A low-loss temperature-stable celsian-based microwave dielectric ceramic material and its preparation method

Abstract

The present invention discloses a low-loss temperature-stable celsian-based microwave dielectric ceramic material and a preparation method thereof. The low-loss temperature-stable celsian-based microwave dielectric ceramic material is sintered from raw materials in the following weight parts: 265-272 parts of graphite tailings, 160-165 parts of BaCO3, 104-112 parts of Al2O3, 5-8 parts of TiO2, and 1-2 parts of CuO. The preparation method includes the following steps: crushing, grinding, and sieving the graphite tailings, calcining and cooling to obtain graphite tailings powder; weighing the raw materials, ball-milling and mixing; drying, calcining, and cooling with the furnace; performing secondary ball-milling and drying; preparing a blank and sintering. The present invention realizes the in-situ synthesis of a CaTiO3 performance enhancement phase, improves the temperature drift characteristics of the celsian-based ceramic material, the temperature coefficient of resonant frequency can be controlled within ±2 ppm / °C, comprehensively improves the microwave dielectric properties of the ceramic material, and enables it to meet the application requirements of millimeter-wave communication devices.

Description

Technical Field

[0001] The present invention belongs to ceramics and their manufacturing methods, and specifically relates to a low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material and its preparation method. Background Art

[0002] With the rapid development of modern communication technologies, especially the upgrading of mobile communication, satellite communication, military radar, and global positioning system (GPS), higher performance requirements are imposed on microwave devices. Microwave dielectric ceramics, with their high dielectric constant (ε r ), high quality factor (Q), and small temperature coefficient of resonant frequency (τ f ), meet the requirements of miniaturization, integration, high reliability, and low cost of microwave circuits. They are key materials for manufacturing microwave dielectric resonators and filters, and related research has increasingly attracted people's attention.

[0003] Chinese Patent with application number 202110436475.5 introduces graphite tailings as raw materials into the microwave dielectric ceramic formula through component compounding, which can form a single barium feldspar solid solution phase, and its loss characteristics are superior to those of anorthite. However, the impurity components in the tailings will increase the dielectric loss of the ceramic material, making the quality factor (Q×f value) of the graphite tailings-based barium feldspar ceramic material always unable to meet the application requirements of millimeter-wave communication. Therefore, how to further improve the loss characteristics (Q) and temperature drift characteristics (τ f ) of the graphite tailings-based barium feldspar microwave dielectric ceramic material system has become a key technical problem to be solved urgently. Summary of the Invention

[0004] Object of the Invention: To overcome the deficiencies in the prior art, the object of the present invention is to provide a barium feldspar-based microwave dielectric ceramic material with excellent dielectric properties, and another object of the present invention is to provide a preparation method of a barium feldspar-based microwave dielectric ceramic material that is convenient to control and can reduce the sintering temperature.

[0005] Technical Solution: A low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material described in the present invention is sintered from the following raw materials in parts by weight: 265 - 272 parts of graphite tailings, 160 - 165 parts of BaCO3, 104 - 112 parts of Al2O3, 5 - 8 parts of TiO2, and 1 - 2 parts of CuO.

[0006] Furthermore, the main phase of the low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material is (Ba, Ca, Cu)Al2Si2O8, and the secondary phase is CaTiO3, where the mass percentage of the main phase is 93 - 95wt%, and the mass percentage of the secondary phase is 5 - 7wt%.

[0007] Furthermore, the relative dielectric constant of the low-loss temperature-stable celsian-based microwave dielectric ceramic material is 7.81 - 9.25, the quality factor is 45248 - 67351 GHz, and the temperature coefficient of resonant frequency is -2 - 2 ppm / °C.

[0008] The preparation method of the above low-loss temperature-stable celsian-based microwave dielectric ceramic material includes the following steps:

[0009] Step S1: Crush, grind and sieve the graphite tailings, calcine them at 700 - 800 °C, and obtain graphite tailings powder after cooling.

[0010] Step S2: Weigh graphite tailings powder, BaCO3, Al2O3, TiO2, La2O3, and CuO powder according to the ratio, and mix them by ball milling.

[0011] Step S3: Dry the product obtained in Step S2, calcine it, and cool it with the furnace.

[0012] Step S4: Perform secondary ball milling on the powder obtained in Step S3, and dry it.

[0013] Step S5: Prepare a blank from the product obtained in Step S4 and sinter it to obtain the low-loss temperature-stable celsian-based microwave dielectric ceramic material.

[0014] Furthermore, in Step S1, the particle size of the tailings powder after crushing, grinding and sieving is 45 - 75 μm.

[0015] Furthermore, in Step S1, the calcination temperature is 700 - 800 °C, and the holding time is 0.5 - 1 h. When the calcination temperature is lower than 700 °C, the Ca component in the ceramic material cannot be thermally decomposed into CaO, and thus cannot react with the additive TiO2 to form CaTiO3 in Step S2, resulting in performance degradation; when the sintering temperature is higher than 800 °C, the Ca component in the graphite tailings powder is completely thermally decomposed into CaO, and CaO can completely react with the additive TiO2 in Step S2, and thus the proportion of Ca element in the (Ba,Ca,Cu)Al2Si2O8 solid solution phase decreases too much, resulting in performance degradation.

[0016] Furthermore, in Step S2, BaCO3, Al2O3, TiO2, and CuO powders are all of analytical purity, the ball milling is wet ball milling, the ball milling speed is 250 - 300 r / min, and the ball milling time is 8 - 12 h.

[0017] Furthermore, in Step S3, the calcination temperature is 950 - 1050 °C, and the holding time is 2 - 4 h. When the calcination temperature is lower than 950 °C, the powder contains raw material phases and is prone to impurity phases during subsequent sintering; when the calcination temperature is higher than 1050 °C, the particle size of the powder becomes larger and the reaction activity becomes poor during subsequent sintering.

[0018] Further, in step S4, the ball milling is wet ball milling, the ball milling speed is 200 - 250 r / min, and the ball milling time is 4 - 6 h.

[0019] Further, in step S5, the sintering temperature is 1150 - 1250 °C, after sintering, it is kept warm for 3 - 5 h, and then cooled with the furnace. If the sintering temperature is lower than 1150 °C, the sintering driving force of the ceramic material is insufficient, the densification decreases, and the performance deteriorates; if the sintering temperature is higher than 1250 °C, the ceramic grains grow abnormally, and the grains are coated during the grain growth process, resulting in an increase in porosity, a decrease in densification, and a deterioration in performance.

[0020] Preparation principle: The graphite tailings are pre - calcined to ensure that part of the Ca composition in the tailings thermally decomposes into CaO, and in the subsequent steps of primary ball milling and calcination, it is mixed evenly with the additive TiO2 and CaTiO3 second phase is in - situ synthesized. Since CaTiO3 is a common positive temperature drift compensator (~ +800 ppm o / C), the introduction of the second phase improves the graphite tailings - based microwave dielectric ceramic material with negative resonance frequency temperature coefficient. In addition, a small amount of CuO is introduced in the primary ball milling, which can eliminate the Ca cation defects caused by the synthesis of the CaTiO3 phase, occupy the Ca lattice sites in the form of ion replacement, and improve the sintering characteristics and loss characteristics of the ceramic material.

[0021] Beneficial effects: Compared with the prior art, the present invention has the following significant features:

[0022] 1. Through the method of combining the pre - calcination of graphite tailings raw materials and the introduction of additives, the solid - phase reaction between the Ca component in the tailings and TiO2 is induced, realizing the in - situ synthesis of the CaTiO3 performance - enhancing phase, improving the temperature drift characteristics of the celsian - based ceramic material. Among them, the resonance frequency temperature coefficient can be controlled within ±2 ppm / °C, comprehensively improving the microwave dielectric properties of the ceramic material, so as to meet the actual application requirements of millimeter - wave communication devices;

[0023] 2. Introducing CuO during the primary ball milling process can eliminate the Ca cation defects caused by the synthesis of the CaTiO3 phase, occupy the Ca lattice sites in the form of ion replacement, and improve the sintering characteristics and dielectric loss characteristics of the celsian - based ceramic material. Among them, the sintering temperature is reduced to 1150 °C, and the Q×f value of the quality factor can exceed 60000 GHz. Brief description of the drawings

[0024] Figure 1 is the XRD pattern of the low - loss temperature - stable celsian - based microwave dielectric ceramic material obtained in Example 2 of the present invention;

[0025] Figure 2 is the XRD pattern of the low - loss temperature - stable celsian - based microwave dielectric ceramic material obtained in Comparative Example 1;

[0026] Figure 3 It is the SEM image of the low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material obtained in Example 2 of the present invention;

[0027] Figure 4 It is the SEM image of the low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material obtained in Comparative Example 2. Detailed implementation manners

[0028] The materials, reagents, instruments, etc. used in the following examples can be obtained from commercial channels without special instructions. The experimental methods without specific conditions in the examples usually follow conventional conditions or the conditions recommended by the manufacturer. The specific composition of the graphite tailings is shown in Table 1 below.

[0029] Table 1 Chemical composition of graphite tailings

[0030]

[0031] Example 1

[0032] A preparation method of a low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material includes the following steps:

[0033] Step S1: Crush, grind and screen the graphite tailings respectively to make the average particle size of the graphite tailings powder 45 μm. Place the crucible containing the graphite tailings powder in a high-temperature muffle furnace and calcine at 700 °C for 0.5 h, then cool naturally.

[0034] Step S2: Weigh 26.5 g of graphite tailings powder, 16.0 g of BaCO3 powder, 10.4 g of Al2O3 powder, 0.8 g of TiO2 powder, and 0.1 g of CuO powder. Mix the five powders and wet ball-mill them at a rotation speed of 250 r / min for 8 h.

[0035] Step S3: Dry the product obtained in Step S2, place it in a muffle furnace and calcine at 950 °C for 2 h, and cool with the furnace.

[0036] Step S4: Perform secondary ball-milling on the calcined powder, wet ball-mill it at a rotation speed of 200 r / min for 4 h, and dry it.

[0037] Step S5: Take out the powder obtained in Step S5, press it into a blank and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1250 °C, and the holding time is 3 h, then cool with the furnace to finally obtain a low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material.

[0038] The phase content (by mass ratio) of the low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material obtained in this example: (Ba, Ca, Cu)Al2Si2O8 accounts for 93.0%, and CaTiO3 accounts for 7.0%.

[0039] Example 2

[0040] A preparation method of a low-loss temperature-stable celsian-based microwave dielectric ceramic material, comprising the following steps:

[0041] Step S1: Crush, grind and sieve graphite tailings respectively to make the average particle size of the graphite tailings powder 50 μm. Place the crucible containing the graphite tailings powder in a high-temperature muffle furnace for calcination at 750 °C, keep the temperature for 1 h, and then cool naturally.

[0042] Step S2: Weigh 26.7 g of graphite tailings powder, 16.1 g of BaCO3 powder, 10.6 g of Al2O3 powder, 0.7 g of TiO2 powder, and 0.12 g of CuO powder. Mix the five powders and wet ball-mill them at a speed of 275 r / min for 10 h.

[0043] Step S3: Dry the product obtained in Step S2, place it in a muffle furnace for calcination at 1000 °C and keep the temperature for 3 h, and cool with the furnace.

[0044] Step S4: Perform secondary ball-milling on the calcined powder, wet ball-mill it at a speed of 250 r / min for 5 h, and dry it.

[0045] Step S5: Take out the powder obtained in Step S5, press it into a blank and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1150 °C, the holding time is 4 h, and then cool with the furnace to finally obtain a low-loss temperature-stable celsian-based microwave dielectric ceramic material.

[0046] The phase content (by mass ratio) of the low-loss temperature-stable celsian-based microwave dielectric ceramic material obtained in this example: (Ba, Ca, Cu)Al2Si2O8 accounts for 93.5%, and CaTiO3 accounts for 6.5%.

[0047] Example 3

[0048] A preparation method of a low-loss temperature-stable celsian-based microwave dielectric ceramic material, comprising the following steps:

[0049] Step S1: Crush, grind and sieve graphite tailings respectively to make the average particle size of the graphite tailings powder 60 μm. Place the crucible containing the graphite tailings powder in a high-temperature muffle furnace for calcination at 800 °C, keep the temperature for 0.5 h, and then cool naturally.

[0050] Step S2: Weigh 26.9 g of graphite tailings powder, 16.2 g of BaCO3 powder, 10.8 g of Al2O3 powder, 0.6 g of TiO2 powder, and 0.14 g of CuO powder. Mix the five powders and wet ball-mill them at a speed of 300 r / min for 11 h.

[0051] Step S3: Dry the product obtained in Step S2, place it in a muffle furnace, calcine it at 1025 °C and hold for 4 h, and then cool it down with the furnace.

[0052] Step S4: Perform secondary ball milling on the calcined powder, wet ball mill it at a rotation speed of 225 r / min for 6 h, and then dry it.

[0053] Step S5: Take out the powder obtained in Step S5, press it into a blank, place it in a high-temperature muffle furnace for sintering, the sintering temperature is 1250 °C, the holding time is 4 h, and then cool it down with the furnace. Finally, a low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material is obtained.

[0054] The phase content (by mass ratio) of the low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material obtained in this example: (Ba, Ca, Cu)Al2Si2O8 accounts for 94.0%, and CaTiO3 accounts for 6.0%.

[0055] Example 4

[0056] A preparation method of a low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material, comprising the following steps:

[0057] Step S1: Crush, grind and sieve graphite tailings respectively to make the average particle size of the graphite tailings powder 70 μm. Place the crucible containing the graphite tailings powder in a high-temperature muffle furnace, calcine it at 750 °C, hold for 1 h, and then cool it naturally.

[0058] Step S2: Weigh 27.1 g of graphite tailings powder, 16.4 g of BaCO3 powder, 11.0 g of Al2O3 powder, 0.55 g of TiO2 powder, and 0.18 g of CuO powder. Mix the five powders and wet ball mill them at a rotation speed of 300 r / min for 12 h.

[0059] Step S3: Dry the product obtained in Step S2, place it in a muffle furnace, calcine it at 975 °C and hold for 4 h, and then cool it down with the furnace.

[0060] Step S4: Perform secondary ball milling on the calcined powder, wet ball mill it at a rotation speed of 200 r / min for 5 h, and then dry it.

[0061] Step S5: Take out the powder obtained in Step S5, press it into a blank, place it in a high-temperature muffle furnace for sintering, the sintering temperature is 1200 °C, the holding time is 5 h, and then cool it down with the furnace. Finally, a low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material is obtained.

[0062] The phase content (by mass ratio) of the low-loss temperature-stable barium feldspar-based microwave dielectric ceramic material obtained in this example: (Ba, Ca, Cu)Al2Si2O8 accounts for 94.5%, and CaTiO3 accounts for 5.5%.

[0063] Example 5

[0064] A preparation method of a low-loss temperature-stable celsian-based microwave dielectric ceramic material, comprising the following steps:

[0065] Step S1: Crush, grind and screen graphite tailings respectively to make the average particle size of the graphite tailings powder 75 μm. Place the crucible containing the graphite tailings powder in a high-temperature muffle furnace for calcination at 700 °C, hold for 0.5 h, and then cool naturally.

[0066] Step S2: Weigh 27.2 g of graphite tailings powder, 16.5 g of BaCO3 powder, 11.2 g of Al2O3 powder, 0.5 g of TiO2 powder, and 0.2 g of CuO powder. Mix the five powders and wet ball-mill them at a speed of 275 r / min for 9 h.

[0067] Step S3: Dry the product obtained in Step S2, place it in a muffle furnace for calcination at 1050 °C and hold for 3 h, and then cool with the furnace.

[0068] Step S4: Perform secondary ball-milling on the calcined powder, wet ball-mill it at a speed of 225 r / min for 4 h, and dry it.

[0069] Step S5: Take out the powder obtained in Step S5, press it into a blank and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1200 °C, the holding time is 5 h, and then cool with the furnace to finally obtain a low-loss temperature-stable celsian-based microwave dielectric ceramic material.

[0070] The phase content (by mass ratio) of the low-loss temperature-stable celsian-based microwave dielectric ceramic material obtained in this example: (Ba, Ca, Cu)Al2Si2O8 accounts for 95.0%, and CaTiO3 accounts for 5.0%.

[0071] Comparative Example 1

[0072] Crush, grind and screen graphite tailings respectively to make the average particle size of the graphite tailings powder 50 μm. Place the crucible containing the graphite tailings powder in a high-temperature muffle furnace for calcination at 750 °C, hold for 1 h, and then cool naturally. Weigh 26.7 g of graphite tailings powder, 16.1 g of BaCO3 powder, 10.6 g of Al2O3 powder, and 0.12 g of CuO powder. Mix the four powders and wet ball-mill them at a speed of 275 r / min for 10 h. Place the dried powder after ball-milling in a muffle furnace for calcination at 1000 °C and hold for 3 h, and then cool with the furnace. Perform secondary ball-milling on the calcined powder, wet ball-mill it at a speed of 250 r / min for 5 h. Press the dried powder into a blank and place it in a high-temperature muffle furnace for sintering. The sintering temperature is 1150 °C, the holding time is 4 h, and then cool with the furnace to obtain a microwave dielectric ceramic material. The phase content (by mass ratio) of the ceramic material: (Ba, Ca, Cu)Al2Si2O8 accounts for 100%.

[0073] Comparative Example 2

[0074] The graphite tailings were crushed, ground and sieved separately to make the average particle size of the graphite tailings powder 50μm. The crucible containing the graphite tailings powder was placed in a high-temperature muffle furnace for calcination at 750℃, kept warm for 1h, and then cooled naturally. Weigh 26.7g of graphite tailings powder, 16.1g of BaCO3 powder, 10.6g of Al2O3 powder, and 0.7g of TiO2 powder, mix the four powders, and wet-mill at a speed of 275r / min for 10h. The ball-milled and dried powder was placed in a muffle furnace for calcination at 1000℃ and kept warm for 3h, and cooled with the furnace. The calcined powder was placed in a ball mill and wet-milled at a speed of 250r / min for 5 hours. The dried powder was pressed into a green compact and sintered in a high-temperature muffle furnace at a sintering temperature of 1150°C for 4 hours. The powder was then cooled in the furnace to obtain a microwave dielectric ceramic material. The phase content of the ceramic material (by mass ratio) is as follows: (Ba, Ca)Al2Si2O8 accounts for 93.4% and CaTiO3 accounts for 6.6%.

[0075] Comparative Example 3

[0076] The graphite tailings were crushed, ground and sieved separately to make the average particle size of the graphite tailings powder 50μm. Weigh 26.7g of graphite tailings powder, 16.1g of BaCO3 powder, 10.6g of Al2O3 powder, 0.7g of TiO2 powder, and 0.12g of CuO powder, mix the five powders, and wet-mill them at a speed of 275r / min for 10h. The dried powder after ball milling was placed in a muffle furnace for calcination at 1000℃ and kept warm for 3h, and then cooled with the furnace. The calcined powder was ball milled for a second time, wet-milled at a speed of 250r / min for 5h, and the dried powder was pressed and sintered in a high-temperature muffle furnace. The sintering temperature was 1150℃, the insulation time was 4h, and then cooled with the furnace to obtain a microwave dielectric ceramic material. The phase content of the ceramic material (by mass ratio): (Ba, Ca, Cu)Al2Si2O8 accounted for 100%.

[0077] Table 2 shows the microwave dielectric properties and sintering properties of the microwave dielectric ceramic materials obtained under different formulations and process conditions for Examples 1-5 and Comparative Examples 1-3. Among them, the ceramic sample prepared in Example 2 has the highest quality factor, a near-zero resonant frequency temperature coefficient, and the lowest sintering temperature, and is the optimal embodiment. Figure 1 As shown in FIG. 1 , the main phase is (Ba, Ca, Cu)Al2Si2O8 and the secondary phase is CaTiO3. Comparative Example 1 prepared a ceramic sample without adding TiO2. Figure 2 As shown, the phase composition of the ceramic sample is (Ba, Ca, Cu)Al2Si2O8. Compared with Example 2, due to the lack of CaTiO3 reinforcement phase, the τf The absolute value is relatively high, and the Q×f value is also relatively low. In Comparative Example 2, a ceramic sample without adding CuO was prepared. Compared with Example 2 (the microscopic morphology is as Figure 3 shown), due to the lack of Cu 2+ to fill the cation and occupy the Ca lattice site, the Q×f value of the sample decreased very significantly. At the same time, the sintering density also decreased, and a large number of pores appeared, as Figure 4 shown. In Comparative Example 3, the graphite tailings powder was not pre-calcined, and the Ca component in the tailings raw material could not exist in the form of CaO, and could not synthesize the CaTiO3 reinforcing phase with the TiO2 additive during the high-temperature calcination process, resulting in a relatively high absolute value of τ f of the ceramic sample, and the Q×f value is also relatively low.

[0078] Table 2 Properties of the materials obtained in Examples 1-5 and Comparative Examples 1-3

[0079]

Claims

1. A preparation method of a low-loss temperature-stable celsian-based microwave dielectric ceramic material, characterized in that, It includes the following steps: Step S1: Crush, grind and screen graphite tailings, calcine them at 700 - 800 °C, and obtain graphite tailings powder after cooling; Step S2: Weigh graphite tailings powder, BaCO3, Al2O3, TiO2, and CuO powder according to a ratio, and ball - mill and mix them; Step S3: Dry the product obtained in Step S2, calcine it, and cool it in the furnace; Step S4: Perform secondary ball - milling on the powder obtained in Step S3, and dry it; Step S5: Prepare a blank from the product obtained in Step S4 and sinter it to obtain a low - loss temperature - stable barium feldspar - based microwave dielectric ceramic material; The low - loss temperature - stable barium feldspar - based microwave dielectric ceramic material is sintered from the following raw materials by weight: 265 - 272 parts of graphite tailings, 160 - 165 parts of BaCO3, 104 - 112 parts of Al2O3, 5 - 8 parts of TiO2, 1 - 2 parts of CuO; The main phase of the low - loss temperature - stable barium feldspar - based microwave dielectric ceramic material is (Ba, Ca, Cu)Al2Si2O8, and the secondary phase is CaTiO3. Among them, the mass percentage of the main phase is 93 - 95 wt%, and the mass percentage of the secondary phase is 5 - 7 wt%.

2. The preparation method of a low-loss temperature-stable celsian-based microwave dielectric ceramic material according to claim 1, characterized in that: The relative dielectric constant of the low - loss temperature - stable barium feldspar - based microwave dielectric ceramic material is 7.81 - 9.25, the quality factor is 45248 - 67351 GHz, and the resonant frequency temperature coefficient is - 2.0 - 2.0 ppm / °C.

3. The preparation method of the low-loss temperature-stable celsian-based microwave dielectric ceramic material according to claim 1, wherein: In Step S1, the particle size of the graphite tailings powder is 45 - 75 μm.

4. The preparation method of the low-loss temperature-stable celsian-based microwave dielectric ceramic material according to claim 1, characterized in that: In Step S1, keep the temperature for 0.5 - 1 h after calcination.

5. The preparation method of the low-loss temperature-stable celsian-based microwave dielectric ceramic material according to claim 1, characterized in that: In Step S2, the powders of BaCO3, Al2O3, TiO2, and CuO are all of analytical purity. The ball - milling is wet ball - milling, the ball - milling speed is 250 - 300 r / min, and the ball - milling time is 8 - 12 h.

6. The preparation method of the low-loss temperature-stable celsian-based microwave dielectric ceramic material according to claim 1, wherein: In Step S3, the calcination temperature is 950 - 1050 °C, and the heat - preservation time is 2 - 4 h.

7. The preparation method of the low-loss temperature-stable celsian-based microwave dielectric ceramic material according to claim 1, wherein: In Step S4, the ball - milling is wet ball - milling, the ball - milling speed is 200 - 250 r / min, and the ball - milling time is 4 - 6 h.

8. The preparation method of the low-loss temperature-stable celsian-based microwave dielectric ceramic material according to claim 1, characterized in that: In Step S5, the sintering temperature is 1150 - 1250 °C, keep the temperature for 3 - 5 h after sintering, and then cool it in the furnace.

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