A magnesium-carbon brick enhanced by vitamin C acid group pretreatment and its preparation method

Abstract

This invention discloses a magnesia-carbon brick reinforced by vitamin C acid group pretreatment, made from the following raw materials in weight percentages: 65-71% fused magnesia aggregate, 15-20% fused magnesia fine powder, 8-12% flake graphite, 3-4% thermosetting phenolic resin binder, 0.3-0.8% vitamin C, 1.0-2.0% aluminum powder, 0.5-1.0% lanthanum oxide, and 1-3% chromium powder. The method for preparing the magnesia-carbon brick disclosed in this invention includes: first, dissolving vitamin C in phenolic resin to form a pretreatment solution, then mixing it with magnesia, graphite, and metal powder through a specific mixing process, followed by pressing and sequential heat treatment to obtain the product. Because the acid groups of vitamin C react with MgO to form a "magnesium ascorbate" transition layer, the green strength, residual carbon content, oxidation resistance, and slag erosion resistance of the magnesia-carbon brick are systematically improved.

Description

Technical Field

[0001] This invention relates to the field of refractory materials technology, and in particular to a magnesia-carbon brick reinforced by vitamin C acid group pretreatment and its preparation method. Background Technology

[0002] Magnesia-carbon bricks are widely used as furnace lining materials in various steelmaking furnaces. They typically use magnesia sand, carbon source, binder, and antioxidant as raw materials. With the continuous development of modern science and technology, the raw material composition of magnesia-carbon bricks has also changed accordingly, aiming to obtain magnesia-carbon bricks of better quality and superior performance. During the manufacturing of magnesia-carbon bricks, the magnesia sand particles, used as aggregates and powders, may have insufficient bonding strength with the binder that encapsulates them due to incompatibility in physical or chemical properties, thus becoming a weak link in the overall structure of the material. Specifically, the problems are as follows: (1) Low green strength: The initial bonding force provided by the phenolic resin binder is limited, and the brick blank is easily damaged during handling and pretreatment, resulting in a low product qualification rate; (2) Lack of anti-oxidation properties at medium and low temperatures: In the range of 200℃ to 600℃, the phenolic resin carbonizes to form an initial carbon network, but the traditional metal antioxidants (such as Al and Si powders) have not been fully activated, leading to the oxidation of graphite and newly formed carbon, causing irreversible structural damage; (3) Insufficient slag resistance at ultra-high temperatures: Under harsh conditions exceeding 1400℃, a stronger anti-erosion barrier is required. Therefore, it is urgent to develop a new type of carbon magnesia brick to fundamentally improve the interfacial bonding problem between magnesia sand and binder. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a magnesia-carbon brick enhanced by vitamin C acid group pretreatment, and also provides a method for preparing the magnesia-carbon brick enhanced by vitamin C acid group pretreatment. Specifically, the following technical solution can be adopted:

[0004] The magnesia-carbon brick based on vitamin C acid group pretreatment enhancement described in this invention is made from the following raw materials in weight percentage: 65-71% fused magnesia aggregate, 15-20% fused magnesia fine powder, 8-12% flake graphite, 3-4% thermosetting phenolic resin binder, 0.3-0.8% vitamin C, 1.0-2.0% aluminum powder, 0.5-1.0% lanthanum oxide, and 1-3% chromium powder.

[0005] This invention overcomes the biases and shortcomings of the prior art by adding vitamin C and using the acid groups of vitamin C to pretreat the surface of magnesia. By enhancing the interfacial bonding and coordinating the sequential reactions of each component during the heat treatment process, the green strength, oxidation resistance and slag erosion resistance of magnesia-carbon bricks are systematically improved.

[0006] Preferably, the chromium powder has a particle size of less than 45 micrometers, and the aluminum powder has a particle size of less than 75 micrometers. Using metal powders within these particle size ranges facilitates more uniform dispersion during mixing, avoids agglomeration and other adverse phenomena, and thus more effectively exerts its antioxidant and reinforcing effects.

[0007] The method for preparing magnesia-carbon bricks based on vitamin C acid group pretreatment enhancement according to the present invention uses the above-mentioned raw material ratio for magnesia-carbon bricks and is carried out according to the following steps:

[0008] (1) Preparation of pretreatment solution: Dissolve all the vitamin C in the formula in the thermosetting phenolic resin binder to form a uniform vitamin C-phenolic resin pretreatment solution.

[0009] (2) Mixing:

[0010] a. Primary dry mixing: Add fused magnesia aggregate and metallic chromium powder to the mixing equipment and dry mix for 3-5 minutes;

[0011] b. Secondary dry mixing: Add fused magnesia powder, flake graphite, aluminum powder and lanthanum oxide to the mixture from step a, and continue dry mixing for 5-8 minutes until homogeneous;

[0012] c. Acid pretreatment and wet mixing: Add the pretreatment solution obtained in step (1) to the dry mixture in step b, and wet mix at 30±5℃ for 20-25 minutes to complete the acid pretreatment of magnesia particles by vitamin C.

[0013] (3) Molding: The mud material obtained in step (2)c is pressed into shape under a pressure of 120-150 MPa to obtain a brick blank;

[0014] (4) Heat treatment: Place the brick blank in a drying kiln, first heat it to 200℃ at a rate of 1℃ / min and keep it at that temperature for 2 hours, then heat it to 250℃ at a rate of 2℃ / min and keep it at that temperature for 24-48 hours.

[0015] Preferably, the preparation process of the vitamin C-phenolic resin pretreatment solution is carried out at room temperature, with a stirring time of 30-60 minutes. Taking the above measures ensures that vitamin C is fully dissolved and uniformly mixed in the thermosetting phenolic resin, while avoiding premature decomposition or uneven dissolution of vitamin C due to excessively high temperature or insufficient stirring, thereby guaranteeing the quality of the pretreatment solution and the effectiveness of subsequent treatments.

[0016] Preferably, the wet mixing process in step (2)c is carried out in a closed mixing equipment. Using closed mixing can effectively reduce solvent evaporation and the introduction of external impurities during the mixing process, ensure the accuracy of the proportions, and at the same time help maintain the temperature and humidity stability of the mixing system, ensuring the uniformity and consistency of the pretreatment reaction.

[0017] Those skilled in the art generally believe that vitamin C decomposes at around 190℃, exhibiting poor thermal stability and producing gases that damage the material structure, thus making it unsuitable for high-performance refractory materials. However, this invention, through a simple acid pretreatment step and strict control of the amount of vitamin C used, successfully transforms what is traditionally considered a disadvantage (vitamin C decomposition and gas production) into a controllable advantage (self-sacrificing oxidation resistance and porosity regulation), systematically solving several technical challenges in magnesia-carbon bricks. Specifically, the benefits are as follows:

[0018] 1. Enhanced Interfacial Bonding: The acidic functional groups of vitamin C react with the MgO surface via an acid-base reaction, generating an in-situ "magnesium ascorbate" transition layer. Since the reaction rate between vitamin C and MgO at room temperature is relatively slow, the following measures are taken in the preparation process of this invention to promote this interfacial reaction: (a) vitamin C is pre-dissolved in a liquid phenolic resin binder to form a pretreatment solution with good fluidity and wettability; (b) wet mixing is performed at 30±5℃ for 20-25 minutes to provide the necessary heat energy for the reaction and ensure sufficient contact time; (c) the large specific surface area of ​​magnesia, especially the fine powder portion, provides a rich interface for the reaction. This transition layer provides strong temporary bonding before the thermosetting phenolic resin cures, increasing the green body strength by more than 40% and reducing the green body handling breakage rate to below 2.1%.

[0019] 2. Temporal protection and enhancement:

[0020] (1) 200-500℃: During the heat treatment of the brick blank, the "magnesium ascorbate" generated by the interface reaction and the small amount of vitamin C that may remain melt and decompose in time. This endothermic process can buffer thermal stress. The reducing gas generated consumes oxygen and achieves "self-sacrifice" anti-oxidation, which increases the carbon residue rate of the material to more than 85% at 500℃. At the same time, the submicron-level temporary channel formed by its decomposition optimizes the exhaust and lays the foundation for low apparent porosity (<4%).

[0021] (2) >500℃: Especially under ultra-high temperature (>1400℃) conditions, the intact carbon network in the magnesia-carbon brick ensures the reinforcing effect of aluminum powder and lanthanum oxide. Furthermore, the chromium powder pre-attached to the aggregate generates high-melting-point carbides (such as Cr3C2 and Cr7C3) at ultra-high temperatures, forming a dense barrier and increasing the slag erosion resistance index by more than 50%.

[0022] 3. Critical Importance of Dosage: This invention ensures the comprehensive performance of magnesia-carbon bricks by strictly controlling the dosage of vitamin C (0.3-0.8%). When the dosage of vitamin C is below 0.3%, it is insufficient to form an effective modified transition layer on the MgO surface, resulting in insignificant improvement in green strength and the inability to form effective "self-sacrificing" protection at medium and low temperatures, making the carbon network susceptible to oxidation and damage. When the dosage of vitamin C exceeds 0.8%, its decomposition and gas production are too vigorous, leading to a significant increase in the apparent porosity of magnesia-carbon bricks (>6%) and a decrease in strength of more than 30%, which in turn damages their final performance. Detailed Implementation

[0023] The embodiments of the present invention will be described in detail below. These embodiments are based on the technical solutions of the present invention and provide detailed implementation methods. However, the scope of protection of the present invention is not limited to the following embodiments.

[0024] All raw materials used in the following examples and comparative examples are industrial grade. The thermosetting phenolic resin binder is ZD05 liquid product from Shengquan Group; vitamin C is ascorbic acid raw powder with a purity of ≥99%; the particle size of metallic chromium powder is <45μm, and the particle size of metallic aluminum powder is <75μm.

[0025] Example 1:

[0026] Prepare the corresponding raw materials according to the weight percentage, including 68.4% fused magnesia aggregate, 13.5% fused magnesia fine powder, 10% flake graphite, 3.5% thermosetting phenolic resin binder, 0.5% vitamin C, 1.5% aluminum powder, 0.6% lanthanum oxide, and 2% chromium powder.

[0027] The preparation of magnesia-carbon bricks using the above raw materials specifically includes the following steps:

[0028] (1) Preparation of pretreatment solution: At room temperature, place the prescribed amount of vitamin C in a liquid thermosetting phenolic resin binder and stir for 30-60 minutes to dissolve it completely, forming a homogeneous vitamin C-phenolic resin pretreatment solution.

[0029] (2) Mixing:

[0030] a. Primary dry mixing: Add fused magnesia aggregate and metallic chromium powder to the mixing equipment and dry mix for 3-5 minutes;

[0031] b. Secondary dry mixing: Add fused magnesia powder, flake graphite, aluminum powder and lanthanum oxide to the mixture from step a, and continue dry mixing for 5-8 minutes until homogeneous;

[0032] c. Acid pretreatment and wet mixing: Add the pretreatment liquid obtained in step (1) to the dry mixture in step b, and wet mix for 20-25 minutes at a temperature of 30±5℃ in a closed mixing equipment to complete the acid pretreatment of magnesia particles by vitamin C.

[0033] (3) Molding: The mud material obtained in step (2)c is pressed into shape under a pressure of 120-150 MPa to obtain a brick blank;

[0034] (4) Heat treatment: Place the brick blank in a drying kiln, first heat it to 200℃ at a rate of 1℃ / min and keep it at that temperature for 2 hours, then heat it to 250℃ at a rate of 2℃ / min and keep it at that temperature for 24-48 hours.

[0035] The core of the above preparation process lies in the in-situ modification of the magnesia surface using the acidic functional groups of vitamin C. This method first dissolves vitamin C in phenolic resin to form a pretreatment solution, which is then mixed with magnesia, graphite, metal powder, etc., through a specific mixing process. The product is then obtained through pressing and sequential heat treatment. The acidic groups of vitamin C react with MgO to generate a "magnesium ascorbate" transition layer. This pretreatment process can enhance the green strength at room temperature and achieve self-sacrificing oxidation resistance in the 200-500℃ range. Furthermore, it synergistically constructs a sequential strengthening system from room temperature to ultra-high temperature with additives such as metallic chromium powder, systematically improving the green strength, residual carbon content, oxidation resistance, and slag erosion resistance of magnesia-carbon bricks.

[0036] Example 2:

[0037] Prepare the corresponding raw materials according to the weight percentage, including 68.4% fused magnesia aggregate, 13.7% fused magnesia fine powder, 10% flake graphite, 3.5% thermosetting phenolic resin binder, 0.3% vitamin C, 1.5% aluminum powder, 0.6% lanthanum oxide, and 2% chromium powder.

[0038] Magnesia-carbon bricks were prepared according to the steps in Example 1.

[0039] Example 3:

[0040] Prepare the corresponding raw materials according to the weight percentage, including 68.4% fused magnesia aggregate, 13.2% fused magnesia fine powder, 10% flake graphite, 3.5% thermosetting phenolic resin binder, 0.8% vitamin C, 1.5% aluminum powder, 0.6% lanthanum oxide, and 2% chromium powder.

[0041] Magnesia-carbon bricks were prepared according to the steps in Example 1.

[0042] Comparative Example 1:

[0043] Prepare the corresponding raw materials according to the weight percentage, including 68.4% fused magnesia aggregate, 14% fused magnesia fine powder, 10% flake graphite, 3.5% thermosetting phenolic resin binder, 1.5% aluminum powder, 0.6% lanthanum oxide, and 2% chromium powder.

[0044] The preparation of magnesia-carbon bricks using the above raw materials specifically includes the following steps:

[0045] (1) Mixing:

[0046] a. Primary dry mixing: Add fused magnesia aggregate and metallic chromium powder to the mixing equipment and dry mix for 3-5 minutes;

[0047] b. Secondary dry mixing: Add fused magnesia powder, flake graphite, aluminum powder and lanthanum oxide to the mixture from step a, and continue dry mixing for 5-8 minutes until homogeneous;

[0048] c. Wet mixing: Add the liquid thermosetting phenolic resin binder to the dry mixture from step b, and wet mix for 20-25 minutes at a temperature of 30±5℃ in a closed mixing equipment.

[0049] (2) Molding: The mud material obtained in step (1)c is pressed into shape under a pressure of 120-150 MPa to obtain a brick blank;

[0050] (3) Heat treatment: Place the brick blank in a drying kiln, first heat it to 200℃ at a rate of 1℃ / min and keep it at that temperature for 2 hours, then heat it to 250℃ at a rate of 2℃ / min and keep it at that temperature for 24-48 hours.

[0051] Comparative Example 2:

[0052] Prepare the corresponding raw materials according to the weight percentage, including 68.4% fused magnesia aggregate, 12.8% fused magnesia fine powder, 10% flake graphite, 3.5% thermosetting phenolic resin binder, 1.2% vitamin C, 1.5% aluminum powder, 0.6% lanthanum oxide, and 2% chromium powder.

[0053] Magnesia-carbon bricks were prepared according to the steps in Example 1.

[0054] The performance of the magnesia-carbon bricks obtained above was tested, and the test results are shown in Table 1.

[0055] Table 1 Performance test results of magnesia-carbon bricks obtained in Examples 1-3 and Comparative Examples 1-2

[0056]

[0057] As shown in Table 1, the magnesia-carbon bricks obtained in Examples 1, 2, and 3 of this invention exhibit superior performance compared to the comparative examples. The magnesia-carbon bricks of Comparative Example 1 (without Vitamin C) show significantly inferior performance across the board, particularly with a noticeably lower residual carbon rate at 500℃, demonstrating the significant advantage of Vitamin C acid group pretreatment in compensating for the lack of antioxidant capacity at medium and low temperatures. While Comparative Example 2 (with excessive Vitamin C) shows better residual carbon rate and antioxidant capacity than Comparative Example 1 due to its reducing properties, its apparent porosity increases sharply to 6.8%, and its room temperature strength decreases by more than 30%. This indicates that excessive use of Vitamin C can severely damage the structural integrity of magnesia-carbon bricks due to excessive gas production. Through repeated experiments, this invention strictly limits the amount of Vitamin C to 0.3-0.8%, thereby ensuring that the obtained magnesia-carbon bricks maintain good overall performance.

[0058] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A magnesia-carbon brick reinforced based on vitamin C acid group pretreatment, characterized in that: The magnesia-carbon bricks are made from the following raw materials in weight percentages: 65-71% fused magnesia aggregate, 15-20% fused magnesia fine powder, 8-12% flake graphite, 3-4% thermosetting phenolic resin binder, 0.3-0.8% vitamin C, 1.0-2.0% aluminum powder, 0.5-1.0% lanthanum oxide, and 1-3% chromium powder. The preparation method of the magnesia-carbon brick is carried out according to the following steps: (1) Preparation of pretreatment solution: Dissolve all the vitamin C in the formula in the thermosetting phenolic resin binder to form a uniform vitamin C-phenolic resin pretreatment solution. (2) Mixing: a. Primary dry mixing: Add fused magnesia aggregate and metallic chromium powder to the mixing equipment and dry mix for 3-5 minutes; b. Secondary dry mixing: Add fused magnesia powder, flake graphite, aluminum powder and lanthanum oxide to the mixture from step a, and continue dry mixing for 5-8 minutes until homogeneous; c. Acid pretreatment and wet mixing: Add the pretreatment solution obtained in step (1) to the dry mixture in step b, and wet mix at 30±5℃ for 20-25 minutes to complete the acid pretreatment of magnesia particles by vitamin C. (3) Molding: The mud material obtained in step (2)c is pressed into shape under a pressure of 120-150 MPa to obtain a brick blank; (4) Heat treatment: Place the brick blank in a drying kiln, first heat it to 200℃ at a rate of 1℃ / min and keep it at that temperature for 2 hours, then heat it to 250℃ at a rate of 2℃ / min and keep it at that temperature for 24-48 hours.

2. The magnesia-carbon brick reinforced by vitamin C acid group pretreatment according to claim 1, characterized in that: The chromium powder has a particle size of less than 45 micrometers, and the aluminum powder has a particle size of less than 75 micrometers.

3. The magnesia-carbon brick reinforced by vitamin C acid group pretreatment according to claim 1, characterized in that: The preparation process of the vitamin C-phenolic resin pretreatment solution is carried out at room temperature, with a stirring time of 30-60 minutes.

4. The magnesia-carbon brick reinforced by vitamin C acid group pretreatment according to claim 1, characterized in that: The wet mixing process in step (2)c is carried out in a closed mixing equipment.

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