A magnesium-carbon composite material and a method for producing the same

Abstract

The present application relates to a kind of magnesium carbon composite material and its preparation method.The technical scheme is: with 60-75wt% magnesium calcium particles, 13-25wt% electric smelting magnesite fine powder and 12-20wt% aluminum calcium carbon particles as raw material, plus 3-6wt% of the raw material aluminates, stirring, compression molding;Then dry 8-24 hours under the condition of 110-200 ℃, cooling, to prepare magnesium carbon composite material.The present application is based on lower grade magnesite fine powder and lower grade graphite fine powder as main raw material to prepare magnesium carbon composite material for high temperature smelting, with the characteristics of simple process and low cost, the prepared magnesium carbon composite material has good thermal shock stability and strong corrosion resistance, and can be used as the lining material of high temperature smelting vessel.

Description

Technical Field

[0001] This invention belongs to the technical field of refractory materials for metallurgy. In particular, it relates to a magnesium-carbon composite material and its preparation method. Background Technology

[0002] Currently, commonly used magnesia-carbon composite refractories are mainly used as lining materials for converters, electric arc furnaces, and ladles. Their main characteristics are excellent high-temperature resistance, strong slag resistance, good thermal shock resistance, and low high-temperature creep. Magnesia-carbon refractories have become important refractory materials in the steel industry and are widely used as linings for metallurgical furnaces and containers. Magnesia-carbon refractories for the steel industry are made primarily from high-quality fused magnesia (MgO ≥ 96%) and high-quality flake graphite (C ≥ 95%), and are mainly used as lining materials for key smelting equipment and containers such as converters, electric arc furnaces, RH furnaces, and ladles.

[0003] High-quality magnesia and flake graphite are commonly used in existing magnesia-carbon refractories, as described in references 1 (Yao Huabo, Yao Suzhe, Luo Chang, et al., Research status and development trend of magnesia-carbon bricks [J]. Journal of Engineering Science, 2018, 40(3):253-268.), 2 (Zhu Yening, Xi Zijian, Su Yuqing, et al., Influence of magnesia grade on the microstructure and composition of magnesia-carbon bricks [J]. Industrial Heating, 2023, 52(3):21-25.), and 3 (Zheng Xiang, Experimental study on damage behavior of magnesia-carbon steel ladle refractories [D]. Northeastern University, 2018). While this has a certain effect on improving its erosion resistance, thermal shock stability, and high-temperature flexural strength, high-quality magnesia and flake graphite are not only expensive, but also generate a small amount of liquid phase during use. As a result, the microstructure of the magnesia-carbon composite material becomes porous during service. Magnesia and graphite are the main raw materials for producing magnesium-carbon composite materials for steel smelting. Given the current shortage of high-quality magnesia and high-purity graphite resources, how to use lower-grade raw materials for the preparation of magnesium-carbon composite materials for high-temperature smelting has attracted the attention of those skilled in the art.

[0004] With the protective development of high-quality magnesite and graphite resources in China, large quantities of lower-grade magnesia and graphite raw materials have not been utilized on a large scale in refractory materials for iron and steel smelting. This is because the high impurity content of magnesia and graphite in the steelmaking industry, especially as raw materials for furnace linings, presents a problem regarding the impact of high impurity content on the high-temperature performance of refractory materials. The main impurity in low-grade magnesia and graphite is SiO2. Its presence can cause the following problems, as shown in references 4 (Zhu Yening. The effect of high-temperature self-consumption reaction of magnesia-carbon bricks on microstructure and properties [D]. North China University of Technology, 2023) and 5 (Yu Lingyue, Wei Juncong, Yang Chun et al. The effect of different carbon sources on the properties of low-carbon magnesia-carbon bricks [J]. Refractory Materials, 2020, 54(4): 338-342): the calcium magnesium olivine liquid phase formed in magnesia at high temperature reduces the material's corrosion resistance; the self-consumption reaction between SiO2 and carbon in graphite (silicon oxide and carbon undergo a reduction reaction at high temperature) consumes the carbon in graphite, destroys the microstructure of the material, and reduces the material's corrosion resistance and other properties. Summary of the Invention

[0005] The present invention aims to overcome the key problems faced in the preparation of high-temperature industrial refractory materials containing high impurities of magnesia and graphite. The purpose is to provide a simple and low-cost method for preparing magnesia-carbon composite materials. The magnesia-carbon composite materials prepared by this method have good thermal shock stability and strong erosion resistance, and can be used as furnace lining materials for containers used in high-temperature smelting.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] Magnesium-aluminum-calcium granules (60–75 wt%), fused magnesia fine powder (13–25 wt%), and aluminum-calcium-carbon granules (12–20 wt%) were used as raw materials. 3–6 wt% of aluminate was added to the raw materials, and the mixture was stirred, pressed, and then dried at 110–200°C for 8–24 hours and cooled to obtain a magnesium-carbon composite material.

[0008] The preparation method of the magnesium aluminum calcium granules is as follows: Magnesia fine powder: spinel-calcium aluminate multiphase material are mixed at a mass ratio of (9-10):1 to obtain a first mixed powder; the first mixed powder is placed in the hopper of a granulation equipment, and 20-30 wt% of aluminate ester is added to the first mixed powder at a rotation speed of 1000-2000 r / min; when particles are formed in the hopper of the granulation equipment, the rotation speed is adjusted to 200-500 r / min; after all the first mixed powder has been converted into particles, the particles are removed, and then the particles are kept at 110-200℃ for 12-24 hours and cooled to obtain magnesium aluminum calcium granules.

[0009] The magnesium-aluminate-calcium granules have a particle size of 0.2–8 mm. The preparation method of the aluminum-calcium-carbon granules is as follows: the graphite fine powder and spinel-calcium aluminate multiphase material are mixed at a mass ratio of (5–6):1 to obtain a second mixed powder. The second mixed powder is placed in the granulation equipment hopper, and 20–30 wt% of aluminate ester is added to the second mixed powder at a rotation speed of 1400–2000 r / min. When particles are formed in the granulation equipment hopper, the rotation speed is adjusted to 800–1380 r / min. After all the second mixed powder has been converted into particles, the particles are taken out and then kept at 110–200℃ for 12–24 hours and cooled to obtain aluminum-calcium-carbon granules. The particle size of the aluminum-calcium-carbon granules is 0.1–2 mm.

[0010] The particle size of the magnesia powder is 1–300 μm; the MgO content in the magnesia powder is 93–95 wt%.

[0011] The spinel-calcium aluminate composite material has a particle size of 1–300 μm; in the spinel-calcium aluminate composite material: MgO content ≥15wt%, Al2O3 content ≥65wt%, and CaO content ≤15wt%.

[0012] The graphite powder has a particle size of 1–300 μm and a carbon content of 92–94 wt%.

[0013] The particle size of the fused magnesia fine powder is 1-300 μm; the MgO content in the fused magnesia fine powder is ≥96 wt%.

[0014] The aluminate contains ≥6wt% Al; the aluminate used for preparing magnesium-carbon composite materials, preparing aluminum-calcium-carbon particles, and preparing aluminum-calcium-carbon particles are the same.

[0015] The pressure during the pressing process is 80–200 MPa.

[0016] By adopting the above technical solution, the present invention has the following advantages compared with the prior art:

[0017] 1. This invention does not require high-temperature firing, the process is simple, and the cost is low.

[0018] 2. The main raw materials used in this invention are pre-formed magnesium-aluminate-calcium granules and aluminum-calcium-carbon granules based on low-grade magnesia fine powder and low-grade graphite fine powder. These pre-formed magnesia-aluminate-calcium granules and aluminum-calcium-carbon granules are added to the refractory material as raw materials. The spinel-calcium aluminate material adsorbs silica impurities in the magnesia and graphite at high temperatures, reducing the silica content in the magnesia and graphite. Simultaneously, a small amount of liquid phase is formed within the particles to improve the thermal shock stability of the refractory material. This is the core technology of this invention, based on the latest research results of the applicant's research team, and is specifically described below:

[0019] 2.1 At the steelmaking temperature (1600℃), the calcium aluminate (CaO·Al2O3) in the spinel-calcium aluminate multiphase material transforms into a melt (liquid phase), which consists of CaO and Al2O3. Among them, CaO has a high adsorption capacity for SiO2 in the system, which can adsorb SiO2 from magnesia and graphite raw materials to generate a stable high-temperature phase dicalcium silicate (CaO·2SiO2). Through thermodynamic calculations to analyze the priority order of reaction (1) and (2), it can be seen that |△G1|<|△G2|. That is, when CaO, MgO and SiO2 coexist, dicalcium silicate (CaO·2SiO2) will be preferentially generated. In other words, calcium oxide in the system will adsorb silicon oxide in the system and transform into a high-temperature phase.

[0020] 2MgO+SiO2→2MgO·SiO2 △G1=-62103.5-10T(kJ / mol) (1)

[0021] 2CaO+SiO2→2CaO·SiO2 △G2=-93937.6-29.735T(kJ / mol) (2)

[0022] 2.2 This invention mixes low-grade magnesia fine powder with spinel-calcium aluminate multiphase material. The applicant performed XRD analysis on the mixed sample before and after heat treatment at 1600℃. Before heat treatment, the main phases of the mixed sample were spinel (MA), calcium aluminate (CA), calcium dialuminate (CA2), periclase (MgO), and calcium magnesium olivine (CMS). The first three minerals originated from the spinel-calcium aluminate multiphase material, while the latter two originated from magnesia. After high-temperature heat treatment, the main minerals of the mixed sample were spinel (MA), calcium dialuminate (CA2), periclase (MgO), and dicalcium silicate (C2S), while calcium aluminate (CA) disappeared, and dicalcium silicate (C2S) was a new product after high-temperature heat treatment. This is due to the results of the thermodynamic analysis above.

[0023] Simultaneously, this invention mixes low-grade graphite powder with a spinel-calcium aluminate multiphase material. The applicant performed XRD analysis on the mixed sample before and after heat treatment at 1600℃. Before heat treatment, the main phases of the mixed sample were spinel (MA), calcium aluminate (CA), calcium disaluminate (CA2), carbon (C), and quartz (SiO2). The first three minerals originated from the spinel-calcium aluminate multiphase material, while the latter two originated from graphite. After high-temperature heat treatment, the main impurity quartz (SiO2) in the mixed sample disappeared, and the newly formed compounds were undetectable in XRD analysis due to their extremely low content.

[0024] The above findings confirm that CaO has the ability to adsorb magnesium oxide and SiO2 impurities in graphite, thereby reducing the adverse effects of SiO2 on the high-temperature physical properties of magnesia and graphite.

[0025] 3. Mixed granulation can effectively prevent the segregation of key components; granulation can uniformly disperse graphite in the material, preventing layered cracking in the molded product; the granulation process can improve the flow characteristics of powdered raw materials and enhance the stability, compactness and segregation-free properties of mold feeding during molding.

[0026] 4. Spinel-calcium aluminate multiphase materials, due to their content of magnesium aluminum spinel (greater than 70%), exhibit good thermal shock stability. Simultaneously, the small amount of liquid phase formed by calcium aluminate (less than 15%) in the multiphase material at steelmaking temperatures also contributes to the material's resistance to thermal shock damage. Mixing and granulating the spinel-calcium aluminate multiphase material with magnesia helps mitigate the adverse effects of magnesia's high coefficient of thermal expansion on the material's thermal shock stability.

[0027] The magnesium-carbon composite material prepared by this invention was tested and found to have the following properties: MgO content: 73.72–80.82 wt%; C content: 9.40–15.67 wt%; compressive strength: 21–40 MPa. Using the GB / T30873-2014 test method for thermal shock resistance of refractory materials (air quenching method), after three heating-cooling cycles, the flexural strength retention rate of the material was 30.5–60.2%. Using the induction furnace dynamic slag resistance test method (temperature 1600℃, holding time 1 hour; chemical composition of the prepared steel slag: CaO 35.21%, SiO2 20.53%, Al2O3 23.84%, MgO 8.25%, total iron content 12.38%), the dynamic slag erosion rate was 1.5–2.3 mm / hour.

[0028] This invention uses low-grade magnesia powder and low-grade graphite powder as main raw materials to prepare magnesium-carbon composite materials for high-temperature smelting. It features simple process and low cost. The prepared magnesium-carbon composite material has good thermal shock stability and strong erosion resistance, and can be used as furnace lining material for containers used in high-temperature smelting. Attached Figure Description

[0029] Figure 1 The results are XRD analysis of the mixed sample of magnesia fine powder and spinel-calcium aluminate multiphase material used in this invention before and after high-temperature heat treatment.

[0030] Figure 2 The results are XRD analysis of the mixed sample of graphite fine powder and spinel-calcium aluminate multiphase material used in this invention before and after high-temperature heat treatment. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of protection thereof.

[0032] A magnesium-carbon composite material and its preparation method. The preparation method described in this specific embodiment is as follows:

[0033] Magnesium-aluminum-calcium granules (60–75 wt%), fused magnesia fine powder (13–25 wt%), and aluminum-calcium-carbon granules (12–20 wt%) were used as raw materials. 3–6 wt% of aluminate was added to the raw materials, and the mixture was stirred, pressed, and then dried at 110–200°C for 8–24 hours and cooled to obtain a magnesium-carbon composite material.

[0034] The preparation method of the magnesium aluminum calcium granules is as follows: Magnesia fine powder: spinel-calcium aluminate multiphase material are mixed at a mass ratio of (9-10):1 to obtain a first mixed powder; the first mixed powder is placed in the hopper of a granulation equipment, and 20-30 wt% of aluminate ester is added to the first mixed powder at a rotation speed of 1000-2000 r / min; when particles are formed in the hopper of the granulation equipment, the rotation speed is adjusted to 200-500 r / min; after all the first mixed powder has been converted into particles, the particles are removed, and then the particles are kept at 110-200℃ for 12-24 hours and cooled to obtain magnesium aluminum calcium granules.

[0035] The particle size of the magnesium aluminum calcium particles is 0.2 to 8 mm.

[0036] The method for preparing the aluminum-calcium-carbon particles is as follows: The graphite powder and spinel-calcium aluminate composite material are mixed at a mass ratio of (5-6):1 to obtain a second mixed powder. The second mixed powder is placed in the granulation equipment hopper, and 20-30 wt% of aluminate ester is added to the second mixed powder at a rotation speed of 1400-2000 r / min. When particles are formed in the granulation equipment hopper, the rotation speed is adjusted to 800-1380 r / min. After all the second mixed powder has been converted into particles, the particles are removed and then kept at 110-200℃ for 12-24 hours, followed by cooling to obtain the aluminum-calcium-carbon particles.

[0037] The particle size of the aluminum-calcium-carbon particles is 0.1–2 mm.

[0038] The MgO content in the fine magnesia powder is 93-95 wt%.

[0039] In spinel-calcium aluminate multiphase materials: MgO content ≥15wt%, Al2O3 content ≥65wt%, CaO content ≤15wt%.

[0040] The carbon content in the graphite powder is 92-94 wt%.

[0041] The MgO content in the fused magnesia fine powder is ≥96wt%.

[0042] The Al content in the aluminate is ≥6wt%.

[0043] The pressure during the pressing process is 80MPa to 200MPa.

[0044] In this specific implementation:

[0045] The particle size of the fine magnesium oxide powder is 1–300 μm;

[0046] The particle size of the spinel-calcium aluminate multiphase material is 1–300 μm;

[0047] The particle size of the graphite powder is 1–300 μm;

[0048] The particle size of the fused magnesia fine powder is 1–300 μm;

[0049] The aluminate used for preparing magnesium-carbon composite materials, the aluminate used for preparing aluminum-calcium-carbon particles, and the aluminate used for preparing aluminum-calcium-carbon particles are the same.

[0050] The details will not be repeated in the examples.

[0051] Example 1

[0052] A magnesium-carbon composite material and its preparation method. The preparation method described in this embodiment is as follows:

[0053] Using 60 wt% magnesium aluminum calcium particles, 25 wt% fused magnesia fine powder and 15 wt% aluminum calcium carbon particles as raw materials, and adding 3 wt% aluminate of the raw materials, the mixture was stirred, pressed into shape, and then dried at 110℃ for 8 hours and cooled to obtain magnesium carbon composite material.

[0054] The pressure during the pressing process is 80 MPa.

[0055] The preparation method of the magnesium aluminum calcium granules is as follows: Magnesia fine powder and spinel-calcium aluminate multiphase material are mixed at a mass ratio of 10:1 to obtain a first mixed powder; the first mixed powder is placed in the hopper of a granulation equipment, and 20 wt% of aluminate ester is added to the first mixed powder at a rotation speed of 1000 r / min; when particles are formed in the hopper of the granulation equipment, the rotation speed is adjusted to 200 r / min; after all the first mixed powder has been converted into particles, the particles are taken out, and then the particles are kept at 110℃ for 12 hours and cooled to obtain magnesium aluminum calcium granules.

[0056] The particle size of the magnesium aluminum calcium particles is 0.2 to 8 mm.

[0057] The method for preparing the aluminum-calcium-carbon particles is as follows: The graphite powder and spinel-calcium aluminate composite material are mixed at a mass ratio of 5:1 to obtain a second mixed powder. The second mixed powder is placed in the granulation equipment hopper, and 20 wt% of aluminate ester is added to the second mixed powder at a rotation speed of 1400 r / min. When particles are formed in the granulation equipment hopper, the rotation speed is adjusted to 800 r / min. After all the second mixed powder has been converted into particles, the particles are removed and then kept at 110℃ for 12 hours, followed by cooling to obtain the aluminum-calcium-carbon particles.

[0058] The particle size of the aluminum-calcium-carbon particles is 0.1–2 mm.

[0059] In this embodiment:

[0060] The MgO content in the fine magnesia powder is 93.01 wt%.

[0061] In the spinel-calcium aluminate multiphase material: MgO content 15.12wt%, Al2O3 content 65.38wt%, and CaO content 14.91wt%.

[0062] The carbon content in the graphite powder is 93.12 wt%.

[0063] The MgO content in the fused magnesia fine powder is 96.98 wt%.

[0064] The aluminate contains 6.06 wt% Al.

[0065] The magnesium-carbon composite material prepared in this embodiment was tested and found to have the following characteristics: MgO content of 75.38 wt%; C content of 13.25 wt%; compressive strength of 21 MPa; flexural strength retention rate of 41.5% after thermal shock test; and dynamic slag erosion resistance rate of 2.1 mm / hour.

[0066] Example 2

[0067] A magnesium-carbon composite material and its preparation method. The preparation method described in this embodiment is as follows:

[0068] Using 62 wt% magnesium aluminum calcium particles, 18 wt% fused magnesia fine powder and 20 wt% aluminum calcium carbon particles as raw materials, and adding 4 wt% aluminate of the raw materials, the mixture was stirred and pressed into shape; then dried at 130°C for 12 hours and cooled to obtain magnesium carbon composite material.

[0069] The pressure during the pressing process is 120 MPa.

[0070] The preparation method of the magnesium aluminum calcium granules is as follows: Magnesia fine powder: spinel-calcium aluminate multiphase material are mixed at a mass ratio of 9.5:1 to obtain a first mixed powder; the first mixed powder is placed in the hopper of a granulation equipment, and 25 wt% of aluminate ester is added to the first mixed powder at a rotation speed of 1300 r / min; when particles are formed in the hopper of the granulation equipment, the rotation speed is adjusted to 300 r / min; after all the first mixed powder has been converted into particles, the particles are taken out, and then the particles are kept at 130℃ for 16 hours and cooled to obtain magnesium aluminum calcium granules.

[0071] The particle size of the magnesium aluminum calcium particles is 0.2 to 8 mm.

[0072] The method for preparing the aluminum-calcium-carbon particles is as follows: The graphite powder and spinel-calcium aluminate composite material are mixed at a mass ratio of 5.5:1 to obtain a second mixed powder. The second mixed powder is placed in the granulation equipment hopper, and 25 wt% of aluminate ester is added to the second mixed powder at a rotation speed of 1600 r / min. When particles are formed in the granulation equipment hopper, the rotation speed is adjusted to 1000 r / min. After all the second mixed powder has been converted into particles, the particles are removed and then kept at 130℃ for 16 hours, followed by cooling to obtain the aluminum-calcium-carbon particles.

[0073] The particle size of the aluminum-calcium-carbon particles is 0.1–2 mm.

[0074] The MgO content in the fine magnesia powder is 94.15 wt%.

[0075] In the spinel-calcium aluminate multiphase material: MgO content 16.21wt%, Al2O3 content 66.35wt%, and CaO content 14.12wt%.

[0076] The carbon content in the graphite powder is 93.95 wt%.

[0077] The MgO content in the fused magnesia fine powder is 97.86 wt%.

[0078] The aluminate contains 6.51 wt% Al.

[0079] The magnesium-carbon composite material prepared in this embodiment was tested and found to have the following characteristics: MgO content of 76.27 wt%; C content of 15.67 wt%; compressive strength of 25 MPa; flexural strength retention rate of 60.2% after thermal shock resistance test; and dynamic slag erosion resistance rate of 1.5 mm / hour.

[0080] Example 3

[0081] A magnesium-carbon composite material and its preparation method. The preparation method described in this embodiment is as follows:

[0082] Using 70 wt% magnesium aluminum calcium particles, 15 wt% fused magnesia fine powder and 15 wt% aluminum calcium carbon particles as raw materials, and adding 5 wt% aluminate of the raw materials, the mixture is stirred and pressed into shape; then dried at 160℃ for 18 hours and cooled to obtain magnesium carbon composite material.

[0083] The pressure during the pressing process is 150 MPa.

[0084] The preparation method of the magnesium aluminum calcium granules is as follows: Magnesia fine powder: spinel-calcium aluminate multiphase material are mixed at a mass ratio of 9:1 to obtain a first mixed powder; the first mixed powder is placed in the hopper of a granulation equipment, and 30 wt% of aluminate ester is added to the first mixed powder at a rotation speed of 1800 r / min; when particles are formed in the hopper of the granulation equipment, the rotation speed is adjusted to 400 r / min; after all the first mixed powder has been converted into particles, the particles are taken out, and then the particles are kept at 180℃ for 20 hours and cooled to obtain magnesium aluminum calcium granules.

[0085] The particle size of the magnesium aluminum calcium particles is 0.2 to 8 mm.

[0086] The method for preparing the aluminum-calcium-carbon particles is as follows: The graphite powder and spinel-calcium aluminate composite material are mixed at a mass ratio of 6:1 to obtain a second mixed powder. The second mixed powder is placed in the granulation equipment hopper, and 30 wt% of aluminate ester is added to the second mixed powder at a rotation speed of 1800 r / min. When particles are formed in the granulation equipment hopper, the rotation speed is adjusted to 1200 r / min. After all the second mixed powder has been converted into particles, the particles are removed and then kept at 170℃ for 20 hours, followed by cooling to obtain the aluminum-calcium-carbon particles.

[0087] The particle size of the aluminum-calcium-carbon particles is 0.1–2 mm.

[0088] The MgO content in the fine magnesia powder is 93.51 wt%.

[0089] In the spinel-calcium aluminate multiphase material: MgO content 15.52wt%, Al2O3 content 65.15wt%, and CaO content 14.25wt%.

[0090] The carbon content in the graphite powder is 93.25 wt%.

[0091] The MgO content in the fused magnesia fine powder is 97.65 wt%.

[0092] The aluminate contains 6.25 wt% Al.

[0093] The magnesium-carbon composite material prepared in this embodiment was tested and found to have the following characteristics: MgO content of 73.72 wt%; C content of 12.62 wt%; compressive strength of 32 MPa; flexural strength retention rate of 50.2% after thermal shock resistance test; and dynamic slag erosion resistance rate of 1.8 mm / hour.

[0094] Example 4

[0095] A magnesium-carbon composite material and its preparation method. The preparation method described in this embodiment is as follows:

[0096] Using 75 wt% magnesium aluminum calcium particles, 13 wt% fused magnesia fine powder and 12 wt% aluminum calcium carbon particles as raw materials, and adding 6 wt% aluminate of the raw materials, the mixture was stirred and pressed into shape; then dried at 200℃ for 24 hours and cooled to obtain magnesium carbon composite material.

[0097] The pressure during the pressing process is 200 MPa.

[0098] The preparation method of the magnesium aluminum calcium granules is as follows: Magnesia fine powder and spinel-calcium aluminate multiphase material are mixed at a mass ratio of 10:1 to obtain a first mixed powder; the first mixed powder is placed in the hopper of a granulation equipment, and 30 wt% of aluminate ester is added to the first mixed powder at a rotation speed of 2000 r / min; when particles are formed in the hopper of the granulation equipment, the rotation speed is adjusted to 500 r / min; after all the first mixed powder has been converted into particles, the particles are taken out, and then the particles are kept at 200℃ for 24 hours and cooled to obtain magnesium aluminum calcium granules.

[0099] The particle size of the magnesium aluminum calcium particles is 0.2 to 8 mm.

[0100] The method for preparing the aluminum-calcium-carbon particles is as follows: The graphite powder and spinel-calcium aluminate composite material are mixed at a mass ratio of 5:1 to obtain a second mixed powder. The second mixed powder is placed in the granulation equipment hopper, and 30 wt% of aluminate ester is added to the second mixed powder at a rotation speed of 2000 r / min. When particles are formed in the granulation equipment hopper, the rotation speed is adjusted to 1380 r / min. After all the second mixed powder has been converted into particles, the particles are removed, and then kept at 200℃ for 24 hours and cooled to obtain aluminum-calcium-carbon particles.

[0101] The particle size of the aluminum-calcium-carbon particles is 0.1–2 mm.

[0102] The MgO content in the fine magnesia powder is 94.95 wt%.

[0103] In the spinel-calcium aluminate multiphase material: MgO content 16.5wt%, Al2O3 content ≥65.72wt%, CaO content 13.52wt%.

[0104] The carbon content in the graphite powder is 92.21 wt%.

[0105] The MgO content in the fused magnesia fine powder is 98.52 wt%.

[0106] The aluminate contains 6.52 wt% Al.

[0107] The magnesium-carbon composite material prepared in this embodiment was tested and found to have the following characteristics: MgO content of 80.82 wt%; C content of 9.4 wt%; compressive strength of 40 MPa; flexural strength retention rate of 30.5% after thermal shock resistance test; and dynamic slag erosion resistance rate of 2.3 mm / hour.

[0108] This specific implementation method has the following advantages compared with the prior art:

[0109] 1. This invention does not require high-temperature firing, the process is simple, and the cost is low.

[0110] 2. The main raw materials used in this invention are self-made magnesium-aluminate-calcium granules and aluminum-calcium-carbon granules based on low-grade magnesia fine powder and low-grade graphite fine powder. The pre-made granules are added to the refractory material in raw material form. The spinel-calcium aluminate multiphase material is used to adsorb silica impurities in the magnesia and graphite, thereby improving the purity of the magnesia and graphite. Simultaneously, a small amount of liquid phase is formed within the granules to enhance the thermal shock resistance of the refractory material. This is the core technology of this invention, based on the latest research results of the patent applicant's research team, and is specifically described below:

[0111] 2.1 At the steelmaking temperature (1600℃), the calcium aluminate (CaO·Al2O3) in the spinel-calcium aluminate multiphase material transforms into a melt (liquid phase), which consists of CaO and Al2O3. Among them, CaO has a high adsorption capacity for SiO2 in the system, which can adsorb SiO2 from magnesia and graphite raw materials to generate a stable high-temperature phase dicalcium silicate (CaO·2SiO2). Through thermodynamic calculations to analyze the priority order of reaction (1) and (2), it can be seen that |△G1|<|△G2|. That is, when CaO, MgO and SiO2 coexist, dicalcium silicate (CaO·2SiO2) will be preferentially generated. In other words, calcium oxide in the system will adsorb silicon oxide in the system and transform into a high-temperature phase.

[0112] 2MgO+SiO2→2MgO·SiO2 △G1=-62103.5-10T(kJ / mol) (1)

[0113] 2CaO+SiO2→2CaO·SiO2 △G2=-93937.6-29.735T(kJ / mol) (2)

[0114] 2.2 In this invention, lower-grade magnesia fine powder and spinel-calcium aluminate multiphase material are mixed. The applicant performed XRD analysis on the mixed sample before and after heat treatment at 1600℃ (results are shown in the figure). Figure 1 As shown, Figure 1 This is the XRD analysis result of the mixed sample of magnesia fine powder and spinel-calcium aluminate multiphase material used in this invention before and after high-temperature heat treatment. Before heat treatment, the main phases of the mixed sample were spinel (MA), calcium aluminate (CA), calcium dialuminate (CA2), periclase (MgO), and calcium magnesium olivine (CMS). The first three minerals originated from the spinel-calcium aluminate multiphase material, while the latter two originated from magnesia. After high-temperature heat treatment, the main minerals of the mixed sample were spinel (MA), calcium dialuminate (CA2), periclase (MgO), and dicalcium silicate (C2S), while calcium aluminate (CA) disappeared, and dicalcium silicate (C2S) became a new product after high-temperature heat treatment. This is due to the results of the thermodynamic analysis above.

[0115] Meanwhile, this invention mixes low-grade graphite powder with spinel-calcium aluminate multiphase material. The applicant performed XRD analysis on the mixed sample before and after heat treatment at 1600℃ (results are shown below). Figure 2 As shown, Figure 2This is the XRD analysis result of the mixed sample of graphite fine powder and spinel-calcium aluminate multiphase material used in this invention before and after high-temperature heat treatment: Before heat treatment, the main phases of the mixed sample were spinel (MA), calcium aluminate (CA), calcium disaluminate (CA2), carbon (C), and quartz (SiO2). The first three minerals originated from the spinel-calcium aluminate multiphase material, and the latter two minerals originated from graphite. After high-temperature heat treatment, the main impurity quartz (SiO2) in the mixed sample disappeared, and the newly formed compounds were too low to be detected in XRD analysis.

[0116] The above findings confirm that CaO has the ability to adsorb magnesium oxide and SiO2 impurities in graphite, thereby reducing the adverse effects of SiO2 on the high-temperature physical properties of magnesia and graphite.

[0117] 3. Mixed granulation can effectively prevent the segregation of key components; granulation can uniformly disperse graphite in the material, preventing layered cracking in the molded product; the granulation process can improve the flow characteristics of powdered raw materials and enhance the stability, compactness and segregation-free properties of mold feeding during molding.

[0118] 4. Spinel-calcium aluminate multiphase materials, due to their content of magnesium aluminum spinel (greater than 70%), exhibit good thermal shock stability. Simultaneously, the small amount of liquid phase formed by the calcium aluminate monophase (less than 15%) in the multiphase material at steelmaking temperatures also contributes to the material's resistance to thermal shock damage. Mixing and granulating the spinel-calcium aluminate multiphase material with magnesia helps mitigate the adverse effects of magnesia's high coefficient of thermal expansion on the material's thermal shock stability.

[0119] The magnesium-carbon composite material prepared by this invention was tested and found to have the following properties: MgO content: 73.72–80.82 wt%; C content: 9.40–15.67 wt%; compressive strength: 21–40 MPa; using the GB / T30873-2014 test method for thermal shock resistance of refractory materials (air quenching method), after 3 heating-cooling cycles, the flexural strength retention rate of the material was 30.5–60.2%; using the dynamic slag resistance test method in an induction furnace (temperature 1600℃, holding for 1 hour; chemical composition of the prepared steel slag: CaO 35.21%, SiO2 20.53%, Al2O3 23.84%, MgO 8.25%, total iron content 12.38%), the dynamic slag erosion rate was 1.5–2.3 mm / hour.

[0120] This invention uses low-grade magnesia powder and low-grade graphite powder as main raw materials to prepare magnesium-carbon composite materials for high-temperature smelting. It features simple process and low cost. The prepared magnesium-carbon composite material has good thermal shock stability and strong erosion resistance, and can be used as furnace lining material for containers used in high-temperature smelting.

Claims

1. A method for preparing a magnesium-carbon composite material, characterized in that... The preparation method of the magnesium-carbon composite material is as follows: Using 60-75 wt% magnesium aluminum calcium particles, 13-25 wt% fused magnesia fine powder and 12-20 wt% aluminum calcium carbon particles as raw materials, and adding 3-6 wt% aluminate of the raw materials, the mixture is stirred, pressed into shape, and then dried at 110-200℃ for 8-24 hours and cooled to obtain magnesium carbon composite material. The preparation method of the magnesium aluminum calcium granules is as follows: Magnesia fine powder: spinel-calcium aluminate multiphase material are mixed at a mass ratio of (9~10):1 to obtain a first mixed powder; the first mixed powder is placed in the granulation equipment hopper, and 20~30wt% of aluminate ester is added to the first mixed powder at a rotation speed of 1000~2000 r / min; when particles are formed in the granulation equipment hopper, the rotation speed is adjusted to 200~500 r / min; after all the first mixed powder has been converted into particles, the particles are taken out, and then the particles are kept at 110~200℃ for 12~24 hours and cooled to obtain magnesium aluminum calcium granules; The particle size of the magnesium aluminum calcium particles is 0.2~8mm; the preparation method of the aluminum calcium carbon particles is: according to the mass ratio of graphite fine powder: spinel-calcium aluminate multiphase material of (5~6):1, mix them to obtain a second mixed powder; The second mixed powder is placed in the hopper of a granulation equipment. At a rotation speed of 1400~2000 r / min, 20~30 wt% of aluminate is added to the second mixed powder. When particles are formed in the hopper of the granulation equipment, the rotation speed is adjusted to 800~1380 r / min. After all the second mixed powder has been converted into particles, the particles are taken out and then kept at 110~200℃ for 12~24 hours and cooled to obtain aluminum-calcium-carbon particles. The particle size of the aluminum-calcium-carbon particles is 0.1~2 mm.

2. The method for preparing the magnesium-carbon composite material according to claim 1, characterized in that, The particle size of the magnesia fine powder is 1~300μm; the MgO content in the magnesia fine powder is 93~95wt%.

3. The method for preparing the magnesium-carbon composite material according to claim 1, characterized in that, The spinel-calcium aluminate composite material has a particle size of 1~300μm; in the spinel-calcium aluminate composite material: MgO content ≥15wt%, Al2O3 content ≥65wt%, CaO content ≤15wt%.

4. The method for preparing the magnesium-carbon composite material according to claim 1, characterized in that, The graphite powder has a particle size of 1~300μm and a C content of 92~94wt%.

5. The method for preparing the magnesium-carbon composite material according to claim 1, characterized in that, The particle size of the fused magnesia fine powder is 1~300μm; the MgO content in the fused magnesia fine powder is ≥96wt%.

6. The method for preparing the magnesium-carbon composite material according to claim 1, characterized in that, The aluminate contains ≥6wt% Al; the aluminate used to prepare magnesium-carbon composite materials is the same as the aluminate used to prepare aluminum-calcium-carbon particles.

7. The method for preparing the magnesium-carbon composite material according to claim 1, characterized in that, The pressure during the pressing process is 80~200MPa.

8. A magnesium-carbon composite material, characterized in that... The magnesium-carbon composite material is a magnesium-carbon composite material prepared by the method for preparing magnesium-carbon composite materials according to any one of claims 1 to 7.

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