High-temperature-resistant magnesia-carbon composite refractory brick and preparation method thereof

Abstract

The invention provides a high-temperature-resistant magnesia-carbon composite refractory brick and a preparation method thereof, and belongs to the technical field of magnesium oxide refractory wall bricks, the refractory brick comprises the following raw materials: double-layer modified magnesium oxide, modified crystalline flake graphite, zircon powder, modified liquid phenolic resin and a benzoxazine cross-linking agent; the double-layer modified magnesium oxide is obtained by firstly coating magnesium oxide with powder phenolic resin, aluminum oxide and zirconium oxide and then coating magnesium oxide with asphalt, micron magnesium oxide, zirconium oxide and calcium oxide; the modified crystalline flake graphite is obtained by coating crystalline flake graphite with strontium hydroxide, asphalt and boron carbide; the modified liquid phenolic resin is formed by mixing liquid phenolic resin with a silane coupling agent and a polyacrylate cross-linked polymer. Double-layer modified magnesium oxide, modified crystalline flake graphite and modified liquid phenolic resin are prepared by adopting special components and a method and are matched with zircon powder and a benzoxazine cross-linking agent for use, and a reasonable forming and sintering process is designed, so that the refractory brick has good high-temperature stability, oxidation resistance, thermal shock resistance and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium oxide refractory wall bricks, and in particular relates to a high temperature resistant magnesium carbon composite refractory brick and a preparation method thereof. Background Art

[0002] With the rapid development of high-temperature industries such as steel and non-ferrous metal smelting, traditional refractory materials are gradually unable to meet the increasingly stringent use conditions. In the process of steel smelting, steelmaking equipment such as converters and electric furnaces need to withstand high temperatures of more than 1600°C, and at the same time they must withstand strong erosion from molten steel and slag, as well as mechanical scouring and thermal shock. For example, the high-alumina bricks and clay bricks used in the early days, although they have certain refractory properties, have poor erosion resistance and thermal shock resistance at high temperatures, and have a short service life. Frequent replacement not only affects production efficiency, but also increases a lot of manpower and material costs.

[0003] In order to solve these problems, researchers began to explore the research and development of new refractory materials. Magnesium oxide materials have become one of the research focuses due to their high melting point (the melting point of magnesium oxide is about 2800℃), good chemical stability and resistance to alkaline slag erosion. However, pure magnesium refractory materials have poor thermal shock resistance and are prone to cracking and peeling when the temperature changes sharply. At the same time, carbon materials have high thermal conductivity, low expansion coefficient and good thermal shock resistance, but their oxidation resistance is insufficient and they are easily oxidized in high-temperature oxygen environments. Based on the respective advantages and disadvantages of magnesium materials and carbon materials, the idea of ​​combining the two to prepare magnesium-carbon composite refractory bricks came into being. Through reasonable formula design and preparation process, magnesium materials and carbon materials form a complementary structure in the brick body, giving full play to the high refractoriness and corrosion resistance of magnesium materials and the thermal shock resistance of carbon materials.

[0004] With the continuous advancement of steel smelting technology, such as the widespread application of new processes such as refining outside the furnace and continuous casting, higher requirements are placed on the performance of magnesium-carbon composite refractory bricks. On the one hand, magnesium-carbon bricks are required to have lower porosity and higher density to improve their corrosion resistance and permeability resistance; on the other hand, their antioxidant properties need to be further enhanced to extend their service life. To this end, various antioxidants are added. However, improper use of various additive components and improper preparation processes will still affect the high-temperature stability, oxidation resistance, thermal shock resistance and other properties of refractory bricks. Therefore, in order to meet the needs of high-performance and high-quality use, it is also necessary to continuously develop magnesium-carbon brick products with better balance of various properties. Summary of the invention

[0005] In order to further balance and improve the high temperature stability, oxidation resistance, thermal shock resistance and other indicators of magnesium carbon bricks, the present invention provides a high temperature resistant magnesium carbon composite refractory brick and its preparation method, adopts special components and methods to prepare double-layer modified magnesium oxide, modified flake graphite and modified liquid phenolic resin, and then uses them in combination with zircon powder and benzoxazine crosslinking agent in a specific proportion, designs reasonable molding and sintering processes, and prepares refractory bricks with good high temperature stability, oxidation resistance and thermal shock resistance, etc., effectively improving the refractory service life of magnesium carbon bricks. Its specific technical scheme is as follows: A high-temperature resistant magnesium-carbon composite refractory brick, the refractory brick comprises the following raw materials in parts by mass: 65-75 parts of double-layer modified magnesium oxide, 15-18 parts of modified flake graphite, 0.5-2 parts of zircon powder, 5-7 parts of modified liquid phenolic resin, and 0.5-1 part of benzoxazine crosslinking agent; the double-layer modified magnesium oxide is magnesium oxide firstly coated with powdered phenolic resin, aluminum oxide and zirconium oxide, and then coated with asphalt, micron magnesium oxide, zirconium oxide and calcium oxide; the modified flake graphite is flake graphite coated with strontium hydroxide, asphalt and boron carbide; the modified liquid phenolic resin is liquid phenolic resin mixed with silane coupling agent and polyacrylate crosslinking polymer.

[0006] Furthermore, the preparation method of the double-layer modified magnesium oxide includes the following steps: according to the mass ratio, magnesium oxide: thermosetting powder phenolic resin: aluminum oxide: zirconium oxide = 100: (4-6): (4-6): (2-4), adding the thermosetting powder phenolic resin to the magnesium oxide and mixing evenly, then adding aluminum oxide and zirconium oxide and mixing evenly, sintering at 500°C to 600°C without oxygen for 1h to 2h, breaking up, and obtaining a layer of modified magnesium oxide; according to the mass ratio, a layer of modified magnesium oxide: asphalt: micron magnesium oxide: zirconium oxide: calcium oxide = 100: (5-8): (2-3): (4-6): (2-3), adding asphalt to a layer of modified magnesium oxide and mixing evenly, then adding micron magnesium oxide, zirconium oxide and calcium oxide and mixing evenly, sintering at 400°C to 500°C without oxygen for 1h to 2h, breaking up, and obtaining a double-layer modified magnesium oxide.

[0007] Furthermore, the magnesium oxide is capacitor magnesium sand; the particle size distribution mass percentage of the magnesium oxide is: the particle size between 3mm and 5mm accounts for 25 to 35 parts, the particle size between 1mm and 3mm accounts for 35 to 45 parts, the particle size between 0.5mm and 1mm accounts for 30 to 40 parts, and the particle size less than 0.5mm accounts for 10 to 15 parts.

[0008] Furthermore, the aluminum oxide and zirconium oxide are premixed uniformly before being added; and the micronized magnesium oxide, zirconium oxide and calcium oxide are premixed uniformly before being added.

[0009] Furthermore, the median particle size of the thermosetting powder phenolic resin is less than 5 μm; the asphalt is medium-temperature modified asphalt, the median particle size of the asphalt is less than 5 μm, the asphalt contains 2wt% to 5wt% zinc phenolsulfonate, and the median particle size of the zinc phenolsulfonate is less than 5 μm; the micron magnesium oxide is capacitor magnesium sand with a median particle size of less than 5 μm; the median particle sizes of the aluminum oxide, zirconium oxide and calcium oxide are all less than 5 μm.

[0010] Furthermore, the preparation method of the modified flake graphite includes the following steps: according to the mass ratio, flake graphite: asphalt: boron carbide: strontium hydroxide = 100: (4-6): (3-5): (1-2), first adding strontium hydroxide to the flake graphite and mixing evenly, then adding asphalt and mixing evenly, and finally adding boron carbide and mixing evenly, sintering at 800°C to 900°C in the absence of oxygen for 1h to 2h, breaking up, and obtaining modified flake graphite.

[0011] Furthermore, the median particle size of the flake graphite is 10 μm to 30 μm; the asphalt is medium-temperature modified asphalt, and the median particle size of the asphalt is less than 5 μm; the median particle sizes of the strontium hydroxide and boron carbide are both less than 3 μm.

[0012] Furthermore, the modified liquid phenolic resin contains 4wt% to 6wt% of silane coupling agent KH-560 and 1.5wt% to 3wt% of polyacrylate cross-linked polymer in the liquid phenolic resin; the liquid phenolic resin is a thermosetting phenolic resin; and the median particle size of the zircon powder is 10μm to 50μm.

[0013] The preparation method of the above-mentioned high-temperature resistant magnesium-carbon composite refractory brick comprises the following steps: mixing double-layer modified magnesium oxide, modified flake graphite and zircon powder evenly according to mass fractions to obtain a mixed powder; mixing modified liquid phenolic resin and benzoxazine crosslinking agent evenly, and then adding them into the mixed powder and mixing evenly to obtain a mixture; filling the mixture into a mold, pressing and molding to obtain a brick blank; sintering the brick blank at 250°C to 300°C in the absence of oxygen for 8h to 10h, then heating to 600°C to 800°C in the absence of oxygen for 4h to 5h, then heating to 1300°C to 1400°C in the absence of oxygen for 2h to 2.5h, cooling to obtain a refractory brick.

[0014] Furthermore, the die pressure of the pressing is 240 MPa to 260 MPa, and the heating rate is 4° C. / min to 6° C. / min.

[0015] The present invention provides a high temperature resistant magnesium carbon composite refractory brick and a preparation method thereof, and the beneficial effects are as follows: 1. Preparation of double-layer modified magnesium oxide: premix alumina and zirconia, then mix with thermosetting powder phenolic resin and magnesium oxide and sinter without oxygen. Alumina and zirconia can improve the high temperature stability and corrosion resistance of magnesium oxide. Thermosetting powder phenolic resin forms a carbon skeleton during the sintering process to enhance the bonding strength of the material. Based on a layer of modified magnesium oxide, asphalt, micron magnesium oxide, zirconium oxide and calcium oxide are added and sintered again without oxygen. Asphalt further improves the density and bonding of the material, micron magnesium oxide can fill pores and increase density, zirconium oxide continues to enhance high temperature performance, and calcium oxide helps improve the slag resistance of the material.

[0016] Among them, the thermosetting powder phenolic resin is first added to the magnesium oxide for mixing, which is conducive to the phenolic resin to evenly wrap the magnesium oxide particles. In the subsequent sintering process, the carbon skeleton formed by the phenolic resin can better combine with the magnesium oxide, thereby enhancing the overall structural strength of the material. Alumina and zirconium oxide are then added for mixing, so that they are evenly distributed between the magnesium oxide particles that have been wrapped by the phenolic resin, giving full play to the role of alumina and zirconium oxide in improving the high temperature stability and corrosion resistance of magnesium oxide, while avoiding the agglomeration of alumina and zirconium oxide, ensuring that the components play a synergistic effect in the system.

[0017] Among them, first adding asphalt to a layer of modified magnesium oxide and mixing it can make the asphalt evenly penetrate into the pores and surface of the modified magnesium oxide layer. During the subsequent sintering, the carbonaceous structure formed by the carbonization of the asphalt can effectively fill the pores and improve the density and bonding of the material. Then add micron magnesium oxide, zirconium oxide and calcium oxide. These substances can further fill the tiny pores on the basis of a layer of modified magnesium oxide wrapped in asphalt, improve the density, while zirconium oxide continues to enhance the high temperature performance, and calcium oxide improves the slag resistance. This order is conducive to the full contact and reaction of each component, forming a uniform microstructure and exerting the best modification effect.

[0018] Asphalt contains zinc phenolsulfonate, which can react with certain components in asphalt or decompose at high temperature to produce some active substances, promote the combination of components, connect them more tightly, reduce pores, enhance the structural stability of refractory bricks, and withstand greater pressure. During the oxygen-free sintering process, it can catalyze the carbonization reaction of organic matter such as asphalt, promote the formation of a more stable carbon structure, improve the high temperature resistance of refractory bricks, and improve high temperature bending resistance. It makes the internal structure of refractory bricks uniform and tightly combined, and can better resist the effects of thermal stress when the temperature changes sharply, reduce the generation and expansion of cracks, and improve thermal shock stability. The stable and tight structure can reduce the contact between oxygen and internal components and slow down the oxidation rate.

[0019] 2. Preparation of modified flake graphite: Strontium hydroxide is added to flake graphite. Strontium hydroxide reacts with some groups on the surface of flake graphite to improve its surface properties, increase its binding force with other components, and generate a composite protective layer of strontium oxide and other phases. Asphalt is added. During the sintering process, the asphalt is carbonized to form a carbonaceous network, which enhances the structural stability and oxidation resistance of flake graphite. The addition of boron carbide can improve the hardness and wear resistance of modified flake graphite, and at the same time, it synergizes with other components at high temperatures to further improve the performance of the material.

[0020] Among them, strontium hydroxide is first added to the flake graphite and mixed, so that strontium hydroxide can fully react with the surface of the flake graphite, improve the surface properties of the flake graphite, increase its surface active sites, and improve the binding force with subsequent added components. Then asphalt is added and mixed evenly. The asphalt can better spread and adhere on the surface of the flake graphite treated with strontium hydroxide, form a uniform carbonaceous network during the sintering process, and enhance the structural stability and oxidation resistance of the flake graphite. Finally, boron carbide is added to make it evenly distributed in the system formed by flake graphite and asphalt, play a role in improving hardness and wear resistance, and at the same time avoid boron carbide being over-wrapped by other ingredients due to premature addition during the mixing process, affecting its full performance.

[0021] 3. In the modified liquid phenolic resin, silane coupling agent can form chemical bonds between inorganic materials such as magnesium oxide and flake graphite and phenolic resin, improve the interface bonding force, and thus enhance the overall performance of refractory bricks. Polyacrylate cross-linked polymer can increase the cross-linking density of phenolic resin, enhance the mechanical properties and heat resistance of the resin, and also promote the fusion of materials, improve uniformity and density, and make refractory bricks more stable at high temperatures.

[0022] 4. Zircon powder has high melting point, high hardness and good chemical stability. It can fill the pores of magnesium-carbon composite refractory bricks, improve the density of the bricks, enhance the corrosion resistance and permeability resistance, and can exist stably at high temperatures, which helps to maintain the structural stability of the bricks.

[0023] 5. Benzoxazine crosslinking agent can undergo crosslinking reaction with phenolic resin to form a three-dimensional network structure, thereby improving the crosslinking degree and heat resistance of the resin, thereby enhancing the strength and high-temperature stability of the refractory bricks, enabling them to better withstand high temperatures and mechanical stress.

[0024] 6. Polyacrylate cross-linked polymer makes the resin matrix more compact by increasing the cross-linking density of phenolic resin. Benzoxazine cross-linking agent forms a stable three-dimensional network structure with phenolic resin. The synergistic effect of the two further improves the heat resistance, mechanical properties and stability of phenolic resin, enables refractory bricks to maintain good structural integrity and performance at high temperatures, and improves its oxidation resistance, thermal shock resistance and other indicators.

[0025] 7. After the refractory bricks are pressed and formed, the gradient temperature sintering is to allow the material to fully complete physical and chemical changes at different temperature stages, gradually remove moisture and organic matter, and promote crystal growth and densification.

[0026] In summary, the double-layer modified magnesium oxide undergoes multi-layer modification treatment, and the thermosetting powder phenolic resin, aluminum oxide, zirconium oxide, micron magnesium oxide, calcium oxide and other additives are sintered to form a tight and complex composite structure with magnesium oxide, which can effectively disperse stress. When heated, the additives in the double-layer modified magnesium oxide can stabilize the crystal structure, inhibit the abnormal growth of magnesium oxide crystals, and enhance the grain boundary bonding force. The multi-layer structure of the double-layer modified magnesium oxide can buffer thermal stress. When the temperature changes sharply, the thermal expansion differences of each layer of material can compensate each other and reduce internal stress concentration. Some components in the double-layer modified magnesium oxide can form a dense protective film on the surface to prevent oxygen from diffusing inward. The additives in the magnesium oxide modification process fill the pores between the magnesium oxide particles and promote the densification of the material during the sintering process. During the modification process of the asphalt, boron carbide, strontium hydroxide and other additives in the modified flake graphite, the asphalt is carbonized at high temperature to form a bonding phase, which enhances the bonding force between the flake graphite and other raw materials; boron carbide improves the hardness and oxidation resistance of the material; strontium hydroxide can participate in the reaction to form a composite protective layer of strontium oxide and other phases. The polyacrylate cross-linked polymer can undergo a cross-linking reaction with the liquid phenolic resin to form a more dense and stable three-dimensional network structure, which enhances the bonding effect of the resin on other raw materials. The polyacrylate cross-linked polymer also has the function of promoting material fusion and improving uniformity and density. The benzoxazine cross-linking agent can promote the cross-linking reaction of the phenolic resin, increase the cross-linking density, and enhance the curing degree and stability of the material. The refractory bricks of the present invention are simple and feasible to produce, have excellent performance, and have good practical value. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific implementation cases, but the present invention is not limited to these embodiments.

[0028] Example 1

[0029] A high temperature resistant magnesium carbon composite refractory brick, the refractory brick comprises the following raw materials by weight: 70 parts of double-layer modified magnesium oxide, 16 parts of modified flake graphite, 1.2 parts of zircon powder, 6 parts of modified liquid phenolic resin, and 0.8 parts of benzoxazine crosslinking agent. The modified liquid phenolic resin is a liquid phenolic resin containing 5wt% of silane coupling agent KH-560 and 2.2wt% of polyacrylate crosslinking polymer; the median particle size of the zircon powder is 24μm.

[0030] The preparation method of a double-layer modified magnesium oxide comprises the following steps: according to the mass ratio, magnesium oxide: thermosetting powder phenolic resin: aluminum oxide: zirconium oxide = 100:5:5:3, aluminum oxide and zirconium oxide are premixed evenly, thermosetting powder phenolic resin is added to magnesium oxide and mixed evenly, then aluminum oxide and zirconium oxide are added and mixed evenly, the temperature is increased to 550°C at a heating rate of 5°C / min, oxygen-free sintering is performed for 1.5 hours, and a layer of modified magnesium oxide is obtained; according to the mass ratio, a layer of modified magnesium oxide: asphalt: micron magnesium oxide: zirconium oxide: calcium oxide = 100:6:2.5:5:2.5, micron magnesium oxide, zirconium oxide and calcium oxide are premixed evenly, asphalt containing 3wt% zinc phenolsulfonate is added to a layer of modified magnesium oxide and mixed evenly, then micron magnesium oxide, zirconium oxide and calcium oxide are added and mixed evenly, the temperature is increased to 450°C at a heating rate of 5°C / min, oxygen-free sintering is performed for 1.5 hours, and a double-layer modified magnesium oxide is obtained.

[0031] Among them, the magnesium oxide is capacitor magnesium sand; the particle size grading mass shares of the magnesium oxide are: 30 parts of the particle size between 3mm and 5mm, 40 parts of the particle size between 1mm and 3mm, 35 parts of the particle size between 0.5mm and 1mm, and 12 parts of the particle size less than 0.5mm.

[0032] The preparation method of modified flake graphite includes the following steps: according to the mass ratio, flake graphite: asphalt: boron carbide: strontium hydroxide = 100:5:4:1.5, first adding strontium hydroxide to flake graphite with a median particle size of 10 μm and mixing evenly, then adding asphalt and mixing evenly, and finally adding boron carbide and mixing evenly, heating to 850°C at a heating rate of 5°C / min, sintering in an oxygen-free environment for 1.5 hours, breaking up, and obtaining modified flake graphite.

[0033] The preparation method of the above-mentioned high-temperature resistant magnesium-carbon composite refractory brick comprises the following steps: mixing double-layer modified magnesium oxide, modified flake graphite and zircon powder evenly according to mass fractions to obtain a mixed powder; mixing modified liquid phenolic resin and benzoxazine crosslinking agent evenly, and then adding them to the mixed powder and mixing evenly to obtain a mixture; filling the mixture into a mold, pressing and molding it with a die head pressure of 250 MPa to obtain a brick blank; sintering the brick blank at 280°C for 9 hours, then heating it to 700°C for 4.5 hours at a heating rate of 5°C / min, and then heating it to 1350°C for 2 hours at a heating rate of 5°C / min, and then cooling it to obtain a refractory brick.

[0034] Example 2

[0035] A high temperature resistant magnesium carbon composite refractory brick, the refractory brick comprises the following raw materials by weight: 65 parts of double-layer modified magnesium oxide, 15 parts of modified flake graphite, 0.5 parts of zircon powder, 5 parts of modified liquid phenolic resin, and 0.5 parts of benzoxazine crosslinking agent. The modified liquid phenolic resin is a liquid phenolic resin containing 4wt% of silane coupling agent KH-560 and 1.5wt% of polyacrylate crosslinking polymer; the median particle size of the zircon powder is 50μm.

[0036] The preparation method of a double-layer modified magnesium oxide comprises the following steps: according to the mass ratio, magnesium oxide: thermosetting powder phenolic resin: aluminum oxide: zirconium oxide = 100:4:4:2, aluminum oxide and zirconium oxide are premixed evenly, thermosetting powder phenolic resin is added to magnesium oxide and mixed evenly, then aluminum oxide and zirconium oxide are added and mixed evenly, the temperature is increased to 500°C at a heating rate of 4°C / min, oxygen-free sintering is performed for 1 hour, and a layer of modified magnesium oxide is obtained; according to the mass ratio, a layer of modified magnesium oxide: asphalt: micron magnesium oxide: zirconium oxide: calcium oxide = 100:5:2:4:2, micron magnesium oxide, zirconium oxide and calcium oxide are premixed evenly, asphalt containing 2wt% zinc phenolsulfonate is added to a layer of modified magnesium oxide and mixed evenly, then micron magnesium oxide, zirconium oxide and calcium oxide are added and mixed evenly, the temperature is increased to 400°C at a heating rate of 4°C / min, oxygen-free sintering is performed for 1 hour, and a double-layer modified magnesium oxide is obtained.

[0037] Among them, the magnesium oxide is capacitor magnesium sand; the particle size grading mass percentage of the magnesium oxide is: the particle size between 3mm and 5mm accounts for 25 parts, the particle size between 1mm and 3mm accounts for 35 parts, the particle size between 0.5mm and 1mm accounts for 30 parts, and the particle size less than 0.5mm accounts for 10 parts.

[0038] The preparation method of modified flake graphite includes the following steps: according to the mass ratio, flake graphite: asphalt: boron carbide: strontium hydroxide = 100:4:3:1, first adding strontium hydroxide to flake graphite with a median particle size of 22 μm and mixing evenly, then adding asphalt and mixing evenly, and finally adding boron carbide and mixing evenly, heating to 800°C at a heating rate of 4°C / min, sintering in an oxygen-free environment for 1 hour, breaking up, and obtaining modified flake graphite.

[0039] The preparation method of the above-mentioned high-temperature resistant magnesium-carbon composite refractory brick comprises the following steps: mixing double-layer modified magnesium oxide, modified flake graphite and zircon powder evenly according to mass fractions to obtain a mixed powder; mixing modified liquid phenolic resin and benzoxazine crosslinking agent evenly, and then adding them to the mixed powder and mixing evenly to obtain a mixture; filling the mixture into a mold, pressing and molding it with a die head pressure of 240 MPa to obtain a brick blank; sintering the brick blank at 250°C for 8 hours, then heating it to 600°C for 4 hours at a heating rate of 4°C / min, then heating it to 1300°C for 2 hours at a heating rate of 4°C / min, cooling it, and obtaining a refractory brick.

[0040] Example 3

[0041] A high temperature resistant magnesium carbon composite refractory brick, the refractory brick comprises the following raw materials by weight: 75 parts of double-layer modified magnesium oxide, 18 parts of modified flake graphite, 2 parts of zircon powder, 7 parts of modified liquid phenolic resin, and 1 part of benzoxazine crosslinking agent. The modified liquid phenolic resin is a liquid phenolic resin containing 6wt% of silane coupling agent KH-560 and 3wt% of polyacrylate crosslinking polymer; the median particle size of the zircon powder is 10μm.

[0042] The preparation method of a double-layer modified magnesium oxide comprises the following steps: according to the mass ratio, magnesium oxide: thermosetting powder phenolic resin: aluminum oxide: zirconium oxide = 100:6:6:4, aluminum oxide and zirconium oxide are premixed evenly, thermosetting powder phenolic resin is added to magnesium oxide and mixed evenly, then aluminum oxide and zirconium oxide are added and mixed evenly, the temperature is increased to 600°C at a heating rate of 6°C / min, oxygen-free sintering is performed for 2 hours, and a layer of modified magnesium oxide is obtained; according to the mass ratio, a layer of modified magnesium oxide: asphalt: micron magnesium oxide: zirconium oxide: calcium oxide = 100:8:3:6:3, micron magnesium oxide, zirconium oxide and calcium oxide are premixed evenly, asphalt containing 5wt% zinc phenolsulfonate is added to a layer of modified magnesium oxide and mixed evenly, then micron magnesium oxide, zirconium oxide and calcium oxide are added and mixed evenly, the temperature is increased to 500°C at a heating rate of 6°C / min, oxygen-free sintering is performed for 2 hours, and a double-layer modified magnesium oxide is obtained.

[0043] Among them, the magnesium oxide is capacitor magnesium sand; the particle size distribution of the magnesium oxide is as follows: the particle size between 3mm and 5mm accounts for 35 parts, the particle size between 1mm and 3mm accounts for 45 parts, the particle size between 0.5mm and 1mm accounts for 40 parts, and the particle size less than 0.5mm accounts for 15 parts.

[0044] The preparation method of modified flake graphite includes the following steps: according to the mass ratio, flake graphite: asphalt: boron carbide: strontium hydroxide = 100:6:5:2, first adding strontium hydroxide to flake graphite with a median particle size of 30 μm and mixing evenly, then adding asphalt and mixing evenly, and finally adding boron carbide and mixing evenly, heating to 900°C at a heating rate of 6°C / min, sintering in an oxygen-free environment for 2 hours, and breaking up to obtain modified flake graphite.

[0045] The preparation method of the above-mentioned high-temperature resistant magnesium-carbon composite refractory brick comprises the following steps: mixing double-layer modified magnesium oxide, modified flake graphite and zircon powder evenly according to mass fractions to obtain a mixed powder; mixing modified liquid phenolic resin and benzoxazine crosslinking agent evenly, and then adding them to the mixed powder and mixing evenly to obtain a mixture; filling the mixture into a mold, pressing and molding it with a die head pressure of 260 MPa to obtain a brick blank; sintering the brick blank at 300°C for 10 hours, then heating it to 800°C for 5 hours at a heating rate of 6°C / min, then heating it to 1400°C for 2.5 hours at a heating rate of 6°C / min, cooling it, and obtaining a refractory brick.

[0046] The raw materials used in the above-mentioned Examples 1 to 3 are as follows: the liquid phenolic resin is a thermosetting phenolic resin, which is sourced from Jinan Dahui Chemical Technology Co., Ltd., model 8022. The median particle size of the thermosetting powder phenolic resin is less than 5 μm, and the thermosetting powder phenolic resin is sourced from Henan Jinrun New Materials Co., Ltd., model JR2123. The asphalt is a medium-temperature modified asphalt, and the median particle size of the asphalt after crushing is less than 5 μm. The medium-temperature modified asphalt is sourced from Jining Chaolian New Materials Technology Co., Ltd., number 34066350. The median particle size of zinc phenolsulfonate after crushing is less than 5 μm, and zinc phenolsulfonate is sourced from Zhongshan Yuanda New Materials Co., Ltd. Micronized magnesium oxide is a capacitor magnesium sand with a median particle size of 3.2 μm. The median particle size of aluminum oxide is 2.8 μm. The median particle size of zirconium oxide is 4.5 μm. The median particle size of calcium oxide is 3.7 μm. The median particle size of strontium hydroxide is 1.4 μm. The median particle size of boron carbide is 2.6 μm. Silane coupling agent KH-560 comes from Dongguan Shanyi Plastic Co., Ltd., model KH560. Polyacrylate cross-linked polymer is polyacrylate cross-linked polymer-6, which comes from Guangzhou Luyuan Chemical Co., Ltd. Benzoxazine cross-linking agent is allylphenol type benzoxazine resin, which comes from Shandong Jiaying Chemical Technology Co., Ltd., model JH-2102. Zircon powder (zirconium silicate) comes from Shijiazhuang Qiadian New Material Technology Co., Ltd.

[0047] Comparative Example 1 In the raw materials of refractory bricks, the double-layer modified magnesium oxide is replaced by magnesium oxide; other methods and parameters are the same as those in Example 1.

[0048] Comparative Example 2 In the refractory brick raw material, the double-layer modified magnesium oxide is not subjected to second-layer modification; other methods and parameters are the same as those in Example 1.

[0049] Comparative Example 3 In the refractory brick raw material, the double-layer modified magnesium oxide is not subjected to first-layer modification; other methods and parameters are the same as those in Example 1.

[0050] Comparative Example 4 In the preparation method of double-layer modified magnesium oxide, the thermosetting powder phenolic resin of one layer of modified magnesium oxide is replaced by asphalt; other methods and parameters are the same as those in Example 1.

[0051] Comparative Example 5 In the preparation method of double-layer modified magnesium oxide, zinc phenolsulfonate is not added to the asphalt; other methods and parameters are the same as in Example 1.

[0052] Comparative Example 6 In the raw materials of refractory bricks, modified flake graphite is replaced by flake graphite; other methods and parameters are the same as those in Example 1.

[0053] Comparative Example 7 In the method for preparing modified flake graphite, no strontium hydroxide is added; other methods and parameters are the same as in Example 1.

[0054] Comparative Example 8 In the method for preparing modified flake graphite, no boron carbide is added; other methods and parameters are the same as in Example 1.

[0055] Comparative Example 9 No polyacrylate cross-linked polymer is added to the modified liquid phenolic resin; other methods and parameters are the same as in Example 1.

[0056] Comparative Example 10 No benzoxazine crosslinking agent is added to the raw materials for refractory bricks, and the mass fraction of the benzoxazine crosslinking agent is replaced by liquid phenolic resin; other methods and parameters are the same as those in Example 1.

[0057] Comparative Example 11 Meanwhile, no polyacrylate cross-linked polymer and benzoxazine cross-linking agent were added, and the mass fraction of benzoxazine cross-linking agent was replaced by liquid phenolic resin; other methods and parameters were the same as those in Example 1.

[0058] Comparative Example 12 In the preparation method of refractory bricks, no gradient temperature increase sintering is performed, and the temperature is directly increased from room temperature to 1350° C. at a heating rate of 5° C. / min and sintered in the absence of oxygen for 2 h; other methods and parameters are the same as in Example 1.

[0059] 1. Sample specifications A cubic specimen with a processing size of 50mm×50mm×50mm is used for the room temperature compressive strength test.

[0060] Rectangular specimens with a processing size of 150 mm × 25 mm × 25 mm were used for high-temperature flexural strength testing.

[0061] Standard brick samples with a processing size of 230 mm × 114 mm × 65 mm were used for thermal shock stability, oxidation resistance, bulk density and apparent porosity tests.

[0062] 2. Testing Items and Methods 1. Normal temperature compressive strength: Place the cube specimen at the center of the loading platform of the universal material testing machine, apply pressure until the specimen is broken, record the breaking load, and calculate the normal temperature compressive strength. The results are shown in Table 1 below.

[0063] 2. High temperature flexural strength (1400℃): Place the rectangular specimen on the flexural fixture in the high temperature furnace of the high temperature flexural testing machine, heat it to 1400℃ at a rate of 10℃ / min, keep it warm for 30 minutes, apply a bending load, record the load when the specimen breaks, and calculate the high temperature flexural strength. The results are shown in Table 1 below.

[0064] 3. Thermal shock stability: Place the brick sample in a high temperature furnace, heat it to 1400℃ at a rate of 15℃ / min, keep it warm for 30 minutes, then quickly take it out and put it in a water tank for rapid cooling for 3 minutes, then take it out and dry it. Repeat this process until the brick sample has a through crack or the amount of peeling exceeds 5%, and record the number of thermal shocks. The results are shown in Table 1 below.

[0065] 4. Antioxidation: First weigh the initial mass of the brick sample m 0 , put it into a high temperature furnace and keep it at 1400℃ in air atmosphere for 10h, take it out and cool it to room temperature, then weigh the mass m 1 ; Calculate the oxidation weight loss rate. The results are shown in Table 1 below.

[0066] 5. Bulk density: Weigh the mass of the dry brick sample m d , put it in water and boil it for 5 hours, take it out and wipe the surface moisture with a wet cloth, then weigh the saturated surface dry mass m s , using the displacement method to measure the mass of the water displaced m w =m s -m d , calculate the volume V of the water displaced (water density is 1g / cm³); calculate the volume density of the brick sample ρ=m d / V. The results are shown in Table 1 below.

[0067] 6. Apparent porosity: First use a true density meter to measure the true density ρt of the brick sample, and then combine it with the measured bulk density ρ to calculate the apparent porosity P=(1-ρ / ρt)×100%. The results are shown in Table 1 below.

[0068] Table 1 Project test results

[0069] It can be seen from the above results that the refractory bricks of Examples 1 to 3 have good high temperature stability, oxidation resistance and thermal shock resistance. The double-layer modified magnesium oxide is subjected to multi-layer modification treatment, and the thermosetting powder phenolic resin, aluminum oxide, zirconium oxide and micron magnesium oxide, calcium oxide and other additives are sintered to form a tight and complex composite structure with magnesium oxide, which can effectively disperse stress. When heated, the additives in the double-layer modified magnesium oxide can stabilize the crystal structure, inhibit the abnormal growth of magnesium oxide crystals, and enhance the grain boundary bonding force. The multi-layer structure of the double-layer modified magnesium oxide can buffer thermal stress. When the temperature changes sharply, the thermal expansion differences of each layer of material can compensate each other and reduce internal stress concentration. Some components (zirconia, etc.) in the double-layer modified magnesium oxide can form a dense protective film on the surface to prevent oxygen from diffusing inward. The additives in the magnesium oxide modification process fill the pores between the magnesium oxide particles and promote the densification of the material during the sintering process. Zinc phenolsulfonate can react with certain components in asphalt, or decompose at high temperature to produce some active substances, promote the combination of components, connect them more tightly, reduce pores, enhance the structural stability of refractory bricks, and be able to withstand greater pressure. In the process of oxygen-free sintering, it can catalyze the carbonization reaction of organic matter such as asphalt, promote the formation of a more stable carbon structure, improve the high temperature resistance of refractory bricks, and improve high temperature bending resistance. Make the internal structure of refractory bricks uniform and tightly combined, and when the temperature changes sharply, it can better resist the effect of thermal stress, reduce the generation and expansion of cracks, and improve thermal shock stability. The stable and tight structure can reduce the contact between oxygen and internal components and slow down the oxidation rate.

[0070] During the modification process of modified flake graphite, additives such as asphalt, boron carbide and strontium hydroxide are used. The asphalt is carbonized at high temperature to form a bonding phase, which enhances the bonding force between flake graphite and other raw materials; boron carbide improves the hardness and oxidation resistance of the material; strontium hydroxide participates in the reaction to form a composite protective layer of strontium oxide and other phases.

[0071] Polyacrylate cross-linked polymers can cross-link with liquid phenolic resins to form a more compact and stable three-dimensional network structure, enhancing the bonding effect of the resin on other raw materials. Polyacrylate cross-linked polymers can also promote material fusion and improve uniformity and density. Benzoxazine cross-linking agents can promote the cross-linking reaction of phenolic resins, increase cross-linking density, and enhance the curing degree and stability of materials.

[0072] Comparative Example 1 replaces the double-layer modified magnesium oxide with magnesium oxide. The magnesium oxide has not been modified, the crystal structure is single, and the strengthening and toughening effect brought by the composite structure is lacking. The bonding force between ordinary magnesium oxide crystals is relatively weak. When subjected to pressure, the crystals are prone to relative slip and dislocation, and cannot effectively resist external forces like the modified structure. Ordinary magnesium oxide has obvious grain boundary weakening at high temperatures, and the crystals are prone to slip and rupture, and the high-temperature stability is poor. Ordinary magnesium oxide has a single thermal expansion coefficient, and there is no barrier and buffering of modified substances. During the thermal shock process, the stress cannot be effectively released, and the thermal shock stability is poor. In terms of oxidation resistance, the refractory brick component of ordinary magnesium oxide has poor bonding, and oxygen is easy to diffuse inward, affecting the overall oxidation resistance. During the preparation process of ordinary magnesium oxide, the particles are not tightly stacked, there are many internal pores, and the loose structure makes the volume density low and the apparent porosity high.

[0073] In comparative example 2, the modified magnesium oxide is not subjected to the second layer of modification, and the protective layer capacity is reduced. The additives such as micron magnesium oxide, zirconium oxide and calcium oxide in the second layer of modification further fill the pores of the modified layer, refine the grains, and form stronger bonding bridges between the particles. Without the second layer of modification, there are more large pores and weak interfaces inside the material. When subjected to force, these defects are prone to stress concentration, leading to the initiation and expansion of cracks. Without the refined structure and stress buffering mechanism formed by the second layer of modification, the material cannot efficiently disperse and absorb thermal stress during thermal shock. The dense structure formed by the second layer of modification can block the penetration of oxygen. Without this layer of protection, oxygen can more easily diffuse into the interior of the brick. Due to the lack of filling and densification of the second layer of modified additives, the pores inside the material increase.

[0074] The modified magnesium oxide in Comparative Example 3 is not subjected to the first layer of modification. The thermosetting powder phenolic resin in the first layer of modification is carbonized to form a carbon skeleton during the sintering process, which enhances the bonding force between the magnesium oxide particles, while aluminum oxide and zirconium oxide improve the stability of the material through solid solution strengthening and other effects. Without the first layer of modification, the bonding between the magnesium oxide particles mainly relies on simple physical accumulation and a small amount of chemical bonding. Under the action of force and high temperature, relative displacement and separation are prone to occur between the particles. The structure formed by the first layer of modification helps to buffer thermal stress and block oxygen. The lack of it makes the material stress concentration phenomenon aggravated during thermal shock. The material microstructure is not uniform and dense enough, and oxygen can easily penetrate.

[0075] Comparative Example 4 replaces the thermosetting powder phenolic resin in a layer of modified magnesium oxide with asphalt. The chemical structure and performance of asphalt are different from those of thermosetting powder phenolic resin. The carbonization process of asphalt at high temperature is relatively complicated, and the carbon structure formed is not as stable and uniform as the carbon skeleton formed after the carbonization of thermosetting powder phenolic resin, and the bonding and strengthening effect on magnesium oxide particles are relatively weak. When subjected to stress or heat, the bonding between particles is easily destroyed. The structure formed after the carbonization of thermosetting powder phenolic resin has a certain barrier effect on oxygen. The decomposition and volatilization behavior of asphalt in the sintering process are different from those of thermosetting powder phenolic resin, resulting in changes in the internal pore structure of the material.

[0076] In comparative example 5, zinc phenolsulfonate is missing from the asphalt. The structural stability and density of the asphalt after sintering are relatively poor, and it is easy to be damaged and peeled off during the mixing and pressing process, and various properties are deteriorated.

[0077] Comparative Example 6 replaces modified flake graphite with flake graphite. The unmodified flake graphite is not tightly bonded to other components and is easy to fall off when subjected to stress. In a high-temperature oxygen environment, unmodified flake graphite is easily oxidized, which reduces the overall oxidation resistance of the material. The synergistic effect between flake graphite and other materials is weakened during thermal shock. The bonding state of unmodified flake graphite and other raw materials affects the overall structure of the material, and the apparent porosity increases.

[0078] In the preparation method of modified flake graphite in Comparative Example 7, strontium hydroxide is not added. Strontium hydroxide reacts chemically with other components during the modification process to generate some compounds with protective effects, and improves the interface bonding between flake graphite and other additives. Without the addition of strontium hydroxide, this protective and interface optimization effect is lost, which affects the overall performance degradation.

[0079] In the preparation method of modified flake graphite in Comparative Example 8, boron carbide is not added. Boron carbide has high hardness and good oxidation resistance. In the modified flake graphite, it can enhance the hardness of the material and improve its ability to resist external forces, while inhibiting the oxidation of flake graphite at high temperatures. The absence of boron carbide destroys the performance balance of the modified flake graphite, causing the material to decline in mechanical properties and oxidation resistance to varying degrees.

[0080] In the modified liquid phenolic resin of Comparative Example 9, no polyacrylate cross-linked polymer is added. The network structure of the phenolic resin after curing is not perfect, the bonding force is relatively weak, and the synergy between the components inside the material is weakened when subjected to force. The lack of polyacrylate cross-linked polymer makes the structure of the bonding phase not tight enough, the fusion of each material is reduced, the uniformity and compactness are affected, and the overall performance of the material is affected.

[0081] In comparative example 10, no benzoxazine crosslinking agent is added to the raw materials of refractory bricks. After the benzoxazine crosslinking agent is replaced by liquid phenolic resin, the degree of crosslinking reaction is reduced, the network structure inside the material is not strong enough, and the structure is easily deformed and damaged under stress and high temperature environment. The lack of benzoxazine crosslinking agent destroys the originally designed crosslinking system, thereby affecting the various properties of the material.

[0082] Comparative Example 11 does not add polyacrylate crosslinking polymer and benzoxazine crosslinking agent at the same time. The crosslinking reaction of phenolic resin is greatly restricted and cannot form an ideal three-dimensional network structure. The bonding force between the components inside the material is greatly weakened, and the resistance of the material drops sharply under stress, thermal shock and oxidation environment. The overall performance balance of the material is completely broken, and various properties are seriously affected.

[0083] In the preparation method of refractory bricks in Comparative Example 12, gradient temperature rise sintering is not performed. Gradient temperature rise sintering is to allow the material to fully complete physical and chemical changes at different temperature stages, gradually remove moisture and organic matter, and promote crystal growth and densification. Directly and quickly raising the temperature to high temperature for sintering, the moisture and organic matter inside the material will not have time to be fully discharged, and a large number of pores and defects will be formed inside the material; at the same time, the reaction and diffusion between the components are uneven, resulting in stress concentration in the internal structure of the material. Direct temperature rise sintering leads to a chaotic internal structure of the material, uneven pore distribution, and imperfect crystal development, which seriously affects the performance of the material.

Claims

1. A high temperature resistant magnesium carbon composite refractory brick, characterized in that: The refractory bricks include the following raw materials in parts by mass: 65 to 75 parts of double-layer modified magnesium oxide, 15 to 18 parts of modified flake graphite, 0.5 to 2 parts of zircon powder, 5 to 7 parts of modified liquid phenolic resin, and 0.5 to 1 part of benzoxazine crosslinking agent; the double-layer modified magnesium oxide is magnesium oxide firstly coated with powdered phenolic resin, aluminum oxide and zirconium oxide, and then coated with asphalt, micron magnesium oxide, zirconium oxide and calcium oxide; the modified flake graphite is flake graphite coated with strontium hydroxide, asphalt and boron carbide; The modified liquid phenolic resin is a liquid phenolic resin mixed with a silane coupling agent and a polyacrylate cross-linked polymer.

2. A high temperature resistant magnesium carbon composite refractory brick according to claim 1, characterized in that: The preparation method of double-layer modified magnesium oxide comprises the following steps: according to the mass ratio, magnesium oxide: thermosetting powder phenolic resin: aluminum oxide: zirconium oxide = 100: (4-6): (4-6): (2-4), adding thermosetting powder phenolic resin to magnesium oxide and mixing evenly, then adding aluminum oxide and zirconium oxide and mixing evenly, sintering at 500-600°C without oxygen for 1h-2h, breaking up to obtain a layer of modified magnesium oxide; according to the mass ratio, one layer of modified magnesium oxide: asphalt: micron magnesium oxide: zirconium oxide: calcium oxide = 100: (5-8): (2-3): (4-6): (2-3), adding asphalt to a layer of modified magnesium oxide and mixing evenly, then adding micron magnesium oxide, zirconium oxide and calcium oxide and mixing evenly, sintering at 400-500°C without oxygen for 1h-2h, breaking up to obtain a double-layer modified magnesium oxide.

3. A high temperature resistant magnesium carbon composite refractory brick according to claim 2, characterized in that: The magnesium oxide is capacitor magnesium sand; the particle size distribution of the magnesium oxide has the following mass shares: the particle size between 3 mm and 5 mm accounts for 25 to 35 parts, the particle size between 1 mm and 3 mm accounts for 35 to 45 parts, the particle size between 0.5 mm and 1 mm accounts for 30 to 40 parts, and the particle size less than 0.5 mm accounts for 10 to 15 parts.

4. A high temperature resistant magnesium carbon composite refractory brick according to claim 2, characterized in that: The aluminum oxide and zirconium oxide are premixed uniformly before being added; the micron magnesium oxide, zirconium oxide and calcium oxide are premixed uniformly before being added.

5. The high temperature resistant magnesium carbon composite refractory brick according to claim 2, characterized in that: The median particle size of the thermosetting powder phenolic resin is less than 5 μm; the asphalt is medium-temperature modified asphalt, and the median particle size of the asphalt is less than 5 μm; the asphalt contains 2wt% to 5wt% zinc phenolsulfonate, and the median particle size of the zinc phenolsulfonate is less than 5 μm; the micron magnesium oxide is capacitor magnesium sand with a median particle size of less than 5 μm; the median particle sizes of the aluminum oxide, zirconium oxide and calcium oxide are all less than 5 μm.

6. The high temperature resistant magnesium carbon composite refractory brick according to claim 1, characterized in that: The preparation method of the modified flake graphite comprises the following steps: according to the mass ratio of flake graphite: asphalt: boron carbide: strontium hydroxide = 100: (4-6): (3-5): (1-2), firstly adding strontium hydroxide to the flake graphite and mixing evenly, then adding asphalt and mixing evenly, and finally adding boron carbide and mixing evenly, sintering at 800° C. to 900° C. in the absence of oxygen for 1 h to 2 h, breaking up, and obtaining the modified flake graphite.

7. A high temperature resistant magnesium carbon composite refractory brick according to claim 6, characterized in that: The median particle size of the flake graphite is 10 μm to 30 μm; the asphalt is medium-temperature modified asphalt, and the median particle size of the asphalt is less than 5 μm; the median particle sizes of the strontium hydroxide and boron carbide are both less than 3 μm.

8. The high temperature resistant magnesium carbon composite refractory brick according to claim 1, characterized in that: The modified liquid phenolic resin contains 4wt% to 6wt% of silane coupling agent KH-560 and 1.5wt% to 3wt% of polyacrylate cross-linked polymer in the liquid phenolic resin; the liquid phenolic resin is a thermosetting phenolic resin; and the median particle size of the zircon powder is 10μm to 50μm.

9. A method for preparing the high temperature resistant magnesium carbon composite refractory brick according to claim 1, characterized in that: The method comprises the following steps: uniformly mixing double-layer modified magnesium oxide, modified flake graphite and zircon powder according to mass fractions to obtain mixed powder; uniformly mixing modified liquid phenolic resin and benzoxazine crosslinking agent, and then adding them into the mixed powder and mixing them uniformly to obtain a mixture; filling the mixture into a mold, pressing and molding to obtain a brick blank; sintering the brick blank at 250°C to 300°C in the absence of oxygen for 8h to 10h, then heating to 600°C to 800°C in the absence of oxygen for 4h to 5h, then heating to 1300°C to 1400°C in the absence of oxygen for 2h to 2.5h, cooling to obtain a refractory brick.

10. The method for preparing a high temperature resistant magnesium carbon composite refractory brick according to claim 9, characterized in that: The die pressure of the pressing is 240MPa-260MPa, and the heating rate is 4°C / min-6°C / min.

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