A high-performance in-situ spinel refractory castable and preparation method thereof

Abstract

The invention relates to the technical field of refractory materials, and specifically to a high-performance in-situ spinel refractory castable and a preparation method thereof. First, MgO-based cement is prepared: boric acid, a catalyst and citric acid are mixed in proportion and dissolved in deionized water to obtain a solution, and then a MgO-based compound is added to the solution. After the reaction, the obtained precipitate is filtered and dried at 80°C and 180°C for 24 hours, respectively, to obtain MgO-based cement for preparing in-situ spinel refractory castable. Subsequently, the MgO-based cement is mixed with plate-like corundum, activated alumina, silicon micropowder, dead-burned magnesium oxide and polycarboxylate water reducer FS20, and an appropriate amount of water is added to prepare an in-situ spinel refractory castable blank by casting and molding, and finally sintered at 1600°C for 3 hours in a CO atmosphere to obtain a high-performance in-situ spinel refractory castable. The prepared MgO-based cement significantly improves the cleanliness, thermal shock resistance and slag erosion resistance of the in-situ spinel refractory castable, and reduces the production cost.

Description

Technical Field

[0001] The invention relates to the technical field of refractory materials, in particular to a high-performance in-situ spinel refractory castable and a preparation method thereof. Background Art

[0002] Clean steel production technology has become one of the priority development directions in the manufacturing industry. Refining outside the furnace is the most important smelting link to improve steel quality and produce clean steel, and it places more stringent requirements on the high-temperature performance of refractory materials. Blowing argon at the bottom of the ladle is an essential means of refining outside the furnace. Argon is blown into the ladle through the permeable element to stir the molten steel, make the temperature and composition of the molten steel uniform, and remove gas and non-metallic inclusions in the molten steel. With the increase in the proportion of molten steel refining outside the furnace, the working environment of the breathable element is becoming more and more severe, and the performance requirements of the breathable element are higher: in order to prevent the infiltration of molten steel and slag, which causes melting loss or even blockage of the breathable element, the breathable element is required to have excellent slag erosion resistance; after the ladle casting is completed and the ladle is turned over and the slag is poured, the residual steel and residual slag on the working surface of the breathable element need to be cleaned by oxygen blowing. The temperature of oxygen blowing cleaning is extremely high, and the breathable element should have sufficient high-temperature mechanical strength; one end of the breathable element contacts the molten steel and the other end contacts the room temperature argon gas, the temperature gradient exceeds 1500℃, and the working end surface temperature changes greatly with the refining process, which requires it to have excellent thermal shock resistance. Calcium aluminate cement combined with in-situ spinel refractory castable is one of the mainstream materials for prefabricated parts of ladle refining breathable elements. However, CaO in calcium aluminate cement binder reacts with silica in steel slag or silica powder (SiO2), alumina (Al2O3) and magnesium oxide (MgO) in castables to form low melting point phases such as anorthite (CaO•A12O3•2SiO2), calcite (2CaO•Al2O3•SiO2) and magnesia (2CaO•MgO•2SiO2), thereby reducing the high temperature damage resistance of refractory materials. Therefore, in-situ spinel refractory castables are gradually developing in the direction of cleanliness and self-binding. The specific technical means is to develop Al2O3-based binders or MgO-based binders suitable for in-situ spinel refractory castables.

[0003] Al2O3-based binders mainly include hydrated alumina and alumina sol. However, hydrated alumina-bound castables have defects such as high water addition, long construction mixing time and poor anti-bursting performance; while alumina sol-bound castables are limited in application due to low green body strength. MgO-based binders can reduce the particle size of in-situ spinel, improve its dispersibility, and further enhance the high-temperature performance of Al2O3-MgO refractory castables. Therefore, MgO-based binders are one of the key materials for the preparation of in-situ spinel refractory castables. The curing mechanism of MgO-based binders originates from the reaction of MgO and water in the gap between refractory aggregates and matrix to generate Mg(OH)2. However, due to the significant difference in bulk density between MgO (density 3.5 g / cm³) and Mg(OH)2 (density 2.4 g / cm³), the volume stability of castables prepared using MgO-based binders is poor. Introducing silicon micropowder into Al2O3-MgO refractory castables can effectively improve the volume stability of MgO, but the addition of silicon micropowder will significantly reduce the high-temperature service performance of the castable; using carboxylic acid to activate the formation of more Mg(OH)2 nucleation sites, the nucleation rate of Mg(OH)2 on the MgO surface is increased, and the expansion effect of Mg(OH)2 is limited, but this restriction effect is limited, resulting in poor drying performance of the castable; using spinel sol with gel properties as a binder can effectively avoid the adverse effects caused by MgO hydration, but the preparation process of spinel sol is complicated and its stability is poor, which limits its industrial application. Summary of the invention

[0004] In order to solve the above problems, the object of the present invention is to provide a high-performance in-situ spinel refractory castable and a preparation method thereof, which specifically comprises the following steps:

[0005] Plate-like corundum, activated alumina, dead-burned magnesia, MgO-based cement, silicon micropowder and polycarboxylic acid water reducer are mixed, and then water is added and mixed evenly to obtain a castable slurry. The castable slurry is cast to obtain a refractory castable body, and then the refractory castable body is sintered in a CO atmosphere at 1600°C for 3 hours to obtain a high-performance in-situ spinel refractory castable.

[0006] The plate-shaped corundum includes two particle sizes: 6-0mm and 325 mesh, and the polycarboxylate water reducer is FS20. By weight, the content of each raw material component is as follows: 6-0mm plate-shaped corundum is 72wt.%, 325 mesh plate-shaped corundum is 12wt.%, active alumina is 5wt.%, dead-burned magnesia is 7wt.%, MgO-based cement is 3wt.%, and silica powder is 1wt.%. The mass of the added polycarboxylate water reducer FS20 is 0.2wt.% of the total mass of the above raw materials, and the mass of the added water should be controlled within the range of making the flow value of the casting slurry greater than 35% and less than 60%.

[0007] Furthermore, the Al2O3 content in the plate-like corundum is greater than 99%; the particle size range of the dead-burned magnesium oxide is greater than 200 mesh and less than 325 mesh, and the MgO content is greater than 98%; the particle size of the silicon micropowder is D50=2.3μm and the SiO2 content is greater than 95%.

[0008] Furthermore, the MgO-based cement is prepared by the following method: boric acid, a catalyst and citric acid are mixed in proportion and dissolved in deionized water to obtain a solution, and then the MgO-based compound is added to the above solution, after the reaction, the mixture obtained after the reaction is filtered, the liquid is discarded, and the precipitate obtained by filtration is placed in an oven, and the MgO-based cement is obtained after drying;

[0009] Further, in the preparation of the MgO-based cement, boric acid, catalyst and citric acid are mixed in a mass ratio of 0.5:8.5:1, and then ground in a ball mill for 45 minutes, and then the ground mixture is dissolved in deionized water and fully stirred at 80°C to obtain a solution, wherein the mass of the deionized water is 80% of the mass of the ground mixture. The reaction time of the reaction is 2h; the filtered precipitate is placed in an oven for drying, and the drying refers to drying at 80°C for 24 hours and then drying at 180°C for 24 hours. The precipitate is a magnesium citrate / magnesium borate complex, and the magnesium borate in the complex produces in-situ boron carbide during pyrolysis, which can improve the antioxidant properties of the castable. The magnesium citrate eventually evolves into an in-situ spinel / nanocarbon fiber composite powder in the castable, which can improve the slag erosion resistance and thermal shock resistance of the castable; the purpose of drying the precipitate at 80°C and 180°C for 24 hours each is to remove the free water and crystal water of the magnesium citrate / magnesium borate complex and give it a gelling property.

[0010] Furthermore, in the preparation of the MgO-based cement, the catalyst is ferrocene or nickel nitrate, and the role of the catalyst is to promote the formation of nano-carbon fibers and improve the thermal shock resistance of the castable; the MgO-based compound is magnesium oxide or magnesium hydroxide; when the MgO-based compound is magnesium oxide, the added mass of the MgO-based compound is 14.0% of the solution mass; when the MgO-based compound is magnesium hydroxide, the added mass of the MgO-based compound is 18.8% of the solution mass.

[0011] Furthermore, the prepared MgO-based cement is in powder form.

[0012] The curing mechanism of MgO-based cement is as follows: When MgO-based cement comes into contact with water, MgO-based cement rapidly ionizes to produce Mg 2+ and C6H5O7 3- ions. Subsequently, Mg 2+ and C6H5O73- A hydrolysis reaction will occur. Mg 2+ Hydrolyze in two steps to generate MgOH + , Mg(OH)2 and H + ; and C6H5O7 3- It is hydrolyzed in three steps to generate HC6H5O7 2- 、H2C6H5O7 - OH - and C6H8O6. Due to Mg 2+ The strong electronegativity of Mg 2+ Reacts with H2O to form [Mg(H2O)6] 2+ When HC6H5O7 2- When the ion concentration reaches saturation, [Mg(H2O)6] 2+ and MgOH + With HC6H5O7 2- The reaction occurs to form [Mg(H2O)6][MgC6H5O7(H2O) n ]2•(8-2n)H2O.

[0013] The present invention also provides a high-performance in-situ spinel refractory castable obtained according to the above preparation method, wherein micron-sized in-situ spinel is evenly distributed inside the high-performance in-situ spinel refractory castable.

[0014] Compared with the prior art, the present invention has the following beneficial effects:

[0015] The high-performance in-situ spinel refractory castable prepared by the present invention adopts a special MgO-based cement. The MgO-based cement prepared by the present invention has the characteristics of simple and reliable preparation process. The MgO-based cement eventually evolves into micron-sized in-situ spinel and nano-carbon fiber in the castable, which not only significantly enhances the dispersibility of the in-situ spinel, but also improves the cleanliness of the castable and reduces the production cost. The castable of the present invention has the advantages of excellent drying performance, low water addition and short construction mixing time. Compared with the traditional Al2O3-MgO refractory castable combined with calcium aluminate cement, the castable of the present invention exhibits more excellent high-temperature mechanical properties, thermal shock resistance and slag erosion resistance, and the construction performance of the castable combined with the castable is similar to that of the castable combined with calcium aluminate cement. In addition, the high-performance in-situ spinel refractory castable prepared by the present invention has excellent volume stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 are macroscopic photographs and SEM images of the MgO-based cement prepared in Example 1 of the present invention, wherein the one marked as (a) in the upper left corner is a macroscopic photograph, and the one marked as (b) in the upper left corner is a SEM image;

[0017] Figure 2 Hydration temperature diagram of MgO-based cement during hydration prepared in Example 1 of the present invention;

[0018] Figure 3 is a SEM image of the MgO-based cement hydration product prepared in Example 1 of the present invention;

[0019] Figure 4 : is a picture of the high-performance in-situ spinel refractory castable prepared in Example 1 of the present invention. Among them, the upper left corner marked with (a) is a macroscopic picture of the cross section of the castable, the upper left corner marked with (b) is a SEM picture of boron carbide, and the upper left corner marked with (c) is a SEM picture of nanocarbon fiber;

[0020] Figure 5 are SEM photos of refractory castable matrices, wherein the one marked as (a) in the upper left corner is a SEM photo of the calcium aluminate cement combined in-situ spinel refractory castable matrix prepared in Comparative Example 1, and the one marked as (b) in the upper left corner is a SEM photo of the high-performance in-situ spinel refractory castable matrix prepared in Example 1;

[0021] Figure 6 These are SEM photographs of refractory castables after thermal shock resistance characterization, wherein the one marked as (a) in the upper left corner is the SEM photograph of the calcium aluminate cement combined in-situ spinel refractory castable prepared in Comparative Example 1 after thermal shock, and the one marked as (b) in the upper left corner is the SEM photograph of the high-performance in-situ spinel refractory castable prepared in Example 1 after thermal shock. DETAILED DESCRIPTION

[0022] In order to better understand the content of the present invention, the present invention will be further described below in conjunction with specific embodiments and drawings. The following embodiments are implemented based on the technology of the present invention, and detailed implementation methods and operating steps are given, but the protection scope of the present invention is not limited to the following embodiments.

[0023] In the embodiments and comparative examples, the refractory castable sample is prepared according to the national standard GB / T 4513.5-2017. Specifically, the raw materials are first prepared according to the proportion of the castable raw materials, poured into a JJ-5 planetary cement mortar mixer and stirred at a low speed for 180 seconds, wherein the low speed specifically refers to a rotation speed of 140 rpm and a revolution speed of 62 rpm; then water is added in proportion and wet mixed for 60 seconds quickly, wherein the fast speed specifically refers to a rotation speed of 285 rpm and a revolution speed of 125 rpm; then the uniformly mixed mixture is poured into a mold (the mold refers to a rectangular mold with a width of 40 mm, a height of 40 mm, and a length of 160 mm and a crucible mold with a diameter of 65 mm and a height of 65 mm), and then the mold is placed on a GZ-85 cement mortar vibrating table and vibrated for 120 seconds; then, the mold is placed on a GZ-85 cement mortar vibrating table and vibrated for 120 seconds. The mold is placed in a constant temperature and humidity curing box (the temperature of the constant temperature and humidity curing box is 35℃±1℃, and the humidity is 50%±8%) for curing for 24 hours; after demolding, the sample is placed in a constant temperature and humidity curing box (the temperature of the constant temperature and humidity curing box is 35℃±1℃, and the humidity is 50%±8%) for curing for 24 hours again; then the sample is placed in an electric constant temperature blast drying oven, and dried at 80℃ and 110℃ for 24 hours respectively; finally, the sample is placed in a high temperature box-type resistance furnace and sintered at 1600℃ for 3 hours.

[0024] The flow value of the castable is characterized by the following method: the flow value of the castable is measured by the jumping table method according to the national standard GB / T 4513.4-2017. Specifically, the uniformly mixed castable slurry is placed on a cement mortar flow tester (a truncated cone cylinder with a height of 60mm, an upper inner diameter of 70mm, and a lower inner diameter of 100mm), the surface is smoothed, and then the cone is removed. After vibrating 75 times at a speed of once per second, the diameter of the castable spread on the glass plate in two mutually perpendicular directions is measured.

[0025] The calculation formula of castable flow value is as follows:

[0026] F=(D-100) / 100*100%

[0027] Where: F—flow value of castable, %;

[0028] D—average diameter of castable spread, mm.

[0029] The setting time of the castable is characterized by the following method: Using a Vicat apparatus, the setting time of the castable is measured according to the national standard GB / T 1346-2011. Specifically, the test mold is placed under the test needle and the test needle is lowered to contact the surface of the castable matrix slurry. The test is performed every 3 minutes. The time measured when the test needle is immersed in the sample by 0.5mm, that is, when the annular attachment begins to leave no trace on the sample, is the setting time.

[0030] The room-temperature flexural strength of the castable sample is characterized by the following method: According to GB / T 3001-2017 standard, the room-temperature flexural strength of the castable is measured by the three-point bending method. The specific process is to place the castable sample on a bracket with a span of 100 mm, press it down at a loading rate of 0.5 N / mm until the sample breaks, record the maximum load that the castable sample bears when it breaks, and calculate the room-temperature flexural strength by the following formula.

[0031]

[0032] Where: M—room temperature flexural strength of castable sample, MPa;

[0033] F—maximum load that the castable sample bears when it breaks, N;

[0034] L—span between brackets, mm;

[0035] b—width of castable sample, mm;

[0036] h—height of castable sample, mm.

[0037] The thermal shock resistance of the castable is characterized by the following method: the castable sample is placed in a thermal shock furnace at 1100°C for 10 min, then the sample is placed in cold water for 3 min, and then the sample is cooled at room temperature for 2 min. The above process is one cycle. After the sample has been cycled three times, the residual flexural strength of the castable is measured. The thermal shock resistance of the castable is evaluated by calculating the residual strength retention rate of the castable. The calculation formula is as follows:

[0038]

[0039] In the formula, R ST —Retention rate of thermal shock residual strength, %;

[0040] δ1—flexural strength of castable after thermal shock, MPa;

[0041] δ2—flexural strength of castable before thermal shock, MPa;

[0042] The slag erosion resistance of the castable is characterized by the following method: the static crucible method is used to determine the slag erosion resistance of the castable according to the national standard GB / T8931-2007. The specific steps of the experiment are as follows: 30g of converter final slag is placed in a castable crucible, the crucible is cylindrical, 65mm in diameter, 65mm in height, with an inner hole on the upper end surface, the inner hole diameter is 42mm, and the depth is 35mm; then the crucible is placed in a high-temperature box-type resistance furnace and sintered at 1600℃ for 3h, and then cut along the axis after natural cooling. The erosion area of ​​the crucible is measured by Adobe Photoshop, and the erosion index is calculated using the formula to evaluate the slag erosion resistance of the castable.

[0043] Erosion index = A2 / A1×100%

[0044] Where: A1 is the area of ​​the cross section of the crucible center hole;

[0045] A2 is the area of ​​slag erosion region.

[0046] The volume stability of the castable is characterized by the following method: the castable matrix slurry is injected into the Leclerc clamp mold, cured at room temperature for 24 hours, and then placed in an oven for 24 hours. The Leclerc clamp is removed and cooled to room temperature, the pointer reading is measured, and the volume change is calculated. If the change exceeds the standard limit of 0.5mm, the volume stability of the castable is judged to be unqualified.

[0047] In the embodiments and comparative examples, the content of H3BO3 in boric acid is greater than 99.5%, the content of Fe(C5H5)2 in ferrocene is greater than 98%, the content of Ni(NO3)2•6H2O in nickel nitrate is greater than 98%; the content of Al2O3 in plate-like corundum is greater than 99%, the particle size range of magnesium oxide is greater than 200 mesh and less than 325 mesh, the content of MgO is greater than 98%, the particle size of silicon micropowder is D50=2.3μm and the content of SiO2 is greater than 95%.

[0048] Embodiment 1:

[0049] Plate-like corundum, activated alumina, dead-burned magnesia, MgO-based cement, silica powder and polycarboxylic acid water reducer FS20 are mixed, and then water is added and mixed evenly to obtain a castable slurry. A refractory castable body is prepared by casting and molding. The refractory castable body is sintered in a CO atmosphere at 1600°C for 3 hours to prepare a high-performance in-situ spinel refractory castable.

[0050] Among them, the content of each raw material component by weight is as follows: plate corundum includes two particle sizes: 6-0mm and 325 mesh, 6-0mm plate corundum is 72wt.%, 325 mesh plate corundum is 12wt.%, active alumina is 5wt.%, dead burned magnesia is 7wt.%, MgO-based cement is 3wt.%, and silica powder is 1wt.%. The mass of polycarboxylate water reducer FS20 added is 0.2wt.% of the total mass of the above raw materials, and the mass of water added is 5.0wt.% of the total mass of the above raw materials. The addition of this mass of water can make the flow value of the casting slurry 38.1%.

[0051] The above-mentioned MgO-based cement is prepared by the following method: boric acid, ferrocene and citric acid are mixed in a mass ratio of 0.5:8.5:1, and the mixture is ground in a ball mill for 45 minutes. The ground mixture is then dissolved in deionized water with a mass of 80% thereof, and fully stirred at 80°C to prepare a solution. Magnesium oxide is then added to the solution, and the mass of the magnesium oxide is 14.0% of the mass of the above-mentioned solution. After 2 hours of reaction, the mixture obtained after the reaction is filtered, the liquid is discarded, and the obtained precipitate is placed in an oven, and dried at 80°C and 180°C for 24 hours respectively to obtain MgO-based cement for preparing in-situ spinel refractory castables.

[0052] After testing, the properties of the in-situ spinel refractory castable prepared in this embodiment are as follows: flow value is 38.1%, setting time is 68 min, volume change is 0.21 mm, room temperature flexural strength of the castable body after drying at 110°C is 8.8 MPa, and the apparent porosity is 12.7%; the room temperature flexural strength after sintering at 1600°C is 35.8 MPa, the apparent porosity is 16.7%, the thermal shock residual strength retention rate is 28.7%, and the slag erosion resistance index is 44.7%.

[0053] Embodiment 2:

[0054] Plate-like corundum, activated alumina, dead-burned magnesia, MgO-based cement, silica powder and polycarboxylic acid water reducer FS20 are mixed, and then water is added and mixed evenly to obtain a castable slurry. A refractory castable body is prepared by casting and molding. The refractory castable body is sintered in a CO atmosphere at 1600°C for 3 hours to prepare a high-performance in-situ spinel refractory castable.

[0055] Among them, by weight, the content of each raw material component is as follows: plate-shaped corundum includes two particle sizes: 6-0mm and 325 mesh, 6-0mm plate-shaped corundum is 72wt.%, 325 mesh plate-shaped corundum is 12wt.%, active alumina is 5wt.%, dead-burned magnesia is 7wt.%, MgO-based cement is 3wt.%, and silica powder is 1wt.%. The mass of the added polycarboxylate water reducer FS20 is 0.2wt.% of the total mass of the above raw materials, and the mass of the added water is 5.0wt.% of the total mass of the above raw materials. The addition of this mass of water can make the flow value of the casting slurry 37.4%.

[0056] The MgO-based cement is prepared by the following method: boric acid, nickel nitrate and citric acid are mixed in a mass ratio of 0.5:8.5:1, and the mixture is ground in a ball mill for 45 minutes. The ground mixture is then dissolved in 80% of deionized water by mass, and fully stirred at 80°C to prepare a solution. Magnesium hydroxide is then added to the solution, and the mass of the magnesium hydroxide is 18.8% of the mass of the above solution. After 2 hours of reaction, the mixture obtained after the reaction is filtered, the liquid is discarded, and the obtained precipitate is placed in an oven and dried at 80°C and 180°C for 24 hours respectively to obtain MgO-based cement for preparing in-situ spinel refractory castables.

[0057] After testing, the performance of the in-situ spinel refractory castable is as follows: flow value is 37.4%, setting time is 71min, volume change is 0.27mm, the room temperature flexural strength of the castable body after drying at 110℃ is 8.4MPa, and the apparent porosity is 12.4%; the room temperature flexural strength after sintering at 1600℃ is 36.7MPa, the apparent porosity is 17.1%, the thermal shock residual strength retention rate is 29.1%, and the slag erosion resistance index is 43.1%.

[0058] Embodiment 3:

[0059] According to the ratio and preparation method of raw materials, polycarboxylate water-reducing agent FS20 and water in Example 1, the difference is that the preparation method of MgO-based cement is different, and the rest is the same as Example 1.

[0060] In this embodiment, MgO-based cement is prepared by the following method: boric acid, ferrocene and citric acid are mixed in a mass ratio of 0.5:8.5:1, and the mixture is ground in a ball mill for 45 minutes. The ground mixture is then dissolved in deionized water whose mass is 80% of that of the citric acid, and stirred at 80°C to prepare a solution. Magnesium hydroxide is then added to the solution, and the mass of the magnesium hydroxide is 18.8% of the mass of the above solution. After 2 hours of reaction, the mixture obtained after the reaction is filtered, the liquid is discarded, and the obtained precipitate is placed in an oven and dried at 80°C and 180°C for 24 hours respectively to obtain MgO-based cement for preparing in-situ spinel refractory castables.

[0061] Embodiment 4:

[0062] According to the ratio and preparation method of raw materials, polycarboxylate water-reducing agent FS20 and water in Example 1, the difference is that the preparation method of MgO-based cement is different, and the rest is the same as Example 1.

[0063] In this embodiment, MgO-based cement is prepared by the following method: boric acid, nickel nitrate and citric acid are mixed in a mass ratio of 0.5:8.5:1, and the mixture is ground in a ball mill for 45 minutes. The ground mixture is then dissolved in deionized water whose mass is 80% of that of the citric acid, and fully stirred at 80°C to prepare a solution. Magnesium oxide is then added to the solution, and the mass of the magnesium oxide is 14.0% of the mass of the above solution. After 2 hours of reaction, the mixture obtained after the reaction is filtered, the liquid is discarded, and the obtained precipitate is placed in an oven and dried at 80°C and 180°C for 24 hours respectively to obtain MgO-based cement for preparing in-situ spinel refractory castables.

[0064] Comparative Example 1:

[0065] In this comparative example, calcium aluminate cement is used as a binder to prepare in-situ spinel refractory castable.

[0066] Plate-like corundum, activated alumina, dead-burned magnesium oxide, calcium aluminate cement, silica powder and polycarboxylic acid water reducer FS20 are mixed, and then water is added and mixed evenly to obtain a castable slurry. A refractory castable body is prepared by casting and molding. The refractory castable body is finally sintered in a CO atmosphere at 1600°C for 3 hours to prepare an in-situ spinel refractory castable.

[0067] Among them, by weight, the content of each raw material component is as follows: plate corundum includes two particle sizes: 6-0mm and 325 mesh, 6-0mm plate corundum is 72wt.%, 325 mesh plate corundum is 12wt.%, active alumina is 5wt.%, dead burned magnesium oxide is 7wt.%, calcium aluminate cement is 3wt.%, and silica powder is 1wt.%. The mass of the added polycarboxylate water reducer FS20 is 0.2wt.% of the total mass of the above raw materials, and the mass of the added water is 3.9wt.% of the total mass of the above raw materials. The addition of this mass of water can make the flow value of the casting slurry 39.6%.

[0068] After testing, the properties of the in-situ spinel refractory castable prepared in this comparative example are as follows: flow value is 39.6%, setting time is 118min, and volume change is 0.31mm; the room-temperature flexural strength of the castable body after drying at 110°C is 9.2MPa, and the apparent porosity is 12.9%; the room-temperature flexural strength after sintering at 1600°C is 41.7MPa, the apparent porosity is 16.9%, the thermal shock residual strength retention rate is 19.8%, and the slag erosion resistance index is 49.1%.

[0069] Figure 1 The macroscopic photograph and SEM image of the MgO-based cement prepared in Example 1 of the present invention are shown in FIG. 1 , wherein the macroscopic photograph is marked as (a) in the upper left corner, and the SEM image is marked as (b) in the upper left corner; Figure 1 As can be seen from the middle figure (a), the MgO-based cement is in powder form and light yellow in color. From figure (b), it can be seen that the MgO-based cement has an irregular particle morphology.

[0070] Figure 2 Hydration temperature diagram of MgO-based cement prepared in Example 1 of the present invention during hydration; When MgO-based cement comes into contact with water, MgO-based cement rapidly ionizes to produce Mg 2+ and C6H5O7 3- ions. Subsequently, Mg 2+ and C6H5O7 3- A hydrolysis reaction will occur. Mg 2+ Hydrolyze in two steps to generate MgOH + , Mg(OH)2 and H + ; and C6H5O7 3- It is hydrolyzed in three steps to generate HC6H5O7 2- 、H2C6H5O7 - OH - and C6H8O6. Due to Mg 2+ The strong electronegativity of Mg 2+ Reacts with H2O to form [Mg(H2O)6] 2+The reaction releases about 1760 kJ / mol of heat, so MgO-based cement immediately exothermic peaks when it comes into contact with water. 2- When the ion concentration reaches saturation, [Mg(H2O)6] 2+ and MgOH + With HC6H5O7 2- The reaction occurs to form [Mg(H2O)6][MgC6H5O7(H2O) n ]2•(8-2n)H2O. This reaction is also accompanied by heat release, corresponding to the second exothermic peak.

[0071] Figure 3 This is a SEM image of the MgO-based cement hydration product prepared in Example 1 of the present invention. The hydration presents a lamellar structure, which can be entangled and interwoven with each other, giving it good gelling properties.

[0072] Figure 4 The following is a picture of the high-performance in-situ spinel refractory castable prepared in Example 1 of the present invention. The upper left corner marked with (a) is a macroscopic picture of the cross section of the castable, the upper left corner marked with (b) is a SEM picture of boron carbide, and the upper left corner marked with (c) is a SEM picture of nanocarbon fiber. Figure 4 As can be seen in the middle figure (a), the cross section of the castable sample is black. This is because the castable is sintered in a reducing atmosphere at 1600℃, generating carbon and boron carbide in situ. Figure 4 As can be seen in the middle figure (b), polyhedral boron carbide appears in the castable, which is due to the in-situ generation of magnesium borate in the magnesium citrate / magnesium borate composite during the thermal decomposition process. Boron carbide has a higher oxygen potential than carbon, and a dense oxide protective film (such as B2O3) is formed on its surface. This film can effectively prevent oxygen from further diffusing into the material, thereby improving the anti-oxidation properties of the castable. Figure 4 As can be seen in the middle figure (c), nanocarbon fibers appear in the castable. These fibers are generated by pyrolysis of magnesium citrate / magnesium borate complex under the action of ferrocene catalyst. Nanocarbon fibers have high thermal conductivity, low thermal expansion coefficient, excellent mechanical properties and high temperature stability, as well as crack passivation and buffering properties. These characteristics enable nanocarbon fibers to effectively reduce thermal stress and inhibit crack propagation, thereby improving the heat resistance of the castable; and nanocarbon fibers have poor wettability with steel slag, which is conducive to improving the castable's resistance to slag erosion. The above microstructures give MgO-based cement combined with in-situ spinel refractory castables excellent thermal shock resistance and slag erosion resistance.

[0073] Figure 5: are SEM photos of refractory castable matrix, wherein the one marked as (a) in the upper left corner is the SEM photo of the calcium aluminate cement combined in-situ spinel refractory castable matrix prepared in Comparative Example 1, and the one marked as (b) in the upper left corner is the SEM photo of the high-performance in-situ spinel refractory castable matrix prepared in Example 1. Figure 5 As can be seen in the middle figure (a), a large amount of glass phase appears in the calcium aluminate cement combined with the in-situ spinel refractory castable matrix. This is because the calcium oxide in the calcium aluminate cement reacts with silica powder and alumina to form a low melting point phase, which will reduce the thermal shock resistance and slag erosion resistance of the castable. Figure 5 As can be seen from the middle figure (b), the high-performance in-situ spinel refractory castable prepared by the present invention has no glass phase, and columnar in-situ spinel can be seen, and the in-situ spinel is micron-sized, which is beneficial to improving the high-temperature mechanical properties and slag erosion resistance of the castable.

[0074] Figure 6 The SEM photos of the refractory castables after thermal shock resistance characterization are shown in Figure 1. The photo marked with (a) in the upper left corner is a SEM photo of the calcium aluminate cement combined in-situ spinel refractory castable prepared in Comparative Example 1 after thermal shock, and the photo marked with (b) in the upper left corner is a SEM photo of the high-performance in-situ spinel refractory castable prepared in Inventive Example 1 after thermal shock. Figure 6 It can be seen from the middle figure (b) that small cracks appeared in the castable after thermal shock, but there were many microcracks. Therefore, it can be known that the high-performance in-situ spinel refractory castable prepared by the present invention is more likely to initiate microcracks during the thermal shock process and the microcracks are not easy to expand. From Figure (a), it can be seen that the calcium aluminate cement combined with the in-situ spinel refractory castable prepared in Comparative Example 1 is easy to expand but not easy to initiate microcracks during the thermal shock process.

[0075] Table 1 Comparison of properties of in-situ spinel refractory castables prepared in Examples 1-2 and Comparative Example 1

[0076] Example 1 Example 2 Comparative Example 1 Flow value 38.1% 37.4 % 39.6% Coagulation time 68min 71 min 118 min Volume change 0.21 mm 0.27 mm 0.31mm Room temperature flexural strength of the blank (110°C) 8.8MPa 8.4MPa 9.2 MPa Apparent porosity of green body (110℃) 12.7% 12.4% 12.9 % Flexural strength at room temperature (1600℃) 35.8 MPa 36.7 MPa 41.7MPa Apparent porosity (1600℃) 16.7% 17.1% 16.9% Thermal shock residual strength retention rate 28.7% 29.1% 19.8% Slag erosion resistance index 44.7% 43.1% 49.1%

[0077] It can be seen from Table 1 that the in-situ spinel refractory castable prepared by the present invention has excellent volume stability (i.e., excellent drying performance), slag erosion resistance and thermal shock resistance, and the flow value and room temperature flexural strength (110°C) of the in-situ spinel refractory castable prepared by the present invention are similar to those of traditional calcium aluminate cement combined castables.

[0078] The above is only an embodiment of the present invention, and does not limit the present invention in any form. The present invention can also have other forms of embodiments according to the above structures and functions, which are not listed one by one. Therefore, any simple modification, equivalent change and modification made by any technician familiar with the profession to the above embodiment according to the technical essence of the present invention without departing from the scope of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high-performance in-situ spinel refractory castable, characterized in that: The specific steps include: The plate-like corundum, activated alumina, dead-burned magnesia, MgO-based cement, silicon micropowder and polycarboxylate water reducer are mixed, and then water is added and mixed evenly to obtain a castable slurry, and the castable slurry is cast to obtain a refractory castable body, and then the refractory castable body is sintered in a CO atmosphere at 1600° C. for 3 hours to obtain a high-performance in-situ spinel refractory castable; The MgO-based cement is prepared by the following method: boric acid, a catalyst and citric acid are mixed in a mass ratio of 0.5:8.5:1, and the mixture is ground in a ball mill for 45 minutes, and then the ground mixture is dissolved in deionized water, and the solution is obtained after being fully stirred at 80° C., wherein the mass of the deionized water is 80% of the mass of the ground mixture, and then the MgO-based compound is added to the above solution, and after the reaction, the reaction time is 2 hours, the mixture obtained after the reaction is filtered, the liquid is discarded, and the precipitate obtained by filtration is placed in an oven, first dried at 80° C. for 24 hours, and then dried at 180° C. for 24 hours, so as to obtain the MgO-based cement; The MgO-based compound is magnesium oxide or magnesium hydroxide; the precipitate is a magnesium citrate / magnesium borate complex; When the MgO-based compound is magnesium oxide, the mass of the added MgO-based compound is 14.0% of the mass of the solution; when the MgO-based compound is magnesium hydroxide, the mass of the added MgO-based compound is 18.8% of the mass of the solution; The catalyst is ferrocene or nickel nitrate.

2. The method for preparing a high-performance in-situ spinel refractory castable according to claim 1, characterized in that: The plate-like corundum includes two particle sizes: 6-0mm and 325 mesh. The polycarboxylate water reducer is FS20. By weight, the content of each raw material component is as follows: 6-0mm plate-like corundum is 72wt.%, 325 mesh plate-like corundum is 12wt.%, active alumina is 5wt.%, dead-burned magnesia is 7wt.%, MgO-based cement is 3wt.%, and silica powder is 1wt.%; the mass of FS20 is 0.2wt.% of the total mass of the above raw materials, and the mass of the added water is controlled within the range that the flow value of the casting slurry is greater than 35% and less than 60%.

3. The method for preparing a high-performance in-situ spinel refractory castable according to claim 1, characterized in that: The Al2O3 content in the plate-like corundum is greater than 99%; the particle size range of the dead-burned magnesium oxide is greater than 200 mesh and less than 325 mesh, and the MgO content is greater than 98%; the particle size of the silicon micropowder is D50=2.3μm and the SiO2 content is greater than 95%.

4. A high-performance in-situ spinel refractory castable obtained by the preparation method according to any one of claims 1 to 3.

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