts by weight of boron carbide are used, its addition has no effect. If it exceeds 5 parts by weight, the refractory exhibits resistance to oxidation, but its hot strength and durability decrease. As for the metal powder, it may comprise any desired metal selected from AQ, Si, Cr, Ni, or it may comprise a mixture of more than one of these metals. The effects of AQ are particularly excellent. Per 100 parts by weight of refractory aggregate, the amount of metal powder should be 1 to 7 parts by weight.
If less than 1 part by weight is used, the addition of the metal powder produces no effect, and if more than 7 parts by weight are used, the resistance to corrosion of the reEractory decreases.
11~90~3 The yrain size-regulated refractory aggregate, boron carbide and metal powder are blended in the above described ratios. A binder such as tar, pitch, phenolic resin, cr furan resin is added. Using conventional methods, this mixture is molded. After being dried at around 200C, an unburned refractory is obtained. If it is instead burned at 900 - 1500C in a reducing atmosphere, a burned refractory is obtained.
The following examples of a refractory according to the present invention illustrate the effects pro~uced by various combinations of components.
Example 1 80 parts by weight of magnesia, 20 parts by weight of graphite, 3 parts by weight of aluminum powder, 0.5 parts by weight of boron carbide, and 5 parts by weight of resol-type phenolic resin as a binder were blended together and then molded under a pressure of 1000 kg/cm2 into standard bricks (230 x 114 x 65 mm) which were then dried at 200C
for 5 hours. At 1400C, the completed unburned bricks had a high hot modulus of rupture of 225 kg/cm2. After oxidizing burning at 1000C for 3 hours, the bricks had a decrease in weight of only 2.8~.
Example 2-5 Using the same method as used for Example 1, carbon-containing refractories having various compositions were prepared and formed in-to unburned standard bricks. The components and physical properties of these refractories according to the present invention are shown in Table 1.
~ 9~3 Comparative Examples 1-3 For the purpose of comparison, three refractories having the compositions shown on the right side of Table 1 were blended and molded in-to standard bricks using the same method as was used in Example 1. Unlike the refractory of the present invention, they did not contain boron carbide and metal powder in combination. As can be seen from the table, these refractories had a much lower hot modulus of rupture and a much greater weight loss during burning at 1000C than does the present refractory, clearly illustrating the beneficial effect of the combination of boron carbide and metal powder.
~1~9093 ~ ... o- ~ ~ ~- ~ ..
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I / t~ h~) ~ 10 ~111:1 a) ~ ,~ ~a~ ~ o I / ,~ ~ ~ ~ ~ ~n~ ~ ~ o ~a ~ u~
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I / ~ a) ,~ ~ 5:: ~ ~ x o ~ ~ .C.C
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Claims
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A carbon-containing refractory comprising: 3 to 30 parts by weight of graphite; 70 to 97 parts by weight of refractory raw materials; 1 to 7 parts by weight of a metal powder, said powder comprising at least one metal selected from aluminum, silicon, iron, and nickel; and 0.3 to 5 parts by weight of boron carbide.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000421635A CA1189093A (en) | 1983-02-15 | 1983-02-15 | Carbon-containing refractory |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000421635A CA1189093A (en) | 1983-02-15 | 1983-02-15 | Carbon-containing refractory |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1189093A true CA1189093A (en) | 1985-06-18 |
Family
ID=4124577
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000421635A Expired CA1189093A (en) | 1983-02-15 | 1983-02-15 | Carbon-containing refractory |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1189093A (en) |
-
1983
- 1983-02-15 CA CA000421635A patent/CA1189093A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |