Composite regenerated magnesia carbon brick and preparation method thereof

Abstract

The invention relates to the technical field of refractory materials, and provides a composite regenerated magnesia carbon brick and a preparation method thereof. The composite regenerated magnesia carbon brick is prepared from the following raw material components in parts by mass: 55 to 65 parts of waste magnesia carbon brick, 40 to 50 parts of fused magnesia, 7 to 10 parts of composite graphite, 3 to 5 parts of antioxidant and 4 to 7 parts of phenolic resin, the composite graphite is of a core-shell structure, and a core in the core-shell structure is magnesium oxide coated graphite; and the shell in the core-shell structure is 1, 3, 5-trimethoxybenzene. According to the technical scheme, the problem that the mechanical property of the composite regenerated magnesia carbon brick is poorer due to poorer wettability of phenolic resin on graphite in related technologies is solved.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, specifically to a composite recycled magnesia-carbon brick and its preparation method. Background Technology

[0002] Magnesia-carbon bricks are made from magnesia, carbon raw materials, binders, and additives. They have strong slag resistance and good thermal conductivity, reducing the risk of thermal cracking of magnesia particles, and are widely used in converter linings. Among them, composite recycled magnesia-carbon bricks are refractory materials made by using recycled waste magnesia-carbon bricks as the main aggregate, combined with additives such as magnesia and graphite, and then undergoing secondary molding with phenolic resin.

[0003] Although composite recycled magnesia-carbon bricks have advantages in terms of cost and environmental protection, they also have the following drawbacks: the graphite surface lacks active groups and is inert, making it difficult to interact with phenolic resin. This results in poor wetting of graphite by phenolic resin, ultimately leading to poor mechanical properties of composite recycled magnesia-carbon bricks. Summary of the Invention

[0004] This invention proposes a composite recycled magnesia-carbon brick and its preparation method, which solves the problem in related technologies where the poor wettability of phenolic resin to graphite leads to poor mechanical properties of the composite recycled magnesia-carbon brick.

[0005] The technical solution of the present invention is as follows: A composite recycled magnesia-carbon brick, the raw materials of which include the following components in parts by weight: 55-65 parts of waste magnesia-carbon brick, 40-50 parts of fused magnesia, 7-10 parts of composite graphite, 3-5 parts of antioxidant, and 4-7 parts of phenolic resin; wherein the composite graphite has a core-shell structure, the core of which is magnesia-coated graphite; and the shell of which is 1,3,5-trimethoxybenzene.

[0006] This invention utilizes waste magnesia-carbon bricks to prepare composite recycled magnesia-carbon bricks, achieving waste reuse, saving on the amount of fused magnesia sand used, and reducing production costs. The addition of antioxidants inhibits carbon oxidation in the composite recycled magnesia-carbon bricks, improving their quality. Phenolic resin, acting as a binder, is uniformly distributed on the surface of the remaining raw materials, forming a continuous carbon network after carbonization, ensuring the strength and corrosion resistance of the composite recycled magnesia-carbon bricks.

[0007] In this invention, the magnesium oxide-coated graphite can be prepared using any conventional method in the art. Preferably, the preparation method of the magnesium oxide-coated graphite includes the following steps: A1. Graphite is ball-milled in a carbon dioxide atmosphere to obtain pretreated graphite; A2. The pretreated graphite is ultrasonically dispersed in water to obtain a suspension; A3. After mixing the suspension with magnesium chloride hexahydrate evenly, add ammonia while stirring to adjust the pH of the solution to 11~11.5, let it stand, and obtain the precipitate; A4. Wash the precipitate until the solution is neutral, filter, dry, and sinter to obtain magnesium oxide-coated graphite.

[0008] In this invention, a co-deposition process is used to prepare magnesium oxide-coated graphite. The magnesium oxide-coated graphite prepared by the above method has good structural stability, and its pre-coated structure is not destroyed during the subsequent 1,3,5-trimethoxybenzene coating process. Finally, a core-shell structured composite graphite is prepared. Using magnesium oxide-coated graphite as the core and 1,3,5-trimethoxybenzene as the shell, it is used as a raw material for composite recycled magnesia-carbon bricks, thereby improving the mechanical properties of the composite recycled magnesia-carbon bricks.

[0009] As a further technical solution, the rotation speed of the ball mill is 350~400 rpm.

[0010] As a further technical solution, the mass ratio of the pretreated graphite to magnesium chloride hexahydrate is 0.5:2.5~3.

[0011] As a further technical solution, the stirring speed is 100~150 rpm.

[0012] In this invention, carboxyl groups are introduced into graphite by ball milling under a carbon dioxide atmosphere. Subsequently, the graphite is mixed with magnesium chloride hexahydrate in an aqueous solution, and magnesium ions are adsorbed onto the graphite surface through a complexation reaction. Then, ammonia is added to adjust the pH of the solution to alkaline, forming magnesium hydroxide-coated graphite. After sintering the magnesium hydroxide-coated graphite, magnesium oxide-coated graphite is prepared.

[0013] As a further technical solution, the raw materials of the composite graphite include magnesium oxide-coated graphite and 1,3,5-trimethoxybenzene in a mass ratio of 100:1~7. Preferably, the mass ratio of magnesium oxide-coated graphite and 1,3,5-trimethoxybenzene is 100:3~5.

[0014] In this invention, the mass ratio of magnesium oxide-coated graphite to 1,3,5-trimethoxybenzene is further specified to be 100:3~5, which further improves the mechanical properties of the composite recycled magnesia-carbon brick.

[0015] As a further technical solution, the preparation method of the composite graphite includes the following steps: ultrasonically dispersing magnesium oxide-coated graphite in ethanol, adding 1,3,5-trimethoxybenzene, mixing evenly, and drying to obtain composite graphite.

[0016] As a further technical solution, the frequency of each ultrasound is independently 50~130kHz, the power of each ultrasound is independently 300~1000W, the temperature of each ultrasound is independently 25~35℃, and the duration of each ultrasound is independently 20~40min.

[0017] As a further technical solution, the mixing is carried out by stirring, and the stirring speed is 150~200 rpm.

[0018] In this invention, the antioxidant can be selected from any conventional antioxidant in the art, such as aluminum powder, silicon powder, magnesium-aluminum alloy powder, magnesium-calcium alloy powder, etc., preferably silicon powder.

[0019] In this invention, the fused magnesia can be produced using any conventional particle size distribution in the art. Preferably, the mass ratio of fused magnesia with a particle size of 3mm < ≤ 5mm, 1mm < ≤ 3mm, 0.074mm < ≤ 1mm, and ≤ 0.074mm is 5:5:3:3. The fused magnesia with a particle size of 3mm < ≤ 5mm is considered large particles, the fused magnesia with a particle size of 1mm < ≤ 3mm is considered medium particles, and the fused magnesia with a particle size of 0.074mm < ≤ 1mm is considered small particles. These three types of fused magnesia constitute the aggregate portion, and are mostly secondary magnesia. The fused magnesia with a particle size ≤ 0.074mm is fine powder that acts as a binder and support, and is mostly primary magnesia. Because if the fine powder melts away first, the particles lose their support and detach, the magnesium oxide content of the fine powder is one grade higher than that of the particles.

[0020] This invention also proposes a method for preparing composite recycled magnesia-carbon bricks, comprising the following steps: B1. After mixing all raw materials except phenolic resin evenly, add phenolic resin and continue mixing to obtain a mixture; B2. After pressing the mixture into shape, heat treatment is performed to obtain composite recycled magnesia-carbon bricks.

[0021] The working principle and beneficial effects of this invention are as follows: In this invention, graphite is first coated with magnesium oxide, followed by coating with 1,3,5-trimethoxybenzene, which improves the mechanical properties of the composite recycled magnesia-carbon bricks. The magnesium oxide coating not only increases the surface roughness of the graphite, facilitating mechanical interlocking between graphite and other raw materials, but also provides polar functional groups such as hydroxyl groups. However, because hydroxyl groups easily form hydrogen bonds, the magnesium oxide-coated graphite molecules exhibit hydrogen bond interactions, making dispersion difficult. Therefore, further coating with 1,3,5-trimethoxybenzene is employed. The coated surface has ether bonds, which cannot form hydrogen bonds with each other, but can form hydrogen bonds with the active groups in phenolic resin. This allows for easy wetting by the phenolic resin and ensures good dispersibility, ultimately improving the mechanical properties of the composite recycled magnesia-carbon bricks. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] In the following embodiments and comparative examples: Waste magnesia-carbon bricks: Composed of waste magnesia-carbon bricks with a particle size of 3mm < ≤ 5mm, 1mm < ≤ 3mm, 0.074mm < ≤ 1mm, and ≤ 0.074mm by mass ratio of 1:1:2:1. Fused magnesia: Composed of fused magnesia with a particle size of 3mm < ≤ 5mm, fused magnesia with a particle size of 1mm < ≤ 3mm, fused magnesia with a particle size of 0.074mm < ≤ 1mm, and fused magnesia with a particle size of ≤ 0.074mm in a mass ratio of 5:5:3:3; among which, the fused magnesia with a particle size of ≤ 0.074mm is grade 1 magnesia with a magnesium oxide content of 97wt%; the fused magnesia with the remaining particle sizes is grade 2 magnesia with a magnesium oxide content of 96wt%. Graphite: 100 mesh, flake graphite with a carbon content of 80wt%~99wt%; Silicon powder: 325 mesh 553 metallic silicon powder; Phenolic resin: 2130 liquid phenolic resin.

[0024] Example 1 S1. Preparation of magnesium oxide-coated graphite: Graphite was ball-milled under a carbon dioxide atmosphere at a pressure of 15 MPa, a rotation speed of 400 rpm, and a time of 60 h to obtain pretreated graphite. 0.5 parts of the pretreated graphite were ultrasonically dispersed in 1000 parts of water at a frequency of 130 kHz, a power of 300 W, a temperature of 35 °C, and a time of 40 min. 2.5 parts of magnesium chloride hexahydrate were added and stirred at 100 rpm for 30 min. Then, while stirring, a 2 mol / L ammonia solution was added at a rate of 2 mL / min until the pH of the solution reached 11. Stirring was continued for 1 h. After standing for 1.5 h, the precipitate was washed until the solution was neutral. The solution was filtered, dried, and sintered at 600 °C for 4 h to obtain magnesium oxide-coated graphite. S2. Preparation of composite graphite: 10 parts of magnesium oxide-coated graphite were ultrasonically dispersed in 20 parts of anhydrous ethanol at an ultrasonic frequency of 70 kHz, a power of 1000 W, a temperature of 35 ℃, and a time of 20 min. 0.1 parts of 1,3,5-trimethoxybenzene were added and stirred at 150 rpm for 20 min. The mixture was then dried to obtain composite graphite. S3. Preparation of composite recycled magnesia-carbon bricks: 55 parts of waste magnesia-carbon bricks, 40 parts of fused magnesia, 7 parts of composite graphite and 3 parts of silicon powder are mixed evenly, and then 4 parts of phenolic resin are added and mixed again. The mixture is transferred to a mold and pressed into shape, and heat-treated at 220℃ for 24 hours to obtain composite recycled magnesia-carbon bricks.

[0025] Example 2 S1. Preparation of magnesium oxide-coated graphite: Graphite was ball-milled under a carbon dioxide atmosphere at a pressure of 15 MPa, a rotation speed of 350 rpm, and a time of 60 h to obtain pretreated graphite. 0.5 parts of the pretreated graphite were ultrasonically dispersed in 1000 parts of water at a frequency of 50 kHz, a power of 1000 W, a temperature of 25 °C, and a time of 20 min. 3 parts of magnesium chloride hexahydrate were added and stirred at 150 rpm for 30 min. Then, while stirring, a 2 mol / L ammonia solution was added at a rate of 2 mL / min until the pH of the solution reached 11.5. Stirring was continued for 1 h. After standing for 1.5 h, the precipitate was washed until the solution was neutral. The solution was filtered, dried, and sintered at 600 °C for 4 h to obtain magnesium oxide-coated graphite. S2. Preparation of composite graphite: 10 parts of magnesium oxide-coated graphite were ultrasonically dispersed in 20 parts of anhydrous ethanol at a frequency of 100 kHz, a power of 500 W, a temperature of 25 ℃, and a time of 40 min. 0.1 parts of 1,3,5-trimethoxybenzene were added and stirred at 200 rpm for 15 min. The mixture was then dried to obtain composite graphite. S3. Preparation of composite recycled magnesia-carbon bricks: 65 parts of waste magnesia-carbon bricks, 50 parts of fused magnesia, 10 parts of composite graphite and 5 parts of silicon powder are mixed evenly, and 7 parts of phenolic resin are added and mixed again. The mixture is then transferred to a mold and pressed into shape. The mixture is heat-treated at 220℃ for 24 hours to obtain composite recycled magnesia-carbon bricks.

[0026] Example 3 The only difference from Example 1 is the addition of 0.3 parts of 1,3,5-trimethoxybenzene.

[0027] Example 4 The only difference from Example 1 is the addition of 0.5 parts of 1,3,5-trimethoxybenzene.

[0028] Example 5 The only difference from Example 1 is the addition of 0.7 parts of 1,3,5-trimethoxybenzene.

[0029] Comparative Example 1 The only difference from Example 1 is that the composite graphite is replaced with an equal amount of graphite.

[0030] Comparative Example 2 S1. Preparation of composite graphite: 10 parts of graphite were ultrasonically dispersed in 20 parts of anhydrous ethanol at a frequency of 70 kHz, a power of 1000 W, a temperature of 35 ℃, and a time of 20 min. 0.1 parts of 1,3,5-trimethoxybenzene were added and stirred at 150 rpm for 20 min. The mixture was then dried to obtain composite graphite. S2. Preparation of composite recycled magnesia-carbon bricks: 55 parts of waste magnesia-carbon bricks, 40 parts of fused magnesia, 7 parts of composite graphite, and 3 parts of silicon powder are mixed evenly, and then 4 parts of phenolic resin are added and mixed again. The mixture is transferred to a mold and pressed into shape, and heat-treated at 220℃ for 24 hours to obtain composite recycled magnesia-carbon bricks.

[0031] Mechanical property testing: (1) Compressive strength: The compressive strength at room temperature shall be tested according to the method in GB / T 5072-2023; (2) Flexural strength: The flexural strength was tested at 1400℃ for 0.5h according to the method in GB / T 3002-2017; The test results are recorded in Table 1.

[0032] Table 1. Test results of mechanical properties of composite recycled magnesia-carbon bricks

[0033] As shown in Table 1, the composite recycled magnesia-carbon bricks provided by this invention have good mechanical properties. Compared with Comparative Examples 1-2, the composite recycled magnesia-carbon bricks obtained in Examples 1-5 have higher room temperature compressive strength and flexural strength at 1400℃×0.5h, indicating that the sequential coating of graphite with magnesium oxide and 1,3,5-trimethoxybenzene improves the mechanical properties of the composite recycled magnesia-carbon bricks.

[0034] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite recycled magnesia-carbon brick, characterized in that, The raw materials include the following components by weight: 55-65 parts of waste magnesia-carbon bricks, 40-50 parts of fused magnesia, 7-10 parts of composite graphite, 3-5 parts of antioxidant, and 4-7 parts of phenolic resin; the composite graphite has a core-shell structure, the core of which is magnesia-coated graphite; the shell of which is 1,3,5-trimethoxybenzene.

2. The composite recycled magnesia-carbon brick according to claim 1, characterized in that, The preparation method of the magnesium oxide-coated graphite includes the following steps: A1. Graphite is ball-milled in a carbon dioxide atmosphere to obtain pretreated graphite; A2. The pretreated graphite is ultrasonically dispersed in water to obtain a suspension; A3. After mixing the suspension with magnesium chloride hexahydrate evenly, add ammonia while stirring to adjust the pH of the solution to 11~11.5, let it stand, and obtain the precipitate; A4. Wash the precipitate until the solution is neutral, filter, dry, and sinter to obtain magnesium oxide-coated graphite.

3. The composite recycled magnesia-carbon brick according to claim 2, characterized in that, The ball mill rotates at a speed of 350-400 rpm.

4. The composite recycled magnesia-carbon brick according to claim 2, characterized in that, The mass ratio of the pretreated graphite to magnesium chloride hexahydrate is 0.5:2.5~3.

5. A composite recycled magnesia-carbon brick according to claim 2, characterized in that, The stirring speed is 100~150 rpm.

6. The composite recycled magnesia-carbon brick according to claim 1, characterized in that, The raw materials for the composite graphite include magnesium oxide-coated graphite and 1,3,5-trimethoxybenzene in a mass ratio of 100:1~7.

7. A composite recycled magnesia-carbon brick according to claim 1, characterized in that, The preparation method of the composite graphite includes the following steps: dispersing magnesium oxide-coated graphite in ethanol by ultrasonication, adding 1,3,5-trimethoxybenzene, mixing evenly, and drying to obtain composite graphite.

8. A composite recycled magnesia-carbon brick according to claim 2 or 7, characterized in that, The frequency of each ultrasound is independently 50~130kHz, the power of each ultrasound is independently 300~1000W, the temperature of each ultrasound is independently 25~35℃, and the duration of each ultrasound is independently 20~40min.

9. A composite recycled magnesia-carbon brick according to claim 7, characterized in that, The mixing is performed by stirring at a speed of 150-200 rpm.

10. A method for preparing composite recycled magnesia-carbon bricks, used to prepare the composite recycled magnesia-carbon bricks according to any one of claims 1 to 9, characterized in that, Includes the following steps: B1. After mixing all raw materials except phenolic resin evenly, add phenolic resin and continue mixing to obtain a mixture; B2. After pressing the mixture into shape, heat treatment is performed to obtain composite recycled magnesia-carbon bricks.

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