Magnesia carbon brick for bottom of stainless steel smelting steel ladle and preparation method of magnesia carbon brick

Abstract

The invention relates to the technical field of refractory materials, in particular to a magnesia carbon brick for the bottom of a stainless steel smelting ladle and a preparation method of the magnesia carbon brick. The method comprises the following steps: immersing graphite into an ethanol solution added with a silane coupling agent to obtain silane-coated graphite; magnesium oxide and an aluminum nitrate solution are subjected to ball milling and then mixed, the mixture is roasted, and magnesium oxide particles with the surfaces coated with MgAl2O4 are obtained; sequentially carrying out cold press molding on the inner layer material, the middle layer material and the outer layer material to obtain a raw material blank; and sintering the raw material blank at high temperature in stages, spraying silica sol to the surface of a sintered body, and curing at high temperature. Through the gradient structure, the outer spinel shell layer and the pre-activated glass cooperate to block slag permeation, the gradient pressing density of the middle layer is combined to buffer thermal stress, the high graphite and the carbon fibers of the inner layer are combined to enhance thermal shock resistance, the breakthrough of dynamic slag resistance is achieved, and a high-stability and low-cost refractory material solution is provided for high-temperature industry; and intensive and sustainable development of equipment is promoted.

Description

Technical Field

[0001] The present invention relates to the technical field of refractory materials, in particular to a magnesia carbon brick for the bottom of a stainless steel smelting ladle and a preparation method thereof. Background Art

[0002] In the steelmaking industry, magnesia-carbon bricks, as a key refractory material for ladle linings, play a crucial role in the cost, efficiency, and quality of molten steel production. Combining the high refractoriness of magnesia with the excellent thermal shock stability and corrosion resistance of carbon, magnesia-carbon bricks can, to a certain extent, meet the harsh working conditions of high temperatures and strong corrosion during steelmaking, ensuring the smooth operation of steel production.

[0003] However, with the continuous development of steel production technology, the performance requirements for ladle refractories are also increasing. In the actual dynamic slag-resistant environment during steelmaking, the molten steel and slag are in a state of continuous agitation. This dynamic environment causes the reaction layer products formed on the surface of the magnesia carbon bricks to be continuously drawn into the slag. At the same time, new reaction layers are constantly generated, forming a continuous dynamic process.

[0004] During this dynamic process, the slag can continuously penetrate into the interior of the magnesia-carbon brick material. The slag will preferentially penetrate the intergranular space of the primary crystal phase, periclase. This slag penetration behavior is extremely destructive. It not only destroys the original structure of the magnesia-carbon brick, significantly reducing its strength and stability, but also leads to a sharp increase in the erosion of the composite material.

[0005] The structural damage and increased corrosion of MgO-C bricks have a range of serious consequences. On the one hand, it shortens the service life of MgO-C bricks, requiring more frequent ladle lining replacements and increasing steel production costs. On the other hand, corroded MgO-C bricks release impurities into the molten steel, adversely affecting the stability of the molten steel and, in turn, the quality of the final steel product. Summary of the Invention

[0006] (1) Technical issues to be resolved

[0007] In view of the technical problem in the prior art, how to form a stable reaction layer in a dynamic anti-slag environment and effectively prevent the penetration of slag.

[0008] (2) Technical solution

[0009] To this end, the first aspect of the present invention provides a method for preparing magnesia carbon bricks for the bottom of a stainless steel smelting ladle, comprising:

[0010] Step 1: immersing graphite in an ethanol solution containing a silane coupling agent, performing ultrasonic treatment, and obtaining silane-coated graphite after drying;

[0011] Step 2: ball-milling magnesium oxide and aluminum nitrate solution, mixing the mixture, and calcining the mixture to obtain magnesium oxide particles coated with MgAl2O4;

[0012] Step 3: cold-pressing the inner layer material, the middle layer material, and the outer layer material containing different amounts of silane-coated graphite and magnesium oxide particles coated with MgAl2O4 in sequence to obtain a raw material blank;

[0013] Step 4: Sintering the raw material blank at high temperature in stages. First, keep the raw material blank at 1200-1300°C, and then sinter it at 1560-1600°C to obtain a sintered body.

[0014] Step 5: Spray the silica sol onto the surface of the sintered body and cure it at high temperature.

[0015] Furthermore, the outer layer material includes: 5% to 8% by weight of silane-coated graphite and 5% to 8% by weight of a phosphate binder, and the remainder is magnesium oxide particles coated with MgAl2O4;

[0016] The intermediate layer material includes: 10% to 15% by weight of silane-coated graphite and 3% to 5% by weight of a phosphate binder, with the remainder being magnesium oxide particles coated with MgAl2O4;

[0017] The inner layer material includes: 18% to 22% by weight of silane-coated graphite, 2% to 4% by weight of carbon fiber, 1% to 3% by weight of phosphate binder, and the remainder is magnesium oxide particles coated with MgAl2O4.

[0018] Furthermore, the cold isostatic pressing layered molding technology is adopted to reduce the pressure and density of the inner layer, outer layer and middle layer in sequence.

[0019] Furthermore, in step 3, the outer layer material has a pressing density of 3.15-3.25 g / cm 3 The pressing density of the middle layer material is 2.95-3.05g / cm 3 The inner layer material pressing density is 3.45-3.55g / cm 3 .

[0020] Further, in step 2, the mass ratio of magnesium oxide to aluminum nitrate solution is 100:(5-8), wherein the concentration of aluminum nitrate solution is 4-6 wt%;

[0021] The Al2O3 coating amount of the mixture after ball milling is 1.2-2.0% of the mass of magnesium oxide;

[0022] During the roasting process, the temperature is raised to 800±20℃ at a rate of 2-3℃ / min and kept at this temperature for 1.5-2 hours.

[0023] Furthermore, the silane coupling agent is epoxy-containing silane, the concentration of the ethanol solution is 18-22 wt %, the ultrasonic treatment temperature is 55-65° C., and the treatment time is 25-35 minutes;

[0024] The drying condition is vacuum drying at 80-100° C. until the moisture content is ≤0.5 wt %.

[0025] Furthermore, the phosphate binder in the outer layer material is modified aluminum phosphate, wherein the molar ratio of P2O5:Al2O3 is (1.8-2.2);

[0026] The phosphate binder in the intermediate layer material is a composite of aluminum dihydrogen phosphate and silica sol, wherein the mass ratio of the composite of aluminum dihydrogen phosphate and silica sol is (3-5):1.

[0027] Furthermore, the first stage sintering is carried out in a nitrogen atmosphere, heating to 1200-1300°C at 5-8°C / min and holding the temperature for 1.5-2 hours;

[0028] In the second stage, switch to argon atmosphere, increase the temperature to 1560-1600°C at 3-5°C / min, and keep it at this temperature for 45-75 minutes.

[0029] Furthermore, in step 5, the silica sol includes 2-3 wt% nano-TiO2, and after spraying, the temperature is raised to 950-1050°C at a rate of 10-15°C / min and cured for 8-12 minutes under the condition of a nitrogen flow rate of 2-5 L / min.

[0030] The second aspect of the present application mentions a magnesia-carbon brick for the bottom of a stainless steel smelting ladle, which is prepared using the preparation method of a magnesia-carbon brick for the bottom of a stainless steel smelting ladle as described in the first aspect above.

[0031] (3) Beneficial effects

[0032] The present invention relates to the technical field of refractory materials, and in particular to a magnesium carbon brick for the bottom of a stainless steel ladle and a preparation method thereof. The method comprises: immersing graphite in an ethanol solution containing a silane coupling agent, ultrasonically treating the brick, and drying the resulting silane-coated graphite; ball-milling magnesium oxide with an aluminum nitrate solution, mixing the mixture, and calcining the resulting mixture to obtain magnesium oxide particles coated with MgAl2O4; sequentially cold-pressing an inner layer material, an intermediate layer material, and an outer layer material containing different amounts of silane-coated graphite and magnesium oxide particles coated with MgAl2O4 to obtain a raw material blank; sintering the raw material blank at high temperature in stages, first maintaining the raw material blank at 1200°C-1300°C, and then sintering the raw material blank at 1560°C-1600°C to obtain a sintered body; and spraying silica sol onto the surface of the sintered body and curing the resulting body at high temperature.

[0033] This application achieves this through the synergistic effect of gradient structure design, interface chemical bonding, and dynamic surface regulation. The gradient structure uses the synergistic effect of the outer layer of active magnesium oxide and silane-modified graphite, using the spinel shell to limit the slag from directly contacting the matrix, and the glass phase generated by the pre-activation treatment preferentially consumes the alkaline components in the slag; the middle layer uses high-purity magnesium oxide as the skeleton, combined with the gradient pressing density design, to buffer thermal stress under high-temperature dynamic scouring and delay the expansion of the slag penetration path; the inner layer is reinforced with high graphite content and carbon fiber, and the high thermal conductivity and scouring resistance of graphite are used to maintain dynamic thermal shock stability. On this basis, the Si-OC / Al-O-Mg chemical bond network formed by the silane coupling agent between graphite and magnesium oxide strengthens the interfacial bonding strength between the gradient layers, inhibits high-temperature oxidation and mechanical peeling; the aluminum phosphate glass phase generated by the reaction of phosphate binder and spinel during staged sintering further fills the pores and optimizes the interlayer transition. At the same time, the surface SiO2-TiO2 gradient coating provides physical isolation through the low thermal expansion coefficient SiO2 layer, and leverages the photocatalytic activity of TiO2 to induce slag phase transformation, dynamically reducing slag viscosity and permeation driving force. This application achieves the adaptive formation of a stable reaction layer in a dynamic anti-slag environment, providing a long-life, highly reliable refractory material solution for high-temperature industrial equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a process flow chart of a method for preparing magnesia-carbon bricks for the bottom of a stainless steel smelting ladle mentioned in this application;

[0035] Figure 2 This is a comparison chart of the bulk density of samples of a method for preparing magnesia-carbon bricks for the bottom of a stainless steel smelting ladle mentioned in this application;

[0036] Figure 3 This is a comparison chart of the apparent porosity of samples obtained from a method for preparing magnesia-carbon bricks for the bottom of a stainless steel smelting ladle mentioned in this application;

[0037] Figure 4 This is a comparison chart of the room temperature compressive strength of samples obtained from a method for preparing magnesia carbon bricks for the bottom of a stainless steel smelting ladle mentioned in this application;

[0038] Figure 5 This is a comparison chart of the room temperature flexural strength of samples obtained from a method for preparing magnesia carbon bricks for the bottom of a stainless steel smelting ladle mentioned in this application;

[0039] Figure 6 This is a comparison chart of the high-temperature flexural strength of samples of a method for preparing magnesia-carbon bricks for the bottom of a stainless steel smelting ladle mentioned in this application. DETAILED DESCRIPTION

[0040] In order to better explain the present invention and facilitate understanding, the present invention is described in detail below through specific implementation methods in conjunction with the accompanying drawings.

[0041] When amount, concentration or other value or parameter are represented with range, preferred range or the range that a series of upper preferred value and lower preferred value limit are expressed, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value and any range lower limit or preferred value, and no matter whether this scope is disclosed separately.For example, when disclosing scope " 1-5 ", described scope should be interpreted as including scope " 1-4 ", " 1-3 ", " 1-2 ", " 1-2 and 4-5 ", " 1-3 and 5 " etc.When numerical range is described in this article, unless otherwise stated, otherwise this scope is intended to include its end value and all integers and fractions within this range.

[0042] In these embodiments, unless otherwise indicated, parts and percentages are by mass. "Parts by mass" refers to the basic unit of measurement representing the mass ratio relationship of multiple components, and 1 part can represent any unit mass, such as being expressed as 1g, or 3.527g, etc. If we say that the mass parts of component A are a parts and the mass parts of component B are b parts, then the ratio a:b of the mass of component A and the mass of component B is represented. Alternatively, the mass of component A is represented as aK and the mass of component B is represented as bK (K is an arbitrary number, representing a multiplication factor). It should not be misunderstood that, unlike parts by mass, the sum of the mass parts of all components is not limited to the limitation of 100 parts. "And / or" is used to represent that one or both of the situations described occur, for example, A and / or B include (A and B) and (A or B).

[0043] refer to Figure 1 The first aspect of the present application mentions a method for preparing magnesia carbon bricks for the bottom of a stainless steel smelting ladle, comprising:

[0044] Step 1: Immerse graphite in an ethanol solution containing a silane coupling agent, perform ultrasonic treatment, and obtain silane-coated graphite after drying; wherein the silane coupling agent is an epoxy-containing silane, illustratively, γ-glycidyloxypropyltrimethoxysilane; the concentration of the ethanol solution is 18-22 wt%; the ultrasonic treatment temperature is 55-65° C., and the treatment time is 25-35 minutes; the drying condition is vacuum drying at 80-100° C. to a moisture content of ≤0.5 wt%.

[0045] It should be noted that after the graphite is treated with a silane coupling agent, the silane coupling agent is hydrolyzed in an ethanol solution to form silanols, which dehydrate and condense with oxygen-containing groups on the graphite surface to form -Si-OC- covalent bonds, making the surface hydrophobic. At the same time, the epoxy group is retained at the other end, reserving active sites for subsequent reactions with the magnesium oxide matrix, thereby enhancing the physical anchoring effect between the graphite and the magnesium oxide matrix. Under high temperature conditions, it can effectively reduce the exfoliation of graphite, enhance the interfacial bonding between graphite and magnesium oxide, and inhibit the oxidation and escape of graphite at high temperatures, thereby avoiding the deterioration of the magnesia-carbon brick structure caused by graphite exfoliation, reducing the penetration rate of slag along the graphite-magnesia sand interface, and improving the stability of the overall structure of the magnesia-carbon brick.

[0046] At the same time, hydrophobic modification reduces the oxidation rate of graphite in a high-temperature oxidizing slag environment and maintains its thermal shock resistance.

[0047] Step 2: ball-milling magnesium oxide and aluminum nitrate solution, mixing them, and calcining the mixture to obtain magnesium oxide particles with MgAl2O4 coated on the surface.

[0048] It should be noted that fused magnesia with a purity of >97% can be used, the main component of which is periclase (MgO crystals), and the mass ratio of magnesium oxide to aluminum nitrate solution is 100:(5-8), to ensure that the Al2O3 generated after the decomposition of aluminum nitrate can completely react to form a single-layer spinel coating, thereby avoiding free Al2O3 residue.

[0049] It should be noted that the concentration of aluminum nitrate solution is 4-6wt%. When the concentration is lower than 4wt%, the content of aluminum nitrate in the solution is relatively small, which makes it difficult for the final Al2O3 coating to reach 1.2-2.0% of the mass of magnesium oxide, thus making the coating incomplete. Part of the magnesium oxide is directly exposed, and when it comes into contact with the slag later, the corrosive ions in the slag (such as Fe 2+ , Ca 2 + ) reacts with magnesium oxide, accelerating the erosion process of magnesium carbon bricks. When the concentration of aluminum nitrate solution is higher than 6wt%, the concentration of aluminum ions in the solution is too high. During ball milling and subsequent processing, the probability of aluminum ions colliding and agglomerating with each other increases, forming local aluminum ion enriched areas. During roasting, the enriched areas will react rapidly to generate larger alumina particles, resulting in local agglomeration. This will then destroy the uniformity of the surface coating of the magnesium oxide particles, form structural defects inside the magnesium carbon bricks, and reduce the overall performance of the material.

[0050] The Al2O3 coating content of the ball-milled mixture is controlled at 1.2-2.0% of the mass of the magnesium oxide. If the coating content is less than 1.2%, the spinel shell is too thin, and its adsorption and blocking effect on the corrosive ions in the slag is limited, and it cannot effectively protect the magnesium oxide core. If the coating content is higher than 2.0%, the spinel shell will be too thick, increasing the cost and affecting the internal structure and performance of the magnesium carbon brick.

[0051] During the calcination process, the temperature is raised to 800±20°C at a rate of 2-3°C / min to avoid the premature formation of amorphous Al2O3. The slow heating rate allows the aluminum nitrate to gradually decompose, generating active Al2O3. The active Al2O3 can better react with the surface MgO in a solid-phase reaction, forming a structurally stable and high-performance MgAl2O4 spinel shell. If the heating rate is too fast, the aluminum nitrate will quickly decompose, generating a large amount of amorphous Al2O2, which has poor reactivity and structural stability, making it unfavorable for the formation of a high-quality spinel shell.

[0052] It should be noted that Fe in the slag 2+ / Ca 2+ The ionic radius is similar to that of the cations in the spinel structure, allowing them to preferentially fill the cation vacancy defects in the MgAl2O4 spinel shell. This allows the corrosive ions in the slag to be fixed in the spinel shell, reducing the number and speed of their diffusion into the MgO core. Furthermore, the spinel shell itself has a high melting point and chemical stability, maintaining its structural integrity in high-temperature and slag environments, further resisting slag erosion. This effectively delays the slag's erosion of the MgO core and improves the slag resistance of the MgO-carbon brick.

[0053] It should be noted that after high-purity fused magnesia is mixed with aluminum nitrate solution, ball milled, and calcined, its surface is coated with nano-spinel (MgAl2O4). The spinel shell provides active sites for high-temperature reactions and limits the direct contact of slag with the core MgO, slowing the penetration of slag into the intergranular space of periclase, thereby improving the ability of magnesia-carbon bricks to resist slag erosion.

[0054] Step 3: cold-pressing the inner layer material, the middle layer material, and the outer layer material containing silane-coated graphite and magnesium oxide particles coated with MgAl2O4 in different amounts in sequence to obtain a raw material blank.

[0055] The outer layer material includes: silane-coated graphite accounting for 5% to 8% by weight and phosphate binder accounting for 5% to 8% by weight, and the balance is magnesium oxide particles coated with MgAl2O4.

[0056] It should be noted that the high phosphate binder content in the outer layer causes the phosphate to form a low-melting-point glass phase during sintering. At high temperatures, the glass phase exhibits excellent fluidity and can act like glue to fill the pores within the material, making the outer layer structure denser. This dense outer layer effectively blocks the intrusion of slag and, at the same time, reacts with alkaline components in the slag, such as CaO and SiO2, consuming these corrosive substances and protecting the inner layer.

[0057] Graphite easily oxidizes and flakes off at high temperatures. Reducing the graphite content can reduce this high-temperature flake phenomenon. At the same time, the outer layer preferentially reacts with the alkaline components in the slag to form high-melting-point calcite (Ca2Al2SiO7). This can adhere to the surface of the magnesia-carbon brick, further preventing slag erosion while consuming the alkaline substances in the slag, reducing the slag's corrosiveness.

[0058] The intermediate layer material includes: 10% to 15% by weight of silane-coated graphite and 3% to 5% by weight of a phosphate binder, and the remainder is magnesium oxide particles coated with MgAl2O4.

[0059] It should be noted that magnesium oxide particles coated with MgAl2O4 have a high melting point and good chemical stability, which can withstand high temperatures and slag corrosion. At the same time, it can also buffer thermal stress and avoid interlayer cracking caused by thermal stress concentration.

[0060] The pressing density is controlled at 3.0g / cm 3 , so that the middle layer has a certain elasticity, which can absorb the impact energy generated during the dynamic anti-slag process and protect the inner and outer layers from excessive impact force.

[0061] The inner layer material includes: 18% to 22% by weight of silane-coated graphite, 2% to 4% by weight of carbon fiber, 1% to 3% by weight of phosphate binder, and the remainder is magnesium oxide particles coated with MgAl2O4.

[0062] The high graphite content in the inner layer provides excellent lubricity and thermal shock resistance, while the carbon fibers create a three-dimensional network structure, enhancing the strength and toughness of the inner layer. The combined effect of these two improves the inner layer's erosion resistance, enabling the magnesia-carbon brick to maintain stable performance even in high-temperature, high-velocity slag erosion environments.

[0063] In this technical solution, the cold isostatic pressing layered molding technology is adopted, and the density is controlled by reducing the pressure in sequence according to the inner layer, outer layer and middle layer.

[0064] This application uses cold isostatic pressing layered molding technology, and the outer layer preferentially reacts with the slag to generate high-melting-point calcium aluminum feldspar (Ca2Al2SiO7) and glass phase, which can effectively consume the alkaline components in the slag and reduce the penetration driving force of the slag; the middle layer can buffer thermal stress and reduce structural damage caused by temperature changes; the inner layer contains highly dense graphite and short fiber reinforcement materials, which can maintain the thermal shock resistance of the magnesia carbon brick and avoid the failure of a single structure under dynamic erosion.

[0065] It should be noted that the outer layer material pressing density is 3.15-3.25g / cm 3 The pressing density of the middle layer material is 2.95-3.05g / cm 3 The inner layer material pressing density is 3.45-3.55g / cm 3 The outer layer has a relatively low density and a slightly higher thermal expansion coefficient, while the inner layer has a high density and a lower thermal expansion coefficient. During temperature increases or decreases, the layers will not generate excessive internal stress due to large thermal expansion differences, thus preventing interlayer delamination. This ensures the structural integrity and stability of the magnesia carbon brick in high-temperature, dynamic, and slag-resistant environments, extending its service life.

[0066] During the subsequent sintering process, the gradient structure forms a continuous transition structure through diffusion reaction, avoiding the problem of interface weakening between different layers. The outer layer preferentially consumes CaO in the slag, providing protection for the middle and inner layers, so that the layers cooperate with each other and work together to improve the performance of magnesia carbon bricks in dynamic slag resistance environment.

[0067] Step 4: Sintering the raw material blank at high temperature in stages. First, keep the raw material blank at 1200-1300°C, and then sinter it at 1560-1600°C to obtain a sintered body.

[0068] In this technical solution, the first stage of sintering is carried out in a nitrogen atmosphere, with the temperature raised at 5-8°C / min to 1200-1300°C and held at this temperature for 1.5-2 hours. The upper temperature limit of this first stage must be below the temperature at which the phosphate volatilizes in large quantities. Aluminum phosphate reacts with spinel to form an aluminophosphate glass phase, which fills the pores within the material, effectively blocking the infiltration channels of slag and achieving densification of the outer layer. Furthermore, the glass phase can achieve self-healing of pores. When tiny pores appear in the material during use, the glass phase can flow and fill the pores to a certain extent, improving the material's slag resistance.

[0069] In the second stage, switch to argon atmosphere, increase the temperature to 1560-1600°C at 3-5°C / min, and keep it at this temperature for 45-75 minutes.

[0070] At 1600℃, MgO and graphite react to form magnesium carbon compound, namely MgxC γ, which can hinder the growth and movement of grains, improving the material's high-temperature stability. The resulting magnesium-carbon eutectic network enhances the material's overall impermeability. It also improves the material's high-temperature plasticity, enabling it to better adapt to thermal and mechanical stresses at high temperatures and reducing the initiation and propagation of cracks.

[0071] This application uses a two-stage sintering process to form a multi-scale cross-linked structure in magnesia carbon bricks. In the first stage, the temperature is kept at around 1200°C to promote the reaction between spinel and phosphate to form aluminum phosphate, filling the pores in the outer layer and improving the density of the outer layer; in the second stage, the temperature is kept at around 1600°C to induce a solid-liquid reaction between MgO and graphite in the middle layer to form a magnesium-carbon eutectic network, thereby improving the overall anti-permeability. The dense glass phase generated in the outer layer, the continuous periclase skeleton formed in the middle layer, and the highly oriented graphite conductive network retained in the inner layer jointly improve the structural strength and corrosion resistance of magnesia carbon bricks.

[0072] Step 5: Spray silica sol onto the surface of the sintered body and cure at high temperature. The silica sol contains 2-3 wt% nano-TiO2. After spraying, heat to 950-1050°C at a rate of 10-15°C / min and cure at a nitrogen flow rate of 2-5 L / min for 8-12 minutes.

[0073] Under high-temperature conditions, the SiO2 layer induces the formation of CaTiO3. During this process, CaTiO3 crystals gradually grow and fill pores, cracks, and other defects on and within the material, preventing further penetration of slag. As CaTiO3 continues to form and accumulate, a continuous or semi-continuous barrier layer forms on the material surface. This layer possesses a certain density and stability, effectively blocking the flow and diffusion of slag, thereby enhancing the material's slag resistance. Because the permeation channels are blocked, slag has difficulty entering the material, reducing its penetration rate. This allows the material to maintain its structural integrity and performance stability for a longer period of time in a high-temperature slag environment.

[0074] During the high-temperature curing process, the silica sol chemically reacts with the aluminophosphate glass phase on the sintered body surface, forming Si-O-Al-Mg chemical bonds. This improves the adhesion between the coating and the sintered body, ensuring that the coating adheres firmly to the material surface and is not easily detached, thus ensuring that the coating effectively and long-term performs its anti-slag function.

[0075] Spraying a silica sol containing 2 wt% TiO2 nanoparticles onto the sintered body and rapidly curing it in nitrogen at 1000°C creates a porous SiO2-TiO2 coating with unique properties. The SiO2 layer has a low coefficient of thermal expansion, which synergizes with the photocatalytic activity of the TiO2 to generate rutile TiO2 in situ at high temperatures, enhancing the surface's resistance to slag adhesion.

[0076] The second aspect of this application provides a magnesia-carbon brick for the bottom of a stainless steel ladle, which is prepared using the method for preparing a magnesia-carbon brick for the bottom of a stainless steel ladle described in the first aspect. It possesses all the benefits mentioned in the first aspect and will not be further elaborated here.

[0077] For a better understanding of the technical solution, exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings.

[0078] Example

[0079] Step 1: Graphite surface modification;

[0080] Raw materials: flake graphite (fixed carbon ≥ 95%, particle size 100 mesh), silane coupling agent (γ-glycidoxypropyltrimethoxysilane). Immerse the graphite in a 20% ethanol solution of the silane coupling agent (ethanol:water = 9:1) and ultrasonicate at 60°C for 30 minutes (power 400W). Remove and vacuum dry at 80°C until the moisture content is ≤ 0.5wt%.

[0081] Step 2: magnesium oxide pre-activation treatment;

[0082] Raw materials: fused magnesia (MgO ≥ 97%, particle size 0.1 mm) and aluminum nitrate solution (Al(NO₃)₃·9H₂O, 6 wt%). Mix the magnesia and aluminum nitrate solution in a mass ratio of 100:6 and ball mill for 2 hours (300 rpm). Calcinate at 800°C for 2 hours (heating rate 5°C / min) to obtain magnesium oxide particles coated with MgAl₂O₄ (Al₂O₃ coating 1.5 wt%).

[0083] Step 3: Gradient layered molding;

[0084] Outer layer: magnesium oxide particles with surface coating of MgAl2O4 (70wt%) + silane-coated graphite (5wt%) + modified aluminum phosphate binder (5wt% P2O5:Al2O3=2:1).

[0085] Middle layer: magnesium oxide particles with surface coating of MgAl2O4 (85wt%) + silane coated graphite (10wt%) + aluminum dihydrogen phosphate binder (5wt%).

[0086] Inner layer: magnesium oxide particles with surface coating of MgAl2O4 (80wt%) + high-density graphite (20wt%) + carbon fiber (3wt%) + aluminum dihydrogen phosphate binder (2wt%).

[0087] Load the mold in the order of outer layer → middle layer → inner layer, and press in layers using cold isostatic pressing:

[0088] Outer layer: pressure 300MPa, density 3.2g / cm3 ; Middle layer: pressure 250MPa, density 3.0g / cm 3 ; Inner layer: pressure 200MPa, density 3.5g / cm 3 The pressure is maintained for 10 minutes, and the green body is obtained by demoulding.

[0089] Step 4: high temperature sintering in stages;

[0090] The first stage: heating to 1200°C at 5°C / min in a nitrogen atmosphere and keeping it at that temperature for 2 hours to promote the reaction between spinel and phosphate to form Al(PO4)3 glass phase.

[0091] Stage 2: Switch to argon atmosphere and heat up to 1600°C at 3°C / min. Hold for 1 hour to form a magnesium-carbon eutectic network. Cool naturally to room temperature.

[0092] Step 5: Spray silica sol (SiO2 content 30wt%, added with 2wt% nano-TiO2) onto the surface of the sintered body (thickness 50μm). Raise the temperature to 1000℃ at 10℃ / min under nitrogen protection and cure for 10 minutes.

[0093] Comparative Example 1: Steps 1 and 5 in the embodiment are omitted, that is, the graphite is not modified and has no surface coating.

[0094] Comparative Example 2: Omitting step 3 of the gradient structure in the embodiment, 80 wt% of magnesium oxide particles coated with MgAl2O4, 10 wt% of silane-coated graphite, and 10% of modified aluminum phosphate binder were mixed.

[0095] Comparative Example 3: Traditional magnesia carbon brick process, i.e. commercial brick.

[0096] The apparent porosity, bulk density, room temperature compressive strength, room temperature flexural strength and high temperature (1400°C) flexural strength of the samples were tested, and the results are shown in Table 1.

[0097] Table 1 Comparison of laboratory performance test data

[0098]

[0099] refer to Figure 2 The volume density of the embodiment is 3.05 g / cm 3 , which is 8.5% higher than that of comparative example 3. Based on the gradient pressing effect in the present application, the particles are packed more tightly, and the spinel-coated magnesium oxide reduces sintering shrinkage pores.

[0100] refer to Figure 3 The apparent porosity of the embodiment is only 4.2%, which is lower than the apparent porosity of 12.6% of Comparative Example 3, which is due to the effective filling of open pores by the phosphate glass phase.

[0101] refer to Figure 4 The compressive strength of the embodiment is 68.5 MPa, which is 65.8% higher than that of comparative example 3. The silane-modified graphite enhances the interface bonding and the compressive strength at room temperature is enhanced.

[0102] refer to Figure 5 The flexural strength of the embodiment is 15.7 MPa, which is 118% higher than that of comparative example 3. The carbon fiber toughened inner layer increases the tortuosity of the crack propagation path.

[0103] refer to Figure 6 The high-temperature flexural strength of the embodiment is 18.6 MPa (1400°C), which is 119% higher than that of comparative example 3. The MgAl2O4-MgO eutectic network remains a continuous phase at high temperatures, and the SiO2-TiO2 coating reduces surface thermal shock stress.

[0104] Table 2 Ladle service life

[0105] Group Example Comparative Example 1 Comparative Example 2 Comparative Example 3 (Commercial Bricks)

[0106] Total heats: 63 54 46 38

[0107] The service life of the ladle containing magnesia carbon bricks is statistically analyzed and shown in Table 2. As can be seen from Table 2, the longest smelting life of the magnesia carbon brick ladle reaches 63 furnaces, which is significantly improved compared with traditional commercial bricks.

[0108] The above describes the basic principles, main features, and advantages of the present invention. However, the above is only a specific embodiment of the present invention, and the technical features of the present invention are not limited to this. Any other implementation methods derived by any person skilled in the art without departing from the technical solution of the present invention should be included in the patent scope of the present invention.

[0109] In the description of the present invention, each embodiment focuses on the differences from other embodiments, and reference can be made to the same or similar parts between the embodiments. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple, and the relevant parts can be referred to the method description.

[0110] In the description of the present invention, relational terms such as first and second are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined. Moreover, the term "comprises", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment comprising a series of elements includes not only those elements, but also includes other elements not clearly listed, or also includes elements inherent to such process, method, article or equipment. In the absence of further restrictions, the elements defined by the statement "comprising a ..." do not exclude the presence of other identical elements in the process, method, article or equipment comprising the elements.

[0111] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0112] In the description of this specification, the terms "one embodiment", "some embodiments", "embodiments", "examples", "specific examples" or "some examples" refer to the specific features, structures, materials or characteristics described in conjunction with the embodiment or example and included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine different embodiments or examples described in this specification and features of different embodiments or examples, unless they are mutually inconsistent.

[0113] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may alter, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A method for preparing magnesia carbon bricks for stainless steel smelting ladle bottom, characterized in that: include: Step 1: immersing graphite in an ethanol solution containing a silane coupling agent, performing ultrasonic treatment, and obtaining silane-coated graphite after drying; Step 2: ball-milling magnesium oxide and aluminum nitrate solution, mixing the mixture, and calcining the mixture to obtain magnesium oxide particles coated with MgAl2O4; Step 3: cold-pressing the inner layer material, the middle layer material, and the outer layer material containing different amounts of silane-coated graphite and magnesium oxide particles coated with MgAl2O4 in sequence to obtain a raw material blank; Step 4: sintering the raw material blank at high temperature in stages, first keeping the raw material blank at 1200° C.-1300° C., and then sintering it at 1560° C.-1600° C. to obtain a sintered body; Step 5: Spray the silica sol onto the surface of the sintered body and cure it at high temperature.

2. The method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to claim 1, characterized in that ； The outer layer material includes: 5% to 8% by weight of silane-coated graphite and 5% to 8% by weight of a phosphate binder, and the remainder is magnesium oxide particles coated with MgAl2O4; The intermediate layer material includes: 10% to 15% by weight of silane-coated graphite and 3% to 5% by weight of a phosphate binder, with the remainder being magnesium oxide particles coated with MgAl2O4; The inner layer material includes: 18% to 22% by weight of silane-coated graphite, 2% to 4% by weight of carbon fiber, 1% to 3% by weight of phosphate binder, and the remainder is magnesium oxide particles coated with MgAl2O4.

3. The method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to claim 1, characterized in that ； The cold isostatic pressing layered molding technology is used to reduce the pressure and density of the inner layer, outer layer and middle layer in sequence.

4. The method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to claim 3, characterized in that ； In step 3, the outer layer material is pressed to a density of 3.15-3.25 g / cm 3 The pressing density of the middle layer material is 2.95-3.05g / cm 3 The inner layer material pressing density is 3.45-3.55g / cm 3 .

5. The method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to claim 1, characterized in that ； In step 2, the mass ratio of the magnesium oxide to the aluminum nitrate solution is 100:(5-8), wherein the concentration of the aluminum nitrate solution is 4-6 wt%; The Al2O3 coating amount of the mixture after ball milling is 1.2-2.0% of the mass of magnesium oxide; During the roasting process, the temperature is raised to 800±20℃ at a rate of 2-3℃ / min and kept at this temperature for 1.5-2 hours.

6. The method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to claim 1, characterized in that: The silane coupling agent is epoxy silane, the concentration of the ethanol solution is 18-22 wt%, the ultrasonic treatment temperature is 55-65 ° C, and the treatment time is 25-35 minutes; The drying condition is vacuum drying at 80-100° C. until the moisture content is ≤0.5 wt %.

7. The method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to claim 2, characterized in that ； The phosphate binder in the outer layer material is modified aluminum phosphate, wherein the molar ratio of P2O5:Al2O3 is (1.8-2.2); The phosphate binder in the intermediate layer material is a composite of aluminum dihydrogen phosphate and silica sol, wherein the mass ratio of the composite of aluminum dihydrogen phosphate and silica sol is (3-5):

1.

8. The method for preparing magnesia carbon bricks for stainless steel smelting ladle bottom according to claim 1, characterized in that ； The first stage of sintering is carried out in a nitrogen atmosphere, heating at 5-8°C / min to 1200-1300°C and keeping the temperature for 1.5-2 hours; In the second stage, switch to argon atmosphere, increase the temperature to 1560-1600°C at 3-5°C / min, and keep it at this temperature for 45-75 minutes.

9. The method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to claim 1, characterized in that ； In step 5, the silica sol includes 2-3 wt% nano-TiO2, and after spraying, the temperature is raised to 950-1050°C at a rate of 10-15°C / min and cured for 8-12 minutes under the condition of a nitrogen flow rate of 2-5 L / min.

10. A magnesia carbon brick for the bottom of a stainless steel smelting ladle, prepared by the method for preparing a magnesia carbon brick for the bottom of a stainless steel smelting ladle according to any one of claims 1 to 9.

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