Modified ball pitch is used as carbon source for blast furnace iron runner pouring material and its preparation method

Abstract

The application discloses a modified ball pitch carbon source castable for a blast furnace tapping channel and a preparation method thereof, and belongs to the technical field of refractory castables. The castable raw material is an Al2O3-SiC-C castable, which contains 2.3-5 wt.% of modified ball pitch; and the modified ball pitch is ball pitch loaded with nano silicon dioxide on the surface. In the preparation process, the roasting process includes heat preservation at 330-370 DEG C for 2.5-4 h. Through optimization of the castable raw material and the roasting process parameters, the oxidation resistance, mechanical properties of the castable, and the synergistic fluidity and microcrystallization of the carbon source can be improved, and the generation of silicon carbide whiskers can be promoted, thereby improving the slag erosion resistance of the castable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of refractory castable, more particularly, to a castable for blast furnace iron runner using modified ball pitch as carbon source and a preparation method thereof. BACKGROUND

[0002] With the increase of blast furnace size and smelting intensity, the amount of blast furnace iron tapping increases, and the load of blast furnace iron runner increases, so it is urgent to improve the comprehensive service performance of the castable of the iron runner to prolong its service life. Carbon materials have poor wettability with molten slag and high thermal conductivity, which can improve the slag resistance and thermal shock resistance of the castable of the iron runner and prolong the service life of the blast furnace iron runner. At present, the carbon source used in the Al2O3-SiC-C castable of the iron runner in industrial production is generally ball pitch.

[0003] Although ball pitch has many advantages such as spherical shape, fluidity and the like compared with traditional liquid or block pitch, there are still the following problems in the actual use of the Al2O3-SiC-C castable of the iron runner: (1) the carbon source is not wetted with water during casting, which is easy to cause aggregation and reduce the slag resistance in the final use process; (2) the carbon residue rate of ball pitch is low, and it is easy to be oxidized during use, which greatly reduces its service life and affects the normal production efficiency; (3) there is no clear baking system for the Al2O3-SiC-C castable using ball pitch as carbon source, and there is no sufficient theoretical guidance, so the final use performance of the castable cannot be effectively guaranteed.

[0004] At present, many studies are devoted to improving the comprehensive performance of the Al2O3-SiC-C castable of the iron runner, and one of the important research directions is the modification treatment of the carbon source. For example, the Chinese patent application with publication number CN113666723A discloses a carbon nanofiber modified carbon-containing refractory castable and a preparation method thereof. According to weight fraction, the refractory castable includes: 100 parts of aggregate, 10-30 parts of cementing material, 8-15 parts of admixture and 0.2-0.8 parts of coagulant; wherein the aggregate is obtained by mixing refractory material and refractory material coating liquid and then sintering; the refractory material coating liquid is a phenolic resin solution modified by cerium ammonium nitrate. The application uses the modified phenolic resin solution to coat the metal oxide commonly used in the aggregate component of the refractory castable, and then sintering, to finally obtain the carbon nanofiber modified carbon-containing refractory castable, so as to effectively improve the slag resistance of the castable. However, the preparation process of the application is relatively complex, the preparation cost is high, it is not easy to realize industrial application, and there is still a lack of clear baking system.

[0005] Furthermore, although Chinese patent application CN106198301A discloses a method and apparatus for formulating a baking regime for refractory castables, specifically: using a temperature control system and a weighing system to monitor the temperature and weight changes of the castable, analyzing the relationship between weight and temperature to obtain the moisture removal rate at different temperature stages, accurately determining the baking effect of different castables at each temperature stage, determining the baking temperature and baking time for the corresponding stage, and formulating the optimal baking regime for the castable, the baking regime in this application is based solely on the moisture removal rate at different temperature stages. This is not applicable to castables containing spherical asphalt with complex low- and medium-temperature thermal behavior, and its specific heating and baking stages are time-consuming and have complex heating curves. Summary of the Invention

[0006] 1. Technical problems to be solved

[0007] To address the technical problems of existing Al2O3-SiC-C castables for blast furnace tapping troughs, such as the carbon source not being wetted by water, weak oxidation resistance, and poor slag erosion resistance, this invention provides a castable for blast furnace tapping troughs using modified spherical pitch as the carbon source and its preparation method. This method uses modified spherical pitch as the carbon source and optimizes the baking curve of the castable, thereby effectively improving the castable's oxidation resistance, mechanical properties, synergistic flowability and microcrystallization of the carbon source, and promoting the formation of silicon carbide whiskers, thus enhancing the castable's slag erosion resistance.

[0008] 2. Technical Solution

[0009] To achieve the above objectives, the technical solution provided by this invention is as follows:

[0010] The first aspect of the present invention provides a castable for blast furnace tapping troughs using modified spherical pitch as a carbon source. The raw material of the castable is an Al2O3-SiC-C material castable containing 2.3 to 5 wt.% modified spherical pitch. The modified spherical pitch is spherical pitch with nano-silica loaded on its surface.

[0011] To address the technical problems existing in current Al2O3-SiC-C castables, this invention improves the resistance to molten iron erosion by modifying the spherical asphalt. Specifically, this invention coats the outer surface of the spherical asphalt with nano-silica, which improves the hydrophilicity of the spherical asphalt and enhances its dispersibility within the castable matrix.

[0012] Further, and more importantly, compared with nano-carbon and fine graphite, both of which are solid and fixed carbon, nano-carbon and fine graphite do not have fluidity in low-temperature baking; while the ball pitch contains amorphous carbon with complex thermal behavior and has fluidity in low-temperature baking; therefore, the thermal behavior of ball pitch in the baking process of castables is essentially different from that of nano-carbon and fine graphite in the baking process of castables. Because ball pitch has more complex low-temperature thermal behavior, it becomes the carbon source of industrialized application of castables. Specifically, after heating, the ball pitch softens and becomes a colloidal state with fluidity, so that when the castables are subsequently baked, on the one hand, the high expansion coefficient of air and the low viscosity of ball pitch combine to make the ball pitch expand rapidly when heated, and the ball pitch penetrates, volatilizes and condenses into the pores inside the castables, thereby improving the density of the material and improving the overall performance of the castables. On the other hand, with the flow of ball pitch in the castable matrix, the nano-silica attached to its surface can be uniformly dispersed on the surface of the ball pitch and uniformly dispersed in the castable matrix along with the ball pitch. The uniformly dispersed nano-silica can have a better nucleation and filling effect. Specifically, the ball pitch will be microcrystallized into graphite during the baking process, and in the subsequent use process, the graphite reacts with the nano-silica on its surface and the silicon powder in the matrix to generate a large amount of spider web-shaped silicon carbide whiskers. The silicon carbide whiskers can more effectively link the aggregates and powders in the matrix and fill the pores, further improving the densification degree of the castables and further reducing the oxygen partial pressure inside the material, thereby improving the oxidation resistance of the castables. In addition, during the use of the castables, due to the uniform distribution of the carbon source in the castables and the hindering of the further penetration of the molten slag by the silicon carbide whiskers, the molten iron erosion resistance of the castables is greatly optimized. At the same time, the silicon carbide whiskers form granular silicon dioxide on their surfaces, filling the pores and further preventing oxygen from penetrating into the matrix. At the same time, it can also react with the aluminum-rich matrix to generate more uniformly distributed mullite phases, effectively improving the bonding between the ball pitch and the aluminum-rich matrix, making it more closely contact with the aluminum-rich matrix, improving the densification degree of the sample, and further improving the overall high-temperature mechanical properties of the sample.

[0013] Further, the particle size of the ball pitch is 0-1 mm.

[0014] Further, the castable raw material further comprises 50-60 wt.% of brown corundum aggregate, 15-23 wt.% of silicon carbide, 11-38 wt.% of dense corundum compounded alpha-alumina micropowder, 4-6 wt.% of calcium aluminate cement, and 1.5-2.0 wt.% of aluminum powder compounded elemental silicon powder.

[0015] Furthermore, the particle size distribution of the brown fused alumina aggregate is as follows: 5-8 mm particles account for 25-45 wt.% of the brown fused alumina aggregate, 3-5 mm particles account for 15-35 wt.% of the brown fused alumina aggregate, 1-3 mm particles account for 15-30 wt.% of the brown fused alumina aggregate, and 0.088-1 mm particles account for 10-25 wt.% of the brown fused alumina aggregate.

[0016] Furthermore, the silicon carbide has a particle size distribution of 40-55 wt% for particles of 0.088-1 mm and 45-60 wt% for particles smaller than 0.088 mm.

[0017] Furthermore, in the dense corundum compound α-alumina micro powder, the mass ratio of dense corundum to α-alumina micro powder is 0.1 to 0.2, and the particle size of the dense corundum is less than 0.045 mm; the α-alumina micro powder is selected with an Al2O3 content ≥98 wt.% and a particle size distribution curve with a bimodal structure, the peak values ​​of the two peaks being 1.2 μm and 2.3 μm, respectively.

[0018] Furthermore, the mass ratio of aluminum powder to elemental silicon powder in the aluminum powder-silicon powder composite is 0.1 to 0.2.

[0019] Furthermore, the calcium aluminate cement is Secar71 pure calcium aluminate cement.

[0020] Furthermore, the water-reducing agent is one or more of sodium tripolyphosphate, sodium hexametaphosphate, and polycarboxylate water-reducing agents imported from BASF, Germany.

[0021] The second aspect of the present invention provides a method for preparing a high-performance blast furnace tapping trough castable using the above-mentioned modified spherical pitch as a carbon source, including a baking process, which includes: keeping the castable at 330-370°C for 2.5-4 hours.

[0022] It should be noted that the optimization of the baking process in this invention, particularly the holding time of the castable at 330–370℃ for 2.5–4 hours, is crucial. Through in-depth research into the complex thermal behavior of spherical asphalt, the inventors discovered that within a certain temperature range, its flowability and dispersibility increase with increasing baking temperature; however, when the temperature exceeds a certain value, its flowability and dispersibility begin to decrease. Simultaneously, XRD pattern analysis of the spherical asphalt at corresponding baking temperatures revealed that as the baking temperature increases, the diffraction peak at 26° (2θ) becomes higher and sharper, indicating that organic matter in the spherical asphalt evaporates, and the degree of carbon microcrystallization in the spherical asphalt further increases. Increased microcrystallization indicates that more carbon sources in the spherical asphalt transform from amorphous carbon to morphological carbon, losing their fluidity. Therefore, within a certain temperature range, as the baking temperature increases, the fluidity of the spherical asphalt improves, but so does its microcrystallization.

[0023] Regarding the forms of moisture in castables, if only three commonly used temperature points—150℃, 550℃, and 800℃—are used for heat preservation to control the evaporation rate of different forms of moisture in the castable, and the baking temperature is improperly selected (i.e., directly heating from 150℃ to 550℃ at the commonly used heating rate of 15–25℃ / h), the residence time within the temperature range of optimal balance between fluidity and microcrystallization is short, quickly exceeding this range, and then microcrystallization becomes the dominant process, resulting in poor fluidity and dispersion of the spherical asphalt. The inventors dedicated themselves to finding the optimal balance between fluidity and microcrystallization of spherical asphalt in castables, ultimately determining that heat preservation at 330–370℃ for 2.5–4 hours allows the spherical asphalt to achieve the optimal balance between fluidity and microcrystallization in the castable matrix. Heat preservation at this temperature allows the modified spherical asphalt to achieve optimal flow expansion in the castable. The castable is baked by further heating from 330 to 370°C, and then the microcrystallization of the spherical asphalt is mainly carried out.

[0024] It should be noted that by maintaining the temperature within the range of 330–370℃ for a period of time, the optimal flow and expansion of the spherical asphalt in the castable matrix is ​​achieved. Based on this, the dispersibility of the nano-silica adhering to its surface is further improved in both the castable matrix and the surface of the spherical asphalt, thereby enabling the nano-silica to achieve better nucleation and filling effects.

[0025] Furthermore, regarding the selection of the heat preservation time, during the baking process of the castable, the heat preservation time within the temperature range of 330–370℃ should be selected as 2.5–4 hours. If the heat preservation time is too short, it will not be conducive to the flow and dispersion of the spherical asphalt in the matrix. When the heat preservation time is greater than 4 hours, the dispersion uniformity of the spherical asphalt in the castable system can no longer be significantly improved. At this time, further extending the heat preservation time will also cause the volatilization and decomposition of some carbon oxides in the spherical asphalt, which will not only fail to have a positive effect on the dispersion effect, but also increase unnecessary energy waste.

[0026] Furthermore, taking the mass of the castable raw materials as the whole, a water-reducing agent accounting for 0.15-0.25% of the mass of the castable raw materials is added externally; the castable raw materials and water-reducing agent are mixed according to the mass ratio and put into a high-power mixer and stirred for 5-10 minutes to obtain a dry mixture. Water accounting for 4.5-5 wt.% of the dry mixture is added externally, and the mixture is stirred in a high-power mixer for 3-5 minutes. The mixture is then cast into shape, cured for 20-24 hours, demolded, and then baked.

[0027] Furthermore, the preparation method of the modified spherical asphalt includes the following specific steps: Step 1: Etching the spherical asphalt and then drying it; Step 2: Immersing the spherical asphalt obtained in Step 1 in a nano-silica sol solution and drying it to obtain the modified spherical asphalt. The unmodified spherical asphalt has a relatively smooth surface and low roughness, at which point silica cannot effectively coat it. Etching can improve the roughness of the spherical asphalt, thereby increasing the adhesion strength of nano-silica on its surface.

[0028] Furthermore, the nano-silica sol solution used in step 2 is alkaline. Alkaline silica sol has a large specific surface area and a porous structure, resulting in excellent adsorption capacity.

[0029] Furthermore, the concentration of the nano-silica sol solution used in step 2 is 20–40 wt.%; the mass ratio of the spherical pitch to the nano-silica sol solution is 1:0.2–0.4. Simultaneously, according to theoretical calculations, the reaction ratio of carbon to silicon dioxide to form silicon carbide whiskers is 3:1. Using a rough-surfaced spherical pitch with a molar ratio of 1:0.2–0.4 to silicon dioxide allows for complete reaction between silicon dioxide and the carbon source to form silicon carbide whiskers. Furthermore, an excess of carbon source provides a reducing environment to promote the reaction, thus fully utilizing the carbon source.

[0030] Furthermore, in step 1, the spherical asphalt is etched, specifically by using an acid solution.

[0031] Furthermore, the baking process also includes: heating from room temperature to 100°C at a heating rate of 15-20°C / h, and holding at 100°C for 45-50 hours; heating from 100°C to 150°C at a heating rate of 15-20°C / h, and holding at 150°C for 65-70 hours; heating from 150°C to between 330-370°C at a heating rate of 15-20°C / h; heating from 330-370°C to 550°C at a heating rate of 20-25°C / h, and holding at 550°C for 65-70 hours; and heating from 550°C to 800°C at a heating rate of 20-25°C / h, and holding at 800°C for 55-60 hours.

[0032] It should be noted that the key point of the baking process in this application is to keep the temperature at 330-370℃ for a period of time so that the fluidity and microcrystallization of the spherical asphalt in the castable matrix can reach the optimal balance. There are no strict requirements for the baking regime before and after the holding temperature, and the existing baking regime can be directly adopted. However, when the above baking process is further adopted, it is beneficial to further ensure the performance of the resulting castable.

[0033] Furthermore, the method for preparing blast furnace tapping trough castable using modified spherical pitch as carbon source is characterized in that the microstructure of the castable prepared after the baking process contains a spiderweb-like silicon carbide whisker structure.

[0034] Furthermore, the oxidation erosion index of the castable obtained after the baking process is less than 17.9%.

[0035] In summary, by adopting the technical solution provided by this invention, the following beneficial effects can be achieved compared with the prior art:

[0036] (1) This invention modifies spherical asphalt by loading nano-silica onto its surface, thereby improving the hydrophilicity of the spherical asphalt, enhancing its dispersibility in the castable matrix, and improving its antioxidant properties, thus increasing the residual carbon content and fully utilizing the carbon source. More importantly, during the subsequent baking process of the castable, the nano-silica loaded on the surface of the spherical asphalt flows with it. The uniformly dispersed nano-silica can act as a nucleation and filling agent, promoting the formation of mullite phase and silicon carbide whiskers, effectively improving the bonding between the spherical asphalt and the matrix, enhancing the overall mechanical properties of the sample, and increasing the density of the sample.

[0037] (2) This invention studies the low-temperature thermal behavior of spherical asphalt and optimizes the baking regime of the castable by keeping it at 330-370℃ for a period of time, which enables the spherical asphalt to achieve the best balance between fluidity and microcrystallization in the castable matrix, achieve the best flow expansion, and further promote the uniform dispersion of nano-silica loaded on the surface of spherical asphalt in the castable matrix, thereby improving the nucleation and filling effect of silica.

[0038] (3) This invention improves the adhesion strength of nano-silica by etching the surface of the spherical asphalt to roughen it. In addition, the experimental method for this modified spherical asphalt is simple, low-cost, and suitable for industrial applications. Attached Figure Description

[0039] Figure 1 This is a SEM image of nano-silica loaded on the surface of the spherical asphalt in Example 1 of the present invention.

[0040] Figure 2 This is a SEM image of the internal microstructure of the castable sample prepared in Example 1 of the present invention. Detailed Implementation

[0041] To further understand the content of this invention, the invention will be described in detail with reference to the embodiments.

[0042] In the following embodiments, sodium tripolyphosphate is used as an example of water-reducing agent. This should not be construed as limiting the water-reducing agent in the technical solution of the present invention. The water-reducing agent can be any one or any combination of two or more of sodium tripolyphosphate, sodium hexametaphosphate, and polycarboxylate water-reducing agents imported from BASF, Germany.

[0043] Example 1

[0044] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source, as detailed below:

[0045] (I) Preparation of modified spherical asphalt:

[0046] S1: At room temperature, dry spherical asphalt with a particle size of 0-1 mm is immersed in an acid solution and allowed to react naturally for 10 min. The acid solution used is a 10 wt.% dilute nitric acid solution. After the etching reaction is completed, the spherical asphalt with a rough surface is obtained by drying at 60℃ for 3 h.

[0047] S2: The rough-surfaced spherical asphalt obtained in S1 is immersed in a 30 wt.% nano-silica sol solution and naturally air-dried in a ventilated place to obtain spherical asphalt with nano-silica adhering to its surface, and the modified spherical asphalt maintains its shape integrity; wherein the nano-silica sol solution used is alkaline with a pH value of 8; the mass ratio of the rough-surfaced spherical asphalt after etching to the mass of nano-silica contained in the nano-silica sol solution is 1:0.3.

[0048] Scanning electron microscope (SEM) image of the prepared spherical pitch with surface-loaded nano-silica is shown below. Figure 1 As shown.

[0049] (II) Preparation method of castable refractory for blast furnace tapping trough

[0050] S1: Raw material formulation: The raw materials of the castable include 55 wt.% brown fused alumina aggregate, 20 wt.% silicon carbide, 15 wt.% dense fused alumina compound α-alumina micro powder, 5 wt.% calcium aluminate cement, 2 wt.% metallic aluminum powder compound elemental silica powder and 3 wt.% modified spherical asphalt.

[0051] The particle size distribution of the brown fused alumina aggregate used is as follows: 36 wt.% of the brown fused alumina aggregate is 5-8 mm, 23 wt.% is 3-5 mm, 23 wt.% is 1-3 mm, and 18 wt.% is 0.088-1 mm.

[0052] The particle size distribution of the silicon carbide used is as follows: 45 wt.% of silicon carbide is 0.088-1 mm, and 55 wt.% of silicon carbide is smaller than 0.088 mm.

[0053] The mass ratio of dense corundum to α-alumina micro powder in the dense corundum compound α-alumina micro powder used is 0.2. Dense corundum is a fine powder with a particle size of less than 0.045 mm. The α-alumina micro powder is selected with an Al2O3 content of ≥98 wt.% and its particle size distribution curve has a bimodal structure with peak values ​​of 1.2 μm and 2.3 μm, respectively.

[0054] The calcium aluminate cement used was Secar71 pure calcium aluminate cement.

[0055] The mass ratio of aluminum powder to elemental silicon powder in the aluminum powder-silicon powder compound is 0.1.

[0056] S2: Taking the castable raw material described in S1 as the whole, add a water-reducing agent with a mass ratio of 0.25% of the castable raw material, wherein the water-reducing agent used is sodium tripolyphosphate.

[0057] The above-mentioned casting material and water-reducing agent are stirred for 8 minutes to obtain a dry mixture; water of 5% by mass of the dry mixture is added; the mixture is stirred in a high-power mixer for 4 minutes, cast into shape, and demolded after curing for 20 hours.

[0058] S3: Bake according to the baking curve, which is as follows: room temperature to 100℃, heating rate of 20℃ / min, hold at 100℃ for 45h; 100℃ to 150℃, heating rate of 20℃ / min, hold at 150℃ for 65h; 150℃ to 350℃, heating rate of 15℃ / min, hold at 350℃ for 3h; 350℃ to 550℃, heating rate of 20℃ / h, hold at 550℃ for 65h; 550℃ to 800℃, heating rate of 25℃ / h, hold at 800℃ for 55h.

[0059] The scanning electron microscope (SEM) image of the blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as a carbon source, after its initial high-temperature service is shown below. Figure 2 As shown. By Figure 2 It can be seen that a large number of spiderweb-like silicon carbide whiskers can be observed in the matrix. Further testing of the above samples showed that the room temperature flexural strength was 11.7 MPa, the room temperature compressive strength was 53.2 MPa, the oxidation erosion index was 15.7%, and the slag erosion depth was 1.4 mm.

[0060] Example 2

[0061] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source, as detailed below:

[0062] (I) Preparation of modified ball asphalt

[0063] S1: At room temperature, dry spherical asphalt with a particle size of 0-1 mm is immersed in an acid solution and allowed to react naturally for 10 min. The acid solution used is a 10 wt.% dilute nitric acid solution. After the etching reaction is completed, the spherical asphalt with a rough surface is obtained by drying at 60℃ for 3 h.

[0064] S2: The rough-surfaced spherical asphalt obtained in S1 is immersed in a 40 wt.% nano-silica sol solution and naturally air-dried in a ventilated place to obtain spherical asphalt with nano-silica adhering to its surface; wherein the nano-silica sol solution used is alkaline with a pH value of 8; the mass ratio of the etched spherical asphalt to the nano-silica contained in the nano-silica sol solution is 1:0.4.

[0065] (II) Preparation method of castable refractory for blast furnace tapping trough

[0066] S1: Raw material formulation: The raw materials of the castable include 50 wt.% brown fused alumina aggregate, 23 wt.% silicon carbide, 18 wt.% dense fused alumina compound α-alumina micro powder, 5 wt.% calcium aluminate cement, 1.5 wt.% metallic aluminum powder compound elemental silica powder and 2.5 wt.% modified spherical asphalt.

[0067] The particle size distribution of the brown fused alumina aggregate used is as follows: 45 wt.% of the brown fused alumina aggregate is 5-8 mm, 15 wt.% is 3-5 mm, 30 wt.% is 1-3 mm, and 10 wt.% is 0.088-1 mm.

[0068] The particle size distribution of the silicon carbide used is as follows: 0.088-1 mm accounts for 55 wt.% of the silicon carbide, and particles smaller than 0.088 mm account for 45 wt.% of the silicon carbide.

[0069] The mass ratio of dense corundum to α-alumina micro powder in the dense corundum compound α-alumina micro powder used is 0.1. Dense corundum is a fine powder with a particle size of less than 0.045 mm. The α-alumina micro powder is selected with an Al2O3 content of ≥98 wt.% and its particle size distribution curve has a bimodal structure with peak values ​​of 1.2 μm and 2.3 μm, respectively.

[0070] The calcium aluminate cement used was Secar71 pure calcium aluminate cement.

[0071] The mass ratio of aluminum powder to elemental silicon powder in the aluminum powder-silicon powder compound is 0.2.

[0072] S2: Taking the castable raw materials described in S1 as a whole, add a water-reducing agent with a mass ratio of 0.15% of the castable raw materials, wherein the water-reducing agent used is sodium tripolyphosphate.

[0073] Mix the above-mentioned casting material and water-reducing agent for 10 minutes to obtain a dry mixture; add water at a mass ratio of 4.5% of the dry mixture; mix in a high-power mixer for 3 minutes, cast into shape, and demold after curing for 24 hours.

[0074] S3: Bake according to the baking curve, which is as follows: room temperature to 100℃, heating rate of 20℃ / min, hold at 100℃ for 50h; 100℃ to 150℃, heating rate of 20℃ / min, hold at 150℃ for 70h; 150℃ to 350℃, heating rate of 15℃ / min, hold at 350℃ for 2.5h; 350℃ to 550℃, heating rate of 20℃ / h, hold at 550℃ for 70h; 550℃ to 800℃, heating rate of 25℃ / h, hold at 800℃ for 60h.

[0075] The blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as the carbon source, showed numerous spiderweb-like silicon carbide whiskers in the matrix after its initial high-temperature service, as observed using a scanning electron microscope. Further testing of the samples revealed the following: room temperature flexural strength was 11.4 MPa, room temperature compressive strength was 51.5 MPa, oxidation erosion index was 16.0%, and slag erosion depth was 1.4 mm.

[0076] Example 3

[0077] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source, as detailed below:

[0078] (I) Preparation of modified ball asphalt

[0079] S1: At room temperature, dry spherical asphalt with a particle size of 0-1 mm is immersed in an acid solution and allowed to react naturally for 10 min. The acid solution used is a 10 wt.% dilute nitric acid solution. After the etching reaction is completed, the spherical asphalt with a rough surface is obtained by drying at 60℃ for 3 h.

[0080] S2: The rough-surfaced spherical asphalt obtained in S1 is immersed in a 20 wt.% nano-silica sol solution and naturally air-dried in a ventilated place to obtain spherical asphalt with nano-silica adhering to its surface; wherein the nano-silica sol solution used is alkaline with a pH value of 8; the mass ratio of the etched spherical asphalt used is 1:0.2.

[0081] (II) Preparation method of castable refractory for blast furnace tapping trough

[0082] S1: Raw material formulation: The castable raw materials include 60 wt.% brown fused alumina aggregate, 15 wt.% silicon carbide, 16 wt.% dense fused alumina compound α-alumina micro powder, 4 wt.% calcium aluminate cement, 2 wt.% metallic aluminum powder compound elemental silica powder and 3 wt.% modified spherical asphalt.

[0083] The particle size distribution of the brown fused alumina aggregate used is as follows: 25 wt.% of the brown fused alumina aggregate is 5-8 mm, 35 wt.% is 3-5 mm, 15 wt.% is 1-3 mm, and 25 wt.% is 0.088-1 mm.

[0084] The particle size distribution of the silicon carbide used is as follows: 40 wt.% of silicon carbide is 0.088-1 mm, and 60 wt.% of silicon carbide is smaller than 0.088 mm.

[0085] The mass ratio of dense corundum to α-alumina micro powder in the dense corundum compound α-alumina micro powder used is 0.15. Dense corundum is a fine powder with a particle size of less than 0.045 mm. The α-alumina micro powder is selected with an Al2O3 content of ≥98 wt.% and its particle size distribution curve has a bimodal structure with peak values ​​of 1.2 μm and 2.3 μm, respectively.

[0086] The calcium aluminate cement used was Secar71 pure calcium aluminate cement.

[0087] The mass ratio of aluminum powder to elemental silicon powder in the aluminum powder-silicon composite is 0.15.

[0088] S2: Taking the castable raw materials described in S1 as a whole, add a water-reducing agent at a mass ratio of 0.2% of the above castable raw materials; wherein the water-reducing agent used is sodium tripolyphosphate.

[0089] Mix the above-mentioned casting material and water-reducing agent for 5 minutes to obtain a dry mixture; add water at a mass ratio of 4.8% of the dry mixture; mix in a high-power mixer for 5 minutes, cast into shape, and demold after curing for 22 hours.

[0090] S3: Bake according to the baking curve, which is as follows: room temperature to 100℃, heating rate of 15℃ / min, hold at 100℃ for 48h; 100℃ to 150℃, heating rate of 15℃ / min, hold at 150℃ for 68h; 150℃ to 350℃, heating rate of 20℃ / min, hold at 350℃ for 4h; 350℃ to 550℃, heating rate of 25℃ / h, hold at 550℃ for 68h; 550℃ to 800℃, heating rate of 20℃ / h, hold at 800℃ for 58h.

[0091] The blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as the carbon source, showed spiderweb-like silicon carbide whiskers in the matrix after its initial high-temperature service, as observed using a scanning electron microscope. Testing revealed that the sample exhibited a room-temperature flexural strength of 11.5 MPa, a room-temperature compressive strength of 52.2 MPa, an oxidation erosion index of 16.5%, and a slag erosion depth of 1.5 mm.

[0092] Example 4

[0093] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source. The difference between this method and Embodiment 1 is that the raw material ratio of the blast furnace tapping trough castable is different. Specifically, the raw materials of the castable contain the following components and their weight percentages: 57 wt.% brown corundum aggregate, 20 wt.% silicon carbide, 13 wt.% dense corundum compounded α-alumina micro powder, 6 wt.% calcium aluminate cement, 1.5 wt.% metallic aluminum powder compounded elemental silica powder, and 2.5 wt.% modified spherical pitch.

[0094] The baking processes differ, specifically: 18℃ / min for heating from room temperature to 100℃, holding at 100℃ for 50 hours; 18℃ / min for heating from 100℃ to 150℃, holding at 150℃ for 70 hours; 18℃ / min for heating from 150℃ to 350℃, holding at 350℃ for 2.5 hours; 22℃ / h for heating from 350℃ to 550℃, holding at 550℃ for 65 hours; and 22℃ / h for heating from 550℃ to 800℃, holding at 800℃ for 55 hours.

[0095] The blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as the carbon source, showed spiderweb-like silicon carbide whiskers in the matrix after its initial high-temperature service, as observed using a scanning electron microscope. Testing revealed that the sample exhibited a room-temperature flexural strength of 11 MPa, a room-temperature compressive strength of 52.7 MPa, an oxidation erosion index of 15.9%, and a slag erosion depth of 1.4 m.

[0096] Example 5

[0097] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical asphalt as a carbon source. The difference between this method and Embodiment 1 is that the baking process is different. Specifically, the heating rate from room temperature to 100℃ is 20℃ / min, and the temperature is held at 100℃ for 45 hours. The heating rate from 100℃ to 150℃ is 20℃ / min, and the temperature is held at 150℃ for 65 hours. The heating rate from 150℃ to 330℃ is 15℃ / min, and the temperature is held at 330℃ for 4 hours. The heating rate from 330℃ to 550℃ is 20℃ / h, and the temperature is held at 550℃ for 65 hours. The heating rate from 550℃ to 800℃ is 25℃ / h, and the temperature is held at 800℃ for 55 hours.

[0098] The blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as the carbon source, showed spiderweb-like silicon carbide whiskers in the matrix after its initial high-temperature service, as observed using a scanning electron microscope. Testing revealed that the sample exhibited a room-temperature flexural strength of 10.5 MPa, a room-temperature compressive strength of 47.8 MPa, an oxidation erosion index of 17.9%, and a slag erosion depth of 1.7 mm.

[0099] Example 6

[0100] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical asphalt as a carbon source. The difference between this method and Embodiment 1 is that the baking process is different. Specifically, the heating rate from room temperature to 100℃ is 20℃ / min, and the temperature is held at 100℃ for 45 hours. The heating rate from 100℃ to 150℃ is 20℃ / min, and the temperature is held at 150℃ for 65 hours. The heating rate from 150℃ to 340℃ is 15℃ / min, and the temperature is held at 340℃ for 3 hours. The heating rate from 340℃ to 550℃ is 20℃ / h, and the temperature is held at 550℃ for 65 hours. The heating rate from 550℃ to 800℃ is 25℃ / h, and the temperature is held at 800℃ for 55 hours.

[0101] The blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as the carbon source, showed spiderweb-like silicon carbide whiskers in the matrix after its initial high-temperature service, as observed using a scanning electron microscope. Testing revealed that the sample exhibited a room-temperature flexural strength of 11.3 MPa, a room-temperature compressive strength of 49.3 MPa, an oxidation erosion index of 16.8%, and a slag erosion depth of 1.5 mm.

[0102] Example 7

[0103] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical asphalt as a carbon source. The difference between this method and Embodiment 1 is that the baking process is different. Specifically, the heating rate from room temperature to 100℃ is 20℃ / min, and the temperature is held at 100℃ for 45 hours. The heating rate from 100℃ to 150℃ is 20℃ / min, and the temperature is held at 150℃ for 65 hours. The heating rate from 150℃ to 360℃ is 15℃ / min, and the temperature is held at 360℃ for 2.5 hours. The heating rate from 360℃ to 550℃ is 20℃ / h, and the temperature is held at 550℃ for 65 hours. The heating rate from 550℃ to 800℃ is 22℃ / h, and the temperature is held at 800℃ for 55 hours.

[0104] The blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as the carbon source, showed spiderweb-like silicon carbide whiskers in the matrix after its initial high-temperature service, as observed using a scanning electron microscope. Testing revealed that the sample exhibited a room-temperature flexural strength of 11.5 MPa, a room-temperature compressive strength of 52.5 MPa, an oxidation erosion index of 16.4%, and a slag erosion depth of 1.5 mm.

[0105] Example 8

[0106] This embodiment provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical asphalt as a carbon source. The difference between this method and Embodiment 1 is that the baking process is different. Specifically, the heating rate from room temperature to 100℃ is 20℃ / min, and the temperature is held at 100℃ for 45 hours. The heating rate from 100℃ to 150℃ is 20℃ / min, and the temperature is held at 150℃ for 65 hours. The heating rate from 150℃ to 370℃ is 15℃ / min, and the temperature is held at 370℃ for 2 hours. The heating rate from 370℃ to 550℃ is 20℃ / h, and the temperature is held at 550℃ for 65 hours. The heating rate from 550℃ to 800℃ is 25℃ / h, and the temperature is held at 800℃ for 55 hours.

[0107] The blast furnace tapping trough castable prepared in this embodiment, using modified spherical pitch as the carbon source, showed spiderweb-like silicon carbide whiskers in the matrix after its initial high-temperature service, as observed using a scanning electron microscope. Testing revealed that the sample exhibited a room-temperature flexural strength of 11.0 MPa, a room-temperature compressive strength of 48.3 MPa, an oxidation erosion index of 17.2%, and a slag erosion depth of 1.6 mm.

[0108] Comparative Example 1

[0109] This comparative example provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source. The difference between this method and Example 1 is that the baking process is different. Specifically, the heating rate from room temperature to 100°C is 20°C / min, and the temperature is held at 100°C for 45 hours; the heating rate from 100°C to 150°C is 20°C / min, and the temperature is held at 150°C for 65 hours; the heating rate from 150°C to 300°C is 15°C / min, and the temperature is held at 300°C for 3 hours; the heating rate from 300°C to 550°C is 20°C / h, and the temperature is held at 550°C for 65 hours; the heating rate from 550°C to 800°C is 25°C / h, and the temperature is held at 800°C for 55 hours.

[0110] The high-performance blast furnace tapping trough castable prepared in this comparative example, using modified spherical pitch as a carbon source, showed a small amount of silicon carbide whiskers in the matrix after its initial high-temperature service, as observed by scanning electron microscopy. Further testing of the samples revealed the following: the castable sample exhibited a room-temperature flexural strength of 9.3 MPa, a room-temperature compressive strength of 41.6 MPa, an oxidation erosion index of 20.2%, and a slag erosion depth of 2.3 mm.

[0111] Comparative Example 2

[0112] This comparative example provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source. The difference between this method and Example 1 is that the baking curves are different. Specifically, the heating rate from room temperature to 100°C is 20°C / min, and the temperature is held at 100°C for 45 hours; the heating rate from 100°C to 150°C is 20°C / min, and the temperature is held at 150°C for 65 hours; the heating rate from 150°C to 320°C is 15°C / min, and the temperature is held at 320°C for 3 hours; the heating rate from 330°C to 550°C is 20°C / h, and the temperature is held at 550°C for 65 hours; the heating rate from 550°C to 800°C is 25°C / h, and the temperature is held at 800°C for 55 hours.

[0113] The high-performance blast furnace tapping trough castable prepared in this comparative example, using modified spherical pitch as a carbon source, showed a small amount of silicon carbide whiskers in the matrix after its initial high-temperature service using a scanning electron microscope. Further testing of the samples revealed the following: room temperature flexural strength was 10.2 MPa, room temperature compressive strength was 44.8 MPa, oxidation erosion index was 18%, and slag erosion depth was 2 mm.

[0114] Comparative Example 3

[0115] This comparative example provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source. The difference between this method and Example 1 is that the baking curves are different. Specifically, the heating rate from room temperature to 100℃ is 20℃ / min, and the temperature is held at 100℃ for 45 hours; the heating rate from 100℃ to 150℃ is 20℃ / min, and the temperature is held at 150℃ for 65 hours; the heating rate from 150℃ to 380℃ is 15℃ / min, and the temperature is held at 380℃ for 3 hours; the heating rate from 320℃ to 550℃ is 20℃ / h, and the temperature is held at 550℃ for 65 hours; the heating rate from 550℃ to 800℃ is 25℃ / h, and the temperature is held at 800℃ for 55 hours.

[0116] The high-performance blast furnace tapping trough castable prepared in this comparative example, using modified spherical pitch as a carbon source, showed silicon carbide whiskers in the matrix after its initial high-temperature service using a scanning electron microscope. Further testing of the samples revealed the following: room temperature flexural strength of 10.3 MPa, room temperature compressive strength of 45.6 MPa, oxidation erosion index of 18.2%, and slag erosion depth of 1.9 mm.

[0117] Comparative Example 4

[0118] This comparative example provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source. The difference between this method and Example 1 is that the baking curves are different. Specifically, the heating rate from room temperature to 100℃ is 20℃ / min, and the temperature is held at 100℃ for 45 hours; the heating rate from 100℃ to 150℃ is 20℃ / min, and the temperature is held at 150℃ for 65 hours; the heating rate from 150℃ to 400℃ is 15℃ / min, and the temperature is held at 400℃ for 3 hours; the heating rate from 400℃ to 550℃ is 20℃ / h, and the temperature is held at 550℃ for 65 hours; the heating rate from 550℃ to 800℃ is 25℃ / h, and the temperature is held at 800℃ for 55 hours.

[0119] The high-performance blast furnace tapping trough castable prepared in this comparative example, using modified spherical pitch as a carbon source, showed silicon carbide whiskers in the matrix after its initial high-temperature service using a scanning electron microscope. Further testing of the samples revealed the following: room temperature flexural strength was 9.8 MPa, room temperature compressive strength was 45.6 MPa, oxidation erosion index was 21.2%, and slag erosion depth was 2.3 mm.

[0120] Comparative Example 5

[0121] This comparative example provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source. The difference between this method and Example 1 is that the baking curves are different. Specifically, the heating rate from room temperature to 100℃ is 20℃ / min, and the temperature is held at 100℃ for 45 hours; the heating rate from 100℃ to 150℃ is 20℃ / min, and the temperature is held at 150℃ for 65 hours; the heating rate from 150℃ to 450℃ is 15℃ / min, and the temperature is held at 450℃ for 3 hours; the heating rate from 450℃ to 550℃ is 20℃ / h, and the temperature is held at 550℃ for 65 hours; the heating rate from 550℃ to 800℃ is 25℃ / h, and the temperature is held at 800℃ for 55 hours.

[0122] The high-performance blast furnace tapping trough castable prepared in this comparative example, using modified spherical pitch as a carbon source, showed silicon carbide whiskers in the matrix after high-temperature service. Further testing of the samples revealed the following: room temperature flexural strength was 6.8 MPa, room temperature compressive strength was 35.0 MPa, oxidation erosion index was 30.5%, and slag erosion depth was 2.7 mm.

[0123] Comparative Example 6

[0124] This comparative example provides a method for preparing a high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source. The difference between this method and Example 1 is that the mass ratio of brown corundum aggregate in the castable raw materials is 54%, and 1 wt.% of nano silica is added. The remaining operations are basically the same.

[0125] The blast furnace tapping trough castable prepared in this comparative example, using modified spherical pitch as the carbon source, showed silicon carbide whiskers in the matrix after high-temperature service, as observed by scanning electron microscopy. Further testing of the samples revealed the following: room temperature flexural strength was 9.6 MPa, room temperature compressive strength was 43.8 MPa, oxidation erosion index was 23.7%, and slag erosion depth was 2.4 mm.

Claims

1. A castable refractory for blast furnace tapping troughs using modified spherical pitch as a carbon source, characterized in that, The castable is an Al2O3-SiC-C material castable, and its raw materials contain 2.3~5wt.% modified spherical asphalt; the modified spherical asphalt is spherical asphalt with nano-silica loaded on its surface; The raw materials of the castable also include 50-60 wt.% brown fused alumina aggregate, 15-23 wt.% silicon carbide, 11-38 wt.% dense fused alumina compound α-alumina micro powder, 4-6 wt.% calcium aluminate cement, and 1.5-2.0 wt.% metallic aluminum powder compound elemental silica powder. The particle size distribution of the brown fused alumina aggregate is as follows: 5-8mm particles account for 25-45 wt.% of the brown fused alumina aggregate, 3-5mm particles account for 15-35 wt.% of the brown fused alumina aggregate, 1-3mm particles account for 15-30 wt.% of the brown fused alumina aggregate, and 0.088-1mm particles account for 10-25 wt.% of the brown fused alumina aggregate.

2. The castable refractory for blast furnace tapping troughs using modified spherical pitch as a carbon source as described in claim 1, characterized in that, The particle size of the spherical asphalt is 0~1mm.

3. The castable refractory for blast furnace tapping troughs using modified spherical pitch as a carbon source as described in claim 1, characterized in that, The silicon carbide has a particle size distribution of 40-55 wt% for particles of 0.088-1 mm and 45-60 wt% for particles smaller than 0.088 mm. And / or the mass ratio of dense corundum to α-alumina micro powder in the dense corundum compound α-alumina micro powder is 0.1~0.2, and the particle size of the dense corundum is less than 0.045mm; the α-alumina micro powder is selected with an Al2O3 content ≥98wt.% and a particle size distribution curve with a bimodal structure, and the peak values ​​of the bimodal peaks are 1.2μm and 2.3μm, respectively; And / or the mass ratio of metallic aluminum powder to elemental silicon powder in the aforementioned metallic aluminum powder compound is 0.1~0.2; And / or the calcium aluminate cement is Secar71 pure calcium aluminate cement; And / or the water-reducing agent is one or more of sodium tripolyphosphate, sodium hexametaphosphate, or polycarboxylate water-reducing agents imported from BASF, Germany.

4. The method for preparing high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source according to any one of claims 1-3, characterized in that, The process includes a baking process, which involves keeping the casting material at 330~370℃ for 2.5~4 hours.

5. The method for preparing high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source according to claim 4, characterized in that, include: Based on the total mass of the castable raw materials, a water-reducing agent of 0.15-0.25% by mass is added externally. The castable raw materials and water-reducing agent are mixed according to the mass ratio and placed in a high-power mixer and stirred for 5-10 minutes to obtain a dry mixture. Water of 4.5-5 wt.% by mass is added to the dry mixture, and it is stirred in a high-power mixer for 3-5 minutes. The mixture is then cast, cured for 20-24 hours, demolded, and then baked.

6. The method for preparing blast furnace tapping trough castable using modified spherical pitch as a carbon source according to claim 4, characterized in that, The specific steps of the preparation method of the modified spherical asphalt are as follows: Step 1: Etch the ball of asphalt and then dry it; Step 2: Impregnate the spherical asphalt obtained in Step 1 in a nano silica sol solution, and then dry it to obtain modified spherical asphalt.

7. The method for preparing blast furnace tapping trough castable using modified spherical pitch as a carbon source according to claim 6, characterized in that, The nano-silica sol solution used in step 2 is alkaline; And / or the concentration of the nano-silica sol solution in step 2 is 20~40 wt.%, and the molar ratio of the spherical pitch used to the nano-silica contained in the nano-silica sol solution is 1:0.2~0.4; And / or etching the spherical asphalt in step 1, specifically by using an acid solution for etching.

8. The method for preparing high-performance blast furnace tapping trough castable using modified spherical pitch as a carbon source according to claim 4, characterized in that, The baking process further includes: heating from room temperature to 100℃ at a heating rate of 15~20℃ / h, and holding at 100℃ for 45~50h; heating from 100℃ to 150℃ at a heating rate of 15~20℃ / h, and holding at 150℃ for 65~70h; heating from 150℃ to between 330~370℃ at a heating rate of 15~20℃ / h; heating from 330~370℃ to 550℃ at a heating rate of 20~25℃ / h, and holding at 550℃ for 65~70h; and heating from 550℃ to 800℃ at a heating rate of 20~25℃ / h, and holding at 800℃ for 55~60h.

9. The method for preparing blast furnace tapping trough castable using modified spherical pitch as a carbon source according to claim 4, characterized in that, The microstructure of the castable prepared after the baking process contains a spider web-like silicon carbide whisker structure. And / or the oxidation erosion index of the castable obtained after baking process is less than 17.9%.

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