Refractory and method for producing same

Abstract

To provide a refractory capable of improving oxidation resistance of the refractory.SOLUTION: The present invention is a refractory containing Al3BC3.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a refractory and a method for producing the same. [Background technology]

[0002] Refractories are manufactured by mixing and kneading raw materials, including at least refractory raw materials and binders, shaping the kneaded raw materials, and heat-treating the shaped body (for example, by firing). Refractory raw materials are composed of a variety of particle sizes, including coarse, medium, and fine powder. The particle size structure and chemical composition (or mineral composition) of the refractory raw materials are designed according to the desired properties of the refractory. In the structure of the refractory, a matrix portion composed mainly of fine powder exists around the coarse and medium particles. The matrix portion contains many pores. In this way, refractories are characterized by being composed of refractory raw materials with a variety of particle sizes, including coarse, medium, and fine powder, and by having many pores.

[0003] Antioxidants are sometimes added to refractory raw materials. This is to prevent the carbon components of the refractory from being oxidized (i.e., decarburized) and the structure of the refractory from becoming embrittled when the refractory is used in an actual machine. For example, Patent Document 1 discloses adding a boron source such as BC as an antioxidant to refractory raw materials.

[0004] The effect of adding BC has been that, as shown in formula 1, BO is generated by oxidation of BC, and a glassy layer of BO is formed on the surface of the refractory structure, which suppresses the penetration of oxygen into the refractory structure. As a result, oxidation of the refractory can be prevented. (Formula 1) B4C+6CO→2B2O3+7C [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-1889 A (see

[0031] ) Summary of the Invention [Problem to be solved by the invention]

[0006] However, adding a large amount of B4C to a refractory to improve its oxidation resistance (for example, adding 5% or more by mass when the mass of the refractory is taken as 100%) also results in the generation of a large amount of B2O3 during heat treatment in manufacturing or during use in the actual machine. At high temperatures, the liquid-phase B2O3, which is a glass component, causes necks to grow between the particles in the fine powder region of the matrix, accelerating liquid-phase sintering. Over-sintering due to liquid-phase sintering reduces heat spalling resistance. Furthermore, an increase in the amount of B2O3, a glass component, reduces the corrosion resistance of the brick structure, which is a problem.

[0007] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a refractory capable of improving the oxidation resistance of the refractory, and a method for producing the same. [Means for solving the problem]

[0008] In order to solve the above problems, one aspect of the present invention is a refractory material containing Al3BC3.

[0009] Another aspect of the present invention is a method for producing an Al3BC3-containing refractory material, which comprises mixing and kneading raw materials containing at least a refractory raw material, Al3BC3, and a binder, forming the kneaded raw materials into a compact, and heat treating the compact. [Effects of the Invention]

[0010] According to the present invention, since the refractory contains Al3BC3, when the refractory is used in an actual plant, (1) B2O3 produced by oxidation of Al3BC3 forms a glass layer on the surface of the refractory structure, and (2) Al2O3 produced by oxidation of Al3BC3 seals pores in the refractory structure, thereby suppressing the penetration of oxygen into the refractory structure. As a result, the oxidation resistance of the refractory can be improved. [Brief explanation of the drawings]

[0011] [Figure 1] This is the Al3BC3 chart recorded in PDF. [Figure 2] This is a COMPO image of a refractory material taken using a scanning electron microscope. [Figure 3] These are the results of an oxidation test at 1000°C for 2 hours. [Figure 4] These are the results of an oxidation test at 1500°C for 2 hours. [Figure 5] 1 is a powder X-ray diffraction chart of a refractory material. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, a refractory and a method for manufacturing the same according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. However, the refractory and the method for manufacturing the same according to the present invention may be embodied in various forms and are not limited to the embodiments described herein. The present embodiment is provided with the intention of enabling those skilled in the art to fully understand the invention by providing sufficient disclosure in the specification. (Refractories)

[0013] First, a refractory according to an embodiment of the present invention will be described. The refractory according to this embodiment has excellent oxidation resistance and contains Al3BC3. This is identified by confirming the presence of Al3BC3 in powder X-ray diffraction. Figure 1 shows an Al3BC3 chart (card number: 01-088-1267) recorded in a database called PDF (Powder Diffraction File), which is used to identify crystalline materials. If a peak is detected in powder X-ray diffraction at the same diffraction angle 2θ as in this chart, it can be said that Al3BC3 is present in the refractory.

[0014] If Al3BC3 is present in a refractory, the reaction shown in Equation 2 occurs within the refractory structure when the refractory is used in an actual plant. (Formula 2) Al3BC3+9 / 2CO→3 / 2Al2O3+1 / 4B4C+29 / 4C The B4C produced in Equation 2 reacts with CO as shown in Equation 1, ultimately producing B2O3. (Formula 1) B4C+6CO→2B2O3+7C

[0015] As shown in formula 2, Al2O3 produced by the oxidation of Al3BC3 seals the pores in the refractory structure, and as shown in formula 1, B2O3 produced by the oxidation of Al3BC3 forms a glass layer on the surface of the refractory structure, thereby suppressing the penetration of oxygen into the refractory structure. As a result, the oxidation resistance of the refractory can be improved.

[0016] The Al3BC3 in refractories originates from the Al3BC3 added to the refractory raw materials. When Al3BC3 is added to the refractory raw materials and the compact is reduced and fired at a temperature below 1400°C, most of the Al3BC3 remains in the refractory, and the presence of Al3BC3 can be confirmed by powder X-ray diffraction.

[0017] Figure 2 is a COMPO image of a refractory that was subjected to reduction firing at 1300°C, taken using a scanning electron microscope. The COMPO image in Figure 2 and the mapping images of Al, O, C, and B using EDS (energy dispersive X-ray spectroscopy) revealed that most of the Al3BC3 remained unreacted after reduction firing. In Figure 2, the unreacted Al3BC3 is shown as "initial reaction Al3BC3 particles."

[0018] Furthermore, from the COMPO images and mapping images of Al, O, C, and B using EDS (energy dispersive X-ray spectroscopy), it was found that a portion of Al3BC3 reacted with CO as shown in Equation 2, producing Al2O3 and B4C. Similar results were obtained not only from elemental analysis using EDS, but also from elemental analysis using microscopic Raman spectroscopy. In Figure 2, the reacted Al3BC3 is represented as "reacted Al3BC3 particles." (Formula 2) Al3BC3+9 / 2CO→3 / 2Al2O3+1 / 4B4C+29 / 4C

[0019] The use of the refractory material of this embodiment is not particularly limited, but because it has excellent oxidation resistance, it is suitable as a plate for a sliding nozzle that is attached to a steelmaking ladle or tundish to control the flow rate of molten steel. (Refractory manufacturing method)

[0020] A method for producing a refractory according to an embodiment of the present invention will now be described. The method for producing a refractory according to the present embodiment is a method for producing an Al3BC3-containing refractory by mixing and kneading raw materials containing at least a refractory raw material, Al3BC3, and a binder, forming the kneaded raw materials into a molded body, and heat treating the molded body.

[0021] The refractory raw material is composed of coarse particles, medium particles, and fine powder. The particle sizes of the coarse particles, medium particles, and fine powder are not particularly limited, and the particle size of the coarse particles is, for example, 1 to 3 mm or more, the particle size of the medium particles is 0.3 to 1 mm, and the particle size of the fine powder is, for example, 10 μm to 0.3 mm. The particle sizes are based on the nominal mesh size of JIS Z 8801:2019. The refractory raw material may be composed of coarse particles and fine powder, or medium particles and fine powder. The refractory raw material may also contain ultrafine powder with a particle size of 10 μm or less.

[0022] The chemical composition (or mineral composition) of the refractory raw material is not particularly limited, and may be, for example, one or more of alumina, mullite, alumina-zirconia, zirconia-mullite, magnesia, and magnesia-spinel. The particle size structure and chemical composition (or mineral composition) of the refractory raw material are designed depending on the desired properties of the refractory product.

[0023] Al3BC3 is added to the refractory raw material. Al3BC3 is added in an amount of 0.2 to 50 mass %, preferably 2 to 40 mass %, and more preferably 3 to 20 mass %, when the mass of the refractory is taken as 100 mass %. Al3BC3 is in the form of powder.

[0024] Adding 0.2 to 50 mass% of Al3BC3 can improve not only the oxidation resistance of the refractory, but also its corrosion resistance and heat spalling resistance. During heat treatment, part of the Al3BC3 reacts to produce Al2O3, which blocks pores, reducing porosity and improving corrosion resistance. In addition, the thermal conductivity (W / mK) improves, improving heat spalling resistance.

[0025] If the amount of Al3BC3 added is less than 0.2 mass%, the effects of improving oxidation resistance, corrosion resistance, and heat spalling resistance are not significant.If the amount of Al3BC3 added is 50 mass% or more, excessive B2O3 is produced in the brick structure at high temperatures, resulting in a decrease in heat spalling resistance or corrosion resistance.

[0026] It is preferable to add one or more of coke, pitch, carbon black, flaky graphite, and artificial graphite as a carbonaceous raw material to the raw material. Since carbonaceous raw materials have high thermal conductivity, adding a carbonaceous raw material to the raw material improves heat spalling resistance. Furthermore, the carbonaceous raw material is a fine powder or ultrafine powder, and the carbonaceous raw material fills pores, improving the strength of the refractory. The carbonaceous material is added in an amount of 1 to 10 mass %, preferably 2 to 5 mass %, when the mass of the refractory is taken as 100 mass %.

[0027] The binder is a phenol resin, etc. The binder is added in an amount of 1 to 10 mass % when the mass of the refractory material is taken as 100 mass %.

[0028] The raw material may contain other conventional additives, such as a silicon compound that reacts with the carbonaceous material to produce silicon carbide, or metallic aluminum as an antioxidant.

[0029] The raw materials are then uniformly kneaded using a kneading device. The kneading time is not particularly limited. Next, the kneaded raw materials are formed into a molded body of a predetermined shape by molding, compression molding, or the like. Next, the molded body is subjected to heat treatment. The heat treatment in this embodiment includes drying and firing. Drying is performed, for example, in an air atmosphere at 90°C to 350°C. Firing is, for example, reduction firing at 500°C to 1500°C. For reduction firing, for example, coke breeze can be used. Firing may be oxidation firing depending on the conditions required for the refractory, and the firing temperature can be appropriately set. Alternatively, drying and firing may be performed in an air atmosphere or an inert gas atmosphere at a predetermined temperature without separating them. The refractory after heat treatment may be impregnated with pitch or resin for the purpose of strengthening the structure, or another heat treatment may be performed after the impregnation treatment. [Example]

[0030] Refractories of Examples 1 to 4 and Comparative Examples 1 and 2 were manufactured. The blending ratios of the raw materials are shown in Table 1. In Examples 1 to 4, Al3BC3 was added as an antioxidant. In Example 1, 2 mass% of Al3BC3 was added, in Example 2, 10 mass% of Al3BC3 was added, in Example 3, 20 mass% of Al3BC3 was added, and in Example 4, 40 mass% of Al3BC3 was added.

[0031] No Al3BC3 was added in Comparative Examples 1 and 2. 1 mass% of B4C was added instead of Al3BC3 in Comparative Example 1. The B content of 1 mass% of B4C in Comparative Example 1 corresponds to the B content of 10 mass% of Al3BC3 in Example 2.

[0032] [Table 1]

[0033] The raw materials shown in Table 1 were mixed and pressure-molded into a 50Φ molded body. Next, after drying at 110°C, reduction firing (embedding firing by breeze) was carried out in an electric furnace at 1300°C for 5 hours. Table 2 shows the evaluation results of the physical properties of the refractories after reduction firing.

[0034] [Table 2]

[0035] In Example 2-4, in which 10 to 40 mass% of Al3BC3 was added, a decrease in porosity was observed. It is thought that Al3BC3 reacted to generate Al2O3 during firing as shown in Reaction Formula 2, and the Al2O3 blocked the pores in the structure. (Formula 2) Al3BC3+9 / 2CO→3 / 2Al2O3+1 / 4B4C+29 / 4C

[0036] In Comparative Examples 1 and 2 and Example 1, the phenolic resin used as a binder volatilized during firing, resulting in a weight loss. In Examples 2 to 4, weight loss due to volatilization of the binder is thought to have occurred, as in Comparative Examples 1 and 2 and Example 1, but weight gain occurred due to the reaction of Equation 2. As shown in Equation 2, the weight theoretically increases by 1.99 times the amount of Al3BC3 added.

[0037] The higher the thermal conductivity, the more improved the thermal spalling resistance. According to the results of the thermal conductivity, the thermal conductivity was improved by adding Al3BC3. Example 2, which added 10 mass% of Al3BC3, showed the highest result.

[0038] To evaluate oxidation resistance, we conducted an oxidation test at 1000°C for 2 hours (Fig. 3) and an oxidation test at 1500°C for 2 hours (Fig. 4). Although refractories are not exposed to such a severe oxidizing atmosphere when used in actual equipment, we heated them in an electric furnace in an air atmosphere in order to evaluate oxidation resistance. After heating, the samples were cut in the center and the cut surface was observed.

[0039] The black areas in Figures 3 and 4 are areas where carbon remains, and the white areas are areas that have been decarburized. The oxide layer thickness is the thickness of the white areas. The weight loss index and the oxide layer thickness index are both indexes relative to Comparative Example 1, which is set at 100. The smaller these values ​​are, the better the oxidation resistance is.

[0040] As shown in Figure 3, in Comparative Example 2, in which no antioxidant was added, the weight loss rate and oxidation layer thickness were large, indicating that oxidation progressed. On the other hand, when Comparative Example 2, in which no antioxidant was added, was compared with Examples 1 to 4, in which Al3BC3 was added, it was found that the weight loss rate and oxidation layer thickness decreased and oxidation resistance improved when even a small amount of Al3BC3 was added. Furthermore, Example 2, which had the same amount of boron as Comparative Example 1, exhibited better oxidation resistance than Comparative Example 1. It was found that Al3BC3 had a greater oxidation prevention effect than B4C. As shown in Examples 2 to 4, the more Al3BC3 was added, the better the oxidation resistance.

[0041] As shown in Figure 4, when an oxidation test was conducted at 1500°C for 2 hours, oxidation progressed considerably, and the black areas almost disappeared in Comparative Example 1, Comparative Example 2, and Example 1. However, Example 1, to which 2 mass% Al3BC3 was added, had a lower weight loss index than Comparative Example 2. It was found that adding even a small amount of Al3BC3 improves oxidation resistance.

[0042] In Example 2, in which 10 mass% of Al3BC3 was added, black areas that were not decarburized were observed inside the refractory, and it was found that the refractory had better oxidation resistance than Comparative Example 1, in which the same amount of boron was added. As shown in Examples 3 and 4, the more the amount of Al3BC3 added, the better the oxidation resistance was.

[0043] As shown in Figure 5, powder X-ray diffraction (XRD) analysis was performed on the refractories after reduction firing at 1300°C. In Examples 1 to 4, in which 2 to 40 mass% of Al3BC3 was added, a peak was detected at the same diffraction angle 2θ as in the Al3BC3 chart recorded in the PDF. It was found that unreacted Al3BC3 remained after reduction firing. As shown in Examples 2 to 4, the peak intensity tended to increase with increasing Al3BC3 addition amount. Note that the diffraction angle 2θ of the main peak was 30.80° in the Al3BC3 chart recorded in the PDF, whereas it was 11.16° in Examples 1 to 4. This is presumably because the Al3BC3 crystals were oriented due to grain growth of Al3BC3 during reduction firing, shifting the main peak to a lower angle.

[0044] In Comparative Examples 1 and 2, in which Al3BC3 was not added, no peak was detected at the same diffraction angle 2θ as in the chart of Al3BC3.

[0045] In Comparative Example 1, in which B4C was added, Al 18 B4O 33 This is thought to be because B4C reacts with CO during reduction firing to produce B2O3 as shown in Equation 1, and this B2O3 then reacts with Al2O3 in the system. (Formula 1) B4C+6CO→2B2O3+7C

[0046] Carbon is also present in the refractory material because it contains carbonaceous materials as raw materials. Carbon can be detected by carbon quantitative analysis.

[0047] Figure 2 shows the results of microstructural observation of Example 2 after reduction firing at 1300°C. From the COMPO image in Figure 2 and the mapping images of Al, O, C, and B obtained using EDS (energy dispersive X-ray spectroscopy), not shown, it was found that almost all of the Al3BC3 remained unreacted after reduction firing. In Figure 2, the unreacted Al3BC3 is represented as "initial reaction Al3BC3 particle." It is presumed that this "initial reaction Al3BC3 particle" has a shell of Al2O3, a core outer periphery of B4C+C, and the interior of the core is Al3BC3.

[0048] Furthermore, from the COMPO image and mapping images of Al, O, C, and B using EDS (not shown), it was found that a portion of the Al3BC3 reacted to produce Al2O3 and B4C. In Figure 2, the reacted Al3BC3 is shown as a "reacted Al3BC3 particle." This "reacted Al3BC3 particle" is presumed to have a shell of Al2O3 and a core of B4C+C.

Claims

1. Al ３ B.C. ３ Refractories containing

2. 2. The refractory according to claim 1, wherein the refractory is a plate for a sliding nozzle.

3. At least refractory raw material, Al ３ B.C. ３ , mixing and kneading raw materials including a binder, The kneaded raw material is formed into a compact, Heat-treat the compact. ３ B.C. ３ Method for producing contained refractories.

4. Al ３ B.C. ３ 4. The method for producing a refractory according to claim 3, wherein the refractory is added in an amount of 0.2 to 50 mass %.

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