Low-carbon magnesia carbon brick and preparation method thereof

Abstract

The invention discloses a low-carbon magnesia carbon brick and a preparation method thereof, and relates to the technical field of weather-resistant magnesia carbon bricks. The low-carbon magnesia carbon brick comprises the following components in parts by mass: 80-90 parts of fused magnesia particles, 15-25 parts of fused magnesia fine powder, 5-10 parts of crystalline flake graphite, 1-5 parts of nano carbon powder, 10-20 parts of phenolic resin, 0.2-1.5 parts of a curing agent, 0.5-3 parts of an antioxidant and 0-8 parts of a modifier. The core lies in a triple synergistic protection mechanism of the antioxidant, and the triple synergistic protection mechanism comprises electron delocalization stable free radicals of a conjugated pi bond system, the physical isolation effect of tert-butyl and the formation of a high-temperature barrier layer of silyl. The graphite oxidation loss is effectively delayed, the resistance to slag permeation is enhanced, and the service performance of the material under the extreme storage condition is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of weather-resistant magnesia-carbon bricks, and in particular to a low-carbon magnesia-carbon brick and a preparation method thereof. Background Art

[0002] As a key refractory material, the weather resistance of magnesia-carbon bricks is directly related to industrial production efficiency and safety. Traditional magnesia-carbon bricks face many weather resistance challenges in long-term storage environments. On the one hand, bricks are prone to oxidation reactions with oxygen during long-term storage, especially the oxidation of graphite components, resulting in a loose brick structure and reduced strength. Oxidation reactions not only consume brick materials but may also generate volatile gases, further exacerbating the spalling and damage of bricks. On the other hand, after being corroded by the environment, magnesia-carbon bricks must also withstand the erosion of oxide-containing slag in the complex smelting environment. This causes the magnesia sand component in the bricks to gradually dissolve, destroying the structural integrity of the bricks and significantly reducing their refractory performance.

[0003] Although existing technologies have attempted to delay graphite oxidation by adding antioxidants, the environmental oxidation and erosion problems cannot be completely solved due to issues such as the amount of antioxidant added and the compatibility of the material with other components of the brick. In addition, under the dual effects of ultraviolet radiation and oxygen-containing free radical corrosion, the internal stress distribution of the brick is uneven during long-term storage, which easily leads to microcracks. These cracks become channels for the penetration of corrosive substances, accelerating the damage of the brick. Therefore, the development of a low-carbon magnesium-carbon brick with stronger weather resistance is of great significance for improving the production efficiency of high-temperature industries such as steel smelting, reducing maintenance costs, and ensuring production safety. The brick needs to achieve comprehensive breakthroughs in anti-oxidation, anti-erosion, structural stability, etc. to meet the requirements of modern industry for high performance of refractory materials. Summary of the Invention

[0004] The present invention aims to provide a low-carbon magnesia-carbon brick that significantly improves its long-term storage resistance to oxidation and corrosion, thereby solving the problem of existing high-carbon bricks being easily oxidized and peeling off under environmental conditions.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a low-carbon magnesia-carbon brick, characterized in that it contains the following components in parts by mass: 80-90 parts of fused magnesia particles, 15-25 parts of fused magnesia fine powder, 5-10 parts of flake graphite, 1-5 parts of nano-carbon powder, 10-20 parts of phenolic resin, 0.2-1.5 parts of curing agent, 0.5-3 parts of antioxidant, and 1-8 parts of modifier; The antioxidant is a compound represented by Formula 1: Formula 1; Z1 in Formula 1 is selected from any one of -CH2-, -C(CH3)2-, -C(=O)-, O, and S.

[0006] Furthermore, the particle size of the fused magnesia particles is 5 mm to 0.1 mm.

[0007] Furthermore, the particle size of the fused magnesia fine powder is less than 0.1 mm.

[0008] Furthermore, the fixed carbon content of the flake graphite is ≥97wt% and the particle size is less than 0.15mm.

[0009] Furthermore, the nano carbon powder is selected from nano carbon black or nano graphene, and has a specific surface area of ​​≥100m 2 / g.

[0010] Furthermore, the phenolic resin is selected from: resol type phenolic resin.

[0011] Furthermore, the curing agent is hexamethylenetetramine.

[0012] Furthermore, the modifier is Al2O3.

[0013] Furthermore, the antioxidant is any one of the compounds shown in the following structures: ; ; .

[0014] A method for preparing a low-carbon magnesia-carbon brick comprises the following steps: (1) Premixing: After heating 1 / 2 parts by mass of the phenolic resin to 100-140° C., adding all parts by mass of the flake graphite, nano-carbon powder and antioxidant, stirring and mixing for 5-15 minutes to obtain a premix; (2) hot mixing: adding the fused magnesia particles and the modifier to the premix, and mixing at 80-120° C. for 5-10 minutes to obtain a hot mix; (3) cold mixing: lowering the temperature of the hot mix to below 60° C., adding the fused magnesia powder, the remaining composite phenolic resin and the curing agent, and mixing for 10-30 minutes until uniform, to obtain a cold mix; (4) Molding: The cold mix is ​​placed into a mold and pressed under a pressure of 100-300 MPa to form the bricks. The formed bricks are heat-treated at 150-250° C. for 12-24 hours to solidify. The solidified bricks are surface-polished to obtain a low-carbon magnesium-carbon brick.

[0015] Furthermore, after curing in step (4), the temperature is lowered to 23-25° C. by air cooling, and the material is trapped at 25-35° C. for 1-4 hours.

[0016] Furthermore, the steps (1) and (4) are carried out under a nitrogen atmosphere.

[0017] The antioxidant described in the present invention achieves high-temperature protection through a triple synergistic mechanism: the core polyphenol mother nucleus contains a conjugated π bond system, and its active hydrogen can preferentially reduce oxygen free radicals to generate phenoloxy free radicals, while the conjugated structure delocalizes the free radical electrons, which can stabilize the free radicals and interrupt chain oxidation at high temperatures; the tert-butyl group in the molecule has high bond energy and hydrophobicity to delay oxidation and inhibit water vapor side reactions; the silane group forms a stable network barrier at high temperatures by virtue of its high bond energy, enhancing the ability to resist slag penetration. Ultimately, through the synergistic effect of the electron delocalization stabilization of the conjugated mother nucleus, the physical isolation of the tert-butyl group, and the protective layer of the silane group, the graphite component in the magnesia carbon brick is dynamically protected, significantly reducing the oxidation loss and slag erosion in the environment, and achieving a breakthrough in weather resistance. The antioxidant described in the present invention mainly plays a long-term weathering role, and can make the magnesia carbon bricks still have good performance after being in the natural environment for a long time.

[0018] This invention addresses the challenges of traditional magnesia-carbon bricks, such as susceptibility to oxidation at high temperatures (graphite oxidation leads to a loose structure) and slag erosion (magnesia dissolution destroys the structure), by optimizing component ratios and synergistic effects. Specifically, fused magnesia particles and fine powder form a dense gradient skeleton, reducing slag penetration channels. Flake graphite and nano-carbon powder synergistically construct a composite carbon network, which, with its high surface area, adsorbs oxidative free radicals and assists in protecting the graphite matrix. Phenolic resin crosslinks and cures under the action of a curing agent, forming a resin-carbon layer that encapsulates the carbon component and magnesia, reducing exposure to oxidation. The modifier, Al₂O₃, forms a high-melting-point compound at high temperatures, filling micropores and inhibiting slag penetration. The key lies in the antioxidant's triple synergistic protective mechanism, which protects the layer and enhances corrosion resistance. The preparation process (premixing antioxidants and carbon components under a nitrogen atmosphere, temperature-controlled curing, and material trapping) ensures uniform component dispersion and structural integrity.

[0019] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly Improved Structural Integrity and Weathering Resistance: This invention utilizes a gradient skeleton design of fused magnesia particles and fine powder, a composite carbon network constructed from flake graphite and nano-carbon powder, and a protective layer formed by cured phenolic resin. This significantly reduces the loosening and flaking of the brick structure caused by oxidation reactions and slag erosion at high temperatures. This enhances the overall stability and damage resistance of the material, ensuring the brick remains dense and strong in complex, high-temperature environments.

[0020] 2. Comprehensively enhanced high-temperature oxidation and corrosion resistance: The key lies in the antioxidant's triple synergistic protection mechanism, including the electron delocalization stabilization of free radicals by the conjugated π bond system, the physical isolation provided by the tert-butyl group, and the formation of a high-temperature barrier layer by the silane group. This effectively delays graphite oxidation loss and enhances resistance to slag penetration, improving the material's service performance under extreme storage conditions.

[0021] 3. Long-term durability is effectively maintained: The present invention exhibits excellent stability in aging exposure tests, with improved retention of compressive strength at room temperature, while maintaining good volume density. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the NMR image of the antioxidant 1 of the present invention. DETAILED DESCRIPTION

[0023] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0024] Preparation Example 1 Synthesis of antioxidant 1: .

[0025] Under a nitrogen atmosphere, 150 ml of DMSO, 16.22 g of potassium phosphate trihydrate, 0.37 g of pyridine-2-carboxylic acid, 0.3 g of CuI, 10.00 g of raw material 1, and 10.68 g of raw material 2 were added to the reaction system in sequence, and the reaction was carried out at 85° C. under a nitrogen atmosphere for 16 h. After cooling, the resulting reaction mixture was extracted with aqueous ammonia solution and methyl tert-butyl ether, and the organic phase was washed five times with water and then twice with a saturated NaCl solution. The combined organic phase was dried over anhydrous magnesium sulfate, spin-dried, and subjected to column chromatography (silica gel column chromatography using a mixed solution of n-heptane and ethyl acetate as eluent) and spin-dried to obtain 12.46 g of intermediate 1.

[0026] Under nitrogen protection, 12.46 g of intermediate 1 and 10.00 g of raw material 3 were dissolved in 150 ml of toluene solution, and 4.72 g of sodium tert-butoxide, 0.67 g of tris(dibenzylideneacetone)dipalladium and 2.48 g of tri-tert-butyl phosphine were added in sequence. The mixture was stirred evenly, heated to 120°C, and refluxed for 10 hours. After the reaction, the temperature was slightly lowered and the mixture was filtered through silica gel. The filtrate was cooled to room temperature and washed three times with water. The organic phase was retained, and the aqueous phase was extracted with ethyl acetate. The organic phases were combined, dried over anhydrous magnesium sulfate, spin-dried, and subjected to column chromatography (silica gel column chromatography with a mixed solution of n-heptane and ethyl acetate as the eluent). The mixture was spin-dried to obtain 15.72 g of antioxidant 1.

[0027] Product structure identification: Mass spectrum of intermediate 1 M / Z MS+H + :508; Mass spectrum of antioxidant 1 M / Z MS+H+ :767; Antioxidant 1 1 H NMR (Chloroform-d, Figure 1 ): δ 8.72 (s, 1H), 7.33 (t, 2H), 7.15 (m, 1H), 7.03 (m, 1H), 6.96 (m, 1H), 6.87 (d, 1H), 6.82-6.76 (m, 2H), 6.50 (m, 1H), 4.27-4.03 (m, 8H), 3.78-3.60 (m, 3H), 2.26-2.12 (m, 3H), 1.50-1.46 (m, 9H), 1.46-1.41 (m, 9H), 1.28-1.18 (m, 9H), 0.76-0.64 (m, 9H).

[0028] Preparation Example 2-Preparation Example 5 In Preparation Examples 2 to 5, antioxidants 2 to 5 were prepared in sequence, referring to the preparation method of Preparation Example 1, replacing raw material 2 therein, and the rest remained the same as Preparation Example 1. For details, see Table 1.

[0029] Table 1.

[0030]

[0031] Example 1 Preparation of a low carbon magnesia carbon brick: 1. Raw material components: Fused magnesia particles: 85 parts (particle size range: 1-3 mm, purchased from: Haicheng Zhonghao Magnesium Industry Co., Ltd.); Fused magnesia fine powder: 20 parts (particle size: <0.1 mm, purchased from Qinghai Western Magnesium Industry Co., Ltd.); Flake graphite: 7 parts (fixed carbon content ≥ 97wt%, particle size: 0.1mm, purchased from Qingdao Jinhui Graphite Co., Ltd.); Nano carbon powder: 3 parts (select nano graphene, specific surface area ≥ 150m 2 / g, purchased from: Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.); Phenolic resin: 15 parts (selected as resol type phenolic resin (phenolic resin 2402), purchased from: Jiangsu Senbo New Materials Co., Ltd.); Curing agent: 1 part (hexamethylenetetramine, purchased from Shandong Xuchen Chemical Technology Co., Ltd.); Antioxidant: 2 parts (choose antioxidant 1); Modifier: 4 parts (Al2O3, purchased from: Zibo Honghao Crystal Materials Co., Ltd.).

[0032] 2. Preparation method: (1) Premixing: Under nitrogen atmosphere, take 7.5 parts of phenolic resin, heat to 120°C, add all the flake graphite (7 parts), nano carbon powder (3 parts) and antioxidant (2 parts), and stir and mix for 10 minutes until uniformly dispersed to obtain a premix; (2) Hot mixing: the premix was transferred to a mixing device, fused magnesia particles (85 parts) and modifier (4 parts) were added, and mixed at 100°C for 8 minutes to obtain a hot mix; (3) Cold mixing: Cool the hot mix to 50°C, add fused magnesia fine powder (20 parts), remaining phenolic resin (7.5 parts) and curing agent (1 part), and mix for 20 minutes until uniform to obtain a cold mix; (4) Molding: The cold mix is ​​placed in a nitrogen atmosphere and pressed into a mold under a pressure of 200 MPa. The formed bricks are placed at 200 ° C for 18 hours for curing. After curing, the brick temperature is lowered to 24 ° C by air cooling and the material is trapped at 30 ° C for 2 hours. The surface of the brick is polished until it is smooth and free of protrusions to obtain a low-carbon magnesium carbon brick.

[0033] Example 2-Example 5 A low-carbon magnesium carbon brick was prepared by referring to the preparation method of Example 1, wherein the antioxidant was replaced with antioxidant 2 to antioxidant 5 prepared in Preparation Example 2 to Preparation Example 5 in sequence, and the rest remained the same as Example 1.

[0034] Comparative Example 1 A low-carbon magnesia-carbon brick was prepared by referring to the preparation method of Example 1, except that the antioxidant was replaced with antioxidant MBZ (CAS: 3030-80-6), and the rest remained the same as Example 1.

[0035] Comparative Example 2 A low-carbon magnesia-carbon brick was prepared by referring to the preparation method of Example 1, except that the antioxidant was replaced with antioxidant 1425 (CAS: 65140-91-2), and the rest remained the same as Example 1.

[0036] Comparative Example 3 A low-carbon magnesium-carbon brick was prepared by referring to the preparation method of Example 1, except that the antioxidant was not added, and the rest of the preparation method remained the same as Example 1.

[0037] Comparative Example 4 A low-carbon magnesium carbon brick was prepared by referring to the preparation method of Example 1, except that the modifier was not added, and the rest of the steps were the same as those of Example 1.

[0038] Comparative Example 5 A low-carbon magnesium carbon brick was prepared by referring to the preparation method of Example 1, except that the nano-carbon powder was not added, and the rest of the steps were the same as those of Example 1.

[0039] Performance testing: 1. The compressive strength at room temperature was determined by referring to the test method in GB / T5072-2023 "Test method for compressive strength of refractory materials at room temperature". The data are shown in Table 2. 2. The high temperature flexural strength at 1250°C × 0.5h was measured with reference to the test method in GB / T3002-2017 “Test method for high temperature flexural strength of refractory materials”. The data are shown in Table 2. 3. The low-carbon magnesia-carbon bricks prepared in the examples and comparative examples were heat treated at 1400°C for 2 h, cooled naturally, and then the bulk density was measured according to the method in GB / T2997-2015 "Test Method for Bulk Density, Apparent Porosity and True Porosity of Dense Shaped Refractory Products". The data are shown in Table 2. 4. The low-carbon MgO-C brick samples prepared in the examples and comparative examples were placed in a xenon lamp aging test chamber and exposed for 4800 hours to test the room temperature compressive strength retention rate. The data are shown in Table 2. Exposure conditions: Radiation intensity: 0.35W / m 2 (at 340nm wavelength); temperature cycle: 80℃ (light phase) to 20℃ (dark phase), 8 hours of light + 4 hours of condensation (simulated rain) per cycle; relative humidity: 50%±5% (light phase), 95%±5% (condensation phase).

[0040] Table 2.

[0041]

[0042] The low-carbon magnesia-carbon bricks of the present invention (Examples 1-5) significantly outperformed the control samples (Comparative Examples 1-5) across multiple key performance indicators. Specifically, the examples demonstrated superior stability and improvement in room-temperature compressive strength, high-temperature flexural strength, bulk density, and room-temperature compressive strength retention, demonstrating enhanced structural integrity and weatherability. In contrast, the comparative examples exhibited a downward trend in strength, density, and retention, with performance degradation being particularly pronounced in the absence of specific antioxidants or key components (such as modifiers or nano-carbon powder), highlighting the effectiveness of the synergistic mechanism of the present invention's components. These trends consistently confirm the advantages of the present invention in long-term antioxidant and corrosion resistance while maintaining the material's long-term durability.

[0043] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A low carbon magnesia carbon brick, characterized in that: The invention comprises the following components in parts by mass: 80-90 parts of fused magnesia particles, 15-25 parts of fused magnesia fine powder, 5-10 parts of flake graphite, 1-5 parts of nano-carbon powder, 10-20 parts of phenolic resin, 0.2-1.5 parts of curing agent, 0.5-3 parts of antioxidant, and 1-8 parts of modifier; The antioxidant is a compound represented by Formula 1: Formula 1; Z1 in Formula 1 is selected from any one of -CH2-, -C(CH3)2-, -C(=O)-, O, and S.

2. A low carbon magnesia carbon brick according to claim 1, characterized in that: The particle size of the fused magnesia particles is 5mm-0.1mm; The particle size of the fused magnesia fine powder is less than 0.1 mm.

3. A low carbon magnesia carbon brick according to claim 1, characterized in that: The fixed carbon content of the flake graphite is ≥97wt% and the particle size is less than 0.15mm.

4. A low carbon magnesia carbon brick according to claim 1, characterized in that: The nano carbon powder is selected from nano carbon black or nano graphene, and has a specific surface area of ​​≥100m 2 / g.

5. The low carbon magnesia carbon brick according to claim 1, characterized in that: The phenolic resin is selected from: resol type phenolic resin.

6. The low carbon magnesia carbon brick according to claim 1, characterized in that: The curing agent is hexamethylenetetramine; The modifier is Al2O3.

7. The low carbon magnesia carbon brick according to claim 1, characterized in that: The antioxidant is any one of the compounds shown in the following structures: ； ； 。 8. A method for preparing a low-carbon magnesia-carbon brick according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Premixing: After heating 1 / 2 parts by mass of the phenolic resin to 100-140° C., adding all parts by mass of the flake graphite, nano-carbon powder and antioxidant, stirring and mixing for 5-15 minutes to obtain a premix; (2) hot mixing: adding the fused magnesia particles and the modifier to the premix, and mixing at 80-120° C. for 5-10 minutes to obtain a hot mix; (3) cold mixing: lowering the temperature of the hot mix to below 60° C., adding the fused magnesia powder, the remaining composite phenolic resin and the curing agent, and mixing for 10-30 minutes until uniform, to obtain a cold mix; (4) Molding: The cold mix is ​​placed into a mold and pressed under a pressure of 100-300 MPa to form the bricks. The formed bricks are heat-treated at 150-250° C. for 12-24 hours to solidify. The solidified bricks are surface-polished to obtain a low-carbon magnesium-carbon brick.

9. The method for preparing a low-carbon magnesia-carbon brick according to claim 8, characterized in that: In the step (4), after curing, the temperature is lowered to 23-25° C. by air cooling, and the material is trapped at 25-35° C. for 1-4 hours.

10. The method for preparing a low-carbon magnesia-carbon brick according to claim 9, characterized in that: The steps (1) and (4) are carried out under a nitrogen atmosphere.

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