JP6131625B2 - Method for producing Al4SiC4 powder and method for producing MgO-C brick - Google Patents

Description

The present invention relates to a method for producing Al ₄ SiC ₄ powder, a method for producing MgO—C brick in which the obtained Al ₄ SiC ₄ powder is blended as a raw material, and MgO—C brick. Specifically, it is a production method of Al ₄ SiC ₄ powder that has improved the effect as an antioxidant for MgO-C brick, and by blending the Al ₄ SiC ₄ powder, in addition to a steelmaking converter and a molten steel pan, The present invention relates to a method for producing MgO—C brick, which is an unfired refractory mainly used in degassing facilities and the like, and further relates to MgO—C brick.

  MgO-C bricks are mainly composed of magnesia raw materials as MgO sources and carbon raw materials such as scaly graphite, powder pitch, petroleum coke, and carbon black as carbon sources, and further as antioxidants for carbon sources. It is a non-fired refractory produced by adding a phenol resin or the like as a binder to Al, Al—Mg alloy and heat-treating at 150 ° C. to 300 ° C.

  This unfired refractory is built and used mainly in degassing furnaces such as converters, ladles, and RH. In these facilities, as various reaction treatments are applied, the temperature of the molten metal becomes higher, and higher oxidation resistance and corrosion resistance are desired than before. For this reason, it has been considered that bricks are further densified to prevent air and slag bricks from entering the bricks.

  Here, as one of the technologies for imparting oxidation resistance to a carbon-containing refractory such as MgO-C brick, a carbon-containing non-added metal powder selected from the group consisting of Al, Si, Cr, Ti, and Mg is added. About the baked refractory, the manufacturing method baked at 500 degrees C or less is described in patent document 1, and the function is explained in full detail as follows. That is, a metal powder having a higher oxygen affinity than carbon is disposed in a mixture of a magnesia raw material refractory powder and carbon powder or a carbon substance that generates carbon by thermal decomposition in a high temperature range, usually 1000 ° C. or higher. An unfired product that is molded and dried or baked at 500 ° C. or lower as necessary is produced as a carbon-containing unfired refractory. When this is used in an actual furnace and heated, an oxide of the metal powder is produced in the refractory, and the volume expansion during the production of the metal oxide closes the particle gap during molding and at the same time provides high strength. It is supposed to achieve.

  However, as described above, the metal Al powder and the like added for preventing the oxidation of the carbon-containing refractory produce voids when they are changed to carbides or oxides. Therefore, it is necessary to reduce the particle size of the metal powder in order to make the brick structure dense. However, reducing the particle size of the metal Al powder or Al-Mg alloy powder increases the risk of explosion at the time of brick production, so that it is currently impossible to use metal powder having a certain particle size or less.

Here, as a technique for preventing void formation associated with the reaction of the antioxidant, a method for producing a carbon-containing unfired refractory to which Al ₄ SiC ₄ is applied is described in Patent Document 2, and the function thereof is as follows. Is described in detail. That is, in the case of metallic Al, it reacts with the surrounding carbon source or carbon monoxide gas in the brick and produces aluminum carbide in the range of 20 μm thickness from the grain surface, but it is metallic Al with a grain size of 40 μm or more. The Al left behind destroys the aluminum carbide on the surface and sequentially evaporates, resulting in voids in the brick structure. On the other hand, when Al ₄ SiC ₄ comes into contact with carbon monoxide gas, it first decomposes into Al gas and SiC and C, and further SiC decomposes into SiO gas and C, so that Al ₄ SiC ₄ exists. All the sites had been replaced with carbon or spinel (MgAl ₂ O ₄ ) as a reaction product, and no voids were formed as in the case of metallic Al.

Patent Document 2 describes that Al ₄ SiC ₄ does not generate voids even when the particle size is large, but it is described that 75 μm or less or 40 μm or less is good considering corrosion resistance. Here, conventionally, Al ₄ SiC ₄ is generally produced by an electric furnace heating method, except for the case where a very small amount is experimentally synthesized by a vapor phase method.

The particle size of Al ₄ SiC ₄ obtained by a normal electric furnace heating method is fine among those applied to carbon-containing refractories, and is about 8 μm on average (see Non-Patent Document 1). Among them, the minimum is 2 μm or more (see Non-Patent Document 2).

Further, among the obtained by the electric furnace heating method, in Non-Patent Document 3, MgO to which Al ₄ SiC ₄ having a particle diameter changed to 0.8-0.3 mm, 0.3 mm-45 μm, and −20 μm was applied. -C brick is evaluated, and the smaller the particle size, the higher the antioxidant effect. An example of synthesizing fine Al ₄ SiC ₄ of about 0.1 μm by CVD has been reported (see Non-Patent Document 4), but this is only experimentally synthesized in a small amount, and the obtained Al ₄ SiC is obtained. _There is no suggestion to apply ₄ to refractories. Moreover, since the synthesis of Al ₄ SiC ₄ powder by this method is not suitable for mass production and the cost becomes extremely high, there is no example applied as an antioxidant for refractories, and it is a fact that it will be put into practical use. It is impossible.

JP 54-163913 A JP-A-8-119719

Refractory 60 [10] p.540-548 (2008) J.Am.Ceram.Soc 86 [6] p.1028-1030 (2003) Refractory 60 [11] p.606-607 (2008) J.Mat.Sci 37 p.335-342 (2002)

As in Patent Document 2 and Non- Patent Document 3, when Al ₄ SiC ₄ synthesized by the electric furnace heating method is used, it is considered that the oxidation resistance is insufficient. Therefore, in the present invention, Al ₄ SiC, which has a particle size smaller than that obtained by the electric furnace heating method, is suitable as an antioxidant in MgO-C brick, and can improve the oxidation resistance than before. It aims at providing the manufacturing method of ₄ powder. Moreover, as intended for the provision of the method of manufacturing a manufacturing method MgO-C brick of adding Al ₄ SiC ₄ flour produced in, and MgO-C brick produced therewith.

As for the MgO-C brick, the inventors conducted various experiments. As the denser structure is used, the corrosion resistance is higher when the actual furnace is used, and the oxidation resistance is improved because it is less susceptible to oxygen attack. In addition, it was found that the more uniform the structure where the difference in density is less likely to occur, the better the spall resistance. Then, it was considered that the matrix structure can be uniformly densified as the particle size of Al ₄ SiC _{4 to be} added is made finer. Therefore, the inventors heated the mixed powder made of the powders of metal Al, metal Si, and C as raw materials by microwaves in an inert gas atmosphere, thereby producing Al ₄ SiC manufactured by an electric furnace heating method. ₄ apparently particle size finer than powder, the average particle diameter of 1μm or less of Al ₄ SiC ₄ powder was found to be able to manufacture. When this was applied as an antioxidant for MgO-C brick, the corrosion resistance, oxidation resistance, and spall resistance were improved as expected, leading to the present invention.

That is, in the present invention, by applying fine Al ₄ SiC ₄ powder synthesized by heating with microwaves as an antioxidant, it is possible to produce MgO-C bricks with higher corrosion resistance and spall resistance than before. The gist of the present invention is as follows.

(1) A mixed powder of metal Al, metal Si, and C having a molar ratio of metal Al to metal Si of 4: 1 is set in an inert gas atmosphere, and the temperature of the mixed powder is set to a value of metal Si by microwave. A method for producing Al ₄ SiC ₄ powder, characterized by producing Al ₄ SiC ₄ powder having an average particle size of 1 μm or less by heating to a melting point or higher.
(2) The method for producing an Al ₄ SiC ₄ powder according to (1), wherein the mixed powder is heated so that a temperature when measured with a radiation thermometer is 1500 ° C. or more.
(3) The Al ₄ SiC ₄ powder according to (1) or (2), wherein the average particle diameter of metal Al is 50 μm or more and 100 μm or less, and the average particle diameter of metal Si is 50 μm or more and 100 μm or less. Manufacturing method.
(4) While mixing the raw material of the MgO-C brick containing the binder and the resin, add Al ₄ SiC ₄ powder having an average particle size of 1 μm or less so that it is at least the same amount as that of the binder and the resin. A method for producing an MgO-C brick, characterized by being produced.
(5) When adding the Al ₄ SiC ₄ powder to the raw material composition of the MgO-C brick, the MgO powder that is one of the raw materials of the MgO-C brick and the Al ₄ SiC ₄ powder are mixed in advance, Thereafter, the remaining blended raw materials are mixed, and the ratio of Al ₄ SiC ₄ powder in the blended raw materials is 10% by mass or less. The method for producing an MgO-C brick according to (4), .
(6) MgO, C, Al ₄ SiC ₄ powder having an average particle size of 1 μm or less, a binder, and a resin are blended in the raw material, and the MgO and the Al ₄ SiC ₄ powder are mixed in advance, and then the remaining raw materials In mixing, when the total blending ratio of MgO and C is 100% by mass, 70 to 99% by mass of MgO and 1 to 30% by mass of C are blended, and the total blending raw material is A method for producing an MgO-C brick, characterized in that the proportion of Al ₄ SiC ₄ powder is 1 to 10% by mass.
( 7 ) A mixed powder of metal Al, metal Si, and C having a molar ratio of metal Al to metal Si of 4: 1 is set in an inert gas atmosphere, and the temperature of the mixed powder is set to a value of metal Si by microwave. The MgO-C brick according to any one of (4) to ( 6 ), which is heated as a melting point or more to produce an Al ₄ SiC ₄ powder having an average particle size of 1 μm or less and then blended as a raw material. Manufacturing method.

In the present invention, by using a production method using microwaves, it is possible to produce finer Al ₄ SiC ₄ powder than that produced by a conventional electric furnace heating method. By manufacturing the MgO-C brick by adding the synthesized Al ₄ SiC ₄ powder, the manufactured MgO-C brick is higher than the conventional one while ensuring the spall resistance equal to or higher than the conventional level. It can be oxidation resistant.

FIG. 1 is an explanatory diagram showing an outline of the microwave irradiation test apparatus used in the examples. FIG. 2 is an SEM photograph of Al ₄ SiC ₄ synthesized by microwave (1600 ° C.) using graphite as C powder (magnification: 5000 times). FIG. 3 is an SEM photograph of Al ₄ SiC ₄ synthesized by microwave (1600 ° C.) using carbon black as C powder (5000 times on the left side and 500 times on the right side). FIG. 4 is a SEM photograph (5000 times) of Al ₄ SiC ₄ synthesized by microwave (1600 ° C.) using mixed powder of graphite and carbon black as C powder. FIG. 5 shows the result of measuring the particle size distribution by laser microtrack for Al ₄ SiC ₄ powder synthesized using microwaves. FIG. 6 is a SEM photograph of Al ₄ SiC ₄ synthesized in an electric furnace (1600 ° C. × 6 h) (5000 times on the left side and 500 times on the right side). FIG. 7 shows the result of measuring the particle size distribution by laser microtrack for Al ₄ SiC ₄ powder synthesized using an electric furnace. FIG. 8 is an explanatory diagram showing an outline of another microwave irradiation test apparatus used in the examples. FIG. 9 is a diagram showing a change in the particle size distribution of the Al ₄ SiC ₄ powder depending on the holding time after the temperature inside the sample reaches 1600 ° C. in the synthesis using microwaves. FIG. 10 is a diagram showing the relationship between the temperature inside the sample and the ratio of the peak intensity of each crystal phase by XRD of the obtained synthetic powder in the synthesis using microwaves. FIG. 11 is a diagram showing the relationship between the temperature holding time at 1600 ° C. and the peak ratio of each crystal phase by XRD of the obtained synthetic powder in the synthesis by the electric furnace. FIG. 12 is a diagram showing an evaluation of the oxidation resistance of MgO—C bricks according to Comparative Example 3 and Invention Examples 8 to 20. FIG. 13 is a diagram evaluating the oxidation resistance of MgO—C bricks according to Comparative Examples 4-6. FIG. 14 is a photograph showing the results of a spall test of MgO—C bricks according to Invention Examples 11-13. FIG. 15 is a photograph showing the results of a spall test of an MgO—C brick according to Comparative Example 7. FIG. 16 is a photograph showing the results of a spall test of an MgO—C brick according to Comparative Example 8. FIG. 17 is an Al mapping diagram of EPMA in the structures after drying and firing for brick production for the MgO—C bricks of Invention Example 11 and Comparative Example 7. FIG. 18 is a powder X-ray diffraction pattern of the MgO—C brick according to Example 6 of the present invention.

Hereinafter, the present invention will be described in detail.
As a raw material for producing the Al ₄ SiC ₄ powder, metal Al, metal Si, and C powder are used. The reaction of Al ₄ SiC ₄ occurs even if the metal Al and the metal Si are not in powder form, but in view of production efficiency, it is preferably in powder form. Below, an example of the manufacturing method of a preferable form is given.

  The raw materials of metal Al powder, metal Si powder, and C powder are mixed at a rotational speed of, for example, about 100 rpm using a mixer such as a planetary mixer to obtain a mixed powder. As for the particle diameter of the raw material, it is preferable that the average particle diameter is 50 μm or more for metal Al and metal Si. From the standpoint of production efficiency, the preferable upper limit of the average particle diameter is 100 μm. This is because the finer the metal powder as a raw material can be uniformly dispersed when mixed, but there is a risk of dust explosion when the average particle size is less than 50 μm.

The mixing ratio (molar ratio) of the metal Al powder, the metal Si powder, and the C powder is theoretically desirably 4: 1: 4. For C powder, even if it is a higher blending ratio than metal Al powder and metal Si powder, there is no problem in the synthesis of Al ₄ SiC ₄ , but the mixing ratio of Al and Si is Al ₈ SiC ₇ , In consideration of the existence of a stable crystal phase such as Al ₄ Si ₂ C _5, it is necessary to adjust Al: Si = 4: 1.

Next, by irradiating the mixed powder of these raw materials with microwaves, the reaction of Al ₄ SiC ₄ can be efficiently advanced, and an Al ₄ SiC ₄ powder having an average particle size of 1 μm or less is produced. be able to. For the microwave irradiation, for example, a 2.45 GHz microwave oscillator using a magnetron as a microwave transmission source can be used.

In the case of Al ₄ SiC ₄ powder synthesis by microwave,
4Al (g) + Si (g) + C → Al ₄ SiC ₄
It is thought that the reaction represented by Therefore, Al ₄ SiC ₄ synthesized through a gas phase reaction of metal Al gas and metal Si gas is synthesized as fine powder.

As the raw material C powder, various C sources such as scaly graphite, powder pitch, petroleum coke, and carbon black can be used. It can be used without problems when not only carbon powder such as carbon black having a particle size of nm order and ultra fine C powder, but also large graphite having a particle size of μm order or more. This is because even if it is graphite of the order of μm or more, it reacts due to surface lattice defects, etc., and the particle size of the Al ₄ SiC ₄ powder after the reaction is averaged almost without being influenced by the particle size of the raw material C powder. It is because it is thought that it is synthesize | combined as a fine powder with a particle size of 1 micrometer or less. The particle size distribution of the raw material powder used in the synthesis, and obtained for mean particle size of Al ₄ SiC ₄ powder is evaluated by the relative amount of particles for each particle size using laser light scattering method.

Here, when a high-frequency current flows through the conductor due to the microwave irradiation, the current density is high on the conductor surface and decreases as the distance from the surface increases. This is called the skin effect. The current density J of the conductor is
In this case, the skin depth d is as follows when the electrical resistance ρ of the conductor, the frequency ω of the current, and the absolute permeability μ of the conductor.

Therefore, when a high-frequency electromagnetic wave such as a microwave is applied to a metal having a low electric resistance, a portion with a high current density is concentrated on the pole surface, and only the skin is heated. Therefore, it is considered that the heating effect improves as the raw material metal Al or metal Si becomes finer. For example, for Si, ρ = 10 ⁻⁷ [Ω] and μ = 1 [H / m]. For example, when a microwave of ω = 2.45 [GHz] is used, the skin depth d is 10 It is about [nm]. From this point of view, it is desirable that the metal powder as the raw material is a fine powder from the viewpoint of the reactivity of Al ₄ SiC ₄ without considering the dust explosion.

By the way, in the case of metal Al, when it reaches a melting point of 660 ° C. and becomes liquid, the vapor pressure of the metal Al gas increases. On the other hand, when the metal Si contained in the raw material mixed powder reaches a melting point of 1414 ° C., the vapor pressure of the metal Si gas becomes higher than when the melting point is below the melting point. Therefore, in the synthesis of Al ₄ SiC ₄ by microwaves, if the temperature in the sample reaches 1500 ° C., the vapor pressure of the metal Si gas becomes high, and Al ₄ SiC ₄ due to the gas phase reaction of both Al and Si. The synthesis reaction is promoted.

Furthermore, uniform heating of the entire raw material mixed powder by microwaves enables synthesis in a short time compared to heating by heat conduction in an electric furnace. In addition, since the reaction between Al gas, Si gas, and C fine powder remains and does not involve a sintering reaction, the grain growth of the synthetic powder is suppressed, and fine Al ₄ SiC ₄ with an average particle size of 1 μm or less can be synthesized. It becomes. Note that the lower limit of the average particle size of Al ₄ SiC ₄ flour obtained by the present invention, experiments of the present inventors, it has been confirmed that the substantially the 50nm.

The microwave heating synthesis reaction occurs locally at the portion where the microwave is absorbed. Therefore, even if the sample internal temperature of the mixed powder is the average temperature of the entire sample, and the sample temperature (that is, the average temperature) is low, the portion that has reacted by absorbing the microwave is a mixture of the metal gas and the C raw material. Because of the reaction, a fine powder with an average particle size of 1 μm or less can be obtained as described above. Therefore, according to the synthesis by microwave heating, a powder having a fine particle size is inevitably obtained. In the present invention, since powdered Al ₄ SiC ₄ is synthesized by microwave heating, an Al ₄ SiC ₄ powder having an average particle size of 1 μm or less can be obtained without particularly pulverizing treatment.

The atmosphere at the time of Al ₄ SiC ₄ synthesis, using an inert gas that does not contribute to Al ₄ SiC ₄ synthesis reaction. Nitrogen gas is undesirable because it reacts with Al and Si to synthesize nitrides. Therefore, it is preferable to use a rare gas as the inert gas. Among them, for example, Ar gas is preferable because it is relatively easily available.

  Although thermocouples may be used for sample temperature measurement during microwave irradiation, as described above, high-frequency current heats the metal surface, so the temperature measurement method using a thermocouple is an accurate measurement of the sample or reaction vessel. The temperature is difficult. In particular, when temperature measurement is performed with a thermocouple in contact with a carbon-containing sample, carbon diffuses and penetrates from the metal surface of the thermocouple, and the portion with high dielectric loss absorbs microwaves and can dissolve during temperature measurement . Therefore, in this invention, it is preferable to measure temperature by the method of isolate | separating a heating part and a temperature measuring part. Specifically, it is preferable to insert an alumina protective tube into the heating unit and measure the temperature with a radiation thermometer from the end of the opposite protective tube. For example, as described in Nippon Steel Corporation (1987), temperature measurement technology has a uniform temperature range from the bottom to a length of more than 5 times the inner diameter of the closed cylinder. Under the conditions, the radiation emissivity from the cylindrical opening is 1. Therefore, in the above method, the radiation emissivity can be set to 1 regardless of the material of the protective tube, and the temperature can be accurately measured with the radiation thermometer.

In the present invention, the temperature of the raw material mixed powder is measured by the temperature measuring method, and irradiation with microwaves so that the temperature is equal to or higher than the melting point of metal Si can efficiently produce Al ₄ SiC ₄ powder. Is preferable. Furthermore, in consideration of temperature variation depending on the temperature measurement position, it is more preferable to irradiate the microwave so that the measurement temperature is 1500 ° C. or higher. In addition, since the effect is saturated when the measurement temperature of the raw material mixed powder exceeds 1600 ° C., the heating temperature of the raw material mixed powder is preferably set to 1600 ° C. or less economically.

Next, a preferred embodiment of a method for producing MgO—C brick when the Al ₄ SiC ₄ powder produced by the above-described method is applied as an antioxidant for MgO—C brick will be described.
When Al ₄ SiC ₄ powder is added as an antioxidant for MgO—C brick, it is preferably added during kneading of the MgO—C brick or before kneading of the clay. Al ₄ SiC ₄ powder synthesized by microwaves is a fine powder with an average particle size of 1 μm or less, and therefore has a high specific surface area and tends to aggregate. Therefore, in order to uniformly disperse the brick in the structure, it is preferable to perform preliminary mixing with the MgO aggregate, and then mix with other raw materials and knead. Thus, oxidation resistance improving effect by the addition of a fine powder of Al ₄ SiC ₄ powder is exhibited. That is, in the method for producing MgO-C brick according to the present invention, Al ₄ SiC ₄ powder synthesized by microwave is added during kneading of the MgO-C brick or before kneading, It can be produced in the same manner as the ordinary MgO-C brick production method.

Next, the mechanism by which oxidation resistance is improved by the method for producing MgO-C brick according to the present invention will be described. Oxidation resistance is the following (1) to (2) in the structure when MgO-C brick containing Al ₄ SiC ₄ is used in actual furnaces such as converters and molten steel pans, degassing facilities, etc. This is considered to be improved by densification of the hot structure due to the reaction.
Al ₄ SiC ₄ → 4Al (g) + SiC + 3C (1)
4Al (g) + SiC + 3C + 4Mg (g) + 12CO (g)
→ 2MgO · Al ₂ O ₃ + (2MgO) · SiO ₂ + 16C (2)

The reaction (1) → (2) is more likely to occur as the temperature is higher or the CO partial pressure is higher. Al ₄ SiC _4, spinel _{(MgO · Al 2 O 3)} , forsterite (2MgO · SiO _2), the density of the C, respectively ^{3.0g / cm 3, 3.6g / cm} 3, 3.2g / cm 3 1.8 g / cm ³ , and considering volume expansion associated with spinel, forsterite, and carbon formation, the volume change is calculated from the stoichiometric ratio by the reaction of (1) → (2), and (142 3 × 2 / 3.6 + 140.6 / 3.2 + 12 × 15 / 1.8) ÷ (184 / 3.0) = 3.7 times. If this volume change is greater than the amount that fills the volatile content of the binder and resin, fine Al ₄ SiC ₄ with an average particle size of 1 μm or less is dispersed throughout, so that the structure becomes dense and acid resistant. It is considered that the chemical conversion is improved. When the average particle size is larger than this, it is considered that there are portions where the structure is not densified due to segregation, and the oxidation resistance is not improved. Therefore, it is considered that the addition amount of the Al ₄ SiC ₄ powder as the antioxidant is sufficient if it is greater than or equal to the amount filling this volatile matter.
Note that Mg and C originally exist as MgO and graphite, and Mg (g) and CO (g) are generated by the MgO-C reaction. When used in an actual furnace where a temperature gradient is generated in brick, Al ₄ SiC _Since these gases are also generated from the region below the reaction temperature range of ₄ , the influence of the decrease in Mg (g) and CO (g) is small. Therefore, only the expansion due to the generation of spinel and forsterite needs to be considered.

From the above, regarding the lower limit of the Al ₄ SiC ₄ addition amount, the volume change due to (1) → (2) is calculated to increase by 0.9 cm ³ per 1 g of Al ₄ SiC ₄ addition amount (Al per 1 g ₄ SiC _{4) When the} volume of the volatile component is 1.1 g / cm ³ , the volatile component is 1.0 times by weight. For this reason, a value higher than this is required as the amount of Al ₄ SiC ₄ added. That is, it is preferable that the volume after oxidation of Al ₄ SiC ₄ powder is equal to or greater than the volume of the portion where the volatile components of the binder and the resin are removed. In actual operation, at least the addition amount (mass) of the binder and the resin Add the same amount of Al ₄ SiC ₄ powder (mass).

Since the addition amount of the resin and the binder needs to be adjusted depending on MgO used for the brick, the particle size of the graphite, etc., it does not take a quantitative value, but is generally about 1 to 3% by mass in the whole raw material. Therefore, the amount of Al ₄ SiC ₄ added is required to be at least 1 to 3% by mass with respect to the entire brick material.

On the other hand, by adding excessively Al ₄ SiC ₄ , the oxidation resistance is further improved, but at the same time, Al ₄ SiC ₄ easily aggregates while taking in the binder. When the mass% is exceeded, Al ₄ SiC ₄ itself aggregates, which may conversely generate voids and lower the oxidation resistance. Therefore, the amount of Al ₄ SiC ₄ added is preferably 1 to 10% by mass in the total blending raw material of MgO—C brick.

  Here, a well-known thing can be used about the binder and resin added to the raw material of MgO-C brick. Among these, the binder mainly plays a role of dispersing the resin, and specific examples thereof include ethylene glycol. The resin is used to increase the strength of the dried MgO-C brick, and specifically includes a phenol resin and the like.

Further, the reaction from (1) to (2) improves the oxidation resistance of the MgO—C brick and at the same time improves the spall resistance. This is because the reaction product is uniformly generated throughout the tissue. When metal Al used as an antioxidant in the past is added to MgO-C brick, Al reacts from the surface and reacts with Mg gas and CO gas in the brick structure to produce spinel. Forms an agglomerated tissue. As a result, a structure having a strength higher than that of the matrix is generated in the vicinity of the Al reaction product, and cracks are generated starting from this vicinity when subjected to thermal shock. On the other hand, in the case of Al ₄ SiC ₄ , Al gas is generated first in the hot state, and this reacts with Mg gas and CO gas to generate spinel throughout the matrix, so that the reactants do not aggregate, It is possible to form a uniform matrix. Finer Al ₄ SiC ₄ can be obtained by microwave synthesis, and MgO-C brick can be dispersed throughout the entire structure. Therefore, MgO-C brick with a structure that is resistant to crack extension and has excellent spall resistance Become.

Further, if the carbon content in the raw material of MgO-C brick is less than 1% by mass, slag permeation increases and damage tends to increase when the actual machine is used. On the contrary, if the carbon content exceeds 30% by mass, the oxidation resistance of the brick tends to be impaired. However, this carbon includes binder carbon and bonded carbon derived from resin. Further, as described above, Al ₄ SiC ₄ generates carbon by the thermal decomposition of the reaction formula (1). Therefore, the compounding amount of carbon in the MgO—C brick raw material is the carbon content derived from this Al ₄ SiC _4. The content rate may be 1 to 30% by mass.

Since the density of Al ₄ SiC ₄ is 3.038 [g / cm ³ ] (from Materials Chemistry and Physics 97 (2006) p.193-199), the particle size of Al ₄ SiC ₄ is temporarily 0.1 μm, 1 μm. If it is 10 μm, the specific surface area is as shown in Table 1 in the theoretical calculation. Therefore, as a result of the particle size distribution measurement by the laser light scattering method (laser microtrack), the particle having a main peak of particle size of 1 μm or less is considered to have a specific surface area of approximately 2 [m ² / g] or more. For the measurement of the specific surface area, for example, a BET method by nitrogen adsorption can be used. Therefore, whether or not the average particle diameter is 1 μm or less can be evaluated by measuring whether or not the specific surface area by the BET method is 2 [m ² / g] or more.

As described above, according to microwave synthesis, it is possible to synthesize Al ₄ SiC ₄ powder that is finer than an electric furnace. As the Al ₄ SiC ₄ powder is refined, the reaction area is increased and the reactivity is increased. Therefore, even when the same amount is added, the oxidation resistance can be improved as compared with the one having a larger particle size. In addition, since the Al ₄ SiC ₄ powder obtained by the present invention uniformly generates a reaction product in the brick structure, a structure in which cracks do not easily occur is developed.

The MgO—C brick produced by applying the Al ₄ SiC ₄ powder obtained by the above synthesis method and produced by the above method is generally used after drying at 200 to 300 ° C. Since the Al ₄ SiC ₄ powder does not aggregate due to the volatilization of the resin and binder during drying, and the Al ₄ SiC ₄ powder does not react and change its shape, it can be used as a fine powder when added by this method. An MgO—C brick containing Al ₄ SiC ₄ powder capable of exhibiting the effect is manufactured. Therefore, even after drying, the Al ₄ SiC ₄ powder has an effect of densifying the structure after firing by the same mechanism as described above in the formulas (1) and (2), and even after drying, the Al ₄ SiC at a high temperature. The reaction form of ₄ is the same as before drying. Therefore, as described above, considering the amount of binder / resin added during brick production and the aggregation behavior of Al ₄ SiC ₄ itself, the optimum blending amount of Al ₄ SiC _{4 having} an average particle size of 1 μm or less in the entire blended raw material is 1-10. It becomes mass%.

Moreover, when manufacturing a MgO-C brick, the conventional manufacturing method can be applied as it is. The blending ratio of the raw materials may be the same as that of conventional MgO-C brick. For example, when the total blending ratio of MgO and C in the blending raw material is 100% by mass, 70 to 99% by mass of MgO and 1 to 30% by mass of C are blended. In addition to MgO, C, Al ₄ SiC ₄ , a binder, and a resin, additives such as a dispersant and other antioxidants may be added as long as the effects of the present invention are not impaired.

(Production of Al ₄ SiC ₄ )
FIG. 1 shows an outline of a microwave irradiation test apparatus. A magnetron type 2.45 GHz microwave oscillator is connected to a tuner for adjusting E wave and H wave, and connected to an atmosphere control type applicator through a waveguide. The tuner and applicator were shielded by quartz glass, and Ar gas was introduced into the applicator from the vicinity of the quartz glass plate to control the atmosphere.

  In the applicator, the reaction vessel containing the sample is covered with an alumina-silica-based heat insulating material having a thickness of 75 mm or more as shown in FIG. The sample temperature is measured by bringing a thermocouple into contact with the bottom or side of the container. The temperature measurement results were continuously recorded by a data logger, and the microwave irradiation was stopped when the sample temperature reached 1000 to 1600 ° C. The heating time required 25 minutes to reach 1000 ° C. and 90 minutes to reach 1600 ° C. Here, a sample (sample) is prepared by using metal Al powder, metal Si powder, and C powder as raw materials, adjusted so that the molar ratio is Al: Si: C = 4: 1: 4, and uniformly mixed. used.

The microwave irradiation output was set under the condition of 10 W or less with respect to 1 g of the sample weight. The microwave irradiation time was set so that the irradiation energy was 5 kWh / kg. The synthetic powder obtained by the microwave irradiation heating was designated as Al ₄ SiC ₄ obtained by microwave synthesis.

With respect to the particle size of the obtained Al ₄ SiC ₄ , the laser absorbance range was set to 0.01-0.2 and the refractive index of Al ₄ SiC ₄ was set to 2.6 using an analyzer by a laser microtrack method. The particle size distribution was measured. The average particle size was calculated based on the average value evaluated at N = 3. Further, when graphite (average particle size 100 to 300 μm) is used as the C raw material, when C fine powder (carbon black, average particle size 50 to 60 nm) is used, and mixed powder of C fine powder and graphite is used. In each case, the results of observation of each post-synthesis sample by SEM are shown in FIGS.

In the case of using graphite, as shown in FIG. 2, it was observed that Al ₄ SiC ₄ reacted and precipitated on the surface of the raw material, but the particle size was synthesized using the fine C powder of FIG. There were no major differences, and in all cases, particles of 1 μm or less occupied a large number. As shown in FIG. 4, it was confirmed that Al ₄ SiC ₄ was synthesized as a fine powder as in FIGS. 2 and 3 even when a mixed powder of C fine powder and graphite was used. On the right side of FIG. 3, a part of the material was deposited in a plate shape, but the ratio was extremely small. Also, the Al ₄ SiC ₄ powder obtained by using these three C material, as shown in FIG. 5, the results of measuring the particle size distribution by laser Microtrac, shows the same particle size distribution in the case of three In both cases, it was confirmed that the peak (main peak) position was 1 μm or less. This agrees well with the result of SEM observation.

On the other hand, the synthesis in the electric furnace performed for comparison was performed using a carbon heater such as a Tamman furnace and a device composed of a carbon crucible as a reaction vessel. In the reaction vessel, the same metal Al powder, metal Si powder, and C powder as those used in microwave irradiation heating are used as raw materials, and the molar ratio is adjusted to be Al: Si: C = 4: 1: 4. A uniformly mixed sample (specimen) was set. The inside of the furnace was made into a reducing atmosphere by flowing Ar gas, and the sample temperature was measured with a thermocouple in contact with the side surface of the carbon crucible. Two types were obtained, one obtained by firing at a temperature of 1600 ° C. for 6 hours under the condition of a thermocouple, and one obtained by firing for 10 hours at 1600 ° C., and the resultant synthetic powder was obtained by electric furnace synthesis. Al ₄ SiC ₄ was used.

FIG. 6 shows the results of observing Al ₄ SiC ₄ powder obtained by a synthesis method using an electric furnace with an SEM. As shown in FIGS. 2 to 4 above, the powder synthesized by microwaves has more particles of 1 μm or less and fewer plate-like particles of several tens of μm than the case of electric furnace synthesis. Further, it is observed that the plate-like particles are present as lower density aggregates than in the case of the electric furnace. On the other hand, as shown in FIG. 6, when synthesized in an electric furnace, it was observed that grains grew to 1 μm or more even in a fine powder form.

The specific surface area of Al ₄ SiC ₄ obtained by microwave synthesis and electric furnace synthesis was calculated from the approximate equation of BET using a nitrogen adsorption 5-point measurement method. Henceforth, the value of this specific surface area was made into BET value. Microwave Synthesis Al ₄ SiC ₄ obtained by, and an electric furnace for 6 hours, the Al ₄ SiC ₄ obtained by calcining for 10 hours and pulverized by a ball mill, and subjected to measurement. Ball milling was performed by rotating a synthetic powder charged in a container filled with 20 mm diameter alumina balls at 100 rpm. Table 2 shows the BET value calculation result at this time. Al ₄ SiC ₄ obtained by microwave synthesis has a high specific surface area compared to the case of electric furnace synthesis and is confirmed to be fine particles.

The particle size distribution of the Al ₄ SiC ₄ powder obtained by the electric furnace synthesis was measured by the laser microtrack method in the same manner as in the case of the Al ₄ SiC ₄ powder obtained by the previous microwave synthesis. The laser absorbance range was 0.01-0.2, the refractive index of Al ₄ SiC ₄ was set to 2.6, and the particle size distribution was calculated from the laser dispersion. The measurement results are shown in FIG. For reference, the results of the Al ₄ SiC ₄ powder obtained by the previous microwave synthesis (when C fine powder is used as the C raw material) are also shown. As can be seen from FIG. 7, Al ₄ SiC ₄ obtained by microwave synthesis has a finer particle size and a narrower peak width than the case of electric furnace synthesis, and thus a synthetic powder having a uniform particle size is obtained. On the other hand, in Al ₄ SiC ₄ obtained by electric furnace synthesis, the peak was present at a position exceeding 1 μm.

  In order to further increase the synthesis efficiency by microwave, the temperature inside the sample was measured. As a temperature measuring method, for example, an apparatus as shown in FIG. 8 is used, in which an alumina protective tube is inserted into the sample, and the temperature of the protective tube heated by the sample temperature rise is measured from above. An alumina protective tube having an inner diameter of 4 to 8 mm was used, and the depth of insertion into the sample was 5 times the inner diameter or more. More accurate microwave irradiation conditions were set from the temperature inside the sample by the radiation temperature measurement temperature.

In the conventional temperature measuring method, when the temperature at the bottom of the reaction vessel rises locally, Al ₄ SiC ₄ may be synthesized in a part of the reaction vessel. The total amount of Al ₄ SiC ₄ can be synthesized. Moreover, when a metal thermocouple is inserted into the sample and microwave irradiation is performed, the metal thermocouple itself receives microwave absorption and becomes a heated object, and it is difficult to measure the temperature of the sample itself by the inventors' experiment. It has been confirmed. In particular, under conditions that require a high temperature, such as Al ₄ SiC ₄ synthesis, the raw material is dissolved in the metal at a high temperature and becomes a microwave absorber, and the metal thermocouple melts due to local microwave absorption. Therefore, continuous temperature measurement inside the sample by a thermocouple in a microwave field is impossible. The temperature measurement using a radiation thermometer not only made it possible to synthesize Al ₄ SiCC ₄ uniformly in the reaction vessel, but also within the range where the average particle diameter does not exceed 1 μm as shown in FIG. It became possible to control the particle size distribution. That is, if the holding time after reaching 1600 ° C. is within 30 minutes, the average particle diameter is 0.2 to 0.3 μm, and if it is over 30 minutes to 60 minutes, the average particle diameter is 0.3 to 0.7 μm, 60 When it exceeded the minute, it became 0.7 μm to 0.8 μm. Regarding FIG. 9, when the temperature inside the sample measured through the alumina protective tube reached 1600 ° C., the synthesis reaction was terminated (holding time 0 minutes), and when the temperature reached 1600 ° C., the holding time was changed. The particle size distribution of the obtained Al ₄ SiC ₄ powder was measured for each case where the synthesis reaction was completed in 30 minutes, 60 minutes, and 120 minutes.

FIG. 10 shows the synthesized powder obtained by synthesizing while measuring the mixed powder temperature by the method of inserting the alumina protective tube and measuring the temperature inside the sample with a radiation thermometer as described above. The XRD is measured, and the peak ratio of each crystal phase with the maximum peak as 100 is shown in a graph. As can be seen from this result, it was possible to synthesize Al ₄ SiC ₄ without impurities by maintaining the melting point (1414 ° C.) or higher of metal Si. Note that the XRD peaks are about Al ₄ SiC ₄ (2θ = 56.10 °), Al ₄ C ₃ (2θ = 55.04 °), SiC (2θ = 35.63 °), Al (2θ = 38.47 °), Si (2θ = 28.45 °) was evaluated, and the XRD peak index was determined with the peak indicating the maximum intensity as 100 in the measurement results at each temperature.

FIG. 10 is a plot of the peak intensity change with respect to the ultimate temperature from the XRD pattern of Al ₄ SiC ₄ obtained by microwave synthesis, whereas the Al ₄ SiC ₄ obtained by electric furnace synthesis is similarly plotted in FIG. FIG. 11 shows a plot of changes in peak intensity with respect to temperature holding time at 1600 ° C. From the results of FIG. 10, it was confirmed that in the synthesis by microwaves, the internal temperature of the container necessary for synthesizing Al ₄ SiC ₄ with high purity needs to be at least 1500 ° C. On the other hand, from the results shown in FIG. 11, it was confirmed that the firing time required for the synthesis of Al ₄ SiC ₄ having a high purity required at least 6 hours in the synthesis using the electric furnace.

(MgO-C brick manufactured by adding Al ₄ SiC ₄ powder)
Comparative Example 1 Electric furnace synthetic Al ₄ SiC ₄ 2.4% added, 13% graphite, 2% binder MgO—C (with premix)
Comparative Example 2 Electric furnace synthetic Al ₄ SiC ₄ 3.6% added, graphite 13%, binder 2% MgO—C (with premix)
Invention Example 3 Microwave synthesized Al ₄ SiC ₄ 2.4% added, graphite 13%, binder 2% MgO—C (no premixing)
Invention Example 4: Microwave synthesized Al ₄ SiC ₄ 3.6% added, graphite 13%, binder 2% MgO—C (no premixing)
Invention Example 5: Microwave synthesized Al ₄ SiC ₄ 2.4% added, 13% graphite, 2% binder MgO—C (with premix)
Invention Example 6 Microwave synthesized Al ₄ SiC ₄ 3.6% added, graphite 13%, binder 2% MgO—C (with premix)
(Note that% here represents mass%.)

As shown in Table 3, the graphite amount is 13%, the binder amount is 2%, Al ₄ SiC ₄ powder synthesized by an electric furnace or microwave is 2.4% or 3.6%, and the balance is MgO. The blended raw materials were kneaded with a high speed mixer, press-molded with a friction press, and dried at 200 to 300 ° C. to produce MgO—C brick. The brick was molded in a normal parallel shape of 114 mm × 230 mm × 65 mm. The binder amount of 2% is a value including a resin (phenol resin, pitch resin, etc.). In kneading, known means such as a wet pan mixer or a kneader or press molding with an oil press can be appropriately employed.

When manufacturing MgO-C brick by adding Al ₄ SiC ₄ powder having an average particle size of 0.3 μm microwave-synthesized at 1500 ° C. by the above method, pre-mixing of MgO particles and Al ₄ SiC ₄ powder is performed beforehand. Table 3 shows the apparent porosity of the bricks when they are performed and when they are not compared with the case where Al ₄ SiC ₄ powder synthesized in an electric furnace is premixed and added. The apparent porosity was measured by a kerosene type according to JIS R 2205.

  In addition, the kneaded product of each blended raw material prepared above was molded into a sample size of φ50 mm × 50 mm, subjected to 1400 ° C. × 10 hr reduction firing in advance, and then subjected to 1400 ° C. × 5 hr test firing in an air atmosphere for acid resistance. Chemical test was conducted. The oxidized thickness was determined by embedding the sample after reduction firing in an epoxy resin, cutting the sample parallel to the bottom surface, and measuring the thickness of the yellowish white discolored portion on the cut surface. The results of the oxidation resistance test are shown in Table 4.

As shown in Table 3, the inventive examples 3 to 6 have a lower apparent porosity as compared with Comparative Examples 1 and 2, and the oxidation thickness is small as shown in Table 4, so that high oxidation resistance is achieved. Confirmed to have. Furthermore, when premixing is performed, the Al ₄ SiC ₄ powder is uniformly dispersed in the brick structure without agglomeration, so that a structure that does not easily generate pores after firing can be formed, and the structure becomes hot and dense. It was. As a result, as shown in Table 4, it was confirmed that the MgO-C brick produced by premixing had a smaller oxidation thickness and a structure with excellent oxidation resistance as compared with the case where premixing was not performed. It was. In addition, Al ₄ SiC ₄ powder synthesized by microwave is finer than when synthesized in an electric furnace, so the apparent porosity is reduced and oxidation resistance is lower than when premixed in an electric furnace synthesized product. The result was improved.

Comparative Example 3 Microwave synthesized Al ₄ SiC ₄ 0% added, graphite 13%, binder 2% MgO—C (with premix)
Invention Example 8: Microwave synthesized Al ₄ SiC ₄ 1.2% added, graphite 13%, binder 2% MgO—C (with premix)
Invention Example 9 ... 4.8% addition of microwave synthesized Al ₄ SiC ₄ , 13% graphite, 2% binder MgO-C (with premix)
Invention Example 10 Microwave synthesized Al ₄ SiC ₄ 6.0% added, 13% graphite, 2% binder MgO—C (with premix)
Invention Example 11 Microwave synthesized Al ₄ SiC ₄ 1.0% added, graphite 3%, binder 2% MgO—C (with premix)
Invention Example 12 Microwave synthesized Al ₄ SiC ₄ 2.0% added, 3% graphite, 2% binder MgO—C (with premix)
Invention Example 13 Microwave synthesized Al ₄ SiC ₄ 3.0% added, 3% graphite, 2% binder MgO—C (with premix)
Invention Example 14 Microwave synthesized Al ₄ SiC ₄ 4.0% added, graphite 3%, binder 2% MgO—C (with premix)
Invention Example 15: 0.5% addition of microwave-synthesized Al ₄ SiC ₄ , 1% graphite, 1.5% binder MgO—C (with premix)
Invention Example 16 Microwave synthesized Al ₄ SiC ₄ 1.0% added, graphite 1%, binder 1.5% MgO—C (with premix)
Invention Example 17 Microwave synthesized Al ₄ SiC ₄ 1.5% added, graphite 1%, binder 1.5% MgO—C (with premix)
Invention Example 18 Microwave synthesized Al ₄ SiC ₄ 2.0% added, graphite 1%, binder 1.5% MgO—C (with premix)
Invention Example 19 MgO—C containing 3.0% microwave synthesized Al ₄ SiC ₄ , 1% graphite and 1.5% binder (with premix)
Invention Example 20 Microwave synthesized Al ₄ SiC ₄ 4.0% added, graphite 1%, binder 1.5% MgO—C (with premix)
(Note that% here represents mass%.)

After the raw material powder reaches 1600 ° C. using microwave heating, the addition amount of Al ₄ SiC ₄ powder having an average particle diameter of 0.3 μm obtained by synthesizing with a retention time of 0 minutes was changed by the above method. A brick was prototyped and subjected to an oxidation resistance test. That is, as in Comparative Example 3 and Invention Examples 8 to 20, graphite 1 to 13%, binder 1.5 to 2%, Al ₄ SiC ₄ obtained by microwave synthesis, 0 to 6%, the balance The raw material containing MgO was kneaded with a high-speed mixer, press-molded with a friction press, and dried at 200 to 300 ° C. to produce MgO-C brick. In the blending at this time, the residual carbon content of the binder is used in addition to the added graphite as the C source of the MgO-C brick. In addition, the said binder amount of 1.5-2% is a value including resin (phenol resin, pitch resin, etc.).

The kneaded material of each blended raw material prepared above is molded into a sample size of φ50 mm × 50 mm, subjected to 1400 ° C. × 10 hr reduction firing in advance, and then subjected to 1400 ° C. × 5 hr test firing in an air atmosphere for oxidation resistance. A test was conducted. The oxidized thickness was determined by embedding the sample after reduction firing in an epoxy resin, cutting the sample parallel to the bottom surface, and measuring the thickness of the yellowish white discolored portion on the cut surface. When the test was performed with respect to various amounts of graphite, the results shown in FIG. 12 were obtained. For MgO-C bricks with the same amount of graphite, it was confirmed that the value of the oxide layer thickness decreased with an increase in the amount of Al ₄ SiC ₄ added. However, even when a large amount of Al ₄ SiC ₄ exceeding the amount of added binder is added to each sample, the oxidation resistance improving effect tends to be saturated. Further, since the oxidation resistance was evaluated by measuring the oxidation thickness, the oxidation thickness was the smallest in the case of 13% graphite in which the carbon amount increased within the same thickness. The result that the graphite 1% is superior in oxidation resistance to the graphite 3% is that the blended raw materials of Examples 8 to 20 of the present invention, including residual carbon such as resin, are mixed with the raw material of 1% graphite. This is probably because there were more C sources as a whole. Overall, the oxidation resistance was good in the order of 13% graphite, 1% graphite, and 3% graphite. In all cases, the oxidation resistance improved as the amount of added Al ₄ SiC ₄ increased, and the amount of each graphite increased. Since the required amount of binder differs depending on the amount of change, the behavior of improving the oxidation resistance with respect to the amount of Al ₄ SiC ₄ added varies with the change in the amount of binder. Note that “Gr” in FIG. 12 represents the amount of graphite added.

Comparative Example 4 Electric furnace synthetic Al ₄ SiC ₄ 0.5% added, graphite 1% MgO—C (with premix)
Comparative Example 5 ... Electric furnace synthetic Al ₄ SiC ₄ 1.0% added, graphite 1% MgO-C (with premix)
Comparative Example 6 ... Electric furnace synthetic Al ₄ SiC ₄ 1.5% added, graphite 1% MgO-C (with premix)
(Note that% here represents mass%.)

An oxidation resistance test was performed on MgO—C brick samples prepared by adding Al ₄ SiC ₄ powder obtained by electric furnace synthesis as in Comparative Examples 4 to 6 described above. FIG. 13 shows the results of measurement of the oxide layer thickness of MgO—C brick to which Al ₄ SiC ₄ powder obtained by the electric furnace synthesis was added. In addition, in FIG. 13, the result of the MgO-C brick sample which concerns on previous invention examples 15-17 is shown collectively.

As shown in the figure, compared with Comparative Examples 4 to 6, the present invention examples 15 to 17 generally have a smaller oxide layer thickness, and the same Al ₄ SiC ₄ powder addition amount is obtained when the microwave synthesized product is added. However, the oxide layer thickness was smaller. The results of the oxidation layer thickness, MgO-C bricks according to the Al ₄ SiC ₄ powder obtained by microwave synthesis, to be excellent in oxidation resistance compared with the case of applying the Al ₄ SiC ₄ powder by an electric furnace synthesis I understood.

Comparative Example 7 ... 1% metal Al added, 3% graphite MgO-C
Comparative Example 8 Electric furnace synthetic Al ₄ SiC ₄ 2.0% addition, graphite 3% MgO-C (with premix)
(Note that% here represents mass%.)

A spall resistance test was performed on the MgO-C bricks described in the comparative examples 7 to 8 and the MgO-C bricks according to the above inventive examples 11 to 13, respectively. In the spall resistance test, a kneaded mixture of raw materials forming each brick was molded into a 40 mm × 40 mm × 160 mm sample, subjected to 1400 ° C. × 10 hr reduction firing in advance, and then 100 mm in hot metal held at 1650 ° C. The evaluation was performed by immersing to the depth for 10 minutes, water-cooling for 10 seconds and then allowing to cool for 5 minutes three times, and confirming the change in acoustic velocity modulus before and after the test and the presence or absence of cracks on the sample surface. The test results are shown in Table 5 and FIG. A sample to which a large amount of Al ₄ SiC ₄ was added showed a high value of acoustic velocity modulus after firing at 1400 ° C., and was confirmed to be dense. After the spall resistance test, none of the Al ₄ SiC ₄ added samples were observed to have cracks or the like on the sample surface, and the sonic elastic modulus after the spall resistance test showed a high value as the addition amount increased. It is known that MgO—C bricks that become dense after firing with conventional additives (metal Al, metal Si, etc.) have low spall resistance. For example, if the Al-added MgO-C brick is used as shown in FIG. 15, cracking / collapse occurs when the same spall resistance test is performed. In contrast, MgO-C brick was fired dense with Al ₄ SiC ₄ added according to the present invention may be a highly calcined sound velocity modulus brick, spalling resistance is high it was confirmed . Further, it was confirmed that the microwave synthesized product was superior in spall resistance compared to the case of Al ₄ SiC ₄ synthesized in the electric furnace of FIG.

Conventionally, before and after the firing of MgO-C bricks when adding metal Al (Comparative Example 7) used as an antioxidant and when adding Al ₄ SiC ₄ (Invention Example 11) according to the present invention FIG. 17 shows an Al mapping diagram of EPMA. In the case of Al, it reacts from the surface and reacts with Mg gas and CO gas in the brick structure to produce an aggregated spinel structure, whereas in the case of Al ₄ SiC ₄ , spinel is generated in the entire matrix and the reaction It was confirmed that the product formed a uniform matrix without aggregation. In other words, it became possible to disperse the entire structure with fine powder by microwave synthesis, and the structure did not easily cause crack extension. As shown in the spall resistance test of FIG. 15, even when the amount of addition of Al ₄ SiC ₄ was sufficiently increased, a brick with high spall resistance was obtained.

Moreover, the result of having performed powder X-ray diffraction about the sample which rotated and grind | pulverized MgO-C brick which concerns on previous invention example 6 at 2 rpm using a table-top ball mill is shown in FIG. As can be seen from this result, Al ₄ SiC ₄ is not altered even after drying in brick production, and MgO—C brick is confirmed to have the reaction characteristics as Al ₄ SiC ₄ as described above. It was done.

Claims (7)

A mixed powder of metal Al, metal Si, and C having a molar ratio of metal Al to metal Si of 4: 1 is heated to a temperature equal to or higher than the melting point of metal Si by microwaves in an inert gas atmosphere. heated, Al ₄ SiC ₄ powder manufacturing method, characterized by producing an average particle size 1μm or less of Al ₄ SiC ₄ powder. 2. The method for producing Al ₄ SiC ₄ powder according to claim 1, wherein the mixed powder is heated so that a temperature when measured by a radiation thermometer is 1500 ° C. or more. 3. The method for producing Al ₄ SiC ₄ powder according to claim 1, wherein the metal Al has an average particle diameter of 50 μm to 100 μm, and the metal Si has an average particle diameter of 50 μm to 100 μm. During the blending of raw materials of MgO-C brick containing a binder and a resin, an Al ₄ SiC ₄ powder having an average particle size of 1 μm or less is added and manufactured so as to be at least the same amount as that of the binder and the resin. The manufacturing method of the MgO-C brick characterized by these. When the Al ₄ SiC ₄ powder is added to the MgO-C brick raw material mixture, the MgO powder, which is one of the MgO-C brick raw materials, and the Al ₄ SiC ₄ powder are mixed in advance, and then the remaining 5. The method for producing an MgO—C brick according to claim 4, wherein the blending raw material is mixed and the proportion of Al ₄ SiC ₄ powder in the blending raw material is 10% by mass or less. The raw material contains MgO, C, Al ₄ SiC ₄ powder having an average particle size of 1 μm or less, a binder, and a resin. The MgO and the Al ₄ SiC ₄ powder are mixed in advance and then mixed with the remaining raw materials. When the total compounding ratio of MgO and C is 100% by mass, 70 to 99% by mass of MgO and 1 to 30% by mass of C are mixed, and the Al ₄ SiC in the entire blended raw material The manufacturing method of the MgO-C brick characterized by being manufactured with the ratio of ₄ powders 1-10 mass%. A mixed powder of metal Al, metal Si, and C having a molar ratio of metal Al to metal Si of 4: 1 is heated to a temperature equal to or higher than the melting point of metal Si by microwaves in an inert gas atmosphere. The method for producing an MgO-C brick according to any one of claims 4 to 6 , wherein an Al ₄ SiC ₄ powder having an average particle size of 1 µm or less is produced by heating and then blended as a raw material.