A low-cost ceramic shell preparation method for large-size titanium alloy casting

Abstract

This invention discloses a low-cost ceramic mold shell preparation method for large-size titanium alloy casting, specifically relating to the field of investment casting technology. The method includes: preparing a yttrium oxide-coated alumina core-shell structure composite powder with a particle size of 12-25 μm and a yttrium oxide coating thickness of 200-800 nm; mixing the composite powder with fine yttrium oxide powder to prepare a surface refractory powder, wherein the fine yttrium oxide powder accounts for 25%-35% and is composed of nano- and submicron-sized yttrium oxide; mixing yttrium sol and silica sol at a ratio of 7:3 to prepare a binder; mixing the refractory powder and binder at a ratio of 2.5-3.5:1 to prepare a surface slurry; applying the slurry and sprinkling alumina sand on the surface of the wax mold to form the surface layer; preparing a back layer slurry using bauxite and silica sol binder to form the back layer; and obtaining the ceramic mold shell after dewaxing and calcination. This invention constructs a composite powder with alumina as the core and yttrium oxide as the shell, and combines a three-peak particle size distribution to significantly reduce material costs while ensuring chemical compatibility.

Description

Technical Field

[0001] This invention belongs to the field of investment casting technology, specifically relating to a low-cost ceramic mold shell preparation method for large-size titanium alloy casting. Background Technology

[0002] Titanium alloys are widely used in high-end equipment fields such as aerospace, marine engineering, and chemical engineering due to their high specific strength, good corrosion resistance, strong heat resistance, and excellent biocompatibility. Investment casting is a near-net-shape forming process for manufacturing complex titanium alloy components, especially suitable for producing castings with complex internal structures and high dimensional accuracy requirements. In recent years, with the increasing demands for lightweight equipment and integrated structural and functional design, titanium alloy castings have shown a trend towards larger size, greater integration, and more complex internal cavities, with the size and weight of individual parts continuously increasing. This change places higher demands on ceramic shells: the shells must simultaneously withstand the high-temperature impact and continuous static pressure of larger tonnage molten metal, while ensuring uniform surface quality across all parts of the large casting.

[0003] In investment casting, the ceramic shell, as a functional component that directly contacts the molten titanium alloy, directly affects the surface quality and alloy properties of the casting. Titanium alloys are highly chemically reactive in the molten state, undergoing interfacial reactions to varying degrees with almost all commonly used oxide ceramic shells, forming an α-contamination layer rich in interstitial elements such as oxygen and carbon on the casting surface. This layer is highly hard and brittle, reducing the casting's plasticity and fatigue performance. For large, integral castings with complex internal structures that are difficult to machine, once a contamination layer forms on the inner cavity surface, it cannot be effectively removed, directly affecting the component's service reliability. Therefore, selecting refractory materials with excellent chemical compatibility with the molten titanium alloy to construct the shell is crucial to ensuring the quality of large titanium alloy castings.

[0004] Among oxide refractory materials, yttrium oxide possesses a high melting point and excellent thermodynamic stability, exhibiting almost no reaction with molten titanium alloys, making it a recognized inert shell material for titanium alloy casting. However, yttrium oxide raw materials are expensive and limited in supply; directly using pure yttrium oxide powder to prepare large ceramic shells leads to a sharp increase in production costs. As shell size increases, the amount of yttrium oxide used multiplies, making the material cost proportion unacceptable. The long shell-making cycle, high material consumption, and difficulty in recycling old shells further exacerbate the economic dilemma of pure yttrium oxide shells, restricting their large-scale industrial application in large-size titanium alloy castings.

[0005] Therefore, reducing the material cost of inert ceramic shells while maintaining high chemical compatibility with titanium alloy melts, and simultaneously meeting the comprehensive requirements of large shells for high-temperature strength, thermal shock resistance, and process feasibility, has become an urgent technical problem to be solved in the field of large titanium alloy precision casting. Summary of the Invention

[0006] The purpose of this invention is to provide a low-cost ceramic mold shell preparation method for large-size titanium alloy casting.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a low-cost ceramic mold shell for large-size titanium alloy casting includes the following steps: Step 1: Prepare yttrium oxide-coated alumina core-shell structured composite powder, wherein the particle size of the composite powder is 12-25 μm and the thickness of the yttrium oxide coating layer is 200-800 nm; Step 2: Prepare the surface refractory powder: Mix the composite powder with yttrium oxide fine powder. Based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 25%-35%, with the remainder being the composite powder. The yttrium oxide fine powder consists of nano-sized yttrium oxide with a particle size of 50-200 nm and submicron-sized yttrium oxide with a particle size of 1-5 μm. The nano-sized yttrium oxide accounts for 10%-25% of the total mass of the yttrium oxide fine powder, and the submicron-sized yttrium oxide accounts for 75%-90% of the total mass of the yttrium oxide fine powder. Step 3: Prepare the binder: Mix yttrium sol and silica sol at a mass ratio of 7:3; Step 4: Prepare the surface slurry: Mix the refractory powder and the binder at a powder-to-liquid mass ratio of 2.5:1-3.5:1, add wetting agent and defoamer, and stir evenly; Step 5, Shell making: Apply the surface layer slurry to the wax mold surface, sprinkle alumina sand, and dry to form the surface layer; apply the back layer slurry prepared with bauxite and silica sol binder, sprinkle sand, and dry to form the back layer; Step 6: Dewaxing and firing to obtain a ceramic shell.

[0008] Furthermore, the composite powder described in step 1 is prepared by the sol-gel method: α-alumina powder is impregnated in yttrium sol precursor, dried, calcined, and the impregnation, drying, and calcination are repeated 2-3 times.

[0009] Furthermore, the particle size of the α-alumina powder is 10-20 μm; during the impregnation process, the mass-to-volume ratio of the α-alumina powder to the yttrium sol precursor is 1:3 (kg / L).

[0010] Furthermore, the preparation method of the yttrium sol precursor is as follows: dissolve yttrium nitrate hexahydrate in anhydrous ethanol to prepare a solution with a concentration of 0.3 mol / L, add acetylacetone, the molar ratio of acetylacetone to yttrium ions is 2:1, adjust the pH to 3-5 with dilute nitric acid, and stir for 2 hours.

[0011] Furthermore, the drying temperature is 80-110℃ and the drying time is 18-24h; the calcination temperature is 700℃ and the calcination time is 3h.

[0012] Furthermore, in step 2, based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 25%, of which nano-sized yttrium oxide accounts for 10% of the total mass of the yttrium oxide fine powder, and submicron-sized yttrium oxide accounts for 90% of the total mass of the yttrium oxide fine powder.

[0013] Furthermore, in step 2, based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 30%, of which nano-sized yttrium oxide accounts for 15% of the total mass of the yttrium oxide fine powder, and submicron-sized yttrium oxide accounts for 85% of the total mass of the yttrium oxide fine powder.

[0014] Furthermore, in step 2, based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 35%, of which nano-sized yttrium oxide accounts for 25% of the total mass of the yttrium oxide fine powder, and submicron-sized yttrium oxide accounts for 75% of the total mass of the yttrium oxide fine powder.

[0015] Furthermore, the surface layer in step 5 is formed by two cycles of applying slurry, sprinkling alumina sand, and drying; the back layer is formed by six cycles of applying slurry, sprinkling bauxite sand, and drying.

[0016] Furthermore, the dewaxing in step 6 is performed using infrared dewaxing; the calcination is performed by heating to 300°C at a heating rate of 3-5°C / min and holding for 2 hours, and then heating to 1050°C and holding for 4 hours.

[0017] The beneficial effects of this invention are: 1. In terms of chemical compatibility, the present invention uses yttrium oxide-coated alumina core-shell structure composite powder as the main refractory material of the shell surface layer. The surface chemical properties of the powder are determined by yttrium oxide. When in contact with the titanium alloy melt, it exhibits chemical stability comparable to pure yttrium oxide, which can effectively inhibit interfacial reactions and reduce the thickness of the α-contamination layer on the surface of the casting.

[0018] 2. Regarding cost control, this invention constructs a composite powder with alumina as the core and yttrium oxide as the shell, reducing the amount of yttrium oxide raw material used while ensuring the chemical inertness of the surface layer. Simultaneously, the shell backing layer is prepared using bauxite and silica sol binder, further reducing the overall material cost. These measures significantly reduce the material cost of the yttrium oxide-based ceramic shell, providing an economically feasible shell solution for the large-scale production of large titanium alloy castings.

[0019] 3. Regarding the density and strength of the shell, this invention mixes yttrium oxide-coated alumina composite powder with nano- and submicron-sized yttrium oxide fine powder in a specific ratio to form a coarse-fine-ultra-fine three-peak particle size distribution. The fine powder fills the gaps between the composite powders, and the ultra-fine nano-sized particles further fill the tiny gaps between the submicron-sized particles, approaching the densest packing, thereby reducing the porosity of the shell surface layer and improving the density and high-temperature strength of the shell.

[0020] 4. Regarding the adhesive system, this invention uses a binder composed of yttrium sol and silica sol in a 7:3 mass ratio. Yttrium sol is the main component, ensuring the chemical inertness of the surface layer; silica sol is the auxiliary component, providing room temperature bonding strength and high temperature strength after calcination, thus taking into account both the process performance and performance of the shell. Attached Figure Description

[0021] Figure 1 This is a diagram of the reaction layer at the interface of the shell sample in Example 1.

[0022] Figure 2 This is a diagram of the reaction layer at the interface of the shell sample in Example 2.

[0023] Figure 3 This is a diagram of the reaction layer at the interface of the shell sample in Example 3.

[0024] Figure 4 This is a diagram of the reaction layer at the interface of the shell sample of Comparative Example 1.

[0025] Figure 5 The bar chart shows the shell strength comparison between Examples 1-3 and Comparative Example 1. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0027] Example 1 This embodiment describes the preparation of a low-cost ceramic mold shell for large-size titanium alloy casting. The specific steps are as follows: Step 1: Prepare yttrium oxide-coated alumina core-shell structured composite powder.

[0028] The composite powder was prepared using a sol-gel method, specifically as follows: 15 μm α-alumina powder was ultrasonically dispersed in anhydrous ethanol for 30 min, followed by thorough drying at 120 °C. Yttrium nitrate hexahydrate was dissolved in anhydrous ethanol to prepare a 0.3 mol / L yttrium nitrate ethanol solution. Acetylacetone was slowly added dropwise under magnetic stirring, with a molar ratio of acetylacetone to yttrium ions of 2:1. After the addition was complete, dilute nitric acid solution was added to adjust the pH of the system to 4, and stirring was continued for 2 h to form a uniform and transparent yttrium sol precursor. The pretreated α-alumina powder was slowly added to the yttrium sol precursor, with a mass-to-volume ratio of α-alumina powder to yttrium sol precursor of 1:3 (kg / L). The mixed slurry was ultrasonically treated for 25 min to ensure thorough dispersion of the powder in the sol. The slurry was then placed in a 50°C water bath and stirred continuously for 6 hours, allowing the sol to slowly condense on the surface of the alumina particles to form a uniform wet gel coating layer. The coated wet gel powder was filtered and separated, then placed in a drying oven and dried at 90°C for 20 hours to obtain the dried coated precursor powder. The dried coated precursor powder was placed in a muffle furnace and calcined at 700°C for 3 hours, followed by furnace cooling. To ensure the coating layer thickness, the above impregnation, drying, and calcination processes were repeated three times to obtain the composite powder. The composite powder prepared by the above process has a particle size of 12-25 μm and a yttrium oxide coating layer thickness of 200-800 nm.

[0029] Step 2: Prepare the surface refractory powder.

[0030] The composite powder obtained in step 1 is mixed with yttrium oxide fine powder. Based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 25%, with the remainder being the composite powder. The yttrium oxide fine powder consists of nano-sized and submicron-sized yttrium oxide. The nano-sized yttrium oxide has a particle size of 50-200 nm and accounts for 10% of the total mass of the yttrium oxide fine powder; the submicron-sized yttrium oxide has a particle size of 1-5 μm and accounts for 90% of the total mass of the yttrium oxide fine powder.

[0031] Step 3: Prepare the adhesive.

[0032] Yttrium sol and silica sol were mixed at a mass ratio of 7:3 to obtain the binder.

[0033] Step 4: Prepare the surface layer slurry.

[0034] Mix the refractory powder prepared in step 2 with the binder prepared in step 3 at a powder-to-liquid mass ratio of 2.5:1, add an appropriate amount of wetting agent and defoamer, and stir thoroughly in a mixer for 3 hours until uniform to obtain the surface slurry.

[0035] Step 5: Shell making.

[0036] A cyclical process of applying slurry, sprinkling alumina sand, and drying is employed. The surface layer slurry is applied to the wax mold surface, followed by sprinkling alumina sand and drying; this process is repeated twice. A back layer slurry is prepared using bauxite and silica sol binder. This back layer slurry is applied, followed by sprinkling bauxite sand and drying; this process is repeated six times to form the back layer. This yields a raw shell blank.

[0037] Step 6: Dewaxing and roasting.

[0038] The unglazed shell is dewaxed using infrared radiation to remove the wax mold. The shell is then placed in a firing furnace and heated to 300℃ at a heating rate of 4℃ / min, held for 2 hours, and then heated to 1050℃ and held for 4 hours to obtain the ceramic shell.

[0039] The ceramic shell prepared in this embodiment has an interfacial reaction layer between the shell sample and the titanium alloy casting as shown in the figure. Figure 1 As shown, the thickness of the interfacial reaction layer is not much different from that of the traditional yttrium oxide shell prepared in Comparative Example 1.

[0040] Example 2 The difference between this embodiment and Embodiment 1 is that: In step 2, yttrium oxide fine powder accounts for 30% of the total mass of refractory powder, of which nano-sized yttrium oxide accounts for 15% of the total mass of fine powder and submicron-sized yttrium oxide accounts for 85% of the total mass of fine powder.

[0041] In step 4, the powder-to-liquid mass ratio of refractory powder to binder is 3:1.

[0042] The remaining steps and process parameters are the same as in Example 1.

[0043] The ceramic shell prepared in this embodiment has an interfacial reaction layer between the shell sample and the titanium alloy casting as shown in the figure. Figure 2 As shown, the thickness of the interfacial reaction layer is not much different from that of the traditional yttrium oxide shell prepared in Comparative Example 1.

[0044] Example 3 The difference between this embodiment and Embodiment 1 is that: In step 2, yttrium oxide fine powder accounts for 35% of the total mass of the refractory powder, of which nano-sized yttrium oxide accounts for 25% of the total mass of the fine powder and submicron-sized yttrium oxide accounts for 75% of the total mass of the fine powder.

[0045] In step 4, the mass ratio of refractory powder to binder is 3.5:1.

[0046] The remaining steps and process parameters are the same as in Example 1.

[0047] The ceramic shell prepared in this embodiment has an interfacial reaction layer between the shell sample and the titanium alloy casting as shown in the figure. Figure 3As shown, the thickness of the interfacial reaction layer is not much different from that of the traditional yttrium oxide shell prepared in Comparative Example 1.

[0048] Example 4 The difference between this embodiment and Embodiment 1 is that the drying temperature in step 1 is 80℃ and the drying time is 24 hours; the impregnation, drying, and calcination processes are repeated twice. The remaining steps and process parameters are the same as in Embodiment 1.

[0049] Tests showed that the thickness of the interface reaction layer between the ceramic shell and the titanium alloy casting prepared in this embodiment was comparable to that of Comparative Example 1. The shell had a room temperature wet strength of 5.32 MPa, a room temperature dry strength of 8.07 MPa, and a high temperature dry strength of 4.85 MPa, which met the casting requirements of the titanium alloy casting.

[0050] Example 5 The difference between this embodiment and Embodiment 1 is that the drying temperature in step 1 is 110℃ and the drying time is 18h. The remaining steps and process parameters are the same as in Embodiment 1.

[0051] Tests showed that the thickness of the interface reaction layer between the ceramic shell and the titanium alloy casting prepared in this embodiment was comparable to that of Comparative Example 1. The shell had a room temperature wet strength of 5.38 MPa, a room temperature dry strength of 8.11 MPa, and a high temperature dry strength of 4.91 MPa, which met the casting requirements of the titanium alloy casting.

[0052] Example 6 The difference between this embodiment and Embodiment 1 is that the impregnation, drying, and calcination processes in step 1 are repeated twice. The remaining steps and process parameters are the same as in Embodiment 1.

[0053] Tests showed that the thickness of the interface reaction layer between the ceramic shell and the titanium alloy casting prepared in this embodiment was comparable to that of Comparative Example 1. The shell had a room temperature wet strength of 5.29 MPa, a room temperature dry strength of 8.05 MPa, and a high temperature dry strength of 4.83 MPa, which met the casting requirements of the titanium alloy casting.

[0054] Comparative Example 1 The traditional yttrium oxide shell preparation method was used as Comparative Example 1, and the specific steps are as follows: Preparation of the surface refractory powder: The surface refractory powder is a mixture of coarse and fine yttrium oxide powder. The coarse powder has a particle size of less than 50 μm, and the fine powder has a particle size of less than 10 μm. The mass ratio of coarse to fine powder is 3:1. Preparation of the slurry: The mixed powder is mixed with a neutral yttrium silicon-based binder at a powder-to-liquid mass ratio of 3:1. Appropriate amounts of wetting agent and defoamer are added, and the mixture is thoroughly stirred in a mixer for 3 hours to obtain the surface slurry. Shell making: A cyclical operation of slurry application, sand sprinkling, and drying is adopted. The surface slurry is applied to the surface of the wax mold, and yttrium oxide sand is sprinkled on it. Two layers of the surface slurry are applied. The back layer uses silica sol and bauxite, and six layers of the back layer are applied. Dewaxing and firing: The shell blank is dewaxed by infrared radiation, and then the shell is placed in a firing furnace. The heating rate is 3-5℃ / min, heated to 300℃ and held for 2 hours, and then heated to 1100℃ and held for 4 hours to obtain a traditional yttrium oxide ceramic shell.

[0055] The ceramic shell prepared in Comparative Example 1 has an interfacial reaction layer between the shell sample and the titanium alloy casting, as shown in Figure 1. Figure 4 As shown.

[0056] Mechanical properties were tested and titanium alloy casting samples were poured for the ceramic shells prepared in Examples 1 to 3 and Comparative Example 1.

[0057] Figures 1 to 4 The images show the interfacial reaction layers between the ceramic shell samples and the titanium alloy castings from Examples 1, 2, 3, and Comparative Example 1, respectively. A comparison reveals that the thickness of the interfacial reaction layer between the ceramic shells prepared in Examples 1 to 3 and the titanium alloy castings is not significantly different from that in Comparative Example 1. This indicates that the ceramic shells prepared in these examples possess chemical inertness comparable to traditional yttrium oxide ceramic shells, effectively suppressing interfacial reactions and reducing the thickness of the α-contamination layer on the casting surface.

[0058] Figure 5 The graph shows a comparison of the strength of four ceramic shell types from Examples 1-3 and Comparative Example 1. Figure 5 It can be seen that the ceramic shells prepared in Examples 1 to 3 have slightly higher strength than the traditional yttrium oxide ceramic shells prepared in Comparative Example 1, which meets the usage conditions for titanium alloy casting.

[0059] Regarding material costs, the ceramic shells prepared in Examples 1 to 3 utilize alumina as the core and yttrium oxide as the shell to construct a composite powder. The composite powder accounts for 65%-75% of the surface refractory powder, significantly reducing the amount of yttrium oxide used. The back layer of the shell is prepared using bauxite and silica sol binder, further reducing the overall material cost. The amount of yttrium oxide used in the ceramic shells prepared in these examples is far lower than in Comparative Example 1, resulting in a significant cost reduction and providing an economically feasible shell solution for the large-scale production of large titanium alloy castings.

[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A method for preparing a low-cost ceramic shell for casting a large-sized titanium alloy, characterized by, Includes the following steps: Step 1: Prepare yttrium oxide-coated alumina core-shell structured composite powder, wherein the particle size of the composite powder is 12-25 μm and the thickness of the yttrium oxide coating layer is 200-800 nm; Step 2: Prepare the surface refractory powder: Mix the composite powder with yttrium oxide fine powder. Based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 25%-35%, with the remainder being the composite powder. The yttrium oxide fine powder consists of nano-sized yttrium oxide with a particle size of 50-200 nm and submicron-sized yttrium oxide with a particle size of 1-5 μm. The nano-sized yttrium oxide accounts for 10%-25% of the total mass of the yttrium oxide fine powder, and the submicron-sized yttrium oxide accounts for 75%-90% of the total mass of the yttrium oxide fine powder. Step 3: Prepare the binder: Mix yttrium sol and silica sol at a mass ratio of 7:3; Step 4: Prepare the surface slurry: Mix the refractory powder and the binder at a powder-to-liquid mass ratio of 2.5:1-3.5:1, add wetting agent and defoamer, and stir evenly; Step 5, Shell making: Apply the surface layer slurry to the wax mold surface, sprinkle alumina sand, and dry to form the surface layer; apply the back layer slurry prepared with bauxite and silica sol binder, sprinkle sand, and dry to form the back layer; Step 6: Dewaxing and firing to obtain a ceramic shell.

2. The method of claim 1, wherein the low cost ceramic shell for large size titanium alloy casting is characterized by, The composite powder described in step 1 is prepared by the sol-gel method: α-alumina powder is impregnated in yttrium sol precursor, dried, and calcined, and the impregnation, drying, and calcination are repeated 2-3 times.

3. The method of claim 2, wherein the low cost ceramic shell for large size titanium alloy casting is characterized by, The particle size of the α-alumina powder is 10-20 μm; during the impregnation process, the mass-to-volume ratio of the α-alumina powder to the yttrium sol precursor is 1:3 (kg / L).

4. The method of claim 2, wherein the low cost ceramic shell for large size titanium alloy casting is characterized by, The preparation method of the yttrium sol precursor is as follows: dissolve yttrium nitrate hexahydrate in anhydrous ethanol to prepare a solution with a concentration of 0.3 mol / L, add acetylacetone, the molar ratio of acetylacetone to yttrium ions is 2:1, adjust the pH to 3-5 with dilute nitric acid, and stir for 2 hours.

5. The method of claim 2, wherein the low cost ceramic shell for large size titanium alloy casting is characterized by, In step 1, the drying temperature is 80-110℃ and the drying time is 18-24h each time; the calcination temperature is 700℃ and the calcination time is 3h.

6. The method of claim 1, wherein the low cost ceramic shell for large size titanium alloy casting is characterized by, In step 2, based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 25%, of which nano-sized yttrium oxide accounts for 10% of the total mass of the yttrium oxide fine powder, and submicron-sized yttrium oxide accounts for 90% of the total mass of the yttrium oxide fine powder.

7. The method of claim 1, wherein the low cost ceramic shell for large size titanium alloy casting is characterized by, In step 2, based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 30%, of which nano-sized yttrium oxide accounts for 15% of the total mass of the yttrium oxide fine powder, and submicron-sized yttrium oxide accounts for 85% of the total mass of the yttrium oxide fine powder.

8. The method of claim 1, wherein the low cost ceramic shell for large size titanium alloy casting is characterized by, In step 2, based on the total mass of the refractory powder, the yttrium oxide fine powder accounts for 35%, of which nano-sized yttrium oxide accounts for 25% of the total mass of the yttrium oxide fine powder, and submicron-sized yttrium oxide accounts for 75% of the total mass of the yttrium oxide fine powder.

9. The method for preparing low-cost ceramic mold shells for large-size titanium alloy casting according to claim 1, characterized in that, The surface layer in step 5 is formed by two cycles of applying slurry, sprinkling alumina sand, and drying; the back layer is formed by six cycles of applying slurry, sprinkling bauxite sand, and drying.

10. The method for preparing low-cost ceramic mold shells for large-size titanium alloy casting according to claim 1, characterized in that, The dewaxing in step 6 is performed using infrared dewaxing; the calcination is performed by heating to 300℃ at a heating rate of 3-5℃ / min and holding for 2 hours, and then heating to 1050℃ and holding for 4 hours.

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