JP2020125220A - Silicon nitride refractory - Google Patents

Abstract

To provide a silicon nitride refractory for a blast furnace tuyere, which has improved spalling resistance and is excellent in flowability, and the texture of which can be elaborated.SOLUTION: The composition of a silicon nitride casting material is as follows: 70-95 mass% of silicon nitride, 2-15 mass% of zirconia, 1-5 mass% of silica ultra-fine powder, and 0.5-5 mass% of metal silicon. By this composition, the silicon nitride casting material can be obtained which is excellent in flowability and the texture of which can be elaborated; and when the casting material is molded into a refractory for a blast furnace tuyere, high spalling resistance can be obtained.SELECTED DRAWING: None

Description

The present invention relates to silicon carbide refractories.

The blast furnace is provided with tuyere made of a heat-resistant alloy, which is a blower opening for blowing hot air into the furnace. A refractory material for the blast furnace tuyere is placed around the tuyere to protect the tuyere and the furnace body skin from deterioration due to heat, slag, gas, etc. In recent years, for refractory materials for blast furnace tuyere, large blocks by casting have been increasingly used for the purpose of shortening the furnace construction period and structural stability. From a material standpoint, a silicon carbide refractory having excellent CO gas resistance, alkali resistance, high thermal conductivity and the like is generally used.

Patent Document 1 aims to "improve fluidity during cast molding to densify a refractory structure to improve alkali resistance", and to "roughly remove silicon carbide whose surface corners are smoothed by abrasion treatment. Blast furnace formed by casting a mixture containing 0.5 to 10% by mass of carbon fine powder, 1 to 12% by mass of metal silicon fine powder and a binder with respect to 100% by mass of a refractory aggregate mainly composed of silicon carbide as a grain portion. "Refractory for tuyere."

Patent Document 2 discloses that "5 to 90% by weight of silicon carbide is used," for the purpose of "being dense with no generation of H ₂ gas, excellent in corrosion resistance, large in cold and hot strength, and excellent in thermal shock resistance". , A castable refractory containing silicon carbide in which 0.5 to 10% by weight of alumina cement and 0.1 to 5% by weight of silicon iron nitride and/or iron powder in terms of Fe are added to 100% by weight of the remaining refractory raw material. ." is disclosed.

In Patent Document 3, as a silicon oxide refractory for blast furnace lining having high oxidation resistance, "addition of 75 to 95% by weight of silicon carbide, 3 to 10% of metallic silicon, and 0.3 to 5% of boron carbide is added. A high-oxidation-resistant silicon carbide refractory for a blast furnace lining, which is characterized in that it is made into a compounded powder, an organic binder is added thereto, and the mixture is kneaded and molded and fired."

JP 2002-195761A JP-A-2-221164 JP-A-60-51667

The tuyere is made of heat-resistant alloy, etc., but water cooling is essential to withstand the high temperature of hot air. Therefore, the refractory for the tuyere of the blast furnace causes a large temperature difference between the portion in contact with the tuyere and the opposite side, and cracks due to spalling are likely to occur. Further, when a large amount of silicon carbide is used for the purpose of improving alkali resistance and heat conduction, the fluidity at the time of cast molding is insufficient, and the structure is inferior in densification as compared with the pressure molded product.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and is a silicon carbide casting material and a blast furnace tuyere capable of improving spalling resistance and excellent in fluidity and capable of densifying the structure. The purpose is to provide refractory materials.

The present invention is a silicon carbide casting material containing 70 to 95 mass% silicon carbide, 2 to 15 mass% zirconia, 1 to 5 mass% ultrafine silica powder, and 0.5 to 5 mass% metallic silicon.

The zirconia (a) preferably has a mass ratio (a/b) of 0.5 to 2.5 with respect to the total amount (b) of ultrafine silica powder and metallic silicon.

The silicon carbide casting material may be cast with a binder to form a precast refractory material.

According to the present invention, it is possible to obtain a silicon carbide casting material having excellent fluidity and capable of densifying the structure, and it is possible to obtain high spalling resistance when formed into a blast furnace tuyere refractory.

<Verification>
In order to make both the spalling resistance and fluidity of the silicon carbide casting material compatible, we verified the effect by adding various raw materials, and found that the hot strength of the casting material was zirconia added to the silicon carbide material. It has been recognized that the spalling resistance is improved and the spalling resistance is significantly improved. Further, ultrafine silica powder for ensuring fluidity as a pouring material and metallic Si silicon are blended in a specific ratio for further improvement of hot strength. This has led to the recognition that tissue embrittlement is suppressed. The reason for this is not clear, but it is presumed that zirconia reacts with ultrafine silica powder and metallic silicon to form zircon and densify.

<Composition>
Each composition of the above casting material will be examined below.

[Silicon Carbide]
The silicon carbide is a main raw material, and is 70 to 95 mass% with respect to 100 mass% of the refractory powder containing a binder. If the silicon carbide content is less than 70% by mass, the slag resistance will decrease, and if it exceeds 95% by mass, the fluidity will decrease. More preferably, it is in the range of 80 to 90 mass %. The purity of silicon carbide is preferably 80% by mass or more, more preferably 90% by mass or more. If the purity of silicon carbide is less than 80% by mass, the slag resistance decreases.

[Zirconia]
The zirconia raw material reacts with ultrafine silica powder, metallic silicon, etc. to contribute to the improvement of hot strength. As the zirconia raw material, any of a fusion raw material, a sintering raw material and a natural raw material can be used as long as the purity is 95% by mass or more. For example, stabilized zirconia, partially stabilized zirconia, unstabilized zirconia, natural baddelite, etc. can be used.

The amount of the zirconia raw material added is 2 to 15% by mass based on 100% by mass of the refractory powder containing the binder. If it is less than 2% by mass, the effect of improving the hot strength cannot be obtained, and if it exceeds 15% by mass, the structure becomes brittle due to the volume change accompanying the phase transformation of zirconia, and the hot strength is lowered. More preferably, it is in the range of 6 to 9 mass %.

[Ultra fine silica powder]
The ultrafine silica powder densifies the work body due to the effect of improving the fluidity and also contributes to the improvement of the hot strength. The SiO ₂ purity is 90% by mass or more. If it is less than 90% by mass, the fluidity is lowered due to the influence of impurities. As the ultrafine silica powder, fumes generated during the production of metallic silicon or during the production of zirconia can be used, but of course high-purity synthetic products can also be used. The addition amount of the ultrafine silica powder is 1 to 5 mass% with respect to 100 mass% of the refractory powder containing the binder. If it is less than 1% by mass, fluidity is insufficient, and if it exceeds 5% by mass, sufficient hot strength cannot be obtained. It is more preferably in the range of 3 to 4% by mass.

[Metallic silicon]
The amount of the metallic silicon added is 0.5 to 5 mass% with respect to 100 mass% of the refractory powder containing the binder. If it is less than 0.5% by mass, hot strength will not be exhibited, and if it exceeds 5% by mass, swelling and cracking of the construction product will occur. More preferably, it is in the range of 1 to 3 mass %.

[Mass ratio of zirconia raw material and ultrafine silica powder + metallic silicon]
By setting the mass ratio a/b of the zirconia raw material (a) and (silica ultrafine powder + metallic silicon) (b) to be in the range of 0.5 to 2.5, the zircon formation reaction is optimized and the hot strength is further improved. Can be improved.

[Calcined alumina]
Further, in the present invention, calcined alumina can be used as a fluidity imparting agent and a sintering aid. The purity is preferably 95% by mass or more. The content of calcined alumina is preferably 10% by mass or less (excluding zero) with respect to 100% by mass of the refractory powder containing a binder. If it exceeds 10% by mass, mullite is formed prior to zircon and interferes with the action of the present invention, which is not preferable.

[Carbon raw material]
A carbon raw material can be used for the purpose of improving slag resistance. As the carbon raw material, for example, scaly graphite, soil graphite, coke, carbon black, pitch and the like can be used. Since the carbon raw material inhibits sintering, it is preferably 5% by mass or less with respect to 100% by mass of the refractory powder containing a binder.

[Dispersant]
In the present invention, a dispersant may be added to impart fluidity. The dispersant is not particularly limited, and inorganic dispersants such as tripolyphosphate, hexametaphosphate, ultrapolyphosphate, and sulfonate, and organic dispersants such as polycarboxylate and polyacrylate are used. can do. Further, plural kinds of dispersants may be used in combination. The amount of the dispersant added is 0.5% by mass or less, preferably 0.05 to 0.3% by mass, based on 100% by mass of the refractory powder containing the binder.

[Curing accelerator, curing retardant]
In the present invention, a curing accelerator or a curing retarder can be added if necessary. As the curing accelerator, for example, slaked lime, calcium chloride, sodium aluminate, lithium carbonate or the like can be used, and a plurality of types of curing accelerators can be used in combination. As the setting retarder, for example, borate, tartrate, citrate, oxalate, gluconate, carbonate, sugar or the like can be used, and plural kinds of setting retarders can be used together. it can. The addition amount of the curing modifier is preferably 0.5% by mass or less by external multiplication with respect to 100% by mass of the refractory powder containing the binder.

[Explosion prevention agent]
The cast material may explode during drying. Therefore, a blast preventing material may be added, and as the blast preventing agent, for example, metal aluminum, aluminum lactate, organic fiber or the like can be used. The amount of the explosion-proof agent added is preferably 5% by mass or less by external multiplication with respect to 100% by mass of the refractory powder containing the binder.

[Antioxidant]
Boron carbide, for example, can be used as the antioxidant. The antioxidant is preferably added in an amount of 5% by mass or less, based on 100% by mass of the refractory powder containing a binder.

The above-mentioned silicon carbide casting material can be molded by kneading with a liquid such as water and pouring it into a mold. It can also be used by molding it into a precast block in advance.

The present invention will be described in detail below with reference to examples and comparative examples. The present invention is not limited to the forms shown in the examples. Each property was evaluated according to the following methods.

<Test formulation>
Tables 1 to 5 show the compounding ratios of Examples and Comparative Examples. In Examples 1 to 36, the amounts of silicon carbide, zirconia, metallic silicon, and fine silica powder were varied within the scope of the present invention. Examples 1 to 9 are examples in which the zirconia fine powder is 2% by mass, Examples 10 to 18 are examples in which the zirconia fine powder is 6% by mass, and Examples 19 to 27 are examples in which the zirconia fine powder is 9% by mass, and Examples. Nos. 28 to 36 are examples in which the zirconia fine powder is 15% by mass, and the amount of silicon carbide (1 mm or less) is adjusted according to the amount of the zirconia fine powder.

On the other hand, Comparative Example 1 is an example in which the amount of silicon carbide is outside the lower limit of the present invention, Comparative Examples 2 and 3 are examples in which the amount of zirconia is outside the range of the present invention, and Comparative Examples 4, 5 and 6 are ultrafine silica powders. Examples in which the amount is out of the range of the present invention and Comparative Examples 7, 8 and 9 are examples in which the amount of metallic silicon is out of the range of the present invention.

In addition, in each table, the additive is the above-mentioned [dispersant] [curing accelerator, curing retarder] [explosion preventing agent] [antioxidant].

<Amount of added water>
The amount of added water was represented by the amount of water which gives a flow value of 135 to 145 in a flow test specified by JIS R2521 (physical test method for alumina cement for refractories). The smaller the amount of added water, the better the fluidity of the composition.

<Creation of test pieces>
The kneaded product was poured into a mold, and after curing, the frame was removed to obtain a molded body. The obtained molded body was dried at 110° C. for 24 hours, put in a pod filled with coke breeze, and reduction-baked at 1500° C. for 3 hours. After firing, it was ground and subjected to a test.

<Apparent porosity>
The apparent porosity was measured according to JIS R2205 (Method for measuring apparent porosity/water absorption/specific gravity of refractory bricks).

<Heat resistant spall resistance>
The heat-resistant spall resistance was evaluated by the elastic modulus decrease rate before and after thermal shock, and the smaller the elastic modulus decrease rate, the higher the spall resistance.

(Rate of elasticity decrease)
The test piece was dipped in hot metal heated to 1500° C. for 3 minutes, and then air-cooled for 7 minutes. This cycle was repeated twice, and the elastic modulus before and after the test was measured. The elastic modulus was calculated from the ultrasonic wave propagation velocity and the sample density.

The elastic modulus decrease rate was expressed as an index by the following formula. The smaller the value of this index, the better the heat resistant spalling property. The elastic modulus decrease rate of 50 or less was expressed as ◯.

Elastic modulus decrease rate={(Elastic modulus before test-Elastic modulus after test)/(Elastic modulus before test)}×100
<Hot bending strength>
The hot bending strength was measured at 1500° C. in a nitrogen atmosphere according to JIS R2656 (testing method for hot bending strength of refractory bricks and refractory insulating bricks). A sample having a hot bending strength of 2 MPa or more was rated as ◯.

It is apparent that the working examples of the present invention have improved hot strength as compared with the comparative examples, have good fluidity, and are dense construction bodies.

As described above, the present invention, by adding zirconia and silica ultrafine powder and metallic silicon to silicon carbide in silicon carbide, it is possible to obtain a casting material having excellent fluidity and capable of densifying the structure, High spalling resistance can be obtained when molded into a blast furnace tuyere refractory.

Claims (4)

70-95% by mass of silicon carbide, 2-15% by mass of zirconia, 1-5% by mass of ultrafine silica powder, and 0.5-5% by mass of metallic silicon. The silicon carbide casting material according to claim 1, which contains 10% by mass or less (excluding zero) of calcined alumina. The silicon carbide casting material according to claim 1 or 2, wherein the zirconia raw material/(silica ultrafine powder+metal silicon) (mass ratio) is in the range of 0.5 to 2.5. A precast refractory formed by molding the silicon carbide casting material according to claim 1.