A low-carbon magnesia-carbon brick and its preparation method

Abstract

This invention discloses a low-carbon magnesia-carbon brick and its preparation method. The low-carbon magnesia-carbon brick is composed of the following components in parts by weight: 40-50 parts by weight of resin-impregnated magnesia aggregate, 45-55 parts by weight of unimpregnated magnesia, 2-4 parts by weight of graphite, 0.5-2.0 parts by weight of nano-carbon black, 1-3 parts by weight of composite antioxidant, and 2.5-4.0 parts by weight of phenolic resin. The preparation method is as follows: unimpregnated magnesia fine powder, nano-carbon black, and composite antioxidant are mixed to obtain mixed raw material A. The resin-impregnated magnesia aggregate, unimpregnated magnesia aggregate, phenolic resin, graphite, and mixed raw material A are added to a mixer in sequence, mixed, pressed into shape, and finally heat-treated. The low-carbon magnesia-carbon brick of this invention significantly improves the thermal shock stability and slag erosion resistance of the material while effectively reducing the carbon content.

Description

Technical Field

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

[0002] Magnesia-carbon bricks are typically composed of magnesia, graphite, antioxidants, and binders. They possess excellent high-temperature resistance, slag erosion resistance, and thermal shock stability, and are widely used as linings in converters, electric furnaces, refining furnaces, and slag lines in steel ladles. Currently, high-carbon-content (12-20 wt%) magnesia-carbon bricks are commonly used in applications with demanding operating conditions. This is because graphite's poor slag wettability, high thermal conductivity, and low coefficient of thermal expansion ensure the performance of magnesia-carbon bricks. With the increasing proportion of low-carbon and ultra-clean steel being smelted, the carbon content in magnesia-carbon bricks must be strictly controlled to avoid affecting the steel composition due to increased carbon content. However, high-carbon-content magnesia-carbon bricks can also lead to accelerated high-temperature oxidation, increased heat loss, and waste of high-quality graphite resources. Simply reducing the graphite content in magnesia-carbon bricks, however, can lead to a sharp deterioration in material properties, especially thermal shock stability and slag erosion resistance. Therefore, how to maintain the excellent thermal shock stability and slag erosion resistance of magnesia-carbon bricks while reducing carbon content is a key research issue.

[0003] To address the aforementioned issues, refractory material researchers have undertaken a series of initiatives: 1) Introducing micro / nano-scale carbon sources, which possess high specific area and can construct continuous carbon network structures with relatively lower carbon content, but suffer from problems such as difficulty in uniform dispersion and high-temperature oxidation; 2) Adding special additives, namely, introducing a second phase with low thermal expansion coefficient and excellent slag erosion resistance, but the cost of the additives used in this method is high and the improvement effect is limited; 3) Controlling the microstructure of the matrix, namely, controlling the in-situ generation of ceramic phases through methods such as introducing catalysts and special atmosphere heat treatment, but suffers from drawbacks such as complex processes, high costs, and poor controllability.

[0004] Magnesia accounts for over 80% of magnesia-carbon bricks, and its high coefficient of thermal expansion and poor slag penetration resistance are significant factors limiting the performance improvement of low-carbon magnesia-carbon bricks. Chinese patent document (CN 108101514) discloses a low-carbon magnesia-carbon brick and its preparation method using magnesia impregnated with tar and pitch as aggregate. The prepared low-carbon magnesia-carbon brick exhibits good thermal shock stability and slag erosion resistance. However, this patent uses tar and pitch as impregnation raw materials, which typically contain toxic carcinogens (such as benzo[a]pyrene), potentially causing environmental and human harm during the preparation and hot-state use of the low-carbon magnesia-carbon brick. Furthermore, the tar and pitch impregnation process requires heat treatment to achieve uniform pitch dispersion, increasing the cost and complexity of the preparation process. In addition, the patent uses fused magnesia aggregate with low apparent porosity and smooth surface for impregnation. The effective space that can be filled by impregnation in the magnesia structure is small, which may result in a relatively low carbon adhesion rate. The patent also does not specify the carbon content of the magnesia aggregate after impregnation, which may limit the beneficial effect of impregnated magnesia on the performance of magnesia-carbon bricks. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to provide a low-carbon magnesia-carbon brick and its preparation method, so as to solve the technical problems mentioned in the background art, such as environmental pollution and complex process caused by the use of raw materials such as tar and asphalt in the preparation of low-carbon magnesia-carbon brick, as well as the technical problems such as the unsatisfactory performance and carbon content of the magnesia-carbon brick prepared therefrom.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] A low-carbon magnesia-carbon brick is composed of the following components in parts by weight: 40-50 parts by weight of resin-impregnated magnesia aggregate, 45-55 parts by weight of unimpregnated magnesia, 2-4 parts by weight of graphite, 0.5-2.0 parts by weight of nano carbon black, 1-3 parts by weight of composite antioxidant and 2.5-4.0 parts by weight of phenolic resin.

[0008] The aforementioned low-carbon magnesia-carbon bricks use resin-impregnated magnesia aggregate, which is made by impregnating magnesia with environmentally friendly resin. The unimpregnated magnesia aggregate uses the same magnesia as the resin-impregnated magnesia aggregate. The magnesia contains 30-50 parts by weight of magnesia with a particle size greater than 3mm and less than or equal to 5mm, and 60-70 parts by weight of magnesia with a particle size greater than 1mm and less than or equal to 3mm. Magnesia with a particle size in the 1-5mm range facilitates the formation of a uniform coating of environmentally friendly resin on the magnesia surface during subsequent impregnation. If the magnesia particles are too small, they may agglomerate during impregnation. Furthermore, controlling the ratio of 3-5mm and 1-3mm magnesia to (30-50):(60-70) helps to obtain the most densely packed magnesia-carbon bricks, thereby increasing the overall bulk density of the material.

[0009] The aforementioned low-carbon magnesia-carbon bricks have an apparent porosity of 10.0~12.0% and a density of 3.00~3.30 g / cm³. 3 The water absorption rate is 3.5~4.5%; the magnesia contains 95.5~96.5 wt% magnesium oxide, 0.3~0.4 wt% silicon dioxide, and 2.5~3.0 wt% calcium oxide, with the remainder being impurities. If the apparent porosity is less than 10%, there are insufficient effective channels for resin wetting, and the ideal impregnation effect cannot be achieved; if the apparent porosity is greater than 12%, the apparent porosity of the corresponding material will increase, which will weaken the strength, oxidation resistance, and slag erosion resistance of the magnesia-carbon bricks. Due to its high porosity, this type of magnesia, after being impregnated with environmentally friendly resin, can produce resin-impregnated magnesia aggregate with high thermal conductivity, which is beneficial for preparing magnesia-carbon bricks with high thermal shock resistance and slag erosion resistance. At the same time, due to the high calcium and low silicon characteristics of this magnesia, the final magnesia-carbon bricks are also beneficial for the purification of molten steel.

[0010] The aforementioned low-carbon magnesia-carbon bricks contain 3-5 wt% environmentally friendly resin in the resin-impregnated magnesia aggregate. This environmentally friendly resin is a thermoplastic phenolic resin with a room temperature viscosity of 3000-4000 mPa·s, a solid content of 70-80 wt%, and a free phenol content of less than or equal to 1 wt%. If the viscosity of the environmentally friendly resin used is higher than 4000 mPa·s, its fluidity is poor, making it difficult to fully impregnate the magnesia, or requiring heating or a longer vacuum treatment time to achieve the desired impregnation effect. If the viscosity of the environmentally friendly resin is lower than 3000 mPa·s, its adhesion and bonding properties are insufficient to firmly adhere to the magnesia aggregate, and it may detach during subsequent mixing, affecting its improvement effect. Free phenol reflects the degree of resin curing, and this indicator reflects resin stability. Low free phenol content indicates higher controllability of the resin preparation process, meaning the resin is more stable. Furthermore, low free phenol content is more environmentally friendly; excessive free phenol content can cause volatiles to be released during the drying or hot-state use of the magnesia-carbon bricks.

[0011] The aforementioned low-carbon magnesium-carbon bricks use environmentally friendly resin produced by Tongcheng New Materials Co., Ltd., with the model number RA-L3101.

[0012] The aforementioned low-carbon magnesia-carbon bricks are composed of unimpregnated magnesia aggregate with a particle size greater than 0.2 mm and less than or equal to 1 mm, and unimpregnated magnesia fine powder with a particle size less than or equal to 0.2 mm. The unimpregnated magnesia aggregate accounts for 45-55 wt% of the total unimpregnated magnesia. Both the unimpregnated magnesia aggregate and the unimpregnated magnesia fine powder are magnesia. By using unimpregnated magnesia with a particle size less than or equal to 1 mm and controlling the ratio of magnesia aggregate with a particle size of 0.2-1 mm to magnesia fine powder with a particle size less than or equal to 0.2 mm, the smaller particles in the unimpregnated magnesia can fill the pores and gaps between the larger particles of the aggregate as much as possible. This allows the unimpregnated magnesia to be combined with the aforementioned resin-impregnated magnesia in a specific proportion to prepare magnesia-carbon bricks with close packing, few pores and gaps, high bulk density, and stable quality.

[0013] The aforementioned low-carbon magnesia-carbon bricks use flake graphite that has passed through a 100-mesh sieve and has a carbon content greater than or equal to 95 wt%. If the graphite particle size is greater than 100 mesh, the dispersibility will not reach an ideal state, making it difficult to form a stable carbon network structure inside the magnesia-carbon bricks. The nano-carbon black has a particle size of 20~800 nm and a carbon content greater than or equal to 99 wt%. Nano-carbon black within this particle size range has moderate dispersibility and can fully fill the micro-nano pores in the magnesia-carbon bricks. The composite antioxidant is a mixture of aluminum powder and boron carbide in a mass ratio of (6~10):1. The composite antioxidant passed through an 180-mesh sieve. The aluminum powder and boron carbide in this ratio work together to effectively improve the oxidation resistance of magnesia-carbon bricks at low, medium, and high temperatures. Furthermore, the aluminum powder can generate spinel in situ in the magnesia-carbon bricks, causing volume expansion, which effectively offsets the adverse effects of the liquid phase caused by the antioxidant effect of boron carbide. The phenolic resin is a thermosetting phenolic resin with a residual carbon content greater than or equal to 36 wt%, a room temperature viscosity of 16000~20000 mPa·s, and a moisture content less than or equal to 4 wt%.

[0014] A method for preparing low-carbon magnesia-carbon bricks includes the following steps:

[0015] Step (1): Prepare resin-impregnated magnesia aggregate using magnesia and environmentally friendly resin as raw materials;

[0016] Step (2): Mix the unimpregnated magnesia fine powder, nano carbon black and composite antioxidant thoroughly to obtain mixed raw material A; the purpose of preferential premixing is to utilize the interaction between fine powders to fully disperse nano carbon black; nano carbon black is at the nano level and is very easy to agglomerate. If it is directly mixed with resin-impregnated magnesia aggregate with larger particles, it will easily lead to agglomeration of nano carbon black and affect its dispersion uniformity.

[0017] Step (3): Add resin-impregnated magnesia aggregate, unimpregnated magnesia aggregate, phenolic resin and graphite to a mixer in sequence to obtain mixed raw material B. The phenolic resin must be added after the resin-impregnated magnesia aggregate and the unimpregnated magnesia aggregate to ensure that the large particles of aggregate are fully wetted by the phenolic resin, so that the graphite and fine powder in mixed raw material A can be fully adhered by the large particles of aggregate when added later. If the resin is added after the fine powder is added, it is easy for the fine powder to agglomerate and affect the overall uniformity of the material.

[0018] Step (4): Add mixed raw material A to mixed raw material B and continue mixing to obtain magnesia-carbon brick slurry;

[0019] Step (5): Press the magnesia-carbon brick slurry into shape to obtain a magnesia-carbon brick green body; heat treat the magnesia-carbon brick green body, and after the heat treatment is completed, the above-mentioned low-carbon magnesia-carbon brick is obtained.

[0020] The preparation method of the above-mentioned low-carbon magnesia-carbon bricks, the preparation method of resin-impregnated magnesia aggregate in step (1) is as follows: place magnesia in an impregnation device and vacuum for 20-30 minutes; then add environmentally friendly resin to the impregnation device, pressurize 1-8 MPa, hold the pressure for 25-35 minutes and then release the pressure to obtain resin-impregnated magnesia aggregate; the mass ratio of magnesia to environmentally friendly resin is 1:1.2-1.6;

[0021] Alternatively, the preparation method of resin-impregnated magnesia aggregate in step (1) is as follows: first, activate and calcine magnesia at 400~500℃ for 1~2h to obtain activated magnesia for impregnation; then place the activated magnesia for impregnation in an impregnation device and vacuum for 20~30min; next, add silane coupling agent to the impregnation device, pressurize 1~5MPa and hold for 5~10min, the amount of silane coupling agent is 0.5~1.0wt% of the mass of the activated magnesia for impregnation; finally, add environmentally friendly resin to the impregnation device, pressurize 5~8MPa and hold for 25~35min and then depressurize to obtain resin-impregnated magnesia aggregate; the mass ratio of the activated magnesia for impregnation to the environmentally friendly resin is 1:1.2~1.6. Thermal activation of magnesia at 400~500℃ can remove water and impurities from the magnesia pores, making the magnesia particles looser and increasing the porosity, which is conducive to the entry of silane coupling agents into the magnesia pores and opens up hydrophobic channels for the impregnation of environmentally friendly resins into magnesia.

[0022] In the above-mentioned method for preparing low-carbon magnesia-carbon bricks, in step (5): the pressing pressure is 150~200MPa, and the holding time is 10~20s; the heat treatment conditions are: 180~220℃ for 8~24h; if the heat treatment temperature is higher than 220℃, it will destroy the cross-linked structure formed by resin curing, and may even cause slight oxidation of graphite, ultimately leading to an increase in apparent porosity, a decrease in bulk density and a decrease in strength of the magnesia-carbon brick; however, if the heat treatment temperature is lower than 180℃, it will lead to incomplete resin curing and unsatisfactory strength of the magnesia-carbon brick; in addition, if the heat treatment time is less than 8h, the resin curing will be insufficient and the resulting cross-linked structure will be unstable; if the treatment time is greater than 24h, not only will energy consumption increase and production efficiency decrease, but it may also weaken the cross-linked structure formed by resin curing. The carbon network structure; the mixing time in step (2) is 10~20min, and the rotation speed is 2500~3000r / min; the mixing time in step (3) is 15~25min; the mixing time in step (4) is 5~15min, and the mixing speed in steps (3) and (4) is 700~900r / min; high speed mixing is used in step (2), while medium and low speed mixing is used in steps (3) and (4). This is because steps (3) and (4) contain large-diameter aggregates. If a mixing speed greater than 900r / min is used, the large-diameter aggregates will be broken, thus affecting the particle size distribution, and even causing the environmentally friendly resin layer of impregnated magnesia to peel off. If the mixing speed in step (2) is less than 2500r / min, the nano carbon black will be difficult to disperse evenly and affect the mixing effect.

[0023] The technical solution of the present invention achieves the following beneficial technical effects:

[0024] 1. The low-carbon magnesia-carbon brick of this invention is environmentally friendly, has excellent thermal shock stability and slag erosion resistance. While effectively reducing the carbon content (total carbon content can be reduced to below 5%), it significantly improves the comprehensive performance of the material and has good practical application effects.

[0025] 2. This invention uses environmentally friendly low-viscosity resin as the impregnation material for magnesia to prepare resin-impregnated magnesia aggregate. Compared with impregnation materials such as tar and asphalt, it is more environmentally friendly, effectively reducing pollution to the environment. Moreover, it does not require heat treatment and the process is simple and efficient. High-purity magnesia aggregate with high porosity is used for impregnation. Its high surface roughness effectively improves the wettability of low-viscosity resin to magnesia. The large number of pores provides an effective channel for low-viscosity resin to enter the interior of high-purity magnesia structure, which can significantly shorten the impregnation time and improve the carbon adhesion rate after vacuum impregnation.

[0026] 3. This invention achieves uniform dispersion of carbon on the surface of magnesia aggregate by controlling the particle size distribution of magnesia, the viscosity of environmentally friendly low-viscosity resin, and using vacuum treatment. This helps to build a stable carbon network structure in the magnesia aggregate structure and solves the problem of uneven dispersion caused by directly introducing nano carbon sources into the matrix in the traditional method.

[0027] 4. After impregnation, the interior of the magnesia aggregate is filled with resin. After high-temperature heat treatment, the resin decomposes and carbonizes, forming a micron-level gap between the magnesia aggregate and the matrix boundary. This reduces structural damage caused by the expansion of magnesia when subjected to thermal shock. Furthermore, the special structure after carbonization can effectively absorb the thermal stress in the structure, thereby effectively improving the thermal shock stability of low-carbon magnesia-carbon bricks.

[0028] 5. After impregnation treatment, most of the open pores and cracks of the magnesia are filled by resin, which effectively reduces the penetration channels of molten slag into the interior of the magnesia structure, thereby improving the slag erosion resistance and permeability of the magnesia-carbon brick. Attached Figure Description

[0029] Figure 1 Macroscopic image of the resin-impregnated magnesia aggregate obtained in Example 1 of this invention;

[0030] Figure 2 Cross-sectional image of the resin-impregnated magnesia aggregate obtained in Example 1 of this invention;

[0031] Figure 3 Scanning electron microscope image of resin-impregnated magnesia aggregate obtained in Example 1 of this invention. Detailed Implementation

[0032] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.

[0033] Example 1

[0034] The preparation method of low-carbon magnesia-carbon bricks in this embodiment includes the following steps:

[0035] Step (1): Prepare resin-impregnated magnesia aggregate using magnesia and environmentally friendly resin as raw materials. The specific method is as follows: place magnesia in an impregnation device and vacuum for 20 minutes; then add environmentally friendly resin to the impregnation device, pressurize to 5 MPa, hold for 25 minutes, and then release the pressure to obtain resin-impregnated magnesia aggregate. During vacuum impregnation, the mass ratio of magnesia to environmentally friendly resin is 2:3 (at this ratio, the volume of environmentally friendly resin during impregnation is 3 to 4 times that of magnesia, which can achieve sufficient impregnation); after vacuum impregnation, most of the pores in the magnesia are filled by low-viscosity resin, and the apparent porosity of the resin-impregnated magnesia aggregate is reduced to 3.0%, and the carbon content is 2.5 wt% and the magnesium oxide content is 95 wt%; the content of environmentally friendly resin in the resin-impregnated magnesia aggregate prepared in this embodiment is 3.5 wt%.

[0036] In this embodiment, the magnesia is made by mixing high-purity magnesia with a particle size greater than 3 mm and less than or equal to 5 mm and high-purity magnesia with a particle size greater than 1 mm and less than or equal to 3 mm in a mass ratio of 3:7; the magnesia used for impregnation has a large number of pores and a rough surface, which can provide an effective channel for resin penetration.

[0037] The apparent porosity of all the magnesia used in this embodiment was 10.2%, and the density was 3.25 g / cm³. 3 The water absorption rate is 3.0%; the magnesium oxide content in the magnesia is 96.5 wt%, the silicon dioxide content is 0.4 wt%, the calcium oxide content is 2.6 wt%, and the remainder is impurities;

[0038] The environmentally friendly resin is produced by Tongcheng New Materials Co., Ltd., and its model is RA-LA3101. Its room temperature viscosity is 3200 mPa·s, solid content is 80 wt%, and free phenol content is 0.5 wt%. This environmentally friendly resin is environmentally friendly and has the advantages of good wettability and low viscosity at room temperature, which is beneficial to improving the impregnation effect.

[0039] Step (2): Mix 286 kg of unimpregnated magnesia fine powder (magnesia with a particle size less than or equal to 0.2 mm), 10 kg of nano carbon black (grade N990, particle size 100~700 nm, and carbon content equal to 99.5 wt%) and 15 kg of composite antioxidant (obtained by mixing aluminum powder and boron carbide in a mass ratio of 8:1 and passing through a 180-mesh sieve) thoroughly for 12 min at a rotation speed of 2700 r / min to obtain mixed raw material A;

[0040] Step (3): 400 kg of resin-impregnated magnesia aggregate prepared in step (1), 234 kg of unimpregnated magnesia aggregate (magnesia with a particle size greater than 0.2 mm and less than or equal to 1 mm), 30 kg of phenolic resin (thermosetting phenolic resin with a residual carbon content of 38 wt%, a room temperature viscosity of 18000 mPa·s, and a moisture content of 4 wt%), and 25 kg of flake graphite (passed through a 100-mesh sieve and with a carbon content of 95 wt%) are added to a mixer in sequence and mixed for 20 min at a speed of 900 r / min to obtain mixed raw material B; the magnesia used in the unimpregnated magnesia fine powder and the unimpregnated magnesia aggregate is exactly the same as that used in the resin-impregnated magnesia aggregate.

[0041] Step (4): Add mixed raw material A to mixed raw material B and continue mixing for 5 minutes at a speed of 900 r / min to obtain magnesia-carbon brick mud.

[0042] Step (5): Press the magnesia-carbon brick slurry at 180 MPa for 15 seconds to obtain magnesia-carbon brick green; heat treat the magnesia-carbon brick green at 180℃ for 12 hours. After the heat treatment, low-carbon magnesia-carbon brick is obtained. The carbon content of the low-carbon magnesia-carbon brick is 4.3 wt%.

[0043] Examples 2-6

[0044] The raw material ratios for Examples 2-6 are shown in Table 1, and the remaining raw materials are the same as those for Example 1. The preparation process parameters for Examples 2-6 are shown in Table 2, and the remaining process steps and parameters are the same as those for Example 1.

[0045] Example 7

[0046] The only difference between this embodiment and embodiment 6 is that the preparation method of resin-impregnated magnesia aggregate in step (1) is different, while the other process steps, process parameters and raw material ratios are exactly the same as in embodiment 6.

[0047] The preparation method of resin-impregnated magnesia aggregate in this embodiment is as follows: First, magnesia is activated and calcined at 450℃ for 2 hours to obtain activated magnesia for impregnation; then, the activated magnesia for impregnation is placed in an impregnation device and vacuumed for 25 minutes; next, a silane coupling agent is added to the impregnation device, pressure is applied at 5 MPa and held for 8 minutes, the silane coupling agent is isobutyltriethoxysilane, and its amount is 1.0 wt% of the mass of the activated magnesia for impregnation; finally, environmentally friendly resin is added to the impregnation device, pressure is applied at 6 MPa and held for 25 minutes, and then the pressure is released to obtain resin-impregnated magnesia aggregate; the mass ratio of the activated magnesia for impregnation to the environmentally friendly resin is 2:3.

[0048] Table 1. Raw material ratio table for Examples 1 to 6

[0049]

[0050] Table 2. Preparation process parameters for each embodiment

[0051]

[0052] Comparative Example 1

[0053] The preparation method of the low-carbon magnesia-carbon brick in this comparative example includes the following steps:

[0054] Step (1): Mix 230 kg of magnesia fine powder (particle size less than or equal to 0.2 mm), 10 kg of nano carbon black (grade N774, particle size 40~100 nm, and carbon content equal to 99.6 wt%) and 25 kg of composite antioxidant (obtained by mixing aluminum powder and boron carbide in a mass ratio of 7:1 and passing through a 180 mesh sieve) thoroughly for 15 min at a rotation speed of 2800 r / min to obtain mixed raw material A;

[0055] Step (2): 450 kg of magnesia aggregate (made by mixing high-purity magnesia with a particle size greater than 3 mm and less than or equal to 5 mm and high-purity magnesia with a particle size greater than 1 mm and less than or equal to 3 mm in a mass ratio of 2:3), 25 kg of phenolic resin (thermosetting phenolic resin with a residual carbon content of 37 wt%, a room temperature viscosity of 19000 mPa·s, and a moisture content of 3.5 wt%) and 30 kg of flake graphite (passed through a 100-mesh sieve and with a carbon content of 97 wt%) are added to a mixer in sequence and mixed for 25 min at a speed of 800 r / min to obtain mixed raw material B;

[0056] Step (3): Add mixed raw material A to mixed raw material B and continue mixing for 10 minutes at a speed of 800 r / min to obtain magnesia-carbon brick mud.

[0057] Step (4): Press the magnesia-carbon brick slurry at 160 MPa for 10 seconds to obtain magnesia-carbon brick green; heat treat the magnesia-carbon brick green at 220℃ for 8 hours. After the heat treatment, low-carbon magnesia-carbon brick is obtained; the carbon content of the low-carbon magnesia-carbon brick is 4.5 wt%.

[0058] The test methods and standards for the magnesia-carbon bricks prepared using the above examples and comparative examples are as follows: The percentage content of phenol, a harmful component, in the volatile organic compounds of magnesia-carbon bricks was determined according to national standard GB / T23985-2009; the high-temperature flexural strength of magnesia-carbon bricks was determined using the three-point bending method (1400℃ for 0.5h, carbon-embedded atmosphere) according to national standard GB / T3002-2017; the slag resistance of magnesia-carbon bricks was determined using the static crucible method (1600℃ air atmosphere treatment for 3h) according to national standard GB / T8931-2007; and the thermal shock stability of magnesia-carbon bricks was determined using the quenching method (1100℃ for 0.5h followed by water cooling, and calculation of residual strength retention rate) according to national standard GB / T30873-2014. A comparison of the corresponding performance indicators of different low-carbon magnesia-carbon bricks is shown in Table 3.

[0059] Table 3 Comparison of indicators between each embodiment and the comparative example

[0060]

[0061] As shown in Table 3, the low-carbon magnesia-carbon bricks prepared according to the various embodiments have significant advantages over those prepared in the comparative examples. Specifically, the phenol content in the volatile organic compounds of the prepared low-carbon magnesia-carbon bricks is less than 24%, the flexural strength at 1400℃ is higher than 11 MPa, the residual strength retention rate after holding at 1100℃ for 0.5 hours and water cooling once is more than 75%, and the slag erosion index is less than 11%. In particular, after improving the preparation method of resin-impregnated magnesia aggregate, the slag erosion index is significantly reduced. Therefore, the prepared low-carbon magnesia-carbon bricks are environmentally friendly and have excellent thermal shock stability and slag resistance.

[0062] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A low-carbon magnesia-carbon brick, characterized in that, It is composed of the following components in parts by weight: 40-50 parts by weight of resin-impregnated magnesia aggregate, 45-55 parts by weight of unimpregnated magnesia, 2-4 parts by weight of graphite, 0.5-2.0 parts by weight of nano carbon black, 1-3 parts by weight of composite antioxidant and 2.5-4.0 parts by weight of phenolic resin. Resin-impregnated magnesia aggregate is made by impregnating magnesia with environmentally friendly resin; the magnesia used in unimpregnated magnesia aggregate is the same as that used in resin-impregnated magnesia aggregate; in the magnesia: 30-50 parts by weight of magnesia with a particle size greater than 3mm and less than or equal to 5mm, and 60-70 parts by weight of magnesia with a particle size greater than 1mm and less than or equal to 3mm. Magnesia has an apparent porosity of 10.0–12.0% and a density of 3.00–3.30 g / cm³. 3 The water absorption rate is 3.5~4.5%; in magnesia: the content of magnesium oxide is 95.5~96.5wt%, the content of silicon dioxide is 0.3~0.4wt%, the content of calcium oxide is 2.5~3.0wt%, and the balance is impurities; The content of environmentally friendly resin in resin-impregnated magnesia aggregate is 3~5wt%; the environmentally friendly resin is thermoplastic phenolic resin with a room temperature viscosity of 3000~4000mPa·s, a solid content of 70~80wt%, and a free phenol content of less than or equal to 1wt%.

2. The low-carbon magnesia-carbon brick according to claim 1, characterized in that, The environmentally friendly resin is produced by Tongcheng New Materials Co., Ltd., and its model number is RA-L3101.

3. The low-carbon magnesia-carbon brick according to any one of claims 1-2, characterized in that, Unimpregnated magnesia consists of unimpregnated magnesia aggregate with a particle size greater than 0.2 mm and less than or equal to 1 mm and unimpregnated magnesia fine powder with a particle size less than or equal to 0.2 mm, and the unimpregnated magnesia aggregate accounts for 45~55 wt% of the total amount of unimpregnated magnesia; both the unimpregnated magnesia aggregate and the unimpregnated magnesia fine powder are magnesia.

4. The low-carbon magnesia-carbon brick according to any one of claims 1-2, characterized in that, The graphite is flake graphite, which passes through a 100-mesh sieve and has a carbon content greater than or equal to 95 wt%; the nano carbon black has a particle size of 20~800 nm and a carbon content greater than or equal to 99 wt%; the composite antioxidant is obtained by mixing aluminum powder and boron carbide in a mass ratio of (6~10):1 and passes through a 180-mesh sieve. The phenolic resin is a thermosetting phenolic resin with a residual carbon content greater than or equal to 36 wt%, a room temperature viscosity of 16,000~20,000 mPa·s, and a moisture content less than or equal to 4 wt%.

5. A method for preparing low-carbon magnesia-carbon bricks as described in claim 1, characterized in that, Includes the following steps: Step (1): Prepare resin-impregnated magnesia aggregate using magnesia and environmentally friendly resin as raw materials; Step (2): Thoroughly mix the unimpregnated magnesia fine powder, nano carbon black and composite antioxidant to obtain mixed raw material A; Step (3): Add resin-impregnated magnesia aggregate, unimpregnated magnesia aggregate, phenolic resin and graphite to a mixer in sequence and mix to obtain mixed raw material B; Step (4): Add mixed raw material A to mixed raw material B and continue mixing to obtain magnesia-carbon brick slurry; Step (5): Press the magnesia-carbon brick slurry at room temperature to obtain a magnesia-carbon brick green body; heat treat the magnesia-carbon brick green body, and after the heat treatment is completed, a low-carbon magnesia-carbon brick is obtained.

6. The method for preparing low-carbon magnesia-carbon bricks according to claim 5, characterized in that, The preparation method of resin-impregnated magnesia aggregate in step (1) is as follows: Magnesia is placed in an impregnation device and vacuumed for 20-30 minutes; then environmentally friendly resin is added to the impregnation device, pressure is applied at 1-8 MPa, pressure is maintained for 25-35 minutes and then pressure is released to obtain resin-impregnated magnesia aggregate; the mass ratio of magnesia to environmentally friendly resin is 1:1.2-1.6; Alternatively, the preparation method of resin-impregnated magnesia aggregate in step (1) is as follows: first, activate and calcine magnesia at 400~500℃ for 1~2h to obtain activated magnesia for impregnation; then place the activated magnesia for impregnation in an impregnation device and vacuum for 20~30min; next, add silane coupling agent to the impregnation device, pressurize 1~3MPa and hold for 5~10min, the amount of silane coupling agent is 0.5~1.0wt% of the mass of the activated magnesia for impregnation; finally, add environmentally friendly resin to the impregnation device, pressurize 5~8MPa and hold for 25~35min and then depressurize to obtain resin-impregnated magnesia aggregate; the mass ratio of the activated magnesia for impregnation to the environmentally friendly resin is 1:1.2~1.

6.

7. The method for preparing low-carbon magnesia-carbon bricks according to claim 5, characterized in that, In step (5): the pressing pressure is 150~200MPa and the holding time is 10~20s; the heat treatment conditions are: 180~220℃ heat treatment for 8~24h; the mixing time in step (2) is 10~20min and the rotation speed is 2500~3000r / min; the mixing time in step (3) is 15~25min; the mixing time in step (4) is 5~15min, and the rotation speed in steps (3) and (4) is 700~900r / min.

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