Low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag corrosion resistance and preparation method of low-carbon magnesia-carbon refractory material

Abstract

The invention discloses a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag corrosion resistance and a preparation method thereof, and relates to the technical field of magnesia-carbon refractory materials. The refractory material comprises the following components in parts by mass: 40-45 parts of 3-5mm fused magnesite, 20-25 parts of 1-3mm fused magnesite, 10-15 parts of fused magnesite less than or equal to 1mm, 8-12 parts of silicon powder, 5-8 parts of a composite additive, 4-6 parts of crystalline flake graphite and 3-5 parts of phenolic resin, and the composite additive is prepared from the following raw materials: alumina powder, lanthanum oxide powder and low-grade andalusite. Impurity phases in the low-grade andalusite are directionally converted into high-melting-point spinel, mullite and rare earth lanthanum aluminate by utilizing the aluminum oxide powder and the lanthanum oxide powder, so that the problem that the low-grade andalusite is difficult to apply in a metallurgical refractory material is solved, and meanwhile, the low-grade andalusite and the andalusite are coordinated to regulate and control the ceramic phase structure and distribution of the refractory material; the thermal shock resistance and the slag corrosion resistance of the refractory material are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to a low-carbon magnesium-carbon refractory material with high thermal shock resistance and slag erosion resistance, and its preparation method. Background Technology

[0002] Due to their excellent resistance to thermal shock and slag erosion, magnesia-carbon refractories have become indispensable basic materials in metallurgical processes, including refining. To meet performance requirements, industrial use of magnesia-carbon refractories with a carbon content of 10–20 wt% presents significant drawbacks: high carbon content easily leads to a carbonization effect in the molten pool during steel decarburization; high thermal conductivity results in large heat losses; and excessive consumption of graphite resources and carbon emissions exacerbate environmental burdens. Therefore, reducing the carbon content of magnesia-carbon refractories is imperative. However, reducing the carbon content inevitably reduces the thermal shock resistance and slag erosion resistance of magnesia-carbon refractories, failing to meet the urgent needs of advanced high-quality clean steel smelting technologies.

[0003] The introduction of high-efficiency additives is one of the effective methods to improve the high-temperature service performance of low-carbon magnesia-carbon refractories, but some problems still exist:

[0004] For example, the patented technology "A method for preparing a high corrosion-resistant low-carbon magnesium-carbon refractory material" (CN202510738149.8) uses Ti3SiC2 powder as an additive to prepare low-carbon magnesium-carbon refractory material, but the Ti3SiC2 raw material has the problem of high cost and is not conducive to industrial application.

[0005] For example, the patent "A Low-Carbon Magnesium-Carbon Refractory Material for Clean Steel Smelting and Its Preparation Method" (CN202411554021.8) discloses a technical solution that uses high-grade andalusite / mullite as a composite additive. The small amount of low-melting-point silica phase generated by the high-temperature decomposition of high-grade andalusite can be transformed into a high-melting-point phase through high-temperature structural reconstruction, thereby improving the performance of the refractory material. However, the high-grade andalusite and mullite raw materials used in this solution are expensive, which is not conducive to low-cost promotion and application. On the other hand, low-grade andalusite, which has large reserves and low prices, has a high content of impurities and inherent low-melting-point phases. Combined with the low-melting-point silica phase generated by its high-temperature decomposition, it will cause an excessive amount of liquid phase inside the refractory material at high temperatures, which will seriously degrade the thermal shock stability and load-bearing performance of the material, making it unusable directly.

[0006] In order to align with the development strategies of clean steel smelting technology innovation, energy conservation and emission reduction in the metallurgical industry, and efficient utilization of resources, this patent aims to prepare refractory additives with both excellent service performance and low cost advantages using low-grade andalusite as raw material. This will improve the service performance and service life of magnesia-carbon refractory materials while realizing the high-value utilization of low-grade and low-cost resources. Summary of the Invention

[0007] The purpose of this invention is to provide a low-carbon magnesium-carbon refractory material with high thermal shock resistance and slag erosion resistance.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: a low-carbon magnesia-carbon refractory material with high thermal shock resistance and erosion resistance, the raw materials comprising the following components by weight: 40-45 parts of 3-5mm fused magnesia, 20-25 parts of 1-3mm fused magnesia, 10-15 parts of ≤1mm fused magnesia, 8-12 parts of silica powder, 5-8 parts of composite additives, 4-6 parts of flake graphite, and 3-5 parts of phenolic resin, wherein the composite additives are prepared by mixing low-grade andalusite powder, alumina powder, and lanthanum oxide powder, followed by microwave sintering and crushing.

[0009] Furthermore, the mass ratio of alumina powder to low-grade andalusite powder is 1:(2-4), and the lanthanum oxide powder accounts for 0.2-0.5 wt% of the total mass of the composite additive.

[0010] Furthermore, the preparation method of the composite additive includes the following steps:

[0011] Alumina powder, low-grade andalusite powder, and lanthanum oxide powder are mixed with water to obtain a mixture, wherein the amount of water added is 3-5 wt%.

[0012] The mixture is pressed and dried under a pressure of 150-180 MPa to obtain a molded blank.

[0013] The shaped preform was microwave sintered at 1150–1200 °C for 30–60 min in a mixed atmosphere of Ar and H2 (H2 volume percentage of 2–3 vol%) to obtain the sintered product.

[0014] The sintered product is crushed to a particle size ≤100μm to obtain the composite additive.

[0015] Specifically, the composite additive is prepared through the following steps:

[0016] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:(2-4), add 0.2-0.5 wt% lanthanum oxide powder and 3-5 wt% water, stir for 15-20 minutes to obtain a mixture;

[0017] Step 2: Press the mixture into shape under a pressure of 150-180 MPa, and dry the shaped blank at 110-150℃ for 24-28 hours; then microwave sinter it in a mixed atmosphere of Ar and H2 at 1150-1200℃ for 30-60 minutes to obtain the sintered product.

[0018] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0019] The gas flow rate of the mixed atmosphere is 50-100 mL / min, and the volume percentage of H2 in the mixed gas is 2-3 vol.

[0020] The microwave sintering parameters are: 3kW, 2.45GHz.

[0021] The alumina powder is α-alumina powder with a particle size of 5-6 μm and a purity of ≥99 wt%; the lanthanum oxide powder has a particle size of 5-6 μm and a purity of ≥99 wt%; the low-grade andalusite powder has a particle size of ≤100 μm, a purity of 70-80 wt%, a SiO2 content of 13-18 wt%, and a Fe2O3 content of 4-6 wt%.

[0022] The purity of the fused magnesia is ≥98wt%.

[0023] The silicon powder has a particle size ≤100μm and a purity ≥99wt%.

[0024] The flake graphite has a particle size ≤150μm and a purity ≥98wt%.

[0025] The phenolic resin is a thermosetting phenolic resin with a viscosity of 1000~2000 mPa·s, free phenol ≤8wt%, and free aldehyde ≤5wt%.

[0026] The preparation method of the aforementioned high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material includes the following steps:

[0027] The raw materials are mixed evenly and pressed into shape under 200 MPa. Then, they are cured at 110–220℃ for 12–18 hours. They are then kept at 1400–1500℃ for 3–5 hours in a carbon-buried atmosphere and allowed to cool naturally to obtain a low-carbon magnesium-carbon refractory material with high thermal shock resistance and slag erosion resistance.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. This invention solves the problem that low-grade andalusite contains high levels of silica and iron oxide impurities, making it difficult to apply in carbon-containing refractory materials. This is achieved by pre-compositing low-grade andalusite with alumina powder and lanthanum oxide powder, and using alumina and lanthanum oxide to induce the directional transformation of low-melting-point impurity phases in low-grade andalusite into high-melting-point phases such as mullite, iron-aluminum spinel, and rare-earth lanthanum aluminate.

[0030] 2. The composite additive prepared in this invention achieves directional composite formation of andalusite, mullite, spinel, and lanthanum aluminate through pre-sintering. Introducing the composite additive into the refractory material results in complementary thermal expansion coefficients and high-temperature performance of the composite phases, regulating the internal ceramic phase structure of the refractory material. Specifically, andalusite is converted into long columnar mullite and a small amount of silica liquid phase in situ at high temperature, repairing cracks and filling pores, effectively blocking oxygen and slag intrusion. Spinel and rare earth lanthanum aluminate partially exist as intergranular phases, inhibiting grain boundary migration, eliminating intergranular pores, and improving the density and mechanical properties of the refractory material. The formed magnesium aluminum spinel, silicon nitride, and mullite ceramic phases enhance the interfacial bonding strength of the refractory material and improve its thermal shock resistance.

[0031] 3. This invention regulates the internal ceramic phase structure and distribution of refractory materials by compounding various raw materials, thereby improving the thermal shock resistance and slag erosion resistance of refractory materials while realizing the high-value utilization of low-grade andalusite, and thus extending the service life of refractory materials. Attached Figure Description

[0032] Figure 1 SEM images of the high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material prepared in this invention. Figure 1 ;

[0033] Figure 2 SEM images of the high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material prepared in this invention. Figure 2 . Detailed Implementation

[0034] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention. It should be noted in advance that the following embodiments were completed in a laboratory setting. Those skilled in the art should understand that the amounts of each component given in the embodiments only represent the ratio between the components, and are not specific limitations.

[0035] This invention provides a method for preparing a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance, as detailed below:

[0036] Using 40-45 parts by weight of 3-5 mm fused magnesia, 20-25 parts by weight of 1-3 mm fused magnesia, 10-15 parts by weight of ≤1 mm fused magnesia, 8-12 parts by weight of silica powder, 5-8 parts by weight of composite additives, 4-6 parts by weight of flake graphite, and 3-5 parts by weight of phenolic resin as raw materials, the mixture is uniformly mixed and pressed into shape under 200 MPa. Then, it is cured at 110-220℃ for 12-18 hours. Finally, it is kept at 1400-1500℃ in a carbon-buried atmosphere for 3-5 hours and then naturally cooled to obtain a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance.

[0037] The above-mentioned composite additive is prepared by the following steps:

[0038] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:(2-4), with lanthanum oxide powder accounting for 0.2-0.5 wt% of the total mass of the composite additive, add 3-5 wt% water, and stir for 15-20 minutes to obtain a mixture;

[0039] Step 2: Press the mixture into shape under a pressure of 150-180 MPa, and dry the shaped blank at 110-150℃ for 24-28 hours; then microwave sinter the shaped blank in a mixed atmosphere of Ar and H2 at 1150-1200℃ for 30-60 minutes to obtain the sintered product.

[0040] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0041] The alumina powder is α-alumina powder with a particle size of 5-6 μm and a purity of ≥99 wt%; the lanthanum oxide powder has a particle size of 5-6 μm and a purity of ≥99 wt%; the low-grade andalusite powder has a particle size of ≤100 μm, a purity of 70-80 wt%, a SiO2 content of 13-18 wt%, and a Fe2O3 content of 4-6 wt%.

[0042] The fused magnesia has a purity ≥98wt%. The silica powder has a particle size ≤100μm and a purity ≥99wt%. The flake graphite has a particle size ≤150μm and a purity ≥98wt%. The phenolic resin is a thermosetting phenolic resin with a viscosity of 1000~2000mPa·s, free phenol ≤8wt%, and free aldehyde ≤5wt%. The gas flow rate of the mixed atmosphere is 50~100mL / min, and the volume percentage of H2 in the mixed gas is 2~3vol%. The microwave sintering parameters are 3kW and 2.45GHz.

[0043] The following is a detailed explanation using a specific example: the low-grade andalusite powder has a particle size ≤100μm, a purity of 75wt%, a SiO2 content of 15wt%, and a Fe2O3 content of 5wt%.

[0044] Example 1

[0045] This embodiment describes the preparation of a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance using the following method:

[0046] Using 40 parts by weight of 3-5 mm fused magnesia, 25 parts by weight of 1-3 mm fused magnesia, 11 parts by weight of ≤1 mm fused magnesia, 10 parts by weight of silica powder, 5 parts by weight of composite additives, 5 parts by weight of flake graphite, and 4 parts by weight of phenolic resin as raw materials, the mixture was uniformly mixed, pressed into shape under 200 MPa, and then cured at 110℃ for 12 h; then kept at 1500℃ for 4 h in a carbon-buried atmosphere and allowed to cool naturally, a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance was obtained.

[0047] The above-mentioned composite additive is prepared by the following steps:

[0048] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:4, add lanthanum oxide powder at 0.3% of the total mass of the composite additive, add 3wt% water, stir for 20 minutes to obtain the mixture;

[0049] Step 2: Press the mixture under 150 MPa pressure to form a molded body, and dry the molded body at 110°C for 28 h; then microwave sinter it at 1150°C for 30 min in a mixed atmosphere of Ar and H2 to obtain the sintered product.

[0050] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0051] After testing, the properties of the high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material prepared in this embodiment are as follows: room temperature compressive strength is 69 MPa, high temperature flexural strength is 13 MPa (1400℃ for 30 min); no cracks after 62 thermal shocks by air cooling method (1100℃ for 30 min); erosion depth is 674 μm (1500℃ for 3 h of erosion).

[0052] Example 2

[0053] This embodiment describes the preparation of a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance using the following method:

[0054] Using 45 parts by weight of 3-5 mm fused magnesia, 20 parts by weight of 1-3 mm fused magnesia, 10 parts by weight of ≤1 mm fused magnesia, 8 parts by weight of silica powder, 8 parts by weight of composite additives, 4 parts by weight of flake graphite, and 5 parts by weight of phenolic resin as raw materials, the mixture was uniformly mixed, pressed into shape under 200 MPa, and then cured at 110℃ for 14 h; then kept at 1450℃ for 4 h in a carbon-buried atmosphere and allowed to cool naturally, a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance was obtained.

[0055] The above-mentioned composite additive is prepared by the following steps:

[0056] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:3, add lanthanum oxide powder at 0.3% of the total mass of the composite additive, add 5wt% water, stir for 15 minutes to obtain the mixture;

[0057] Step 2: Press the mixture under 160 MPa pressure to form a preform, and dry the preform at 120°C for 26 h; then microwave sinter it at 1150°C for 40 min in a mixed atmosphere of Ar and H2 to obtain the sintered product.

[0058] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0059] After testing, the properties of the high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material prepared in this embodiment are as follows: room temperature compressive strength is 69 MPa, high temperature flexural strength is 15 MPa (1400℃ for 30 min); no cracks after 65 air-cooled thermal shocks (1100℃ for 30 min); erosion depth is 668 μm (1500℃ for 3 h of erosion).

[0060] Example 3

[0061] This embodiment describes the preparation of a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance using the following method:

[0062] Using 42 parts by weight of 3-5 mm fused magnesia, 20 parts by weight of 1-3 mm fused magnesia, 11 parts by weight of ≤1 mm fused magnesia, 12 parts by weight of silica powder, 56 parts by weight of composite additives, 6 parts by weight of flake graphite, and 3 parts by weight of phenolic resin as raw materials, the mixture was uniformly mixed, pressed into shape under 200 MPa, and then cured at 110℃ for 15 h; then kept at 1400℃ for 5 h in a carbon-buried atmosphere and allowed to cool naturally, a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance was obtained.

[0063] The above-mentioned composite additive is prepared by the following steps:

[0064] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:2, add lanthanum oxide powder at 0.4% of the total mass of the composite additive, add 4wt% water, stir for 18 minutes to obtain the mixture;

[0065] Step 2: Press the mixture under 180 MPa pressure to form a molded body, and dry the molded body at 150°C for 26 h; then microwave sinter it at 1200°C for 60 min in a mixed atmosphere of Ar and H2 to obtain the sintered product.

[0066] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0067] After testing, the high thermal shock resistance and slag erosion resistance of the low-carbon magnesium-carbon refractory material prepared in this embodiment have the following properties: room temperature compressive strength of 67 MPa, high temperature flexural strength of 12 MPa (1400℃ for 30 min); no cracks after 53 air-cooled thermal shocks (1100℃ for 30 min); erosion depth of 831 μm (1500℃ for 3 h).

[0068] Example 4

[0069] This embodiment describes the preparation of a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance using the following method:

[0070] Using 40 parts by weight of 3-5 mm fused magnesia, 20 parts by weight of 1-3 mm fused magnesia, 15 parts by weight of ≤1 mm fused magnesia, 9 parts by weight of silica powder, 7 parts by weight of composite additives, 5 parts by weight of flake graphite, and 4 parts by weight of phenolic resin as raw materials, the mixture was uniformly mixed, pressed into shape under 200 MPa, and then cured at 110℃ for 18 h; then kept at 1500℃ for 3 h in a carbon-buried atmosphere and allowed to cool naturally to obtain a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance.

[0071] The above-mentioned composite additive is prepared by the following steps:

[0072] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:4, add lanthanum oxide powder at 0.2% of the total mass of the composite additive, add 5wt% water, stir for 16 minutes to obtain the mixture;

[0073] Step 2: Press the mixture under 170 MPa pressure to form a blank, and dry the blank at 140°C for 25 h; then microwave sinter it at 1150°C for 50 min in a mixed atmosphere of Ar and H2 to obtain the sintered product.

[0074] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0075] After testing, the high thermal shock resistance and slag erosion resistance of the low-carbon magnesium-carbon refractory material prepared in this embodiment have the following properties: room temperature compressive strength of 69 MPa, high temperature flexural strength of 13 MPa (1400℃ for 30 min); no cracks after 59 thermal shocks by air cooling method (1100℃ for 30 min); erosion depth of 650 μm (1500℃ for 3 h of erosion).

[0076] Example 5

[0077] This embodiment describes the preparation of a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance using the following method:

[0078] Using 41 parts by weight of 3-5 mm fused magnesia, 24 parts by weight of 1-3 mm fused magnesia, 12 parts by weight of ≤1 mm fused magnesia, 11 parts by weight of silica powder, 5 parts by weight of composite additives, 4 parts by weight of flake graphite, and 3 parts by weight of phenolic resin as raw materials, the mixture was uniformly mixed, pressed into shape under 200 MPa, and then cured at 110℃ for 16 h; then kept at 1400℃ for 5 h in a carbon-buried atmosphere and naturally cooled, a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance was obtained.

[0079] The above-mentioned composite additive is prepared by the following steps:

[0080] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:2, add lanthanum oxide powder at 0.5% of the total mass of the composite additive, add 4wt% water, stir for 19 minutes to obtain the mixture;

[0081] Step 2: Press the mixture under 170 MPa pressure to form a molded body, and dry the molded body at 120°C for 24 h; then microwave sinter it at 1200°C for 60 min in a mixed atmosphere of Ar and H2 to obtain the sintered product.

[0082] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0083] After testing, the high thermal shock resistance and slag erosion resistance of the low-carbon magnesium-carbon refractory material prepared in this embodiment have the following properties: room temperature compressive strength of 65 MPa, high temperature flexural strength of 12 MPa (1400℃ for 30 min); no cracks after 50 air-cooled thermal shock cycles (1100℃ for 30 min); erosion depth of 840 μm (1500℃ for 3 h).

[0084] Example 6

[0085] This embodiment describes the preparation of a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance using the following method:

[0086] Using 40 parts by weight of 3-5 mm fused magnesia, 20 parts by weight of 1-3 mm fused magnesia, 14 parts by weight of ≤1 mm fused magnesia, 10 parts by weight of silica powder, 6 parts by weight of composite additives, 5 parts by weight of flake graphite, and 5 parts by weight of phenolic resin as raw materials, the mixture is uniformly mixed, pressed into shape under 200 MPa, and then cured at 110℃ for 12 h; then kept at 1400℃ for 5 h in a carbon-buried atmosphere and naturally cooled, a low-carbon magnesia-carbon refractory material with thermal shock resistance and slag erosion resistance is obtained.

[0087] The above-mentioned composite additive is prepared by the following steps:

[0088] Step 1: Mix alumina powder and low-grade andalusite powder at a mass ratio of 1:3, add lanthanum oxide powder at 0.3% of the total mass of the composite additive, add 5wt% water, stir for 20 minutes to obtain the mixture;

[0089] Step 2: Press the mixture under 150 MPa pressure to form a molded body, and dry the molded body at 140°C for 26 h; then microwave sinter it at 1200°C for 50 min in a mixed atmosphere of Ar and H2 to obtain the sintered product.

[0090] Step 3: Crush the sintered product to a particle size ≤100μm to obtain the composite additive.

[0091] After testing, the high thermal shock resistance and slag erosion resistance of the low-carbon magnesium-carbon refractory material prepared in this embodiment have the following properties: room temperature compressive strength of 66 MPa, high temperature flexural strength of 15 MPa (1400℃ for 30 min); no cracks after 60 air-cooled thermal shock cycles (1100℃ for 30 min); erosion depth of 739 μm (1500℃ for 3 h).

[0092] Compared with the prior art, the present invention has the following characteristics:

[0093] This invention uses fused magnesia, silica powder, flake graphite, composite additives, and phenolic resin as raw materials. The materials are mixed, machine-pressed, cured, and then heat-treated in a carbon-buried atmosphere to obtain a low-carbon magnesia-carbon refractory material with high thermal shock resistance and slag erosion resistance. The entire process is very simple and suitable for large-scale production. All raw materials used in this invention are commercially available, resulting in low production costs. Low-grade andalusite is particularly inexpensive and produced in large quantities.

[0094] Comparative Example 1

[0095] A low-carbon magnesia-carbon refractory material is basically the same as in Example 1, except that alumina powder, low-grade andalusite powder, and lanthanum oxide powder are directly added as raw materials for the refractory material without pre-preparing composite additives. After testing, the performance of the low-carbon magnesia-carbon refractory material prepared in this comparative example is as follows: room temperature compressive strength is 42 MPa, high temperature flexural strength is 6 MPa (after holding at 1400℃ for 30 min); no cracks were observed after 31 thermal shock cycles using the air-cooling method (after holding at 1100℃ for 30 min); and the erosion depth is 751 μm (after erosion at 1500℃ for 3 h). The performance of the refractory material in this comparative example is reduced. This is mainly because the free silica and iron oxide impurities in the low-grade andalusite powder are easy to react with the refractory material components to form low-melting-point compounds. At the same time, the high-temperature decomposition of andalusite produces liquid silica, resulting in a large number of low-melting-point phases in the refractory material system. These low-melting-point phases are easy to soften and melt at high temperatures, which reduces the performance of the refractory material. Directly adding powder leads to the deterioration of the high-temperature creep resistance, flexural strength and thermal shock resistance of the refractory material.

[0096] Comparative Example 2

[0097] A low-carbon magnesia-carbon refractory material is basically the same as that in Example 1, except that the composite additives are different. An equal amount of high-grade andalusite powder is used instead of low-grade andalusite powder. The high-grade andalusite powder has a purity of 85% and an iron oxide content of 1%. Testing showed that the low-carbon magnesia-carbon refractory material prepared in this comparative example has the following properties: room temperature compressive strength of 53 MPa, high-temperature flexural strength of 9 MPa (after holding at 1400℃ for 30 min); no cracks after 44 thermal shock cycles using the air-cooling method (after holding at 1100℃ for 30 min); and an erosion depth of 837 μm (after erosion at 1500℃ for 3 h). The performance of the refractory material in this comparative example is reduced, mainly because the use of high-grade andalusite powder results in very little iron-aluminum spinel, leading to an imbalance in the internal microstructure and phase structure distribution of the system, and a significant reduction in the synergistic effect between the phase structures.

[0098] Comparative Example 3

[0099] A low-carbon magnesia-carbon refractory material is basically the same as that in Example 1, except that the composite additive is different. Lanthanum oxide powder is not added to the composite additive, while the ratio of alumina powder and low-grade andalusite remains unchanged. The performance of the low-carbon magnesia-carbon refractory material prepared in this comparative example is as follows: room temperature compressive strength is 51 MPa, high-temperature flexural strength is 8 MPa (1400℃ for 30 min); no cracks were observed after 39 thermal shock cycles using the air-cooling method (1100℃ for 30 min); and the erosion depth is 994 μm (1500℃ for 3 h). The reason for the reduced performance in this comparative example may be that lanthanum oxide can optimize the crystal structure, and the generated high-melting-point rare-earth lanthanum aluminate phase can act as a bridge at the interface and promote the densification of the material during sintering. However, in this comparative example, after replacing lanthanum oxide with alumina, the system phase structure lacks the high-melting-point rare-earth lanthanum aluminate phase, resulting in the loss of crystal structure regulation and interface bridging effects, and a significant reduction in the synergistic effect between the phase structures.

[0100] Comparative Example 4

[0101] A low-carbon magnesia-carbon refractory material is basically the same as that in Example 1, except that the composite additive is different, with an equal amount of mullite powder replacing low-grade andalusite powder. Testing showed that the low-carbon magnesia-carbon refractory material prepared in this comparative example has the following properties: room temperature compressive strength of 57 MPa, high-temperature flexural strength of 9 MPa (after holding at 1400℃ for 30 min); no cracks after 46 air-cooled thermal shock cycles (after holding at 1100℃ for 30 min); and an erosion depth of 862 μm (after erosion at 1500℃ for 3 h). The reason for the decreased performance of this comparative example compared to Example 1 may be due to the specific composite additive of this invention, which forms a specific ratio of mullite and iron-aluminum spinel combination within the refractory material, regulating the crystal structure and microstructure, and significantly improving the refractory performance. However, the high cost of mullite raw materials increases the material cost.

[0102] Comparative Example 5

[0103] A low-carbon magnesia-carbon refractory material is basically the same as in Example 1, except that lanthanum oxide is added as a raw material, and the composite additives contain only alumina and low-grade andalusite. The performance of the low-carbon magnesia-carbon refractory material prepared in this comparative example is as follows: room temperature compressive strength is 57 MPa, high temperature flexural strength is 8 MPa (after holding at 1400℃ for 30 min); no cracks were observed after 40 thermal shock cycles using the air-cooling method (after holding at 1100℃ for 30 min); and the erosion depth is 753 μm (after erosion at 1500℃ for 3 h). The reduced performance of this comparative example may be due to a significant decrease in the crystal morphology regulation and interfacial bridging effect of lanthanum oxide, resulting in a significant reduction in the synergistic effect between the phase structures of the system.

[0104] This invention uses low-grade andalusite as raw material to prepare composite refractory additives and successfully applies them to low-carbon magnesia-carbon refractory materials, realizing the high-value utilization of low-grade andalusite, which has significant economic and social value.

[0105] This invention addresses the problem that low-grade andalusite, containing high levels of silica and iron oxide impurities, is difficult to apply in carbon-containing refractory materials. By combining low-grade andalusite with alumina powder and lanthanum oxide powder, the alumina and lanthanum oxide powder induce the directional transformation of the low-melting phase to form high-melting-point spinel and mullite, while lanthanum oxide regulates the crystal phase formation. This solves the problem that the direct application of low-grade andalusite degrades the performance of magnesia-carbon refractory materials.

[0106] The composite additive prepared in this invention consists of andalusite, alumina, mullite, spinel, and rare earth lanthanum aluminate. When this composite additive is introduced into refractory materials, andalusite decomposes at high temperatures to generate long columnar mullite. Figure 1 The composite additive contains a small amount of low-melting silica phase, which repairs cracks and fills pores, effectively preventing oxygen and slag intrusion. The spinel and lanthanum aluminate components exist as intergranular phases, inhibiting grain boundary migration, eliminating intergranular porosity, and further improving the density of the refractory material. Alumina reacts during the heat treatment of the refractory material to generate aluminum nitride and magnesium aluminum spinel ceramic phases. Figure 2 This improves the interfacial bonding strength of materials and enhances their thermomechanical strength.

[0107] After testing, the low-carbon magnesium-carbon refractory material with high thermal shock resistance and slag erosion resistance prepared by this invention has excellent performance: room temperature compressive strength is 65-70 MPa, high temperature flexural strength is 11-15 MPa (1400℃ for 30 min); no cracks after 50-65 air-cooled thermal shocks (1100℃ for 30 min); erosion depth is 650-840 μm (1500℃ for 3 h).

[0108] In summary, this invention features low cost and simple process; and the low-carbon magnesium-carbon refractory material prepared by this invention has excellent thermal shock resistance and erosion resistance.

[0109] The above embodiments are preferred implementations of the present invention. In addition, the present invention can be implemented in other ways. Any obvious substitutions without departing from the concept of the present technical solution are within the protection scope of the present invention.

[0110] Finally, it should be emphasized that, in order to make it easier for those skilled in the art to understand the improvements of the present invention compared with the prior art, some descriptions of the present invention have been simplified, and for clarity, some other elements have been omitted from this application. Those skilled in the art should realize that these omitted elements can also constitute the content of the present invention.

Claims

1. A low-carbon magnesium-carbon refractory material with high thermal shock resistance and slag erosion resistance, characterized in that, The raw materials include the following components in parts by weight: 40-45 parts of 3-5mm fused magnesia, 20-25 parts of 1-3mm fused magnesia, 10-15 parts of ≤1mm fused magnesia, 8-12 parts of silica powder, 5-8 parts of composite additives, 4-6 parts of flake graphite, and 3-5 parts of phenolic resin. The composite additives are prepared by mixing low-grade andalusite powder, alumina powder, and lanthanum oxide powder, followed by microwave sintering and crushing.

2. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 1, characterized in that, The mass ratio of alumina powder to low-grade andalusite powder is 1:(2-4), and the lanthanum oxide powder accounts for 0.2-0.5 wt% of the total mass of the composite additive.

3. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 1, characterized in that, The preparation method of the composite additive includes the following steps: Alumina powder, low-grade andalusite powder, and lanthanum oxide powder are mixed with water to obtain a mixture, wherein the amount of water added is 3-5 wt%. The mixture is pressed and dried under a pressure of 150-180 MPa to obtain a molded blank. The shaped preform was microwave sintered at 1150–1200℃ for 30–60 min in a mixed atmosphere of Ar and H2 to obtain the sintered product. The sintered product is crushed to a particle size ≤100μm to obtain the composite additive.

4. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 1, characterized in that: The alumina powder is α-alumina powder with a particle size of 5-6 μm and a purity of ≥99 wt%; the lanthanum oxide powder has a particle size of 5-6 μm and a purity of ≥99 wt%; the low-grade andalusite powder has a particle size of ≤100 μm, a purity of 70-80 wt%, a SiO2 content of 13-18 wt%, and a Fe2O3 content of 4-6 wt%.

5. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 1, characterized in that: The purity of the fused magnesia is ≥98wt%.

6. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 1, characterized in that: The silicon powder has a particle size ≤100μm and a purity ≥99wt%.

7. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 1, characterized in that: The flake graphite has a particle size ≤150μm and a purity ≥98wt%.

8. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 1, characterized in that: The phenolic resin is a thermosetting phenolic resin with a viscosity of 1000~2000 mPa·s, free phenol ≤8wt%, and free aldehyde ≤5wt%.

9. The high thermal shock resistance and slag erosion resistance low-carbon magnesium-carbon refractory material according to claim 3, characterized in that: The gas flow rate of the mixed atmosphere is 50-100 mL / min, and the volume percentage of H2 in the mixed gas is 2-3 vol.

10. A method for preparing a high thermal shock resistant and slag erosion resistant low-carbon magnesium-carbon refractory material according to any one of claims 1-9, characterized in that, Includes the following steps: The raw materials are mixed evenly and pressed into shape under 200 MPa. Then, they are cured at 110–220℃ for 12–18 hours. They are then kept at 1400–1500℃ for 3–5 hours in a carbon-buried atmosphere and allowed to cool naturally to obtain a low-carbon magnesium-carbon refractory material with high thermal shock resistance and slag erosion resistance.

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