Carbon-free steel ladle castable products and processes

Abstract

This invention provides a carbon-free steel ladle castable product and process. The mass percentage of each raw material is as follows: corundum particles 60-70 wt%, magnesium aluminum spinel particles 1-5 wt%, α-alumina micro powder 2-15 wt%, corundum micro powder 5-10 wt%, fused magnesia micro powder 1-6 wt%, magnesium aluminum spinel micro powder 1-5 wt%, composite sintering accelerator 0.1-5 wt%, composite explosion-proof agent 0.05-0.2 wt%, binder 1-10 wt%, and water-reducing agent 0.05-0.25 wt%. This invention improves the corrosion resistance of the steel ladle castable matrix and effectively enhances the service performance of the castable under high-temperature conditions.

Description

Technical Field

[0001] This invention belongs to the field of refractory materials and relates to a carbon-free steel ladle castable product and process. Background Technology

[0002] With the development of continuous casting and ladle refining technologies, some refining processes have been transferred from steelmaking furnaces to ladles. Ladles are not only high-temperature containers for storing molten steel, but also have the function of refining molten steel in a vacuum, making them a unique metallurgical equipment. The quality of refractory castables used in ladles directly affects the quality of molten steel and smelting efficiency.

[0003] Electric arc furnace (EAF) ladles operate under demanding conditions: high tapping temperatures (1640℃-1690℃), a wide variety of steel grades, a broad range of slag basicities, and long refining times. While current mainstream refractory materials used for ladle linings meet the requirements of current refining technologies, they still present several challenges in terms of their structure, high-temperature flexural strength, thermal shock resistance, erosion resistance, and the harmless treatment of inclusions in the steel. Common magnesia-carbon bricks offer excellent high-temperature flexural strength, thermal shock resistance, and erosion resistance, but the carbon within them easily seeps into the molten steel, leading to increased carbon content and offering no significant advantage for producing high-grade steels.

[0004] Existing carbon-free steel ladle castables based on corundum spinel do not increase the carbon content of molten steel. They mainly use magnesium aluminum spinel, fused magnesia, and corundum as raw materials, and are composed of advanced micro powder bonding technology and a certain amount of additives. They have higher mechanical strength and abrasion resistance than high alumina refractory castables and mullite refractory castables, but their high-temperature performance is inferior to that of magnesia-carbon bricks. Summary of the Invention

[0005] This invention provides a carbon-free steel ladle castable product and process, which overcomes the shortcomings of the prior art and effectively enhances the high-temperature service performance of steel ladle castable.

[0006] To achieve the above technical effects, the present invention adopts the following technical solution: This invention provides a carbon-free steel ladle castable product, wherein the mass percentage of each raw material is as follows: corundum particles 60-70wt%, magnesium aluminum spinel particles 1-5wt%, α-alumina micro powder 2-15wt%, corundum micro powder 5-10wt%, fused magnesia micro powder 1-6wt%, magnesium aluminum spinel micro powder 1-5wt%, composite sintering accelerator 0.1-5wt%, composite explosion retardant 0.05-0.2wt%, binder 1-10wt%, and water-reducing agent 0.05-0.25wt%.

[0007] Preferably, the corundum particles are one or more of tabular corundum and white corundum; the particle size of the tabular corundum and white corundum particles is 1-0 mm, 3-1 mm, and 6-3 mm. The particle size of the tabular corundum and white corundum particles includes three types: 1-0 mm, 3-1 mm, and 6-3 mm.

[0008] Preferably, the particle size of the magnesium aluminum spinel particles is 1-0 mm.

[0009] Preferably, the particle size of the α-alumina micro powder is less than 1 μm.

[0010] Preferably, the corundum powder includes one or more of tabular corundum powder and white corundum powder, with a particle size of less than 0.045 mm.

[0011] Preferably, the particle size of the fused magnesia powder is less than 0.075 mm, and the particle size of the magnesium aluminum spinel powder is less than 0.075 mm.

[0012] Preferably, the composite sintering accelerator is nano-sized calcium carbonate and active magnesium oxide, and the ratio of nano-sized calcium carbonate to active magnesium oxide is 1:1.

[0013] Preferably, the composite explosion-proof agent is a modified explosion-proof fiber.

[0014] Preferably, the water-reducing agent is one or more of sodium tripolyphosphate, sodium hexametaphosphate, and polycarboxylic acid polymers; the binder is high-purity calcium aluminate cement.

[0015] A manufacturing process for a carbon-free steel ladle castable product includes the following steps: 1) Co-grinding: The prepared α-alumina micro powder, corundum micro powder, fused magnesia micro powder, magnesium aluminum spinel micro powder, composite sintering accelerator, composite explosion-proof agent, binder, and water-reducing agent are dry-mixed in a planetary ball mill. 2) Mixing: After the corundum raw material is mixed evenly in the mixer, add the mixing powder and dry mix for 1-2 minutes, then add water and mix for 2-3 minutes; 3) Molding: Fix the mold on the vibration table and fill it while vibrating. The vibration time should not exceed 3 minutes. 4) Curing: Place the sample with the mold under conditions of humidity not less than 90% and temperature of 20℃±1℃ for 24 hours before demolding; 5) Drying: Place the green sample at 110℃ and dry for 24 hours; 6) Firing: The dried sample was kept in a high-temperature furnace at 1600℃ for 3 hours.

[0016] Preferably, the dry mixing time in step 1) is 30 min; and the stirring time in step 2) is 30 s.

[0017] The beneficial effects of this invention are as follows: This invention solves the problem of insufficient high-temperature service performance of ladle castables in the prior art. By selecting raw materials such as corundum, magnesium aluminum spinel, α-alumina micro powder, and composite sintering accelerator, and making certain component distributions, an aluminum magnesium calcium solid solution is generated in situ in the ladle castable, which improves the corrosion resistance of the ladle castable matrix. At the same time, the addition of composite anti-explosion agent effectively enhances the service performance of the castable under high-temperature conditions.

[0018] The advantages of this invention compared to the prior art are as follows: 1) The preparation process of the ladle castable provided by this invention adds a co-grinding process, in which the matrix part is placed in a planetary ball mill for mixing and ball milling, reducing the particle size of α-alumina micro powder and fused magnesia in the matrix, improving the uniformity of matrix distribution, enhancing the reactivity between matrices, and enabling the matrix part to react in situ under high temperature to generate an aluminum-magnesium-calcium solid solution, namely Ca2Mg2Al. 28 O 46 With CaMg2Al 16 O 27 This invention effectively improves the room temperature and high temperature physical properties of the castable, enhancing its high temperature flexural strength and corrosion resistance. 2) The invention adds a composite sintering accelerator to the material, mainly composed of nano-sized calcium carbonate and active magnesium oxide. By controlling the ratio of nano-sized calcium carbonate and active magnesium oxide in the composite sintering accelerator, the ratio of calcium, magnesium, and aluminum elements in the castable matrix is ​​made close to 7:5:88. This ratio is the theoretical ratio of the aluminum-magnesium-calcium solid solution phase. A suitable ratio promotes the full reaction of the castable matrix to form an aluminum-magnesium-calcium solid solution, improving the corrosion resistance of the carbon-free steel ladle castable. 3) By adding a composite explosion-proof agent to the material, compared with common explosion-proof fibers, the modified explosion-proof fiber provided by this invention has a 5-15μm thick silane coupling agent coating on its surface. Due to the increased fiber weight, it can significantly improve the fiber dispersion problem in the casting. In addition, organic fibers will burn off at high temperature to form pores. When the coating on the surface of the modified explosion-proof fiber is heated, the silane coupling agent decomposes at high temperature to provide a silicon source, which forms silicon carbide or silicon carbon oxygen crystal nuclei with the carbon of the organic fiber inside the pores. These nuclei gradually grow and fill the pores, improving the thermal shock resistance and corrosion resistance of the casting. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Example 1 The carbon-free steel ladle castable product of this embodiment is prepared from the following raw materials by mass percentage: Raw materials include: The plate-shaped corundum particles with a particle size ≤ 5 mm, wherein w(Al2O3) ≥ 99% and the mass percentage is 70%; w(Al2O3) refers to the mass percentage content of Al2O3; Plate-shaped corundum micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥99% and mass percentage is 8%; Magnesium aluminum spinel particles with a particle size ≤1mm, wherein w(Al2O3)≥70% and the mass percentage is 3%; Magnesium aluminum spinel micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥70% and mass percentage is 8%; α-alumina micro powder with a particle size ≤1μm, wherein w(Al2O3)≥99% and the mass percentage is 2%; Fused magnesia with a particle size ≤0.075mm, wherein w(MgO)≥99% and the mass percentage is 4%; w(MgO) refers to the mass percentage content of MgO; The binder is pure calcium aluminate cement, with a mass percentage of 5%; the composite sintering accelerator is nano-sized calcium carbonate and active magnesium oxide in a ratio of 1:1, with a mass percentage of 1.5%; the water-reducing agent is an anisotropic carboxylic acid polymer, with a mass percentage of 0.2%.

[0021] The composite explosion-proof agent is a modified explosion-proof fiber with a mass percentage of 0.1%. In this embodiment, the composite explosion-proof agent is obtained by soaking polyethylene fiber in silane coupling agent and anhydrous ethanol, ultrasonically dispersing it, and drying it to obtain a modified explosion-proof fiber, wherein the mass ratio of silane coupling agent to anhydrous ethanol is 1:0.5.

[0022] The preparation process is as follows: 1) Co-grinding: Dry mix the prepared α-alumina micro powder, corundum micro powder, fused magnesia micro powder, magnesium aluminum spinel micro powder, composite sintering accelerator, composite explosion-proof agent, binder, and water-reducing agent in a planetary ball mill for 30 minutes. 2) Mixing: After the corundum raw material is mixed evenly in the mixer, the mixed powder is added and then dry-mixed for 1-2 minutes, and then water is added and mixed for 2-3 minutes; in step 2, the mixing time can be 30 seconds. 3) Molding: Fix the mold on the vibration table and fill it while vibrating. The vibration time should not exceed 3 minutes. 4) Curing: Place the sample with the mold under conditions of humidity not less than 90% and temperature of 20℃±1℃ for 24 hours before demolding; 5) Drying: Place the green sample at 110℃ and dry for 24 hours; 6) Firing: The dried sample was kept in a high-temperature furnace at 1600℃ for 3 hours.

[0023] The performance and effects of the prepared carbon-free steel ladle castable products are shown in Tables 1 and 2.

[0024] Example 2 The carbon-free steel ladle castable product of this embodiment is prepared from the following raw materials by mass percentage: wherein, the raw materials include: Plate-shaped corundum particles with a particle size ≤5mm, wherein w(Al2O3)≥99% and mass percentage is 65%; Plate-shaped corundum micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥99% and mass percentage is 8%. Magnesium aluminum spinel particles with a particle size ≤1mm, wherein w(Al2O3)≥70% and the mass percentage is 3%; Magnesium aluminum spinel micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥70% and mass percentage is 8%. α-alumina micro powder with a particle size ≤1μm, wherein w(Al2O3)≥99% and the mass percentage is 7%; Fused magnesia with a particle size ≤0.075mm, wherein w(MgO)≥99% and mass percentage is 4%; The binder is pure calcium aluminate cement, with a mass percentage of 5%.

[0025] The composite sintering accelerator is composed of nano-sized calcium carbonate and active magnesium oxide in a 1:1 ratio, with a mass percentage of 1.5%. The composite explosion-proof agent is a modified explosion-proof fiber, with a mass percentage of 0.1%. The water-reducing agent is a polycarboxylic acid type polymer, with a mass percentage of 0.2%. In this embodiment, the composite explosion-proof agent is obtained by soaking polyethylene fiber in silane coupling agent and anhydrous ethanol, ultrasonically dispersing it, and drying it to obtain a modified explosion-proof fiber, wherein the mass ratio of silane coupling agent to anhydrous ethanol is 1:0.5.

[0026] The above raw materials are taken according to the proportions. After the matrix is ​​dry-mixed, it is then mixed evenly with the aggregate in a mixer. Water is added and stirred. The mixture is then placed on a vibrating table and vibrated to form the shape. After drying, the green body is fired in a high-temperature furnace at 1600℃ for 3 hours. Other process steps are the same as in Example 1.

[0027] The properties and effects of the prepared carbon-free steel ladle castable are shown in Tables 1 and 2.

[0028] Example 3 The carbon-free steel ladle castable in this embodiment is prepared from the following raw materials by mass percentage: wherein the raw materials include: Plate-shaped corundum particles with a particle size ≤5mm, wherein w(Al2O3)≥99% and mass percentage is 60%; Plate-shaped corundum micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥99% and mass percentage is 8%. Magnesium aluminum spinel particles with a particle size ≤1mm, wherein w(Al2O3)≥70% and the mass percentage is 3%; Magnesium aluminum spinel micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥70% and mass percentage is 8%. α-alumina micro powder with a particle size ≤1μm, wherein w(Al2O3)≥99% and mass percentage is 12%; Fused magnesia with a particle size ≤0.075mm, wherein w(MgO)≥99% and mass percentage is 4%; The binder is pure calcium aluminate cement, with a mass percentage of 5%.

[0029] The composite sintering accelerator is composed of nano-sized calcium carbonate and active magnesium oxide in a 1:1 ratio, with a mass percentage of 1.5%; the composite explosion-proof agent is modified explosion-proof fiber, with a mass percentage of 0.1%; and the water-reducing agent is a polycarboxylic acid type polymer, with a mass percentage of 0.2%.

[0030] In this embodiment, the composite explosion-proof agent is obtained by soaking polyethylene fiber in silane coupling agent and anhydrous ethanol, ultrasonically dispersing it, and drying it to obtain a modified explosion-proof fiber, wherein the mass ratio of silane coupling agent to anhydrous ethanol is 1:0.5.

[0031] The above raw materials are taken according to the proportions. After the matrix is ​​dry-mixed, it is then mixed evenly with the aggregate in a mixer. Water is added and stirred. The mixture is then placed on a vibrating table and vibrated to form the shape. After drying, the green body is fired in a high-temperature furnace at 1600℃ for 3 hours. Other process steps are the same as in Example 1.

[0032] The properties and effects of the prepared carbon-free steel ladle castable are shown in Tables 1 and 2.

[0033] Example 4 The carbon-free steel ladle castable in this embodiment is prepared from the following raw materials by mass percentage: wherein the raw materials include: White corundum particles with a particle size ≤5mm, wherein w(Al2O3)≥99% and mass percentage is 65%; White corundum micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥99% and mass percentage is 8%. Magnesium aluminum spinel particles with a particle size ≤1mm, wherein w(Al2O3)≥70% and the mass percentage is 3%; Magnesium aluminum spinel micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥70% and mass percentage is 8%. α-alumina micro powder with a particle size ≤1μm, wherein w(Al2O3)≥99% and the mass percentage is 7%; Fused magnesia with a particle size ≤0.075mm, wherein w(MgO)≥99% and mass percentage is 4%; The binder is pure calcium aluminate cement, with a mass percentage of 5%.

[0034] The composite sintering accelerator is composed of nano-sized calcium carbonate and active magnesium oxide in a 1:1 ratio, with a mass percentage of 1.5%; the composite explosion-proof agent is modified explosion-proof fiber, with a mass percentage of 0.1%; and the water-reducing agent is a polycarboxylic acid type polymer, with a mass percentage of 0.2%.

[0035] In this embodiment, the composite explosion-proof agent is obtained by soaking polyethylene fiber in silane coupling agent and anhydrous ethanol, ultrasonically dispersing it, and drying it to obtain a modified explosion-proof fiber, wherein the mass ratio of silane coupling agent to anhydrous ethanol is 1:0.5.

[0036] The above raw materials are taken according to the proportions. After the matrix is ​​dry-mixed, it is then mixed evenly with the aggregate in a mixer. Water is added and stirred. The mixture is then placed on a vibrating table and vibrated to form the shape. After drying, the green body is fired in a high-temperature furnace at 1600℃ for 3 hours. Other process steps are the same as in Example 1.

[0037] The properties and effects of the prepared carbon-free steel ladle castable are shown in Tables 1 and 2.

[0038] Example 5 The carbon-free steel ladle castable in this embodiment is prepared from the following raw materials by mass percentage: wherein the raw materials include: White corundum particles with a particle size ≤5mm, wherein w(Al2O3)≥99% and mass percentage is 65%; White corundum micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥99% and mass percentage is 8%. Magnesium aluminum spinel particles with a particle size ≤1mm, wherein w(Al2O3)≥70% and the mass percentage is 3%; Magnesium aluminum spinel micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥70% and mass percentage is 8%. α-alumina micro powder with a particle size ≤1μm, wherein w(Al2O3)≥99% and mass percentage is 8%; Fused magnesia with a particle size ≤0.075mm, wherein w(MgO)≥99% and mass percentage is 4%; The binder is pure calcium aluminate cement, accounting for 5% by mass. The composite sintering accelerator is nano-grade calcium carbonate and active magnesium oxide in a 1:1 ratio, accounting for 1.5% by mass; the composite explosion-proof agent is modified explosion-proof fiber, accounting for 0.1% by mass; and the water-reducing agent is sodium tripolyphosphate, accounting for 0.2% by mass.

[0039] In this embodiment, the composite explosion-proof agent is obtained by soaking polyethylene fiber in silane coupling agent and anhydrous ethanol, ultrasonically dispersing it, and drying it to obtain a modified explosion-proof fiber, wherein the mass ratio of silane coupling agent to anhydrous ethanol is 1:0.5.

[0040] The above raw materials are taken according to the proportions. After the matrix is ​​dry-mixed, it is then mixed evenly with the aggregate in a mixer. Water is added and stirred. The mixture is then placed on a vibrating table and vibrated to form the shape. After drying, the green body is fired in a high-temperature furnace at 1600℃ for 3 hours. Other process steps are the same as in Example 1.

[0041] The properties and effects of the prepared carbon-free steel ladle castable are shown in Tables 1 and 2.

[0042] Example 6 The carbon-free steel ladle castable in this embodiment is prepared from the following raw materials by mass percentage: wherein the raw materials include: White corundum particles with a particle size ≤5mm, wherein w(Al2O3)≥99% and mass percentage is 65%; White corundum micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥99% and mass percentage is 8%. Magnesium aluminum spinel particles with a particle size ≤1mm, wherein w(Al2O3)≥70% and the mass percentage is 3%; Magnesium aluminum spinel micro powder with a particle size ≤0.075mm, wherein w(Al2O3)≥70% and mass percentage is 8%. α-alumina micro powder with a particle size ≤1μm, wherein w(Al2O3)≥99% and the mass percentage is 7%; Fused magnesia with a particle size ≤0.075mm, wherein w(MgO)≥99% and mass percentage is 4%; The binder is pure calcium aluminate cement, accounting for 5% by mass. The composite sintering accelerator is nano-grade calcium carbonate and active magnesium oxide in a 1:1 ratio, accounting for 1.5% by mass; the composite explosion-proof agent is modified explosion-proof fiber, accounting for 0.1% by mass; and the water-reducing agent is sodium hexametaphosphate, accounting for 0.2% by mass.

[0043] The above raw materials are taken according to the proportions. After the matrix is ​​dry-mixed, it is then mixed evenly with the aggregate in a mixer. Water is added and stirred. The mixture is then placed on a vibrating table and vibrated to form the shape. After drying, the green body is fired in a high-temperature furnace at 1600℃ for 3 hours. Other process steps are the same as in Example 1.

[0044] The properties and effects of the prepared carbon-free steel ladle castable are shown in Tables 1 and 2.

[0045] Comparative Example 1 The raw material composition of this comparative example is the same as that of the castable in Example 1. The difference is that no sintering accelerator was added to control the ratio of magnesium oxide, calcium oxide and aluminum oxide in the matrix, and no composite explosion-proof agent was added.

[0046] The static crucible method was used to test the erosion of castables by steel slag. In this invention, steel slag taken from the factory was used for the erosion resistance test. First, the castable was made into a crucible sample. The sample was heated to 1600°C in a high-temperature furnace and held at that temperature for 3 hours to allow the steel slag to fully melt. Then, it was cooled to room temperature with the furnace. The crucible was then cut along the central axis to observe the erosion of the crucible.

[0047] Table 1 Example 1 18.9 3.01 34.1 155.7 8.9 Example 2 19.6 2.99 33.7 150.9 8.4 Example 3 19.0 3.00 30.6 143.8 7.5 Example 4 19.8 2.99 33.2 151.4 8.2 Example 5 22.0 2.94 26.8 142.2 7.3 Example 6 21.9 2.93 25.3 140.4 7.3 Comparative Example 1 17.1 3.06 23.1 138.6 6.5 Table 2 Example 1 slight penetration No cracks Example 2 slight penetration No cracks Example 3 slight penetration No cracks Example 4 slight penetration No cracks Example 5 slight penetration No cracks Example 6 slight penetration No cracks Comparative Example 1 Severe infiltration Cracks The above description is only for illustrating the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A carbon-free steel ladle castable product, characterized in that, The mass percentage of each raw material is as follows: corundum particles 60-70wt%, magnesium aluminum spinel particles 1-5wt%, α-alumina micro powder 2-15wt%, corundum micro powder 5-10wt%, fused magnesia micro powder 1-6wt%, magnesium aluminum spinel micro powder 1-5wt%, composite sintering accelerator 0.1-5wt%, composite explosion-proof agent 0.05-0.2wt%, binder 1-10wt%, and water-reducing agent 0.05-0.25wt%. The composite sintering accelerator is nano-sized calcium carbonate and active magnesium oxide, with a ratio of 1:1 between nano-sized calcium carbonate and active magnesium oxide. The composite explosion-proof agent is a modified explosion-proof fiber, which is prepared by soaking polyethylene fiber in silane coupling agent and anhydrous ethanol, ultrasonically dispersing it, and drying it to obtain a modified explosion-proof fiber, wherein the mass ratio of silane coupling agent to anhydrous ethanol is 1:0.

5. The water-reducing agent is one or more of sodium tripolyphosphate and sodium hexametaphosphate; the binder is high-purity calcium aluminate cement.

2. The carbon-free steel ladle castable product according to claim 1, characterized in that, The corundum particles are one or more of tabular corundum and white corundum; the particle size of the tabular corundum and white corundum particles is 1-0 mm, 3-1 mm, and 6-3 mm.

3. The carbon-free steel ladle castable product according to claim 1, characterized in that, The particle size of the magnesium aluminum spinel particles is 1-0 mm.

4. The carbon-free steel ladle castable product according to claim 1, characterized in that, The particle size of the α-alumina micro powder is less than 1 μm.

5. The carbon-free steel ladle castable product according to claim 1, characterized in that, The corundum micro powder includes one or more of tabular corundum micro powder and white corundum micro powder, with a particle size of less than 0.045 mm.

6. The carbon-free steel ladle castable product according to claim 1, characterized in that, The particle size of the fused magnesia powder is less than 0.075 mm, and the particle size of the magnesium aluminum spinel powder is less than 0.075 mm.

7. The manufacturing process of the carbon-free steel ladle castable product according to claim 1, characterized in that, Includes the following steps: 1) Co-grinding: The prepared α-alumina micro powder, corundum micro powder, fused magnesia micro powder, magnesium aluminum spinel micro powder, composite sintering accelerator, composite explosion-proof agent, binder, and water-reducing agent are dry-mixed in a planetary ball mill. 2) Mixing: After the corundum raw material is mixed evenly in the mixer, add the mixing powder and dry mix for 1-2 minutes, then add water and mix for 2-3 minutes; 3) Molding: Fix the mold on the vibration table and fill it while vibrating. The vibration time should not exceed 3 minutes. 4) Curing: Place the sample with the mold under conditions of humidity not less than 90% and temperature of 20℃±1℃ for 24 hours before demolding; 5) Drying: Place the green sample at 110℃ and dry for 24 hours; 6) Firing: The dried sample was kept in a high-temperature furnace at 1600℃ for 3 hours.