Preparation process of high thermal shock resistance magnesium-carbon brick
By using a composite layer structure of modified graphite and modified phenolic resin, the problem of reduced strength in magnesia-carbon bricks caused by microcrystalline graphite content was solved, and the high thermal shock resistance and high-temperature flexural strength of magnesia-carbon bricks were improved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- YINGKOU JIUZHOU REFRACTORY MATERIAL CO LTD
- Filing Date
- 2026-04-28
- Publication Date
- 2026-07-10
AI Technical Summary
Increasing the microcrystalline graphite content leads to a decrease in the strength of magnesia-carbon bricks, and also results in problems such as weak interfacial bonding, decreased bulk density, and reduced high-temperature flexural strength.
A composite layer structure of modified graphite and modified phenolic resin is adopted. The pores are created by the decomposition of ammonium bicarbonate in the modified phenolic resin, the micropores are blocked by liquid phase B2O3, the nano ZrO2 is used for toughening, the impurities are captured by TiO2, and LDH generates MgO and Al2O4 spinel anchor points to connect graphite and magnesia, forming chemical bonds.
It improves the thermal shock resistance and high-temperature flexural strength of magnesia-carbon bricks, prevents gas accumulation and microcrack propagation, enhances interfacial bonding strength, and maintains high-temperature stability.
Smart Images
Figure CN122102732B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of magnesia-carbon brick technology, specifically a preparation process for magnesia-carbon bricks with high thermal shock resistance. Background Technology
[0002] Magnesia-carbon bricks are key refractory materials in high-temperature industries such as iron and steel metallurgy and non-ferrous metal smelting. In modern steelmaking processes, furnace lining refractory materials are frequently subjected to the combined effects of thermal shock from molten steel, chemical erosion from slag, and mechanical stress. Especially during operations such as hot metal addition and tapping, the furnace shell temperature changes drastically in a very short time, generating a large thermal stress gradient, leading to thermal shock damage (stripping and cracking) of the refractory material. Therefore, thermal shock resistance is one of the most critical indicators for evaluating the performance of magnesia-carbon bricks. Microcrystalline graphite is one of the important carbon sources for magnesia-carbon bricks, and the introduction of graphite is a major technical means to improve the thermal shock resistance of magnesia-carbon bricks. Microcrystalline graphite has high thermal conductivity, a low coefficient of thermal expansion, and weak interlayer bonding energy absorption characteristics, which can quickly homogenize temperature gradients, alleviate thermal stress accumulation, and absorb crack propagation energy. Therefore, appropriately increasing the amount of microcrystalline graphite added can significantly improve thermal shock resistance.
[0003] However, simply increasing the content of microcrystalline graphite can have several negative effects. First, the weak bonding between microcrystalline graphite and magnesia makes it a vulnerable area where cracks preferentially initiate during thermal shock in bricks. Second, graphite has a much lower density than refractory aggregates such as magnesia, and its large-scale introduction leads to a decrease in bulk density and an increase in porosity, resulting in a significant decrease in room-temperature compressive strength as the graphite content increases. Finally, if the graphite used is not pure enough, the accompanying impurities (such as SiO2, CaO, Fe2O3, and Al2O3) will react with the components in magnesia at high temperatures to form low-melting-point silicate minerals or glassy phases. These low-melting substances soften and flow, dissolving and eroding the solid MgO particles, leading to mineral erosion and volume shrinkage. This forms annular pore bands around the graphite particles, completely destroying the structural continuity between the graphite and magnesia aggregates, and significantly reducing high-temperature flexural strength and thermal shock stability. Summary of the Invention
[0004] (1) Technical problems to be solved
[0005] The purpose of this invention is to provide a preparation process for magnesia-carbon bricks with high thermal shock resistance, so as to solve the problem that the strength of magnesia-carbon bricks decreases due to increasing the microcrystalline graphite content.
[0006] (2) Technical solution
[0007] To achieve the above objectives, on the one hand, the present invention provides a preparation process for magnesia-carbon bricks with high thermal shock resistance, comprising the following steps:
[0008] S1. Place fused magnesia in a mixer and dry mix, then add aluminum powder, modified graphite, and phenolic resin in sequence, and mix evenly to obtain a mixture.
[0009] S2. Load the mixture into a mold and press it into shape using a hydraulic friction brick press at a pressure of 150~180MPa and a holding time of 30~45s to obtain a brick blank;
[0010] S3. Place the brick blank in a curing furnace, introduce nitrogen for protection, heat to 195~205℃ at a heating rate of 0.8~1.2℃ / min, hold for 22~26 hours, and obtain magnesia-carbon bricks after cooling;
[0011] The modified graphite has a composite layer structure, with the core being LDH-titanium ester modified microcrystalline graphite and the shell being modified phenolic resin.
[0012] The modified phenolic resin is a boric acid-modified phenolic resin containing ammonium bicarbonate, B4C nanoparticles, and nano ZrO2.
[0013] Furthermore, the magnesia-carbon brick comprises the following components in parts by weight: 80-85 parts of fused magnesia, 12-16 parts of modified graphite, 3-4.5 parts of phenolic resin, and 1-2 parts of aluminum powder.
[0014] Furthermore, the preparation method of the modified graphite includes the following steps:
[0015] S11. Under an ice-water bath, concentrated sulfuric acid and concentrated nitric acid are stirred and mixed, microcrystalline graphite is added, stirred evenly, heated, and stirred to react. The resulting reaction solution is slowly poured into ice water, the solid is collected by suction filtration, washed with deionized water, dried in an oven, ground and sieved to obtain oxidized microcrystalline graphite.
[0016] S12. Disperse oxidized microcrystalline graphite in anhydrous toluene / ethanol mixed solvent, add tetrabutyl titanate, reflux and stir, filter, and purify by Soxhlet extraction with anhydrous ethanol as extraction solvent, and dry to obtain the first compound.
[0017] S13. Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water by stirring, add the first compound, disperse by ultrasonication, slowly add NaOH dropwise under stirring to adjust the pH, transfer the resulting mixture to a high-pressure reactor lined with polytetrafluoroethylene, heat the mixture to react, filter the resulting reaction solution, wash with deionized water, dry in an oven, grind and sieve to obtain the second compound;
[0018] S14. The second compound is immersed in modified phenolic resin, the vacuum pump is turned on, the impregnation and coating are performed, the material is discharged and filtered, dried at room temperature, cured in stages, and then ground and sieved after cooling to obtain modified graphite.
[0019] Furthermore, the mass of the modified phenolic resin is 12-18% of the second compound.
[0020] Furthermore, the stage curing is carried out in a forced-air oven and is divided into three stages: the decomposition and pore-forming stage, with the temperature raised to 50~100℃; the preliminary curing stage, with the temperature raised to 120℃ and held for 30 minutes; and the complete curing stage, with the temperature raised to 175~185℃ and held for 2 hours.
[0021] Furthermore, the preparation method of the modified phenolic resin includes the following steps:
[0022] S21. Phenol and boric acid are mixed, heated to react, paraformaldehyde is added in batches, NaOH is added dropwise to adjust the pH, polycondensation is carried out at a higher temperature, and dehydration is carried out under reduced pressure to obtain boric acid modified phenolic resin.
[0023] S22. Ammonium bicarbonate, B4C nanoparticles and nano ZrO2 are added sequentially to anhydrous ethanol and ultrasonically dispersed. Then boric acid-modified phenolic resin is added and ultrasonically dispersed again. Anhydrous ethanol is added to adjust the viscosity to obtain modified phenolic resin.
[0024] Furthermore, the mass of the B4C nanoparticles is 20-24% of the solid content of the boric acid-modified phenolic resin; the mass of the ammonium bicarbonate is 2-3% of the solid content of the boric acid-modified phenolic resin; and the mass of the nano ZrO2 is 4-6% of the solid content of the boric acid-modified phenolic resin.
[0025] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:
[0026] 1. In the low-temperature stage, ammonium bicarbonate in the modified phenolic resin decomposes to create pores. As the temperature rises, LDH undergoes a decomposition reaction, and the microporous channels promptly guide out H2O and CO2 gases, eliminating the internal pressure caused by the accumulation of gas due to the sealing of the outer shell and preventing the internal gas pressure of the particles from cracking and damaging the outer shell. As the temperature rises, after the formation of the B2O3 liquid phase, the B2O3 liquid phase automatically penetrates into the micropores and seals them under the action of capillary force and wetting. At the same time, during thermal shock, the stress concentration field generated at the crack tip triggers the phase transformation of nano-ZrO2, which actively clamps and heals the microcracks caused by expansion, achieving active toughening. This, together with the passive filling of the B2O3 liquid phase, forms a dual protection.
[0027] 2. During the high-temperature stage, the titanate coupling groups on the modified graphite surface decompose, generating nano-TiO2 in situ on the graphite surface. TiO2 captures impurities such as CaO and Fe2O3 in the graphite, forming a high-melting-point phase. Meanwhile, MgO generated from the decomposition of LDH preferentially captures SiO2 to form Mg2SiO4, preventing SiO2 from forming low-melting-point MgSiO3 or a glassy phase when MgO is insufficient, thus avoiding damage to the matrix. The impurity-capturing functions of TiO2 and MgO complement each other. Simultaneously, LDH decomposes to generate a mixture of MgO and Al2O3, which are then converted in situ into MgAl2O4 spinel during subsequent high-temperature use, forming a rigid ceramic anchor framework on the graphite surface. This chemically bonds the graphite to the magnesia matrix, significantly improving the interfacial bonding strength.
[0028] 3. The alkaline environment of the MgO nanophase lowers the activation energy of B4C oxidation, accelerating its oxidation to B2O3. The liquid phase characteristics of the generated B2O3 allow it to spontaneously penetrate, under capillary force, into the micropores formed by the decomposition of ammonium bicarbonate, the nanopores left by the dehydration of LDH, the annular pore bands formed after the loss of low-melting-point impurities, and the microcracks newly generated during thermal shock. Furthermore, the B2O3 liquid phase reacts with nano-ZrO2 at high temperatures to form a zirconium-boron composite oxide glass phase. This glass phase fills the pores and microcracks, providing high-temperature sealing and toughening effects. Attached Figure Description
[0029] Figure 1 This is a flowchart illustrating the preparation process of the magnesium-carbon bricks of this invention.
[0030] Figure 2 This is a microstructure diagram of the magnesium-carbon brick of the present invention at low temperature;
[0031] Figure 3 This is a microstructure diagram of the magnesium-carbon brick of the present invention at high temperature. Detailed Implementation
[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 skilled in the art without creative effort are within the scope of protection of the present invention.
[0033] Example 1: This example discloses a preparation process for high thermal shock resistant magnesia-carbon bricks, including the following steps:
[0034] S1. Place fused magnesia in a mixer and dry mix, then add aluminum powder, modified graphite, and phenolic resin in sequence, and mix evenly to obtain a mixture.
[0035] S2. Load the mixture into a mold and press it into shape using a hydraulic friction brick press at a pressure of 150~180MPa and a holding time of 30~45s to obtain a brick blank;
[0036] S3. Place the brick blank in a curing furnace, introduce nitrogen for protection, heat to 195~205℃ at a heating rate of 0.8~1.2℃ / min, hold for 22~26 hours, and obtain magnesia-carbon bricks after cooling;
[0037] The modified graphite has a composite layer structure, with the core being LDH-titanium ester modified microcrystalline graphite and the shell being modified phenolic resin.
[0038] The modified phenolic resin is a boric acid-modified phenolic resin containing ammonium bicarbonate, B4C nanoparticles, and nano ZrO2.
[0039] It should be noted that, as Figure 1 The diagram shown is a flowchart of the preparation of magnesia-carbon bricks in Example 1 of the present invention. The fused magnesia includes 5-8mm coarse aggregate, 3-5mm medium aggregate, 1-3mm fine aggregate, and ≤0.088mm fine powder.
[0040] The magnesia-carbon brick comprises the following components in parts by weight: 85 parts fused magnesia, 16 parts modified graphite, 4.5 parts phenolic resin, and 2 parts aluminum powder.
[0041] The method for preparing the modified graphite includes the following steps:
[0042] S11. Under an ice-water bath, 375 mL of concentrated sulfuric acid and 125 mL of concentrated nitric acid were stirred and mixed. 100 g of microcrystalline graphite was added and stirred evenly. The temperature was raised to 58-62 °C and the reaction was stirred. The resulting reaction solution was slowly poured into 2 L of ice water. The solid was collected by suction filtration and washed with deionized water until the pH of the filtrate was 6.5-7. The filtrate was dried in an oven at 80 °C for 12 h and ground through a 75 μm sieve to obtain oxidized microcrystalline graphite.
[0043] S12. 100g of oxidized microcrystalline graphite was dispersed in 750mL of toluene / ethanol mixed solvent (volume ratio 3:1), 4g of tetrabutyl titanate was added, the mixture was refluxed and stirred at 60℃ for 4h, filtered, and purified by Soxhlet extraction with anhydrous ethanol as the extraction solvent. The mixture was dried at 80℃ for 10h, ground and passed through a 75μm sieve to obtain the first compound.
[0044] S13. Dissolve 24.5g MgCl2·6H2O and 9.7g AlCl3·6H2O in 200mL deionized water, add 50g of the first compound, and sonicate for 10min. While stirring, slowly add NaOH to adjust the pH to 9.5~10.5, and continue stirring for 30min. Transfer the resulting mixture to a high-pressure reactor lined with polytetrafluoroethylene, heat to 120~122℃ and react for 12~18h. Filter the resulting reaction solution, wash with deionized water until the pH of the filtrate is about 7, dry in an oven at 80℃ for 12h, grind through a 75μm sieve to obtain the second compound.
[0045] S14. Immerse 100g of the second compound in modified phenolic resin, turn on the vacuum pump, maintain a negative pressure of -0.085~-0.095MPa, immerse and coat for 25~35min, filter through a 200-mesh sieve after unloading, air dry at room temperature for 2~4h, stage curing, and after cooling, grind through a 75μm sieve to obtain modified graphite.
[0046] The mass of the modified phenolic resin is 18% of the second compound.
[0047] The stage curing is carried out in a forced-air drying oven and is divided into three stages: the decomposition and pore-forming stage, with the temperature raised to 50~100℃; the preliminary curing stage, with the temperature raised to 120℃ and held for 30 minutes; and the complete curing stage, with the temperature raised to 175~185℃ and held for 2 hours.
[0048] It should be noted that the decomposition and pore-forming stage is divided into two steps. First, the temperature is raised to 50~60℃ and kept for 30 minutes to allow ammonium bicarbonate to begin to decompose in large quantities. Then, the temperature is raised to 80~100℃ and kept for 60 minutes to allow the remaining components to decompose completely.
[0049] The preparation method of the modified phenolic resin includes the following steps:
[0050] S21. Mix 94g of phenol and 18g of boric acid, heat to 100~120℃ and react for 1~2h. After the reaction is complete, cool to 80~90℃, add 40g of paraformaldehyde in batches, add NaOH dropwise to adjust the pH to 8.5~9.5, heat to 90~110℃ for polycondensation reaction, dehydrate under reduced pressure to obtain boric acid modified phenolic resin.
[0051] S22. Add 1.5g ammonium bicarbonate, 12g B4C nanoparticles and 3g nano ZrO2 to 50mL anhydrous ethanol in sequence, and sonicate for 30min. Then add 50g boric acid modified phenolic resin, and continue to sonicate for 10min. Add anhydrous ethanol to adjust the viscosity to 200-500mPa·s to obtain modified phenolic resin.
[0052] The mass of the B4C nanoparticles is 24% of the solid content of the boric acid-modified phenolic resin; the mass of the ammonium bicarbonate is 3% of the solid content of the boric acid-modified phenolic resin; and the mass of the nano ZrO2 is 6% of the solid content of the boric acid-modified phenolic resin.
[0053] Example 2: This example is based on Example 1, but differs from Example 1 in that the magnesia-carbon brick in this example includes the following components in parts by weight: 83 parts fused magnesia, 14 parts modified graphite, 3.7 parts phenolic resin, and 1.5 parts aluminum powder.
[0054] The other components and preparation methods are the same as in Example 1.
[0055] Example 3: This example is based on Example 1, but differs from Example 1 in that the magnesia-carbon brick in this example includes the following components in parts by weight: 80 parts of fused magnesia, 12 parts of modified graphite, 3 parts of phenolic resin, and 1 part of aluminum powder.
[0056] The other components and preparation methods are the same as in Example 1.
[0057] Example 4: This example is based on Example 1, but differs from Example 1 in that the mass of the modified phenolic resin in this example is 12% of the second compound.
[0058] The other components and preparation methods are the same as in Example 1.
[0059] Example 5: This example is based on Example 1, but differs from Example 1 in that the mass of the B4C nanoparticles in this example is 20% of the solid content of the boric acid modified phenolic resin; the mass of the ammonium bicarbonate is 2% of the solid content of the boric acid modified phenolic resin; and the mass of the nano ZrO2 is 4% of the solid content of the boric acid modified phenolic resin.
[0060] The other components and preparation methods are the same as in Example 1.
[0061] Comparative Example 1: This comparative example is based on Example 1, but differs from Example 1 in that the modified phenolic resin in this comparative example does not contain ammonium bicarbonate.
[0062] The preparation method of the modified phenolic resin includes the following steps:
[0063] S21. Mix 94g of phenol and 18g of boric acid, heat to 100~120℃ and react for 1~2h. After the reaction is complete, cool to 80~90℃, add 40g of paraformaldehyde in batches, add NaOH dropwise to adjust the pH to 8.5~9.5, heat to 90~110℃ for polycondensation reaction, dehydrate under reduced pressure to obtain boric acid modified phenolic resin.
[0064] S22. Add 12g of B4C nanoparticles and 3g of nano ZrO2 sequentially to 50mL of anhydrous ethanol, and ultrasonically disperse for 30min. Then add 50g of boric acid modified phenolic resin, and continue ultrasonic dispersion for 10min. Add anhydrous ethanol to adjust the viscosity to 200-500mPa·s to obtain modified phenolic resin.
[0065] The other components and preparation methods are the same as in Example 1.
[0066] Comparative Example 2: This comparative example is based on Example 1, but differs from Example 1 in that the modified phenolic resin in this comparative example does not contain B4C nanoparticles.
[0067] The preparation method of the modified phenolic resin includes the following steps:
[0068] S21. Mix 94g of phenol and 18g of boric acid, heat to 100~120℃ and react for 1~2h. After the reaction is complete, cool to 80~90℃, add 40g of paraformaldehyde in batches, add NaOH dropwise to adjust the pH to 8.5~9.5, heat to 90~110℃ for polycondensation reaction, dehydrate under reduced pressure to obtain boric acid modified phenolic resin.
[0069] S22. Add 1.5g ammonium bicarbonate and 3g nano ZrO2 sequentially to 50mL anhydrous ethanol, ultrasonically disperse for 30min, then add 50g boric acid modified phenolic resin, continue ultrasonic dispersion for 10min, add anhydrous ethanol to adjust the viscosity to 200-500mPa·s, and obtain modified phenolic resin.
[0070] The other components and preparation methods are the same as in Example 1.
[0071] Comparative Example 3: This comparative example is based on Example 1, but differs from Example 1 in that the modified phenolic resin in this comparative example does not contain nano ZrO2.
[0072] The preparation method of the modified phenolic resin includes the following steps:
[0073] S21. Mix 94g of phenol and 18g of boric acid, heat to 100~120℃ and react for 1~2h. After the reaction is complete, cool to 80~90℃, add 40g of paraformaldehyde in batches, add NaOH dropwise to adjust the pH to 8.5~9.5, heat to 90~110℃ for polycondensation reaction, dehydrate under reduced pressure to obtain boric acid modified phenolic resin.
[0074] S22. Add 1.5g ammonium bicarbonate and 12g B4C nanoparticles sequentially to 50mL anhydrous ethanol, and ultrasonically disperse for 30min. Then add 50g boric acid modified phenolic resin, and continue ultrasonic dispersion for 10min. Add anhydrous ethanol to adjust the viscosity to 200-500mPa·s to obtain modified phenolic resin.
[0075] The other components and preparation methods are the same as in Example 1.
[0076] Comparative Example 4: This comparative example is based on Example 1, but differs from Example 1 in that the modified graphite in this comparative example is not modified with titanate.
[0077] The method for preparing the modified graphite includes the following steps:
[0078] S11. Under an ice-water bath, 375 mL of concentrated sulfuric acid and 125 mL of concentrated nitric acid were mixed and stirred while being added. 100 g of microcrystalline graphite was added and stirred until homogeneous. The temperature was raised to 58-62 °C and the reaction was stirred. The resulting reaction solution was slowly poured into 2 L of ice water. The solid was collected by suction filtration and washed with deionized water until the pH of the filtrate was 6.5-7. The filtrate was dried in an oven at 80 °C for 12 h and then ground through a 75 μm sieve to obtain oxidized microcrystalline graphite.
[0079] S12. Dissolve 24.5g MgCl2·6H2O and 9.7g AlCl3·6H2O in 200mL deionized water, add 50g oxidized microcrystalline graphite, and sonicate for 10min. While stirring, slowly add NaOH to adjust the pH to 9.5~10.5, and continue stirring for 30min. Transfer the resulting mixture to a high-pressure reactor lined with polytetrafluoroethylene, heat to 120~122℃ and react for 12~18h. Filter the resulting reaction solution, wash with deionized water until the pH of the filtrate is about 7, dry in an oven at 80℃ for 12h, grind through a 75μm sieve to obtain the third compound.
[0080] S13. Immerse 100g of the third compound in modified phenolic resin, turn on the vacuum pump, maintain a negative pressure of -0.085~-0.095MPa, immerse and coat for 25~35min, filter through a 200-mesh sieve after unloading, air dry at room temperature for 2~4h, stage curing, and after cooling, grind through a 75μm sieve to obtain modified graphite.
[0081] The other components and preparation methods are the same as in Example 1.
[0082] Comparative Example 5: This comparative example is based on Example 1, but differs from Example 1 in that the modified graphite in this comparative example is not modified with LDH.
[0083] The method for preparing the modified graphite includes the following steps:
[0084] S11. Under an ice-water bath, 375 mL of concentrated sulfuric acid and 125 mL of concentrated nitric acid were mixed and stirred while being added. 100 g of microcrystalline graphite was added and stirred until homogeneous. The temperature was raised to 58-62 °C and the reaction was stirred. The resulting reaction solution was slowly poured into 2 L of ice water. The solid was collected by suction filtration and washed with deionized water until the pH of the filtrate was 6.5-7. The filtrate was dried in an oven at 80 °C for 12 h and then ground through a 75 μm sieve to obtain oxidized microcrystalline graphite.
[0085] S12. 100g of oxidized microcrystalline graphite was dispersed in 750mL of toluene / ethanol mixed solvent (volume ratio 3:1), 4g of tetrabutyl titanate was added, the mixture was refluxed and stirred at 60℃ for 4h, filtered, and purified by Soxhlet extraction with anhydrous ethanol as the extraction solvent. The mixture was dried at 80℃ for 10h, ground and passed through a 75μm sieve to obtain the first compound.
[0086] S13. Immerse 100g of the first compound in modified phenolic resin, turn on the vacuum pump, maintain a negative pressure of -0.085~-0.095MPa, immerse and coat for 25~35min, filter through a 200-mesh sieve after unloading, air dry at room temperature for 2~4h, stage curing, and after cooling, grind through a 75μm sieve to obtain modified graphite.
[0087] The other components and preparation methods are the same as in Example 1.
[0088] Comparative Example 6: This comparative example is based on Example 1, but differs from Example 1 in that the modified graphite in this comparative example does not contain modified phenolic resin.
[0089] The method for preparing the modified graphite includes the following steps:
[0090] S11. Under an ice-water bath, 375 mL of concentrated sulfuric acid and 125 mL of concentrated nitric acid were mixed and stirred while being added. 100 g of microcrystalline graphite was added and stirred until homogeneous. The temperature was raised to 58-62 °C and the reaction was stirred. The resulting reaction solution was slowly poured into 2 L of ice water. The solid was collected by suction filtration and washed with deionized water until the pH of the filtrate was 6.5-7. The filtrate was dried in an oven at 80 °C for 12 h and then ground through a 75 μm sieve to obtain oxidized microcrystalline graphite.
[0091] S12. 100g of oxidized microcrystalline graphite was dispersed in 750mL of toluene / ethanol mixed solvent (volume ratio 3:1), 4g of tetrabutyl titanate was added, the mixture was refluxed and stirred at 60℃ for 4h, filtered, and purified by Soxhlet extraction with anhydrous ethanol as the extraction solvent. The mixture was dried at 80℃ for 10h, ground and passed through a 75μm sieve to obtain the first compound.
[0092] S13. Dissolve 24.5g MgCl2·6H2O and 9.7g AlCl3·6H2O in 200mL deionized water, add 50g of the first compound, and sonicate for 10min. While stirring, slowly add NaOH to adjust the pH to 9.5~10.5, and continue stirring for 30min. Transfer the resulting mixture to a high-pressure reactor lined with polytetrafluoroethylene, heat to 120~122℃ and react for 12~18h. Filter the resulting reaction solution, wash with deionized water until the pH of the filtrate is about 7, dry in an oven at 80℃ for 12h, grind through a 75μm sieve to obtain modified graphite.
[0093] The other components and preparation methods are the same as in Example 1.
[0094] Comparative Example 7: This comparative example is based on Example 1, but differs from Example 1 in that the modified graphite in the magnesia-carbon brick described in this comparative example is microcrystalline graphite.
[0095] The magnesia-carbon brick comprises the following components in parts by weight: 85 parts fused magnesia, 16 parts microcrystalline graphite, 4.5 parts phenolic resin, and 2 parts aluminum powder.
[0096] The other components and preparation methods are the same as in Example 1.
[0097] Comparative Example 8: This comparative example is based on Example 1, but differs from Example 1 in that the magnesia-carbon bricks described in this comparative example are traditional magnesia-carbon bricks with low microcrystalline graphite content.
[0098] The magnesia-carbon brick comprises the following components in parts by weight: 85 parts fused magnesia, 5 parts microcrystalline graphite, 4.5 parts phenolic resin, and 2 parts aluminum powder.
[0099] The other components and preparation methods are the same as in Example 1.
[0100] Experimental verification:
[0101] Experiment 1:
[0102] (1) Cut each group of magnesia-carbon bricks into 160mm×40mm×40mm samples and conduct thermal shock resistance tests according to GB / T 30758-2014. Calculate the strength retention rate after 15 cycles of thermal shock and supplement with water quenching. After keeping the sample at 1100℃ for 20min, immediately immerse it in flowing water to cool it. Record the number of cycles until the sample breaks or macroscopic cracks appear.
[0103] (2) The high-temperature flexural strength of the sample at 1400℃ was measured with reference to GB / T 3002-2017.
[0104] Table 1: Thermal shock resistance and high-temperature flexural strength tests of magnesia-carbon bricks:
[0105]
[0106] Table 1 shows the test results of thermal shock resistance and high-temperature flexural strength of the magnesia-carbon brick of the present invention. Compared with Comparative Examples 7 and 8, Comparative Example 7 has a higher graphite content and stronger thermal shock resistance but poorer high-temperature flexural strength. Comparative Example 8 is a traditional magnesia-carbon brick with a low graphite content, which has good high-temperature flexural strength but poor thermal shock resistance. In contrast, Example 1, which has modified graphite, has both higher thermal shock resistance and higher high-temperature flexural strength.
[0107] Experiment 2:
[0108] (1) Test the bulk density and apparent porosity of magnesia-carbon bricks according to GB / T 2997;
[0109] (2) Test the compressive strength of magnesia-carbon bricks at room temperature according to GB / T 5072;
[0110] (3) Test the room temperature flexural strength of magnesia-carbon bricks according to GB / T 3001;
[0111] (4) Test the linear change rate according to GB / T 5988;
[0112] Table 2: Basic properties of magnesia-carbon bricks:
[0113]
[0114] Table 2 shows the test results of the basic properties of magnesia-carbon bricks. Compared to Comparative Example 7, Example 1 has a significantly higher bulk density and a significantly lower apparent porosity, indicating that the modification treatment effectively improved the compactness of the brick, offsetting the density decrease caused by the high graphite content. The room temperature compressive strength of Example 1 is significantly higher than that of Comparative Example 7 and close to that of the traditional magnesia-carbon brick in Comparative Example 8, indicating that the high graphite content after modification in this invention does not lead to a significant decrease in strength. Figure 2 The diagram shown is a microstructure of the magnesia-carbon brick of the present invention at low temperature. Figure 3 This is a microstructure diagram of the magnesium-carbon brick of the present invention at high temperature. In the low temperature stage, ammonium bicarbonate in the modified phenolic resin decomposes to create pores. When the temperature rises, the B2O3 liquid phase fills most of the matrix pores under capillary force and wetting action, thereby improving the compactness of the magnesium-carbon brick and significantly reducing the apparent porosity.
[0115] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A preparation process for high thermal shock resistant magnesia-carbon bricks, characterized in that, Includes the following steps: S1. Place fused magnesia in a mixer and dry mix. Then, add aluminum powder, modified microcrystalline graphite, and phenolic resin in sequence and mix thoroughly to obtain the mixture. S2. Load the mixture into a mold and press it into shape using a hydraulic friction brick press at a pressure of 150~180MPa and a holding time of 30~45s to obtain a brick blank; S3. Place the brick blank in a curing furnace, introduce nitrogen for protection, heat to 195~205℃ at a heating rate of 0.8~1.2℃ / min, hold for 22~26 hours, and obtain magnesia-carbon brick after cooling; The modified microcrystalline graphite has a composite layer structure, with the core being LDH-titanium ester modified microcrystalline graphite and the shell being modified phenolic resin. The modified phenolic resin is a boric acid-modified phenolic resin containing ammonium bicarbonate, B4C nanoparticles, and nano ZrO2. The method for preparing the modified microcrystalline graphite includes the following steps: S11. Under an ice-water bath, concentrated sulfuric acid and concentrated nitric acid are stirred and mixed, microcrystalline graphite is added, stirred evenly, heated, and stirred to react. The resulting reaction solution is slowly poured into ice water, the solid is collected by suction filtration, washed with deionized water, dried in an oven, ground and sieved to obtain oxidized microcrystalline graphite. S12. Disperse oxidized microcrystalline graphite in anhydrous toluene / ethanol mixed solvent, add tetrabutyl titanate, reflux and stir, filter, and purify by Soxhlet extraction with anhydrous ethanol as extraction solvent, and dry to obtain the first compound. S13. Dissolve MgCl2·6H2O and AlCl3·6H2O in deionized water by stirring, add the first compound, disperse by ultrasonication, slowly add NaOH dropwise under stirring to adjust the pH, transfer the resulting mixture to a high-pressure reactor lined with polytetrafluoroethylene, heat the mixture to react, filter the resulting reaction solution, wash with deionized water, dry in an oven, grind and sieve to obtain the second compound; S14. The second compound is immersed in modified phenolic resin, the vacuum pump is turned on, the impregnation and coating are performed, the material is discharged and filtered, dried at room temperature, cured in stages, and ground and sieved after cooling to obtain modified microcrystalline graphite.
2. The preparation process of a high thermal shock resistant magnesia-carbon brick according to claim 1, characterized in that, The magnesia-carbon brick comprises the following components in parts by weight: 80-85 parts of fused magnesia, 12-16 parts of modified microcrystalline graphite, 3-4.5 parts of phenolic resin, and 1-2 parts of aluminum powder.
3. The preparation process of a high thermal shock resistant magnesia-carbon brick according to claim 1, characterized in that, The mass of the modified phenolic resin is 12-18% of the second compound.
4. The preparation process of a high thermal shock resistant magnesia-carbon brick according to claim 1, characterized in that, The curing process is carried out in a forced-air oven and consists of three stages: the decomposition and pore-forming stage, where the temperature is raised to 50-100℃; the preliminary curing stage, where the temperature is raised to 120℃ and held for 30 minutes; and the complete curing stage, where the temperature is raised to 175-185℃ and held for 2 hours.
5. The preparation process of a high thermal shock resistant magnesia-carbon brick according to claim 1, characterized in that, The preparation method of the modified phenolic resin includes the following steps: S21. Phenol and boric acid are mixed, heated to react, paraformaldehyde is added in batches, NaOH is added dropwise to adjust the pH, polycondensation is carried out at a higher temperature, and dehydration is carried out under reduced pressure to obtain boric acid modified phenolic resin. S22. Ammonium bicarbonate, B4C nanoparticles and nano ZrO2 are added sequentially to anhydrous ethanol and ultrasonically dispersed. Then boric acid-modified phenolic resin is added and ultrasonically dispersed again. Anhydrous ethanol is added to adjust the viscosity to obtain modified phenolic resin.
6. The preparation process of a high thermal shock resistant magnesia-carbon brick according to claim 5, characterized in that, The mass of the B4C nanoparticles is 20-24% of the solid content of the boric acid-modified phenolic resin; the mass of the ammonium bicarbonate is 2-3% of the solid content of the boric acid-modified phenolic resin; and the mass of the nano ZrO2 is 4-6% of the solid content of the boric acid-modified phenolic resin.